Studies on interaction of an intramolecular charge transfer fluorescence probe: 4'-dimethylamino-2,5-dihydroxychalcone with DNA.

PubMed

Xu, Zhicheng; Bai, Guan; Dong, Chuan

2005-10-15

The interaction of a new intramolecular charge transfer probe, namely 4'-dimethylamino-2,5-dihydroxychalcone (DMADHC), with calf thymus DNA has been studied. Compared to the spectral characteristics of the free form in aqueous solution, the fluorescence of DMADHC enhanced dramatically accompanying a blueshift of the emission maxima in the presence of DNA. The absorption and fluorescence spectra, salt concentration effect, KI quenching, fluorescence polarization, and DNA denaturation experiments were given. These results give evidence that the DMADHC molecule is inserted into the base-stacking domain of the DNA double helix. The intrinsic binding constant and the binding site number were estimated. The analytical characteristics were also given.

Tryptophan and ATTO 590: mutual fluorescence quenching and exciplex formation.

PubMed

Bhattacharjee, Ujjal; Beck, Christie; Winter, Arthur; Wells, Carson; Petrich, Jacob W

2014-07-24

Investigation of fluorescence quenching of probes, such as ATTO dyes, is becoming an increasingly important topic owing to the use of these dyes in super-resolution microscopies and in single-molecule studies. Photoinduced electron transfer is their most important nonradiative pathway. Because of the increasing frequency of the use of ATTO and related dyes to investigate biological systems, studies are presented for inter- and intramolecular quenching of ATTO 590 with tryptophan. In order to examine intramolecular quenching, an ATTO 590-tryptophan conjugate was synthesized. It was determined that tryptophan is efficiently quenching ATTO 590 fluorescence by excited-state charge transfer and two charge transfer complexes are forming. In addition, it was discovered that an exciplex (whose lifetime is 5.6 ns) can be formed between tryptophan and ATTO 590, and it is suggested that the possibility of such exciplex formation should be taken into account when protein fluorescence is monitored in a system tagged with ATTO dyes.

Single Molecule Spectroelectrochemistry of Interfacial Charge Transfer Dynamics In Hybrid Organic Solar Cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pan, Shanlin

2014-11-16

Our research under support of this DOE grant is focused on applied and fundamental aspects of model organic solar cell systems. Major accomplishments are: 1) we developed a spectroelectorchemistry technique of single molecule single nanoparticle method to study charge transfer between conjugated polymers and semiconductor at the single molecule level. The fluorescence of individual fluorescent polymers at semiconductor surfaces was shown to exhibit blinking behavior compared to molecules on glass substrates. Single molecule fluorescence excitation anisotropy measurements showed the conformation of the polymer molecules did not differ appreciably between glass and semiconductor substrates. The similarities in molecular conformation suggest thatmore » the observed differences in blinking activity are due to charge transfer between fluorescent polymer and semiconductor, which provides additional pathways between states of high and low fluorescence quantum efficiency. Similar spectroelectrochemistry work has been done for small organic dyes for understand their charge transfer dynamics on various substrates and electrochemical environments; 2) We developed a method of transferring semiconductor nanoparticles (NPs) and graphene oxide (GO) nanosheets into organic solvent for a potential electron acceptor in bulk heterojunction organic solar cells which employed polymer semiconductor as the electron donor. Electron transfer from the polymer semiconductor to semiconductor and GO in solutions and thin films was established through fluorescence spectroscopy and electroluminescence measurements. Solar cells containing these materials were constructed and evaluated using transient absorption spectroscopy and dynamic fluorescence techniques to understand the charge carrier generation and recombination events; 3) We invented a spectroelectorchemistry technique using light scattering and electroluminescence for rapid size determination and studying electrochemistry of single NPs in an electrochemical cell. For example, we are able to use this technique to track electroluminescence of single Au NPs, and the electrodeposition of individual Ag NPs in-situ. These metallic NPs are useful to enhance light harvesting in organic photovoltaic systems. The scattering at the surface of an indium tin oxide (ITO) working electrode was measured during a potential sweep. Utilizing Mie scattering theory and high resolution scanning electron microscopy (SEM), the scattering data were used to calculate current-potential curves depicting the electrodeposition of individual Ag NPs. The oxidation of individual presynthesized and electrodeposited Ag NPs was also investigated using fluorescence and DFS microscopies. Our work has produced 1 US provisional patent, 15 published manuscripts, 1 submitted and two additional in-writing manuscripts. 5 graduate students, 1 postdoctoral student, 1 visiting professor, and two undergraduate students have received research training in the area of electrochemistry and optical spectroscopy under support of this award.« less

New fluorescent probes for visual proteins. Part II. 5-(Oxo)penta-2,4-dienyl-p-(N,N-dimethylamino)benzoate.

PubMed

Papper, Vladislav; Kharlanov, Vladimir; Schädel, Sandra; Maretzki, Dieter; Rettig, Wolfgang

2003-12-01

A new dual-fluorescent compound, 5-(oxo)penta-2,4-dienyl-p-(N,N-dimethylamino)benzoate (1), a derivative of dimethylaminobenzoic acid, has been synthesised and studied photophysically. This compound continues the series of potential fluorescent probes for visual and proton-pumping opsin proteins. The photophysical behaviour of this molecule, including charge-transfer interaction in the ground state and dual-fluorescence emission, is similar to that of the previously studied analogue cis-3-(oxo)propenyl-p-(N,N-dimethylamino)benzoate (cis-2). The presence of several theoretically calculated conformers of compound 2 was suggested to be responsible for the observed strongly red-shifted absorption and excitation wavelength dependence. These photophysical anomalies were also observed for molecule 1, though the models put forward to explain them in the cases of 1 and 2 are rather different. Based on theoretical calculations and experimental results, we propose that some of the stable conformers might be connected with either a charge-transfer complex or mesomeric interactions in the ground state. Upon changing the electronic nature of the oxo-pentadienyl acceptor moiety, e.g. protonation, chemical or biochemical reaction, the charge-transfer absorption disappears, which leads to a dramatic increase in the fluorescence quantum yield.

Improvements of low-detection-limit filter-free fluorescence sensor developed by charge accumulation operation

NASA Astrophysics Data System (ADS)

Tanaka, Kiyotsugu; Choi, Yong Joon; Moriwaki, Yu; Hizawa, Takeshi; Iwata, Tatsuya; Dasai, Fumihiro; Kimura, Yasuyuki; Takahashi, Kazuhiro; Sawada, Kazuaki

2017-04-01

We developed a low-detection-limit filter-free fluorescence sensor by a charge accumulation technique. For charge accumulation, a floating diffusion amplifier (FDA), which included a floating diffusion capacitor, a transfer gate, and a source follower circuit, was used. To integrate CMOS circuits with the filter-free fluorescence sensor, we adopted a triple-well process to isolate transistors from the sensor on a single chip. We detected 0.1 nW fluorescence under the illumination of excitation light by 1.5 ms accumulation, which was one order of magnitude greater than that of a previous current detection sensor.

The Case Against Charge Transfer Interactions in Dissolved Organic Matter Photophysics.

PubMed

McKay, Garrett; Korak, Julie A; Erickson, Paul R; Latch, Douglas E; McNeill, Kristopher; Rosario-Ortiz, Fernando L

2018-01-16

The optical properties of dissolved organic matter influence chemical and biological processes in all aquatic ecosystems. Dissolved organic matter optical properties have been attributed to a charge-transfer model in which donor-acceptor complexes play a primary role. This model was evaluated by measuring the absorbance and fluorescence response of organic matter isolates to changes in solvent temperature, viscosity, and polarity, which affect the position and intensity of spectra for known donor-acceptor complexes of organic molecules. Absorbance and fluorescence spectral shape were largely unaffected by these changes, indicating that the distribution of absorbing and emitting species was unchanged. Overall, these results call into question the wide applicability of the charge-transfer model for explaining organic matter optical properties and suggest that future research should explore other models for dissolved organic matter photophysics.

Noncovalent binding of xanthene and phthalocyanine dyes with graphene sheets: the effect of the molecular structure revealed by a photophysical study.

PubMed

Zhang, Xian-Fu; Liu, Su-Ping; Shao, Xiao-Na

2013-09-01

The fluorescence and absorption properties of several xanthene and phthalocyanine dyes were measured in the presence and absence of chemically derived graphene (CDG) sheets. The interaction of pyronine Y (PYY) with graphene sheets was compared with that of rhodamine 6G (R6G) to reveal the effect of the molecular structure. Although the presence of the perpendicular benzene moiety in a R6G or phthalocyanine molecule does cause the difficulty for forming dye-CDG complex and make CDG less efficient in quenching the fluorescence intensity and shortening the fluorescence lifetime, it does not affect the band position of charge transfer absorption, suggesting that no molecular shape change occurred in a dye molecule caused by the interaction with CDG sheets. The spectroscopic and thermodynamic data indicated that the dye-CDG binding is of charge transfer nature, while the dynamic fluorescence quenching is due to photoinduced energy and electron transfer. Copyright © 2013 Elsevier B.V. All rights reserved.

Evaluation of the charge transfer efficiency of organic thin-film photovoltaic devices fabricated using a photoprecursor approach.

PubMed

Masuo, Sadahiro; Sato, Wataru; Yamaguchi, Yuji; Suzuki, Mitsuharu; Nakayama, Ken-ichi; Yamada, Hiroko

2015-05-01

Recently, a unique 'photoprecursor approach' was reported as a new option to fabricate a p-i-n triple-layer organic photovoltaic device (OPV) through solution processes. By fabricating the p-i-n architecture using two kinds of photoprecursors and a [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) as the donor and the acceptor, the p-i-n OPVs afforded a higher photovoltaic efficiency than the corresponding p-n devices and i-devices, while the photovoltaic efficiency of p-i-n OPVs depended on the photoprecursors. In this work, the charge transfer efficiency of the i-devices composed of the photoprecursors and PC71BM was investigated using high-sensitivity fluorescence microspectroscopy combined with a time-correlated single photon counting technique to elucidate the photovoltaic efficiency depending on the photoprecursors and the effects of the p-i-n architecture. The spatially resolved fluorescence images and fluorescence lifetime measurements clearly indicated that the compatibility of the photoprecursors with PC71BM influences the charge transfer and the photovoltaic efficiencies. Although the charge transfer efficiency of the i-device was quite high, the photovoltaic efficiency of the i-device was much lower than that of the p-i-n device. These results imply that the carrier generation and carrier transportation efficiencies can be increased by fabricating the p-i-n architecture.

Donor-σ-Acceptor Motifs: Thermally Activated Delayed Fluorescence Emitters with Dual Upconversion.

PubMed

Geng, Yan; D'Aleo, Anthony; Inada, Ko; Cui, Lin-Song; Kim, Jong Uk; Nakanotani, Hajime; Adachi, Chihaya

2017-12-22

A family of organic emitters with a donor-σ-acceptor (D-σ-A) motif is presented. Owing to the weakly coupled D-σ-A intramolecular charge-transfer state, a transition from the localized excited triplet state ( 3 LE) and charge-transfer triplet state ( 3 CT) to the charge-transfer singlet state ( 1 CT) occurred with a small activation energy and high photoluminescence quantum efficiency. Two thermally activated delayed fluorescence (TADF) components were identified, one of which has a very short lifetime of 200-400 ns and the other a longer TADF lifetime of the order of microseconds. In particular, the two D-σ-A materials presented strong blue emission with TADF properties in toluene. These results will shed light on the molecular design of new TADF emitters with short delayed lifetimes. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Thermally-Activated, Delayed Fluorescence in O,B,O- and N,B,O-Strapped Boron Dipyrromethene Derivatives.

PubMed

Stachelek, Patrycja; Alsimaree, Abdulrahman A; Alnoman, Rua B; Harriman, Anthony; Knight, Julian G

2017-03-16

A small series of boron dipyrromethene (BODIPY) dyes has been synthesized whereby the boron atom is constrained in a five-membered ring formed from either o-dihydroxypyridine or o-aminophenol. In the latter case, the amino group has been converted into the corresponding amide derivative so as to curtail the possibility for light-induced charge transfer from strap to BODIPY. These compounds are weakly emissive in fluid solution but cleavage of the strap, by treatment with a photoacid generator, restores strong fluorescence. Surprisingly, the same compounds remain weakly fluorescent in a rigid glass at 80 K where light-induced charge transfer is most unlikely. In fluid solution, the fluorescence quantum yield increases with increasing temperature due to a thermally activated step but does not correlate with the thermodynamics for intramolecular charge transfer. It is proposed that the strap causes rupture of the potential energy surface for the excited state, creating traps that provide new routes by which the wave packet can return to the ground state. Access to the trap from the excited state is reversible, leading to the delayed emission. Analysis of the temperature dependent emission intensities allows estimation of the kinetic parameters associated with entering and leaving the trap.

Determination of human serum albumin using an intramolecular charge transfer fluorescence probe: 4'-dimethylamino-2,5-dihydroxychalcone.

PubMed

Xu, Zhicheng; Yang, Weibing; Dong, Chuan

2005-09-15

A new intramolecular charge transfer fluorescence probe, namely, 4'-dimethylamino-2,5-dihydroxychalcone (DMADHC), exhibited dramatic enhancement of fluorescence intensity with an accompanying blue shift of the emission maximum when the concentration of human serum albumin (HSA) was increased. Binding to HSA also caused a progressive shift in the absorption spectrum of DMADHC, and a clear isosbestic point appeared. The binding site number and binding constant were calculated. Thermodynamic parameters were given and possible binding site was speculated. The optimum conditions for the determination of HSA were also investigated. A new, fast, and simple spectrofluorimetric method for the determination of HSA was developed. In the detection of HSA in samples of human plasma, this method gave values close to that of the Erythrosin B method.

The Case Against Charge Transfer Interactions in Dissolved Organic Matter Optical Properties

NASA Astrophysics Data System (ADS)

McKay, G.; Korak, J.; Erickson, P. R.; Latch, D. E.; McNeill, K.; Rosario-Ortiz, F.

2017-12-01

The optical properties of dissolved organic matter influence chemical and biological processes in all aquatic ecosystems. Organic matter optical properties have been used by scientists and engineers for decades for remote sensing, in situ monitoring, and characterizing laboratory samples to track dissolved organic carbon concentration and character. However, there is still a lack of understanding of the origin of organic matter optical properties, which could conflict with other empirical fluorescence interpretation methods (e.g. PARAFAC). Organic matter optical properties have been attributed to a charge-transfer model in which donor-acceptor complexes play a primary role. This model was evaluated by measuring the absorbance and fluorescence response of organic matter isolates to perturbations in solvent temperature, viscosity, and polarity, which affect the position and intensity of spectra for known donor-acceptor complexes of organic molecules. Absorbance and fluorescence spectral shape were unaffected by these perturbations, indicating that the distribution of absorbing and emitting species was unchanged. These results call into question the wide applicability of the charge-transfer model for explaining organic matter optical properties and suggest that future research should explore other models for organic matter photophysics.

Shedding light on the photostability of two intermolecular charge-transfer complexes between highly fluorescent bis-1,8-naphthalimide dyes and some π-acceptors: A spectroscopic study in solution and solid states

NASA Astrophysics Data System (ADS)

Refat, Moamen S.; Ismail, Lamia A.; Adam, Abdel Majid A.

2015-01-01

Given the great importance of the various uses of 1,8-naphthalimides in the trends of biology, medicine and industry, the current study focused on extending the scope of these dyes by introducing some of their charge-transfer (CT) complexes. For this purpose, two highly fluorescent bis-1,8-naphthalimide dyes and their complexes with some π-acceptors have been synthesized and characterized spectroscopically. The π-acceptors include picric acid (PA), chloranilic acid (CLA), tetracyanoquinodimethane (TCNQ) and dichlorodicyanobenzoquinone (DDQ). The molecular structure, spectroscopic and fluorescence properties as well as the binding modes were deduced from IR, UV-vis and 1H NMR spectral studies. The binding ratio of complexation was determined to be 1:1 according to the elemental analyses and photometric titrations. It has been found that the order of acceptance ability for the different acceptors is TCNQ > DDQ > CLA > PA. The photostability of 1,8-naphthalimide dye as a donor and its charge-transfer complex doped in polymethyl methacrylate/PMMA were exposed to UV-Vis radiation and the change in the absorption spectra was achieved at different times during irradiation period.

Blue Thermally Activated Delayed Fluorescence Polymers with Nonconjugated Backbone and Through-Space Charge Transfer Effect.

PubMed

Shao, Shiyang; Hu, Jun; Wang, Xingdong; Wang, Lixiang; Jing, Xiabin; Wang, Fosong

2017-12-13

We demonstrate novel molecular design for thermally activated delayed fluorescence (TADF) polymers based on a nonconjugated polyethylene backbone with through-space charge transfer effect between pendant electron donor (D) and acceptor (A) units. Different from conventional conjugated D-A polymers with through-bond charge transfer effect, the nonconjugated architecture avoids direct conjugation between D and A units, enabling blue emission. Meanwhile, spatial π-π interaction between the physically separated D and A units results in both small singlet-triplet energy splitting (0.019 eV) and high photoluminescence quantum yield (up to 60% in film state). The resulting polymer with 5 mol % acceptor unit gives efficient blue electroluminescence with Commission Internationale de l'Eclairage coordinates of (0.176, 0.269), together with a high external quantum efficiency of 12.1% and low efficiency roll-off of 4.9% (at 1000 cd m -2 ), which represents the first example of blue TADF nonconjugated polymer.

Approximate description of Stokes shifts in ICT fluorescence emission

NASA Astrophysics Data System (ADS)

Saielli, Giacomo; Braun, David; Polimeno, Antonino; Nordio, Pier Luigi

1996-07-01

The time-resolved emission spectrum of a dual fluorescent prototype system like DMABN is associated with an intramolecular adiabatic charge-transfer reaction and the simultaneous relaxation of the polarization coordinate describing the dynamic behaviour of the polar solvent. The dynamic Stokes shift of the frequency maximum of the long-wavelength emission band related to the charge-transfer (CT) state towards the red region is interpreted as a consequence of a kinetic pathway which deviates from steepest descent to the CT state, the rate-determining step being the solvent relaxation. The present stochastic treatment is based on the assumption that internal and solvent coordinates could be described separately, neglecting coupling elements in the case of slow solvent relaxation.

Charge-transfer-based terbium MOF nanoparticles as fluorescent pH sensor for extreme acidity.

PubMed

Qi, Zewan; Chen, Yang

2017-01-15

Newly emerged metal organic frameworks (MOFs) have aroused the great interest in designing functional materials by means of its flexible structure and component. In this study, we used lanthanide Tb 3+ ions and small molecular ligands to design and assemble a kind of pH-sensitive MOF nanoparticle based on intramolecular-charge-transfer effect. This kind of made-to-order MOF nanoparticle for H + is highly specific and sensitive and could be used to fluorescently indicate pH value of strong acidic solution via preset mechanism through luminescence of Tb 3+ . The long luminescence lifetime of Tb 3+ allows eliminating concomitant non-specific fluorescence by time-revised fluorescence techniques, processing an advantage in sensing H + in biological media with strong autofluorescence. Our method showed a great potential of MOF structures in designing and constructing sensitive sensing materials for specific analytes directly via the assembly of functional ions/ligands. Copyright © 2016 Elsevier B.V. All rights reserved.

The effect of intermolecular hydrogen bonding on the fluorescence of a bimetallic platinum complex.

PubMed

Zhao, Guang-Jiu; Northrop, Brian H; Han, Ke-Li; Stang, Peter J

2010-09-02

The bimetallic platinum complexes are known as unique building blocks and arewidely utilized in the coordination-driven self-assembly of functionalized supramolecular metallacycles. Hence, photophysical study of the bimetallic platinum complexes will be very helpful for the understanding on the optical properties and further applications of coordination-driven self-assembled supramolecular metallacycles. Herein, we report steady-state and time-resolved spectroscopic experiments as well as quantum chemistry calculations to investigate the significant intermolecular hydrogen bonding effects on the intramolecular charge transfer (ICT) fluorescence of a bimetallic platinum compound 4,4'-bis(trans-Pt(PEt(3))(2)OTf)benzophenone 3 in solution. We demonstrated that the fluorescent state of compound 3 can be assigned as a metal-to-ligand charge transfer (MLCT) state. Moreover, it was observed that the formation of intermolecular hydrogen bonds can effectively lengthen the fluorescence lifetime of 3 in alcoholic solvents compared with that in hexane solvent. At the same time, the electronically excited states of 3 in solution are definitely changed by intermolecular hydrogen bonding interactions. As a consequence, we propose a new fluorescence modulation mechanism by hydrogen bonding to explain different fluorescence emissions of 3 in hydrogen-bonding solvents and nonhydrogen-bonding solvents.

Time-resolved fluorescence study of exciplex formation in diastereomeric naproxen-pyrrolidine dyads.

PubMed

Khramtsova, Ekaterina A; Plyusnin, Viktor F; Magin, Ilya M; Kruppa, Alexander I; Polyakov, Nikolay E; Leshina, Tatyana V; Nuin, Edurne; Marin, M Luisa; Miranda, Miguel A

2013-12-19

The influence of chirality on the elementary processes triggered by excitation of the (S,S)- and (R,S)- diastereoisomers of naproxen-pyrrolidine (NPX-Pyr) dyads has been studied by time-resolved fluorescence in acetonitrile-benzene mixtures. In these systems, the quenching of the (1)NPX*-Pyr singlet excited state occurs through electron transfer and exciplex formation. Fluorescence lifetimes and quantum yields revealed a significant difference (around 20%) between the (S,S)- and (R,S)- diastereomers. In addition, the quantum yields of exciplexes differed by a factor of 2 regardless of solvent polarity. This allows us to suggest a similar influence of the chiral centers on the local charge transfer resulting in exciplex and full charge separation that leads to ion-biradicals. A simplified scheme is proposed to estimate a set of rate constant values (k1-k5) for the elementary stages in each solvent system.

Recent Advances in Macrocyclic Fluorescent Probes for Ion Sensing.

PubMed

Wong, Joseph K-H; Todd, Matthew H; Rutledge, Peter J

2017-01-25

Small-molecule fluorescent probes play a myriad of important roles in chemical sensing. Many such systems incorporating a receptor component designed to recognise and bind a specific analyte, and a reporter or transducer component which signals the binding event with a change in fluorescence output have been developed. Fluorescent probes use a variety of mechanisms to transmit the binding event to the reporter unit, including photoinduced electron transfer (PET), charge transfer (CT), Förster resonance energy transfer (FRET), excimer formation, and aggregation induced emission (AIE) or aggregation caused quenching (ACQ). These systems respond to a wide array of potential analytes including protons, metal cations, anions, carbohydrates, and other biomolecules. This review surveys important new fluorescence-based probes for these and other analytes that have been reported over the past five years, focusing on the most widely exploited macrocyclic recognition components, those based on cyclam, calixarenes, cyclodextrins and crown ethers; other macrocyclic and non-macrocyclic receptors are also discussed.

Highly fluorescent carbon dots for visible sensing of doxorubicin release based on efficient nanosurface energy transfer.

PubMed

Wang, Beibei; Wang, Shujun; Wang, Yanfang; Lv, Yan; Wu, Hao; Ma, Xiaojun; Tan, Mingqian

2016-01-01

To prepare fluorescent carbon dots for loading cationic anticancer drug through donor-quenched nanosurface energy transfer in visible sensing of drug release. Highly fluorescent carbon dots (CDs) were prepared by a facile hydrothermal approach from citric acid and o-phenylenediamine. The obtained CDs showed a high quantum yield of 46 % and exhibited good cytocompatibility even at 1 mg/ml. The cationic anticancer drug doxorubicin (DOX) can be loaded onto the negatively charged CDs through electrostatic interactions. Additionally, the fluorescent CDs feature reversible donor-quenched mode nanosurface energy transfer. When loading the energy receptor DOX, the donor CDs' fluorescence was switched "off", while it turned "on" again after DOX release from the surface through endocytic uptake. Most DOX molecules were released from the CDs after 6 h incubation and entered cell nuclear region after 8 h, suggesting the drug delivery system may have potential for visible sensing in drug release.

Imaging the photoinduced charge injection in CdS/TiO2 nanoparticles by the sequential fluorescence mapping method

NASA Astrophysics Data System (ADS)

Frederice, Rafael; Lencione, Diego; Gehlen, Marcelo H.

2017-03-01

The combination of a sensitizer and TiO2 nanoparticles forming a photocatalytic material is a central issue in many fields of applied photochemistry. The charge injection of emissive sensitizers into the conduction band of the semiconductor TiO2 may form a photoactive region that becomes dark, or it has a very low emission signal due to the generation of sensitizer radicals. However, by sequential coupling of a selected photoredox dye, such as resazurin, the dark region may become fluorescent at the interfaces where the charge injection has taken place due to the concomitant formation of fluorescent resorufin by cascade electron transfer. Using this strategy and a total internal reflection fluorescence microscopy (TIRFM) image, the charge injection in TiO2/CdS and SiO2/TiO2/CdS nanoparticles is investigated The method allows the charge injection efficiency of the excited CdS into TiO2 to be evaluated qualitatively, explaining the differences observed for these photocatalytic materials in H2 generation.

Imaging the photoinduced charge injection in CdS/TiO2 nanoparticles by the sequential fluorescence mapping method.

PubMed

Frederice, Rafael; Lencione, Diego; Gehlen, Marcelo H

2017-02-10

The combination of a sensitizer and TiO 2 nanoparticles forming a photocatalytic material is a central issue in many fields of applied photochemistry. The charge injection of emissive sensitizers into the conduction band of the semiconductor TiO 2 may form a photoactive region that becomes dark, or it has a very low emission signal due to the generation of sensitizer radicals. However, by sequential coupling of a selected photoredox dye, such as resazurin, the dark region may become fluorescent at the interfaces where the charge injection has taken place due to the concomitant formation of fluorescent resorufin by cascade electron transfer. Using this strategy and a total internal reflection fluorescence microscopy (TIRFM) image, the charge injection in TiO 2 /CdS and SiO 2 /TiO 2 /CdS nanoparticles is investigated The method allows the charge injection efficiency of the excited CdS into TiO 2 to be evaluated qualitatively, explaining the differences observed for these photocatalytic materials in H 2 generation.

"Inverted" Solvent Effect on Charge Transfer in the Excited State.

PubMed

Nau; Pischel

1999-10-04

Faster in cyclohexane than in acetonitrile is the fluorescence quenching of the azoalkane 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by amines and sulfides. Although this photoreaction is induced by charge transfer (CT; see picture) and exciplexes are formed, the increase in the dipole moment of the exciplex is not large enough to offset the solvent stabilization of the excited reactants, and an "inverted" solvent effect results.

Energy and charge transfer dynamics between Alq3 and CdSeS nanocrystals.

PubMed

Zhang, Shuping; Liu, Yuqiang; Yang, Yanqiang

2010-03-01

The photoluminescence properties of the blend films consisting of organic small molecules and nanocrystals (NCs)--Alq3 and CdSeS NCs--were studied by steady-state and time-resolved photoluminescence (PL) spectroscopy with different excited wavelengths. Both the fluorescence intensity and lifetime are intensively dependent on the NC concentration. The detailed analysis of experiment data proves that Forster energy transfer from the Alq3 to the NCs exists simultaneously with the charge transfer and both compete with each other in the blend films.

Study of protein-probe interaction and protective action of surfactant sodium dodecyl sulphate in urea-denatured HSA using charge transfer fluorescence probe methyl ester of N,N-dimethylamino naphthyl acrylic acid.

PubMed

Mahanta, Subrata; Singh, Rupashree Balia; Guchhait, Nikhil

2009-03-01

We have demonstrated that the intramolecular charge transfer (ICT) probe Methyl ester of N,N-dimethylamino naphthyl acrylic acid (MDMANA) serves as an efficient reporter of the proteinous microenvironment of Human Serum Albumin (HSA). This work reports the binding phenomenon of MDMANA with HSA and spectral modulation thereupon. The extent of binding and free energy change for complexation reaction along with efficient fluorescence resonance energy transfer from Trp-214 of HSA to MDMANA indicates strong binding between probe and protein. Fluorescence anisotropy, red edge excitation shift, acrylamide quenching and time resolved measurements corroborate the binding nature of the probe with protein and predicts that the probe molecule is located at the hydrophobic site of the protein HSA. Due to the strong binding ability of MDMANA with HSA, it is successfully utilized for the study of stabilizing action of anionic surfactant Sodium Dodecyl Sulphate to the unfolding and folding of protein with denaturant urea in concentration range 1M to 9M.

Analysis of S2QA- charge recombination with the Arrhenius, Eyring and Marcus theories.

PubMed

Rantamäki, Susanne; Tyystjärvi, Esa

2011-01-01

The Q band of photosynthetic thermoluminescence, measured in the presence of a herbicide that blocks electron transfer from PSII, is associated with recombination of the S(2)Q(A)(-) charge pair. The same charge recombination reaction can be monitored with chlorophyll fluorescence. It has been shown that the recombination occurs via three competing routes of which one produces luminescence. In the present study, we measured the thermoluminescence Q band and the decay of chlorophyll fluorescence yield after a single turnover flash at different temperatures from spinach thylakoids. The data were analyzed using the commonly used Arrhenius theory, the Eyring rate theory and the Marcus theory of electron transfer. The fitting error was minimized for both thermoluminescence and fluorescence by adjusting the global, phenomenological constants obtained when the reaction rate theories were applied to the multi-step recombination reaction. For chlorophyll fluorescence, all three theories give decent fits. The peak position of the thermoluminescence Q band is correct by all theories but the form of the Q band is somewhat different in curves predicted by the three theories. The Eyring and Marcus theories give good fits for the decreasing part of the thermoluminescence curve and Marcus theory gives the closest fit for the rising part. Copyright © 2011 Elsevier B.V. All rights reserved.

Effect of Viscosity and Polar Properties of Solvent on Dynamics of Photoinduced Charge Transfer in BTA-1 Cation — Derivative of Thioflavin T

NASA Astrophysics Data System (ADS)

Gogoleva, S. D.; Stsiapura, V. I.

2018-05-01

It was found that the spectral and fluorescent properties of BTA-1C cation in protic and aprotic solvents differ. It was shown that for solutions in long-chain alcohols viscosity is the main factor that determines the dynamics of intramolecular charge transfer in the excited state of the BTA-1C molecule. In the case of aprotic solvents a correlation was found between the rate constant of twisted intramolecular charge transfer (TICT) during rotation of fragments of the molecule in relation to each other in the excited state and the solvent relaxation rate: k TICT 1/τ S .

Influence of dehydrated nanotubed titanic acid on charge transport and luminescent properties of polymer light-emitting diodes with fluorescent dye

NASA Astrophysics Data System (ADS)

Qian, Lei; Bera, Debasis; Jin, Zhen-Sheng; Du, Zu-Liang; Xu, Zheng; Teng, Feng; Liu, Wei

2007-09-01

In this paper, we discuss the influence of dehydrated nanotubed titanic acid (DNTA) on charge transport and luminescent properties of polymer light-emitting diodes (PLEDs) doped with fluorescent dye. Photoluminescence results confirm the efficient energy transfer from PVK to 4-(dicyanom-ethylene)-2- t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) and tris-(8-hydroxtquinoline) aluminum (Alq 3) in a DNTA-doped device. The device showed lower turn-on voltages and higher charge current by doping with DNTA, which also caused a shift in the exciton's recombination region.

Efficient modulation of optical and electrical properties of X-shaped thermally activated delayed fluorescence emitters by substitution.

PubMed

Fan, Jianzhong; Wang, Xin; Lin, Lili; Wang, Chuankui

2016-08-01

A series of X-shaped thermally activated delayed fluorescence (TADF) emitters are systematically studied by first-principles calculations. Effects of the cyano group adding to the acceptor unit and the hydroxyl group adding to the donor part on the optical and electrical properties are analyzed. It is found that both kinds of groups can efficiently increase the emission wavelength to realize full-color emission. Although they play different roles in modulating the energy level of frontier orbitals, the S-T energy gap, the reorganization energy and transfer integral for different molecules, they can efficiently increase the charge transfer rate and reduce the difference of electron transfer rate and hole transfer rate. These results indicate that these designed strategies are efficient to achieve balanced charge transfer rates and modulate emission colors. By analyzing the energy matching between the TADF emitters and three kinds of hosts, the emission spectra of the 3,5-bis(N-carbazolyl)benzene (mcp) and the absorption spectra of most TADF emitters have a large overlap, which provides helpful information in application of these TADF molecules.

Controlling photophysics of styrylnaphthalimides through TICT, fluorescence and E,Z-photoisomerization interplay.

PubMed

Panchenko, Pavel A; Arkhipova, Antonina N; Fedorova, Olga A; Fedorov, Yuri V; Zakharko, Marina A; Arkhipov, Dmitry E; Jonusauskas, Gediminas

2017-01-04

The photophysical properties of naphthalimide dyes NI1-3 with electron releasing 4-methoxy- (NI1), 3,4-dimethoxystyryl- (NI2) and dimethylaminostyryl (NI3) groups are examined in a variety of protic and aprotic solvents. All compounds demonstrate positive solvatochromism in the steady-state absorption and fluorescence spectra. The analysis of the dependence of the Stokes shift on the polarity of the solvent using the Lippert-Mataga equation allowed us to determine the change in the dipole moment upon excitation. The obtained data correspond to the formation of highly polar charge transfer states. Based on the transient absorption spectra and time-resolved fluorescence measurements, the presence of two different emissive states was definitely proved. The primarily formed planar Local Excited (LE) state dominates in non-polar solvents like cyclohexane and toluene where it relaxes mostly through fluorescence and E,Z-isomerisation pathways. In polar solvents, an alternative relaxation channel emerges that consists of twisting around single bond between styryl and naphthalimide fragments, which leads to the formation of a Twisted Intramolecular Charge Transfer (TICT) state. The factors affecting the fluorescence of TICT states are discussed. The observed spectral effects are rationalized using quantum-chemical calculations, X-ray data and NMR spectroscopy.

Dual Mechanism of an Intramolecular Charge Transfer (ICT)-FRET-Based Fluorescent Probe for the Selective Detection of Hydrogen Peroxide.

PubMed

Liang, Xiao; Xu, Xiaoyi; Qiao, Dan; Yin, Zheng; Shang, Luqing

2017-12-14

A dual-mechanism intramolecular charge transfer (ICT)-FRET fluorescent probe for the selective detection of H 2 O 2 in living cells has been designed and synthesized. This probe used a coumarin-naphthalimide hybrid as the FRET platform and a boronate moiety as the recognition group. Upon the addition of H 2 O 2 , the probe exhibited a redshifted (73 nm) fluorescence emission, and the ratio of fluorescence intensities at λ=558 and 485 nm (F 558 /F 485 ) shifted notably (up to 100-fold). Moreover, there was a good linearity (R 2 =0.9911) between the ratio and concentration of H 2 O 2 in the range of 0 to 60 μm, with a limit of detection of 0.28 μm (signal to noise ratio (S/N)=3). This probe could also detect enzymatically generated H 2 O 2 . Importantly, it could be used to visualize endogenous H 2 O 2 produced by stimulation from epidermal growth factor. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

An intramolecular charge transfer process based fluorescent probe for monitoring subtle pH fluctuation in living cells.

PubMed

Sun, Mingtai; Du, Libo; Yu, Huan; Zhang, Kui; Liu, Yang; Wang, Suhua

2017-01-01

It is crucial to monitor intracellular pH values and their fluctuation since the organelles of cells have different pH distribution. Herein we construct a new small molecule fluorescent probe HBT-O for monitoring the subtle pH values within the scope of neutral to acid in living cells. The probe exhibited good water solubility, a marked turquoise to olivine emission color change in response to pH, and tremendous fluorescence hypochromatic shift of ∼50nm (1718cm -1 ) as well as the increased fluorescence intensity when the pH value changed from neutral to acid. Thus, the probe HBT-O can distinguish the subtle changes in the range of normal pH values from neutral to acid with significant fluorescence changes. These properties can be attributed to the intramolecular charge transfer (ICT) process of the probe upon protonation in buffer solutions at varied pH values. Moreover, the probe was reversible and nearly non-toxic for living cells. Then the probe was successfully used to detect pH fluctuation in living cells by exhibiting different fluorescence colors and intensity. These findings demonstrate that the probe will find useful applications in biology and biomedical research. Copyright © 2016 Elsevier B.V. All rights reserved.

Excited State Charge Transfer reaction with dual emission from 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile: Spectral measurement and theoretical density functional theory calculation

NASA Astrophysics Data System (ADS)

Jana, Sankar; Dalapati, Sasanka; Ghosh, Shalini; Kar, Samiran; Guchhait, Nikhil

2011-07-01

The excited state intramolecular charge transfer process in donor-chromophore-acceptor system 5-(4-dimethylamino-phenyl)-penta-2,4-dienenitrile (DMAPPDN) has been investigated by steady state absorption and emission spectroscopy in combination with Density Functional Theory (DFT) calculations. This flexible donor acceptor molecule DMAPPDN shows dual fluorescence corresponding to emission from locally excited and charge transfer state in polar solvent. Large solvatochromic emission shift, effect of variation of pH and HOMO-LUMO molecular orbital pictures support excited state intramolecular charge transfer process. The experimental findings have been correlated with the calculated structure and potential energy surfaces based on the Twisted Intramolecular Charge Transfer (TICT) model obtained at DFT level using B3LYP functional and 6-31+G( d, p) basis set. The theoretical potential energy surfaces for the excited states have been generated in vacuo and acetonitrile solvent using Time Dependent Density Functional Theory (TDDFT) and Time Dependent Density Functional Theory Polarized Continuum Model (TDDFT-PCM) method, respectively. All the theoretical results show well agreement with the experimental observations.

Experimental and Theoretical Aspects of Excited State Electron Transfer and Related Phenomena: Conference Held in Honour of Zbigniew R. Grabowski in Pultusk, Poland on September 27-October 2, 1992

DTIC Science & Technology

1992-10-01

DBMBF2 ) undergoes photoreaction with olefins through a partial electron transfer that leads to cycloaddition or sensitized Diels - Alder reactions. We...8217 Fluorescence. 10:00 J.M. WARMAN: Photon-induced Intramolecular Charge Sepaiation Studied byTime-Resolved Microwave Conductivity. 10:30 Coffee 11:)) W...26 Photon-Induced Intramolecular Charge Separation Studied by Time-Resolved Microwave Conductivity John M. Warman IRI, Delft University of Technology

Effect of intramolecular charge transfer on fluorescence and singlet oxygen production of phthalocyanine analogues.

PubMed

Vachova, Lenka; Novakova, Veronika; Kopecky, Kamil; Miletin, Miroslav; Zimcik, Petr

2012-10-14

Intramolecular charge transfer (ICT) was studied on a series of magnesium, metal-free and zinc complexes of unsymmetrical tetrapyrazinoporphyrazines and tribenzopyrazinoporphyrazines bearing two dialkylamino substituents (donors) and six alkylsulfanyl or aryloxy substituents (non-donors). The dialkylamino substituents were responsible for ICT that deactivated excited states and led to considerable decrease of fluorescence and singlet oxygen quantum yields. Photophysical and photochemical properties were compared to corresponding macrocycles that do not bear any donor centers. The data showed high feasibility of ICT in the tetrapyrazinoporphyrazine macrocycle and significantly lower efficiency of this deactivation process in the tribenzopyrazinoporphyrazine type molecules. Considerable effect of non-donor peripheral substituents on ICT was also described. The results imply that tetrapyrazinoporphyrazines may be more suitable for development of new molecules investigated in applications based on ICT.

Interfacial Charge Transfer States in Condensed Phase Systems

NASA Astrophysics Data System (ADS)

Vandewal, Koen

2016-05-01

Intermolecular charge transfer (CT) states at the interface between electron-donating (D) and electron-accepting (A) materials in organic thin films are characterized by absorption and emission bands within the optical gap of the interfacing materials. CT states efficiently generate charge carriers for some D-A combinations, and others show high fluorescence quantum efficiencies. These properties are exploited in organic solar cells, photodetectors, and light-emitting diodes. This review summarizes experimental and theoretical work on the electronic structure and interfacial energy landscape at condensed matter D-A interfaces. Recent findings on photogeneration and recombination of free charge carriers via CT states are discussed, and relations between CT state properties and optoelectronic device parameters are clarified.

Photoabsorption of green and red fluorescent protein chromophore anions in vacuo.

PubMed

Wan, Songbo; Liu, Shasha; Zhao, Guangjiu; Chen, Maodu; Han, Keli; Sun, Mengtao

2007-09-01

Photoabsorption properties of green and red fluorescent protein chromophore anions in vacuo were investigated theoretically, based on the experimental results in gas phase [Phys. Rev. Lett. 2001, 87, 228102; Phys. Rev. Lett. 2003, 90, 118103]. Their calculated transition energies in absorption with TD-DFT and ZINDO methods are directly compared to the experimental reports in gas phase, and the calculations with ZINDO method can correctly reproduce the absorption spectra. The orientation and strength of their transition dipole moments were revealed with transition density. We also showed the orientation and result of their intramolecular charge transfer with transition difference density. The calculated results show that with the increase of the extended conjugated system, the orientation of transition dipole moments and the orientation of charge transfer can be reversed. They are the linear responds with the external electric fields. These theoretical results reveal the insight understanding of the photoinduced dynamics of green and red fluorescent protein chromophore anions and cations in vacuo.

Photophysics of a coumarin based Schiff base in solvents of varying polarities

NASA Astrophysics Data System (ADS)

Ghosh, Saptarshi; Roy, Nayan; Singh, T. Sanjoy; Chattopadhyay, Nitin

2018-01-01

The present work reports detailed photophysics of a coumarin based Schiff base, namely, (E)-7-(((8-hydroxyquinolin-2-yl)methylene)amino)-4-methyl-2H-chromen-2-one (HMC) in different solvents of varying polarity exploiting steady state absorption, fluorescence and time resolved fluorescence spectroscopy. The dominant photophysical features of HMC are discussed in terms of emission from an intramolecular charge transfer (ICT) excited state. Molecular orbital (MO) diagrams as obtained from DFT based computational analysis confirms the occurrence of charge transfer from 8‧-hydroxy quinoline moiety of the molecule to the coumarin part. The notable difference in the photophysical response of HMC from its analogous coumarin (C480) lies in a lower magnitude of fluorescence quantum yield of the former, particularly in the solvents of low polarity, which is rationalized by considering the higher rate of non-radiative decay of HMC in apolar solvents. Phosphorescence emission as well as phosphorescence lifetime of HMC has also been reported in 77 K frozen matrix.

Fluorescent Polystyrene Films for the Detection of Volatile Organic Compounds Using the Twisted Intramolecular Charge Transfer Mechanism.

PubMed

Borelli, Mirko; Iasilli, Giuseppe; Minei, Pierpaolo; Pucci, Andrea

2017-08-06

Thin films of styrene copolymers containing fluorescent molecular rotors were demonstrated to be strongly sensitive to volatile organic compounds (VOCs). Styrene copolymers of 2-[4-vinyl(1,1'-biphenyl)-4'-yl]-cyanovinyljulolidine (JCBF) were prepared with different P(STY- co -JCBF)(m) compositions (m% = 0.10-1.00) and molecular weights of about 12,000 g/mol. Methanol solutions of JCBF were not emissive due to the formation of the typical twisted intramolecular charge transfer (TICT) state at low viscosity regime, which formation was effectively hampered by adding progressive amounts of glycerol. The sensing performances of the spin-coated copolymer films (thickness of about 4 µm) demonstrated significant vapochromism when exposed to VOCs characterized by high vapour pressure and favourable interaction with the polymer matrix such as THF, CHCl₃ and CH₂Cl₂. The vapochromic response was also reversible and reproducible after successive exposure cycles, whereas the fluorescence variation scaled linearly with VOC concentration, thus suggesting future applications as VOC optical sensors.

CMOS image sensor with lateral electric field modulation pixels for fluorescence lifetime imaging with sub-nanosecond time response

NASA Astrophysics Data System (ADS)

Li, Zhuo; Seo, Min-Woong; Kagawa, Keiichiro; Yasutomi, Keita; Kawahito, Shoji

2016-04-01

This paper presents the design and implementation of a time-resolved CMOS image sensor with a high-speed lateral electric field modulation (LEFM) gating structure for time domain fluorescence lifetime measurement. Time-windowed signal charge can be transferred from a pinned photodiode (PPD) to a pinned storage diode (PSD) by turning on a pair of transfer gates, which are situated beside the channel. Unwanted signal charge can be drained from the PPD to the drain by turning on another pair of gates. The pixel array contains 512 (V) × 310 (H) pixels with 5.6 × 5.6 µm2 pixel size. The imager chip was fabricated using 0.11 µm CMOS image sensor process technology. The prototype sensor has a time response of 150 ps at 374 nm. The fill factor of the pixels is 5.6%. The usefulness of the prototype sensor is demonstrated for fluorescence lifetime imaging through simulation and measurement results.

Free volume dependent fluorescence property of PMMA composite: Positron annihilation studies

NASA Astrophysics Data System (ADS)

Ravindrachary, V.; Praveena, S. D.; Bhajantri, R. F.; Ismayil, Crasta, Vincent

2013-02-01

The free volume related fluorescence properties of chalcone chromophore [1-(4-methylphenyl)-3-(4-N, N, dimethylaminophenyl)-2-propen-1-one doped Poly(methyl methacrylate) have been studied using fluorescence spectroscopy and Positron Annihilation lifetime spectroscopy techniques. The fluorescence spectra show that the fluorescence behavior depends on the free volume dependent polymer microstructure and varies with dopant concentration with in the composite. The origin and variation of fluorescence is understood by twisted internal charge transfer state as well as free volume. The Positron annihilation study shows that the free volume related microstructure of the composite is vary with doping level.

Photo-degradation behaviour of roseoflavin in some aqueous solutions

NASA Astrophysics Data System (ADS)

Tyagi, A.; Penzkofer, A.; Mathes, T.; Hegemann, P.

2010-03-01

An absorption and emission spectroscopic characterization of roseoflavin (8-dimethylamino-8-demethyl-riboflavin, RoF) in aqueous solutions was carried out. The studies were concentrated on roseoflavin in pH 8 phosphate buffer. Absorption cross-section spectra, fluorescence excitation spectra, fluorescence quantum distributions, fluorescence quantum yields and fluorescence lifetimes were determined. The fluorescence of RoF is quenched by photo-induced intra-molecular charge-transfer at room temperature. The photo-degradation of RoF in un-buffered water, in Tris-HCl buffer, and in phosphate buffer was studied. Phosphate buffer and to a smaller extent Tris buffer catalyse the RoF photo-degradation. Photo-excitation of the primary photoproduct, 8-methylamino-riboflavin (8-MNH-RF), enhanced the RoF degradation by triplet 8-MNH-RF - singlet RoF excitation transfer with subsequent triplet-state RoF degradation.

Quenching of fluorescence of conjugated poly(p-phenylene) polymers by benzil and dimethylaminobenzil molecules

NASA Astrophysics Data System (ADS)

Bagnich, S. A.; Knyukshto, V. N.

2006-11-01

We have studied the mechanisms for quenching of the fluorescence of conjugated poly(p-phenylene) polymers by benzil and dimethylaminobenzil molecules. We have shown that molecules in the diketone series are quenching agents for the fluorescence of the indicated polymers, and can serve as singlet-triplet converters capable of populating the triplet state of the polymer. We have observed that the efficiency of quenching of the fluorescence of the studied polymers depends considerably on the presence of bulky side groups in the polymer or in the activator molecules. Based on analysis of the data obtained, we conclude that in the case of a rigid planar structure for the polymer, a significant contribution to quenching of its fluorescence comes from not only singlet-singlet energy transfer but also charge transfer, leading to formation of intermolecular complexes (exciplexes).

Relating Trp-Glu dipeptide fluorescence to molecular conformation: the role of the discrete Chi 1 and Chi 2 angles.

PubMed

Eisenberg, Azaria Solomon; Juszczak, Laura J

2013-07-05

Molecular dynamics (MD), coupled with fluorescence data for charged dipeptides of tryptophanyl glutamic acid (Trp-Glu), reveal a detailed picture of how specific conformation affects fluorescence. Fluorescence emission spectra and time-resolved emission measurements have been collected for all four charged species. MD simulations 20 to 30 ns in length have also been carried out for the Trp-Glu species, as simulation provides aqueous phase conformational data that can be correlated with the fluorescence data. The calculations show that each dipeptide species is characterized by a similar set of six, discrete Chi 1, Chi 2 dihedral angle pairs. The preferred Chi 1 angles--60°, 180°, and 300°--play the significant role in positioning the terminal amine relative to the indole ring. A Chi 1 angle of 60° results in the arching of the backbone over the indole ring and no interaction of the ring with the terminal amine. Chi 1 values of 180° and 300° result in an extension of the backbone away from the indole ring and a NH3 cation-π interaction with indole. This interaction is believed responsible for charge transfer quenching. Two fluorescence lifetimes and their corresponding amplitudes correlate with the Chi 1 angle probability distribution for all four charged Trp-Glu dipeptides. Fluorescence emission band maxima are also consistent with the proposed pattern of terminal amine cation quenching of fluorescence. Copyright © 2013 Wiley Periodicals, Inc.

Ultrafast dynamics of differently aligned COOH-DTE-BODIPY conjugates linked to the surface of TiO2

NASA Astrophysics Data System (ADS)

Schweighöfer, Felix; Yüce, Imanuel; Dworak, Lars; Guo, Peng; Zastrow, Marc; Mayer, Kerstin; Barta, Christoph; Liebmann, Diana; Ziebart, Nandor; Rück-Braun, Karola; Wachtveitl, Josef

2018-02-01

The photoinduced dynamics of two DTE-BODIPY conjugates A, B with carboxylic acid anchoring groups coupled to the surface of TiO2 were studied by ultrafast transient absorption spectroscopy. For compound A, with an orthogonal orientation of the BODIPY chromophore and the photoswitchable DTE unit, a charge separated state could not be reliably detected. Nevertheless, besides the energy transfer from the BODIPY to the ring-closed DTE-c, indications for an electron transfer reaction were found by analyzing fluorescence quenching on TiO2 in steady state fluorescence measurements. For compound B with a parallel orientation of chromophore and photoswitch, a charge separated state was conclusively identified for the coupled dyad (TiO2) via the observation of a positive absorption signal (at λ pr  >  610 nm) at later delay times. An electron transfer rate of 7  ×  1010 s-1 can be extracted, indicating slower processes in the dyads in comparison to previously published electron transfer reactions of DTE compounds coupled to TiO2.

Ultrafast dynamics of differently aligned COOH-DTE-BODIPY conjugates linked to the surface of TiO2.

PubMed

Schweighöfer, Felix; Yüce, Imanuel; Dworak, Lars; Guo, Peng; Zastrow, Marc; Mayer, Kerstin; Barta, Christoph; Liebmann, Diana; Ziebart, Nandor; Rück-Braun, Karola; Wachtveitl, Josef

2018-01-05

The photoinduced dynamics of two DTE-BODIPY conjugates A, B with carboxylic acid anchoring groups coupled to the surface of TiO 2 were studied by ultrafast transient absorption spectroscopy. For compound A, with an orthogonal orientation of the BODIPY chromophore and the photoswitchable DTE unit, a charge separated state could not be reliably detected. Nevertheless, besides the energy transfer from the BODIPY to the ring-closed DTE-c, indications for an electron transfer reaction were found by analyzing fluorescence quenching on TiO 2 in steady state fluorescence measurements. For compound B with a parallel orientation of chromophore and photoswitch, a charge separated state was conclusively identified for the coupled dyad (TiO 2 ) via the observation of a positive absorption signal (at λ pr   >  610 nm) at later delay times. An electron transfer rate of 7  ×  10 10 s -1 can be extracted, indicating slower processes in the dyads in comparison to previously published electron transfer reactions of DTE compounds coupled to TiO 2 .

Photoinduced intramolecular charge transfer (ICT) reaction in trans-methyl p-(dimethylamino) cinnamate: A combined fluorescence measurement and quantum chemical calculations

NASA Astrophysics Data System (ADS)

Chakraborty, Amrita; Kar, Samiran; Guchhait, Nikhil

2006-01-01

The photophysical behaviour of trans-methyl p-(dimethylamino) cinnamate ( t-MDMAC) donor-acceptor system has been investigated by steady-state absorption and emission spectroscopy and quantum chemical calculations. The molecule t-MDMAC shows an emission from the locally excited state in non-polar solvents. In addition to weak local emission, a strong solvent dependent red shifted fluorescence in polar aprotic solvents is attributed to highly polar intramolecular charge transfer state. However, the formation of hydrogen-bonded clusters with polar protic solvents has been suggested from a linear correlation between the observed red shifted fluorescence band maxima with hydrogen bonding parameters ( α). Calculations by ab initio and density functional theory show that the lone pair electron at nitrogen center is out of plane of the benzene ring in the global minimum ground state structure. In the gas phase, a potential energy surface along the twist coordinate at the donor (-NMe 2) and acceptor (-CH = CHCOOMe) sites shows stabilization of S 1 state and destabilization S 2 and S 0 states. A similar potential energy calculation along the twist coordinate in acetonitrile solvent using non-equilibrium polarized continuum model also shows more stabilization of S 1 state relative to other states and supports solvent dependent red shifted emission properties. In all types of calculations it is found that the nitrogen lone pair is delocalized over the benzene ring in the global minimum ground state and is localized on the nitrogen centre at the 90° twisted configuration. The S 1 energy state stabilization along the twist coordinate at the donor site and localized nitrogen lone pair at the perpendicular configuration support well the observed dual fluorescence in terms of proposed twisted intramolecular charge transfer (TICT) model.

pH-Dependent Optical Properties of Synthetic Fluorescent Imidazoles

PubMed Central

Berezin, Mikhail Y.; Kao, Jeff; Achilefu, Samuel

2010-01-01

An imidazole moiety is often found as an integral part of fluorophores in a variety of fluorescent proteins and many such proteins possess pH dependent light emission. In contrast, synthetic fluorescent compounds with incorporated imidazoles are rare and have not been studied as pH probes. In this report, the richness of imidazole optical properties, including pH sensitivity, was demonstrated via a novel imidazole-based fluorophore 1H-imidazol-5-yl-vinyl-benz[e]indolium. Three species corresponding to protonated, neutral and deprotonated imidazoles were identified in the broad range of pH 1-12. The absorption and emission bands of each species were assigned by comparative spectral analysis with synthesized mono- and di-N-methylated fluorescent imidazole analogues. pKa analysis in the ground and the excited states showed photoacidic properties of the fluorescent imidazoles due to the excited state proton transfer (ESPT). This effect was negligible for substituted imidazoles. The assessment of a pH sensitive center in the imidazole ring revealed the switching of the pH sensitive centers from 1-N in the ground state to 3-N in the excited state. The effect was attributed to the unique kind of the excited state charge transfer (ESCT) resulting in a positive charge swapping between two nitrogens. PMID:19212987

Charge transfer optical absorption and fluorescence emission of 4-(9-acridyl)julolidine from long-range-corrected time dependent density functional theory in polarizable continuum approach.

PubMed

Kityk, A V

2014-07-15

A long-range-corrected time-dependent density functional theory (LC-TDDFT) in combination with polarizable continuum model (PCM) have been applied to study charge transfer (CT) optical absorption and fluorescence emission energies basing on parameterized LC-BLYP xc-potential. The molecule of 4-(9-acridyl)julolidine selected for this study represents typical CT donor-acceptor dye with strongly solvent dependent optical absorption and fluorescence emission spectra. The result of calculations are compared with experimental spectra reported in the literature to derive an optimal value of the model screening parameter ω. The first absorption band appears to be quite well predictable within DFT/TDDFT/PCM with the screening parameter ω to be solvent independent (ω ≈ 0.245 Bohr(-1)) whereas the fluorescence emission exhibits a strong dependence on the range separation with ω-value varying on a rising solvent polarity from about 0.225 to 0.151 Bohr(-1). Dipolar properties of the initial state participating in the electronic transition have crucial impact on the effective screening. Copyright © 2014 Elsevier B.V. All rights reserved.

Ultrafast fluorescence quenching dynamics of Atto655 in the presence of N-acetyltyrosine and N-acetyltryptophan in aqueous solution: proton-coupled electron transfer versus electron transfer.

PubMed

Zhang, Ying; Yuan, Shuwei; Lu, Rong; Yu, Anchi

2013-06-20

We studied the ultrafast fluorescence quenching dynamics of Atto655 in the presence of N-acetyltyrosine (AcTyr) and N-acetyltryptophan (AcTrp) in aqueous solution with femtosecond transient absorption spectroscopy. We found that the charge-transfer rate between Atto655 and AcTyr is about 240 times smaller than that between Atto655 and AcTrp. The pH value and D2O dependences of the excited-state decay kinetics of Atto655 in the presence of AcTyr and AcTrp reveal that the quenching of Atto655 fluorescence by AcTyr in aqueous solution is via a proton-coupled electron-transfer (PCET) process and that the quenching of Atto655 fluorescence by AcTrp in aqueous solution is via an electron-transfer process. With the version of the semiclassical Marcus ET theory, we derived that the electronic coupling constant for the PCET reaction between Atto655 and AcTyr in aqueous solution is 8.3 cm(-1), indicating that the PCET reaction between Atto655 and AcTyr in aqueous solution is nonadiabatic.

p-Dimethylaminobenzamide as an ICT dual fluorescent neutral receptor for anions under proton coupled electron transfer sensing mechanism

NASA Astrophysics Data System (ADS)

Wu, Fang-Ying; Jiang, Yun-Bao

2002-04-01

The intramolecular charge transfer (ICT) dual fluorescence of p-dimethylaminobenzamide (DMABA) in acetonitrile was found to show highly sensitive response to HSO 4- over several other anions such as H 2PO 4-,AcO - and ClO 4-. In the presence of bisulfate anion the dual fluorescence intensity ratio and the total intensity of DMABA decreased while the dual emission band positions remained unchanged. Absorption titration indicated that a 1:1 hydrogen bonding complex was formed between bisulfate anion and DMABA, which gave a binding constant of 2.02×10 4 mol-1 l that is two orders of magnitude higher than those for other anions. The obvious isotopic effect observed in the fluorescence quenching [ K SV( HSO4-)/K SV( DSO4-)=1.63 ] suggests that the hydrogen atom moving is an important reaction coordinate. It was assumed that the dual fluorescence response was due to proton coupled electron transfer mediated by hydrogen bonds within the 1:1 HSO 4--DMABA hydrogen-bonding complex.

A charge transfer amplified fluorescent Hg2+ complex for detection of picric acid and construction of logic functions.

PubMed

Kumar, Manoj; Reja, Shahi Imam; Bhalla, Vandana

2012-12-07

A chemosensor 3 based on the N,N-dimethylaminocinnamaldehyde has been synthesized which shows fluorescence turn-on response with Hg(2+) ions, and the in situ prepared 3-Hg(2+) complex has been used for detection of picric acid via electrostatic interaction and construction of a combinatorial logic circuit with NOR and INHIBIT logic functions.

Fast intramolecular electron transfer and dual fluorescence. Configurational change of the amino nitrogen (pyramidal{yields}planar)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Haar, Th. von der; Hebecker, A.; Il'Ichev, Yu.

1996-04-01

The fast excited state intramolecular charge transfer (ICT) and dual fluorescence observed with several 4-aminobenzonitriles is discussed. It is shown that the magnitude of the energy gap between the two lowest excited states determines the occurrence or absence of ICT. The photophysical behavior of a series of four 4-aminobenzonitriles in which the amino nitrogen atom is part of a four- to seven-membered heterocyclic ring, P4C to P7C, is studied by using time-resolved fluorescence measurements. The ICT rate constant strongly decreases with decreasing ring size. With P4C in diethyl ether ICT does not occur. This is attributed to the increase ofmore » the amino nitrogen inversion barrier with decreasing ring size. The change of the amino nitrogen from pyramidal to planar is considered to be an important reaction coordinate. The photophysics of the 4-aminobenzonitriles is different from that of other ICT systems such as donor/acceptor-substituted stilbenes and 9,9'-bianthryl, which are governed by the charge distribution and macroscopic Coulombic interaction in their CT states.« less

Fast intramolecular electron transfer and dual fluorescence. Configurational change of the amino nitrogen (pyramidal-->planar)

NASA Astrophysics Data System (ADS)

von der Haar, Th.; Hebecker, A.; Il'Ichev, Yu.; Kühnle, W.; Zachariasse, K. A.

1996-04-01

The fast excited state intramolecular charge transfer (ICT) and dual fluorescence observed with several 4-aminobenzonitriles is discussed. It is shown that the magnitude of the energy gap between the two lowest excited states determines the occurrence or absence of ICT. The photophysical behavior of a series of four 4-aminobenzonitriles in which the amino nitrogen atom is part of a four- to seven-membered heterocyclic ring, P4C to P7C, is studied by using time-resolved fluorescence measurements. The ICT rate constant strongly decreases with decreasing ring size. With P4C in diethyl ether ICT does not occur. This is attributed to the increase of the amino nitrogen inversion barrier with decreasing ring size. The change of the amino nitrogen from pyramidal to planar is considered to be an important reaction coordinate. The photophysics of the 4-aminobenzonitriles is different from that of other ICT systems such as donor/acceptor-substituted stilbenes and 9,9'-bianthryl, which are governed by the charge distribution and macroscopic Coulombic interaction in their CT states.

A novel fluorescence probe based on triphenylamine Schiff base for bioimaging and responding to pH and Fe3.

PubMed

Wang, Lei; Yang, Xiaodong; Chen, Xiuli; Zhou, Yuping; Lu, Xiaodan; Yan, Chenggong; Xu, Yikai; Liu, Ruiyuan; Qu, Jinqing

2017-03-01

A novel fluorescence probe 1 based on triphenylamine was synthesized and characterized by NMR, IR, high resolution mass spectrometry and elemental analysis. Its fluorescence was quenched when pH below 2. There was a linear relationship between the fluorescence intensity and pH value ranged from 2 to 7. And its fluorescence emission was reversibility in acidic and alkaline solution. Furthermore, it exhibited remarkable selectivity and high sensitivity to Fe 3+ and was able to detect Fe 3+ in aqueous solution with low detection limit of 0.511μM. Job plot showed that the binding stoichiometry of 1 with Fe 3+ was 1:1. Further observations of 1 H NMR titration suggested that coordination interaction between Fe 3+ and nitrogen atom on CN bond promoted the intramolecular charge transfer (ICT) or energy transfer process causing fluorescence quenching. Additionally, 1 was also able to be applied for detecting Fe 3+ in living cell and bioimaging. Copyright © 2016. Published by Elsevier B.V.

A Double Decarboxylation in Superfolder Green Fluorescent Protein Leads to High Contrast Photoactivation.

PubMed

Slocum, Joshua D; Webb, Lauren J

2017-07-06

A photoactivatable variant of superfolder green fluorescent protein (GFP) was created by replacing the threonine at position 203 with aspartic acid. Photoactivation by exposure of this mutant to UV light resulted in conversion of the fluorophore from the neutral to the negatively charged form, accompanied by a ∼95-fold increase in fluorescence under 488 nm excitation. Mass spectrometry before and after exposure to UV light revealed a change in mass of 88 Da, attributed to the double decarboxylation of Glu 222 and Asp 203. Kinetics studies and nonlinear power-dependence of the initial rate of photoconversion indicated that the double decarboxylation occurred via a multiphoton absorption process at 254 nm. In addition to providing a photoactivatable GFP with robust folding properties, a detailed mechanistic understanding of this double decarboxylation in GFP will lead to a better understanding of charge transfer in fluorescent proteins.

Toward designed singlet fission: solution photophysics of two indirectly coupled covalent dimers of 1,3-diphenylisobenzofuran.

PubMed

Johnson, Justin C; Akdag, Akin; Zamadar, Matibur; Chen, Xudong; Schwerin, Andrew F; Paci, Irina; Smith, Millicent B; Havlas, Zdeněk; Miller, John R; Ratner, Mark A; Nozik, Arthur J; Michl, Josef

2013-04-25

In order to identify optimal conditions for singlet fission, we are examining the photophysics of 1,3-diphenylisobenzofuran (1) dimers covalently coupled in various ways. In the two dimers studied presently, the coupling is weak. The subunits are linked via the para position of one of the phenyl substituents, in one case (2) through a CH2 linker and in the other (3) directly, but with methyl substituents in ortho positions forcing a nearly perpendicular twist between the two joint phenyl rings. The measurements are accompanied with density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Although in neat solid state, 1 undergoes singlet fission with a rate constant higher than 10(11) s(-1); in nonpolar solutions of 2 and 3, the triplet formation rate constant is less than 10(6) s(-1) and fluorescence is the only significant event following electronic excitation. In polar solvents, fluorescence is weaker because the initial excited singlet state S1 equilibrates by sub-nanosecond charge transfer with a nonemissive dipolar species in which a radical cation of 1 is attached to a radical anion of 1. Most of this charge transfer species decays to S0, and some is converted into triplet T1 with a rate constant near 10(8) s(-1). Experimental uncertainties prevent an accurate determination of the number of T1 excitations that result when a single S1 excitation changes into triplet excitation. It would be one if the charge-transfer species undergoes ordinary intersystem crossing and two if it undergoes the second step of two-step singlet fission. The triplet yield maximizes below room temperature to a value of roughly 9% for 3 and 4% for 2. Above ∼360 K, some of the S1 molecules of 3 are converted into an isomeric charge-transfer species with a shorter lifetime, possibly with a twisted intramolecular charge transfer (TICT) structure. This is not observed in 2.

Theoretical and Experimental Studies of N,N-Dimethyl-N'-Picryl-4,4'-Stilbenediamine.

PubMed

Papper, Vladislav; Wu, Yuanyuan; Kharlanov, Vladimir; Sukharaharja, Ayrine; Steele, Terry W J; Marks, Robert S

2018-01-01

N,N-dimethyl-N'-picryl-4,4'-stilbenediamine (DMPSDA) was prepared, purified and crystallised in a form of black lustrous crystals, and its absorption and fluorescence spectra were recorded in cyclohexane, acetonitrile and dimethyl sulfoxide. Non-emissive intramolecular charge transfer state (ICT) was clearly observed in this molecule in all three solvents. Theoretical calculations demonstrating a betaine electronic structure of the trinitrophenyl group in the ground state of the molecule and a charge transfer nature of the long wavelength transition S 0  → S 1 supported the experimental observations of the ICT formation in the molecule.

Charge-Transfer-Induced Fluorescence Quenching of Anthracene Derivatives and Selective Detection of Picric Acid.

PubMed

Santra, Dines Chandra; Bera, Manas Kumar; Sukul, Pradip Kumar; Malik, Sudip

2016-02-01

2,6-Divinylpyridine-appended anthracene derivatives flanked by two alkyl chains at the 9,10-position of the core have been designed, synthesized, and characterized by NMR, MALDI-TOF, FTIR, and single-crystal XRD. These anthracene derivatives are able to recognize picric acid (2,4,6-trinitrophenol, PA) selectively down to parts per billion (ppb) level in aqueous as well as nonaqueous medium. Fluorescence emission of these derivatives in solution is significantly quenched by adding trace amounts of PA, even in the presence of other competing analogues, such as 2,4-dinitrophenol (2,4-DNP), 4-nitrophenol (NP), nitrobenzene (NB), benzoic acid (BA), and phenol (PH). The high sensitivity of these derivatives toward PA is considered as a combined effect of the proton-induced intramolecular charge transfer (ICT) as well as electron transfer from the electron-rich anthracene to the electron-deficient PA. Moreover, visual detection of PA has been successfully demonstrated in the solid state by using different substrates. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Far-red/near-infrared fluorescence light-up probes for specific in vitro and in vivo imaging of a tumour-related protein

NASA Astrophysics Data System (ADS)

Chen, Chao; Hua, Yongquan; Hu, Yawen; Fang, Yuan; Ji, Shenglu; Yang, Zhimou; Ou, Caiwen; Kong, Deling; Ding, Dan

2016-03-01

As lysosomal protein transmembrane 4 beta (LAPTM4B) is an important biomarker for many solid tumours, development of small-molecule fluorescence light-up probes for detection and imaging of LAPTM4B proteins is particularly valuable. In this work, we reported the design and synthesis of a far-red/near-infrared (FR/NIR) fluorescence light-up probe DBT-2EEGIHGHHIISVG, which could specifically visualize LAPTM4B proteins in cancer cells and tumour-bearing live mice. DBT-2EEGIHGHHIISVG was synthesized by the conjugation of two LAPTM4B-binding peptide ligands (EEGIHGHHIISVG) with one environment-sensitive fluorogen, 4,7-di(thiophen-2-yl)-2,1,3-benzothiadiazole (DBT). Owing to the intramolecular charge transfer character of DBT, DBT-2EEGIHGHHIISVG is weakly emissive in aqueous solution, but switches to fluoresce upon LAPTM4B proteins specifically bind to the peptide ligand of the probe, which provide the DBT with hydrophobic microenvironment, greatly reducing its charge transfer effect with water. It is found that DBT-2EEGIHGHHIISVG can achieve targeted imaging of LAPTM4B proteins in HepG2 cancer cells and visualize LAPTM4B protein-expressed tumour tissues of live mice in a selective and high-contrast manner.

Synthesis, crystal structure and DFT studies of a dual fluorescent ketamine: Structural changes in the ground and excited states

NASA Astrophysics Data System (ADS)

Latha, V.; Balakrishnan, C.; Neelakantan, M. A.

2015-07-01

A fluorescent probe 2Z,2‧Z-3,3‧-(4,4‧-methylenebis(4,1-phenylene) bis(azanediyl))bis (1,3-diphenylprop-2-en-1-one) (L) was synthesized and characterized by IR, 1H NMR, ESI-mass, UV-visible and fluorescence spectral techniques. The single crystal analysis illustrates the existence of L in ketamine form. The crystal structure is stabilized by intramolecular and intermolecular hydrogen bonding. The thermal stability of L was studied by TG analysis. The fluorescence spectrum of L shows dual emission, and is due to excited state intramolecular proton transfer (ESIPT) process. This is supported by the high Stokes shift value. Electronic structure calculations of L in the ground and excited state have been carried out using DFT and TD-DFT at B3LYP/6-31G (d,p) level, respectively. The vibrational spectrum was computed at this level and compared with experimental values. Major orbital contributions for the electronic transitions were assigned with the help of TD-DFT. The changes in the Mulliken charge, bond lengths and bond angles between the ground and excited states of the tautomers demonstrate that twisted intramolecular charge transfer (TICT) process occurs along with ESIPT in the excited state.

A turn-on type stimuli-responsive fluorescent dye with specific solvent effect: Implication for a new prototype of paper using water as the ink

NASA Astrophysics Data System (ADS)

Hu, Xiaochen; Liu, Yang; Duan, Yuai; Han, Jingqi; Li, Zhongfeng; Han, Tianyu

2017-09-01

In this study, we reported the photoluminescence (PL) behaviour of a new intramolecular charge transfer (ICT) compound, ((E)-2-(((2-hydroxynaphthalen-1-yl)methylene)amino)benzoic acid, (HABA), which shows ICT solvent effect in aprotic solvents as confirmed by absorption and emission spectra. While in protic solvents including water and ethanol, the charge transfer (CT) band significantly reduces. Remarkable fluorescence enhancement in the blue region was also observed for HABA in polar protic solvents. We described such phenomena as ;specific solvent effect;. It can be ascribed to the hydrogen bonding formation between HABA and protic solvents, which not only causes significant reduction in the rate of internal conversion but also elevates the energy gap. Density functional theory (DFT) calculations as well as the dynamics analysis were performed to further verify the existence of hydrogen bonding complexes. Stronger emission turn-on effect was observed on HABA solid film when it is treated with water and base solution. The stimuli-responsive fluorescence of HABA enables a new green printing technique that uses water/base as the ink, affording fluorescent handwritings highly distinct from the background. Thermoanalysis of the dye suggests the nice thermostability, which is highly desired for real-world printing in a wide temperature range.

Fluorescent Sensing of Fluoride in Cellular System

PubMed Central

Jiao, Yang; Zhu, Baocun; Chen, Jihua; Duan, Xiaohong

2015-01-01

Fluoride ions have the important roles in a lot of physiological activities related with biological and medical system, such as water fluoridation, caries treatment, and bone disease treatment. Great efforts have been made to develop new methods and strategies for F- detection in the past decades. Traditional methods for the detection of F- including ion chromatography, ion-selective electrodes, and spectroscopic techniques have the limitations in the biomedicine research. The fluorescent probes for F- are very promising that overcome some drawbacks of traditional fluoride detection methods. These probes exhibit high selectivity, high sensitivity as well as quick response to the detection of fluoride anions. The review commences with a brief description of photophysical mechanisms for fluorescent probes for fluoride, including photo induced electron transfer (PET), intramolecular charge transfer (ICT), fluorescence resonance energy transfer (FRET), and excited-state intramolecular proton transfer (ESIPT). Followed by a discussion about common dyes for fluorescent fluoride probes, such as anthracene, naphalimide, pyrene, BODIPY, fluorescein, rhodamine, resorufin, coumarin, cyanine, and near-infrared (NIR) dyes. We divide the fluorescent probes for fluoride in cellular application systems into nine groups, for example, type of hydrogen bonds, type of cleavage of Si-O bonds, type of Si-O bond cleavage and cylization reactions, etc. We also review the recent reported carriers in the delivery of fluorescent fluoride probes. Seventy-four typical fluorescent fluoride probes are listed and compared in detail, including quantum yield, reaction medium, excitation and emission wavelengths, linear detection range, selectivity for F-, mechanism, and analytical applications. Finally, we discuss the future challenges of the application of fluorescent fluoride probes in cellular system and in vivo. We wish that more and more excellent fluorescent fluoride probes will be developed and applied in the biomedicine field in the future. PMID:25553106

Self-powered fluorescence display devices based on a fast self-charging/recharging battery (Mg/Prussian blue).

PubMed

Zhang, Hui; Yu, You; Zhang, Lingling; Zhai, Yiwen; Dong, Shaojun

2016-11-01

Stimuli-responsive (such as voltage and/or light) fluorescence display systems have attracted particular attention in their promising fields of application. However, there are few examples of self-powered fluorescence display devices. Here we designed and fabricated a self-powered fluorescence display device based on a fast-charging/recharging battery. The specially designed battery was composed of a Prussian blue (PB) cathode and a magnesium metal anode with a high theoretical redox potential difference (∼2.8 V). Moreover, smartly adding a trace amount of NaClO in the electrolyte could realize oxidizing PW to PB ∼480 times faster than when oxidizing without NaClO, leading to the fast self-charging and high power density (maximum power density of 13.34 mW cm -2 , about two to three orders of magnitude larger than previous bio-fuel cells) of the Mg/PB battery. Most importantly, PB was used as not only the cathodic catalyst but also as an electrochromic material, making it possible to construct a self-powered and rechargeable electrochromic fluorescence display with only two electrodes. Besides, fluorescent [Ru(bpy) 3 ] 2+ -doped silica nanoparticles (Ru@SiO 2 ), were selected as the fluorescence resonance energy transfer (FRET) donor to match PB (FRET acceptor). To the best of our knowledge, we demonstrated a self-powered and rechargeable electrochromic fluorescence display with only two electrodes for the first time.

Interaction of single-walled carbon nanotubes with poly(propyl ether imine) dendrimers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jayamurugan, G.; Rajesh, Y. B. R. D.; Jayaraman, N.

2011-03-14

We study the complexation of nontoxic, native poly(propyl ether imine) dendrimers with single-walled carbon nanotubes (SWNTs). The interaction was monitored by measuring the quenching of inherent fluorescence of the dendrimer. The dendrimer-nanotube binding also resulted in the increased electrical resistance of the hole doped SWNT, due to charge-transfer interaction between dendrimer and nanotube. This charge-transfer interaction was further corroborated by observing a shift in frequency of the tangential Raman modes of SWNT. We also report the effect of acidic and neutral pH conditions on the binding affinities. Experimental studies were supplemented by all atom molecular dynamics simulations to provide amore » microscopic picture of the dendrimer-nanotube complex. The complexation was achieved through charge transfer and hydrophobic interactions, aided by multitude of oxygen, nitrogen, and n-propyl moieties of the dendrimer.« less

Evidence for excited state intramolecular charge transfer in benzazole-based pseudo-stilbenes.

PubMed

Santos, Fabiano da Silveira; Descalzo, Rodrigo Roceti; Gonçalves, Paulo Fernando Bruno; Benvenutti, Edilson Valmir; Rodembusch, Fabiano Severo

2012-08-21

Two azo compounds were obtained through the diazotization reaction of aminobenzazole derivatives and N,N-dimethylaniline using clay montmorillonite KSF as catalyst. The synthesized dyes were characterized using elemental analysis, Fourier transform infrared spectroscopy, and (13)C and (1)H NMR spectroscopy in solution. Their photophysical behavior was studied using UV-vis and steady-state fluorescence in solution. These dyes present intense absorption in the blue region. The spectral features of the azo compounds can be related to the pseudo-stilbene type as well as the E isomer of the dyes. Excitation at the absorption maxima does not produce emissive species in the excited state. However, excitation around 350 nm allowed dual emission of fluorescence, from both a locally excited (LE, short wavelength) and an intramolecular charge transfer (ICT, long wavelength) state, which was corroborated by a linear relation of the fluorescence maximum (ν(max)) versus the solvent polarity function (Δf) from the Lippert-Mataga correlation. Evidence of TICT in these dyes was discussed from the viscosity dependence of the fluorescence intensity in the ICT emission band. Theoretical calculations were also performed in order to study the geometry and charge distribution of the dyes in their ground and excited electronic states. Using DFT methods at the theoretical levels BLYP/Aug-cc-pVDZ, for geometry optimizations and frequency calculations, and B3LYP/6-311+G(2d), for single-point energy evaluations, the calculations revealed that the least energetic and most intense photon absorption leads to a very polar excited state that relaxes non-radioactively, which can be associated with photochemical isomerization.

Coupled sensitizer-catalyst dyads: electron-transfer reactions in a perylene-polyoxometalate conjugate.

PubMed

Odobel, Fabrice; Séverac, Marjorie; Pellegrin, Yann; Blart, Errol; Fosse, Céline; Cannizzo, Caroline; Mayer, Cédric R; Elliott, Kristopher J; Harriman, Anthony

2009-01-01

Ultrafast discharge of a single-electron capacitor: A variety of intramolecular electron-transfer reactions are apparent for polyoxometalates functionalized with covalently attached perylene monoimide chromophores, but these are restricted to single-electron events. (et=electron transfer, cr=charge recombination, csr=charge-shift reaction, PER=perylene, POM=polyoxometalate).A new strategy is introduced that permits covalent attachment of an organic chromophore to a polyoxometalate (POM) cluster. Two examples are reported that differ according to the nature of the anchoring group and the flexibility of the linker. Both POMs are functionalized with perylene monoimide units, which function as photon collectors and form a relatively long-lived charge-transfer state under illumination. They are reduced to a stable pi-radical anion by electrolysis or to a protonated dianion under photolysis in the presence of aqueous triethanolamine. The presence of the POM opens up an intramolecular electron-transfer route by which the charge-transfer state reduces the POM. The rate of this process depends on the molecular conformation and appears to involve through-space interactions. Prior reduction of the POM leads to efficient fluorescence quenching, again due to intramolecular electron transfer. In most cases, it is difficult to resolve the electron-transfer products because of relatively fast reverse charge shift that occurs within a closed conformer. Although the POM can store multiple electrons, it has not proved possible to use these systems as molecular-scale capacitors because of efficient electron transfer from the one-electron-reduced POM to the excited singlet state of the perylene monoimide.

FRET Sensor for Erythrosine Dye Based on Organic Nanoparticles: Application to Analysis of Food Stuff.

PubMed

Mahajan, Prasad G; Bhopate, Dhanaji P; Kolekar, Govind B; Patil, Shivajirao R

2016-07-01

An aqueous suspension of fluorescent nanoparticles (PHNNPs) of naphthol based fluorescent organic compound 1-[(Z)-(2-phenylhydrazinylidene) methyl] naphthalene -2-ol (PHN) were prepared using reprecipitation method shows bathochromically shifted aggregation induced enhanced emission (AIEE) in the spectral region where erythrosine (ETS) food dye absorbs strongly. The average size of 72.6 nm of aqueous suspension of PHNNPs obtained by Dynamic light scattering results shows a narrow particle size distribution. The negative zeta potential of nano probe (-22.6 mV) responsible to adsorb oppositely charged analyte on its surface and further permit to bind nano probe and analyte within the close distance proximity required for efficient fluorescence resonance energy transfer (FRET) to take place from donor (PHNNPs) to acceptor (ETS). Systematic FRET experiments performed by measuring fluorescence quenching of PHNNPs with successive addition of ETS solution exploited the use of the PHNNPs as a novel nano probe for the detection of ETS in aqueous solution with extremely lower limit of detection equal to 3.6 nM (3.1 ng/mL). The estimation of photo kinetic and thermodynamic parameters such as quenching rate constant, enthalpy change (∆H), Gibbs free energy change (∆G) and entropy change (∆S) was obtained by the quenching results obtained at different constant temperatures which were found to fit the well-known Stern-Volmer relation. The mechanism of binding and fluorescence quenching of PHNNPs by ETS food dye is proposed on the basis of results obtained in photophysical studies, thermodynamic parameter, energy transfer efficiency, critical energy transfer distance (R0) and distance of approach between donor-acceptor molecules (r). The proposed FRET method based on fluorescence quenching of PHNNPs was successfully applied to develop an analytical method for estimation of ETS from food stuffs without interference of other complex ingredients. Graphical Abstract A fluorescent organic nanoprobe developed for the detection of erythrosine (ETS) food dye in aqueous medium based on fluorescence resonance energy transfer (FRET). The FRET process between donor (nanoparticles) and acceptor (ETS dye) arises due to oppositely charge attraction through hydrophobic interactions. The proposed method was successfully applied to quantitative determination of ETS dye in food stuff sample collected from local market.

Fluorescence turn-on responses of anionic and cationic conjugated polymers toward proteins: effect of electrostatic and hydrophobic interactions.

PubMed

Pu, Kan-Yi; Liu, Bin

2010-03-11

Cationic and anionic poly(fluorenyleneethynylene-alt-benzothiadiazole)s (PFEBTs) are designed and synthesized via Sonagashira coupling reaction to show light-up signatures toward proteins. Due to the charge transfer character of the excited states, the fluorescence of PFEBTs is very weak in aqueous solution, while their yellow fluorescence can be enhanced by polymer aggregation. PFEBTs show fluorescence turn-on rather than fluorescence quenching upon complexation with proteins. Both electrostatic and hydrophobic interactions between PFEBTs and proteins are found to improve the polymer fluorescence, the extent of which is dependent on the nature of the polymer and the protein. Changes in solution pH adjust the net charges of proteins, providing an effective way to manipulate electrostatic interactions and in turn the increment in the polymer fluorescence. In addition, the effect of protein digestion on the fluorescence of polymer/protein complexes is probed. The results indicate that electrostatic interaction induced polymer fluorescence increase cannot be substantially reduced through cleaving protein into peptide fragments. In contrast, hydrophobic interactions, mainly determined by the hydrophobicity of proteins, can be minimized by digestion, imparting a light-off signature for the polymer/protein complexes. This study thus not only highlights the opportunities of exerting nonspecific interactions for protein sensing but also reveals significant implications for biosensor design.

A new selective fluorene-based fluorescent internal charge transfer (ICT) sensor for sugar alcohols in aqueous solution.

PubMed

Hosseinzadeh, Rahman; Mohadjerani, Maryam; Pooryousef, Mona

2016-03-01

Sugar alcohols, such as sorbitol, are commonly used as a replacement for sucrose in the food industry, applied as starting material for vitamin C synthesis, and involved as one of the causative factors in diabetic complications. Therefore, their detection and quantification in aqueous solution are necessary. The reversible covalent interactions between boronic acids and diols are the basis of efficient methods for the detection of saccharides. Herein, we report a new internal charge transfer (ICT) fluorene-based fluorescent boronic acid sensor (1) 2-[(9,9-dimethyl-9H-fluoren-2-yl-amino)methyl] phenyl boronic acid that shows significant fluorescence changes upon addition of saccharides. The boronic acid has high affinity (K a = 1107.9 M(-1)) and selectivity for sorbitol at pH = 8.31. It showed a linear response toward sorbitol in the concentration range from 1.0 × 10(-5) to 6.0 × 10(-4) mol L(-1) with the detection limit of 7.04 × 10(-6) mol L(-1). Sensor 1 was used to detect sorbitol in real samples with good recovery.

Quantum dots as optical labels for ultrasensitive detection of polyphenols.

PubMed

Akshath, Uchangi Satyaprasad; Shubha, Likitha R; Bhatt, Praveena; Thakur, Munna Singh

2014-07-15

Considering the fact that polyphenols have versatile activity in-vivo, its detection and quantification is very much important for a healthy diet. Laccase enzyme can convert polyphenols to yield mono/polyquinones which can quench Quantum dots fluorescence. This phenomenon of charge transfer from quinones to QDs was exploited as optical labels to detect polyphenols. CdTe QD may undergo dipolar interaction with quinones as a result of broad spectral absorption due to multiple excitonic states resulting from quantum confinement effects. Thus, "turn-off" fluorescence method was applied for ultrasensitive detection of polyphenols by using laccase. We observed proportionate quenching of QDs fluorescence with respect to polyphenol concentration in the range of 100 µg to 1 ng/mL. Also, quenching of the photoluminescence was highly efficient and stable and could detect individual and total polyphenols with high sensitivity (LOD-1 ng/mL). Moreover, proposed method was highly efficient than any other reported methods in terms of sensitivity, specificity and selectivity. Therefore, a novel optical sensor was developed for the detection of polyphenols at a sensitive level based on the charge transfer mechanism. Copyright © 2014 Elsevier B.V. All rights reserved.

Introduction of a specific binding domain on myoglobin surface by new chemical modification.

PubMed

Hayashi, T; Ando, T; Matsuda, T; Yonemura, H; Yamada, S; Hisaeda, Y

2000-11-01

A new myoglobin, reconstituted with a modified zinc protoporphyrin, having a total of four ammonium groups at the terminal of the two propionate side chains was constructed to introduce a substrate binding site. The protein with a positively charged patch on the surface formed a stable complex with negatively charged substrates, such as hexacyanoferrate(III) and anthraquinonesulfonate via an electrostatic interaction. The complexation was monitored by fluorescence quenching due to singlet electron transfer from the photoexcited reconstituted zinc myoglobin to the substrates. The binding properties were evaluated by Stern-Volmer plots from the fluorescence quenching of the zinc myoglobin by a quencher. Particularly, anthraquinone-2,7-disulfonic acid showed a high affinity with a binding constant of 1.5 x 10(5) M(-1) in 10 mM phosphate buffer, pH 7.0. In contrast, the plots upon the addition of anthraquinone-2-sulfonic acid at different ionic strengths indicated that the complex was formed not only by an electrostatic interaction but also by a hydrophobic contact. The findings from the fluorescence studies conclude that the present system is a useful model for discussion of electron transfer via non-covalently linked donor-acceptor pairing on the protein surface.

Multisite constrained model of trans-4-(N,N-dimethylamino)-4'-nitrostilbene for structural elucidation of radiative and nonradiative excited states.

PubMed

Lin, Cheng-Kai; Wang, Yu-Fu; Cheng, Yuan-Chung; Yang, Jye-Shane

2013-04-18

A constrained model compound of trans-4-(N,N-dimethylamino)-4'-nitrostilbene (DNS), namely, compound DNS-B3 that is limited to torsions about the phenyl-nitro C-N bond and the central C═C bond, was prepared to investigate the structural nature of the radiative and nonradiative states of electronically excited DNS. The great similarities in solvent-dependent electronic spectra, fluorescence decay times, and quantum yields for fluorescence (Φf) and trans → cis photoisomerization (Φtc) between DNS and DNS-B3 indicate that the fluorescence is from a planar charge-transfer state and torsion of the nitro group is sufficient to account for the nonradiative decay of DNS. This conclusion is supported by TDDFT calculations on DNS-B3 in dichloromethane. The structure at the conical intersection for internal conversion is associated with not only a twisting but also a pyramidalization of the nitro group. The mechanism of the NO2 torsion is discussed in terms of the effects of solvent polarity, the substituents, and the volume demand. The differences and analogies of the NO2- vs amino-twisted intramolecular charge-transfer (TICT) state of trans-aminostilbenes are also discussed.

Spectroscopic and molecular docking studies on the charge transfer complex of bovine serum albumin with quinone in aqueous medium and its influence on the ligand binding property of the protein.

PubMed

Satheshkumar, Angupillai; Elango, Kuppanagounder P

2014-09-15

The spectral techniques such as UV-Vis, (1)H NMR and fluorescence and electrochemical experiments have been employed to investigate the interaction between 2-methoxy-3,5,6-trichloro-1,4-benzoquinone (MQ; a water soluble quinone) and bovine serum albumin (BSA) in aqueous medium. The fluorescence of BSA was quenched by MQ via formation of a 1:1 BSA-MQ charge transfer adduct with a formation constant of 3.3×10(8) L mol(-1). Based on the Forster's theory the binding distance between them is calculated as 2.65 nm indicating high probability of binding. For the first time, influence of quinone on the binding property of various types of ligands such as aspirin, ascorbic acid, nicotinimide and sodium stearate has also been investigated. The results indicated that the strong and spontaneous binding existing between BSA and MQ, decreased the intensity of binding of these ligands with BSA. Since Tryptophan (Trp) is the basic residue present in BSA, a comparison between binding property of Trp-MQ adduct with that of BSA-MQ with these ligands has also been attempted. 1H NMR titration study indicated that the Trp forms a charge transfer complex with MQ, which reduces the interaction of Trp with the ligands. Molecular docking study supported the fact that the quinone interacts with the Trp212 unit of the BSA and the free energy change of binding (ΔG) for the BSA-MQ complex was found to be -46 kJ mol(-1), which is comparable to our experimental free energy of binding (-49 kJ mol(-1)) obtained from fluorescence study. Copyright © 2014 Elsevier B.V. All rights reserved.

Spectroscopic and molecular docking studies on the charge transfer complex of bovine serum albumin with quinone in aqueous medium and its influence on the ligand binding property of the protein

NASA Astrophysics Data System (ADS)

Satheshkumar, Angupillai; Elango, Kuppanagounder P.

2014-09-01

The spectral techniques such as UV-Vis, 1H NMR and fluorescence and electrochemical experiments have been employed to investigate the interaction between 2-methoxy-3,5,6-trichloro-1,4-benzoquinone (MQ; a water soluble quinone) and bovine serum albumin (BSA) in aqueous medium. The fluorescence of BSA was quenched by MQ via formation of a 1:1 BSA-MQ charge transfer adduct with a formation constant of 3.3 × 108 L mol-1. Based on the Forster’s theory the binding distance between them is calculated as 2.65 nm indicating high probability of binding. For the first time, influence of quinone on the binding property of various types of ligands such as aspirin, ascorbic acid, nicotinimide and sodium stearate has also been investigated. The results indicated that the strong and spontaneous binding existing between BSA and MQ, decreased the intensity of binding of these ligands with BSA. Since Tryptophan (Trp) is the basic residue present in BSA, a comparison between binding property of Trp-MQ adduct with that of BSA-MQ with these ligands has also been attempted. 1H NMR titration study indicated that the Trp forms a charge transfer complex with MQ, which reduces the interaction of Trp with the ligands. Molecular docking study supported the fact that the quinone interacts with the Trp212 unit of the BSA and the free energy change of binding (ΔG) for the BSA-MQ complex was found to be -46 kJ mol-1, which is comparable to our experimental free energy of binding (-49 kJ mol-1) obtained from fluorescence study.

Hydrogen bond strengthening induces fluorescence quenching of PRODAN derivative by turning on twisted intramolecular charge transfer

NASA Astrophysics Data System (ADS)

Yang, Yonggang; Li, Donglin; Li, Chaozheng; Liu, YuFang; Jiang, Kai

2017-12-01

Researchers have proposed different effective mechanisms of hydrogen bonding (HB) on the fluorescence of 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and its derivatives. Herein, excited state transition and dynamics analysis confirm that the fluorescence of PD (a derivative of PRODAN with ethyl replaced by 3-hydroxy-2,2-dimethylpropan) emits from the planar intramolecular charge transfer (PICT) state rather than twist ICT (TICT) state, because the fluorescence emission and surface hopping from the TICT state to the twist ground (T-S0) state is energy forbidden. Nevertheless, the strengthening of intramolecular-HB (intra-HB) and intermolecular-HB (inter-HB) of PD-(methanol)2 smooth the pathway of surface hopping from TICT to T-S0 state and the external conversion going to planar ground state by decreasing the energy difference of the two states. This smoothing changes the fluorescence state of PD-(methanol)2 to the TICT state in which fluorescence emission does not occur but surface hopping, leading to the partial fluorescence quenching of PD in methanol solvent. This conclusion is different from previous related reports. Moreover, the inter-HB strengthening of PD-methanol in PICT state induces the cleavage of intra-HB and a fluorescence red-shift of 54 nm compared to PD. This red-shift increases to 66 nm for PD-(methanol)2 for the strengthening of the one intra-HB and two inter-HBs. The dipole moments of PD-methanol and PD-(methanol)2 respectively increase about 10.3D and 8.1D in PICT state compared to PD. The synergistic effect of intra-HB and inter-HB induces partial quenching of PD in methanol solvent by turning on the TICT state and fluorescence red-shift. This work gives a reasonable description on the fluorescence red-shift and partial quenching of PD in methanol solvent, which will bring insight into the study of spectroscopic properties of molecules owning better spectral characteristics.

Hydrogen bond strengthening induces fluorescence quenching of PRODAN derivative by turning on twisted intramolecular charge transfer.

PubMed

Yang, Yonggang; Li, Donglin; Li, Chaozheng; Liu, YuFang; Jiang, Kai

2017-12-05

Researchers have proposed different effective mechanisms of hydrogen bonding (HB) on the fluorescence of 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and its derivatives. Herein, excited state transition and dynamics analysis confirm that the fluorescence of PD (a derivative of PRODAN with ethyl replaced by 3-hydroxy-2,2-dimethylpropan) emits from the planar intramolecular charge transfer (PICT) state rather than twist ICT (TICT) state, because the fluorescence emission and surface hopping from the TICT state to the twist ground (T-S 0 ) state is energy forbidden. Nevertheless, the strengthening of intramolecular-HB (intra-HB) and intermolecular-HB (inter-HB) of PD-(methanol) 2 smooth the pathway of surface hopping from TICT to T-S 0 state and the external conversion going to planar ground state by decreasing the energy difference of the two states. This smoothing changes the fluorescence state of PD-(methanol) 2 to the TICT state in which fluorescence emission does not occur but surface hopping, leading to the partial fluorescence quenching of PD in methanol solvent. This conclusion is different from previous related reports. Moreover, the inter-HB strengthening of PD-methanol in PICT state induces the cleavage of intra-HB and a fluorescence red-shift of 54nm compared to PD. This red-shift increases to 66nm for PD-(methanol) 2 for the strengthening of the one intra-HB and two inter-HBs. The dipole moments of PD-methanol and PD-(methanol) 2 respectively increase about 10.3D and 8.1D in PICT state compared to PD. The synergistic effect of intra-HB and inter-HB induces partial quenching of PD in methanol solvent by turning on the TICT state and fluorescence red-shift. This work gives a reasonable description on the fluorescence red-shift and partial quenching of PD in methanol solvent, which will bring insight into the study of spectroscopic properties of molecules owning better spectral characteristics. Copyright © 2017 Elsevier B.V. All rights reserved.

In vivo imaging of endogenous enzyme activities using luminescent 1,2-dioxetane compounds.

PubMed

Tseng, Jen-Chieh; Kung, Andrew L

2015-06-24

Here we present a non-invasive imaging method for visualizing endogenous enzyme activities in living animals. This optical imaging method is based on an energy transfer principle termed chemically initiated electron exchange luminescence (CIEEL). The light energy is provided by enzymatic activation of metastable 1,2-dioxetane substrates, whose protective groups are removed by hydrolytic enzymes such as β-galactosidase and alkaline phosphatase. In the presence of a nearby fluorescent recipient, the chemical energy within the activated substrate is then transferred via formation of a charge-transfer complex with the fluorophore, a mechanism closely related to glow stick chemistry. Efficient CIEEL energy transfer requires close proximity between the trigger enzyme and the fluorescent recipient. Using cells stained with fluorescent dialkylcarbocyanines as the energy recipients, we demonstrated CIEEL imaging of cellular β-galactosidase or alkaline phosphatase activity. In living animals, we used a similar approach to non-invasively image alkaline phosphatase activity in the peritoneal cavity. In this report, we provide proof-of-concept for CIEEL imaging of in vivo enzymatic activity. In addition, we demonstrate the use of CIEEL energy transfer for visualizing elevated alkaline phosphatase activity associated with tissue inflammation in living animals.

AIE active multianalyte fluorescent probe for the detection of Cu2+, Ni2+ and Hg2+ ions.

PubMed

Pannipara, Mehboobali; Al-Sehemi, Abdullah G; Irfan, Ahmad; Assiri, Mohammed; Kalam, Abul; Al-Ammari, Yahya S

2018-08-05

A novel pyrazolyl chromene derivative (Probe 1) displaying aggregation induced emission (AIE) properties that capable of sensing of multiple metal ions has been designed and synthesized. The multi analyte probe exhibits selective sensing for Cu 2+ and Ni 2+ ions via fluorescence turn-off mechanism and ratiometric selectivity for Hg 2+ ions in aqueous media. The extent of binding of the probe with sensitive metal ions has been demonstrated. The experimental results were further investigated by computational means by optimizing the ground state geometries of Probe 1 and its various metal complexes for Probe 1-Ni, Probe 1-Hg and Probe 1-Cu using density functional theory (DFT) at B3LYP/6-31+g(d,p) (LANL2DZ) level. On the basis of binding energies, the stability of metal complexes has been studied. In Probe 1-Ni and Probe 1-Cu complexes, charge transfer has been observed from Probe 1 to metal ions revealing ligand to metal charge transfer (LMCT) while in Probe1-Hg complex LMCT as well as intra-molecular charge tranfer (ICT) within Probe 1. Copyright © 2018 Elsevier B.V. All rights reserved.

Revealing the spin–vibronic coupling mechanism of thermally activated delayed fluorescence

PubMed Central

Etherington, Marc K.; Gibson, Jamie; Higginbotham, Heather F.; Penfold, Thomas J.; Monkman, Andrew P.

2016-01-01

Knowing the underlying photophysics of thermally activated delayed fluorescence (TADF) allows proper design of high efficiency organic light-emitting diodes. We have proposed a model to describe reverse intersystem crossing (rISC) in donor–acceptor charge transfer molecules, where spin–orbit coupling between singlet and triplet states is mediated by one of the local triplet states of the donor (or acceptor). This second order, vibronically coupled mechanism describes the basic photophysics of TADF. Through a series of measurements, whereby the energy ordering of the charge transfer (CT) excited states and the local triplet are tuned in and out of resonance, we show that TADF reaches a maximum at the resonance point, substantiating our model of rISC. Moreover, using photoinduced absorption, we show how the populations of both singlet and triplet CT states and the local triplet state change in and out of resonance. Our vibronic coupling rISC model is used to predict this behaviour and describes how rISC and TADF are affected by external perturbation. PMID:27901046

Revealing the spin-vibronic coupling mechanism of thermally activated delayed fluorescence

NASA Astrophysics Data System (ADS)

Etherington, Marc K.; Gibson, Jamie; Higginbotham, Heather F.; Penfold, Thomas J.; Monkman, Andrew P.

2016-11-01

Knowing the underlying photophysics of thermally activated delayed fluorescence (TADF) allows proper design of high efficiency organic light-emitting diodes. We have proposed a model to describe reverse intersystem crossing (rISC) in donor-acceptor charge transfer molecules, where spin-orbit coupling between singlet and triplet states is mediated by one of the local triplet states of the donor (or acceptor). This second order, vibronically coupled mechanism describes the basic photophysics of TADF. Through a series of measurements, whereby the energy ordering of the charge transfer (CT) excited states and the local triplet are tuned in and out of resonance, we show that TADF reaches a maximum at the resonance point, substantiating our model of rISC. Moreover, using photoinduced absorption, we show how the populations of both singlet and triplet CT states and the local triplet state change in and out of resonance. Our vibronic coupling rISC model is used to predict this behaviour and describes how rISC and TADF are affected by external perturbation.

The importance of charge-transfer interactions in determining chromophoric dissolved organic matter (CDOM) optical and photochemical properties.

PubMed

Sharpless, Charles M; Blough, Neil V

2014-04-01

Absorption of sunlight by chromophoric dissolved natural organic matter (CDOM) is environmentally significant because it controls photic zone depth and causes photochemistry that affects elemental cycling and contaminant fate. Both the optics (absorbance and fluorescence) and photochemistry of CDOM display unusual properties that cannot easily be ascribed to a superposition of individual chromophores. These include (i) broad, unstructured absorbance that decreases monotonically well into the visible and near IR, (ii) fluorescence emission spectra that all fall into a single envelope regardless of the excitation wavelength, and (iii) photobleaching and photochemical quantum yields that decrease monotonically with increasing wavelength. In contrast to a simple superposition model, these phenomena and others can be reasonably well explained by a physical model in which charge-transfer interactions between electron donating and accepting chromophores within the CDOM control the optical and photophysical properties. This review summarizes current understanding of the processes underlying CDOM photophysics and photochemistry as well as their physical basis.

Protein-membrane interaction and fatty acid transfer from intestinal fatty acid-binding protein to membranes. Support for a multistep process.

PubMed

Falomir-Lockhart, Lisandro J; Laborde, Lisandro; Kahn, Peter C; Storch, Judith; Córsico, Betina

2006-05-19

Fatty acid transfer from intestinal fatty acid-binding protein (IFABP) to phospholipid membranes occurs during protein-membrane collisions. Electrostatic interactions involving the alpha-helical "portal" region of the protein have been shown to be of great importance. In the present study, the role of specific lysine residues in the alpha-helical region of IFABP was directly examined. A series of point mutants in rat IFABP was engineered in which the lysine positive charges in this domain were eliminated or reversed. Using a fluorescence resonance energy transfer assay, we analyzed the rates and mechanism of fatty acid transfer from wild type and mutant proteins to acceptor membranes. Most of the alpha-helical domain mutants showed slower absolute fatty acid transfer rates to zwitterionic membranes, with substitution of one of the lysines of the alpha2 helix, Lys27, resulting in a particularly dramatic decrease in the fatty acid transfer rate. Sensitivity to negatively charged phospholipid membranes was also reduced, with charge reversal mutants in the alpha2 helix the most affected. The results support the hypothesis that the portal region undergoes a conformational change during protein-membrane interaction, which leads to release of the bound fatty acid to the membrane and that the alpha2 segment is of particular importance in the establishment of charge-charge interactions between IFABP and membranes. Cross-linking experiments with a phospholipid-photoactivable reagent underscored the importance of charge-charge interactions, showing that the physical interaction between wild-type intestinal fatty acid-binding protein and phospholipid membranes is enhanced by electrostatic interactions. Protein-membrane interactions were also found to be enhanced by the presence of ligand, suggesting different collisional complex structures for holo- and apo-IFABP.

Concise and Efficient Fluorescent Probe via an Intromolecular Charge Transfer for the Chemical Warfare Agent Mimic Diethylchlorophosphate Vapor Detection.

PubMed

Yao, Junjun; Fu, Yanyan; Xu, Wei; Fan, Tianchi; Gao, Yixun; He, Qingguo; Zhu, Defeng; Cao, Huimin; Cheng, Jiangong

2016-02-16

Sarin, used as chemical warfare agents (CWAs) for terrorist attacks, can induce a number of virulent effects. Therefore, countermeasures which could realize robust and convenient detection of sarin are in exigent need. A concise charge-transfer colorimetric and fluorescent probe (4-(6-(tert-butyl)pyridine-2-yl)-N,N-diphenylaniline, TBPY-TPA) that could be capable of real-time and on-site monitoring of DCP vapor was reported in this contribution. Upon contact with DCP, the emission band red-shifted from 410 to 522 nm upon exposure to DCP vapor. And the quenching rate of TBPY-TPA reached up to 98% within 25 s. Chemical substances such as acetic acid (HAc), dimethyl methylphosphonate (DMMP), pinacolyl methylphosphonate (PAMP), and triethyl phosphate (TEP) do not interfere with the detection. A detection limit for DCP down to 2.6 ppb level is remarkably achieved which is below the Immediately Dangerous to Life or Health concentration. NMR data suggested that a transformation of the pyridine group into pyridinium salt via a cascade reaction is responsible for the sensing process which induced the dramatic fluorescent red shift. All of these data suggest TBPY-TPA is a promising fluorescent sensor for a rapid, simple, and low-cost method for DCP detection, which could be easy to prepare as a portable chemosensor kit for its practical application in real-time and on-site monitoring.

Extended Fluorescent Resonant Energy Transfer in DNA Constructs

NASA Astrophysics Data System (ADS)

Oh, Taeseok

This study investigates the use of surfactants and metal cations for the enhancement of long range fluorescent resonant energy transfer (FRET) and the antenna effect in DNA structures with multiple fluorescent dyes. Double-stranded (ds) DNA structures were formed by hybridization of 21mer DNA oligonucleotides with different arrangements of three fluorescent TAMRA donor dyes with two different complementary 21mer oligonucleotides with one fluorescent TexasRed acceptor dye. In such DNA structures, hydrophobic interactions between the fluorescent dyes in close proximity produces dimerization which along with other quenching mechanisms leads to significant reduction of fluorescent emission properties. Addition of the surfactants Triton X-100, cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) along with sodium cations (Na+) and divalent magnesium cations (Mg 2+) were tested for their ability to reduce quenching of the fluorescent dyes and improve overall fluorescent emission, the long range FRET and the antenna effect properties. When the neutral (uncharged) surfactant Triton X-100 was added to the FRET ds-DNA hybrid structures with three TAMRA donors and one TexasRed acceptor, dye dimerization and emission quenching remained unaffected. However, for the positively charged CTAB surfactant at concentrations of 100 uM or higher, the neutralization of the negatively charged ds-DNA backbone by the cationic surfactant micelles was found to reduce TAMRA dye dimerization and emission quenching and improve TexasRed quantum yield, resulting in much higher FRET efficiencies and an enhanced antenna effect. This improvement is likely due to the CTAB molecules covering or sheathing the fluorescent donor and acceptor dyes which breaks up the dimerized dye complexes and prevents further quenching from interactions with water molecules and guanine bases in the DNA structure. While the negatively charged SDS surfactant alone was not able to reduce dimerization and emission quenching due to repulsive forces between DNA and SDS micelles, the addition of cations such as sodium ions (Na+) and divalent magnesium ions (Mg2+) did lead to a significant reduction in the dimerization and emission quenching resulting in much higher FRET efficiency and an enhanced antenna effect. It appears that when the repulsive electrostatic forces are screened by the cations (Mg2+ in particular), the SDS micelles can approach the FRET ds-DNA structures thereby sheathing or insulating the TAMRA and TexasRed dyes. Overall, the study provides a viable strategy for using combinations of surfactants and cations to reduce adverse fluorescent dye and other quenching mechanisms and improve the overall long distance FRET efficiency and the antenna effect in DNA structures with multi-donor and single acceptor fluorescent dye groups.

Molecular-Scale Investigation of Heavy Metal Ions at a Charged Langmuir Monolayer

NASA Astrophysics Data System (ADS)

Rock, William; Qiao, Baofu; Uysal, Ahmet; Bu, Wei; Lin, Binhua

Solvent extraction - the surfactant-aided preferential transfer of a species from an aqueous to an organic phase - is an important technique used in heavy and precious metal refining and reprocessing. Solvent extraction requires transfer through an oil/water interface, and interfacial interactions are expected to control transfer kinetics and phase stability, yet these key interactions are poorly understood. Langmuir monolayers with charged headgroups atop concentrated salt solutions containing heavy metal ions act as a model of solvent extraction interfaces; studies of ions at a charged surface are also fundamentally important to many other phenomena including protein solvation, mineral surface chemistry, and electrochemistry. We probe these charged interfaces using a variety of surface-sensitive techniques - vibrational sum frequency generation (VSFG) spectroscopy, x-ray reflectivity (XRR), x-ray fluorescence near total reflection (XFNTR), and grazing incidence diffraction (GID). We integrate experiments with Molecular Dynamics (MD) simulations to uncover the molecular-level interfacial structure. This work is supported by the U.S. DOE, BES, Contract DE-AC02-06CH11357. ChemMatCARS is supported by NSF/CHE-1346572.

Efficient fluorescence energy transfer system between CdTe-doped silica nanoparticles and gold nanoparticles for turn-on fluorescence detection of melamine.

PubMed

Gao, Feng; Ye, Qingqing; Cui, Peng; Zhang, Lu

2012-05-09

We here report an efficient and enhanced fluorescence energy transfer system between confined quantum dots (QDs) by entrapping CdTe into the mesoporous silica shell (CdTe@SiO₂) as donors and gold nanoparticles (AuNPs) as acceptors. At pH 6.50, the CdTe@SiO₂-AuNPs assemblies coalesce to form larger clusters due to charge neutralization, leading to the fluorescence quenching of CdTe@SiO₂ as a result of energy transfer. As compared with the energy transfer system between unconfined CdTe and AuNPs, the maximum fluorescence quenching efficiency of the proposed system is improved by about 27.0%, and the quenching constant, K(sv), is increased by about 2.4-fold. The enhanced quenching effect largely turns off the fluorescence of CdTe@SiO₂ and provides an optimal "off-state" for sensitive "turn-on" assay. In the present study, upon addition of melamine, the weak fluorescence system of CdTe@SiO₂-AuNPs is enhanced due to the strong interactions between the amino group of melamine and the gold nanoparticles via covalent bond, leading to the release of AuNPs from the surfaces of CdTe@SiO₂; thus, its fluorescence is restored. A "turn-on" fluorimetric method for the detection of melamine is proposed based on the restored fluorescence of the system. Under the optimal conditions, the fluorescence enhanced efficiency shows a linear function against the melamine concentrations ranging from 7.5 × 10⁻⁹ to 3.5 × 10⁻⁷ M (i.e., 1.0-44 ppb). The analytical sensitivity is improved by about 50%, and the detection limit is decreased by 5.0-fold, as compared with the analytical results using the CdTe-AuNPs system. Moreover, the proposed method was successfully applied to the determination of melamine in real samples with excellent recoveries in the range from 97.4 to 104.1%. Such a fluorescence energy transfer system between confined QDs and AuNPs may pave a new way for designing chemo/biosensing.

A fluorescent probe based on nitrogen doped graphene quantum dots for turn off sensing of explosive and detrimental water pollutant, TNP in aqueous medium

NASA Astrophysics Data System (ADS)

Kaur, Manjot; Mehta, Surinder K.; Kansal, Sushil Kumar

2017-06-01

This paper reports the carbonization assisted green approach for the fabrication of nitrogen doped graphene quantum dots (N-GQDs). The obtained N-GQDs displayed good water dispersibility and stability in the wide pH range. The as synthesized N-GQDs were used as a fluorescent probe for the sensing of explosive 2,4,6-trinitrophenol (TNP) in aqueous medium based on fluorescence resonance energy transfer (FRET), molecular interactions and charge transfer mechanism. The quenching efficiency was found to be linear in proportion to the TNP concentration within the range of 0-16 μM with detection limit (LOD) of 0.92 μM. The presented method was successfully applied to the sensing of TNP in tap and lake water samples with satisfactory results. Thus, N-GQDs were used as a selective, sensitive and turn off fluorescent sensor for the detection of perilous water contaminant i.e. TNP.

A fluorescent probe based on nitrogen doped graphene quantum dots for turn off sensing of explosive and detrimental water pollutant, TNP in aqueous medium.

PubMed

Kaur, Manjot; Mehta, Surinder K; Kansal, Sushil Kumar

2017-06-05

This paper reports the carbonization assisted green approach for the fabrication of nitrogen doped graphene quantum dots (N-GQDs). The obtained N-GQDs displayed good water dispersibility and stability in the wide pH range. The as synthesized N-GQDs were used as a fluorescent probe for the sensing of explosive 2,4,6-trinitrophenol (TNP) in aqueous medium based on fluorescence resonance energy transfer (FRET), molecular interactions and charge transfer mechanism. The quenching efficiency was found to be linear in proportion to the TNP concentration within the range of 0-16μM with detection limit (LOD) of 0.92μM. The presented method was successfully applied to the sensing of TNP in tap and lake water samples with satisfactory results. Thus, N-GQDs were used as a selective, sensitive and turn off fluorescent sensor for the detection of perilous water contaminant i.e. TNP. Copyright © 2017 Elsevier B.V. All rights reserved.

An artificial tongue fluorescent sensor array for identification and quantitation of various heavy metal ions.

PubMed

Xu, Wang; Ren, Changliang; Teoh, Chai Lean; Peng, Juanjuan; Gadre, Shubhankar Haribhau; Rhee, Hyun-Woo; Lee, Chi-Lik Ken; Chang, Young-Tae

2014-09-02

Herein, a small-molecule fluorescent sensor array for rapid identification of seven heavy metal ions was designed and synthesized, with its sensing mechanism mimicking that of a tongue. The photoinduced electron transfer and intramolecular charge transfer mechanism result in combinatorial interactions between sensor array and heavy metal ions, which lead to diversified fluorescence wavelength shifts and emission intensity changes. Upon principle component analysis (PCA), this result renders clear identification of each heavy metal ion on a 3D spatial dispersion graph. Further exploration provides a concentration-dependent pattern, allowing both qualitative and quantitative measurements of heavy metal ions. On the basis of this information, a "safe-zone" concept was proposed, which provides rapid exclusion of versatile hazardous species from clean water samples based on toxicity characteristic leaching procedure standards. This type of small-molecule fluorescent sensor array could open a new avenue for multiple heavy metal ion detection and simplified water quality analysis.

Studies of bio-mimetic medium of ionic and non-ionic micelles by a simple charge transfer fluorescence probe N,N-dimethylaminonapthyl-(acrylo)-nitrile

NASA Astrophysics Data System (ADS)

Samanta, Anuva; Paul, Bijan Kumar; Guchhait, N.

2011-05-01

In this report we have studied micellization process of anionic, cationic and non-ionic surfactants using N,N-dimethylaminonapthyl-(acrylo)-nitrile (DMANAN) as an external fluorescence probe. Micropolarity, microviscosity, critical micellar concentration of these micelles based on steady state absorption and fluorescence and time resolved emission spectroscopy of the probe DMANAN show that the molecule resides in the micelle-water interface for ionic micelles and in the core for the non-ionic micelle. The effect of variation of pH of the micellar solution as well as fluorescence quenching measurements of DMANAN provide further support for the location of the probe in the micelles.

Highly selective and sensitive turn-on fluorescent sensor for detection of Al3+ based on quinoline-base Schiff base

NASA Astrophysics Data System (ADS)

Wang, Yang; Ma, Zhong-Ying; Zhang, De-Long; Deng, Jia-Li; Chen, Xiong; Xie, Cheng-Zhi; Qiao, Xin; Li, Qing-Zhong; Xu, Jing-Yuan

2018-04-01

A new aluminum ion fluorescent probe (4-(diethylamino)-2-hydroxybenzylidene)isoquinoline-1-carbohydrazide (HL1) has been conveniently synthesized and characterized. HL1 exhibited a highly selective and pronounced enhancement for Al3+ in the fluorescence emission over other common cations by forming a 2:1 complex, with a recognition mechanism based on excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT). The strong fluorescent emission can be observed even at ppm level concentration of the probe in the presence of Al3+ with 41 fold intensity enhancement at 545 nm. HL1 displays good linear relationship with Al3+ in the low concentration and the limit of detection is 8.08 × 10-8 mol/L. Similar molecules with different substituents on salicylaldehyde phenyl ring were synthesized for studying the structure-activity relationship. Density-functional theory (DFT) calculations are in agreement with the proposed mechanism. It is confirmed that HL1 could be used to detect Al3+ ions in real sample by fluorescence spectrometry and Al3+ ions in cells by bioimaging.

Biophysical characterization of the fluorescent protein voltage probe VSFP2.3 based on the voltage-sensing domain of Ci-VSP.

PubMed

Lundby, Alicia; Akemann, Walther; Knöpfel, Thomas

2010-11-01

A voltage sensitive phosphatase was discovered in the ascidian Ciona intestinalis. The phosphatase, Ci-VSP, contains a voltage-sensing domain homologous to those known from voltage-gated ion channels, but unlike ion channels, the voltage-sensing domain of Ci-VSP can reside in the cell membrane as a monomer. We fused the voltage-sensing domain of Ci-VSP to a pair of fluorescent reporter proteins to generate a genetically encodable voltage-sensing fluorescent probe, VSFP2.3. VSFP2.3 is a fluorescent voltage probe that reports changes in membrane potential as a FRET (fluorescence resonance energy transfer) signal. Here we report sensing current measurements from VSFP2.3, and show that VSFP2.3 carries 1.2 e sensing charges, which are displaced within 1.5 ms. The sensing currents become faster at higher temperatures, and the voltage dependence of the decay time constants is temperature dependent. Neutralization of an arginine in S4, previously suggested to be a sensing charge, and measuring associated sensing currents indicate that this charge is likely to reside at the membrane-aqueous interface rather than within the membrane electric field. The data presented give us insights into the voltage-sensing mechanism of Ci-VSP, which will allow us to further improve the sensitivity and kinetics of the family of VSFP proteins.

Voltage-dependent dynamic FRET signals from the transverse tubules in mammalian skeletal muscle fibers.

PubMed

DiFranco, Marino; Capote, Joana; Quiñonez, Marbella; Vergara, Julio L

2007-12-01

Two hybrid voltage-sensing systems based on fluorescence resonance energy transfer (FRET) were used to record membrane potential changes in the transverse tubular system (TTS) and surface membranes of adult mice skeletal muscle fibers. Farnesylated EGFP or ECFP (EGFP-F and ECFP-F) were used as immobile FRET donors, and either non-fluorescent (dipicrylamine [DPA]) or fluorescent (oxonol dye DiBAC(4)(5)) lipophilic anions were used as mobile energy acceptors. Flexor digitorum brevis (FDB) muscles were transfected by in vivo electroporation with pEGFP-F and pECFP-F. Farnesylated fluorescent proteins were efficiently expressed in the TTS and surface membranes. Voltage-dependent optical signals resulting from resonance energy transfer from fluorescent proteins to DPA were named QRET transients, to distinguish them from FRET transients recorded using DiBAC(4)(5). The peak DeltaF/F of QRET transients elicited by action potential stimulation is twice larger in fibers expressing ECFP-F as those with EGFP-F (7.1% vs. 3.6%). These data provide a unique experimental demonstration of the importance of the spectral overlap in FRET. The voltage sensitivity of QRET and FRET signals was demonstrated to correspond to the voltage-dependent translocation of the charged acceptors, which manifest as nonlinear components in current records. For DPA, both electrical and QRET data were predicted by radial cable model simulations in which the maximal time constant of charge translocation was 0.6 ms. FRET signals recorded in response to action potentials in fibers stained with DiBAC(4)(5) exhibit DeltaF/F amplitudes as large as 28%, but their rising phase was slower than those of QRET signals. Model simulations require a time constant for charge translocation of 1.6 ms in order to predict current and FRET data. Our results provide the basis for the potential use of lipophilic ions as tools to test for fast voltage-dependent conformational changes of membrane proteins in the TTS.

Direct Observation of Excimer-Mediated Intramolecular Electron Transfer in a Cofacially-Stacked Perylene Bisimide Pair.

PubMed

Sung, Jooyoung; Nowak-Król, Agnieszka; Schlosser, Felix; Fimmel, Benjamin; Kim, Woojae; Kim, Dongho; Würthner, Frank

2016-07-27

We have elucidated excimer-mediated intramolecular electron transfer in cofacially stacked PBIs tethered by two phenylene-butadiynylene loops. The electron transfer between energetically equivalent PBIs is revealed by the simultaneous observation of the PBI radical anion and cation bands in the transient absorption spectra. The fluorescence decay time of the excimer states is in good agreement with the rise time of PBI radical bands in transient absorption spectra suggesting that the electron transfer dynamics proceed via the excimer state. We can conclude that the excimer state effectuates the efficient charge transfer in the cofacially stacked PBI dimer.

Dielectric controlled excited state relaxation pathways of a representative push-pull stilbene: a mechanistic study using femtosecond fluorescence up-conversion technique.

PubMed

Rafiq, Shahnawaz; Sen, Pratik

2013-02-28

Femtosecond fluorescence up-conversion technique was employed to reinvestigate the intriguing dependence of fluorescence quantum yield of trans-4-dimethylamino-4(')-nitrostilbene (DNS) on dielectric properties of the media. In polar solvents, such as methanol and acetonitrile, the two time components of the fluorescence transients were assigned to intramolecular charge transfer (ICT) dynamics and to the depletion of the ICT state to the ground state via internal conversion along the torsional coordinate of nitro moiety. The viscosity independence of the first time component indicates the absence of any torsional coordinate in the charge transfer process. In slightly polar solvent (carbon tetrachloride) the fluorescence transients show a triple exponential behavior. The first time component was assigned to the formation of the ICT state on a 2 ps time scale. Second time component was assigned to the relaxation of the ICT state via two torsion controlled channels. First channel involves the torsional motion about the central double bond leading to the trans-cis isomerization via a conical intersection or avoided crossing. The other channel contributing to the depopulation of ICT state involves the torsional coordinates of dimethylanilino and∕or nitrophenyl moieties and leads to the formation of a conformationally relaxed state, which subsequently relaxes back to the ground state radiatively, and is responsible for the high fluorescence quantum yield of DNS in slightly polar solvents such as carbon tetrachloride, toluene, etc. The excited singlet state which is having a dominant π-π∗ character may also decay via intersystem crossing to the n-π∗ triplet manifold and thus accounts for the observed triplet yield of the molecule in slightly polar solvents.

Dielectric controlled excited state relaxation pathways of a representative push-pull stilbene: A mechanistic study using femtosecond fluorescence up-conversion technique

NASA Astrophysics Data System (ADS)

Rafiq, Shahnawaz; Sen, Pratik

2013-02-01

Femtosecond fluorescence up-conversion technique was employed to reinvestigate the intriguing dependence of fluorescence quantum yield of trans-4-dimethylamino-4'-nitrostilbene (DNS) on dielectric properties of the media. In polar solvents, such as methanol and acetonitrile, the two time components of the fluorescence transients were assigned to intramolecular charge transfer (ICT) dynamics and to the depletion of the ICT state to the ground state via internal conversion along the torsional coordinate of nitro moiety. The viscosity independence of the first time component indicates the absence of any torsional coordinate in the charge transfer process. In slightly polar solvent (carbon tetrachloride) the fluorescence transients show a triple exponential behavior. The first time component was assigned to the formation of the ICT state on a 2 ps time scale. Second time component was assigned to the relaxation of the ICT state via two torsion controlled channels. First channel involves the torsional motion about the central double bond leading to the trans-cis isomerization via a conical intersection or avoided crossing. The other channel contributing to the depopulation of ICT state involves the torsional coordinates of dimethylanilino and/or nitrophenyl moieties and leads to the formation of a conformationally relaxed state, which subsequently relaxes back to the ground state radiatively, and is responsible for the high fluorescence quantum yield of DNS in slightly polar solvents such as carbon tetrachloride, toluene, etc. The excited singlet state which is having a dominant π-π* character may also decay via intersystem crossing to the n-π* triplet manifold and thus accounts for the observed triplet yield of the molecule in slightly polar solvents.

Intramolecular charge transfer effects on 4-hydroxy-3-methoxybenzaldehyde

NASA Astrophysics Data System (ADS)

Rajendiran, N.; Balasubramanian, T.

2008-03-01

The absorption and fluorescence spectral characteristics of 4-hydroxy-3-methoxybenzaldehyde (HMB) have been studied in different solvents, pH and β-cyclodextrin (β-CD) and compared with 4-hydroxy-3,5-dimethoxybenzaldehyde (HDMB). The inclusion complex of HMB with β-CD is analysed by UV-vis, fluorimetry, FT-IR, 1H NMR, SEM and AM1 methods. In HMB, the normal emission (B band) is originates from a locally excited state and the longer emission (A band) is due to intramolecular charge transfer state (ICT). The OH group of HMB is present in the interior part of the β-CD cavity and aldehyde group present in the upper part of the β-CD cavity.

Enhancing SERS by Means of Supramolecular Charge Transfer

NASA Technical Reports Server (NTRS)

Wong, Eric; Flood, Amar; Morales, Alfredo

2009-01-01

In a proposed method of sensing small quantities of molecules of interest, surface enhanced Raman scattering (SERS) spectroscopy would be further enhanced by means of intermolecular or supramolecular charge transfer. There is a very large potential market for sensors based on this method for rapid detection of chemical and biological hazards. In SERS, the Raman signals (vibrational spectra) of target molecules become enhanced by factors of the order of 108 when those molecules are in the vicinities of nanostructured substrate surfaces that have been engineered to have plasmon resonances that enhance local electric fields. SERS, as reported in several prior NASA Tech Briefs articles and elsewhere, has remained a research tool and has not yet been developed into a practical technique for sensing of target molecules: this is because the short range (5 to 20 nm) of the field enhancement necessitates engineering of receptor molecules to attract target molecules to the nanostructured substrate surfaces and to enable reliable identification of the target molecules in the presence of interferants. Intermolecular charge-transfer complexes have been used in fluorescence-, photoluminescence-, and electrochemistry-based techniques for sensing target molecules, but, until now, have not been considered for use in SERS-based sensing. The basic idea of the proposed method is to engineer receptor molecules that would be attached to nanostructured SERS substrates and that would interact with the target molecules to form receptor-target supramolecular charge-transfer complexes wherein the charge transfer could be photoexcited.

A naphthalimide fluorophore with efficient intramolecular PET and ICT processes: application in molecular logic.

PubMed

Wang, Haixia; Wu, Haixia; Xue, Lin; Shi, Yan; Li, Xiyou

2011-08-07

A novel 4-amino-1,8-naphthalimide (NDI) with two different metal cation receptors connected at 4-amino or imide nitrogen positions respectively was designed and prepared. Significant internal charge transfer (ICT) as well as photoinduced electron transfer (PET) from the receptors to NDI is revealed by the shifted UV-vis absorption spectra and significant fluorescence quenching. Both Zn(2+) and Cu(2+) can coordinate selectively with the two cation receptors in this molecule with different affinities. The coordination of Zn(2+) with the receptor at imide nitrogen hindered the PET process and accordingly restored the quenched fluorescence of NDI. But the coordination of Zn(2+) at 4-amino position blocked the ICT process and caused significant blue-shift on the absorption peak with the fluorescence intensity unaffected. Similarly, coordination of Cu(2+) with the receptor at imide nitrogen can block the PET process, but can not restore the quenched fluorescence of compound 3 due to the paramagnetic properties of Cu(2+), which quench the fluorescence significantly instead. With Cu(2+) and Zn(2+) as two chemical inputs and absorption or fluorescence as output, several logic gate operations, such as OR, NOR and INHIBIT, can be achieved.

Electron transfer in silicon-bridged adjacent chromophores: the source for blue-green emission.

PubMed

Bayda, Malgorzata; Angulo, Gonzalo; Hug, Gordon L; Ludwiczak, Monika; Karolczak, Jerzy; Koput, Jacek; Dobkowski, Jacek; Marciniak, Bronislaw

2017-05-10

Si-Bridged chromophores have been proposed as sources for blue-green emission in several technological applications. The origin of this dual emission is to be found in an internal charge transfer reaction. The current work is an attempt to describe the details of these processes in these kinds of substances, and to design a molecular architecture to improve their performance. Nuclear motions essential for intramolecular charge transfer (ICT) can involve processes from twisted internal moieties to dielectric relaxation of the solvent. To address these issues, we studied ICT between adjacent chromophores in a molecular compound containing N-isopropylcarbazole (CBL) and 1,4-divinylbenzene (DVB) linked by a dimethylsilylene bridge. In nonpolar solvents emission arises from the local excited state (LE) of carbazole whereas in solvents of higher polarity dual emission was detected (LE + ICT). The CT character of the additional emission band was concluded from the linear dependence of the fluorescence maxima on solvent polarity. Electron transfer from CBL to DVB resulted in a large excited-state dipole moment (37.3 D) as determined from a solvatochromic plot and DFT calculations. Steady-state and picosecond time-resolved fluorescence experiments in butyronitrile (293-173 K) showed that the ICT excited state arises from the LE state of carbazole. These results were analyzed and found to be in accordance with an adiabatic version of Marcus theory including solvent relaxation.

Mixing of Exciton and Charge-Transfer States in Photosystem II Reaction Centers: Modeling of Stark Spectra with Modified Redfield Theory

PubMed Central

Novoderezhkin, Vladimir I.; Dekker, Jan P.; van Grondelle, Rienk

2007-01-01

We propose an exciton model for the Photosystem II reaction center (RC) based on a quantitative simultaneous fit of the absorption, linear dichroism, circular dichroism, steady-state fluorescence, triplet-minus-singlet, and Stark spectra together with the spectra of pheophytin-modified RCs, and so-called RC5 complexes that lack one of the peripheral chlorophylls. In this model, the excited state manifold includes a primary charge-transfer (CT) state that is supposed to be strongly mixed with the pure exciton states. We generalize the exciton theory of Stark spectra by 1), taking into account the coupling to a CT state (whose static dipole cannot be treated as a small parameter in contrast to usual excited states); and 2), expressing the line shape functions in terms of the modified Redfield approach (the same as used for modeling of the linear responses). This allows a consistent modeling of the whole set of experimental data using a unified physical picture. We show that the fluorescence and Stark spectra are extremely sensitive to the assignment of the primary CT state, its energy, and coupling to the excited states. The best fit of the data is obtained supposing that the initial charge separation occurs within the special-pair PD1PD2. Additionally, the scheme with primary electron transfer from the accessory chlorophyll to pheophytin gave a reasonable quantitative fit. We show that the effectiveness of these two pathways is strongly dependent on the realization of the energetic disorder. Supposing a mixed scheme of primary charge separation with a disorder-controlled competition of the two channels, we can explain the coexistence of fast sub-ps and slow ps components of the Phe-anion formation as revealed by different ultrafast spectroscopic techniques. PMID:17526589

Fabrication and charge/energy-transfer study of 4,7-bis(4-triphenylamino)benzo- 2,1,3-thiadiazole/CuPc composite films

NASA Astrophysics Data System (ADS)

Zhu, Yuanyuan; Gu, Shuangxi; Wei, Xiao; Xue, Minzhao; Zhang, Qing; Sheng, Qiaorong; Liu, Yangang

2010-12-01

Composite films of 4,7-bis(4-triphenylamino)benzo-2,1,3-thiadiazole (TBT) and copper phthalocyanine (CuPc) are fabricated via protonation-coelectrophoretic deposition from nitromethane solutions of TBT/CuPc mixture in the presence of trifluoroacetic acid as a protonation reagent. A nanospheres-nanowires interpenetrating network structure is obtained when the molar percentage of TBT is 70%. Furthermore, the existence of TBT makes α-phased CuPc be partly transformed into the β-phase, and simultaneously, CuPc disorganizes the TBT unit cells. The blue shift on the absorption edge of TBT and the significant fluorescence quenching in the composite films indicate energy/charge transfer and donor-acceptor (D-A) heterojunction formation. Then these results are proved from another point of view: the mutual overlap of absorption and emission spectra of TBT and CuPc lead to a bidirectional Förster resonance energy transfer at the interface; the molecular energy levels calculated from the results of cyclic voltammetry theoretically determine that there exist a D-A heterojunction and charge transfer from TBT to CuPc. Finally, from the investigation of the field-induced surface photovoltage spectra, it can be concluded that this charge transfer results in efficient dissociation of the photoinduced excitons in the composite films, followed by the generation of a strong photovoltage response.

Excited state complex formation between methyl glyoxal and some aromatic bio-molecules: a fluorescence quenching study

NASA Astrophysics Data System (ADS)

Banerjee, D.; Mandal, A.; Mukherjee, S.

2003-01-01

Fluorescence quenching of some important aromatic bio-molecules (ABM) such as 3-aminophthalhydrazide (luminol), tryptophan (Try), phenylalanine and tyrosine (Tyr) by methyl glyoxal (MG) has been studied employing different spectroscopic techniques. The interaction of MG with ABM in the excited state has been analysed using Stern-Volmer (S-V) mechanism. In the case of MG-luminol system time correlated single photon counting (TCSPC) technique has also been applied to explain the S-V mechanism. The bimolecular rate constants obtained are found to be higher than the rate constant for diffusion controlled process. A plausible explanation of the quenching mechanism has been discussed on the basis of hydrogen bonding, charge transfer and energy transfer interaction between the colliding species.

Tuning the Direction of Intramolecular Charge Transfer and the Nature of the Fluorescent State in a T-Shaped Molecular Dyad.

PubMed

Felouat, Abdellah; D'Aléo, Anthony; Charaf-Eddin, Azzam; Jacquemin, Denis; Le Guennic, Boris; Kim, Eunsun; Lee, Kwang Jin; Woo, Jae Heun; Ribierre, Jean-Charles; Wu, Jeong Weon; Fages, Frédéric

2015-06-18

Controlling photoinduced intramolecular charge transfer at the molecular scale is key to the development of molecular devices for nanooptoelectronics. Here, we describe the design, synthesis, electronic characterization, and photophysical properties of two electron donor-acceptor molecular systems that consist of tolane and BF2-containing curcuminoid chromophoric subunits connected in a T-shaped arrangement. The two π-conjugated segments intersect at the electron acceptor dioxaborine core. From steady-state electronic absorption and fluorescence emission, we find that the photophysics of the dialkylamino-substituted analogue is governed by the occurrence of two closely lying excited states. From DFT calculations, we show that excitation in either of these two states results in a distinct shift of the electron density, whether it occurs along the curcuminoid or tolane moiety. Femtosecond transient absorption spectroscopy confirmed these findings. As a consequence, the nature of the emitting state and the photophysical properties are strongly dependent on solvent polarity. Moreover, these characteristics can also be switched by protonation or complexation at the nitrogen atom of the amino group. These features set new approaches toward the construction of a three-terminal molecular system in which the lateral branch would transduce a change of electronic state and ultimately control charge transport in a molecular-scale device.

Fluorescence turn-on detection of alkaline phosphatase activity based on controlled release of PEI-capped Cu nanoclusters from MnO2 nanosheets.

PubMed

Zhang, Yunyi; Li, Yongxin; Zhang, Cuiyun; Zhang, Qingfeng; Huang, Xinan; Yang, Meiding; Shahzad, Sohail Anjum; Lo, Kenneth Kam-Wing; Yu, Cong; Jiang, Shichun

2017-08-01

A fluorescence turn-on assay for alkaline phosphatase (ALP) activity is developed through the controlled release of polyethyleneimine-capped copper nanoclusters (PEI-capped CuNCs) from the MnO 2 nanosheets. In an aqueous solution, the positively charged PEI-capped CuNCs could be adsorbed onto the surface of the negatively charged MnO 2 nanosheets. Such adsorption through favorable electrostatic interactions could efficiently quench the nanocluster fluorescence emission via resonance energy transfer from the PEI-capped CuNCs to the MnO 2 nanosheets. 2-Phospho-L-ascorbic acid (AAP) could be hydrolyzed to L-ascorbic acid (AA) in the presence of ALP. AA could reduce MnO 2 into Mn 2+ and trigger the disintegration of the MnO 2 nanosheets. As a result, the CuNCs were released and the quenched fluorescence was recovered efficiently. The detection strategy is simple, inexpensive, sensitive, selective, with low toxicity, and has better biocompatibility. The newly fabricated biosensor for ALP activity will potentially make it a robust candidate for numerous biological and biomedical applications.

A theoretical investigation of two typical two-photon pH fluorescent probes.

PubMed

Xu, Zhong; Ren, Ai-Min; Guo, Jing-Fu; Liu, Xiao-Ting; Huang, Shuang; Feng, Ji-Kang

2013-01-01

Intracellular pH plays an important role in many cellular events, such as cell growth, endocytosis, cell adhesion and so on. Some pH fluorescent probes have been reported, but most of them are one-photon fluorescent probes, studies about two-photon fluorescent probes are very rare. In this work, the geometrical structure, electronic structure and one-photon properties of a series of two-photon pH fluorescent probes have been theoretically studied by using density functional theory (DFT) method. Their two-photon absorption (TPA) properties are calculated using the method of ZINDO/sum-over-states method. Two types of two-photon pH fluorescent probes have been investigated by theoretical methods. The mechanisms of the Photoinduced Charge Transfer (PCT) probes and the Photoinduced Electron Transfer (PET) probes are verified specifically. Some designed strategies of good two-photon pH fluorescent probes are suggested on the basis of the investigated results of two mechanisms. For the PCT probes, substituting a stronger electron-donating group for the terminal methoxyl group is an advisable choice to increase the TPA cross section. For the PET probes, the TPA cross sections increase upon protonation. © 2012 Wiley Periodicals, Inc. Photochemistry and Photobiology © 2012 The American Society of Photobiology.

Extrinsic Fluorescent Dyes as Tools for Protein Characterization

PubMed Central

Hawe, Andrea; Sutter, Marc

2008-01-01

Noncovalent, extrinsic fluorescent dyes are applied in various fields of protein analysis, e.g. to characterize folding intermediates, measure surface hydrophobicity, and detect aggregation or fibrillation. The main underlying mechanisms, which explain the fluorescence properties of many extrinsic dyes, are solvent relaxation processes and (twisted) intramolecular charge transfer reactions, which are affected by the environment and by interactions of the dyes with proteins. In recent time, the use of extrinsic fluorescent dyes such as ANS, Bis-ANS, Nile Red, Thioflavin T and others has increased, because of their versatility, sensitivity and suitability for high-throughput screening. The intention of this review is to give an overview of available extrinsic dyes, explain their spectral properties, and show illustrative examples of their various applications in protein characterization. PMID:18172579

Study on fluorescence characteristics of duloxetine hydrochloride

NASA Astrophysics Data System (ADS)

Liu, Xiangping; Du, Yingxiang; Wu, Xiulan

2008-12-01

The fluorescence characteristics of duloxetine hydrochloride are studied in this paper. The fluorescence emission spectra of duloxetine demonstrate that intramolecular charge-transfer takes place between thiophene ring and napthalenyloxy group upon irradiation. The effects of excitation light, solvent system, variation of solution pH value, metal ions and vitamin C on the fluorescence spectra of duloxetine hydrochloride are elucidated, respectively. A spectrofluorometric method of quantitative determination of duloxetine in dosage form is reported for the first time, the linear range is 7.14 × 10 -8 mol/L to 1.43 × 10 -5 mol/L, the linear correlation coefficient r is equal to 0.9997, and the detection limit is 3.5 × 10 -8 mol/L. The accuracy and the precision are satisfactory.

Light and colour as analytical detection tools: a journey into the periodic table using polyamines to bio-inspired systems as chemosensors.

PubMed

Lodeiro, Carlos; Capelo, José Luis; Mejuto, Juan Carlos; Oliveira, Elisabete; Santos, Hugo M; Pedras, Bruno; Nuñez, Cristina

2010-08-01

This critical review describes some developments on the chemistry of fluorescent and colorimetric molecular probes or chemosensors, based on polyamines and associated compounds having oxygen and/or sulfur as donor atoms. The reported systems are essentially based on some selected published work in this field in the last five years, and in the work developed by the authors from 2000 onwards. Some interesting properties beyond sensing molecules, ions or/and cations by fluorescence, colorimetry as well as by MALDI-TOF MS spectrometry can arise from these systems. A short brief on different examples activated by PET (photoinduced electron transfer), ICT (internal charge transfer) and EET (electronic energy transfer) phenomena will be provided. Finally the introduction of bio-inspired compounds derived from emissive amino acid or short peptide systems and nanoparticle devices to detect metal ions will be reviewed (202 references).

Optical and electrical nano eco-sensors using alternative deposition of charged layer

NASA Astrophysics Data System (ADS)

Ahmed, Syed Rahin; Hong, Seong Cheol; Lee, Jaebeom

2011-03-01

This review focuses on layer by layer (LBL) assembly-based nano ecological sensor (hereafter, eco-sensor) for pesticide detection, which is one of the most versatile methods. The effects of pesticides on human health and on the environment (air, water, soil, plants, and animals) are of great concern due to their increasing use. We highlight two of the most popular detecting methods, i.e., fluorescence and electrochemical detection of pesticides on an LBL assembly. Fluorescence materials are of great interest among researchers for their sensitivity and reliable detection, and electrochemical processes allow us to investigate synergistic interactions among film components through charge transfer mechanisms in LBL film at the molecular level. Then, we noted some prospective directions for development of different types of sensing systems.

Tricolor emission of a fluorescent heteroditopic ligand over a concentration gradient of zinc(II) ions.

PubMed

Sreenath, Kesavapillai; Clark, Ronald J; Zhu, Lei

2012-09-21

The internal charge transfer (ICT) type fluoroionophore arylvinyl-bipy (bipy = 2,2'-bipyridyl) is covalently tethered to the spirolactam form of rhodamine to afford fluorescent heteroditopic ligand 4. Compound 4 can be excited in the visible region, the emission of which undergoes sequential bathochromic shifts over an increasing concentration gradient of Zn(ClO(4))(2) in acetonitrile. Coordination of Zn(2+) stabilizes the ICT excited state of the arylvinyl-bipy component of 4, leading to the first emission color shift from blue to green. At sufficiently high concentrations of Zn(ClO(4))(2), the nonfluorescent spirolactam component of 4 is transformed to the fluorescent rhodamine, which turns the emission color from green to orange via intramolecular fluorescence resonance energy transfer (FRET) from the Zn(2+)-bound arylvinyl-bipy fluorophore to rhodamine. While this work offers a new design of ratiometric chemosensors, in which sequential analyte-induced emission band shifts result in the sampling of multiple colors at different concentration ranges (i.e., from blue to green to orange as [Zn(2+)] increases in the current case), it also reveals the nuances of rhodamine spirolactam chemistry that have not been sufficiently addressed in the published literature. These issues include the ability of rhodamine spirolactam as a fluorescence quencher via electron transfer, and the slow kinetics of spirolactam ring-opening effected by Zn(2+) coordination under pH neutral aqueous conditions.

APTS and rGO co-functionalized pyrenated fluorescent nanonets for representative vapor phase nitroaromatic explosive detection

NASA Astrophysics Data System (ADS)

Guo, Linjuan; Zu, Baiyi; Yang, Zheng; Cao, Hongyu; Zheng, Xuefang; Dou, Xincun

2014-01-01

For the first time, flexible PVP/pyrene/APTS/rGO fluorescent nanonets were designed and synthesized via a one-step electrospinning method to detect representative subsaturated nitroaromatic explosive vapor. The functional fluorescent nanonets, which were highly stable in air, showed an 81% quenching efficiency towards TNT vapor (~10 ppb) with an exposure time of 540 s at room temperature. The nice performance of the nanonets was ascribed to the synergistic effects induced by the specific adsorption properties of APTS, the fast charge transfer properties and the effective π-π interaction with pyrene and TNT of rGO. Compared to the analogues of TNT, the PVP/pyrene/APTS/rGO nanonets showed notable selectivity towards TNT and DNT vapors. The explored functionalization method opens up brand new insight into sensitive and selective detection of vapor phase nitroaromatic explosives.For the first time, flexible PVP/pyrene/APTS/rGO fluorescent nanonets were designed and synthesized via a one-step electrospinning method to detect representative subsaturated nitroaromatic explosive vapor. The functional fluorescent nanonets, which were highly stable in air, showed an 81% quenching efficiency towards TNT vapor (~10 ppb) with an exposure time of 540 s at room temperature. The nice performance of the nanonets was ascribed to the synergistic effects induced by the specific adsorption properties of APTS, the fast charge transfer properties and the effective π-π interaction with pyrene and TNT of rGO. Compared to the analogues of TNT, the PVP/pyrene/APTS/rGO nanonets showed notable selectivity towards TNT and DNT vapors. The explored functionalization method opens up brand new insight into sensitive and selective detection of vapor phase nitroaromatic explosives. Electronic supplementary information (ESI) available: Vapor pressure of TNT and its analogues, fluorescence quenching kinetics, fluorescence quenching efficiencies and additional SEM images. See DOI: 10.1039/c3nr04960d

Photophysical processes of some benzimidazole derivatives

NASA Astrophysics Data System (ADS)

Chen, Zhaobin; Zhang, Caihong; Feng, Liheng

2005-11-01

The photophysical properties of N-(α-naphthyl)-benzimidazole (α-NABI), N-(β-naphthyl)-benzimidazole (β-NABI) and N-(α-pyridyl)-benzimidazole (α-PYBI) were studied and α-NYBI exhibit intramolecular charge transfer fluorescence in polar solvents. The fluorescence of benzimidazoles can be quenched by acetic acid and the existence of exciplexes was observed between the benzimidazole derivatives and acetic acid. Particularly, the maximum emission peak of solution of α-PYBI in mixed solvent, ether and acetic acid, presents obvious red-shift with the increase of concentration of acetic acid in the mixed solvent.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sessler, J. L.; Sathiosatham, M.; Brown, C. T.

The synthesis of a new, noncovalent anthracene-dimethylaniline dyad (ensemble I) held together via guanosine-cytidine Watson-Crick base-pairing interactions is reported. Upon excitation at 420 nm, photoinduced electron-transfer from the dimethylaniline donor to the singlet excited state of the anthracene acceptor occurs, as inferred from a combination of time-resolved fluorescence quenching and transient absorption measurements. In toluene at room temperature, the rate constants for photoinduced intraensemble electron-transfer and subsequent back-electron-transfer (charge recombination) are k{sub CS} = (3.5 {+-} 0.03) x 10{sup 10} s{sup -1} and k{sub CR} = (1.42 {+-} 0.03) x 10{sup 9} s{sup -1}, respectively.

Highly selective and sensitive turn-on fluorescent sensor for detection of Al3+ based on quinoline-base Schiff base.

PubMed

Wang, Yang; Ma, Zhong-Ying; Zhang, De-Long; Deng, Jia-Li; Chen, Xiong; Xie, Cheng-Zhi; Qiao, Xin; Li, Qing-Zhong; Xu, Jing-Yuan

2018-04-15

A new aluminum ion fluorescent probe (4-(diethylamino)-2-hydroxybenzylidene)isoquinoline-1-carbohydrazide (HL 1 ) has been conveniently synthesized and characterized. HL 1 exhibited a highly selective and pronounced enhancement for Al 3+ in the fluorescence emission over other common cations by forming a 2:1 complex, with a recognition mechanism based on excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT). The strong fluorescent emission can be observed even at ppm level concentration of the probe in the presence of Al 3+ with 41 fold intensity enhancement at 545 nm. HL 1 displays good linear relationship with Al 3+ in the low concentration and the limit of detection is 8.08 × 10 -8  mol/L. Similar molecules with different substituents on salicylaldehyde phenyl ring were synthesized for studying the structure-activity relationship. Density-functional theory (DFT) calculations are in agreement with the proposed mechanism. It is confirmed that HL 1 could be used to detect Al 3+ ions in real sample by fluorescence spectrometry and Al 3+ ions in cells by bioimaging. Copyright © 2018 Elsevier B.V. All rights reserved.

Micelle-induced versatile performance of amphiphilic intramolecular charge-transfer fluorescent molecular sensors.

PubMed

Wang, Jiaobing; Qian, Xuhong; Qian, Junhong; Xu, Yufang

2007-01-01

A series of amphiphilic intramolecular charge-transfer fluorescent molecular sensors AS1-3, equipped with a rod-shaped hydrophobic 2-phenylbenzoxazole fluorophore and a hydrophilic tetraamide Hg(2+)-ion receptor, have been prepared. These sensor molecules could be incorporated into the hydrophobic sodium dodecyl sulfate (SDS) micelle, which is confirmed by the clear spectral blue shift and emission enhancement observed at the critical micelle concentration of SDS. Systematic examination of the sensor-Hg(2+) complexation, by using both UV/visible and fluorescence spectroscopy, indicates that SDS significantly modulates both the binding event and signal transformation of these sensor molecules. The potential advantages are fourfold: 1) SDS substantially increases the Hg(2+)-ion association constant and results in an amplified sensitivity. 2) SDS initiates spectral features which facilitate Hg(2+)-ion analysis, for example, in addition to the strengthened fluorescence of the free sensors AS1-3, the original "on-off" response of AS2 toward the Hg(2+) ion is transformed into a self-calibrated two-wavelength ratiometric signal, while for AS3, Hg(2+)-ion complexation in the presence of SDS results in a 180 nm blue shift, which is preferred to the 51 nm spectral shift obtained without SDS. 3) Thermoreversible tuning of the dynamic detection range is realized. 4) Highly specific Hg(2+)-ion identification could be achieved by using the SDS-induced fingerprint emission (358 nm) of the AS2-Hg(2+) complex. Altogether, this work demonstrates a convenient and powerful strategy that remarkably elevates the performance of a given fluorescent molecular sensor. It also implies that for a specific utilization, much attention should be paid to the microenvironment in which the sensor resides, as the behavior of the sensor might be different from that in the bulk solution.

Investigations on the photoreactions of phenothiazine and phenoxazine in presence of 9-cyanoanthracene by using steady state and time resolved spectroscopic techniques.

PubMed

Bardhan, Munmun; Mandal, Paulami; Tzeng, Wen-Bih; Ganguly, Tapan

2010-09-01

By using electrochemical, steady state and time resolved (fluorescence lifetime and transient absorption) spectroscopic techniques, detailed investigations were made to reveal the mechanisms of charge separation or forward electron transfer reactions within the electron donor phenothiazine (PTZH) or phenoxazine (PXZH) and well known electron acceptor 9-cyanoanthracene (CNA). The transient absorption spectra suggest that the charge separated species formed in the excited singlet state resulted from intermolecular photoinduced electron transfer reactions within the donor PTZH (or PXZH) and CNA acceptor relaxes to the corresponding triplet state. Though alternative mechanisms of via formations of contact neutral radical by H-transfer reaction have been proposed but the observed results obtained from the time resolved measurements indicate that the regeneration of ground state reactants is primarily responsible due to direct recombination of triplet contact ion-pair (CIP) or solvent-separated ion-pair (SSIP).

Photoinduced Charge Shifts and Electron Transfer in Viologen-Tetraphenylborate Complexes: Push-Pull Character of the Exciplex.

PubMed

Santos, Willy G; Budkina, Darya S; Deflon, Victor M; Tarnovsky, Alexander N; Cardoso, Daniel R; Forbes, Malcolm D E

2017-06-14

Viologen-tetraarylborate ion-pair complexes were prepared and investigated by steady-state and time-resolved spectroscopic techniques such as fluorescence and femtosecond transient absorption. The results highlight a charge transfer transition that leads to changes in the viologen structure in the excited singlet state. Femtosecond transient absorption reveals the formation of excited-state absorption and stimulated emission bands assigned to the planar (k obs < 10 12 s -1 ) and twisted (k obs ∼ 10 10 s -1 ) structures between two pyridinium groups in the viologen ion. An efficient photoinduced electron transfer from the tetraphenylborate anionic moiety to the viologen dication was observed less than 1 μs after excitation. This is a consequence of the push-pull character of the electron donor twisted viologen structure, which helps formation of the borate triplet state. The borate triplet state is deactivated further via a second electron transfer process, generating viologen cation radical (V •+ ).

Exciplex: An Intermolecular Charge-Transfer Approach for TADF.

PubMed

Sarma, Monima; Wong, Ken-Tsung

2018-04-03

Organic materials that display thermally activated delayed fluorescence (TADF) are a striking class of functional materials that have witnessed a booming progress in recent years. In addition to pure TADF emitters achieved by the subtle manipulations of intramolecular charge transfer processes with sophisticated molecular structures, a new class of efficient TADF-based OLEDs with emitting layer formed by blending electron donor and acceptor molecules that involve intermolecular charge transfer have also been fabricated. In contrast to pure TADF materials, the exciplex-based systems can realize small ΔEST (0-0.05 eV) much more easily since the electron and hole are positioned on two different molecules, thereby giving small exchange energy. Consequently, exciplex-based OLEDs have the prospective to maximize the TADF contribution and achieve theoretical 100% internal quantum efficiency. Therefore, the challenging issue of achieving small ΔEST in organic systems could be solved. In this article, we summarize and discuss the latest and most significant developments regarding these rapidly evolving functional materials, wherein the majority of the reported exciplex forming systems are categorized into two sub-groups, viz. (a) exciplex as TADF emitters and (b) those as hosts for fluorescent, phosphorescent and TADF dopants according to their structural features and applications. The working mechanisms of the direct electroluminescence from the donor/acceptor interface and the exciplex-forming systems as co-host for the realization of high efficiency OLEDs are reviewed and discussed. This article delivers a summary of the current progresses and achievements of exciplex-based researches and points out the future challenges to trigger more research endeavors to this growing field.

Intermolecular interaction approach for TADF (Conference Presentation)

NASA Astrophysics Data System (ADS)

Wong, Ken-Tsung

2016-09-01

Materials with thermally activated delayed fluorescence (TADF) have recently emerged as new fluorescent emitters for highly efficient organic light-emitting diodes (OLEDs). Molecule with TADF behavior needs to have a small singlet-triplet energy difference (ΔES-T) that allows the up-conversion from nonradiative triplet state (T1) to radiative singlet state (S1) via reverse intersystem crossing (RISC) process. Generally, molecules with small ΔES-T can be obtained via carefully manipulate the degree of "intramolecular" charge transfer (ICT) between electron-donating and -accepting components, such that the electron exchange energy that contributes to ΔES-T, can be minimized. Alternatively, excited state with small ΔES-T can be feasibly realized via "intermolecular" charge transfer occurring at the interface between spatially separating donor (D) and acceptor (A) molecules. Because the exchange energy decreases as the HOMO-LUMO separation distance increases, theoretically, the intermolecular D/A charge transfer state (or exciplex) should have rather small ΔES-T, leading to efficient TADF. However, it is still a challenge to access highly efficient exciplex systems. This is mainly because exciplex formation is commonly accompanied with a large red shift of emission spectra and long radiative lifetime, which tend to diminish photoluminescence quantum yield (PLQY) as well as electroluminescence (EL) performance. Until now, exciplex-based OLEDs with external quantum efficiency (EQE) above 10% are still limited. By judicious selection of donor and acceptor, the formation of efficient exciplex can be feasibly achieved. In this conference, our recent efforts on highly efficient exciplexes using C3-symmetry triazine acceptors and various donors, and their device characteristics will be presented.

A fluorescent pH probe for acidic organelles in living cells.

PubMed

Chen, Jyun-Wei; Chen, Chih-Ming; Chang, Cheng-Chung

2017-09-26

A water-soluble pH sensor, 2-(6-(4-aminostyryl)-1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)-N, N-dimethylethanamine (ADA), was synthesized based on the molecular design of photoinduced electron transfer (PET) and intramolecular charge transfer (ICT). The fluorescence emission response against a pH value is in the range 3-6, which is suitable for labelling intracellular pH-dependent microenvironments. After biological evolution, ADA is more than a pH biosensor because it is also an endocytosis pathway tracking biosensor that labels endosomes, late endosomes, and lysosome pH gradients. From this, the emissive aggregates of ADA and protonated-ADA in these organs were evaluated to explore how this probe stresses emission colour change to cause these unique cellular images.

Ultrafast optical excitations in supramolecular metallacycles with charge transfer properties.

PubMed

Flynn, Daniel C; Ramakrishna, Guda; Yang, Hai-Bo; Northrop, Brian H; Stang, Peter J; Goodson, Theodore

2010-02-03

New organometallic materials such as two-dimensional metallacycles and three-dimensional metallacages are important for the development of novel optical, electronic, and energy related applications. In this article, the ultrafast dynamics of two different platinum-containing metallacycles have been investigated by femtosecond fluorescence upconversion and transient absorption. These measurements were carried out in an effort to probe the charge transfer dynamics and the rate of intersystem crossing in metallacycles of different geometries and dimensions. The processes of ultrafast intersystem crossing and charge transfer vary between the two different classes of metallacyclic systems studied. For rectangular anthracene-containing metallacycles, the electronic coupling between adjacent ligands was relatively weak, whereas for the triangular phenanthrene-containing structures, there was a clear interaction between the conjugated ligand and the metal complex center. The transient lifetimes increased with increasing conjugation in that case. The results show that differences in the dimensionality and structure of metallacycles result in different optical properties, which may be utilized in the design of nonlinear optical materials and potential new, longer-lived excited state materials for further electronic applications.

Anion-cation charge-transfer properties and spectral studies of [M(phen)3][Cd4(SPh)10] (M = Ru, Fe, and Ni).

PubMed

Jiang, Jian-Bing; Bian, Guo-Qing; Zhang, Ya-Ping; Luo, Wen; Zhu, Qin-Yu; Dai, Jie

2011-10-07

Three anion-cation compounds 1-3 with formula [M(phen)(3)][Cd(4)(SPh)(10)]·Sol (M = Ru(2+), Fe(2+), and Ni(2+), Sol = MeCN and H(2)O) have been synthesized and characterized by single-crystal analysis. Both the cations and anion are well-known ions, but the properties of the co-assembled compounds are interesting. Molecular structures and charge-transfer between the cations and anions in crystal and even in solution are discussed. These compounds are isomorphous and short inter-ion interactions are found in these crystals, such as π···π stacking and C-H···π contacts. Both spectroscopic and theoretical calculated results indicate that there is anion-cation charge-transfer (ACCT) between the Ru-phen complex dye and the Cd-SPh cluster, which plays an important role in their photophysical properties. The intensity of the fluorescent emission of the [Ru(phen)(3)](2+) is enhanced when the cation interacts with the [Cd(4)(SPh)(10)](2-) anion. The mechanism for the enhancement of photoluminescence has been proposed.

Cd(II)-terpyridine-based complex as a ratiometric fluorescent probe for pyrophosphate detection in solution and as an imaging agent in living cells.

PubMed

Jiao, Shu-Yan; Li, Kun; Zhang, Wei; Liu, Yan-Hong; Huang, Zeng; Yu, Xiao-Qi

2015-01-21

The terpyridine anthracene ligand was synthesized and characterized. is a ratiometric fluorescent probe for Cd(2+) with a recognition mechanism based on intramolecular charge transfer (ICT). An complex was isolated, and its structure was established using single-crystal XRD. The complex was able to serve as a novel reversible chemosensing ensemble to allow ratiometric response to pyrophosphate (PPi) in aqueous media. Moreover, the fluorescence imaging in living cells from these two emission channels suggested that was a ratiometric probe for Cd(2+), and the in situ generated complex was also a ratiometric ensemble for PPi detection in living cells.

Improved Charge-Transfer Fluorescent Dyes

NASA Technical Reports Server (NTRS)

Meador, Michael

2005-01-01

Improved charge-transfer fluorescent dyes have been developed for use as molecular probes. These dyes are based on benzofuran nuclei with attached phenyl groups substituted with, variously, electron donors, electron acceptors, or combinations of donors and acceptors. Optionally, these dyes could be incorporated as parts of polymer backbones or as pendant groups or attached to certain surfaces via self-assembly-based methods. These dyes exhibit high fluorescence quantum yields -- ranging from 0.2 to 0.98, depending upon solvents and chemical structures. The wavelengths, quantum yields, intensities, and lifetimes of the fluorescence emitted by these dyes vary with (and, hence, can be used as indicators of) the polarities of solvents in which they are dissolved: In solvents of increasing polarity, fluorescence spectra shift to longer wavelengths, fluorescence quantum yields decrease, and fluorescence lifetimes increase. The wavelengths, quantum yields, intensities, and lifetimes are also expected to be sensitive to viscosities and/or glass-transition temperatures. Some chemical species -- especially amines, amino acids, and metal ions -- quench the fluorescence of these dyes, with consequent reductions in intensities, quantum yields, and lifetimes. As a result, the dyes can be used to detect these species. Another useful characteristic of these dyes is a capability for both two-photon and one-photon absorption. Typically, these dyes absorb single photons in the ultraviolet region of the spectrum (wavelengths < 400 nm) and emit photons in the long-wavelength ultraviolet, visible, and, when dissolved in some solvents, near-infrared regions. In addition, these dyes can be excited by two-photon absorption at near-infrared wavelengths (600 to 800 nm) to produce fluorescence spectra identical to those obtained in response to excitation by single photons at half the corresponding wavelengths (300 to 400 nm). While many prior fluorescent dyes exhibit high quantum yields, solvent-polarity- dependent fluorescence behavior, susceptibility to quenching by certain chemical species, and/or two-photon fluorescence, none of them has the combination of all of these attributes. Because the present dyes do have all of these attributes, they have potential utility as molecular probes in a variety of applications. Examples include (1) monitoring curing and deterioration of polymers; (2) monitoring protein expression; (3) high-throughput screening of drugs; (4) monitoring such chemical species as glucose, amines, amino acids, and metal ions; and (5) photodynamic therapy of cancers and other diseases.

Visualization of oxygen transfer across the air-water interface using a fluorescence oxygen visualization method.

PubMed

Lee, Minhee

2002-04-01

Oxygen concentration fields in a water body were visualized by the fluorescence oxygen visualization (FOV) method. Pyrenebutyric acid (PBA) was used as a fluorescent indicator of oxygen, and an intensive charge coupled-device (ICCD) camera as an image detector. Sequential images (over 2000 images) of the oxygen concentration field around the surface water of the tank (1 x 1 x 0.75 m3) were produced during the 3 h experiment. From image processing, the accurate pathway of oxygen-rich, cold water at the water surface was also visualized. The amount of oxygen transferred through the air-water interface during the experiment was measured and the oxygen transfer coefficient (K(L)) was determined as 0.22 m/d, which was much higher than that is expected in molecular diffusion. Results suggest that vertical penetration of cold water was the main pathway of oxygen in the water body in the tank. The average velocity of cold water penetrating downward in water body was also measured from consecutive images and the value was 0.3-0.6 mm/s. The FOV method used in this research should have wide application in experimental fluid mechanics and can also provide a phenomenological description of oxygen transfer under physically realizable natural conditions in lakes and reservoirs.

Specificity and kinetics of alpha-synuclein binding to model membranes determined with fluorescent excited state intramolecular proton transfer (ESIPT) probe.

PubMed

Shvadchak, Volodymyr V; Falomir-Lockhart, Lisandro J; Yushchenko, Dmytro A; Jovin, Thomas M

2011-04-15

Parkinson disease is characterized cytopathologically by the deposition in the midbrain of aggregates composed primarily of the presynaptic neuronal protein α-synuclein (AS). Neurotoxicity is currently attributed to oligomeric microaggregates subjected to oxidative modification and promoting mitochondrial and proteasomal dysfunction. Unphysiological binding to membranes of these and other organelles is presumably involved. In this study, we performed a systematic determination of the influence of charge, phase, curvature, defects, and lipid unsaturation on AS binding to model membranes using a new sensitive solvatochromic fluorescent probe. The interaction of AS with vesicular membranes is fast and reversible. The protein dissociates from neutral membranes upon thermal transition to the liquid disordered phase and transfers to vesicles with higher affinity. The binding of AS to neutral and negatively charged membranes occurs by apparently different mechanisms. Interaction with neutral bilayers requires the presence of membrane defects; binding increases with membrane curvature and rigidity and decreases in the presence of cholesterol. The association with negatively charged membranes is much stronger and much less sensitive to membrane curvature, phase, and cholesterol content. The presence of unsaturated lipids increases binding in all cases. These findings provide insight into the relation between membrane physical properties and AS binding affinity and dynamics that presumably define protein localization in vivo and, thereby, the role of AS in the physiopathology of Parkinson disease.

Triarylborane-Based Materials for OLED Applications.

PubMed

Turkoglu, Gulsen; Cinar, M Emin; Ozturk, Turan

2017-09-13

Multidisciplinary research on organic fluorescent molecules has been attracting great interest owing to their potential applications in biomedical and material sciences. In recent years, electron deficient systems have been increasingly incorporated into fluorescent materials. Triarylboranes with the empty p orbital of their boron centres are electron deficient and can be used as strong electron acceptors in conjugated organic fluorescent materials. Moreover, their applications in optoelectronic devices, energy harvesting materials and anion sensing, due to their natural Lewis acidity and remarkable solid-state fluorescence properties, have also been investigated. Furthermore, fluorescent triarylborane-based materials have been commonly utilized as emitters and electron transporters in organic light emitting diode (OLED) applications. In this review, triarylborane-based small molecules and polymers will be surveyed, covering their structure-property relationships, intramolecular charge transfer properties and solid-state fluorescence quantum yields as functional emissive materials in OLEDs. Also, the importance of the boron atom in triarylborane compounds is emphasized to address the key issues of both fluorescent emitters and their host materials for the construction of high-performance OLEDs.

Absorption and fluorescence spectroscopic characterization of BLUF domain of AppA from Rhodobacter sphaeroides

NASA Astrophysics Data System (ADS)

Zirak, P.; Penzkofer, A.; Schiereis, T.; Hegemann, P.; Jung, A.; Schlichting, I.

2005-08-01

The BLUF domain of the transcriptional anti-repressor protein AppA from the non-sulfur anoxyphototrophic purple bacterium Rhodobacter sphaeroides was characterized by absorption and emission spectroscopy. The BLUF domain constructs AppA 148 (consisting of amino-acid residues 1-148) and AppA 126 (amino-acid residues 1-126) are investigated. The cofactor of the investigated domains is found to consist of a mixture of the flavins riboflavin, FMN, and FAD. The dark-adapted domains exist in two different active receptor conformations (receptor states) with different sub-nanosecond fluorescence lifetimes (BLUF r,f and BLUF r,sl) and a small non-interacting conformation (BLUF nc). The active receptor conformations are transformed to putative signalling states (BLUF s,f and BLUF s,sl) of low fluorescence efficiency and picosecond fluorescence lifetime by blue-light excitation (light-adapted domains). In the dark at room temperature both signalling states recover back to the initial receptor states with a time constant of about 17 min. A quantum yield of signalling state formation of about 25% was determined by intensity dependent transmission measurements. A photo-cycle scheme is presented including photo-induced charge transfer complex formation, charge recombination, and protein binding pocket reorganisation.

Intramolecular Charge-Transfer Interaction of Donor-Acceptor-Donor Arrays Based on Anthracene Bisimide.

PubMed

Iwanaga, Tetsuo; Ogawa, Marina; Yamauchi, Tomokazu; Toyota, Shinji

2016-05-20

We designed anthracene bisimide (ABI) derivatives having two triphenylamine (TPA) groups as donor units at the 9,10-positions to form a novel π-conjugated donor-acceptor system. These compounds and their analogues with ethynylene linkers were synthesized by Suzuki-Miyaura and Sonogashira coupling reactions, respectively. In UV-vis spectra, the linker-free derivatives showed broad absorption bands arising from intramolecular charge-transfer interactions. Introducing ethynylene linkers resulted in a considerable red shift of the absorption bands. In fluorescence spectra, the ethynylene derivatives showed intense emission bands at 600-650 nm. Their photophysical and electrochemical properties were compared with those of the corresponding mono TPA derivatives on the basis of theoretical calculations and cyclic voltammetry to evaluate the intramolecular electronic interactions between the donor and acceptor units.

Complexation induced fluorescence and acid-base properties of dapoxyl dye with γ-cyclodextrin: a drug-binding application using displacement assays.

PubMed

Pal, Kaushik; Mallick, Suman; Koner, Apurba L

2015-06-28

Host-guest complexation of dapoxyl sodium sulphonate (DSS), an intramolecular charge transfer dye with water-soluble and non-toxic macrocycle γ-cyclodextrin (γ-CD), has been investigated in a wide pH range. Steady-state absorption, fluorescence and time-resolved fluorescence measurements confirm the positioning of DSS into the hydrophobic cavity of γ-CD. A large fluorescence enhancement ca. 30 times, due to 1 : 2 complex formation and host-assisted guest-protonation have been utilised for developing a method for the utilisation of CD based drug-delivery applications. A simple fluorescence-displacement based approach is implemented at physiological pH for the assessment of binding strength of pharmaceutically useful small drug molecules (ibuprofen, paracetamol, methyl salicylate, salicylic acid, aspirin, and piroxicam) and six important antibiotic drugs (resazurin, thiamphenicol, chloramphenicol, ampicillin, kanamycin, and sorbic acid) with γ-CD.

An insight into non-emissive excited states in conjugated polymers

NASA Astrophysics Data System (ADS)

Hu, Zhongjian; Willard, Adam P.; Ono, Robert J.; Bielawski, Christopher W.; Rossky, Peter J.; vanden Bout, David A.

2015-09-01

Conjugated polymers in the solid state usually exhibit low fluorescence quantum yields, which limit their applications in many areas such as light-emitting diodes. Despite considerable research efforts, the underlying mechanism still remains controversial and elusive. Here, the nature and properties of excited states in the archetypal polythiophene are investigated via aggregates suspended in solvents with different dielectric constants (ε). In relatively polar solvents (ε>~ 3), the aggregates exhibit a low fluorescence quantum yield (QY) of 2-5%, similar to bulk films, however, in relatively nonpolar solvents (ε<~ 3) they demonstrate much higher fluorescence QY up to 20-30%. A series of mixed quantum-classical atomistic simulations illustrate that dielectric induced stabilization of nonradiative charge-transfer (CT) type states can lead to similar drastic reduction in fluorescence QY as seen experimentally. Fluorescence lifetime measurement reveals that the CT-type states exist as a competitive channel of the formation of emissive exciton-type states.

Excited-State Dynamics of Biological Molecules in Solution: Photoinduced Charge Transfer in Oxidatively Damaged DNA and Deactivation of Violacein in Viscous Solvents

NASA Astrophysics Data System (ADS)

Beckstead, Ashley Ann

UV radiation from the sun is strongly absorbed by DNA, and the resulting electronic excited states can lead to the formation of mutagenic photoproducts. Decades of research have brought to light the excited-state dynamics of single RNA and DNA nucleobases, but questions remain about the nature of excited states accessed in DNA strands. In this thesis, I present ultrafast spectroscopic observations of photoinduced electron transfer from the oxidatively damaged bases, 8-oxo-7,8-dihydro-2'-deoxyguanosine, 5-hydroxy-2'-deoxycytidine and 5-hydroxy-2'-deoxyuridine, to adenine in three dinucleotides. The results reveal that charge transfer states are formed on a timescale faster than our instrumental resolution (<0.5 ps), and back electron transfer efficiently returns the excited-state population to the ground state on timescales from tens to hundreds of ps. In addition to recent spectroscopic observations of charge transfer state species in DNA by other groups, our results have augmented understanding of the long-lived transient signals observed in DNA strands. The observation of photoinduced electron transfer in these oxidatively damaged nucleobases also supports a recent proposal regarding the role of oxidative products in pre-RNA catalysis. I discuss these observations in the contexts of fundamental DNA excited-state dynamics and prebiotic chemical evolution. In this thesis, I also present the first ultrafast spectroscopic investigation of violacein, a pigment isolated from Antarctic bacteria. Despite claims for the photoprotective role of this pigment, there has never been a spectroscopic analysis of excited-state deactivation in violacein. Emission spectra, fluorescence quantum yields and excited-state lifetimes of violacein in various solvents were measured for the first time. Both the fluorescence quantum yield and excited-state lifetime of violacein increase in increasingly viscous solvents, suggesting a large-scale motion mediates excited-state deactivation. I compare these results to similar observations of viscosity-dependent excited-state decay rates in other molecules. I also consider the relevance of violacein's excited-state properties to the hypothesized sunscreening role of violacein. Overall, the studies presented in this dissertation illustrate how ultrafast spectroscopic techniques can be used to unravel complex biomolecular excited-state dynamics in solution.

Origin of the F685 and F695 fluorescence in photosystem II.

PubMed

Andrizhiyevskaya, Elena G; Chojnicka, Agnieszka; Bautista, James A; Diner, Bruce A; van Grondelle, Rienk; Dekker, Jan P

2005-06-01

The emission spectra of CP47-RC and core complexes of Photosystem II (PS II) were measured at different temperatures and excitation wavelengths in order to establish the origin of the emission and the role of the core antenna in the energy transfer and charge separation processes in PS II. Both types of particles reveal strong dependences of spectral shape and yield on temperature. The results indicate that the well-known F-695 emission at 77 K arises from excitations that are trapped on a red-absorbing CP47 chlorophyll, whereas the F-685 nm emission at 77 K arises from excitations that are transferred slowly from 683 nm states in CP47 and CP43 to the RC, where they are trapped by charge separation. We conclude that F-695 at 77 K originates from the low-energy part of the inhomogeneous distribution of the 690 nm absorbing chlorophyll of CP47, while at 4 K the fluorescence originates from the complete distribution of the 690 nm chlorophyll of CP47 and from the low-energy part of the inhomogeneous distribution of one or more CP43 chlorophylls.

An aqueous friendly chemosensor derived from vitamin B6 cofactor for colorimetric sensing of Cu2 + and fluorescent turn-off sensing of Fe3 +

NASA Astrophysics Data System (ADS)

Sharma, Darshna; Kuba, Aman; Thomas, Rini; Kumar, Rajender; Choi, Heung-Jin; Sahoo, Suban K.

2016-01-01

Chemosensor L derived from vitamin B6 cofactor pyridoxal-5-phosphate was investigated for the selective detection of Cu2 + and Fe3 + in aqueous medium. Sensor L formed a 1:1 complex with Cu2 + and displays a perceptible color change from colorless to yellow brown with the appearance of a new charge transfer band at 450 nm. In contrast, the fluorescence of L was quenched selectively in the presence of Fe3 + without any interference from other metal ions including Cu2 +.

A FRET sensor enables quantitative measurements of membrane charges in live cells.

PubMed

Ma, Yuanqing; Yamamoto, Yui; Nicovich, Philip R; Goyette, Jesse; Rossy, Jérémie; Gooding, J Justin; Gaus, Katharina

2017-04-01

Membrane charge has a critical role in protein trafficking and signaling. However, quantification of the effective electrostatic potential of cellular membranes has remained challenging. We developed a fluorescence membrane charge sensor (MCS) that reports changes in the membrane charge of live cells via Förster resonance energy transfer (FRET). MCS is permanently attached to the inner leaflet of the plasma membrane and shows a linear, reversible and fast response to changes of the electrostatic potential. The sensor can monitor a wide range of cellular treatments that alter the electrostatic potential, such as incorporation and redistribution of charged lipids and alterations in cytosolic ion concentration. Applying the sensor to T cell biology, we used it to identify charged membrane domains in the immunological synapse. Further, we found that electrostatic interactions prevented spontaneous phosphorylation of the T cell receptor and contributed to the formation of signaling clusters in T cells.

Theoretical investigation on ratiometric two-photon fluorescent probe for Zn2+ detection based on ICT mechanism

NASA Astrophysics Data System (ADS)

Huang, Shuang; Yang, Bao-Zhu; Ren, Ai-Min

2016-06-01

OPA (one-photon absorption), TPA (two-photon absorption) and fluorescence properties of a free ligand L upon coordination with Zn2+, and the regeneration with CN- were investigated in theory. According to our research, OPA spectra of ligand L show red-shift binding with Zn2+ while blue-shift with CN-. The fluorescence spectra and TPA wavelength are shifted in the same situation as those of OPA spectra. The value of TPA cross-section decreased at first, and then increased to 1813 GM for [L-Zn(CN)4]2-. Intramolecular charge transfer (ICT) mechanism was investigated by natural bond orbital (NBO) analysis. It demonstrates that L is hopeful to be a good ratiometric fluorescent probe for zinc ion detection in solution, and it can regenerate after CN- was introduced.

A Zn(2+)-responsive highly sensitive fluorescent probe and 1D coordination polymer based on a coumarin platform.

PubMed

Kumar, Virendra; Kumar, Ajit; Diwan, Uzra; Upadhyay, K K

2013-09-28

A coumarin-based Schiff base (receptor 1) exhibited fluorescence enhancement selectively with Zn(2+) at a nanomolar level in near-aqueous medium (EtOH-H2O; 1:1, v/v). The response was instantaneous with a detection limit of 3.26 × 10(-9) M. The sensing event is supposed to incorporate a combinational effect of intramolecular charge transfer (ICT), chelation-enhanced fluorescence (CHEF) and C[double bond, length as m-dash]N isomerization mechanisms. Various spectroscopic methods, viz. IR, UV-visible, fluorescence and NMR in association with single crystal XRD studies, were used for thorough investigation of the structure of receptor 1 as well as of the sensing event. The Zn(2+) complex of receptor 1 exhibited a very nice 1D chain coordination polymeric framework in its single crystal XRD.

A novel reaction-based colorimetric and ratiometric fluorescent sensor for cyanide anion with a large emission shift and high selectivity.

PubMed

Wang, Shaodan; Fei, Xiaoliang; Guo, Jing; Yang, Qingbiao; Li, Yaoxian; Song, Yan

2016-01-01

A hybrid carbazole-hemicyanine dye (Cac) has been developed as a novel colorimetric and ratiometric fluorescent sensor for cyanide detection. Upon treatment with cyanide, Cac displayed a remarkable fluorescence ratiometric response, with the emission wavelength displaying a very large emission shift (214 nm). The detection of cyanide was performed via the nucleophilic addition of cyanide anion to the indolium group of the sensor, which resulted in the blocking of the intramolecular charge transfer (ICT) process in the sensor, inducing a ratiometric fluorescence change and simultaneously an obvious color change. Furthermore, competitive anions did not showed any significant changes both in color and emission intensity ratio (I381/I595), indicating the high selectivity of the sensor to CN(-). Copyright © 2015 Elsevier B.V. All rights reserved.

A Quninolylthiazole Derivatives as an ICT-Based Fluorescent Probe of Hg(II) and its Application in Ratiometric Imaging in Live HeLa Cells.

PubMed

Bai, Jian-Ying; Xie, Yu-Zhong; Wang, Chang-Jiang; Fang, Shu-Qing; Cao, Lin-Nan; Wang, Ling-Li; Jin, Jing-Yi

2018-05-28

As a structural analogue of pyridylthiazole, 2-(2-benzothiazoyl)-phenylethynylquinoline (QBT) was designed as a fluorescent probe for Hg(II) based on an intramolecular charge transfer (ICT) mechanism. The compound was synthesized in three steps starting from 6-bromo-2-methylquinoline, with moderate yield. Corresponding studies on the optical properties of QBT indicate that changes in the fluorescence ratio of QBT in response to Hg(II) could be quantified based on dual-emission changes. More specifically, the emission spectrum of QBT before and after interactions with Hg(II) exhibited a remarkable red shift of about 120 nm, which is rarely reported in ICT-based fluorescent sensors. Finally, QBT was applied in the two-channel imaging of Hg(II) in live HeLa cells.

Aggregation induced emission enhancement (AIEE) characteristics of quinoline based compound - A versatile fluorescent probe for pH, Fe(III) ion, BSA binding and optical cell imaging

NASA Astrophysics Data System (ADS)

Manikandan, Irulappan; Chang, Chien-Huei; Chen, Chia-Ling; Sathish, Veerasamy; Li, Wen-Shan; Malathi, Mahalingam

2017-07-01

Novel benzimidazoquinoline derivative (AVT) was synthesized through a substitution reaction and characterized by various spectral techniques. Analyzing the optical properties of AVT under absorption and emission spectral studies in different environments exclusively with respect to solvents and pH, intriguing characteristics viz. aggregation induced emission enhancement (AIEE) in the THF solvent and 'On-Off' pH sensing were found at neutral pH. Sensing nature of AVT with diverse metal ions and bovine serum albumin (BSA) was also studied. Among the metal ions, Fe3 + ion alone tunes the fluorescence intensity of AVT probe in aqueous medium from ;turn-on; to ;turn-off; through ligand (probe) to metal charge transfer (LMCT) mechanism. The probe AVT in aqueous medium interacts strongly with BSA due to Fluorescence Resonance Energy Transfer (FRET) and the conformational change in BSA was further analyzed using synchronous fluorescence techniques. Docking study of AVT with BSA reveals that the active site of binding is tryptophan residue which is also supported by the experimental results. Interestingly, fluorescent AVT probe in cells was examined through cellular imaging studies using BT-549 and MDA-MB-231 cells. Thus, the single molecule probe based detection of multiple species and stimuli were described.

Nanomolar pyrophosphate detection and nucleus staining in living cells with simple terpyridine-Zn(II) complexes.

PubMed

Chao, Duobin; Ni, Shitan

2016-05-20

Great efforts have been made to develop fluorescent probes for pyrophosphate (PPi) detection. Nucleus staining with fluorescence microscopy has been also widely investigated. But fluorescent probes for PPi detection with high sensitivity in water medium and nucleus staining with low-cost non-precious metal complexes in living cells are still challenging. Herein, we report simple terpyridine-Zn(II) complexes for selective nanomolar PPi detection over ATP and ADP in water based on aggregation induced emission (AIE) and intramolecular charge transfer (ICT). In addition, these terpyridine-Zn(II) complexes were successfully employed for nucleus staining in living cells. These results demonstrated simply obtained terpyridine-Zn(II) complexes are powerful tool for PPi detection and the development of PPi-related studies.

Up-Conversion Intersystem Crossing Rates in Organic Emitters for Thermally Activated Delayed Fluorescence: Impact of the Nature of Singlet vs Triplet Excited States.

PubMed

Samanta, Pralok K; Kim, Dongwook; Coropceanu, Veaceslav; Brédas, Jean-Luc

2017-03-22

The rates for up-conversion intersystem crossing (UISC) from the T 1 state to the S 1 state are calculated for a series of organic emitters with an emphasis on thermally activated delayed fluorescence (TADF) materials. Both the spin-orbit coupling and the energy difference between the S 1 and T 1 states (ΔE ST ) are evaluated, at the density functional theory (DFT) and time-dependent DFT levels. The calculated UISC rates and ΔE ST values are found to be in good agreement with available experimental data. Our results underline that small ΔE ST values and sizable spin-orbit coupling matrix elements have to be simultaneously realized in order to facilitate UISC and ultimately TADF. Importantly, the spatial separation of the highest occupied and lowest unoccupied molecular orbitals of the emitter, a widely accepted strategy for the design of TADF molecules, does not necessarily lead to a sufficient reduction in ΔE ST ; in fact, either a significant charge-transfer (CT) contribution to the T 1 state or a minimal energy difference between the local-excitation and charge-transfer triplet states is required to achieve a small ΔE ST . Also, having S 1 and T 1 states of a different nature is found to strongly enhance spin-orbit coupling, which is consistent with the El-Sayed rule for ISC rates. Overall, our results indicate that having either similar energies for the local-excitation and charge-transfer triplet states or the right balance between a substantial CT contribution to T 1 and somewhat different natures of the S 1 and T 1 states, paves the way toward UISC enhancement and thus TADF efficiency improvement.

Visible light excitable Zn2+ fluorescent sensor derived from an intramolecular charge transfer fluorophore and its in vitro and in vivo application.

PubMed

Qian, Fang; Zhang, Changli; Zhang, Yumin; He, Weijiang; Gao, Xiang; Hu, Ping; Guo, Zijian

2009-02-04

The UV- and sensor-induced interferences to living systems pose a barrier for in vivo Zn(2+) imaging. In this work, an intramolecular charge transfer (ICT) fluorophore of smaller aromatic plane, 4-amino-7-nitro-2,1,3-benzoxadiazole, was adopted to construct visible light excited fluorescent Zn(2+) sensor, NBD-TPEA. This sensor demonstrates a visible ICT absorption band, a large Stokes shift, and biocompatibility. It emits weakly (Phi = 0.003) without pH dependence at pH 7.1-10.1, and the lambda(ex) and lambda(em) are 469 (epsilon(469) = 2.1 x 10(4) M(-1) cm(-1)) and 550 nm, respectively. The NBD-TPEA displays distinct selective Zn(2+)-amplified fluorescence (Phi = 0.046, epsilon(469) = 1.4 x 10(4) M(-1) cm(-1)) with emission shift from 550 to 534 nm, which can be ascribed to the synergic Zn(2+) coordination by the outer bis(pyridin-2-ylmethyl)amine (BPA) and 4-amine. The Zn(2+) binding ratio of NBD-TPEA is 1:1. By comparison with its analogues NBD-BPA and NBD-PMA, which have no Zn(2+) affinity, the outer BPA in NBD-TPEA should be responsible for the Zn(2+)-induced photoinduced electron transfer blockage as well as for the enhanced Zn(2+) binding ability of 4-amine. Successful intracellular Zn(2+) imaging on living cells with NBD-TPEA staining exhibited a preferential accumulation at lysosome and Golgi with dual excitability at either 458 or 488 nm. The intact in vivo Zn(2+) fluorescence imaging on zebrafish embryo or larva stained with NBD-TPEA revealed two zygomorphic luminescent areas around its ventricle which could be related to the Zn(2+) storage for the zebrafish development. Moreover, high Zn(2+) concentration in the developing neuromasters of zebrafish can be visualized by confocal fluorescence imaging. This study demonstrates a novel strategy to construct visible light excited Zn(2+) fluorescent sensor based on ICT fluorophore other than xanthenone analogues. Current data show that NBD-TPEA staining can be a reliable approach for the intact in vivo Zn(2+) imaging of zebrafish larva as well as for the clarification of subcellular distribution of Zn(2+) in vitro.

A red-emitting indolium fluorescence probe for membranes - flavonoids interactions.

PubMed

Gao, Qingyun; Liu, Han; Ding, Qiongjie; Du, Jinya; Liu, Chunlin; Yang, Wei; Shen, Ping; Yang, Changying

2018-05-01

The red-emitting indolium derivative compound (E)-2-(4-(diphenylamino)styryl)-1,3,3-trimethyl-3H-indol-1-ium iodide (H3) was demonstrated as a sensitive membrane fluorescence probe. The probe located at the interface of liposomes when mixed showed much fluorescence enhancement by inhibiting the twisted intramolecular charge transfer state. After ultrasonic treatment, it penetrated into lipid bilayers with the emissions leveling off and a rather large encapsulation efficiency (71.4%) in liposomes. The ζ-potential and particle size measurement confirmed that the charged indolium group was embedded deeply into lipid bilayers. The probe was then used to monitor the affinities of antioxidant flavonoids for membranes. It was verified that quercetin easily interacted with liposomes and dissociated the probe from the internal lipid within 60 s under the condition of simply mixing. The assessment of binding affinities of six flavonoids and the coincident results with their antioxidation activities indicated that it was a promising membrane probe for the study of drug bio-affinities. Copyright © 2018 John Wiley & Sons, Ltd.

Intramolecular charge transfer of 4-(dimethylamino)benzonitrile probed by time-resolved fluorescence and transient absorption: No evidence for two ICT states and a {pi}{sigma}{sup *} reaction intermediate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zachariasse, Klaas A.; Druzhinin, Sergey I.; Senyushkina, Tamara

2009-12-14

For the double exponential fluorescence decays of the locally excited (LE) and intramolecular charge transfer (ICT) states of 4-(dimethylamino)benzonitrile (DMABN) in acetonitrile (MeCN) the same times {tau}{sub 1} and {tau}{sub 2} are observed. This means that the reversible LE<-->ICT reaction, starting from the initially excited LE state, can be adequately described by a two state mechanism. The most important factor responsible for the sometimes experimentally observed differences in the nanosecond decay time, with {tau}{sub 1}(LE)<{tau}{sub 1}(ICT), is photoproduct formation. By employing a global analysis of the LE and ICT fluorescence response functions with a time resolution of 0.5 ps/channel inmore » 1200 channels reliable kinetic and thermodynamic data can be obtained. The arguments presented in the literature in favor of a {pi}{sigma}* state with a bent CN group as an intermediate in the ICT reaction of DMABN are discussed. From the appearance of an excited state absorption (ESA) band in the spectral region between 700 and 800 nm in MeCN for N,N-dimethylanilines with CN, Br, F, CF{sub 3}, and C(=O)OC{sub 2}H{sub 2} p-substituents, it is concluded that this ESA band cannot be attributed to a {pi}{sigma}{sup *} state, as only the C-C{identical_to}N group can undergo the required 120 deg. bending.« less

Excited State Structural Dynamics of Carotenoids and ChargeTransfer Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Tassle, Aaron Justin

This dissertation describes the development andimplementation of a visible/near infrared pump/mid-infrared probeapparatus. Chapter 1 describes the background and motivation ofinvestigating optically induced structural dynamics, paying specificattention to solvation and the excitation selection rules of highlysymmetric molecules such as carotenoids. Chapter 2 describes thedevelopment and construction of the experimental apparatus usedthroughout the remainder of this dissertation. Chapter 3 will discuss theinvestigation of DCM, a laser dye with a fluorescence signal resultingfrom a charge transfer state. By studying the dynamics of DCM and of itsmethyl deuterated isotopomer (an otherwise identical molecule), we areable to investigate the origins of the charge transfer statemore » and provideevidence that it is of the controversial twisted intramolecular (TICT)type. Chapter 4 introduces the use of two-photon excitation to the S1state, combined with one-photon excitation to the S2 state of thecarotenoid beta-apo-8'-carotenal. These 2 investigations show evidencefor the formation of solitons, previously unobserved in molecular systemsand found only in conducting polymers Chapter 5 presents an investigationof the excited state dynamics of peridinin, the carotenoid responsiblefor the light harvesting of dinoflagellates. This investigation allowsfor a more detailed understanding of the importance of structuraldynamics of carotenoids in light harvesting.« less

Spectroscopic and theoretical studies of charge-transfer interaction of 1-(2-pyridylazo)-2-napthol with nitroaromatics

NASA Astrophysics Data System (ADS)

Karmakar, Animesh; Singh, Bula

2017-05-01

1-(2-Pyridylazo)-2-napthol (hereafter 1Q) is widely used as a chelating ligand applied in chelatometric, spectrophotometric analysis of metal ions. It appeared from the literature survey that no inclusion complex of 1Q was reported with nitroaromatics. The formation of charge-transfer complex gives an opportunity to improve the physico-chemical properties of different donors. So the complex of 1Q with 4-nitrophenol (4-NP), 2,4-dinitrophenol (2,4-DNP), picric acid (PA), and 3,5-dinitrosalicylic acid (3,5-DNSA) was described in this work in methanol medium. The ground and excited state binding constants and other spectroscopic data have been determined using UV-vis and fluorescence spectroscopic studies. All the complexes have been synthesized and characterized using FT-IR, 1H NMR, and elemental analysis. Spectroscopic data reveal that 1Q joins by a N+sbnd Hsbnd O- type hydrogen bond with nitroaromatics. Job's plot of the continuous variation of absorbance indicates that stoichiometry of CT-complex was 1:1. Thermal stability of the synthesized complex has determined by TGA-DTA analysis. Energy-minimization DFT calculation further supported the formation of the H-bonded charge-transfer adduct.

Synthesis of pyridine-fused perylene imides with an amidine moiety for hydrogen bonding.

PubMed

Ito, Satoru; Hiroto, Satoru; Shinokubo, Hiroshi

2013-06-21

Pyridine-fused perylene tetracarboxylic acid bisimides (PBIs) were synthesized via Suzuki-Miyaura coupling and acid condensation. The fused PBIs with electron-donating substituents exhibited an intramolecular charge transfer interaction. One of the N-alkyl substituents was selectively removed with BBr3 to create an amidine guest binding site. A hydrogen bonding interaction with pentafluorobenzoic acid changed the absorption spectra and enhanced fluorescence.

Fluorometric "Switch-on" Detection of Heparin Based on a System Composed of Rhodamine-labeled Chitosan Oligosaccharide Lactate, and Graphene Oxide.

PubMed

Yun, Kyusik; Zhong, Linlin

2018-05-16

A novel fluorescence "Switch on" for the detection of heparin based on the RhB-COL/GO system was achieved. A strong fluorescence dye, Rhodamine B, was modified by chitosan oligosaccharide lactate (COL), which plays a major role in the formation of a positively charged RhB-COL complex. RhB-COL was soluble and stable in solution, which was characterized by using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. GO sheets quenched the fluorescence intensity of RhB-COL due to electron transfer from RhB to the GO surface. The decrease in fluorescence intensity of RhB-COL with increasing GO concentration was recorded using a Cary Eclipse fluorescence spectrophotometer. On the other hand, the addition of heparin replaced GO to bind with the RhB-COL surface via an electrostatic and noncovalent bond due to the abundant negative charge, which resulted in recovery of the fluorescence intensity. This RhB-COL/GO system possessed high selectivity and good sensitivity for the detection of heparin compared to other biomolecules, such as glycine, D-glucose, hyaluronic acid, L-glutamic acid, and ascorbic acid. The linear response toward heparin was measured over the range, 0-1.8 U·mL-1, with a low detection limit of 0.04 U·mL-1. The satisfactory sensing performance of RhB-COL/GO for heparin supports new "switch-on" sensor applications in heparin-related biomedical detection. © 2018 IOP Publishing Ltd.

Fluorometric ‘switch-on’ detection of heparin based on a system composed of rhodamine-labeled chitosan oligosaccharide lactate, and graphene oxide

NASA Astrophysics Data System (ADS)

Zhong, Linlin; Yun, Kyusik

2018-07-01

A novel fluorescence ‘Switch on’ for the detection of heparin based on the RhB-COL/GO system was achieved. A strong fluorescence dye, Rhodamine B, was modified by chitosan oligosaccharide lactate (COL), which plays a major role in the formation of a positively charged RhB-COL complex. RhB-COL was soluble and stable in solution, which was characterized by using Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy. GO sheets quenched the fluorescence intensity of RhB-COL due to electron transfer from RhB to the GO surface. The decrease in fluorescence intensity of RhB-COL with increasing GO concentration was recorded using a Cary Eclipse fluorescence spectrophotometer. On the other hand, the addition of heparin replaced GO to bind with the RhB-COL surface via an electrostatic and noncovalent bond due to the abundant negative charge, which resulted in recovery of the fluorescence intensity. This RhB-COL/GO system possessed high selectivity and good sensitivity for the detection of heparin compared to other biomolecules, such as glycine, D-glucose, hyaluronic acid, L-glutamic acid, and ascorbic acid. The linear response toward heparin was measured over the range, 0–1.8 U · ml‑1, with a low detection limit of 0.04 U · ml‑1. The satisfactory sensing performance of RhB-COL/GO for heparin supports new ‘switch-on’ sensor applications in heparin-related biomedical detection.

Synthesis of yellow and red fluorescent 1,3a,6a-triazapentalenes and the theoretical investigation of their optical properties† †Electronic supplementary information (ESI) available: the experimental details for the synthesis of the triazapentalenes and the fluorescent cell staining, the absorption and fluorescence spectra, and the 1H and 13C NMR spectra. Also given are the molecular orbitals, the natural charges, the dipole moments, and the Cartesian coordinates of the triazapentalenes (1a, 1b, 1g, 1e, and 1f). See DOI: 10.1039/c4sc02780a Click here for additional data file.

PubMed Central

Osawa, Ayumi; Mera, Akane; Tano, Fumi; Chuman, Yoshiro; Sakuda, Eri; Taketsugu, Tetsuya; Sakaguchi, Kazuyasu; Kitamura, Noboru

2015-01-01

To expand the originally developed fluorescent 1,3a,6a-triazapentalenes as fluorescent labelling reagents, the fluorescence wavelength of the 1,3a,6a-triazapentalenes was extended to the red color region. Based on the noteworthy correlation of the fluorescence wavelength with the inductive effect of the 2-substituent, electron-deficient 2-(2-cyano-4-methoxycarbonylphenyl)-1,3a,6a-triazapentalene and 2-(2,6-dicyano-4-methoxycarbonylphenyl)-1,3a,6a-triazapentalene were synthesized. The former exhibited yellow fluorescence and the latter exhibited red fluorescence, and both compounds exhibited large Stokes shifts, and the 1,3a,6a-triazapentalene system enabled the same fluorescent chromophore to cover the entire region of visible wavelengths. The potential applications of the 1,3a,6a-triazapentalenes as fluorescent probes in the fields of the life sciences were investigated, and the 1,3a,6a-triazapentalene system was clearly proven to be useful as a fluorescent reagent for live cell imaging. Quantum chemical calculations were performed to investigate the optical properties of the 1,3a,6a-triazapentalenes. These calculations revealed that the excitation involves a significant charge-transfer from the 1,3a,6a-triazapentalene skeleton to the 2-substituent. The calculated absorption and fluorescence wavelengths showed a good correlation with the experimental ones, and thus the system could enable the theoretical design of substituents with the desired optical properties. PMID:29560196

N,N-Diethylamine appended binuclear Zn(ii) complexes: highly selective and sensitive fluorescent chemosensors for picric acid.

PubMed

Kumar, Amit; Kumar, Ashish; Pandey, Daya Shankar

2016-05-28

Novel binuclear Zn(ii) complexes (1-2) derived from bis-chelating salen type ligands (H2L(1) and H2L(2)) possessing N,N-diethylamine moieties on the periphery of the molecules have been synthesized and thoroughly characterized by satisfactory elemental analyses and spectral (FT-IR, (1)H, (13)C NMR, UV-vis, fluorescence and ESI-MS) studies. The structures of H2L(1) and 1 have been authenticated by single crystal X-ray diffraction analyses. Complexes 1 and 2 strongly fluoresce and act as highly selective and sensitive chemosensors for picric acid in different organic as well as aqueous media. Both 1 and 2 showed strong potential to detect traces of PA in vapour/solid phase through contact mode analysis. Spectral and theoretical (DFT) studies suggested that the observed fluorescence quenching may be associated with ground state (GS) charge transfer as well as electrostatic interactions between 1/2 and PA. The fluorescence lifetime for the representative complex 1 displayed a double exponential curve and unaltered lifetime (τav, 0.63 nm) in the absence and presence of PA and strongly suggested that quenching follows a static mechanism. Further, DFT calculations on 1 and 2 strongly supported the static mechanism through GS charge transfer between complexes and PA. In addition, (1)H NMR spectral studies on 1-2 in the presence of PA firmly advocated strong hydrogen bonding and π-π stacking between the phenolic rings of 1-2 and the aromatic ring of PA. These complexes are capable of detecting PA either individually or in a competitive environment of other nitro- explosives. Florescence spectral studies on the model complex M lacking N,N-diethylamine groups revealed moderate selectivity and sensitivity towards PA and supported the key role of N,N-diethylamine moieties in the selectivity and sensitivity of complexes.

Chimeric green fluorescent protein-aequorin as bioluminescent Ca2+ reporters at the single-cell level

PubMed Central

Baubet, Valérie; Le Mouellic, Hervé; Campbell, Anthony K.; Lucas-Meunier, Estelle; Fossier, Philippe; Brûlet, Philippe

2000-01-01

Monitoring calcium fluxes in real time could help to understand the development, the plasticity, and the functioning of the central nervous system. In jellyfish, the chemiluminescent calcium binding aequorin protein is associated with the green fluorescent protein and a green bioluminescent signal is emitted upon Ca2+ stimulation. We decided to use this chemiluminescence resonance energy transfer between the two molecules. Calcium-sensitive bioluminescent reporter genes have been constructed by fusing green fluorescent protein and aequorin, resulting in much more light being emitted. Chemiluminescent and fluorescent activities of these fusion proteins have been assessed in mammalian cells. Cytosolic Ca2+ increases were imaged at the single-cell level with a cooled intensified charge-coupled device camera. This bifunctional reporter gene should allow the investigation of calcium activities in neuronal networks and in specific subcellular compartments in transgenic animals. PMID:10860991

Ratiometric Array of Conjugated Polymers-Fluorescent Protein Provides a Robust Mammalian Cell Sensor.

PubMed

Rana, Subinoy; Elci, S Gokhan; Mout, Rubul; Singla, Arvind K; Yazdani, Mahdieh; Bender, Markus; Bajaj, Avinash; Saha, Krishnendu; Bunz, Uwe H F; Jirik, Frank R; Rotello, Vincent M

2016-04-06

Supramolecular complexes of a family of positively charged conjugated polymers (CPs) and green fluorescent protein (GFP) create a fluorescence resonance energy transfer (FRET)-based ratiometric biosensor array. Selective multivalent interactions of the CPs with mammalian cell surfaces caused differential change in FRET signals, providing a fingerprint signature for each cell type. The resulting fluorescence signatures allowed the identification of 16 different cell types and discrimination between healthy, cancerous, and metastatic cells, with the same genetic background. While the CP-GFP sensor array completely differentiated between the cell types, only partial classification was achieved for the CPs alone, validating the effectiveness of the ratiometric sensor. The utility of the biosensor was further demonstrated in the detection of blinded unknown samples, where 121 of 128 samples were correctly identified. Notably, this selectivity-based sensor stratified diverse cell types in minutes, using only 2000 cells, without requiring specific biomarkers or cell labeling.

Sensitizing of pyrene fluorescence by β-cyclodextrin-modified TiO2 nanoparticles.

PubMed

Shown, Indrajit; Ujihara, Masaki; Imae, Toyoko

2010-12-15

TiO(2) nanoparticles were synthesized by hydrolysis of tetraisopropyl orthotitanate in an aqueous solution of cyclodextrin. The β-cyclodextrin-modified spherical TiO(2) nanoparticles were water-dispersible and had an average particle diameter of 4.4 ± 1 nm. Pyrene fluorescence was enhanced by increasing the concentration of β-cyclodextrin-modified TiO(2) nanoparticle and the sensitization effect was triply stronger than the case of the β-cyclodextrin only. The increase in a concentration of host (β-cyclodextrin) changes its microenvironment for guest (pyrene), that is, the interaction of pyrene with apolar cavity of β-cyclodextrin increases, resulting in enhancement of fluorescence. The sensitization behavior of pyrene fluorescence in the presence of TiO(2) nanoparticles occurs from the increase in the extinction coefficient of pyrene, demonstrating the charge transfer between pyrene and metal oxide nanoparticle. Crown Copyright © 2010. Published by Elsevier Inc. All rights reserved.

Magnetic field effect in organic light emitting diodes based on donor-acceptor exciplexes showing thermally activated delayed fluorescence

NASA Astrophysics Data System (ADS)

Baniya, S.; Pang, Z.; Sun, D.; Basel, T.; Zhai, Y.; Kwon, O.; Choi, H.; Vardeny, Z. V.

2016-09-01

A new type of organic light-emitting diode (OLED) has emerged that shows enhanced operational stability and large internal quantum efficiency approaching 100%, which is based on exciplexes in donor-acceptor (D-A) blends having thermally activated delayed fluorescence (TADF) when doped with fluorescent emitters. We have investigated magnetoelectroluminescence (MEL) and magneto-conductivity in such TADF-based OLEDs, as well as magnetophotoluminescence (MPL) in thin films based on the OLEDs active layers, with various fluorescence emitters. We found that both MEL and MPL responses are thermally activated with substantially lower activation energy compared to that in the pristine undoped D-A exciplex host blend. In addition, both MPL and MEL steeply decrease with the emitters' concentration. This indicates the existence of a loss mechanism, whereby the triplet charge-transfer state in the D-A exciplex host blend may directly decay to the lowest, non-emissive triplet state of the additive fluorescent emitter molecules.

Quantitatively Mapping Cellular Viscosity with Detailed Organelle Information via a Designed PET Fluorescent Probe

PubMed Central

Liu, Tianyu; Liu, Xiaogang; Spring, David R.; Qian, Xuhong; Cui, Jingnan; Xu, Zhaochao

2014-01-01

Viscosity is a fundamental physical parameter that influences diffusion in biological processes. The distribution of intracellular viscosity is highly heterogeneous, and it is challenging to obtain a full map of cellular viscosity with detailed organelle information. In this work, we report 1 as the first fluorescent viscosity probe which is able to quantitatively map cellular viscosity with detailed organelle information based on the PET mechanism. This probe exhibited a significant ratiometric fluorescence intensity enhancement as solvent viscosity increases. The emission intensity increase was attributed to combined effects of the inhibition of PET due to restricted conformational access (favorable for FRET, but not for PET), and the decreased PET efficiency caused by viscosity-dependent twisted intramolecular charge transfer (TICT). A full map of subcellular viscosity was successfully constructed via fluorescent ratiometric detection and fluorescence lifetime imaging; it was found that lysosomal regions in a cell possess the highest viscosity, followed by mitochondrial regions. PMID:24957323

Fluorescent and colorimetric molecular recognition probe for hydrogen bond acceptors.

PubMed

Pike, Sarah J; Hunter, Christopher A

2017-11-22

The association constants for formation of 1 : 1 complexes between a H-bond donor, 1-naphthol, and a diverse range of charged and neutral H-bond acceptors have been measured using UV/vis absorption and fluorescence emission titrations. The performance of 1-naphthol as a dual colorimetric and fluorescent molecular recognition probe for determining the H-bond acceptor (HBA) parameters of charged and neutral solutes has been investigated in three solvents. The data were employed to establish self-consistent H-bond acceptor parameters (β) for benzoate, azide, chloride, thiocyanate anions, a series of phosphine oxides, phosphate ester, sulfoxide and a tertiary amide. The results demonstrate both the transferability of H-bond parameters between different solvents and the utility of the naphthol-based dual molecular recognition probe to exploit orthogonal spectroscopic techniques to determine the HBA properties of neutral and charged solutes. The benzoate anion is the strongest HBA studied with a β parameter of 15.4, and the neutral tertiary amide is the weakest H-bond acceptor investigated with a β parameter of 8.5. The H-bond acceptor strength of the azide anion is higher than that of chloride (12.8 and 12.2 respectively), and the thiocyanate anion has a β value of 10.8 and thus is a significantly weaker H-bond acceptor than both the azide and chloride anions.

Double-Resonance Facilitated Decomposion of Emission Spectra

NASA Astrophysics Data System (ADS)

Kato, Ryota; Ishikawa, Haruki

2016-06-01

Emission spectra provide us with rich information about the excited-state processes such as proton-transfer, charge-transfer and so on. In the cases that more than one excited states are involved, emission spectra from different excited states sometimes overlap and a decomposition of the overlapped spectra is desired. One of the methods to perform a decomposition is a time-resolved fluorescence technique. It uses a difference in time evolutions of components involved. However, in the gas-phase, a concentration of the sample is frequently too small to carry out this method. On the other hand, double-resonance technique is a very powerful tool to discriminate or identify a common species in the spectra in the gas-phase. Thus, in the present study, we applied the double-resonance technique to resolve the overlapped emission spectra. When transient IR absorption spectra of the excited state are available, we can label the population of the certain species by the IR excitation with a proper selection of the IR wavenumbers. Thus, we can obtain the emission spectra of labeled species by subtracting the emission spectra with IR labeling from that without IR. In the present study, we chose the charge-transfer emission spectra of cyanophenyldisilane (CPDS) as a test system. One of us reported that two charge-transfer (CT) states are involved in the intramolecular charge-transfer (ICT) process of CPDS-water cluster and recorded the transient IR spectra. As expected, we have succeeded in resolving the CT emission spectra of CPDS-water cluster by the double resonance facilitated decomposion technique. In the present paper, we will report the details of the experimental scheme and the results of the decomposition of the emission spectra. H. Ishikawa, et al., Chem. Phys. Phys. Chem., 9, 117 (2007).

Further Insights on the Chemical Structure of Humic Substances (HS) and Chromophoric Dissolved Organic Matter (CDOM) in Relation to their Optical/Chemical Properties

NASA Astrophysics Data System (ADS)

Del Vecchio, R.; Schendorf, T. M.; Koech, K.; Blough, N. V.

2016-02-01

HS have been studied extensively over the last decades, yet the structural basis of their optical properties is still highly debated. Aromatic ketones, aldehydes and quinones along with carboxylic groups and phenolic moieties are significant constituents of HS, however their contribution to the optical properties has only recently been investigated. Chemical manipulation of selected functional groups thus represents an extremely promising approach to highlight the contribution of such groups to the HS (and CDOM) optical properties. Chemical reduction (and re-oxidation) along with pH titrations are employed herein to assess the relative contribution of aromatic ketones/aldehydes/quinones and carboxylic groups/phenolic moieties, respectively to the optical properties of HS (and CDOM). Results indicate that (a) the contribution of quinones to HS absorption and fluorescence is minor (or nil), while that of aromatic ketones (and aldehydes) is significant; (b) phenolic groups contribute more than carboxylic acids to the HS optical properties; (c) the effects of borohydride reduction and pH on the long-wavelength absorption and fluorescence is consistent with charge-transfer interactions between carbonyl and phenolic groups (as well as aromatic carboxylic acids, but to a smaller extent). Results will be presented within the context of our proposed charge-transfer model.

Effect of the Semiconductor Quantum Dot Shell Structure on Fluorescence Quenching by Acridine Ligand

NASA Astrophysics Data System (ADS)

Linkov, P. A.; Vokhmintcev, K. V.; Samokhvalov, P. S.; Laronze-Cochard, M.; Sapi, J.; Nabiev, I. R.

2018-02-01

The main line of research in cancer treatment is the development of methods for early diagnosis and targeted drug delivery to cancer cells. Fluorescent semiconductor core/shell nanocrystals of quantum dots (e.g., CdSe/ZnS) conjugated with an anticancer drug, e.g., an acridine derivative, allow real-time tracking and control of the process of the drug delivery to tumors. However, linking of acridine derivatives to a quantum dot can be accompanied by quantum dot fluorescence quenching caused by electron transfer from the quantum dot to the organic molecule. In this work, it has been shown that the structure of the shell of the quantum dot plays the decisive role in the process of photoinduced charge transfer from the quantum dot to the acridine ligand, which is responsible for fluorescence quenching. It has been shown that multicomponent ZnS/CdS/ZnS shells of CdSe cores of quantum dots, which have a relatively small thickness, make it possible to significantly suppress a decrease in the quantum yield of fluorescence of quantum dots as compared to both the classical ZnS thin shell and superthick shells of the same composition. Thus, core/multicomponent shell CdSe/ZnS/CdS/ZnS quantum dots can be used as optimal fluorescent probes for the development of systems for diagnosis and treatment of cancer with the use of anticancer compounds based on acridine derivatives.

Investigation of electronic band structure and charge transfer mechanism of oxidized three-dimensional graphene as metal-free anodes material for dye sensitized solar cell application

NASA Astrophysics Data System (ADS)

Loeblein, Manuela; Bruno, Annalisa; Loh, G. C.; Bolker, Asaf; Saguy, Cecile; Antila, Liisa; Tsang, Siu Hon; Teo, Edwin Hang Tong

2017-10-01

Dye-sensitized solar cells (DSSCs) offer an optimal trade-off between conversion-efficiency and low-cost fabrication. However, since all its electrodes need to fulfill stringent work-function requirements, its materials have remained unchanged since DSSC's first report early-90s. Here we describe a new material, oxidized-three-dimensional-graphene (o-3D-C), with a band gap of 0.2 eV and suitable electronic band-structure as alternative metal-free material for DSSCs-anodes. o-3D-C/dye-complex has a strong chemical bonding via carboxylic-group chemisorption with full saturation after 12 sec at capacity of ∼450 mg/g (600x faster and 7x higher than optimized metal surfaces). Furthermore, fluorescence quenching of life-time by 28-35% was measured demonstrating charge-transfer from dye to o-3D-C.

Electronic structural dependence of the photophysical properties of fluorescent heteroditopic ligands - implications in designing molecular fluorescent indicators.

PubMed

Younes, Ali H; Zhang, Lu; Clark, Ronald J; Davidson, Michael W; Zhu, Lei

2010-12-07

Two fluorescent heteroditopic ligands (2a and 2b) for zinc ion were synthesized and studied. The efficiencies of two photophysical processes, intramolecular charge transfer (ICT) and photoinduced electron transfer (PET), determine the magnitudes of emission bathochromic shift and enhancement, respectively, when a heteroditopic ligand forms mono- or dizinc complexes. The electron-rich 2b is characterized by a high degree of ICT in the excited state with little propensity for PET, which is manifested in a large bathochromic shift of emission upon Zn(2+) coordination without enhancement in fluorescence quantum yield. The electron-poor 2a displays the opposite photophysical consequence where Zn(2+) binding results in greatly enhanced emission without significant spectral shift. The electronic structural effects on the relative efficiencies of ICT and PET in 2a and 2b as well as the impact of Zn(2+)-coordination are probed using experimental and computational approaches. This study reveals that the delicate balance between various photophysical pathways (e.g. ICT and PET) engineered in a heteroditopic ligand is sensitively dependent on the electronic structure of the ligand, i.e. whether the fluorophore is electron-rich or poor, whether it possesses a donor-acceptor type of structure, and where the metal binding occurs.

Gas response behaviour and photochemistry of borondiketonate in acrylic polymer matrices for sensing applications.

PubMed

Arias Espinoza, Juan Diego; Sazhnikov, Viacheslav; Smits, Edsger C P; Ionov, Dmirity; Kononevich, Yuriy; Yakimets, Iryna; Alfimov, Mikael; Schoo, Herman F M

2014-11-01

The fluorescent spectra in combination with gas response behavior of acrylic polymers doped with dibenzoyl(methanato)boron difluoride (DBMBF2) were studied by fluorescence spectroscopy and time-resolved fluorescence lifetime. The role of acrylic matrix polarity upon the fluorescence spectra and fluorescence lifetime was analyzed. Changes in emission of the dye doped polymers under exposure to toluene, n-hexane and ethanol were monitored. The fluorescence lifetimes were measured for the singlet excited state as well as the exciplex formed between DBMBF2 and toluene. A reduction of the transition energy to the first singlet-excited state in the four polymers was observed, compared to solution. Reversible exciplex formation, viz. a red shifted fluorescence emission was perceived when exposing the polymers to toluene, while for hexane and ethanol only reversible reduction of the fluorescence occurred. Longer singlet and shorter exciplex lifetimes were observed for non-polar matrixes. The latter mechanism is explained in function of the lower charge transfer character of the exciplex in non-polar matrixes. Additionally, the quantum yield of the dye in the polymer matrix increased almost seventh-fold compared to values for solution.

Nonadiabatic Photo-Process Involving the πσ* State in Intramolecular Charge Transfer: a Concerted Spectroscopic and Computational Study 4-(DIMETHYLAMINO)BENZETHYNE and 4-(DIMETHYLAMINO)BENZONITRILE.

NASA Astrophysics Data System (ADS)

Fujiwara, Takashige; Segarra-Martí, Javier; Coto, Pedro B.

2014-06-01

The ubiquitous nature of the low-lying πσ* state in the photo-excited aromatic molecules or biomolecules is widely recognized to play an important role in nonadiabatic photo-process such as photodissociation or intramolecular charge transfer (ICT). For instance, the O--H elimination channel in phenol is attributed to the state-cross of the repulsive πσ* state that exhibits a conical intersection with the lowest bright ππ* state and with the ground state, leading to ultrafast electronic deactivation. A similar decay pathway has been found in the ICT formation of 4-(dialkylamino)benzonitriles in a polar environment, where an initially photoexcited Frank-Condon state bifurcates in the presence of a dark intermediate πσ* state that crosses the fluorescent ππ* state, followed by a conical intersection with the twisted intramolecular charge transfer (TICT) state. We proposed such a two-fold decay mechanism that πσ*-state highly mediates intramolecular charge transfer in 4-(dialkylamino)benzonitriles, which is supported from both our high-level ab initio calculations and ultrafast laser spectroscopies in the previous study. 4-(Dimethylamino)benzethyne (DMABE) is isoelectronic with 4-(dimethylamino)benzonitrile (DMABN), and the electronic structures and electronic spectra of the two molecules bear very close resemblance. However, DMABN does show the ICT formation in a polar environment, whereas DMABE does not. To probe the photophysical differences among the low-lying excited-state configurations, we performed concerted time-resolved laser spectroscopies and high level ab initio multireference perturbation theory quantum-chemical (CASPT2//CASSCF) computations on the two molecules. In this paper we demonstrate the importance of the bound excited-state of a πσ* configuration that induce highly πσ*-state mediated intramolecular charge transfer in 4-(dialkylamino)benzonitriles.

Fluorescent rhenium-naphthalimide conjugates as cellular imaging agents.

PubMed

Langdon-Jones, Emily E; Symonds, Nadine O; Yates, Sara E; Hayes, Anthony J; Lloyd, David; Williams, Rebecca; Coles, Simon J; Horton, Peter N; Pope, Simon J A

2014-04-07

A range of biologically compatible, fluorescent rhenium-naphthalimide conjugates, based upon the rhenium fac-tricarbonyl core, has been synthesized. The fluorescent ligands are based upon a N-functionalized, 4-amino-derived 1,8-naphthalimide core and incorporate a dipicolyl amine binding unit to chelate Re(I); the structural variations accord to the nature of the alkylated imide with ethyl ester glycine (L(1)), 3-propanol (L(2)), diethylene glycol (L(3)), and benzyl alcohol (L(4)) variants. The species are fluorescent in the visible region between 505 and 537 nm through a naphthalimide-localized intramolecular charge transfer, with corresponding fluorescent lifetimes of up to 9.8 ns. The ligands and complexes were investigated for their potential as imaging agents for human osteoarthritic cells and protistan fish parasite Spironucleus vortens using confocal fluorescence microscopy. The results show that the specific nature of the naphthalimide structure serves to control the uptake and intracellular localization of these imaging agents. Significant differences were noted between the free ligands and complexes, with the Re(I) complex of L(2) showing hydrogenosomal localization in S. vortens.

PEGylation of Concanavalin A to decrease nonspecific interactions in a fluorescent glucose sensor

NASA Astrophysics Data System (ADS)

Abraham, Alexander A.; Cummins, Brian M.; Locke, Andrea K.; Grunlan, Melissa A.; Coté, Gerard L.

2014-02-01

The ability of people with diabetes to both monitor and regulate blood sugar levels is limited by the conventional "finger-prick" test that provides intermittent, single point measurements. Toward the development of a continuous glucose monitoring (CGM) system, the lectin, Concanavalin A (ConA), has been utilized as a component in a Förster resonance energy transfer (FRET), competitive glucose binding assay. Recently, to avoid reversibility problems associated with ConA aggregation, a suitable competing ligand labeled with 8-aminopyrene-1,3,6-trisulfonic acid trisodium salt (APTS) has been engineered. However, its ability to function as part of a glucose sensing assay is compromised due to the negative charge (at physiological pH) of native ConA that gives rise to non-specific binding with other ConA groups as well as with electrostatically charged assay-delivery carriers. To minimize these undesirable interactions, we have conjugated ConA with monomethoxy-poly(ethylene glycol) (mPEG) (i.e. "PEGylation"). In this preliminary research, fluorescently-labeled ConA was successfully PEGylated with mPEG-Nhydroxylsuccinimide( succinimidyl carbonate) (mPEG-NHS(SC)). The FRET response of APTS-labeled competing ligand (donor) conveyed an increase in the fluorescence intensity with increasing glucose concentrations.

Mechanism Underlying the Nucleobase-Distinguishing Ability of Benzopyridopyrimidine (BPP).

PubMed

Kochman, Michał A; Bil, Andrzej; Miller, R J Dwayne

2017-11-02

Benzopyridopyrimidine (BPP) is a fluorescent nucleobase analogue capable of forming base pairs with adenine (A) and guanine (G) at different sites. When incorporated into oligodeoxynucleotides, it is capable of differentiating between the two purine nucleobases by virtue of the fact that its fluorescence is largely quenched when it is base-paired to guanine, whereas base-pairing to adenine causes only a slight reduction of the fluorescence quantum yield. In the present article, the photophysics of BPP is investigated through computer simulations. BPP is found to be a good charge acceptor, as demonstrated by its positive and appreciably large electron affinity. The selective quenching process is attributed to charge transfer (CT) from the purine nucleobase, which is predicted to be efficient in the BPP-G base pair, but essentially inoperative in the BPP-A base pair. The CT process owes its high selectivity to a combination of two factors: the ionization potential of guanine is lower than that of adenine, and less obviously, the site occupied by guanine enables a greater stabilization of the CT state through electrostatic interactions than the one occupied by adenine. The case of BPP illustrates that molecular recognition via hydrogen bonding can enhance the selectivity of photoinduced CT processes.

Femtosecond excited state studies of the two-center three-electron bond driven twisted internal charge transfer dynamics in 1,8-bis(dimethylamino)naphthalene.

PubMed

Balkowski, Grzegorz; Szemik-Hojniak, Anna; van Stokkum, Ivo H M; Zhang, Hong; Buma, Wybren J

2005-04-28

Femtosecond fluorescence upconversion and transient absorption experiments have been performed to monitor the photoinduced electronic, geometry, and solvent relaxation dynamics of 1,8-bis(dimethylamino)naphthalene dissolved in methylcyclohexane or n-hexane, n-dodecane, dichloromethane, and acetonitrile. The data have been analyzed by using a sequential global analysis method that gives rise to species associated difference spectra. The spectral features in these spectra and their dynamic behavior enable us to associate them with specific processes occurring in the molecule. The experiments show that the internal charge-transfer lpi* state is populated after internal conversion from the 1La state. In the lpi state the molecule is concluded to be subject to a large-amplitude motion, thereby confirming our previous predictions that internal charge transfer in this state is accompanied by the formation of a two-center three-electron bond between the two nitrogen atoms. Solvent relaxation and vibrational cooling in the lpi* state cannot be separated in polar solvents, but in apolar solvents a distinct vibrational cooling process in the lpi* state is discerned. The spectral and dynamic characteristics of the final species created in the experiments are shown to correspond well with what has been determined before for the relaxed emissive lpi state.

Fluorescent quantum dot hydrophilization with PAMAM dendrimer

NASA Astrophysics Data System (ADS)

Potapkin, Dmitry V.; Geißler, Daniel; Resch-Genger, Ute; Goryacheva, Irina Yu.

2016-05-01

Polyamidoamine (PAMAM) dendrimers were used to produce CdSe core/multi-shell fluorescent quantum dots (QDs) which are colloidally stable in aqueous solutions. The size, charge, and optical properties of QDs functionalized with the 4th (G4) and 5th (G5) generation of PAMAM were compared with amphiphilic polymer-covered QDs and used as criteria for the evaluation of the suitability of both water solubilization methods. As revealed by dynamic and electrophoretic light scattering (DLS and ELS), the hydrodynamic sizes of the QDs varied from 30 to 65 nm depending on QD type and dendrimer generation, with all QDs displaying highly positive surface charges, i.e., zeta potentials of around +50 mV in water. PAMAM functionalization yielded stable core/multi-shell QDs with photoluminescence quantum yields ( Φ) of up to 45 %. These dendrimer-covered QDs showed a smaller decrease in their Φ upon phase transfer compared with QDs made water soluble via encapsulation with amphiphilic brush polymer bearing polyoxyethylene/polyoxypropylene chains.

Photoelectrical, photophysical and photocatalytic properties of Al based MOFs: MIL-53(Al) and MIL-53-NH{sub 2}(Al)

DOE Office of Scientific and Technical Information (OSTI.GOV)

An, Yang; Li, Huiliang; Liu, Yuanyuan, E-mail: yyliu@sdu.edu.cn

Two Al based MOFs (MIL-53(Al) and MIL-53-NH{sub 2} (Al)) were synthesized, and their photoelectrical, photophysical and photocatalytic properties towards oxygen evolution from water were investigated. Different from the ligand to metal charge transfer process previously reported, we proposes a new photocatalytic mechanism based on electron tunneling according to the results of theoretical calculation, steady state and time resolved fluorescence spectra. The organic linkers absorb photons, giving rise to electrons and holes. Then, the photogenerated electrons tunnel through the AlO{sub 6}-octahedra, which not only inhibit the recombination of photogenerated charge carriers, but also is a key factor to the photocatalytic activitymore » of Al based MOFs. - Graphical abstract: The photoelectrical, photophysical and photocatalytic properties towards oxygen evolution from water of two Al based MOFs were investigated. A new photocatalytic mechanism was proposed based on electron tunneling according to the results of both theoretical calculation and steady state, time resolved fluorescence spectra. The electron tunneling process not only inhibit the recombination of photogenerated charge carriers, but also is a key factor to the photocatalytic activity of Al based MOFs.« less

Novel Galvanic Corrosion Inhibitors: Synthesis, Characterization, Fabrication and Testing

DTIC Science & Technology

2007-09-30

have attempted to develop methods based on chemical structural modification to prevent galvanically-induced composite corrosion. [9, 10-12] These...of the two metallopolymers 11 and 12 show characteristic MLCT (metal-to-ligand charge transfer) absorption band of tris(bipyridyl)Ru(II) unit at k...showed absorption band at 450 nm and emission band at 325 nm of tris(bipyridyl)Ru(II) units in its respective UV-vis and fluorescence spectra. Very

Interfacial charge transfer between CdTe quantum dots and Gram negative vs. Gram positive bacteria.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dumas, E.; Gao, C.; Suffern, D.

Oxidative toxicity of semiconductor and metal nanomaterials to cells has been well established. However, it may result from many different mechanisms, some requiring direct cell contact and others resulting from the diffusion of reactive species in solution. Published results are contradictory due to differences in particle preparation, bacterial strain, and experimental conditions. It has been recently found that C{sub 60} nanoparticles can cause direct oxidative damage to bacterial proteins and membranes, including causing a loss of cell membrane potential (depolarization). However, this did not correlate with toxicity. In this study we perform a similar analysis using fluorescent CdTe quantum dots,more » adapting our tools to make use of the particles fluorescence. We find that two Gram positive strains show direct electron transfer to CdTe, resulting in changes in CdTe fluorescence lifetimes. These two strains also show changes in membrane potential upon nanoparticle binding. Two Gram negative strains do not show these effects - nevertheless, they are over 10-fold more sensitive to CdTe than the Gram positives. We find subtoxic levels of Cd{sup 2+} release from the particles upon irradiation of the particles, but significant production of hydroxyl radicals, suggesting that the latter is a major source of toxicity. These results help establish mechanisms of toxicity and also provide caveats for use of certain reporter dyes with fluorescent nanoparticles which will be of use to anyone performing these assays. The findings also suggest future avenues of inquiry into electron transfer processes between nanomaterials and bacteria.« less

Photoinduced Electron Transfer and Hole Migration in Nanosized Helical Aromatic Oligoamide Foldamers.

PubMed

Li, Xuesong; Markandeya, Nagula; Jonusauskas, Gediminas; McClenaghan, Nathan D; Maurizot, Victor; Denisov, Sergey A; Huc, Ivan

2016-10-07

A series of photoactive triads have been synthesized and investigated in order to elucidate photoinduced electron transfer and hole migration mechanism across nanosized, rigid helical foldamers. The triads are comprised of a central helical oligoamide foldamer bridge with 9, 14, 18, 19, or 34 8-amino-2-quinolinecarboxylic acid repeat units, and of two chromophores, an N-terminal oligo(para-phenylenevinylene) electron donor and a C-terminal perylene bis-imide electron acceptor. Time-resolved fluorescence and transient absorption spectroscopic studies showed that, following photoexcitation of the electron acceptor, fast electron transfer occurs initially from the oligoquinoline bridge to the acceptor chromophore on the picosecond time scale. The oligo(para-phenylenevinylene) electron donor is oxidized after a time delay during which the hole migrates across the foldamer from the acceptor to the donor. The charge separated state that is finally generated was found to be remarkably long-lived (>80 μs). While the initial charge injection rate is largely invariant for all foldamer lengths (ca. 60 ps), the subsequent hole transfer to the donor varies from 1 × 10 9 s -1 for the longest sequence to 17 × 10 9 s -1 for the shortest. In all cases, charge transfer is very fast considering the foldamer length. Detailed analysis of the process in different media and at varying temperatures is consistent with a hopping mechanism of hole transport through the foldamer helix, with individual hops occurring on the subpicosecond time scale (k ET = 2.5 × 10 12 s -1 in CH 2 Cl 2 ). This work demonstrates the possibility of fast long-range hole transfer over 300 Å (through bonds) across a synthetic modular bridge, an achievement that had been previously observed principally with DNA structures.

Highly photostable "super"-photoacids for ultrasensitive fluorescence spectroscopy.

PubMed

Finkler, Björn; Spies, Christian; Vester, Michael; Walte, Frederick; Omlor, Kathrin; Riemann, Iris; Zimmer, Manuel; Stracke, Frank; Gerhards, Markus; Jung, Gregor

2014-03-01

The photoacid 8-hydroxypyren-1,3,6-trisulfonic acid (HPTS, pyranine) is a widely used model compound for the examination of excited state proton transfer (ESPT). We synthesized five "super"-photoacids with varying hydrophilicity and acidity on the basis of HPTS. By chemical modification of the three sulfonic acid substituents, the photoacidity is enhanced by up to more than five logarithmic units from pK*≈ 1.4 to ∼-3.9 for the most acidic compound. As a result, nearly quantitative ESPT in DMSO can be observed. The novel photoacids were characterized by steady-state and time-resolved fluorescence techniques showing distinctively red shifted spectra compared to HPTS while maintaining a high quantum yield near 90%. Photostability of the compounds was checked by fluorescence correlation spectroscopy (FCS) and was found to be adequately high for ultrasensitive fluorescence spectroscopy. The described photoacids present a valuable palette for a wide range of applications, especially when the properties of HPTS, i.e. highly charged, low photostability and only moderate excited state acidity, are limiting.

Augmenting light coverage for photosynthesis through YFP-enhanced charge separation at the Rhodobacter sphaeroides reaction centre

DOE PAGES

Grayson, Katie J.; Faries, Kaitlyn M.; Huang, Xia; ...

2017-01-05

Photosynthesis uses a limited range of the solar spectrum, so enhancing spectral coverage could improve the efficiency of light capture. Here, we show that a hybrid reaction centre (RC)/yellow fluorescent protein (YFP) complex accelerates photosynthetic growth in the bacterium Rhodobacter sphaeroides. The structure of the RC/YFP-light-harvesting 1 (LH1) complex shows the position of YFP attachment to the RC-H subunit, on the cytoplasmic side of the RC complex. Fluorescence lifetime microscopy of whole cells and ultrafast transient absorption spectroscopy of purified RC/YFP complexes show that the YFP–RC intermolecular distance and spectral overlap between the emission of YFP and the visible-region (Qmore » X) absorption bands of the RC allow energy transfer via a Fo¨rster mechanism, with an efficiency of 40±10%. Finally, this proof-of-principle study demonstrates the feasibility of increasing spectral coverage for harvesting light using non-native genetically-encoded light-absorbers, thereby augmenting energy transfer and trapping in photosynthesis.« less

Augmenting light coverage for photosynthesis through YFP-enhanced charge separation at the Rhodobacter sphaeroides reaction centre

PubMed Central

Grayson, Katie J.; Faries, Kaitlyn M.; Huang, Xia; Qian, Pu; Dilbeck, Preston; Martin, Elizabeth C.; Hitchcock, Andrew; Vasilev, Cvetelin; Yuen, Jonathan M.; Niedzwiedzki, Dariusz M.; Leggett, Graham J.; Holten, Dewey; Kirmaier, Christine; Neil Hunter, C.

2017-01-01

Photosynthesis uses a limited range of the solar spectrum, so enhancing spectral coverage could improve the efficiency of light capture. Here, we show that a hybrid reaction centre (RC)/yellow fluorescent protein (YFP) complex accelerates photosynthetic growth in the bacterium Rhodobacter sphaeroides. The structure of the RC/YFP-light-harvesting 1 (LH1) complex shows the position of YFP attachment to the RC-H subunit, on the cytoplasmic side of the RC complex. Fluorescence lifetime microscopy of whole cells and ultrafast transient absorption spectroscopy of purified RC/YFP complexes show that the YFP–RC intermolecular distance and spectral overlap between the emission of YFP and the visible-region (QX) absorption bands of the RC allow energy transfer via a Förster mechanism, with an efficiency of 40±10%. This proof-of-principle study demonstrates the feasibility of increasing spectral coverage for harvesting light using non-native genetically-encoded light-absorbers, thereby augmenting energy transfer and trapping in photosynthesis. PMID:28054547

Electron-rich triphenylamine-based sensors for picric acid detection.

PubMed

Chowdhury, Aniket; Mukherjee, Partha Sarathi

2015-04-17

This paper demonstrates the role of solvent in selectivity and sensitivity of a series of electron-rich compounds for the detection of trace amounts of picric acid. Two new electron-rich fluorescent esters (6, 7) containing a triphenylamine backbone as well as their analogous carboxylic acids (8, 9) have been synthesized and characterized. Fluorescent triphenylamine coupled with an ethynyl moiety constitutes π-electron-rich selective and sensitive probes for electron-deficient picric acid (PA). In solution, the high sensitivity of all the sensors toward PA can be attributed to a combined effect of the ground-state charge-transfer complex formation and resonance energy transfer between the sensor and analyte. The acids 8 and 9 also showed enhanced sensitivity for nitroaromatics in the solid state, and their enhanced sensitivity could be attributed to exciton migration due to close proximity of the neighboring acid molecules, as evident from the X-ray diffraction study. The compounds were found to be quite sensitive for the detection of trace amount of nitroaromatics in solution, solid, and contact mode.

Augmenting light coverage for photosynthesis through YFP-enhanced charge separation at the Rhodobacter sphaeroides reaction centre

NASA Astrophysics Data System (ADS)

Grayson, Katie J.; Faries, Kaitlyn M.; Huang, Xia; Qian, Pu; Dilbeck, Preston; Martin, Elizabeth C.; Hitchcock, Andrew; Vasilev, Cvetelin; Yuen, Jonathan M.; Niedzwiedzki, Dariusz M.; Leggett, Graham J.; Holten, Dewey; Kirmaier, Christine; Neil Hunter, C.

2017-01-01

Photosynthesis uses a limited range of the solar spectrum, so enhancing spectral coverage could improve the efficiency of light capture. Here, we show that a hybrid reaction centre (RC)/yellow fluorescent protein (YFP) complex accelerates photosynthetic growth in the bacterium Rhodobacter sphaeroides. The structure of the RC/YFP-light-harvesting 1 (LH1) complex shows the position of YFP attachment to the RC-H subunit, on the cytoplasmic side of the RC complex. Fluorescence lifetime microscopy of whole cells and ultrafast transient absorption spectroscopy of purified RC/YFP complexes show that the YFP-RC intermolecular distance and spectral overlap between the emission of YFP and the visible-region (QX) absorption bands of the RC allow energy transfer via a Förster mechanism, with an efficiency of 40+/-10%. This proof-of-principle study demonstrates the feasibility of increasing spectral coverage for harvesting light using non-native genetically-encoded light-absorbers, thereby augmenting energy transfer and trapping in photosynthesis.

Modulated electron-multiplied fluorescence lifetime imaging microscope: all-solid-state camera for fluorescence lifetime imaging.

PubMed

Zhao, Qiaole; Schelen, Ben; Schouten, Raymond; van den Oever, Rein; Leenen, René; van Kuijk, Harry; Peters, Inge; Polderdijk, Frank; Bosiers, Jan; Raspe, Marcel; Jalink, Kees; Geert Sander de Jong, Jan; van Geest, Bert; Stoop, Karel; Young, Ian Ted

2012-12-01

We have built an all-solid-state camera that is directly modulated at the pixel level for frequency-domain fluorescence lifetime imaging microscopy (FLIM) measurements. This novel camera eliminates the need for an image intensifier through the use of an application-specific charge coupled device design in a frequency-domain FLIM system. The first stage of evaluation for the camera has been carried out. Camera characteristics such as noise distribution, dark current influence, camera gain, sampling density, sensitivity, linearity of photometric response, and optical transfer function have been studied through experiments. We are able to do lifetime measurement using our modulated, electron-multiplied fluorescence lifetime imaging microscope (MEM-FLIM) camera for various objects, e.g., fluorescein solution, fixed green fluorescent protein (GFP) cells, and GFP-actin stained live cells. A detailed comparison of a conventional microchannel plate (MCP)-based FLIM system and the MEM-FLIM system is presented. The MEM-FLIM camera shows higher resolution and a better image quality. The MEM-FLIM camera provides a new opportunity for performing frequency-domain FLIM.

Excited state properties of peridinin: Observation of a solvent dependence of the lowest excited singlet state lifetime and spectral behavior unique among carotenoids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bautista, J.A.; Connors, R.E.; Raju, B.B.

1999-10-14

The spectroscopic properties and dynamic behavior of peridinin in several different solvents were studied by steady-state absorption, fluorescence, and transient optical spectroscopy. The lifetime of the lowest excited singlet state of peridinin is found to be strongly dependent on solvent polarity and ranges from 7 ps in the strongly polar solvent trifluoroethanol to 172 ps in the nonpolar solvents cyclohexane and benzene. The lifetimes show no obvious correlation with solvent polarizability, and hydrogen bonding of the solvent molecules to peridinin is not an important factor in determining the dynamic behavior of the lowest excited singlet state. The wavelengths of emissionmore » maxima, the quantum yields of fluorescence, and the transient absorption spectra are also affected by the solvent environment. A model consistent with the data and supported by preliminary semiempirical calculations invokes the presence of a charge transfer state in the excited state manifold of peridinin to account for the observations. The charge transfer state most probably results from the presence of the lactone ring in the {pi}-electron conjugation of peridinin analogous to previous findings on aminocoumarins and related compounds. The behavior of peridinin reported here is highly unusual for carotenoids, which generally show little dependence of the spectral properties and lifetimes of the lowest excited singlet state on the solvent environment.« less

Impacts of side chain and excess energy on the charge photogeneration dynamics of low-bandgap copolymer-fullerene blends

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huo, Ming-Ming, E-mail: hithuomm@163.com; Zhang, Jian-Ping, E-mail: jpzhang@chem.ruc.edu.cn, E-mail: hjhzlz@iccas.ac.cn; Department of Chemistry, Renmin University of China, Beijing 100872

2014-02-28

Primary charge photogeneration dynamics in neat and fullerene-blended films of a pair of alternating benzo[1,2-b:4,5-b{sup ′}]dithiophene (BDT) and thieno[3,4-b]thiophene (TT) copolymers are comparatively studied by using near-infrared, time-resolved absorption (TA) spectroscopy under low excitation photon fluence. PBDTTT-E and PBDTTT-C, differed merely in the respective TT-substituents of ester (-E) and carbonyl (-C), show distinctly different charge photogeneration dynamics. The pair of neat PBDTTT films show exciton lifetimes of ∼0.1 ns and fluorescence quantum yields below 0.2%, as well as prominent excess-energy enhanced exciton dissociation. In addition, PBDTTT-C gives rise to >50% higher P{sup •+} yield than PBDTTT-E does irrespective to themore » excitation photon energy. Both PBDTTT-E:PC{sub 61}BM and PBDTTT-C:PC{sub 61}BM blends show subpicosecond exciton lifetimes and nearly unitary fluorescence quenching efficiency and, with respect to the former blend, the latter one shows substantially higher branching ratio of charge separated (CS) state over interfacial charge transfer (ICT) state, and hence more efficient exciton-to-CS conversion. For PBDTTT-C:PC{sub 61}BM, the ultrafast charge dynamics clearly show the processes of ICT-CS interconversion and P{sup •+} migration, which are possibly influenced by the ICT excess energy. However, such processes are relatively indistinctive in the case of PBDTTT-E:PC{sub 61}BM. The results strongly prove the importance of ICT dissociation in yielding free charges, and are discussed in terms of the film morphology and the precursory solution-phase macromolecular conformation.« less

A napthelene-pyrazol conjugate: Al(III) ion-selective blue shifting chemosensor applicable as biomarker in aqueous solution.

PubMed

Mukherjee, Manjira; Pal, Siddhartha; Lohar, Somenath; Sen, Buddhadeb; Sen, Supriti; Banerjee, Samya; Banerjee, Snehasis; Chattopadhyay, Pabitra

2014-10-07

A newly synthesized and crystalographically characterized napthelene–pyrazol conjugate, 1-[(5-phenyl-1H-pyrazole-3-ylimino)-methyl]-naphthalen-2-ol (HL) behaves as an Al(III) ion-selective chemosensor through internal charge transfer (ICT)-chelation-enhanced fluorescence (CHEF) processes in 100 mM HEPES buffer (water–DMSO 5:1, v/v) at biological pH with almost no interference of other competitive ions. This mechanism is readily studied from electronic, fluorimetric and (1)H NMR titration. The probe (HL) behaved as a highly selective fluorescent sensor for Al(III) ions as low as 31.78 nM within a very short response time (15–20 s). The sensor (HL), which has no cytotoxicity, is also efficient in detecting the distribution of Al(III) ions in HeLa cells via image development under fluorescence microscope.

Synthesis, Luminescent Properties of aza-Boron-Diquinomethene Difluoride Complexes and Their Application for Fluorescent Security Inks.

PubMed

Gu, Long; Liu, Rui; Shi, Hong; Wang, Qiang; Song, Guangliang; Zhu, Xiaolin; Yuan, Shidong; Zhu, Hongjun

2016-03-01

Two aza-boron-diquinomethene (aza-BODIQU) complexes bearing phenyl and carbazyl substituents were synthesized and characterized. Their photophysical properties were investigated systematically via spectroscopic and theoretical methods. Both complexes exhibit strong (1)π-π* transition absorptions (λ(abs) = 400-540 nm) and intense fluorescent emissions (λ(em) = 440-600 nm, Φ(PL) = 0.93 and 0.78) in CH2Cl2 solution and in solid state at room temperature. Compared to the complex with phenyl groups, the complex bearing carbazyl groups shows significant bathochromic shift in both absorption and emission. This could be attributed to the larger π-electron conjugation of the carbazole unit and intramolecular charge transfer feature from carbazole to aza-BODIQU component. In addition, the complexes exhibit intense photoluminescence and good stability on antacid, anti-alkali and stability in printing ink samples, which makes them potential dopants for the application of fluorescent security inks.

Broadband polarized emission from P(NDI2OD-T2) polymer.

PubMed

Ulrich, Steve; Sutch, Tabitha; Szulczewski, Greg; Schweizer, Matthias; Barbosa, Newton; Araujo, Paulo

2018-05-18

We investigate the P(NDI2OD-T2) photophysical properties via absorbance and fluorescence spectroscopy, in association with the experimental approach baptized Stokes Spectroscopy, which provides valuable material information through the acquisition and analysis of the fluorescence polarization degree. By changing solvents and using different samples such as solutions, thick, and thin films, it is possible to control the polarization degree spectrum associated to the fluorescence emitted by the polymer's isolated chains and aggregates. We show that the polarization degree could become a powerful tool to obtain information related to the samples morphology, which is connected to their microscopic structure. Moreover, the polarization degree spectra suggest that depolarization effects linked to energy and charge transfer mechanisms are likely taking place. Our findings indicate that P(NDI2OD-T2) polymers are excellent candidates for the advancement of organic technologies that rely on the emission and detection of polarized lights. © 2018 IOP Publishing Ltd.

APTS and rGO co-functionalized pyrenated fluorescent nanonets for representative vapor phase nitroaromatic explosive detection.

PubMed

Guo, Linjuan; Zu, Baiyi; Yang, Zheng; Cao, Hongyu; Zheng, Xuefang; Dou, Xincun

2014-01-01

For the first time, flexible PVP/pyrene/APTS/rGO fluorescent nanonets were designed and synthesized via a one-step electrospinning method to detect representative subsaturated nitroaromatic explosive vapor. The functional fluorescent nanonets, which were highly stable in air, showed an 81% quenching efficiency towards TNT vapor (∼10 ppb) with an exposure time of 540 s at room temperature. The nice performance of the nanonets was ascribed to the synergistic effects induced by the specific adsorption properties of APTS, the fast charge transfer properties and the effective π-π interaction with pyrene and TNT of rGO. Compared to the analogues of TNT, the PVP/pyrene/APTS/rGO nanonets showed notable selectivity towards TNT and DNT vapors. The explored functionalization method opens up brand new insight into sensitive and selective detection of vapor phase nitroaromatic explosives.

Theoretical study of chromophores for biological sensing: Understanding the mechanism of rhodol based multi-chromophoric systems

NASA Astrophysics Data System (ADS)

Rivera-Jacquez, Hector J.; Masunov, Artëm E.

2018-06-01

Development of two-photon fluorescent probes can aid in visualizing the cellular environment. Multi-chromophore systems display complex manifolds of electronic transitions, enabling their use for optical sensing applications. Time-Dependent Density Functional Theory (TDDFT) methods allow for accurate predictions of the optical properties. These properties are related to the electronic transitions in the molecules, which include two-photon absorption cross-sections. Here we use TDDFT to understand the mechanism of aza-crown based fluorescent probes for metals sensing applications. Our findings suggest changes in local excitation in the rhodol chromophore between unbound form and when bound to the metal analyte. These changes are caused by a charge transfer from the aza-crown group and pyrazol units toward the rhodol unit. Understanding this mechanism leads to an optimized design with higher two-photon excited fluorescence to be used in medical applications.

Theoretical study of chromophores for biological sensing: Understanding the mechanism of rhodol based multi-chromophoric systems.

PubMed

Rivera-Jacquez, Hector J; Masunov, Artëm E

2018-06-05

Development of two-photon fluorescent probes can aid in visualizing the cellular environment. Multi-chromophore systems display complex manifolds of electronic transitions, enabling their use for optical sensing applications. Time-Dependent Density Functional Theory (TDDFT) methods allow for accurate predictions of the optical properties. These properties are related to the electronic transitions in the molecules, which include two-photon absorption cross-sections. Here we use TDDFT to understand the mechanism of aza-crown based fluorescent probes for metals sensing applications. Our findings suggest changes in local excitation in the rhodol chromophore between unbound form and when bound to the metal analyte. These changes are caused by a charge transfer from the aza-crown group and pyrazol units toward the rhodol unit. Understanding this mechanism leads to an optimized design with higher two-photon excited fluorescence to be used in medical applications. Copyright © 2018 Elsevier B.V. All rights reserved.

Self-Assembly of New Arene-Ruthenium Rectangles Containing Triptycene Building Block and Their Application in Fluorescent Detection of Nitro Aromatics

PubMed Central

Dubey, Abhishek; Mishra, Anurag; Min, Jin Wook; Lee, Min Hyung; Kim, Hyunuk; Stang, Peter J.; Chi, Ki-Whan

2014-01-01

A suite of two new tetraruthenium metallarectangles 5 and 6 have been obtained from [2 + 2] self-assemblies between dipyridylethynyltriptycene 2 and one of the two dinuclear arene ruthenium clips, [Ru2 (μ-η4-OO∩OO) (η6-p-cymene)2][OTf]2 ; (OO∩OO = oxalate 3; 6,11-dihydroxy-5,12-naphthacenedionato (dotq) 4; OTf = triflate). These molecular rectangles are fully characterized by 1H NMR spectroscopy, electrospray mass spectrometry. A single crystal of 6 was suitable for X-ray diffraction structural characterization. These new metallarectangles showed fluorescence behavior in solution, have been examined for emission quenching effects with various aromatic compounds, and show high quenching selectivity and sensitivity towards nitroaromatics, particularly picric acid and trinitrotoluene. Excited-state charge transfer from the rectangles to nitro aromatic substrates can be used to develop selective fluorescent sensors for nitro aromatics. PMID:26321767

Broadband polarized emission from P(NDI2OD-T2) polymer

NASA Astrophysics Data System (ADS)

Ulrich, Steven V.; Sutch, Tabitha; Szulczewski, Greg; Schweizer, Matthias; Barbosa Neto, Newton M.; Araujo, Paulo T.

2018-07-01

We investigate the P(NDI2OD-T2) photophysical properties via absorbance and fluorescence spectroscopy, in association with the experimental approach baptized Stokes Spectroscopy, which provides valuable material information through the acquisition and analysis of the fluorescence polarization degree. By changing solvents and using different samples such as solutions, thick, and thin films, it is possible to control the polarization degree spectrum associated to the fluorescence emitted by the polymer’s isolated chains and aggregates. We show that the polarization degree could become a powerful tool to obtain information related to the samples morphology, which is connected to their microscopic structure. Moreover, the polarization degree spectra suggest that depolarization effects linked to energy and charge transfer mechanisms are likely taking place. Our findings indicate that P(NDI2OD-T2) polymers are excellent candidates for the advancement of organic technologies that rely on the emission and detection of polarized lights.

High-potential perfluorinated phthalocyanine-fullerene dyads for generation of high-energy charge-separated states: formation and photoinduced electron-transfer studies.

PubMed

Das, Sushanta K; Mahler, Andrew; Wilson, Angela K; D'Souza, Francis

2014-08-25

High oxidation potential perfluorinated zinc phthalocyanines (ZnF(n)Pcs) are synthesised and their spectroscopic, redox, and light-induced electron-transfer properties investigated systematically by forming donor-acceptor dyads through metal-ligand axial coordination of fullerene (C60) derivatives. Absorption and fluorescence spectral studies reveal efficient binding of the pyridine- (Py) and phenylimidazole-functionalised fullerene (C60Im) derivatives to the zinc centre of the F(n)Pcs. The determined binding constants, K, in o-dichlorobenzene for the 1:1 complexes are in the order of 10(4) to 10(5) M(-1); nearly an order of magnitude higher than that observed for the dyad formed from zinc phthalocyanine (ZnPc) lacking fluorine substituents. The geometry and electronic structure of the dyads are determined by using the B3LYP/6-31G* method. The HOMO and LUMO levels are located on the Pc and C60 entities, respectively; this suggests the formation of ZnF(n)Pc(.+)-C60Im(.-) and ZnF(n)Pc(.+)-C60Py(.-) (n=0, 8 or 16) intra-supramolecular charge-separated states during electron transfer. Electrochemical studies on the ZnPc-C60 dyads enable accurate determination of their oxidation and reduction potentials and the energy of the charge-separated states. The energy of the charge-separated state for dyads composed of ZnF(n)Pc is higher than that of normal ZnPc-C60 dyads and reveals their significance in harvesting higher amounts of light energy. Evidence for charge separation in the dyads is secured from femtosecond transient absorption studies in nonpolar toluene. Kinetic evaluation of the cation and anion radical ion peaks reveals ultrafast charge separation and charge recombination in dyads composed of perfluorinated phthalocyanine and fullerene; this implies their significance in solar-energy harvesting and optoelectronic device building applications. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Blocking Energy-Loss Pathways for Ideal Fluorescent Organic Light-Emitting Diodes with Thermally Activated Delayed Fluorescent Sensitizers.

PubMed

Zhang, Dongdong; Song, Xiaozeng; Cai, Minghan; Duan, Lian

2018-02-01

Organic light-emitting diodes (OLEDs) based on thermally activated delayed fluorescence-sensitized fluorescence (TSF) offer the possibility of attaining an ultimate high efficiency with low roll-off utilizing noble-metal free, easy-to-synthesize, pure organic fluorescent emitters. However, the performances of TSF-OLEDs are still unsatisfactory. Here, TSF-OLEDs with breakthrough efficiencies even at high brightnesses by suppressing the competitive deactivation processes, including direct charge recombination on conventional fluorescent dopants (CFDs) and Dexter energy transfer from the host to the CFDs, are demonstrated. On the one hand, electronically inert terminal-substituents are introduced to protect the electronically active core of the CFDs; on the other hand, delicate device structures are designed to provide multiple energy-funneling paths. As a result, unprecedentedly high maximum external quantum efficiency/power efficiency of 24%/71.4 lm W -1 in a green TSF-OLED are demonstrated, which remain at 22.6%/52.3 lm W -1 even at a high luminance of 5000 cd m -2 . The work unlocks the potential of TSF-OLEDs, paving the way toward practical applications. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Manipulating the Surface Chemistry of Quantum Dots for Sensitive Ratiometric Fluorescence Detection of Sulfur Dioxide.

PubMed

Li, Huihui; Zhu, Houjuan; Sun, Mingtai; Yan, Yehan; Zhang, Kui; Huang, Dejian; Wang, Suhua

2015-08-11

Herein, we report a novel approach to the rapid visual detection of gaseous sulfur dioxide (SO2) by manipulating the surface chemistry of 3-aminopropyltriethoxysilane (APTS)-modified quantum dots (QDs) using fluorescent coumarin-3-carboxylic acid (CCA) for specific reaction with SO2. The CCA molecules are attached to the surface amino groups of the QDs through electrostatic attraction, thus the fluorescence of CCA is greatly suppressed because of the formation of an ion-pair complex between the ATPS-modified QDs and CCA. Such an interaction is vulnerable to SO2 because SO2 can readily react with surface amino groups to form strong charge-transfer complexes and subsequently release the strongly fluorescent CCA molecules. The mechanism has been carefully verified through a series of control experiments. Upon exposure to different amounts of SO2, the fluorescent color of the nanoparticle-based sensor displays continuously changes from red to blue. Most importantly, the approach owns high selectivity for SO2 and a tolerance of interference, which enables the sensor to detect SO2 in a practical application. Using this fluorescence-based sensing method, we have achieved a visual detection limit of 6 ppb for gaseous SO2.

A new fluorescent probe for distinguishing Zn2+ and Cd2+ with high sensitivity and selectivity.

PubMed

Tan, Yiqun; Gao, Junkuo; Yu, Jiancan; Wang, Ziqi; Cui, Yuanjing; Yang, Yu; Qian, Guodong

2013-08-28

A new fluorescence probe for distinguishing Zn(2+) and Cd(2+) is designed and synthesized. For the first time to our knowledge, this probe can recognize similar metal ions by coherently utilizing intramolecular charge transfer (ICT) and different electronic affinities of various metal ions, instead of by selective coordination alone, which may be interfered with and lose its selectivity easily in a complicated environment, providing a distinct recognition even by the naked eye for Zn(2+) and Cd(2+) with the sensitivity at the ppb level. This design strategy may initiate a straightforward approach for the selective detection of various metal ions with similar chemical properties in extensive applications such as environmental, industrial, and bio-science.

Pressure-induced emission band separation of the hybridized local and charge transfer excited state in a TPE-based crystal.

PubMed

Liu, Xuedan; Li, Aisen; Xu, Weiqing; Ma, Zhiyong; Jia, Xinru

2018-05-08

We herein report a newly synthesized simple molecule, named TPE[double bond, length as m-dash]C4, with twisted D-A structure. TPE[double bond, length as m-dash]C4 showed two intrinsic emission bands ascribed to the locally excited (LE) state and the intramolecular charge transfer (ICT) state, respectively. In the crystal state, the LE emission band is usually observed. However, by applying hydrostatic pressure to the powder sample and the single crystal sample of TPE[double bond, length as m-dash]C4, dual-fluorescence (445 nm and 532 nm) was emerged under high pressure, owing to the pressure-induced emission band separation of the hybridized local and charge transfer excited state (HLCT). It is found that the emission of TPE[double bond, length as m-dash]C4 is generally determined by the ratio of the LE state to the ICT state. The ICT emission band is much more sensitive to the external pressure than the LE emission band. The HLCT state leads to a sample with different responsiveness to grinding and hydrostatic pressure. This study is of significance in the molecular design of such D-A type molecules and in the control of photoluminescence features by molecular structure. Such results are expected to pave a new way to further understand the relationship between the D-A molecular structure and stimuli-responsive properties.

Spectroscopic analysis and charge transfer interaction studies of 4-benzyloxy-2-nitroaniline insecticide: A density functional theoretical approach

NASA Astrophysics Data System (ADS)

Arul Dhas, D.; Hubert Joe, I.; Roy, S. D. D.; Balachandran, S.

2015-01-01

A widespread exploration on the intra-molecular charge transfer interaction through an efficient π-conjugated path from a strong electron-donor group (amino) to a strong electron-acceptor group (nitro) has been carried out using FTIR, FT-Raman, UV-Vis, fluorescence and NMR spectra on insecticide compound 4-benzyloxy-2-nitroaniline. Density functional theory method is used to determine optimized molecular geometry, harmonic vibrational wavenumbers and intensities using 6-311G(d,p) basis set by means of Gaussian 09W program suit. A comprehensive investigation on the sp2 to sp3 hybridization and non-planarity property has been performed. Natural bond orbital analysis is used to study the existence of C-H⋯O, N-H⋯O and C-H⋯π proper and improper hydrogen bonds. The HOMO and LUMO analysis reveals the possibility of charge transfer within the molecule. A complete assignment of the experimental absorption peaks in the ultraviolet region has also been performed. Isotropic chemical shifts of 13C, 1H, 15N and 18O NMR and nuclear spin-spin coupling constants have been computed using the gauge-invariant atomic orbital method. The biological activity of substituent amino and nitro groups are evident from the hydrogen bonds through which the target amino acids are linked to the drug as evidenced from molecular docking.

Photophysics of detection of explosive vapours via luminescence quenching of thin films: impact of inter-molecular interactions.

PubMed

Shoaee, Safa; Fan, Shengqiang; Burn, Paul L; Shaw, Paul E

2016-09-21

Fluorescence-based detection of explosive analytes requires an understanding of the nature of the excited state responsible for the luminescence response of a sensing material. Many measurements are carried out to elucidate the fundamental photophysical properties of an emissive material in solution. However, simple transfer of the understanding gained from the solution measurements to the solid-state can lead to errors. This is in part due to the absence of inter-molecular interactions of the chromophores in solution, which are present in the solid-state. To understand the role of inter-molecular interactions on the detection of explosive analytes we have chosen dendrimers from two different families, D1 and D2, which allow facile control of the inter-molecular interactions through the choice of dendrons and emissive chromophores. Using ultrafast transient absorption spectroscopy we find that the solution photoinduced absorption (PA) for both materials can be explained in terms of the generation of singlet excitons, which decay to the ground state, or intersystem cross (ISC) to form a triplet exciton. In neat films however, we observe different photophysical behaviours; first, ISC to the triplet state does not occur, and second, depending on the chromophore, charge transfer and charge separated states are formed. Furthermore, we find that when either dendrimer is interfaced with analyte vapour, the singlet state is strongly quenched, generating a charge transfer state that undergoes geminate recombination.

Photoinduced electron transfer in fixed distance chlorophyll-quinone donor-acceptor molecules

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wasielewski, M.R.; Johnson, D.G.; Svec, W.A.

1987-01-01

A series of fixed distance chlorophyll-quinone donor-acceptor molecules have been prepared. The donor consists of either methyl pyropheophorbide a or methyl pyrochlorophyllide a, while the acceptor is either benzoquinone or naphthoquinone. The acceptors are fused to a triptycene spacer group, which in turn is attached to the donors at their vinyl groups. Picosecond transient absorption measurements have been used to identify electron transfer from the lowest excited singlet state of the donor to the acceptor as the mechanism of fluorescence quenching in these molecules. The charge separation rate constants increase from 2 x 10/sup 10/ s/sup -1/ to 4 xmore » 10/sup 11/ s/sup -1/ as the free energy of charge separation increases, while the radical pair recombination rate constants decrease from 1.2 x 10/sup 11/ s/sup -1/ to 2 x 10/sup 9/ s/sup -1/ as the free energy of recombination increases. The resulting total reorganization energy lambda = 0.9 eV.« less

Synthesis and Exciton Dynamics of Donor-Orthogonal Acceptor Conjugated Polymers: Reducing the Singlet-Triplet Energy Gap.

PubMed

Freeman, David M E; Musser, Andrew J; Frost, Jarvist M; Stern, Hannah L; Forster, Alexander K; Fallon, Kealan J; Rapidis, Alexandros G; Cacialli, Franco; McCulloch, Iain; Clarke, Tracey M; Friend, Richard H; Bronstein, Hugo

2017-08-16

The presence of energetically low-lying triplet states is a hallmark of organic semiconductors. Even though they present a wealth of interesting photophysical properties, these optically dark states significantly limit optoelectronic device performance. Recent advances in emissive charge-transfer molecules have pioneered routes to reduce the energy gap between triplets and "bright" singlets, allowing thermal population exchange between them and eliminating a significant loss channel in devices. In conjugated polymers, this gap has proved resistant to modification. Here, we introduce a general approach to reduce the singlet-triplet energy gap in fully conjugated polymers, using a donor-orthogonal acceptor motif to spatially separate electron and hole wave functions. This new generation of conjugated polymers allows for a greatly reduced exchange energy, enhancing triplet formation and enabling thermally activated delayed fluorescence. We find that the mechanisms of both processes are driven by excited-state mixing between π-π*and charge-transfer states, affording new insight into reverse intersystem crossing.

Interaction of proflavin with aromatic amines in homogeneous and micellar media: Photoinduced electron transfer probed by magnetic field effect

NASA Astrophysics Data System (ADS)

Chakraborty, Brotati; Basu, Samita

2010-02-01

Photoinduced electron transfer (PET) between proflavin (PF +) and two aromatic amines viz., dimethylaniline (DMA) and 4,4'-bis(dimethylamino)diphenylmethane (DMDPM) is studied in homogeneous and heterogeneous media using steady-state as well as time-resolved fluorescence spectroscopy and laser flash photolysis with an associated magnetic field. Ionic micelles have been used to study the effect of charge of proflavin on PET with amines. Magnetic field effect on PET reactions reveals that the parent spin-state of precursors of PET for DMA-PF + system is singlet while for DMDPM-PF + system is triplet, implying that the dynamics of PET is influenced by the structure of the donor.

Single-molecule electrocatalysis by single-walled carbon nanotubes.

PubMed

Xu, Weilin; Shen, Hao; Kim, Yoon Ji; Zhou, Xiaochun; Liu, Guokun; Park, Jiwoong; Chen, Peng

2009-12-01

We report a single-molecule fluorescence study of electrocatalysis by single-walled carbon nanotubes (SWNTs) at single-reaction resolution. Applying super-resolution optical imaging, we find that the electrocatalysis occurs at discrete, nanometer-dimension sites on SWNTs. Single-molecule kinetic analysis leads to an electrocatalytic mechanism, allowing quantification of the reactivity and heterogeneity of individual reactive sites. Combined with conductivity measurements, this approach will be powerful to interrogate how the electronic structure of SWNTs affects the electrocatalytic interfacial charge transfer, a process fundamental to photoelectrochemical cells.

Environment sensitive fluorescent analogue of biologically active oxazoles differentially recognizes human serum albumin and bovine serum albumin: Photophysical and molecular modeling studies

NASA Astrophysics Data System (ADS)

Maiti, Jyotirmay; Biswas, Suman; Chaudhuri, Ankur; Chakraborty, Sandipan; Chakraborty, Sibani; Das, Ranjan

2017-03-01

An environment sensitive fluorophore, 4-(5-(4-(dimethylamino)phenyl)oxazol-2-yl)benzoic acid (DMOBA), that closely mimics biologically active 2,5-disubstituited oxazoles has been designed to probe two homologous serum proteins, human serum albumin (HSA) and bovine serum albumin (BSA) by means of photophysical and molecular modeling studies. This fluorescent analogue exhibits solvent polarity sensitive fluorescence due to an intramolecular charge transfer in the excited state. In comparison to water, the steady state emission spectra of DMOBA in BSA is characterized by a greater blue shift ( 10 nm) and smaller Stokes' shift ( 5980 cm- 1) in BSA than HSA (Stokes'shift 6600 cm- 1), indicating less polar and more hydrophobic environment of the dye in the former than the latter. The dye-protein binding interactions are remarkably stronger for BSA than HSA which is evident from higher value of the association constant for the DMOBA-BSA complex (Ka 5.2 × 106 M- 1) than the DMOBA-HSA complex (Ka 1.0 × 106 M- 1). Fӧrster resonance energy transfer studies revealed remarkably less efficient energy transfer (8%) between the donor tryptophans in BSA and the acceptor DMOBA dye than that (30%) between the single tryptophan moiety in HSA and the dye, which is consistent with a much larger distance between the donor (tryptophan)-acceptor (dye) pair in BSA (34.5 Å) than HSA (25.4 Å). Site specific competitive binding assays have confirmed on the location of the dye in Sudlow's site II of BSA and in Sudlow's site I of HSA, respectively. Molecular modeling studies have shown that the fluorescent analogue is tightly packed in the binding site of BSA due to strong steric complementarity, where, binding of DMOBA to BSA is primarily dictated by the van der Waals and hydrogen bonding interactions. In contrast, in HSA the steric complementarity is less significant and binding is primarily guided by polar interactions and van der Waals interactions appear to be less significant in the formation of the HSA-DMOBA complex. Electrostatic interactions contribute significantly in the binding of DMOBA to HSA (- 2.09 kcal/mol) compared to BSA (- 0.47 kcal/mol). Electrostatic surface potential calculation reveals that the DMOBA binding site within HSA is highly charged compared to BSA.

Characterization, photophysical and DFT calculation study on 2-(2,4-difluorophenyl)-1-(4-methoxyphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline ligand.

PubMed

Jayabharathi, Jayaraman; Thanikachalam, Venugopal; Venkatesh Perumal, Marimuthu

2012-09-01

The synthesized imidazole derivative 2-(2,4-difluorophenyl)-1-(4-methoxyphenyl)-1H-imidazo[4,5-f][1,10] phenanthroline (dfpmpip) has been characterized using IR, mass, (1)H, (13)C NMR and elemental analysis. The photophysical properties of dfpmpip have been studied using UV-visible and fluorescence spectroscopy in different solvents. The solvent effect on the absorption and fluorescence bands has been analyzed by a multi-component linear regression. Theoretically calculated bond lengths, bond angles and dihedral angles are found to be slightly higher than that of X-ray Diffraction (XRD) values of its parent compound. The charge distribution has been calculated from the atomic charges by non-linear optical (NLO) and natural bond orbital (NBO) analysis. Since the synthesized imidazole derivative has the largest μ(g)β(0) value, the reported imidazole can be used as potential NLO material. The energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels and the molecular electrostatic potential (MEP) energy surface studies evidenced the existence of intramolecular charge transfer (ICT) within the molecule. Theoretical calculations regarding the chemical potential (μ), hardness (η) and electrophilicity index (ω) have also been calculated. Copyright © 2012 Elsevier B.V. All rights reserved.

Systems approach to excitation-energy and electron transfer reaction networks in photosystem II complex: model studies for chlorophyll a fluorescence induction kinetics.

PubMed

Matsuoka, Takeshi; Tanaka, Shigenori; Ebina, Kuniyoshi

2015-09-07

Photosystem II (PS II) is a protein complex which evolves oxygen and drives charge separation for photosynthesis employing electron and excitation-energy transfer processes over a wide timescale range from picoseconds to milliseconds. While the fluorescence emitted by the antenna pigments of this complex is known as an important indicator of the activity of photosynthesis, its interpretation was difficult because of the complexity of PS II. In this study, an extensive kinetic model which describes the complex and multi-timescale characteristics of PS II is analyzed through the use of the hierarchical coarse-graining method proposed in the authors׳ earlier work. In this coarse-grained analysis, the reaction center (RC) is described by two states, open and closed RCs, both of which consist of oxidized and neutral special pairs being in quasi-equilibrium states. Besides, the PS II model at millisecond scale with three-state RC, which was studied previously, could be derived by suitably adjusting the kinetic parameters of electron transfer between tyrosine and RC. Our novel coarse-grained model of PS II can appropriately explain the light-intensity dependent change of the characteristic patterns of fluorescence induction kinetics from O-J-I-P, which shows two inflection points, J and I, between initial point O and peak point P, to O-J-D-I-P, which shows a dip D between J and I inflection points. Copyright © 2015 Elsevier Ltd. All rights reserved.

Photophysical parameters and fluorescence quenching of 7-diethylaminocoumarin (DEAC) laser dye

NASA Astrophysics Data System (ADS)

El-Mossalamy, E. H.; Obaid, A. Y.; El-Daly, S. A.

2011-10-01

The optical properties including electronic absorption spectrum, emission spectrum, fluorescence quantum yield, and dipole moment of electronic transition of 7-diethylaminocoumarin (DEAC) laser dye have been measured in different solvents. Both electronic absorption and fluorescence spectra are red shifted as the polarity of the medium increases, indicating that the dipole moment of molecule increases on excitation. The fluorescence quantum yield of DEAC decreases as the polarity of solvent increases, a result of the role of solvent polarity in stabilization of the twisting of the intramolecular charge transfer (TICT) in excited state, which is a non-emissive state, as well as hydrogen bonding with the hetero-atom of dye. The emission spectrum of DEAC has also been measured in cationic (CTAC) and anionic (SDS) micelles, the intensity increases as the concentration of surfactant increases, and an abrupt change in emission intensity is observed at critical micelle concentration (CMC) of surfactant. 2×10 -3 mol dm -3 of DEAC gives laser emission in the blue region on pumping with nitrogen laser ( λex=337.1 nm). The laser parameters such as tuning range, gain coefficient ( α), emission cross section ( σe), and half-life energy have been calculated in different solvents, namely acetone, dioxane , ethanol, and dimethyforamide (DMF). The photoreactivity of DEAC has been studied in CCl 4 at a wavelength of 366 nm. The values of photochemical yield ( ϕc) and rate constant ( k) are determined. The interaction of organic acceptors such as picric acid (PA), tetracyanoethylene (TCNE), and 7,7,8,8-tetracynoquinonedimethane (TCNQ) with DEAC is also studied using fluorescence measurements in acetonitrile (CH 3CN); from fluorescence quenching study we assume the possible electron transfer from excited donor DEAC to organic acceptor forming non-emissive exciplex.

Preparation of K+-Doped Core-Shell NaYF4:Yb, Er Upconversion Nanoparticles and its Application for Fluorescence Immunochromatographic Assay of Human Procalcitonin.

PubMed

Tang, Jie; Lei, Lijiang; Feng, Hui; Zhang, Hongman; Han, Yuwang

2016-11-01

In the present study, we reported a convenient route to prepare well dispersed and functionalized K + -doped core-shell upconversion nanoparticles (UCP) by layer-by-layer (LbL) assembly of polyelectrolytes. UCP was firstly transferred to aqueous phase using cationic surfactant cetyl trimethyl ammonium bromide (CTAB) via hydrophobic interaction without removing the existing oleic acid (OA). Then the positively charged hydrophilic UCP@CTAB was further alternately deposited with negatively charged [poly (sodium 4-styrenesulfonate)] (PSS), positively charged [poly (allylamine hydrochloride)] (PAH) and negatively charged [poly (acrylic acid)] (PAA). The final carboxyl functionalized UCP@CTAB@PSS@PAH@PAA was then conjugated with monoclonal antibody1 (AB1) of procalcitonin (PCT), resulting in successful detection of PCT antigens based on the immunochromatographic assay (ICA). Linear response was achieved from 0 to 10 ng/mL, and the lowest limit of detection (LLD) was 0.18 ng/mL.

Determination of dihydralazine based on chemiluminescence resonance energy transfer of hollow carbon nanodots

NASA Astrophysics Data System (ADS)

Han, Suqin; Fan, Zheyan; Chen, Xiaoxia; Wu, Yunfang; Wang, Jianbo

2017-08-01

The famous weak chemiluminescence (CL) system of potassium permanganate and sodium bisulfite (KMnO4-HSO3-) was enhanced by the hollow fluorescent carbon nanodots (HCNs). The investigation of mechanism revealed that the enhanced CL was induced by the excited-state HCNs (HCNs*), which could be produced from the electron-transfer annihilation of positively charged HCNs (HCNsrad +) and negatively charged HCNs (HCNsrad -) as well as by CL resonance energy transfer (CRET) from excited SO2 (SO2*)/1O2 to HCNs. The dihydralazine sulfate (DHZS) had a diminishing effect on the CL of HCNs-KMnO4-HSO3- system due to the competitive consumption of rad O2-. Under the optimal conditions, the reduced CL signal with the concentration of DHZS was linear in the range of 1.0 × 10- 7-7.0 × 10- 5 mol/L with a detection limit of 3.0 × 10- 8 mol/L. The relative standard deviation for seven repeated determination of 5.0 × 10- 6 mol/L DHZS was 2.1%. The established method was applied to the determination of DHZS in pharmaceutical preparations, human urine and plasma samples with good precision and accuracy.

Investigation of Exciton Recombination Zone in Quantum Dot Light-Emitting Diodes Using a Fluorescent Probe.

PubMed

Huang, Xiaoyu; Zhang, Heng; Xu, Dingxin; Wen, Feng; Chen, Shuming

2017-08-23

Exciton recombination zone, where the photons are generated, can greatly affect the performance, such as the efficiency and color purity, of the quantum dot (QD) light-emitting diodes (QLEDs). To probe the exciton recombination zone, 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) is doped into the charge transport layer as a fluorescent sensor; by monitoring the Förster resonant energy transfer (FRET) between QD and DCJTB, the location of the recombination zone can be determined. It is found that the electron transport layer (ETL) has a great impact on the recombination zone. For example, in QLEDs with ZnMgO ETL, the recombination zone is near the interface of the QD/hole transport layer (HTL) and is shifted to the interface of the QD/ETL as the driving voltage is increased, whereas in devices with 1,3,5-tris(2-N-phenylbenzimidazolyl) benzene (TPBi) ETL, the recombination zone is close to the interface of the QD/ETL and moved to the interface of the QD/HTL with the increase in the driving voltage. Our results can also clarify the light emission mechanism in QLEDs. In devices with ZnMgO ETL, the emission is dominated by the direct charge recombination, whereas in devices with TPBi ETL, the emission is contributed by both FRET and direct charge recombination. Our studies suggest that fluorescent probe can be a powerful tool for investigating the exciton recombination zone, light emission mechanism, and other fundamental processes in QLEDs.

Charging YOYO-1 on Capillary Wall for Online DNA Intercalation and Integrating This Approach with Multiplex PCR and Bare Narrow Capillary–Hydrodynamic Chromatography for Online DNA Analysis

PubMed Central

2016-01-01

Multiplex polymerase chain reaction (PCR) has been widely utilized for high-throughput pathogen identification. Often, a dye is used to intercalate the amplified DNA fragments, and identifications of the pathogens are carried out by DNA melting curve analysis or gel electrophoresis. Integrating DNA amplification and identification is a logic path toward maximizing the benefit of multiplex PCR. Although PCR and gel electrophoresis have been integrated, replenishing the gels after each run is tedious and time-consuming. In this technical note, we develop an approach to address this issue. We perform multiplex PCR inside a capillary, transfer the amplified fragments to a bare narrow capillary, and measure their lengths online using bare narrow capillary–hydrodynamic chromatography (BaNC-HDC), a new technique recently developed in our laboratory for free-solution DNA separation. To intercalate the DNA with YOYO-1 (a fluorescent dye) for BaNC-HDC, we flush the capillary column with a YOYO-1 solution; positively charged YOYO-1 is adsorbed (or charged) onto the negatively charged capillary wall. As DNA molecules are driven down the column for separation, they react with the YOYO-1 stored on the capillary wall and are online-intercalated with the dye. With a single YOYO-1 charging, the column can be used for more than 40 runs, although the fluorescence signal intensities of the DNA peaks decrease gradually. Although the dye-DNA intercalation occurs during the separation, it does not affect the retention times, separation efficiencies, or resolutions. PMID:25555111

Synthesis, characterization, and spectroscopic investigation of benzoxazole conjugated Schiff bases.

PubMed

Santos, Fabiano S; Costa, Tania M H; Stefani, Valter; Gonçalves, Paulo F B; Descalzo, Rodrigo R; Benvenutti, Edilson V; Rodembusch, Fabiano S

2011-11-24

Two Schiff bases were synthesized by reaction of 2-(4'-aminophenyl)benzoxazole derivatives with 4-N,N-diethylaminobenzaldehyde. UV-visible (UV-vis) and steady-state fluorescence in solution were applied in order to characterize its photophysical behavior. The Schiff bases present absorption in the UV region with fluorescence emission in the blue-green region, with a large Stokes' shift. The UV-vis data indicates that each dye behaves as two different chromophores in solution in the ground state. The fluorescence emission spectra of the dye 5a show that an intramolecular proton transfer (ESIPT) mechanism takes place in the excited state, whereas a twisted internal charge transfer (TICT) state is observed for the dye 5b. Theoretical calculations were performed in order to study the conformation and polarity of the molecules at their ground and excited electronic states. Using density functional theory (DFT) methods at theoretical levels BLYP/Aug-SV(P) for geometry optimizations and B3LYP/6-311++G(2d,p) for single-point energy evaluations, the calculations indicate that the lowest energy conformations are in all cases nonplanar and that the dipole moments of the excited state relaxed structures are much larger than those of the ground state structures, which corroborates the experimental UV-vis absorption results.

Hidden Charge States in Soft-X-Ray Laser-Produced Nanoplasmas Revealed by Fluorescence Spectroscopy

NASA Astrophysics Data System (ADS)

Schroedter, L.; Müller, M.; Kickermann, A.; Przystawik, A.; Toleikis, S.; Adolph, M.; Flückiger, L.; Gorkhover, T.; Nösel, L.; Krikunova, M.; Oelze, T.; Ovcharenko, Y.; Rupp, D.; Sauppe, M.; Wolter, D.; Schorb, S.; Bostedt, C.; Möller, T.; Laarmann, T.

2014-05-01

Highly charged ions are formed in the center of composite clusters by strong free-electron laser pulses and they emit fluorescence on a femtosecond time scale before competing recombination leads to neutralization of the nanoplasma core. In contrast to mass spectrometry that detects remnants of the interaction, fluorescence in the extreme ultraviolet spectral range provides fingerprints of transient states of high energy density matter. Spectra from clusters consisting of a xenon core and a surrounding argon shell show that a small fraction of the fluorescence signal comes from multiply charged xenon ions in the cluster core. Initially, these ions are as highly charged as the ions in the outer shells of pure xenon clusters with charge states up to at least 11+.

Energy transfer by way of an exciplex intermediate in flexible boron dipyrromethene-based allosteric architectures.

PubMed

Mula, Soumyaditya; Elliott, Kristopher; Harriman, Anthony; Ziessel, Raymond

2010-10-07

We have designed and synthesized a series of modular, dual-color dyes comprising a conventional boron dipyrromethene (Bodipy) dye, as a yellow emitter, and a Bodipy dye possessing extended conjugation that functions as a red emitter. A flexible tether of variable length, built from ethylene glycol residues, connects the terminal dyes. A critical design element of this type of dyad relates to a secondary amine linkage interposed between the conventional Bodipy and the tether. Cyclic voltammetry shows both Bodipy dyes to be electroactive and indicates that the secondary amine is quite easily oxidized. The ensuing fluorescence quenching is best explained in terms of the rapid formation of an intermediate charge-transfer state. In fact, exciplex-type emission is observed in weakly polar solvents and over a critical temperature range. In the dual-color dyes, direct excitation of the yellow emitter results in the appearance of red fluorescence, indicating that the exciplex is likely involved in the energy-transfer event, and provides for a virtual Stokes shift of 5000 cm(-1). Replacing the red emitter with a higher energy absorber (namely, pyrene) facilitates the collection of near-UV light and extends the virtual Stokes shift to 8000 cm(-1). Modulation of the efficacy of intramolecular energy transfer is achieved by preorganization of the connector in the presence of certain cations. This latter behavior, which is fully reversible, corresponds to an artificial allosteric effect.

Probing conformational dynamics by photoinduced electron transfer

NASA Astrophysics Data System (ADS)

Neuweiler, Hannes; Herten, Dirk P.; Marme, N.; Knemeyer, J. P.; Piestert, Oliver; Tinnefeld, Philip; Sauer, Marcus

2004-07-01

We demonstrate how photoinduced electron transfer (PET) reactions can be successfully applied to monitor conformational dynamics in individual biopolymers. Single-pair fluorescence resonance energy transfer (FRET) experiments are ideally suited to study conformational dynamics occurring on the nanometer scale, e.g. during protein folding or unfolding. In contrast, conformational dynamics with functional significance, for example occurring in enzymes at work, often appear on much smaller spatial scales of up to several Angströms. Our results demonstrate that selective PET-reactions between fluorophores and amino acids or DNA nucleotides represent a versatile tool to measure small-scale conformational dynamics in biopolymers on a wide range of time scales, extending from nanoseconds to seconds, at the single-molecule level under equilibrium conditions. That is, the monitoring of conformational dynamics of biopolymers with temporal resolutions comparable to those within reach using new techniques of molecular dynamic simulations. We present data about structural changes of single biomolecules like DNA hairpins and peptides by using quenching electron transfer reactions between guanosine or tryptophan residues in close proximity to fluorescent dyes. Furthermore, we demonstrate that the strong distance dependence of charge separation reactions on the sub-nanometer scale can be used to develop conformationally flexible PET-biosensors. These sensors enable the detection of specific target molecules in the sub-picomolar range and allow one to follow their molecular binding dynamics with temporal resolution.

Photoinduced intramolecular charge transfer in a cross-conjugated push-pull enediyne: implications toward photoreaction.

PubMed

Singh, Anuja; Pati, Avik Kumar; Mishra, Ashok Kumar

2018-05-30

Push-pull organic fluorophores are important owing to their interesting optoelectronical properties. Here we report the photophysics of a new cross-conjugated push-pull enediynyl dye which belongs to an unexplored class of π-conjugated donor-acceptor systems. Two N,N-dimethylaniline moieties serve as donors and one pyrene ring functions as an acceptor via a common Y-shaped 'enediyne' bridge which facilitates the cross-electronic communication. The dye exhibits dual emission from locally excited (LE) and intramolecular charge transfer (ICT) states. While the LE emission is dominant in non-polar solvents, the ICT emission predominates in polar solvents. Time-resolved fluorescence decay experiments reveal a relatively shorter lifetime component (∼0.5-0.9 ns) belonging to an ICT state and a relatively longer lifetime species (∼1.6-2.8 ns) corresponding to the LE state. The strong ICT behavior of the dye is manifested through the huge red-shift (4166 cm-1) of the emission spectra from non-polar cyclohexane to polar N,N-dimethylformamide. In contrast to many small push-pull organic dyes, the LE and ICT states of the push-pull enediynyl dye follow the same excitation pathway. The dominant red-shifted ICT emission (∼550 nm) intensity of the dye in polar solvent decreases with a concomitant appearance of the blue-shifted LE emission (∼385 nm) upon prolonged exposure to photons. This opens up a new photophysical strategy of achieving high contrast two fluorescence color conversion from yellow to blue.

Means and method of detection in chemical separation procedures

DOEpatents

Yeung, Edward S.; Koutny, Lance B.; Hogan, Barry L.; Cheung, Chan K.; Ma, Yinfa

1993-03-09

A means and method for indirect detection of constituent components of a mixture separated in a chemical separation process. Fluorescing ions are distributed across the area in which separation of the mixture will occur to provide a generally uniform background fluorescence intensity. For example, the mixture is comprised of one or more charged analytes which displace fluorescing ions where its constituent components separate to. Fluorescing ions of the same charge as the charged analyte components cause a displacement. The displacement results in the location of the separated components having a reduced fluorescence intensity to the remainder of the background. Detection of the lower fluorescence intensity areas can be visually, by photographic means and methods, or by automated laser scanning.

Means and method of detection in chemical separation procedures

DOEpatents

Yeung, E.S.; Koutny, L.B.; Hogan, B.L.; Cheung, C.K.; Yinfa Ma.

1993-03-09

A means and method are described for indirect detection of constituent components of a mixture separated in a chemical separation process. Fluorescing ions are distributed across the area in which separation of the mixture will occur to provide a generally uniform background fluorescence intensity. For example, the mixture is comprised of one or more charged analytes which displace fluorescing ions where its constituent components separate to. Fluorescing ions of the same charge as the charged analyte components cause a displacement. The displacement results in the location of the separated components having a reduced fluorescence intensity to the remainder of the background. Detection of the lower fluorescence intensity areas can be visually, by photographic means and methods, or by automated laser scanning.

Interaction of cinnamic acid derivatives with serum albumins: A fluorescence spectroscopic study

NASA Astrophysics Data System (ADS)

Singh, T. Sanjoy; Mitra, Sivaprasad

2011-03-01

Cinnamic acid (CA) derivatives are known to possess broad therapeutic applications including anti-tumor activity. The present study was designed to determine the underlying mechanism and thermodynamic parameters for the binding of two CA based intramolecular charge transfer (ICT) fluorescent probes, namely, 4-(dimethylamino) cinnamic acid (DMACA) and trans-ethyl p-(dimethylamino) cinnamate (EDAC), with albumins by fluorescence spectroscopy. Stern-Volmer analysis of the tryptophan fluorescence quenching data in presence of the added ligand reveals fluorescence quenching constant ( κq), Stern-Volmer constant ( KSV) and also the ligand-protein association constant ( Ka). The thermodynamic parameters like enthalpy (Δ H) and entropy (Δ S) change corresponding to the ligand binding process were also estimated. The results show that the ligands bind into the sub-domain IIA of the proteins in 1:1 stoichiometry with an apparent binding constant value in the range of 10 4 dm 3 mol -1. In both the cases, the spontaneous ligand binding to the proteins occur through entropy driven mechanism, although the interaction of DMACA is relatively stronger in comparison with EDAC. The temperature dependence of the binding constant indicates the induced change in protein secondary structure.

Proton triggered emission and selective sensing of picric acid by the fluorescent aggregates of 6,7-dimethyl-2,3-bis-(2-pyridyl)-quinoxaline.

PubMed

Mazumdar, Prativa; Maity, Samir; Shyamal, Milan; Das, Debasish; Sahoo, Gobinda Prasad; Misra, Ajay

2016-03-14

A heteroatom containing organic fluorophore 6,7-dimethyl-2,3-bis-(2-pyridyl)-quinoxaline (BPQ) is weakly emissive in solution but its emission properties are highly enhanced in the aggregated state due to the restriction of intramolecular rotation (RIR) and large amplitude vibrational modes, demonstrating the phenomenon, aggregation induced emission enhancement (AIEE). It has strong proton capture capability, allowing reversible fluorescence switching in basic and acidic medium and the emission color changes from blue to green in the aggregated state through protonation. It has been explained as a competition between intramolecular charge transfers (ICTs) and the AIEE phenomena at a lower pH range (pH ∼1-4). Such behavior enables it as a fluorescent pH sensor for detection in acidic and basic medium. Morphologies of the particles are characterized using optical and field emission scanning electron microscopic (FESEM) studies. The turn off fluorescence properties of aggregated BPQ have been utilized for the selective detection of picric acid and the fluorescence quenching is explained due to ground state complexation with a strong quenching constant, 7.81 × 10(4) M(-1).

A fluorescent paramagnetic Mn metal–organic framework based on semi-rigid pyrene tetra­carboxylic acid: sensing of solvent polarity and explosive nitroaromatics

PubMed Central

Bajpai, Alankriti; Mukhopadhyay, Arindam; Krishna, Manchugondanahalli Shivakumar; Govardhan, Savitha; Moorthy, Jarugu Narasimha

2015-01-01

An Mn metal–organic framework (Mn-MOF), Mn-L, based on a pyrene-tetraacid linker (H4 L), displays a respectable fluorescence quantum yield of 8.3% in spite of the presence of the paramagnetic metal ions, due presumably to fixation of the metal ions in geometries that do not allow complete energy/charge-transfer quenching. Remarkably, the porous Mn-L MOF with ∼25% solvent-accessible volume exhibits a heretofore unprecedented solvent-dependent fluorescence emission maximum, permitting its use as a probe of solvent polarity; the emission maxima in different solvents correlate excellently with Reichardt’s solvent polarity parameter (E T N). Further, the applicability of Mn-L to the sensing of nitroaromatics via fluorescence quenching is demonstrated; the detection limit for TNT is shown to be 125 p.p.m. The results bring out the fact that MOFs based on paramagnetic metal ions can indeed find application when the quenching mechanisms are attenuated by certain geometries of the organic linkers of the MOF. PMID:26306197

A fluorescent paramagnetic Mn metal-organic framework based on semi-rigid pyrene tetra-carboxylic acid: sensing of solvent polarity and explosive nitroaromatics.

PubMed

Bajpai, Alankriti; Mukhopadhyay, Arindam; Krishna, Manchugondanahalli Shivakumar; Govardhan, Savitha; Moorthy, Jarugu Narasimha

2015-09-01

An Mn metal-organic framework (Mn-MOF), Mn-L, based on a pyrene-tetraacid linker (H4 L), displays a respectable fluorescence quantum yield of 8.3% in spite of the presence of the paramagnetic metal ions, due presumably to fixation of the metal ions in geometries that do not allow complete energy/charge-transfer quenching. Remarkably, the porous Mn-L MOF with ∼25% solvent-accessible volume exhibits a heretofore unprecedented solvent-dependent fluorescence emission maximum, permitting its use as a probe of solvent polarity; the emission maxima in different solvents correlate excellently with Reichardt's solvent polarity parameter (E T (N)). Further, the applicability of Mn-L to the sensing of nitroaromatics via fluorescence quenching is demonstrated; the detection limit for TNT is shown to be 125 p.p.m. The results bring out the fact that MOFs based on paramagnetic metal ions can indeed find application when the quenching mechanisms are attenuated by certain geometries of the organic linkers of the MOF.

Improving surface and defect center chemistry of fluorescent nanodiamonds for imaging purposes--a review.

PubMed

Nagl, Andreas; Hemelaar, Simon Robert; Schirhagl, Romana

2015-10-01

Diamonds are widely used for jewelry owing to their superior optical properties accounting for their fascinating beauty. Beyond the sparkle, diamond is highly investigated in materials science for its remarkable properties. Recently, fluorescent defects in diamond, particularly the negatively charged nitrogen-vacancy (NV(-)) center, have gained much attention: The NV(-) center emits stable, nonbleaching fluorescence, and thus could be utilized in biolabeling, as a light source, or as a Förster resonance energy transfer donor. Even more remarkable are its spin properties: with the fluorescence intensity of the NV(-) center reacting to the presence of small magnetic fields, it can be utilized as a sensor for magnetic fields as small as the field of a single electron spin. However, a reproducible defect and surface and defect chemistry are crucial to all applications. In this article we review methods for using nanodiamonds for different imaging purposes. The article covers (1) dispersion of particles, (2) surface cleaning, (3) particle size selection and reduction, (4) defect properties, and (5) functionalization and attachment to nanostructures, e.g., scanning probe microscopy tips.

A novel colorimetric and "turn-on" fluorimetric chemosensor for selective recognition of CN- ions based on asymmetric azine derivatives in aqueous media

NASA Astrophysics Data System (ADS)

Pei, Peng-Xiang; Hu, Jing-Han; Long, Chen; Ni, Peng-Wei

2018-06-01

A novel chemosensor 2-((Z)-(((E)-quinolin-2-ylmethylene)hydrazono)methyl)phenol PX has been successfully designed and synthesized, which showed both colorimetric and "turn-on" fluorescence responses for CN- in DMSO/H2O (3:2, v/v; pH = 7.20) solution. The sensor could respond effectively to the stimulation of CN- ions via deprotonation and sensing mechanism of intramolecular charge transfer (ICT). Moreover, the sensor PX was successfully utilized to detect CN- in bitter almond, and the detection limit on fluorescence response of PX towards CN- was down to 4.5 × 10-7 M. Test strips containing PX were also prepared, which could act as a practical colorimetric tool to detect CN- in aqueous media.

The photophysical properties of 1H-pyrazolo[3,4-b]quinoxalines derivatives and their possible optoelectronic application

NASA Astrophysics Data System (ADS)

Uchacz, Tomasz; Wojtasik, Katarzyna; Szlachcic, Paweł; Gondek, Ewa; Pokladko-Kowar, Monika; Danel, Andrzej; Stadnicka, Katarzyna

2018-06-01

In the manuscript, photophysical, electrochemical and electroluminescent properties of the series of phenyl/methyl substituted 1H-pyrazolo[3,4-b]quinoxalines have been investigated. The fluorescent properties of these compounds varied significantly depending on the presence of phenyl substituent and its position in the molecule. Compared with the 1,3-dimethylpyrazoloquinoxaline (parent molecule), phenyl at the third position of pyrazole ring enhanced the fluorescence by increasing contribution of π-π* transitions, whereas 1-phenyl substituent led to the formation of polarity-dependent charge transfer state. The molecules were also tested as potential luminophores in double layer OLED devices fabricated by solution processing techniques. The investigated pyrazoloquinoxaline based OLED's emitted green light with appreciable brightness up to 2820 cd/m2.

Supramolecular complex of a fused zinc phthalocyanine-zinc porphyrin dyad assembled by two imidazole-C60 units: ultrafast photoevents.

PubMed

Follana-Berná, Jorge; Seetharaman, Sairaman; Martín-Gomis, Luis; Charalambidis, Georgios; Trapali, Adelais; Karr, Paul A; Coutsolelos, Athanassios G; Fernández-Lázaro, Fernando; D'Souza, Francis; Sastre-Santos, Ángela

2018-03-14

A new zinc phthalocyanine-zinc porphyrin dyad (ZnPc-ZnP) fused through a pyrazine ring has been synthesized as a receptor for imidazole-substituted C 60 (C 60 Im) electron acceptor. Self-assembly via metal-ligand axial coordination and the pertinent association constants in solution were determined by 1 H-NMR, UV-Vis and fluorescence titration experiments at room temperature. The designed host was able to bind up to two C 60 Im electron acceptor guest molecules to yield C 60 Im:ZnPc-ZnP:ImC 60 donor-acceptor supramolecular complex. The spectral data showed that the two binding sites behave independently with binding constants similar in magnitude. Steady-state fluorescence studies were indicative of an efficient singlet-singlet energy transfer from zinc porphyrin to zinc phthalocyanine within the fused dyad. Accordingly, the transient absorption studies covering a wide timescale of femto-to-milli seconds revealed ultrafast energy transfer from 1 ZnP* to ZnPc (k EnT ∼ 10 12 s -1 ) in the fused dyad. Further, a photo induced electron transfer was observed in the supramolecularly assembled C 60 Im:ZnPc-ZnP:ImC 60 donor-acceptor complex leading to charge separated states, which persisted for about 200 ns.

Photoinduced electron transfer (PET) versus excimer formation in supramolecular p/n-heterojunctions of perylene bisimide dyes and implications for organic photovoltaics.

PubMed

Nowak-Król, Agnieszka; Fimmel, Benjamin; Son, Minjung; Kim, Dongho; Würthner, Frank

2015-01-01

Foldamer systems comprised of two perylene bisimide (PBI) dyes attached to the conjugated backbones of 1,2-bis(phenylethynyl)benzene and phenylethynyl-bis(phenylene)indane, respectively, were synthesized and investigated with regard to their solvent-dependent properties. UV/Vis absorption and steady-state fluorescence spectra show that both foldamers exist predominantly in a folded H-aggregated state consisting of π-π-stacked PBIs in THF and in more random conformations with weaker excitonic coupling between the PBIs in chloroform. Time-resolved fluorescence spectroscopy and transient absorption spectroscopy reveal entirely different relaxation pathways for the photoexcited molecules in the given solvents, i.e. photoinduced electron transfer leading to charge separated states for the open conformations (in chloroform) and relaxation into excimer states with red-shifted emission for the stacked conformations (in THF). Supported by redox data from cyclic voltammetry and Rehm-Weller analysis we could relate the processes occurring in these solution-phase model systems to the elementary processes in organic solar cells. Accordingly, only if relaxation pathways such as excimer formation are strictly avoided in molecular semiconductor materials, excitons may diffuse over larger distances to the heterojunction interface and produce photocurrent via the formation of electron/hole pairs by photoinduced electron transfer.

Interaction of albumin with perylene-diimides with aromatic substituents

NASA Astrophysics Data System (ADS)

Farooqi, Mohammed; Penick, Mark; Burch, Jessica; Negrete, George; Brancaleon, Lorenzo

2015-03-01

Polyaromatic hydrocarbons (PAH) binding to proteins remains one of the fundamental aspects of research in biophysics. Ligand binding can regulate the function of proteins. Binding to small ligands remains a very important aspect in the study of the function of many proteins. Perylene diimide or PDI derivatives have attracted initial interest as industrial dyes and pigments. Recently, much attention has been focused on their strong π - π stacks resulting from the large PDI aromatic core. These PDI stacks have distinct optical properties, and provide informative models that mimic the light-harvesting system and initial charge separation and charge transfer in the photosynthetic system. The absorption property of PDI derivatives may be largely tuned from visible to near-infrared region by chemical modifications at the bay-positions. We are currently studying a new class of PDI derivatives with substituents made of the side chains of aromatic amino acids (Tyrosine, Tryptophan and Phenylalanine). We have looked at the fluorescence absorption and emission of these PDIs in water and other organic solvents. PDIs show evidence of dimerization and possible aggregation. We also present binding studies of these PDIs with Human Serum Albumin (HSA). The binding was studied using fluorescence emission quenching of the HSA Tryptophan residue. Stern-Volmer equation is used to derive the quenching constants. PDI binding to HSA also has an effect on the fluorescence emission of the PDIs themselves by red shifting the spectra. Funded by RCMI grant.

Optical and photoacoustic dual-modality imaging guided synergistic photodynamic/photothermal therapies

NASA Astrophysics Data System (ADS)

Yan, Xuefeng; Hu, Hao; Lin, Jing; Jin, Albert J.; Niu, Gang; Zhang, Shaoliang; Huang, Peng; Shen, Baozhong; Chen, Xiaoyuan

2015-01-01

Phototherapies such as photodynamic therapy (PDT) and photothermal therapy (PTT), due to their specific spatiotemporal selectivity and minimal invasiveness, have been widely investigated as alternative treatments of malignant diseases. Graphene and its derivatives not only have been used as carriers to deliver photosensitizers for PDT, but also as photothermal conversion agents (PTCAs) for PTT. Herein, we strategically designed and produced a novel photo-theranostic platform based on sinoporphyrin sodium (DVDMS) photosensitizer-loaded PEGylated graphene oxide (GO-PEG-DVDMS) for enhanced fluorescence/photoacoustic (PA) dual-modal imaging and combined PDT and PTT. The GO-PEG carrier drastically improves the fluorescence of loaded DVDMS via intramolecular charge transfer. Concurrently, DVDMS significantly enhances the near-infrared (NIR) absorption of GO for improved PA imaging and PTT. The cancer theranostic capability of the as-prepared GO-PEG-DVDMS was carefully investigated both in vitro and in vivo. This novel theranostics is well suited for fluorescence/PA dual-modal imaging and synergistic PDT/PTT.

Fluorescent carbon quantum dot hydrogels for direct determination of silver ions.

PubMed

Cayuela, A; Soriano, M L; Kennedy, S R; Steed, J W; Valcárcel, M

2016-05-01

The paper reports for the first time the direct determination of silver ion (Ag(+)) using luminescent Carbon Quantum Dot hydrogels (CQDGs). Carbon Quantum Dots (CQDs) with different superficial moieties (passivate-CQDs with carboxylic groups, thiol-CQDs and amine-CQDs) were used to prepare hybrid gels using a low molecular weight hydrogelator (LMWG). The use of the gels results in considerable fluorescence enhancement and also markedly influences selectivity. The most selective CQDG system for Ag(+) ion detection proved to be those containing carboxylic groups onto their surface. The selectivity towards Ag(+) ions is possibly due to its flexible coordination sphere compared with other metal ions. This fluorescent sensing platform is based on the strong Ag-O interaction which can quench the photoluminescence of passivate-CQDs (p-CQDs) through charge transfer. The limit of detection (LOD) and quantification (LOQ) of the proposed method were 0.55 and 1.83µgmL(-1), respectively, being applied in river water samples. Copyright © 2016 Elsevier B.V. All rights reserved.

Light harvesting and charge management by Ni4S3 modified metal-organic frameworks and rGO in the process of photocatalysis.

PubMed

Liu, Duanduan; Jin, Zhiliang; Zhang, Yongke; Wang, Guorong; Ma, Bingzhen

2018-06-01

Harvesting and charge management is obtained by means of Ni 4 S 3 modified Metal-organic Frameworks (MOF) and rGO, namely, the Uio-66 (Zr)/rGO combined with Ni 4 S 3 photocatalyst was successfully prepared with the solvothermal method. The Ni 4 S 3 acted as the electron transfer agent greatly improve the electrons transmission from the excited state dye to the rGO/MOF surface for proton reduction reaction. The hydrogen production amount over EY-sensitized rGO/MOF/Ni 4 S 3 photocatalyst has reached 280 μmol for 5 h, which is about 14 times than that of the pure Ni 4 S 3 photocatalyst and 185 times than that of the pure rGO/MOF photocatalyst under visible light irradiation (λ ≥ 420 nm). In the composite, the rGO acts as electron-transfer mediator and Ni 4 S 3 serves as H 2 -evolution active site. A series of studies shown that the Ni 4 S 3 modified MOF and rGO provided more active sites and improved the efficiency of photo-generated charge separation by means of several characterizations such as SEM, XRD, XPS, Element Mapping, UV-vis DRS, BET, Photocurrent, Voltammetric Scanning, Fluorescence Spectra and FTIR. and the results of which were in good agreement with each other. The photoelectron migration rate and photogenerated charge separation efficiency of the composite can be obviously increased with graphene as a good electron acceptor and transfer medium and Ni 4 S 3 as hydrogen producing active site. Copyright © 2018 Elsevier Inc. All rights reserved.

Modulation of nitrogen vacancy charge state and fluorescence in nanodiamonds using electrochemical potential

PubMed Central

Karaveli, Sinan; Gaathon, Ophir; Wolcott, Abraham; Sakakibara, Reyu; Shemesh, Or A.; Peterka, Darcy S.; Boyden, Edward S.; Owen, Jonathan S.; Yuste, Rafael; Englund, Dirk

2016-01-01

The negatively charged nitrogen vacancy (NV−) center in diamond has attracted strong interest for a wide range of sensing and quantum information processing applications. To this end, recent work has focused on controlling the NV charge state, whose stability strongly depends on its electrostatic environment. Here, we demonstrate that the charge state and fluorescence dynamics of single NV centers in nanodiamonds with different surface terminations can be controlled by an externally applied potential difference in an electrochemical cell. The voltage dependence of the NV charge state can be used to stabilize the NV− state for spin-based sensing protocols and provides a method of charge state-dependent fluorescence sensing of electrochemical potentials. We detect clear NV fluorescence modulation for voltage changes down to 100 mV, with a single NV and down to 20 mV with multiple NV centers in a wide-field imaging mode. These results suggest that NV centers in nanodiamonds could enable parallel optical detection of biologically relevant electrochemical potentials. PMID:27035935

Modulation of nitrogen vacancy charge state and fluorescence in nanodiamonds using electrochemical potential.

PubMed

Karaveli, Sinan; Gaathon, Ophir; Wolcott, Abraham; Sakakibara, Reyu; Shemesh, Or A; Peterka, Darcy S; Boyden, Edward S; Owen, Jonathan S; Yuste, Rafael; Englund, Dirk

2016-04-12

The negatively charged nitrogen vacancy (NV(-)) center in diamond has attracted strong interest for a wide range of sensing and quantum information processing applications. To this end, recent work has focused on controlling the NV charge state, whose stability strongly depends on its electrostatic environment. Here, we demonstrate that the charge state and fluorescence dynamics of single NV centers in nanodiamonds with different surface terminations can be controlled by an externally applied potential difference in an electrochemical cell. The voltage dependence of the NV charge state can be used to stabilize the NV(-) state for spin-based sensing protocols and provides a method of charge state-dependent fluorescence sensing of electrochemical potentials. We detect clear NV fluorescence modulation for voltage changes down to 100 mV, with a single NV and down to 20 mV with multiple NV centers in a wide-field imaging mode. These results suggest that NV centers in nanodiamonds could enable parallel optical detection of biologically relevant electrochemical potentials.

Modulation of nitrogen vacancy charge state and fluorescence in nanodiamonds using electrochemical potential

NASA Astrophysics Data System (ADS)

Karaveli, Sinan; Gaathon, Ophir; Wolcott, Abraham; Sakakibara, Reyu; Shemesh, Or A.; Peterka, Darcy S.; Boyden, Edward S.; Owen, Jonathan S.; Yuste, Rafael; Englund, Dirk

2016-04-01

The negatively charged nitrogen vacancy (NV-) center in diamond has attracted strong interest for a wide range of sensing and quantum information processing applications. To this end, recent work has focused on controlling the NV charge state, whose stability strongly depends on its electrostatic environment. Here, we demonstrate that the charge state and fluorescence dynamics of single NV centers in nanodiamonds with different surface terminations can be controlled by an externally applied potential difference in an electrochemical cell. The voltage dependence of the NV charge state can be used to stabilize the NV- state for spin-based sensing protocols and provides a method of charge state-dependent fluorescence sensing of electrochemical potentials. We detect clear NV fluorescence modulation for voltage changes down to 100 mV, with a single NV and down to 20 mV with multiple NV centers in a wide-field imaging mode. These results suggest that NV centers in nanodiamonds could enable parallel optical detection of biologically relevant electrochemical potentials.

Resonance energy transfer between sites in rat liver glutathione S-transferase, 1-1, selectively modified at cysteine-17 and cysteine-111.

PubMed

Hu, L; Colman, R F

1997-02-18

Monobromobimane (mBBr) can label both Cys111 and Cys17 of rat liver glutathione S-transferase, 1-1 (GST 1-1). However, selective modification of Cys111 was achieved by the maleimide-based sulfhydryl reagents N-ethylmaleimide (NEM) and fluorescein 5-maleimide (NFM). Incubation of GST 1-1 with 5 mM NEM for 30 min at pH 7.5 and 25 degrees C leads to the formation of modified enzyme with 92% residual activity toward 1-chloro-2,4-dinitrobenzene and completely blocks Cys111 from subsequent reaction with either NFM or mBBr. Reaction of GST 1-1 with 0.2 mM NFM under the same conditions affords a modified enzyme with only 14% residual activity even though NFM and NEM target the same Cys111. The results indicate that when the bulky fluorescein is covalently bound to Cys111, the ligand projects into both the xenobiotic binding site and the glutathione site. After NEM or NFM modification of GST 1-1, the enzyme was further modified by monobromobimane at Cys17 with loss of activity. Together with the only tryptophan (Trp20), fluorescein linked to Cys111 and bimane to Cys17 provide three fluorescent probes to study the solution structure of GST 1-1. Fluorescence spectral analysis suggests that Trp20 and bimane linked to Cys17 are located in a relatively hydrophobic environment, while fluorescein linked to Cys111 is located in a charged environment. These fluorescent probes constitute three sets of donor-acceptor pairs for the measurement of fluorescence energy transfer, and distances calculated from such measurements are 20 A between Trp20 and bimane at Cys17, 19 A between Trp20 and fluorescein at Cys111, and < 22 A between bimane at Cys17 and fluorescein at Cys111. Molecular modeling studies indicate that fluorescein lies between the two subunits, is surrounded by charged residues, and is extended into the xenobiotic binding site. They also suggest that mBBr must approach from the dimer interface in order to reach the reaction site at Cys17.

Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant.

PubMed

Zhang, Tianyou; Zhao, Bo; Chu, Bei; Li, Wenlian; Su, Zisheng; Yan, Xingwu; Liu, Chengyuan; Wu, Hairuo; Gao, Yuan; Jin, Fangming; Hou, Fuhua

2015-05-15

Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies.

Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant

NASA Astrophysics Data System (ADS)

Zhang, Tianyou; Zhao, Bo; Chu, Bei; Li, Wenlian; Su, Zisheng; Yan, Xingwu; Liu, Chengyuan; Wu, Hairuo; Gao, Yuan; Jin, Fangming; Hou, Fuhua

2015-05-01

Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies.

Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant

PubMed Central

Zhang, Tianyou; Zhao, Bo; Chu, Bei; Li, Wenlian; Su, Zisheng; Yan, Xingwu; Liu, Chengyuan; Wu, Hairuo; Gao, Yuan; Jin, Fangming; Hou, Fuhua

2015-01-01

Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies. PMID:25975371

Beyond superquenching: Hyper-efficient energy transfer from conjugated polymers to gold nanoparticles

PubMed Central

Fan, Chunhai; Wang, Shu; Hong, Janice W.; Bazan, Guillermo C.; Plaxco, Kevin W.; Heeger, Alan J.

2003-01-01

Gold nanoparticles quench the fluorescence of cationic polyfluorene with Stern–Volmer constants (KSV) approaching 1011 M—1, several orders of magnitude larger than any previously reported conjugated polymer–quencher pair and 9–10 orders of magnitude larger than small molecule dye–quencher pairs. The dependence of KSV on ionic strength, charge and conjugation length of the polymer, and the dimensions (and thus optical properties) of the nanoparticles suggests that three factors account for this extraordinary efficiency: (i) amplification of the quenching via rapid internal energy or electron transfer, (ii) electrostatic interactions between the cationic polymer and anionic nanoparticles, and (iii) the ability of gold nanoparticles to quench via efficient energy transfer. As a result of this extraordinarily high KSV, quenching can be observed even at subpicomolar concentrations of nanoparticles, suggesting that the combination of conjugated polymers with these nanomaterials can potentially lead to improved sensitivity in optical biosensors. PMID:12750470

Femtosecond-picosecond laser photolysis studies on the dynamics of excited charge-transfer complexes: Aromatic hydrocarbon-acid anhydride, -tetracyanoethylene, and -tetracyanoquinodimethane systems in acetonitrile solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Asahi, Tsuyoshi; Mataga, Noboru

1991-03-07

Formation processes of contact ion pairs (CIP) from the excited Franck-Condon (FC) state of charge-transfer (CT) complexes of aromatic hydrocarbons with acid anhydride as well as cyano compound acceptors in acetonitrile solution and charge recombination (CR) rates (k{sub CR}{sup CIP}) of produced CIP states have been investigated by femtosecond and picosecond laser phototlysis and time-resolved absorption spectral measurements covering a wide range of free energy gap-{Delta}G{degree}{sub ip} between the ion pair and the ground state. It has been confirmed that the CIP formation becomes faster and k{sub CR}{sup CIP} of the produced CIP increases with increase of the strengths ofmore » the electron donor (D) and acceptor (A) in the complex, i.e., with decrease of the {minus}{Delta}G{degree}{sub ip} value. This peculiar energy gap dependence of k{sub CR}{sup CIP}, quite different from the bell-shaped one observed in the case of the solvent-separated ion pairs (SSIP) or loose ion pairs (LIP) formed by encounter between fluorescer and quencher in the fluoresence quenching reaction, has been interpreted by assuming the change of electronic and geometrical structures of CIP depending on the strengths of D and A.« less

Semiconductor Nanorod–Carbon Nanotube Biomimetic Films for Wire-Free Photostimulation of Blind Retinas

PubMed Central

2014-01-01

We report the development of a semiconductor nanorod-carbon nanotube based platform for wire-free, light induced retina stimulation. A plasma polymerized acrylic acid midlayer was used to achieve covalent conjugation of semiconductor nanorods directly onto neuro-adhesive, three-dimensional carbon nanotube surfaces. Photocurrent, photovoltage, and fluorescence lifetime measurements validate efficient charge transfer between the nanorods and the carbon nanotube films. Successful stimulation of a light-insensitive chick retina suggests the potential use of this novel platform in future artificial retina applications. PMID:25350365

Ratiometric and colorimetric near-infrared sensors for multi-channel detection of cyanide ion and their application to measure β-glucosidase

PubMed Central

Xing, Panfei; Xu, Yongqian; Li, Hongjuan; Liu, Shuhui; Lu, Aiping; Sun, Shiguo

2015-01-01

A near-infrared sensor for cyanide ion (CN−) was developed via internal charge transfer (ICT). This sensor can selectively detect CN− either through dual-ratiometric fluorescence (logarithm of I414/I564 and I803/I564) or under various absorption (356 and 440 nm) and emission (414, 564 and 803 nm) channels. Especially, the proposed method can be employed to measure β-glucosidase by detecting CN− traces in commercial amygdalin samples. PMID:26549546

Highly Efficient Simplified Single-Emitting-Layer Hybrid WOLEDs with Low Roll-off and Good Color Stability through Enhanced Förster Energy Transfer.

PubMed

Zhang, Dongdong; Cai, Minghan; Zhang, Yunge; Zhang, Deqiang; Duan, Lian

2015-12-30

Single-emitting layer hybrid white organic light-emitting diodes (SEL-hybrid-WOLEDs) usually suffer from low efficiency, significant roll-off, and poor color stability, attributed to the incomplete energy transfer from the triplet states of the blue fluorophores to the phosphors. Here, we demonstrate highly efficient SEL-hybrid-WOLEDs with low roll-off and good color-stability utilizing blue thermally activated delayed fluorescence (TADF) materials as the host emitters. The triplet states of the blue TADF host emitter can be up-converted into its singlet states, and then the energy is transferred to the complementary phosphors through the long-range Förster energy transfer, enhancing the energy transfer from the host to the dopant. Simplified SEL-hybrid-WOLEDs achieve the highest forward-viewing external quantum efficiency (EQE) of 20.8% and power efficiency of 51.2 lm/W with CIE coordinates of (0.398, 0.456) at a luminance of 500 cd/m(2). The device EQE only slightly drops to 19.6% at a practical luminance of 1000 cd/m(2) with a power efficiency of 38.7 lm/W. Furthermore, the spectra of the device are rather stable with the raising voltage. The reason can be assigned to the enhanced Förster energy transfer, wide charge recombination zone, as well as the bipolar charge transporting ability of the host emitter. We believe that our work may shed light on the future development of highly efficient SEL-hybrid-WOLEDs with simultaneous low roll-off and good color stability.

Quenching mechanism of Zn(salicylaldimine) by nitroaromatics.

PubMed

Germain, Meaghan E; Vargo, Thomas R; McClure, Beth Anne; Rack, Jeffrey J; Van Patten, P Gregory; Odoi, Michael; Knapp, Michael J

2008-07-21

Nitroaromatics and nitroalkanes quench the fluorescence of Zn(Salophen) (H2Salophen = N,N'-phenylene-bis-(3,5-di- tert-butylsalicylideneimine); ZnL(R)) complexes. A structurally related family of ZnL(R) complexes (R = OMe, di-tBu, tBu, Cl, NO2) were prepared, and the mechanisms of fluorescence quenching by nitroaromatics were studied by a combined kinetics and spectroscopic approach. The fluorescent quantum yields for ZnL(R) were generally high (Phi approximately 0.3) with sub-nanosecond fluorescence lifetimes. The fluorescence of ZnL(R) was quenched by nitroaromatic compounds by a mixture of static and dynamic pathways, reflecting the ZnL(R) ligand bulk and reduction potential. Steady-state Stern-Volmer plots were curved for ZnL(R) with less-bulky substituents (R = OMe, NO2), suggesting that both static and dynamic pathways were important for quenching. Transient Stern-Volmer data indicated that the dynamic pathway dominated quenching for ZnL(R) with bulky substituents (R = tBu, DtBu). The quenching rate constants with varied nitroaromatics (ArNO2) followed the driving force dependence predicted for bimolecular electron transfer: ZnL* + ArNO2 --> ZnL(+) + ArNO2(-). A treatment of the diffusion-corrected quenching rates with Marcus theory yielded a modest reorganization energy (lambda = 25 kcal/mol), and a small self-exchange reorganization energy for ZnL*/ZnL(+) (ca. 20 kcal/mol) was estimated from the Marcus cross-relation, suggesting that metal phenoxyls may be robust biological redox cofactors. Electronic structure calculations indicated very small changes in bond distances for the ZnL --> ZnL(+) oxidation, suggesting that solvation was the dominant contributor to the observed reorganization energy. These mechanistic insights provide information that will be helpful to further develop ZnL(R) as sensors, as well as for potential photoinduced charge transfer chemistry.

Absorption and emission behaviour of trans- p-coumaric acid in aqueous solutions and some organic solvents

NASA Astrophysics Data System (ADS)

Putschögl, M.; Zirak, P.; Penzkofer, A.

2008-01-01

The absorption and fluorescence behaviour of trans- p-coumaric acid ( trans-4-hydroxycinnamic acid) is investigated in buffered aqueous solution over a wide range from pH 1 to pH 12, in un-buffered water, and in some organic solvents. Absorption cross-section spectra, fluorescence quantum distributions, fluorescence quantum yields, and degrees of fluorescence polarisation are measured. p-Coumaric acid exists in different ionic forms in aqueous solution depending on the pH. There is an equilibrium between the neutral form ( p-CAH 2) and the single anionic form ( p-CAH -) at low pH (p Kna ≈ 4.9), and between the single anionic and the double anionic form ( p-CA 2-) at high pH (p Kaa ≈ 9.35). In the organic solvents studied trans- p-coumaric acid is dissolved in its neutral form. The fluorescence quantum yield of trans- p-coumaric acid in aqueous solution is ϕF ≈ 1.4 × 10 -4 for the neutral and the single anionic form, while it is ϕF ≈ 1.3 × 10 -3 for the double anionic form. For trans- p-coumaric acid in organic solvents fluorescence quantum yields in the range from 4.8 × 10 -5 (acetonitrile) to 1.5 × 10 -4 (glycerol) were measured. The fluorescence spectra are 7700-10,000 cm -1 Stokes shifted in aqueous solution, and 5400-8200 cm -1 Stokes shifted in the studied organic solvents. Decay paths responsible for the low fluorescence quantum yields are discussed (photo-isomerisation and internal conversion for p-CA 2-, solvent-assisted intra-molecular charge-transfer or ππ ∗ to nπ ∗ transfer and internal conversion for p-CAH 2 and p-CAH -). The solvent dependence of the first ππ ∗ electronic transition frequency and of the fluorescence Stokes shift of p-CAH 2 is discussed in terms of polar solute-solvent interaction effects. Thereby the ground-state and excite-state molecular dipole moments are extracted.

Reduced graphene oxide and porphyrin. An interactive affair in 2-D.

PubMed

Wojcik, Aleksandra; Kamat, Prashant V

2010-11-23

Photoexcited cationic 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin tetra(p-toluenesulfonate) (TMPyP) undergoes charge-transfer interaction with chemically reduced graphene oxide (RGO). Formation of the ground-state TMPyP-RGO complex in solution is marked by the red-shift of the porphyrin absorption band. This complexation was analyzed by Benesi-Hildebrand plot. Porphyrin fluorescence lifetime reduced from 5 to 1 ns upon complexation with RGO, indicating excited-state interaction between singlet excited porphyrin and RGO. Femtosecond transient absorption measurements carried out with TMPyP adsorbed on RGO film revealed fast decay of the singlet excited state, followed by the formation of a longer-living product with an absorption maximum around 515 nm indicating the formation of a porphyrin radical cation. The ability of TMPyP-RGO to undergo photoinduced charge separation was further confirmed from the photoelectrochemical measurements. TMPyP-RGO coated conducting glass electrodes are capable of generating photocurrent under visible excitation. These results are indicative of the electron transfer between photoexcited porphyrin and RGO. The role of graphene in accepting and shuttling electrons in light-harvesting assemblies is discussed.

Attaching naphthalene derivatives onto BODIPY for generating excited triplet state and singlet oxygen: Tuning PET-based photosensitizer by electron donors

NASA Astrophysics Data System (ADS)

Zhang, Xian-Fu; Feng, Nan

2018-01-01

meso-Naphthalene substituted BODIPY compounds were prepared in a facile one pot reaction. The naphthalene functionalization of BODIPY leads up to a 5-fold increase in the formation efficiency of excited triplet state and singlet oxygen in polar solvents. Steady state and time resolved fluorescence, laser flash photolysis, and quantum chemistry methods were used to reveal the mechanism. All measured data and quantum chemical results suggest that these systems can be viewed as electron donor-acceptor (D-A) pair (BODIPY acts as the acceptor), photoinduced charge transfer (PCT) or photoinduced electron transfer (PET) occurs upon photo excitation (D-A + hν → Dδ +-Aδ -, 0 < δ ≤ 1), and the charge recombination induced the formation of triplet state (Dδ +-Aδ - → D-A (T1). These novel PCT- or PET-based photosensitizers (PSs) show different features from traditional PSs, such as the strong tunability by facile structural modification and good selectivity upon medium polarity. The new character for this type of PSs can lead to important applications in organic oxygenation reactions and photodynamic therapy of tumors.

Synthesis, characterization, and nonlinear optical (NLO) properties of truxene-cored diphenylamine derivatives

NASA Astrophysics Data System (ADS)

Li, Fusheng; Zhao, Baodong; Chen, Yu; Zhang, Yufei; Wang, Tao; Xue, Song

2017-10-01

Three star-shaped compounds based on a truxene core (FS11, FS12 and FS13) were prepared. The truxene core is incorporating with asymmetric diphenylamines, including one phenyl of diphenylamine substituted by methoxy group and the other phenyl substituted by tolyl, fluorophenyl and phenylethynyl for FS11, FS12 and FS13, respectively. Their one-photon, two-photon absorption, geometric structures, electrochemical behavior and thermal properties were investigated. The absorption maxima of charge transfer band for FS11, FS12 and FS13 are 375 nm, 373 nm and 383 nm, and the corresponding molar extinction coefficients of FS11, FS12 and FS13 is 79,950 M- 1 cm- 1, 67,220 M- 1 cm- 1 and 108,780 M- 1 cm- 1. The ;pull-push; structure promotes charge transfer between asymmetric diphenylamine branches and the truxene core. Their two-photon absorbtion property is measured by two-photon induced fluorescence. The maximum two-photon cross-sections values of FS11, FS12 and FS13 are excited at 750 nm, which are 260 GM, 204GM and 367 GM, respectively.

Theoretical study on the optical response behavior to hydrogen chloride gas of a series of Schiff-base-based star-shaped structures.

PubMed

Wang, Fei; Qi, Tianhong; Su, Zhongmin; Xie, Yuzhong

2018-02-17

Schiff-base compounds have many applications in the field of optoelectronic materials and chemical sensing because of their appealing coordination ability, and simple and easily accessible use in structural modification. Herein, five kinds of star-shaped Schiff-base compounds were designed and their optical response behavior to hydrogen chloride (HCl) gas was studied using dependent/time-dependent density functional theory (DFT/TDDFT). Moreover, the relationship between structures and properties was investigated upon changing the benzene group into N atom or triazine group at the core-position and introducing a methoxyl (-OCH 3 ) or nitro (-NO 2 ) group into the star-shaped Schiff-bases at the tail of the branches. The results show that all five Schiff-bases could be candidates for HCl gas sensing materials. Furthermore, introducing an electron-donating group at either the core or the tail forms a charge transfer channel with the electron deficient H-bonded imino group, which is convenient for charge transfer and subsequently promotes a red-shift in absorption spectra and fluorescence quenching.

Photoinduced intramolecular charge transfer and photophysical characteristics of (2Z)-3-[4-(dimethylamino) phenyl]-2-(2-methylphenyl) prop-2-ene-nitrile (DPM) in different media

NASA Astrophysics Data System (ADS)

Asiri, Abdullah M.; El-Daly, Samy A.; Alamry, Khalid A.; Arshad, Muhammad Nadeem; Pannipara, Mehboobali

2015-10-01

A new fluorophore, (2Z)-3-[4-(dimethylamino) phenyl]-2-(2-methylphenyl) prop-2-ene-nitrile (DPM), was synthesized by knoevenagel condensation of 4-(dimethylamino) benzaldehyde and 2-methylbenzyl cyanide in ethanol using NaOH as base. The electronic absorption and emission characteristic of DPM was studied in different solvents. The X-ray crystallographic structure of DPM was also investigated. A crystalline solid of DPM gives a strong green emission at about 533 nm; these phenomena are important for the application of DPM dye in organic photo emitting diode. DPM exhibits a red shift in its emission spectrum as solvent polarity increases, indicating a large change in the dipole moment of dye molecule upon excitation due to intramolecular charge transfer in excited DPM*. The fluorescence quantum yield depends strongly on the properties of the solvents, which was attributed to positive and negative solvatokinetic effects. The DPM dye displays solubilization in cationic (CTAB) micelle and could be used as a probe to determine the critical micelle concentration (CMC) of CTAB.

Photoinduced ICT vs. excited rotamer intercoversion in two quadrupolar polyaromatic N-methylpyridinium cations.

PubMed

Cesaretti, A; Carlotti, B; Elisei, F; Fortuna, C G; Spalletti, A

2018-01-24

The excited state dynamics of two quadrupolar polyaromatic N-methylpyridinium cations have been fully investigated in order to acquire detailed information on their photo-induced behavior. The two molecules are symmetric push-pull compounds having a D-π-A + -π-D motif, with the same electron-acceptor central unit (A = N-methylpyridinium) and two distinctive electron-donor polyaromatic side groups (D), namely naphthyl and pyrenyl substituents. Both molecules undergo charge transfer during the absorption, as revealed by a significant solvatochromism exhibited with solvent polarity, but the fate of their excited state was found to be markedly different. The careful analysis of the data gathered from femtosecond-resolved fluorescence up-conversion and transient absorption experiments, supported by DFT quantum mechanical calculations and temperature-dependent stationary measurements, shows the leading role of intramolecular charge transfer, assisted by symmetry breaking, in the pyrenyl derivative and that of rotamer interconversion in the naphthtyl one. Both excited state processes are controlled by the viscosity rather than polarity of the solvent, and they occur during inertial solvation in low-viscous media and lengthening up to tens of picoseconds in highly viscous solvents.

Photochemically stable fluorescent heteroditopic ligands for zinc ion.

PubMed

Zhang, Lu; Zhu, Lei

2008-11-07

Photochemically stable fluorescent heteroditopic ligands (9 and 10) for zinc ion were prepared and studied. Two independent metal coordination-driven photophysical processes, chelation-enhanced fluorescence (CHEF) and internal (or intramolecular) charge transfer (ICT), were designed into our heteroditopic ligand framework. This strategy successfully relates three coordination states of a ligand, non-, mono-, and dicoordinated, to three fluorescence states, fluorescence OFF, ON at one wavelength, and ON at another wavelength. This ligand platform has provided chemical foundation for applications such as the quantification of zinc concentration over broad ranges (Zhang, L.; Clark, R. J.; Zhu, L. Chem.-Eur. J. 2008, 14, 2894-2903) and molecular logic functions (Zhang, L.; Whitfield, W. A.; Zhu, L. Chem. Commun. 2008, 1880-1882). The binding stoichiometries of dipicolylamino and 2,2'-bipyridyl, the two binding sites featured in heteroditopic ligands 7-10, were studied in acetonitrile using both Job's method of continuous variation and isothermal titration calorimetry (ITC). The fluorescence enhancement of 7-10 upon the formation of monozinc complexes (defined as the fluorescence quantum yield ratio of monozinc complex and free ligand) is qualitatively related to the highest occupied molecular orbital (HOMO) energy levels of their fluorophores. This is consistent with our hypothesis on the thermodynamics of the coordination-driven photophysical processes embodied in the designed heteroditopic system, which was supported by cyclic voltammetry studies. In conclusion, compounds 9 and 10 not only possess better photochemical stability but also display a higher degree of fluorescence turn-on upon formation of monozinc complexes than their vinyl counterparts 7 and 8.

Chromenoquinoline-based thiol probes: a study on the quencher position for controlling fluorescent Off-On characteristics.

PubMed

Kand, Dnyaneshwar; Kalle, Arunasree Marasanapalli; Talukdar, Pinaki

2013-02-13

The design, synthesis and thiol sensing ability of chromenoquinoline-based fluorescent probes 4, 5 and 6 and are reported here. The relative position of the maleimide moiety was varied along the chromenoquinoline fluorophore to decrease the background fluorescence. Lower background fluorescence in probes 4 and 6 was rationalized by the smaller k(r)/k(nr) values compared to that of probe 5. An intramolecular charge transfer (ICT) mechanism was proposed for quenching and the extent was dependent on the position of the maleimide quencher. Fluorescent Off-On characteristics were evaluated by theoretical calculations. All probes were selective only towards thiol containing amino acids. Thiol sensing by probes 4 and 6 were much better compared to 5. Probe 4 displayed a better fluorescence response for less hindered thiol (185-, 223- and 156-fold for Hcy, Cys and GSH, respectively), while for probe 6, a higher enhancement in fluorescence was observed with more hindered thiols (180-, 205- and 245-fold for Hcy, Cys and GSH, respectively). The better response to bulkier thiol, GSH by probe 6 was attributed to the steric crowding at the C-4 position and bulkiness of the GSH group which force the succinimide unit to be in a nearly orthogonal conformation. This spatial arrangement was important in reducing the fluorescence quenching ability of the succinimide moiety. The application of probes 4, 5 and 6 was demonstrated by naked eye detection thiols using a 96-well plate system as well as by live-cell imaging.

Thylakoid membrane model of the Chl a fluorescence transient and P700 induction kinetics in plant leaves.

PubMed

Belyaeva, N E; Bulychev, A A; Riznichenko, G Yu; Rubin, A B

2016-12-01

A new Thylakoid model is presented, which describes in detail the electron/proton transfer reactions between membrane protein complexes including photosystems II and I (PSII, PSI), cytochrome (Cyt) b 6 f, mobile plastoquinone PQ pool in the thylakoid membrane, plastocyanin in lumen and ferredoxin in stroma, reduction of NADP via FNR and cyclic electron transfer. The Thylakoid model parameters were fitted both to Chl fluorescence induction data (FI) and oxido-reductions of P700 (ΔA 810 ) measured from 20 μs up to 20 s in pea leaves. The two-wave kinetics of FI and ΔA 810 (O(JI)PSM and OABCDE) were described quantitatively, provided that the values of membrane electrochemical potential components ΔΨ(t), pH L (t)/pH S (t) are in physiologically relevant ranges. The time courses on the time scale from nanoseconds to tens of seconds of oxido-reduction changes of ET components as well as concentrations of proton/ions (K + , Cl - ) were calculated. We assume a low constant FNR activity over this period. Charge movements across the thylakoid membrane by passive leakage and active ATPase transport and proton buffer reactions are simulated. The dynamics of charge fluxes during photosynthetic induction under low light (PFD 200 μmol photons m -2  s -1 ) were analyzed. The initial wave of P700 oxidation within 20 ms during independent operation of PSI and PSII was followed after 50 ms by PSI donor-side reduction from reduced PQ pool via Cyt b 6 f site. The Cyt b 6 f reactions contribute to the stabilization of fluxes in the time range 1 s < t < 10 s. The detailed analysis of Chl a fluorescence at the PSM stage (t > 10 s) would need the investigation of FNR activation effect in order to explain the transitions between cyclic and linear electron transport.

Protonation-induced ultrafast torsional dynamics in 9-anthrylbenzimidazole: a pH activated molecular rotor.

PubMed

Nandi, Amitabha; Kushwaha, Archana; Das, Dipanwita; Ghosh, Rajib

2018-03-07

We report the photophysical properties and excited state dynamics of 9-anthrylbenzimidazole (ANBI) which exhibits protonation-induced molecular rotor properties. In contrast to the highly emissive behavior of neutral ANBI, protonation of the benzimidazole group of ANBI induces efficient nonradiative deactivation by ultrafast torsional motion around the bond connecting the anthracene and benzimidazole units, as revealed by ultrafast transient absorption and fluorescence spectroscopy. Contrary to viscosity-independent fluorescence of neutral dyes, protonated ANBI is shown to display linear variation of emission yield and lifetime with solvent viscosity. The protonation-induced molecular rotor properties in the studied system are shown to be driven by enhanced charge transfer and are corroborated by quantum chemical calculations. Potential application as a microviscosity sensor of acidic regions in a heterogeneous environment by these proton-activated molecular rotor properties of ANBI is discussed.

Trapping Dynamics in Photosystem I-Light Harvesting Complex I of Higher Plants Is Governed by the Competition Between Excited State Diffusion from Low Energy States and Photochemical Charge Separation.

PubMed

Molotokaite, Egle; Remelli, William; Casazza, Anna Paola; Zucchelli, Giuseppe; Polli, Dario; Cerullo, Giulio; Santabarbara, Stefano

2017-10-26

The dynamics of excited state equilibration and primary photochemical trapping have been investigated in the photosystem I-light harvesting complex I isolated from spinach, by the complementary time-resolved fluorescence and transient absorption approaches. The combined analysis of the experimental data indicates that the excited state decay is described by lifetimes in the ranges of 12-16 ps, 32-36 ps, and 64-77 ps, for both detection methods, whereas faster components, having lifetimes of 550-780 fs and 4.2-5.2 ps, are resolved only by transient absorption. A unified model capable of describing both the fluorescence and the absorption dynamics has been developed. From this model it appears that the majority of excited state equilibration between the bulk of the antenna pigments and the reaction center occurs in less than 2 ps, that the primary charge separated state is populated in ∼4 ps, and that the charge stabilization by electron transfer is completed in ∼70 ps. Energy equilibration dynamics associated with the long wavelength absorbing/emitting forms harbored by the PSI external antenna are also characterized by a time mean lifetime of ∼75 ps, thus overlapping with radical pair charge stabilization reactions. Even in the presence of a kinetic bottleneck for energy equilibration, the excited state dynamics are shown to be principally trap-limited. However, direct excitation of the low energy chlorophyll forms is predicted to lengthen significantly (∼2-folds) the average trapping time.

Environment sensitive fluorescent analogue of biologically active oxazoles differentially recognizes human serum albumin and bovine serum albumin: Photophysical and molecular modeling studies.

PubMed

Maiti, Jyotirmay; Biswas, Suman; Chaudhuri, Ankur; Chakraborty, Sandipan; Chakraborty, Sibani; Das, Ranjan

2017-03-15

An environment sensitive fluorophore, 4-(5-(4-(dimethylamino)phenyl)oxazol-2-yl)benzoic acid (DMOBA), that closely mimics biologically active 2,5-disubstituited oxazoles has been designed to probe two homologous serum proteins, human serum albumin (HSA) and bovine serum albumin (BSA) by means of photophysical and molecular modeling studies. This fluorescent analogue exhibits solvent polarity sensitive fluorescence due to an intramolecular charge transfer in the excited state. In comparison to water, the steady state emission spectra of DMOBA in BSA is characterized by a greater blue shift (~10nm) and smaller Stokes' shift (~5980cm -1 ) in BSA than HSA (Stokes'shift~6600cm -1 ), indicating less polar and more hydrophobic environment of the dye in the former than the latter. The dye-protein binding interactions are remarkably stronger for BSA than HSA which is evident from higher value of the association constant for the DMOBA-BSA complex (K a ~5.2×10 6 M -1 ) than the DMOBA-HSA complex (K a ~1.0×10 6 M -1 ). Fӧrster resonance energy transfer studies revealed remarkably less efficient energy transfer (8%) between the donor tryptophans in BSA and the acceptor DMOBA dye than that (30%) between the single tryptophan moiety in HSA and the dye, which is consistent with a much larger distance between the donor (tryptophan)-acceptor (dye) pair in BSA (34.5Å) than HSA (25.4Å). Site specific competitive binding assays have confirmed on the location of the dye in Sudlow's site II of BSA and in Sudlow's site I of HSA, respectively. Molecular modeling studies have shown that the fluorescent analogue is tightly packed in the binding site of BSA due to strong steric complementarity, where, binding of DMOBA to BSA is primarily dictated by the van der Waals and hydrogen bonding interactions. In contrast, in HSA the steric complementarity is less significant and binding is primarily guided by polar interactions and van der Waals interactions appear to be less significant in the formation of the HSA-DMOBA complex. Electrostatic interactions contribute significantly in the binding of DMOBA to HSA (-2.09kcal/mol) compared to BSA (-0.47kcal/mol). Electrostatic surface potential calculation reveals that the DMOBA binding site within HSA is highly charged compared to BSA. Copyright © 2016 Elsevier B.V. All rights reserved.

Induction of chromosome aberrations in human cells by charged particles

NASA Technical Reports Server (NTRS)

Wu, H.; Durante, M.; George, K.; Yang, T. C.

1997-01-01

Chromosome aberrations induced by high-energy charged particles in normal human lymphocytes and human fibroblasts have been investigated. The charged particles included 250 MeV/nucleon protons, 290 MeV/nucleon carbon ions and 1 GeV/nucleon iron ions. The energies of the charged particles were higher than in most of the studies reported in the literature. Lymphocytes were stimulated to grow immediately after irradiation, while fibroblasts were incubated at 37 degrees C for 24 h for repair. Chromosomes were collected at the first mitosis after irradiation and chromosome aberrations were scored using the fluorescence in situ hybridization (FISH) technique with a whole-chromosome 4 probe. Chromosome aberrations were classified as reciprocal exchanges, incomplete exchanges, deletions and complex exchanges. The relative biological effectiveness (RBE) for each type of aberration was calculated by dividing a dose of 4 Gy by the dose of the charged particles producing the same effect as 4 Gy of gamma rays. Results of this study showed that complex aberrations have the highest RBE for radiation of high linear energy transfer (LET) for human lymphocytes, but for fibroblasts, the greatest effect was for incomplete exchanges. For both lymphocytes and fibroblasts, iron ions induced a similar fraction of aberrant cells.

Solute Dynamics In Liquid Systems: Experiments and Molecular Dynamics Simulations

NASA Astrophysics Data System (ADS)

Rumble, Christopher A.

This work reports on explorations into the effect of the liquid environment on the dynamics and kinetics of a range solute processes. The first study (Chapter 3) explores the photoisomerization of the rotor probe 9-(2-carboxy-2-cyanovinyl)julolidine, or CCVJ. Rotor probes are a class of fluorophores that undergo photo-induced isomerization reactions resulting in non-radiative relaxation out of the excited state. Literature reports had suggested that CCVJ exhibited a 'flow effect,' in which the emission intensity of CCVJ increases when the fluorophore solution is flowed at modest rates. Using steady-state and time-resolved fluorescence and 1H-NMR spectroscopy we show that the flow effect can be attributed to creation of a mixture of fluorescent and non-fluorescent CCVJ isomers by the excitation. The next study, Chapter 4, examines the the fluorescence of DNA G-quadruplex structures (GQSs), non-helical single-stranded DNA structures that exhibit quantum yields significantly higher than helical DNA or its constituent bases. By using a constant GQS core sequence we show that the addition of 'dangling' nucleotides can modulate emission from the GQS whereas conventional quenchers do not. The emission can also be altered by changes in temperature and addition of crowding reagents such as poly(ethylene glycol). Using time-resolved emission spectroscopy we show that GQS emission can be approximately dissected into two emitting populations with distinct kinetics. Chapters 5 and 6 report on the effects of solvation on charge transfer reactions in conventional molecular solvents and ionic liquid/conventional solvent mixtures. In Chapter 5 the excited state intramolecular proton transfer reaction of 40-N,N-diethylamino-3-hydroxyflavone (DEAHF) is studied using sub-picosecond Kerr-gated emission spectroscopy in mixtures of acetonitrile and propylene carbonate. Previous studies of DEAHF tautomerization had shown that the proton transfer rate and equilibrium constant are highly dependent on both solvation dynamics and solvent polarity. Using acetonitrile/propylene carbonate mixtures, which have nearly identical polarity but have solvation times that vary over an order of magnitude, we were able to demonstrate that fast solvation dynamics introduces a barrier to the reaction and slows down the proton transfer rate. In Chapter 6 the intramolecular electron transfer reaction of 9-(4-biphenyl)-10-methylacridinium (BPAc+) is studied in mixtures of an ionic liquid and acetonitrile. Using KGE and picosecond time-correlated single photon counting measurements we show that the BPAc+ electron transfer rate is highly correlated with the mixture solvation time, consistent with rates observed in conventional solvents. Finally, Chapters 7 and 8 are an exploration of solute rotational dynamics in ionic liquids (ILs). Solute rotations in these unique solvents have been shown to be non-diffusive and poorly predicted by hydrodynamic theories of friction. We set out to explore the mechanisms of solute rotation in ILs using a combination of experimental methods and molecular dynamics (MD) simulations. In Chapter 7 the rotational dynamics of benzene and the IL cation 1- ethyl-3-methylimidizolium are studied using a combination of 2H longitudinal spin relaxation (T1) measurements and MD simulations. Using the simulations for guidance, we were able to interpret T1 measurements outside of the extreme narrowing limit. After the realism of the simulations was validated, they were then used to show that benzene exhibits markedly different dynamics for 'spinning' about the C6 symmetry axis and 'tumbling' (rotation of the C6 axis), and that large amplitude jump motions and orientational caging are prominent features of benzene's rotations in ILs. Chapter 8 extends the benzene work to examine the effect of molecular size and charge distribution on solute rotational dynamics in ILs. Combining fluorescence anisotropy and T1 relaxation measurements with MD simulations of a carefully chosen set of probe molecules we show that molecular charge has only a modest effect of friction experienced by a rotating solute, whereas an increase in molecular size results in a substantial increase in rotation times. After validation of the simulations, we showed that large amplitude jumps and orientational caging dynamics, similar to what was observed with benzene, are also present in these solutes.

Multicolor fluorescence of a styrylquinoline dye tuned by metal cations.

PubMed

Shiraishi, Yasuhiro; Ichimura, Chizuru; Sumiya, Shigehiro; Hirai, Takayuki

2011-07-18

A styrylquinoline dye with a dipicolylamine (DPA) moiety (1) has been synthesized. The dye 1 in acetonitrile demonstrates multicolor fluorescence upon addition of different metal cations. Compound 1 shows a green fluorescence without cations. Coordination of 1 with Cd(2+) shows a blue emission, while with Hg(2+) and Pb(2+) exhibits yellow and orange emissions, respectively. The different fluorescence spectra are due to the change in intramolecular charge transfer (ICT) properties of 1 upon coordination with different cations. The DPA and quinoline moieties of 1 behave as the electron donor and acceptor units, respectively, and both units act as the coordination site for metal cations. Cd(2+) coordinates with the DPA unit. This reduces the donor ability of the unit and decreases the energy level of HOMO. This results in an increase in HOMO-LUMO gap and blue shifts the emission. Hg(2+) or Pb(2+) coordinate with both DPA and quinoline units. The coordination with the quinoline unit decreases the energy level of LUMO. This results in a decrease in HOMO-LUMO gap and red shifts the emission. Addition of two different metal cations successfully creates intermediate colors; in particular, the addition of Cd(2+) and Pb(2+) at once creates a bright white fluorescence. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

II-VI colloidal quantum-dot/quantum-rod heterostructures under electric field effect and their energy transfer rate to graphene

NASA Astrophysics Data System (ADS)

Zahra, H.; Elmaghroui, D.; Fezai, I.; Jaziri, S.

2016-11-01

We theoretically investigate the energy transfer between a CdSe/CdS Quantum-dot/Quantum-rod (QD/QR) core/shell structure and a weakly doped graphene layer, separated by a dielectric spacer. A numerical method assuming the realistic shape of the type I and quasi-type II CdSe/CdS QD/QR is developed in order to calculate their energy structure. An electric field is applied for both types to manipulate the carriers localization and the exciton energy. Our evaluation for the isolated QD/QR shows that a quantum confined Stark effect can be obtained with large negative electric filed while a small effect is observed with positive ones. Owing to the evolution of the carriers delocalization and their excitonic energy versus the electric field, both type I and quasi-type II QD/QR donors are suitable as sources of charge and energy. With a view to improve its absorption, the graphene sheet (acceptor) is placed at different distances from the QD/QR (donor). Using the random phase approximation and the massless Dirac Fermi approximation, the quenching rate integral is exactly evaluated. That reveals a high transfer rate that can be obtained with type I QD/QR with no dependence on the electric field. On the contrary, a high dependence is obtained for the quasi-type II donor and a high fluorescence rate from F = 80 kV/cm. Rather than the exciton energy, the transition dipole is found to be responsible for the evolution of the fluorescence rate. We find also that the fluorescence rate decreases with increasing the spacer thickness and shows a power low dependence. The QD/QR fluorescence quenching can be observed up to large distance which is estimated to be dependent only on the donor exciton energy.

A highly Selective Fluorescent Sensor for Monitoring Cu2+ Ion: Synthesis, Characterization and Photophysical Properties.

PubMed

Aderinto, Stephen Opeyemi; Xu, Yuling; Peng, Hongping; Wang, Fei; Wu, Huilu; Fan, Xuyang

2017-01-01

A new fluorescent sensor, 4-allylamine-N-(N-salicylidene)-1,8-naphthalimide (1), anchoring a naphthalimide moiety as fluorophore and a Schiff base group as receptor, was synthesized and characterized. The photophysical properties of sensor 1 were conducted in organic solvents of different polarities. Our study revealed that, depending on the solvent polarity, the fluorescence quantum yields varied from 0.59 to 0.89. The fluorescent activity of the sensor was monitored and the sensor was consequently applied for the detection of Cu 2+ with high selectivity over various metal ions by fluorescence quenching in Tris-HCl (pH = 7.2) buffer/DMF (1:1, v/v) solution. From the binding stoichiometry, it was indicated that a 1:1 complex was formed between Cu 2+ and the sensor 1. The fluorescence intensity was linear with Cu 2+ in the concentration range 0.5-5 μM. Moreso, the detection limit was calculated to be 0.32 μM, which is sufficiently low for good sensitivity of Cu 2+ ion. The binding mode was due to the intramolecular charge transfer (ICT) and the coordination of Cu 2+ with C = N and hydroxyl oxygen groups of the sensor 1. The sensor proved effective for Cu 2+ monitoring in real water samples with recovery rates of 95-112.6 % obtained.

Alkynyl-naphthalimide Fluorophores: Gold Coordination Chemistry and Cellular Imaging Applications.

PubMed

Langdon-Jones, Emily E; Lloyd, David; Hayes, Anthony J; Wainwright, Shane D; Mottram, Huw J; Coles, Simon J; Horton, Peter N; Pope, Simon J A

2015-07-06

A range of fluorescent alkynyl-naphthalimide fluorophores has been synthesized and their photophysical properties examined. The fluorescent ligands are based upon a 4-substituted 1,8-naphthalimide core and incorporate structural variations (at the 4-position) to tune the amphiphilic character: chloro (L1), 4-[2-(2-aminoethoxy)ethanol] (L2), 4-[2-(2-methoxyethoxy)ethylamino] (L3), piperidine (L4), morpholine (L5), 4-methylpiperidine (L6), and 4-piperidone ethylene ketal (L7) variants. The amino-substituted species (L2-L7) are fluorescent in the visible region at around 517-535 nm through a naphthalimide-localized intramolecular charge transfer (ICT), with appreciable Stokes' shifts of ca. 6500 cm(-1) and lifetimes up to 10.4 ns. Corresponding two-coordinate Au(I) complexes [Au(L)(PPh3)] were isolated, with X-ray structural studies revealing the expected coordination mode via the alkyne donor. The Au(I) complexes retain the visible fluorescence associated with the coordinated alkynyl-naphthalimide ligand. The ligands and complexes were investigated for their cytotoxicity across a range of cell lines (LOVO, MCF-7, A549, PC3, HEK) and their potential as cell imaging agents for HEK (human embryonic kidney) cells and Spironucleus vortens using confocal fluorescence microscopy. The images reveal that these fluorophores are highly compatible with fluorescence microscopy and show some clear intracellular localization patterns that are dependent upon the specific nature of the naphthalimide substituent.

Multiple Surface Regions on the Niemann-Pick C2 Protein Facilitate Intracellular Cholesterol Transport.

PubMed

McCauliff, Leslie A; Xu, Zhi; Li, Ran; Kodukula, Sarala; Ko, Dennis C; Scott, Matthew P; Kahn, Peter C; Storch, Judith

2015-11-06

The cholesterol storage disorder Niemann-Pick type C (NPC) disease is caused by defects in either of two late endosomal/lysosomal proteins, NPC1 and NPC2. NPC2 is a 16-kDa soluble protein that binds cholesterol in a 1:1 stoichiometry and can transfer cholesterol between membranes by a mechanism that involves protein-membrane interactions. To examine the structural basis of NPC2 function in cholesterol trafficking, a series of point mutations were generated across the surface of the protein. Several NPC2 mutants exhibited deficient sterol transport properties in a set of fluorescence-based assays. Notably, these mutants were also unable to promote egress of accumulated intracellular cholesterol from npc2(-/-) fibroblasts. The mutations mapped to several regions on the protein surface, suggesting that NPC2 can bind to more than one membrane simultaneously. Indeed, we have previously demonstrated that WT NPC2 promotes vesicle-vesicle interactions. These interactions were abrogated, however, by mutations causing defective sterol transfer properties. Molecular modeling shows that NPC2 is highly plastic, with several intense positively charged regions across the surface that could interact favorably with negatively charged membrane phospholipids. The point mutations generated in this study caused changes in NPC2 surface charge distribution with minimal conformational changes. The plasticity, coupled with membrane flexibility, probably allows for multiple cholesterol transfer routes. Thus, we hypothesize that, in part, NPC2 rapidly traffics cholesterol between closely appositioned membranes within the multilamellar interior of late endosomal/lysosomal proteins, ultimately effecting cholesterol egress from this compartment. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

Coulomb repulsion in short polypeptides.

PubMed

Norouzy, Amir; Assaf, Khaleel I; Zhang, Shuai; Jacob, Maik H; Nau, Werner M

2015-01-08

Coulomb repulsion between like-charged side chains is presently viewed as a major force that impacts the biological activity of intrinsically disordered polypeptides (IDPs) by determining their spatial dimensions. We investigated short synthetic models of IDPs, purely composed of ionizable amino acid residues and therefore expected to display an extreme structural and dynamic response to pH variation. Two synergistic, custom-made, time-resolved fluorescence methods were applied in tandem to study the structure and dynamics of the acidic and basic hexapeptides Asp6, Glu6, Arg6, Lys6, and His6 between pH 1 and 12. (i) End-to-end distances were obtained from the short-distance Förster resonance energy transfer (sdFRET) from N-terminal 5-fluoro-l-tryptophan (FTrp) to C-terminal Dbo. (ii) End-to-end collision rates were obtained for the same peptides from the collision-induced fluorescence quenching (CIFQ) of Dbo by FTrp. Unexpectedly, the very high increase of charge density at elevated pH had no dynamical or conformational consequence in the anionic chains, neither in the absence nor in the presence of salt, in conflict with the common view and in partial conflict with accompanying molecular dynamics simulations. In contrast, the cationic peptides responded to ionization but with surprising patterns that mirrored the rich individual characteristics of each side chain type. The contrasting results had to be interpreted, by considering salt screening experiments, N-terminal acetylation, and simulations, in terms of an interplay of local dielectric constant and peptide-length dependent side chain charge-charge repulsion, side chain functional group solvation, N-terminal and side chain charge-charge repulsion, and side chain-side chain as well as side chain-backbone interactions. The common picture that emerged is that Coulomb repulsion between water-solvated side chains is efficiently quenched in short peptides as long as side chains are not in direct contact with each other or the main chain.

Charge transfer in TATB and HMX under extreme conditions.

PubMed

Zhang, Chaoyang; Ma, Yu; Jiang, Daojian

2012-11-01

Charge transfer is usually accompanied by structural changes in materials under different conditions. However, the charge transfer in energetic materials that are subjected to extreme conditions has seldom been explored by researchers. In the work described here, the charge transfer in single molecules and unit cells of the explosives TATB and HMX under high temperatures and high pressures was investigated by performing static and dynamic calculations using three DFT methods, including the PWC functional of LDA, and the BLYP and PBE functionals of GGA. The results showed that negative charge is transferred from the nitro groups of molecular or crystalline TATB and HMX when they are heated. All DFT calculations for the compressed TATB unit cell indicate that, generally, negative charge transfer occurs to its nitro groups as the compression increases. PWC and PBE calculations for crystalline HMX show that negative charge is first transferred to the nitro groups but, as the compression increases, the negative charge is transferred from the nitro groups. However, the BLYP calculations indicated that there was gradual negative charge transfer to the nitro groups of HMX, similar to the case for TATB. The unrelaxed state of the uniformly compressed TATB causes negative charge to be transferred from its nitro groups, in contrast to what is seen in the relaxed state. Charge transfer in TATB is predicted to occur much more easily than in HMX.

Ultrafast spectroscopic investigation of a fullerene poly(3-hexylthiophene) dyad

NASA Astrophysics Data System (ADS)

Banerji, Natalie; Seifter, Jason; Wang, Mingfeng; Vauthey, Eric; Wudl, Fred; Heeger, Alan J.

2011-08-01

We present the femtosecond spectroscopic investigation of a covalently linked dyad, PCB-P3HT, formed by a segment of the conjugated polymer P3HT (regioregular poly(3-hexylthiophene)) that is end capped with the fullerene derivative PCB ([6,6]-phenyl-C61-butyric acid ester), adapted from PCBM. The fluorescence of the P3HT segment in tetrahydrofuran (THF) solution is reduced by 64% in the dyad compared to a control compound without attached fullerene (P3HT-OH). Fluorescence upconversion measurements reveal that the partial fluorescence quenching of PCB-P3HT in THF is multiphasic and occurs on an average time scale of 100 ps, in parallel to excited-state relaxation processes. Judging from ultrafast transient absorption experiments, the origin of the quenching is excitation energy transfer from the P3HT donor to the PCB acceptor. Due to the much higher solubility of P3HT compared to PCB in THF, the PCB-P3HT dyad molecules self-assemble into micelles. When pure C60 is added to the solution, it is incorporated into the fullerene-rich center of the micelles. This dramatically increases the solubility of C60 but does not lead to significant additional quenching of the P3HT fluorescence by the C60 contained in the micelles. In PCB-P3HT thin films drop-cast from THF, the micelle structure is conserved. In contrast to solution, quantitative and ultrafast (<150 fs) charge separation occurs in the solid-state films and leads to the formation of long-lived mobile charge carriers with characteristic transient absorption signatures similar to those that have been observed in P3HT:PCBM bulk heterojunction blends. While π-stacking interactions between neighboring P3HT chains are weak in the micelles, they are strong in thin films drop-cast from ortho-dichlorobenzene. Here, PCB-P3HT self-assembles into a network of long fibers, clearly seen in atomic force microscopy images. Ultrafast charge separation occurs also for the fibrous morphology, but the transient absorption experiments show fast loss of part of the charge carriers due to intensity-induced recombination and annihilation processes and monomolecular interfacial trap-mediated or geminate recombination. The yield of the long-lived charge carriers in the highly organized fibers is however comparable to that obtained with annealed P3HT:PCBM blends. PCB-P3HT can therefore be considered as an active material in organic photovoltaic devices.

Ultrafast fluorescence upconversion technique and its applications to proteins.

PubMed

Chosrowjan, Haik; Taniguchi, Seiji; Tanaka, Fumio

2015-08-01

The basic principles and main characteristics of the ultrafast time-resolved fluorescence upconversion technique (conventional and space-resolved), including requirements for nonlinear crystals, mixing spectral bandwidth, acceptance angle, etc., are presented. Applications to flavoproteins [wild-type (WT) FMN-binding protein and its W32Y, W32A, E13R, E13K, E13Q and E13T mutants] and photoresponsive proteins [WT photoactive yellow protein and its R52Q mutant in solution and as single crystals] are demonstrated. For flavoproteins, investigations elucidating the effects of ionic charges on ultrafast electron transfer (ET) dynamics are summarized. It is shown that replacement of the ionic amino acid Glu13 and the resulting modification of the electrostatic charge distribution in the protein chromphore-binding pocket substantially alters the ultrafast fluorescence quenching dynamics and ET rate in FMN-binding protein. It is concluded that, together with donor-acceptor distances, electrostatic interactions between ionic photoproducts and other ionic groups in the proteins are important factors influencing the ET rates. In WT photoactive yellow protein and the R52Q mutant, ultrafast photoisomerization dynamics of the chromophore (deprotonated trans-p-coumaric acid) in liquid and crystal phases are investigated. It is shown that the primary dynamics in solution and single-crystal phases are quite similar; hence, the photocycle dynamics and structural differences observed at longer time scales arise mostly from the structural restraints imposed by the crystal lattice rigidity versus the flexibility in solution. © 2014 FEBS.

Molecular control of pentacene/ZnO photoinduced charge transfer

NASA Astrophysics Data System (ADS)

Spalenka, Josef W.; Paoprasert, Peerasak; Franking, Ryan; Hamers, Robert J.; Gopalan, Padma; Evans, Paul G.

2011-03-01

Photoinduced charge transfer modifies the device properties of illuminated pentacene field effect transistors (FETs) incorporating ZnO quantum dots at the gate insulator/pentacene interface. The transferred charge is trapped on electronic states associated with the ZnO quantum dots, with a steady state population approximately proportional to the rate of organic-inorganic charge transfer. Trapped charge shifts the threshold voltage of the FETs, providing the means to evaluate the rate of organic/inorganic charge transfer and the effects of interface modification. Monolayers of the wide-gap alkane stearic acid and the conjugated oligomer terthiophene attached to the ZnO suppress or permit charge transfer, respectively.

Transient absorption spectroscopy of a monofullerene C60-bis-(pyropheophorbide a) molecular system in polar and nonpolar environments

NASA Astrophysics Data System (ADS)

Al Omari, S.; Ermilov, E. A.; Helmreich, M.; Jux, N.; Hirsch, A.; Röder, B.

2004-09-01

The population dynamics of the excited and ground states of the monofullerene-bis (pyropheophorbide a) complex (FP1) were studied in polar (DMF) and nonpolar (toluene) solvents using picosecond transient absorption techniques. A strong quenching of the fluorescence signal of FP1 was observed in both solvents, in comparison to the fluorescence of bis (pyropheophorbide a) (P2). This quenching is due to an intramolecular photoinduced electron transfer from the pyropheophorbide a (pyroPheo) moiety to the fullerene C60 monoadduct. In DMF the charge-separated (CS) state of FP1 has a lifetime of 0.32 ns and undergoes a direct transition to the ground state, resulting in a very low value of photosensitised singlet oxygen generation. In toluene, energy transfer from the first excited triplet state of pyroPheo, which has been populated via relaxation of the CS state, generates a considerable amount of singlet oxygen. The lifetime of the CS state in the nonpolar solvent was estimated to be 0.29 ns. It was also shown that in both DMF and toluene the first excited singlet state as well as the triplet state of the fullerene moiety in FP1 are not occupied.

Novel multistep BRET-FRET energy transfer using nanoconjugates of firefly proteins, quantum dots, and red fluorescent proteins

NASA Astrophysics Data System (ADS)

Alam, Rabeka; Zylstra, Joshua; Fontaine, Danielle M.; Branchini, Bruce R.; Maye, Mathew M.

2013-05-01

Sequential bioluminescence resonance energy transfer (BRET) and fluorescence resonance energy transfer (FRET) from firefly luciferase to red fluorescent proteins using quantum dot or rod acceptor/donor linkers is described. The effect of morphology and tuned optical properties on the efficiency of this unique BRET-FRET system was evaluated.Sequential bioluminescence resonance energy transfer (BRET) and fluorescence resonance energy transfer (FRET) from firefly luciferase to red fluorescent proteins using quantum dot or rod acceptor/donor linkers is described. The effect of morphology and tuned optical properties on the efficiency of this unique BRET-FRET system was evaluated. Electronic supplementary information (ESI) available: Experimental details, Fig. S1 and Table S1-S4. See DOI: 10.1039/c3nr01842c

Synthesis of TiO2-poly(3-hexylthiophene) hybrid particles through surface-initiated Kumada catalyst-transfer polycondensation.

PubMed

Boon, Florian; Moerman, David; Laurencin, Danielle; Richeter, Sébastien; Guari, Yannick; Mehdi, Ahmad; Dubois, Philippe; Lazzaroni, Roberto; Clément, Sébastien

2014-09-30

TiO2/conjugated polymers are promising materials in solar energy conversion where efficient photoinduced charge transfers are required. Here, a "grafting-from" approach for the synthesis of TiO2 nanoparticles supported with conjugated polymer brushes is presented. Poly(3-hexylthiophene) (P3HT), a benchmark material for organic electronics, was selectively grown from TiO2 nanoparticles by surface-initiated Kumada catalyst-transfer polycondensation. The grafting of the polymer onto the surface of the TiO2 nanoparticles by this method was demonstrated by (1)H and (13)C solid-state NMR, X-ray photoelectron spectrometry, thermogravimetric analysis, transmission electron microscopy, and UV-visible spectroscopy. Sedimentation tests in tetrahydrofuran revealed improved dispersion stability for the TiO2@P3HT hybrid material. Films were produced by solvent casting, and the quality of the dispersion of the modified TiO2 nanoparticles was evaluated by atomic force microscopy. The dispersion of the P3HT-coated TiO2 NPs in the P3HT matrix was found to be homogeneous, and the fibrillar structure of the P3HT matrix was maintained which is favorable for charge transport. Fluorescence quenching measurements on these hybrid materials in CHCl3 indicated improved photoinduced electron-transfer efficiency. All in all, better physicochemical properties for P3HT/TiO2 hybrid material were reached via the surface-initiated "grafted-from" approach compared to the "grafting-onto" approach.

Photosynthetic antenna-reaction center mimicry with a covalently linked monostyryl boron-dipyrromethene-aza-boron-dipyrromethene-C60 triad.

PubMed

Shi, Wen-Jing; El-Khouly, Mohamed E; Ohkubo, Kei; Fukuzumi, Shunichi; Ng, Dennis K P

2013-08-19

An efficient functional mimic of the photosynthetic antenna-reaction center has been designed and synthesized. The model contains a near-infrared-absorbing aza-boron-dipyrromethene (ADP) that is connected to a monostyryl boron-dipyrromethene (BDP) by a click reaction and to a fullerene (C60 ) using the Prato reaction. The intramolecular photoinduced energy and electron-transfer processes of this triad as well as the corresponding dyads BDP-ADP and ADP-C60 have been studied with steady-state and time-resolved absorption and fluorescence spectroscopic methods in benzonitrile. Upon excitation, the BDP moiety of the triad is significantly quenched due to energy transfer to the ADP core, which subsequently transfers an electron to the fullerene unit. Cyclic and differential pulse voltammetric studies have revealed the redox states of the components, which allow estimation of the energies of the charge-separated states. Such calculations show that electron transfer from the singlet excited ADP ((1) ADP*) to C60 yielding ADP(.+) -C60 (.-) is energetically favorable. By using femtosecond laser flash photolysis, concrete evidence has been obtained for the occurrence of energy transfer from (1) BDP* to ADP in the dyad BDP-ADP and electron transfer from (1) ADP* to C60 in the dyad ADP-C60 . Sequential energy and electron transfer have also been clearly observed in the triad BDP-ADP-C60 . By monitoring the rise of ADP emission, it has been found that the rate of energy transfer is fast (≈10(11)  s(-1) ). The dynamics of electron transfer through (1) ADP* has also been studied by monitoring the formation of C60 radical anion at 1000 nm. A fast charge-separation process from (1) ADP* to C60 has been detected, which gives the relatively long-lived BDP-ADP(.+) C60 (.-) with a lifetime of 1.47 ns. As shown by nanosecond transient absorption measurements, the charge-separated state decays slowly to populate mainly the triplet state of ADP before returning to the ground state. These findings show that the dyads BDP-ADP and ADP-C60 , and the triad BDP-ADP-C60 are interesting artificial analogues that can mimic the antenna and reaction center of the natural photosynthetic systems. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Noncharged and Charged Monodendronised Perylene Bisimides as Highly Fluorescent Labels and their Bioconjugates.

PubMed

Huth, Katharina; Heek, Timm; Achazi, Katharina; Kühne, Christian; Urner, Leonhard H; Pagel, Kevin; Dernedde, Jens; Haag, Rainer

2017-04-06

A series of water-soluble, hydroxylated and sulphated, polyglycerol (PG) dendronised, monofunctional perylene bisimides (PBIs) were synthesised in three generations. Their photophysical properties were determined by absorption and emission spectroscopy and their suitability as potential biolabels examined by biological in vitro studies after bioconjugation. It could be shown that the photophysical properties of the PBI labels can be improved by increasing the sterical demand and ionic charge of the attached dendron. Thereby, charged labels show superior suppression of aggregation over charge neutral labels owing to electrostatic repulsion forces on the PG-dendron. The ionic charges also enabled a reduction in dendron generation while retaining the labels' outstanding fluorescence quantum yields (FQYs) up to 100 %. These core-unsubstituted perylene derivatives were successfully applied as fluorescent labels upon bioconjugation to the therapeutic antibody cetuximab. The dye-antibody conjugates showed a strongly enhanced aggregation tendency compared to the corresponding free dyes. Biological evaluation by receptor-binding, cellular uptake, and cytotoxicity studies revealed that labelling did not affect the antibody's function, which renders the noncharged and charged dendronised PBIs suitable candidates as fluorescent labels in biological imaging. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Subtle spectral effects accompanying the assembly of bacteriochlorophylls into cyclic light harvesting complexes revealed by high-resolution fluorescence spectroscopy

NASA Astrophysics Data System (ADS)

Rätsep, Margus; Pajusalu, Mihkel; Linnanto, Juha Matti; Freiberg, Arvi

2014-10-01

We have observed that an assembly of the bacteriochloropyll a molecules into B850 and B875 groups of cyclic bacterial light-harvesting complexes LH2 and LH1, respectively, results an almost total loss of the intra-molecular vibronic structure in the fluorescence spectrum, and simultaneously, an essential enhancement of its phonon sideband due to electron-phonon coupling. While the suppression of the vibronic coupling in delocalized (excitonic) molecular systems is predictable, as also confirmed by our model calculations, a boost of the electron-phonon coupling is rather unexpected. The latter phenomenon is explained by exciton self-trapping, promoted by mixing the molecular exciton states with charge transfer states between the adjacent chromophores in the tightly packed B850 and B875 arrangements. Similar, although less dramatic trends were noted for the light-harvesting complexes containing chlorophyll pigments.

A DFT Study of Pyrrole-Isoxazole Derivatives as Chemosensors for Fluoride Anion

PubMed Central

Jin, Ruifa; Sun, Weidong; Tang, Shanshan

2012-01-01

The interactions between chemosensors, 3-amino-5-(4,5,6,7-tetrahydro-1H-indol-2-yl)isoxazole-4-carboxamide (AIC) derivatives, and different anions (F− Cl−, Br−, AcO−, and H2PO4−) have been theoretically investigated using DFT approaches. It turned out that the unique selectivity of AIC derivatives for F− is ascribed to their ability of deprotonating the host sensors. Frontier molecular orbital (FMO) analyses have shown that the vertical electronic transitions of absorption and emission for the sensing signals are characterized as intramolecular charge transfer (ICT). The study of substituent effects suggests that all the substituted derivatives are expected to be promising candidates for fluoride chemosensors both in UV-vis and fluorescence spectra except for derivative with benzo[d]thieno[3,2-b]thiophene fragment that can serve as ratiometric fluorescent fluoride chemosensor only. PMID:23109833

Photophysical Diversity of Water-Soluble Fluorescent Conjugated Polymers Induced by Surfactant Stabilizers for Rapid and Highly Selective Determination of 2,4,6-Trinitrotoluene Traces.

PubMed

Alizadeh, Naader; Akbarinejad, Alireza; Ghoorchian, Arash

2016-09-21

The increasing application of fluorescence spectroscopy in development of reliable sensing platforms has triggered a lot of research interest for the synthesis of advanced fluorescent materials. Herein, we report a simple, low-cost strategy for the synthesis of a series of water-soluble conjugated polymer nanoparticles with diverse emission range using cationic (hexadecyltrimethylammonium bromide, CTAB), anionic (sodium dodecylbenzenesulfonate, SDBS), and nonionic (TX114) surfactants as the stabilizing agents. The role of surfactant type on the photophisical and sensing properties of resultant polymers has been investigated using dynamic light scattering (DLS), FT-IR, UV-vis, fluorescence, and energy dispersive X-ray (EDS) spectroscopies. The results show that the surface polarity, size, and spectroscopic and sensing properties of conjugated polymers could be well controlled by the proper selection of the stabilizer type. The fluorescent conjugated polymers exhibited fluorescence quenching toward nitroaromatic compounds. Further studies on the fluorescence properties of conjugated polymers revealed that the emission of the SDBS stabilized polymer, N-methylpolypyrrole-SDBS (NMPPY-SDBS), is strongly quenched by 2,4,6-trinitrotoluene molecule with a large Stern -Volmer constant of 59 526 M(-1) and an excellent detection limit of 100 nM. UV-vis and cyclic voltammetry measurements unveiled that fluorescence quenching occurs through a charge transfer mechanism between electron rich NMPPY-SDBS and electron deficient 2,4,6-trinitrotoluene molecules. Finally, the as-prepared conjugated polymer and approach were successfully applied to the determination of 2,4,6-trinitrotoluene in real water samples.

Coordination-Driven Self-Assembly of M3L2 Trigonal Cages from Pre-organized Metalloligands Incorporating Octahedral Metal Centers and Fluorescent Detection of Nitroaromatics

PubMed Central

Wang, Ming; Vajpayee, Vaishali; Shanmugaraju, Sankarasekaran; Zheng, Yao-Rong; Zhao, Zhigang; Kim, Hyunuk

2011-01-01

The design and preparation of novel M3L2 trigonal cages via coordination-driven self-assembly of pre-organized metalloligands containing octahedral aluminum(III), gallium(III), or ruthenium(II) centers is described. By employing tritopic or dinuclear linear metalloligands and appropriate complementary subunits, M3L2 trigonal-bipyramidal and trigonal prismatic cages are self-assembled under mild conditions. These 3-D cages were characterized with multinuclear NMR spectroscopy (1H and 31P) and high-resolution electronic spray mass spectrometry (HR-ESI-MS). The structure of one such trigonal prismatic cage, self-assembled from an arene ruthenium metalloligand, was confirmed via single-crystal X-ray crystallography. The fluorescent nature of these prisms, due to the presence of their electron-rich ethynyl functionalities, prompted photophysical studies which revealed that electron-deficient nitroaromatics are effective quenchers of the cages' emission. Excited state charge transfer from the prisms to the nitroaromatic substrates can be used as the basis for developing selective and discriminatory turn-off fluorescent sensors for nitroaromatics. PMID:21214171

Dynamics of charge-transfer excitons in type-II semiconductor heterostructures

NASA Astrophysics Data System (ADS)

Stein, M.; Lammers, C.; Richter, P.-H.; Fuchs, C.; Stolz, W.; Koch, M.; Vänskä, O.; Weseloh, M. J.; Kira, M.; Koch, S. W.

2018-03-01

The formation, decay, and coherence properties of charge-transfer excitons in semiconductor heterostructures are investigated by applying four-wave-mixing and terahertz spectroscopy in combination with a predictive microscopic theory. A charge-transfer process is identified where the optically induced coherences decay directly into a charge-transfer electron-hole plasma and exciton states. It is shown that charge-transfer excitons are more sensitive to the fermionic electron-hole substructure than regular excitons.

Comprehensive investigation of the excited-state dynamics of push-pull triphenylamine dyes as models for photonic applications.

PubMed

Ishow, Eléna; Clavier, Gilles; Miomandre, Fabien; Rebarz, Mateusz; Buntinx, Guy; Poizat, Olivier

2013-09-07

A series of emitting push-pull triarylamine derivatives, models of their widely used homologues in photonics and organic electronics, was investigated by steady-state and time-resolved spectroscopy. Their structural originality stems from the sole change of the electron-withdrawing substituent X (-H: 1, -CN: 2, -NO2: 3, -CHC(CN)2: 4), giving rise to efficient emission tuning from blue to red upon increasing the X electron-withdrawing character. All compounds are highly fluorescent in alkanes. The more polar compounds 2-4 undergo considerable Stokes shift and emission quenching in polar solvents. Femtosecond transient absorption data allowed us to identify the nature of the emissive state which varies as a function of the compound and surrounding polarity. A long-lived ππ* excited state with weak charge transfer character was found for 1. This excited state evolves into a long-lived ICT state with red-shifted emission for 2 in polar solvents. For 3 and 4, the ICT state is directly populated in all solvents. Long-lived and emissive in n-hexane, it relaxes in toluene to a new ICT' conformation with stronger charge transfer character and enhanced Stokes shift. In more polar THF, ethanol, and nitrile solvents, ICT relaxes to a dark excited state ICT'' with viscosity-dependent kinetics (<10 ps). The ICT'' state lifetime drops with increasing solvent polarity (150 ps for 3 in THF, 8.5 ps in butyronitrile, 1.9 ps in acetonitrile), denoting an efficient radiationless deactivation to the ground state (back charge transfer). This result reveals a very small S0-S1 energy gap at the relaxed ICT'' geometry, with a possible close-lying S0-S1 conical intersection, which suggests that the ICT → ICT'' process results from a structural change involving a large-amplitude molecular distortion. This fast structural change can account for the strong fluorescence quenching observed for 3 and 4 in polar solvents. Finally, the magnitude of intersystem crossing between the singlet and triplet excited states largely depends on the electron-deficient X unit and the solvent itself. These observations help one conclude on the prevailing role played by the electron-withdrawing groups and the surrounding polarity in the photophysical performances of triphenylamine derivatives, largely employed in numerous emissive solid-state devices.

Organic photochemical storage of solar energy. Progress report, February 1, 1979-January 31, 1980

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, G. II

1980-02-01

Study of valence isomerization of organic compounds has focused on two mechanisms of photosensitization involving either electron donor-acceptor interaction or energy transfer. The quenching of fluorescent sensitizers by isomerizable substrates results in the formation of excited complexes. These sensitizer-substrate pairs are highly polarized, leading to changes in bond order for the substrates. For several substrates such as quadricyclene, hexamethyldewarbenzene, and a nonbornadiene derivative, this perturbation results in efficient valence isomerization. Isomerization observed on irradiation of charge transfer complexes of isomerizable substrates is consistent with a similar exciplex - template mechanism. The energy transfer mechanism of photosensitization has been studied bymore » measuring the temperature dependence of quantum yield for isomerization of dimethyl norbornadiene-2,3-dicarboxylate sensitized by benzanthrone. From temperature and quencher concentration profiles quenching constants have been obtained which are consistent with an endoergic triplet energy transfer mechanism. The thermal upconversion of the low energy triplet of benzanthrone results in a threefold increase in isomerization quantum yield over a 90/sup 0/ temperature range.« less

Forster resonance energy transfer in the system of human serum albumin-xanthene dyes

NASA Astrophysics Data System (ADS)

Kochubey, V. I.; Pravdin, A. B.; Melnikov, A. G.; Konstantinova, I.; Alonova, I. V.

2016-04-01

The processes of interaction of fluorescent probes: eosin and erythrosine with human serum albumin (HSA) were studied by the methods of absorption and fluorescence spectroscopy. Extinction coefficients of probes were determined. Critical transfer radius and the energy transfer efficiency were defined by fluorescence quenching of HSA. Analysis of the excitation spectra of HSA revealed that the energy transfer process is carried out mainly between tryptophanyl and probes.

Twisted intramolecular charge transfer investigation of semi organic L-Glutamic acid hydrochloride single crystal for organic light-emitting and optical limiting applications

NASA Astrophysics Data System (ADS)

Joy, Lija K.; George, Merin; Alex, Javeesh; Aravind, Arun; Sajan, D.; Vinitha, G.

2018-03-01

Single crystals of L-Glutamic acid hydrochloride (LGHCl) were grown by slow evaporation solution technique and good crystalline perfection was confirmed by Powder X-ray diffraction studies. The complete vibrational studies of the compound were analyzed by FT-IR, FT-Raman and UV-visible spectra combined with Normal Coordinate Analysis (NCA) following the scaled quantum mechanical force field methodology and density functional theory (DFT). Twisted Intramolecular Charge Transfer (ICT) occurs due to the presence of strong ionic intra-molecular Nsbnd H⋯O hydrogen bonding was confirmed by Hirshfeld Surface analysis. The existence of intermolecular Nsbnd H⋯Cl hydrogen bonds due to the interaction between the lone pair of oxygen with the antibonding orbital was established by NBO analysis. The Z-scan result indicated that the title molecule exhibits saturable absorption behavior. The attractive third-order nonlinear properties suggest that LGHCl can be a promising candidate for the design and development devices for optical limiting applications. LGHCL exhibits distinct emission in the blue region of the fluorescence lifetime which proves to be a potential candidate for blue- Organic light-emitting diodes (OLEDs) fabrication.

Synthesis and property of solvatochromic fluorophore based on D-pi-A molecular system: 2-[[3-cyano-4-(N-ethyl-N-(2-hydroxyethyl)amino)styryl]-5,5-dimethylfuran-2(5H)-ylidene]malononitrile dye.

PubMed

Son, Young-A; Gwon, Seon-Yeong; Lee, Sue-Yoen; Kim, Sung-Hoon

2010-01-01

2-[[3-Cyano-4-(N-ethyl-N-(2-hydroxyethyl)amino)styryl]-5,5-dimethylfuran-2(5H)-ylidene]malononitrile styryl dye was prepared by the condensation of 4-[(2-hydroxy-ethyl)-methyl-amino]-benzaldehyde (donor moiety) with 2-cyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (acceptor moiety). The corresponding design, synthesis and solvatochromic characteristics of the intramolecular charge-transfer (ICT) dye chromophore were discussed and determined. Optical properties such as absorption and fluorescence emission spectra were monitored in several solvent media with different polarity. In this determination, the prepared dye chromophore showed positive solvatochromism effect and the resulting solvatochromic characteristics were studied with semiempirical calculations. The energy potentials of this dye chromophore such as HOMO and LUMO values were calculated by computational simulation approaches using Material Studio 4.3. Furthermore, the functions as a molecular switching sensor with pH stimulation of alkali-acid addition were determined in DMSO, which was operated by deprotonation/protonation effects based on intramolecular charge-transfer system. Copyright 2009 Elsevier B.V. All rights reserved.

Donor-acceptor-donor thienyl/bithienyl-benzothiadiazole/quinoxaline model oligomers: experimental and theoretical studies.

PubMed

Pina, João; de Melo, J Seixas; Breusov, D; Scherf, Ullrich

2013-09-28

A comprehensive spectral and photophysical investigation of four donor-acceptor-donor (DAD) oligomers consisting of electron-deficient 2,1,3-benzothiadiazole or quinoxaline moieties linked to electron-rich thienyl or bithienyl units has been undertaken. Additionally, a bis(dithienyl) substituted naphthalene was also investigated. The D-A-D nature of these oligomers resulted in the presence of an intramolecular charge transfer (ICT) state, which was further substantiated by solvatochromism studies (analysis with the Lippert-Mataga formalism). Hereby, significant differences have been obtained for the fluorescence quantum yields of the oligomers in the non-polar solvent methylcyclohexane vs. the polar ethanol. The study was further complemented with the determination of the optimized ground-state molecular geometries for the oligomers together with the prediction of the lowest vertical one-electron excitation energy and the relevant molecular orbital contours using DFT calculations. The electronic transitions show a clear HOMO to LUMO charge-transfer character. In contrast to the thiophene oligomers (the oligothiophenes with n = 1-7), where the intersystem crossing (ISC) yield decreases with n, the studied DAD oligomers were found to show an increase in the ISC efficiency with the number of (donor) thienyl units.

Evaluation of the Intramolecular Charge-Transfer Properties in Solvatochromic and Electrochromic Zinc Octa(carbazolyl)phthalocyanines.

PubMed

Majeed, Shereen A; Ghazal, Basma; Nevonen, Dustin E; Goff, Philip C; Blank, David A; Nemykin, Victor N; Makhseed, Saad

2017-10-02

2,3,9,10,16,17,23·24-Octakis-(9H-carbazol-9-yl) phthalocyaninato zinc(II) (3) and 2,3,9,10,16,17,23·24-octakis-(3,6-di-tert-butyl-9H-carbazole) phthalocyaninato zinc(II) (4) complexes were prepared and characterized by NMR and UV-vis spectroscopies, magnetic circular dichroism (MCD), matrix-assisted laser desorption ionization mass spectrometry, and X-ray crystallography. UV-vis and MCD data are indicative of the interligand charge-transfer nature of the broad band observed in 450-500 nm range for 3 and 4. The redox properties of 3 and 4 were probed by electrochemical and spectro-electrochemical methods, which are suggestive of phthalocyanine-centered first oxidation and reduction processes. Photophysics of 3 and 4 were investigated by steady-state fluorescence and time-resolved transient absorption spectroscopy demonstrating the influence of the carbazole substituents on deactivation from the first excited state in 3 and 4. Protonation of the meso-nitrogen atoms in 3 results in much faster deactivation kinetics from the first excited state. Spectroscopic data were correlated with density functional theory (DFT) and time-dependent DFT calculations on 3 and 4.

Optical properties of humic substances and CDOM: effects of borohydride reduction.

PubMed

Ma, Jiahai; Del Vecchio, Rossana; Golanoski, Kelli S; Boyle, Erin S; Blough, Neil V

2010-07-15

Treatment of Suwanee River humic (SRHA) and fulvic (SRFA) acids, a commercial lignin (LAC), and a series of solid phase extracts (C18) from the Middle Atlantic Bight (MAB extracts) with sodium borohydride (NaBH(4)), a selective reductant of carbonyl-containing compounds including quinones and aromatic ketones, produces a preferential loss of visible absorption (> or = 50% for SRFA) and substantially enhanced, blue-shifted fluorescence emission (2- to 3-fold increase). Comparison of the results with those obtained from a series of model quinones and hydroquinones demonstrates that these spectral changes cannot be assigned directly to the absorption and emission of visible light by quinones/hydroquinones. Instead, these results are consistent with a charge transfer model in which the visible absorption is due primarily to charge transfer transitions arising among hydroxy- (methoxy-) aromatic donors and carbonyl-containing acceptors. Unlike most of the model hydroquinones, the changes in optical properties of the natural samples following NaBH(4) reduction were largely irreversible in the presence of air and following addition of a Cu(2+) catalyst, providing tentative evidence that aromatic ketones (or other similar carbonyl-containing structures) may play a more important role than quinones in the optical properties of these materials.

Charge-transfer cross sections in collisions of ground-state Ca and H+

NASA Astrophysics Data System (ADS)

Dutta, C. M.; Oubre, C.; Nordlander, P.; Kimura, M.; Dalgarno, A.

2006-03-01

We have investigated collisions of Ca(4s2) with H+ in the energy range of 200eV/u-10keV/u using the semiclassical molecular-orbital close-coupling (MOCC) method with 18 coupled molecular states ( 11Σ+1 and seven Π+1 states) to determine charge-transfer cross sections. Except for the incoming channel 6Σ+1 , the molecular states all correspond to charge-transfer channels. Inclusion of Ca2+-H- is crucial in the configuration-interaction calculation for generating the molecular wave functions and potentials. Because of the Coulomb attraction, the state separating to Ca2+-H- creates many avoided crossings, even though at infinite separation it lies energetically above all other states that we included. Because of the avoided crossings between the incoming channel 6Σ+1 and the energetically close charge-transfer channel 7Σ+1 the charge-transfer interaction occurs at long range. This makes calculations of charge-transfer cross sections by the MOCC method very challenging. The total charge-transfer cross sections increase monotonically from 3.4×10-15cm2 at 200eV/u to 4.5×10-15cm2 at 10keV/u . Charge transfer occurs mostly to the excited Ca+(5p) state in the entire energy range, which is the sum of the charge transfer to 7Σ+1 and 4Π+1 . It accounts for ˜47% of the total charge transfer cross sections at 200eV/u . However, as the energy increases, transfer to Ca+(4d) increases, and at 10keV/u the charge-transfer cross sections for Ca+(5p) and Ca+(4d) become comparable, each giving ˜38% of the total cross section.

ICT-Isomerization-Induced Turn-On Fluorescence Probe with a Large Emission Shift for Mercury Ion: Application in Combinational Molecular Logic.

PubMed

Bhatta, Sushil Ranjan; Mondal, Bijan; Vijaykumar, Gonela; Thakur, Arunabha

2017-10-02

A unique turn-on fluorescent device based on a ferrocene-aminonaphtholate derivative specific for Hg 2+ cation was developed. Upon binding with Hg 2+ ion, the probe shows a dramatic fluorescence enhancement (the fluorescence quantum yield increases 58-fold) along with a large red shift of 68 nm in the emission spectrum. The fluorescence enhancement with a red shift may be ascribed to the combinational effect of C═N isomerization and an extended intramolecular charge transfer (ICT) mechanism. The response was instantaneous with a detection limit of 2.7 × 10 -9 M. Upon Hg 2+ recognition, the ferrocene/ferrocenium redox peak was anodically shifted by ΔE 1/2 = 72 mV along with a "naked eye" color change from faint yellow to pale orange for this metal cation. Further, upon protonation of the imine nitrogen, the present probe displays a high fluorescence output due to suppression of the C═N isomerization process. Upon deprotonation using strong base, the fluorescence steadily decreases, which indicates that H + and OH - can be used to regulate the off-on-off fluorescence switching of the present probe. Density functional theory studies revealed that the addition of acid leads to protonation of the imine N (according to natural bond orbital analysis), and the resulting iminium proton forms a strong H-bond (2.307 Å) with one of the triazole N atoms to form a five-membered ring, which makes the molecule rigid; hence, enhancement of the ICT process takes place, thereby leading to a fluorescence enhancement with a red shift. The unprecedented combination of H + , OH - , and Hg 2+ ions has been used to generate a molecular system exhibiting the INHIBIT-OR combinational logic operation.

Manipulating charge transfer excited state relaxation and spin crossover in iron coordination complexes with ligand substitution

DOE PAGES

Zhang, Wenkai; Kjaer, Kasper S.; Alonso-Mori, Roberto; ...

2016-08-25

Developing light-harvesting and photocatalytic molecules made with iron could provide a cost effective, scalable, and environmentally benign path for solar energy conversion. To date these developments have been limited by the sub-picosecond metal-to-ligand charge transfer (MLCT) electronic excited state lifetime of iron based complexes due to spin crossover – the extremely fast intersystem crossing and internal conversion to high spin metal-centered excited states. We revitalize a 30 year old synthetic strategy for extending the MLCT excited state lifetimes of iron complexes by making mixed ligand iron complexes with four cyanide (CN –) ligands and one 2,2'-bipyridine (bpy) ligand. This enablesmore » MLCT excited state and metal-centered excited state energies to be manipulated with partial independence and provides a path to suppressing spin crossover. We have combined X-ray Free-Electron Laser (XFEL) Kβ hard X-ray fluorescence spectroscopy with femtosecond time-resolved UV-visible absorption spectroscopy to characterize the electronic excited state dynamics initiated by MLCT excitation of [Fe(CN) 4(bpy)] 2–. The two experimental techniques are highly complementary; the time-resolved UV-visible measurement probes allowed electronic transitions between valence states making it sensitive to ligand-centered electronic states such as MLCT states, whereas the Kβ fluorescence spectroscopy provides a sensitive measure of changes in the Fe spin state characteristic of metal-centered excited states. Here, we conclude that the MLCT excited state of [Fe(CN) 4(bpy)] 2– decays with roughly a 20 ps lifetime without undergoing spin crossover, exceeding the MLCT excited state lifetime of [Fe(2,2'-bipyridine) 3] 2+ by more than two orders of magnitude.« less

An ultrafast spectroscopic and quantum mechanical investigation of multiple emissions in push-pull pyridinium derivatives bearing different electron donors.

PubMed

Carlotti, B; Benassi, E; Cesaretti, A; Fortuna, C G; Spalletti, A; Barone, V; Elisei, F

2015-08-28

A joint experimental and theoretical approach, involving state-of-the-art femtosecond fluorescence up-conversion measurements and quantum mechanical computations including vibronic effects, was employed to get a deep insight into the excited state dynamics of two cationic dipolar chromophores (Donor-π-Acceptor(+)) where the electron deficient portion is a N-methyl pyridinium and the electron donor a trimethoxyphenyl or a pyrene, respectively. The ultrafast spectroscopic investigation, and the time resolved area normalised emission spectra in particular, revealed a peculiar multiple emissive behaviour and allowed the distinct emitting states to be remarkably distinguished from solvation dynamics, occurring in water in a similar timescale. The two and three emissions experimentally detected for the trimethoxyphenyl and pyrene derivatives, respectively, were associated with specific local emissive minima in the potential energy surface of S1 on the ground of quantum-mechanical calculations. A low polar and planar Locally Excited (LE) state together with a highly polar and Twisted Intramolecular Charge Transfer (TICT) state is identified to be responsible for the dual emission of the trimethoxyphenyl compound. Interestingly, the more complex photobehaviour of the pyrenyl derivative was explained considering the contribution to the fluorescence coming not only from the LE and TICT states but also from a nearly Planar Intramolecular Charge Transfer (PICT) state, with both the TICT and the PICT generated from LE by progressive torsion around the quasi-single bond between the methylpyridinium and the ethene bridge. These findings point to an interconversion between rotamers for the pyrene compound taking place in its excited state against the Non-equilibrated Excited Rotamers (NEER) principle.

Consideration of Cost of Care in Pediatric Emergency Transfer-An Opportunity for Improvement.

PubMed

Gattu, Rajender K; De Fee, Ann-Sophie; Lichenstein, Richard; Teshome, Getachew

2017-05-01

Pediatric interhospital transfers are an economic burden to the health care, especially when deemed unnecessary. Physicians may be unaware of the cost implications of pediatric emergency transfers. A cost analysis may be relevant to reduce cost. To characterize children transferred from outlying emergency departments (EDs) to pediatric ED (PED) with a specific focus on transfers who were discharged home in 12 hours or less after transfer without intervention in PED and analyze charges associated with them. Charts of 352 patients (age, 0-18 years) transferred from 31 outlying EDs to PED during July 2009 to June 2010 were reviewed. Data were collected on the range, unit charge and volume of services provided in PED, length of stay, and final disposition. The average charge per patient transfer is calculated based on unit charge times total service units per 1000 patients per year and divided by 1000. Hospital charges were divided into fixed and variable. Of 352 patients transferred, 108 (30.7%) were admitted to pediatric inpatient service, 42 (11.9%) to intensive care; 36 (10.2%) went to the operating room, and 166 (47.2%) were discharged home. The average hospital charge per transfer was US $4843. Most (89%) of the charges were fixed, and 11% were variable. One hundred one (28.7%) patients were discharged home from PED in 12 hours or less without intervention. The hospital charges for these transfers were US $489,143. Significant number of transfers was discharged 12 hours or less without any additional intervention in PED. Fixed charges contribute to majority of total charges. Cost saving can be achieved by preventing unnecessary transfer.

Nonequilibrium electrokinetic effects in beds of ion-permselective particles.

PubMed

Leinweber, Felix C; Tallarek, Ulrich

2004-12-21

Electrokinetic transport of fluorescent tracer molecules in a bed of porous glass beads was investigated by confocal laser scanning microscopy. Refractive index matching between beads and the saturating fluid enabled a quantitative analysis of intraparticle and extraparticle fluid-side concentration profiles. Kinetic data were acquired for the uptake and release of electroneutral and counterionic tracer under devised conditions with respect to constant pressure-driven flow through the device and the effect of superimposed electrical fields. Transport of neutral tracer is controlled by intraparticle mass transfer resistance which can be strongly reduced by electroosmotic flow, while steady-state distributions and bead-averaged concentrations are unaffected by the externally applied fields. Electrolytes of low ionic strength caused the transport through the charged (mesoporous) beads to become highly ion-permselective, and concentration polarization is induced in the bulk solution due to the superimposed fields. The depleted concentration polarization zone comprises extraparticle fluid-side mass transfer resistance. Ionic concentrations in this diffusion boundary layer decrease at increasing field strength, and the flux densities approach an upper limit. Meanwhile, intraparticle transport of counterions by electromigration and electroosmosis continues to increase and finally exceeds the transport from bulk solution into the beads. A nonequilibrium electrical double layer is induced which consists of mobile and immobile space charge regions in the extraparticle bulk solution and inside a bead, respectively. These electrical field-induced space charges form the basis for nonequilibrium electrokinetic phenomena. Caused by the underlying transport discrimination (intraparticle electrokinetic vs extraparticle boundary-layer mass transfer), the dynamic adsorption capacity for counterions can be drastically reduced. Further, the extraparticle mobile space charge region leads to nonlinear electroosmosis. Flow patterns can become highly chaotic, and electrokinetic instability mixing is shown to increase lateral dispersion. Under these conditions, the overall axial dispersion of counterionic tracer can be reduced by more than 2 orders of magnitude, as demonstrated by pulse injections.

Initiation of oncogenic transformation in human mammary epithelial cells by charged particles

NASA Technical Reports Server (NTRS)

Yang, T. C.; Georgy, K. A.; Craise, L. M.; Durante, M.

1997-01-01

Experimental studies have shown that high linear-energy transfer (LET) charged particles can be more effective than x-rays and gamma-rays in inducing oncogenic transformation in cultured cells and tumors in animals. Based on these results, experiments were designed and performed with an immortal human mammary epithelial cell line (H184B5), and several clones transformed by heavy ions were obtained. Cell fusion experiments were subsequently done, and results indicate that the transforming gene(s) is recessive. Chromosome analysis with fluorescence in situ hybridization (FISH) techniques also showed additional translocations in transformed human mammary epithelial cells. In addition, studies with these cell lines indicate that heavy ions can effectively induce deletion, break, and dicentrics. Deletion of tumor suppressor gene(s) and/or formation of translocation through DNA double strand breaks is a likely mechanism for the initiation of oncogenic transformation in human mammary epithelial cells.

Leveraging zinc interstitials and oxygen vacancies for sensitive biomolecule detection through selective surface functionalization

NASA Astrophysics Data System (ADS)

Radha Shanmugam, Nandhinee; Muthukumar, Sriram; Chaudhry, Shajee; Prasad, Shalini

2015-03-01

In this study, functionally engineered EIS technique was implemented to investigate the influence of surface functionalization on sensitivity of biomolecule detection using nanostructured ZnO platform. Organic molecules with thiol and carboxylic functional groups were chosen to control biomolecule immobilization on zinc and oxygen-terminated 2D planar and 1D nanostructured ZnO surfaces. The amount of functionalization and its influence on charge perturbations at the ZnO-electrolyte interface were studied using fluorescence and EIS measurements. We observed the dependence of charge transfer on both the polarity of platform and concentration of cross-linker molecules. Such selectively modified surfaces were used for detection of cortisol, a major stress indicator. Results demonstrated preferential binding of thiol groups to Zn terminations and thus leveraging ZnO interstitials increases the sensitivity of detection over larger dynamic range with detection limit at 10fg/mL.

Dual emission of chalcone-analogue dyes emitting in the red region

NASA Astrophysics Data System (ADS)

Fayed, Tarek A.; Awad, Mohamed K.

2004-08-01

The photophysical properties of new synthesized chalcones namely; 1-(4 '-R-phenyl)-5-(4 '-dimethylaminophenyl)-2,4- pentadien-1-one, [R=H ( 1), Cl ( 2) and OCH 3 ( 3)] were studied in different solvents by using steady-state absorption and emission spectroscopy. The fluorescence spectra of these chalcones exhibit dual emission in medium and polar solvents. The dual emission was attributed to population of a polar locally excited (LE) state and a highly dipolar intramolecular charge transfer (ICT) state. The changes in dipole moments upon excitation were calculated from the solvatochromic plots. The total fluorescence quantum yields ( φf) were also determined, and their values are strongly dependent on the nature of substitutent and the solvent polarity. Semiempirical molecular orbital calculations using the atom superposition and electron delocalization molecular orbital (ASED-MO) method were also performed to investigate the molecular and electronic structures of these chalcones in both the ground and excited state. The change of the dipole moment upon excitation was explained on the basis of changes in the charge redistribution over the whole skeleton of the molecules, which agree well with the experimental results. Also, the nature and energy of the electronic transitions were elucidated and discussed in relation to the experimental data.

Coherent stimulated light emission (lasing) in covalently linked chlorophyll dimers

PubMed Central

Hindman, James C.; Kugel, Roger; Wasielewski, Michael R.; Katz, Joseph J.

1978-01-01

The covalently linked chlorophyll a dimer exhibits remarkably different properties in the folded and open configurations. In the folded configuration the absorption maximum is at 695 nm and the fluorescence maximum is at 730 nm. Laser output at 733 and 735 nm is obtained for solutions in wet benzene and 0.1 M ethanol/toluene, respectively. Measurements of fluorescence lineshapes, made with a transverse excited atmospheric (TEA) nitrogen laser for excitation, show the lifetime shortening associated with stimulated emission resulting from appreciable concentrations of molecules in S1 excited states. In contrast, the open dimer has absorption and fluorescence spectra essentially the same as those of chlorophyll a monomer. Unlike either the folded dimer or chlorophyll a monomer, the open dimer shows no laser emission or fluorescene lifetime shortening. It does not appear that the behavior of the open dimer can be explained in terms of excimer or triplet formation or by nonradiative decay processes. It is suggested that absorption of the exciting radiation by S1, leading to the formation of an exciplex or charge transfer state, may be involved. Significantly, no large changes in fluorescence quantum yield or fluorescence lifetime are observed for these dimers as compared to monomer chlorophyll. This suggests that concentration quenching and lifetime shortening in condensed chlorophyll systems involve more than the simple proximity of two chlorophyll molecules. Images PMID:16592524

Photophysics of 4-dimethylamino-4'-cyanostilbene and 4-azetidinyl-4'-cyanostilbene. Time-resolved fluorescence and trans-cis photoisomerisation

NASA Astrophysics Data System (ADS)

Il'ichev, Yurii V.; Kühnle, Wolfgang; Zachariasse, Klaas A.

1996-11-01

The fluorescence decays of trans-4-dimethylamino-4'-cyanostilbene (DCS) and trans-4-azetidinyl-4'-cyanostilbene (ACS) in an unpolar (n-heptane) and a polar (acetonitrile) solvent are single exponential down to a time resolution of around 5 ps and dual fluorescence is not observed. The dipole moment increases in two steps: from 7 D in the ground state via 13 D (DCS) or 10 D (ACS) for the Franck-Condon excited state to 21 D (DCS) or 22 D (ACS) for the relaxed fluorescing CT state. This means that the intramolecular charge transfer (ICT) in the excited state at most involves an intermediate with a subpicosecond lifetime. The presence of the azetidinyl group in ACS does not slow down the ICT reaction, contrary to what has been found for the 4-aminobenzonitriles, showing that inversion of the amino group is not an important reaction coordinate here. The activation energy Etc for trans-cis photoisomerisation is determined from the fluorescence decays in n-heptane (14.0 kJ/mol, DCS) and in acetonitrile (22.7 kJ/mol, DCS and 22.5 kJ/mol, ACS). This increase of Etc with solvent polarity, opposite to what has been found for trans-stilbene, shows that the photoisomerisation transition state is less polar than the CT state.

An excellent fluorescent dye with a twistable aromatic chain and its axially chiral crystals.

PubMed

Ma, Yan; Hao, Rui; Shao, Guangsheng; Wang, Yuan

2009-04-30

A new organic fluorescent dye, 2,4-dichloro-6-[p-(N,N-diethylamino)biphenylyl]-1,3,5-triazine (DBQ), with an electron withdrawing-donating pair bridged by a twistable aromatic chain has been synthesized. DBQ exhibits high fluorescence quantum yields (0.96 in hexane and 0.71 in THF), high extinction coefficients, and an excitation window extending up to approximately 480 nm. Due to the strong intramolecular charge transfer character, DBQ shows obviously solvent-dependent Stokes shifts with a value as high as 6360 cm(-1) in THF and controllable fluorescence emission in the visible region from "blue" to "orange". The axially chiral structures of DBQ crystals were clearly revealed by the X-ray analyses and CD spectroscopy measurements. Two enantiomers of DBQ were obtained by spontaneous resolution upon crystallization without any chiral auxiliary. The low rotation barriers around the interannular bonds in DBQ molecules resulted in an efficient and selective multiplication of each of the chiral structures when DBQ crystallized in THF at room temperature in the presence of an enantiopure crystal seed, leaving racemized DBQ molecules in the solution. The special crystalline properties of DBQ provided a new approach to the design and synthesis of organic chiral crystals. The photophysical properties of DBQ make it promising in the preparation of new fluorescent probes with high sensitivity.

Triarylamine-Cored Dendritic Molecular Gel for Efficient Colorometric, Fluorometric, and Impedometeric Detection of Picric Acid.

PubMed

Mondal, Sanjoy; Bairi, Partha; Das, Sujoy; Nandi, Arun K

2018-04-11

Detection of nitroaromatics at ultralow concentration is a major security concern in defense, forensics, and environmental science. To this end, a new triarylamine-cored dendritic gelator (OGR) was synthesized, which produced thermoreversible, thixotropic, and fluorescent gels in n-octanol. On gelation, both π-π* transitions and the emission peak of the gelator show redshifts with a 4.5-fold increase of fluorescence intensity in the gel state indicating J-aggregation. The nitrogen lone-pair electrons of OGR make it a donor, and electron transfer occurs to acceptor nitroaromatics causing fluorescence quenching, which is further promoted due to its acidity. The Stern-Volmer rate constants measured for different nitroaromatics showed that it senses picric acid (PA) best. The contact-mode technique with OGR-treated paper strips can allow naked-eye detection of PA under UV light down to 10 -11  m concentration within 30 s. Reusability of the gel is achieved by treating OGR@PA x with NaOH solution. Impedance spectroscopic results indicated a decrease of both charge-transport resistance and Warburg impedance on successive addition of PA. The limits of detection of PA determined from fluorescence and impedance measurements match well. Thus, the OGR gel is a reusable, low-cost, specific sensor for PA by naked-eye colorimetric, fluorescence, and impedance techniques. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Trace Detection of RDX, HMX and PETN Explosives Using a Fluorescence Spot Sensor

PubMed Central

Wang, Chen; Huang, Helin; Bunes, Benjamin R.; Wu, Na; Xu, Miao; Yang, Xiaomei; Yu, Li; Zang, Ling

2016-01-01

1,3,5-trinitroperhydro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and pentaerythritol tetranitrate (PETN), the major components in plastic explosives, pose a significant threat to public safety. A quick, sensitive, and low-cost detection method for these non-volatile explosives is eagerly demanded. Here we present a fluo-spot approach, which can be employed for in situ detection of trace amount of explosives. The sensor molecule is a charge-transfer fluorophore, DCM, which is strongly fluorescent in its pristine state, but non-fluorescent after the quick reaction with NO2· (or NO2+) generated from the UV photolysis of RDX, HMX (or PETN). When fabricated within silica gel TLC plate, the fluo-spot sensor features high sensitivity owing to the large surface area and porous structure of the substrate. The sensor reaction mechanism was verified by various experimental characterizations, including chromatography, UV-Vis absorption and fluorescence spectroscopy, MS and 1H NMR spectrometry. The fluo-spot also demonstrated high selectivity towards RDX, HMX and PETN, as no significant fluorescence quenching was observed for other chemical compounds including common nitro-aromatic explosives and inorganic oxidative compounds. The DCM sensor can also be used as an economical spray kit to directly spot the explosives by naked eyes, implying great potential for quick, low-cost trace explosives detection. PMID:27146290

Trace Detection of RDX, HMX and PETN Explosives Using a Fluorescence Spot Sensor.

PubMed

Wang, Chen; Huang, Helin; Bunes, Benjamin R; Wu, Na; Xu, Miao; Yang, Xiaomei; Yu, Li; Zang, Ling

2016-05-05

1,3,5-trinitroperhydro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and pentaerythritol tetranitrate (PETN), the major components in plastic explosives, pose a significant threat to public safety. A quick, sensitive, and low-cost detection method for these non-volatile explosives is eagerly demanded. Here we present a fluo-spot approach, which can be employed for in situ detection of trace amount of explosives. The sensor molecule is a charge-transfer fluorophore, DCM, which is strongly fluorescent in its pristine state, but non-fluorescent after the quick reaction with NO2· (or NO2(+)) generated from the UV photolysis of RDX, HMX (or PETN). When fabricated within silica gel TLC plate, the fluo-spot sensor features high sensitivity owing to the large surface area and porous structure of the substrate. The sensor reaction mechanism was verified by various experimental characterizations, including chromatography, UV-Vis absorption and fluorescence spectroscopy, MS and (1)H NMR spectrometry. The fluo-spot also demonstrated high selectivity towards RDX, HMX and PETN, as no significant fluorescence quenching was observed for other chemical compounds including common nitro-aromatic explosives and inorganic oxidative compounds. The DCM sensor can also be used as an economical spray kit to directly spot the explosives by naked eyes, implying great potential for quick, low-cost trace explosives detection.

A fluorescent imaging technique for quantifying spray deposits on plant leaves

USDA-ARS?s Scientific Manuscript database

Because of the unique characteristics of electrostatically-charged sprays, use of traditional methods to quantify deposition from these sprays has been challenging. A new fluorescent imaging technique was developed to quantify spray deposits from electrostatically-charged sprays on natural plant lea...

Plasmonic Solar Cells: From Rational Design to Mechanism Overview.

PubMed

Jang, Yoon Hee; Jang, Yu Jin; Kim, Seokhyoung; Quan, Li Na; Chung, Kyungwha; Kim, Dong Ha

2016-12-28

Plasmonic effects have been proposed as a solution to overcome the limited light absorption in thin-film photovoltaic devices, and various types of plasmonic solar cells have been developed. This review provides a comprehensive overview of the state-of-the-art progress on the design and fabrication of plasmonic solar cells and their enhancement mechanism. The working principle is first addressed in terms of the combined effects of plasmon decay, scattering, near-field enhancement, and plasmonic energy transfer, including direct hot electron transfer and resonant energy transfer. Then, we summarize recent developments for various types of plasmonic solar cells based on silicon, dye-sensitized, organic photovoltaic, and other types of solar cells, including quantum dot and perovskite variants. We also address several issues regarding the limitations of plasmonic nanostructures, including their electrical, chemical, and physical stability, charge recombination, narrowband absorption, and high cost. Next, we propose a few potentially useful approaches that can improve the performance of plasmonic cells, such as the inclusion of graphene plasmonics, plasmon-upconversion coupling, and coupling between fluorescence resonance energy transfer and plasmon resonance energy transfer. This review is concluded with remarks on future prospects for plasmonic solar cell use.

Excited state intramolecular charge transfer reaction in binary mixtures of water and tertiary butanol (TBA): alcohol mole fraction dependence.

PubMed

Pradhan, Tuhin; Ghoshal, Piue; Biswas, Ranjit

2008-02-07

The excited state intramolecular charge transfer reaction of 4-(1-azetidinyl)benzonitrile (P4C) has been studied in water-tertiary butanol (TBA) mixtures at different alcohol mole fractions by using steady state and time-resolved fluorescence spectroscopy. The ratio between the areas under the locally excited (LE) and charge transferred (CT) emission bands is found to exhibit a sharp rise at alcohol mole fraction approximately 0.04, a value at which several thermodynamic properties of this mixture is known to show anomalous change due to the enhancement of H-bonding network. The radiative rate associated with the LE emission also shows a maximum at this TBA mole fraction. Although the structural transition from the water-like tetrahedral network to the alcohol-like chain is reflected in the red shift of the absorption spectrum up to TBA mole fraction approximately 0.10, the emission bands (both LE and CT) show the typical nonideal alcohol mole fraction dependence at all TBA mole fractions. Quantum yield, CT radiative rate as well as transition moments also exhibit a nonideal alcohol mole fraction dependence. The time-resolved emission decay of P4C has been found to be biexponential at all TBA mole fractions, regardless of emission collection around either the LE or the CT bands. The time constant associated with the slow component (tau(slow)) shows a minimum at TBA mole fraction approximately 0.04, whereas such a minimum for the fast time constant, tau(fast) (representing the rate of LE --> CT conversion reaction) is not observed. The nonobservation of the minimum in tau(fast) might be due to the limited time resolution employed in our experiments.

Convergent Synthesis and Photoinduced Processes in Multi-Chromophoric Rotaxanes1

PubMed Central

Megiatto, Jackson D.; Li, Ke; Schuster, David I.; Palkar, Amit; Herranz, M. Ángeles; Echegoyen, Luis; Abwandner, Silke; de Miguel, Gustavo; Guldi, Dirk M.

2010-01-01

A series of [2]rotaxane materials, in which [60]fullerene is linked to a macrocycle and ferrocene (Fc) moieties are placed at the termini of a thread, both of which possess a central Cu(I)-1,10-phenanthroline [Cu(phen)2]+ complex, were synthesized by self-assembly using Sauvage metal template methodology. Two types of threads were constructed, one with terminal ester linkages, and a second with terminal 1,2,3-triazole linkages derived from Cu(I)-catalyzed “click” 1,3-cycloaddition reactions. Model compounds lacking the fullerene moiety were prepared in an analogous manner. The ability of the interlocked Fc-[Cu(phen)2]+-C60 hybrids to undergo electron transfer upon photoexcitation was investigated by means of time-resolved fluorescence and transient absorption spectroscopy, using excitation wavelengths directed at the fullerene and [Cu(phen)2]+ subunits. The energies of the electronic excited states and charge separated (CS) states that might be formed upon photoexcitation were determined from spectroscopic and electrochemical data. These studies showed that MLCT excited states of the copper complex in the fullerenerotaxanes were quenched by electron transfer to the fullerene, resulting in charge separated states with oxidized copper and reduced fullerene moieties, (Fc)2-[Cu(phen)2]2+-C60•−. Even though electron transfer from Fc to the oxidized copper complex is predicted to be exergonic by 0.18 eV, no unequivocal evidence in support of such a process was obtained. The conclusion that Fc plays no role in the photoinduced processes in our systems rests on the lack of enhancement of the lifetime of the charge separated state as measured by decay of C60•− at ~ 1000 nm, since one-electron oxidized Fc is very difficult to detect spectroscopically in the 500–800 nm spectral region. PMID:20518479

Quantum Theory of Atoms in Molecules Charge-Charge Transfer-Dipolar Polarization Classification of Infrared Intensities.

PubMed

Duarte, Leonardo J; Richter, Wagner E; Silva, Arnaldo F; Bruns, Roy E

2017-10-26

Fundamental infrared vibrational transition intensities of gas-phase molecules are sensitive probes of changes in electronic structure accompanying small molecular distortions. Models containing charge, charge transfer, and dipolar polarization effects are necessary for a successful classification of the C-H, C-F, and C-Cl stretching and bending intensities. C-H stretching and in-plane bending vibrations involving sp 3 carbon atoms have small equilibrium charge contributions and are accurately modeled by the charge transfer-counterpolarization contribution and its interaction with equilibrium charge movement. Large C-F and C═O stretching intensities have dominant equilibrium charge movement contributions compared to their charge transfer-dipolar polarization ones and are accurately estimated by equilibrium charge and the interaction contribution. The C-F and C-Cl bending modes have charge and charge transfer-dipolar polarization contribution sums that are of similar size but opposite sign to their interaction values resulting in small intensities. Experimental in-plane C-H bends have small average intensities of 12.6 ± 10.4 km mol -1 owing to negligible charge contributions and charge transfer-counterpolarization cancellations, whereas their average out-of-plane experimental intensities are much larger, 65.7 ± 20.0 km mol -1 , as charge transfer is zero and only dipolar polarization takes place. The C-F bending intensities have large charge contributions but very small intensities. Their average experimental out-of-plane intensity of 9.9 ± 12.6 km mol -1 arises from the cancellation of large charge contributions by dipolar polarization contributions. The experimental average in-plane C-F bending intensity, 5.8 ± 7.3 km mol -1 , is also small owing to charge and charge transfer-counterpolarization sums being canceled by their interaction contributions. Models containing only atomic charges and their fluxes are incapable of describing electronic structure changes for simple molecular distortions that are of interest in classifying infrared intensities. One can expect dipolar polarization effects to also be important for larger distortions of chemical interest.

Resonance fluorescence revival in a voltage-controlled semiconductor quantum dot

NASA Astrophysics Data System (ADS)

Reigue, Antoine; Lemaître, Aristide; Gomez Carbonell, Carmen; Ulysse, Christian; Merghem, Kamel; Guilet, Stéphane; Hostein, Richard; Voliotis, Valia

2018-02-01

We demonstrate systematic resonance fluorescence recovery with near-unity emission efficiency in single quantum dots embedded in a charge-tunable device in a wave-guiding geometry. The quantum dot charge state is controlled by a gate voltage, through carrier tunneling from a close-lying Fermi sea, stabilizing the resonantly photocreated electron-hole pair. The electric field cancels out the charging/discharging mechanisms from nearby traps toward the quantum dots, responsible for the usually observed inhibition of the resonant fluorescence. Fourier transform spectroscopy as a function of the applied voltage shows a strong increase in the coherence time though not reaching the radiative limit. These charge controlled quantum dots can act as quasi-perfect deterministic single-photon emitters, with one laser pulse converted into one emitted single photon.

Near-IR core-substituted naphthalenediimide fluorescent chemosensors for zinc ions: ligand effects on PET and ICT channels.

PubMed

Lu, Xinyu; Zhu, Weihong; Xie, Yongshu; Li, Xin; Gao, Yuan; Li, Fuyou; Tian, He

2010-07-26

Near-IR (NIR) emission can offer distinct advantages for both in vitro and in vivo biological applications. Two NIR fluorescent turn-on sensors N,N'-di-n-butyl-2-(N-{2-[bis(pyridin-2-ylmethyl)amino]ethyl})-6-(N-piperidinyl)naphthalene-1,4,5,8-tetracarboxylic acid bisimide and N,N'-di- n-butyl-2-[N,N,N'-tri(pyridin-2-ylmethyl)amino]ethyl-6-(N-piperidinyl)naphthalene-1,4,5,8-tetracarboxylic acid bisimide (PND and PNT) for Zn(2+) based on naphthalenediimide fluorophore are reported. Our strategy was to choose core-substituted naphthalenediimide (NDI) as a novel NIR fluorophore and N,N-di(pyridin-2-ylmethyl)ethane-1,2-diamine (DPEA) or N,N,N'-tri(pyridin-2-ylmethyl)ethane-1,2-diamine (TPEA) as the receptor, respectively, so as to improve the selectivity to Zn(2+). In the case of PND, the negligible shift in absorption and emission spectra is strongly suggestive that the secondary nitrogen atom (directly connected to the NDI moiety, N(1)) is little disturbed with Zn(2+). The fluorescence enhancement of PND with Zn(2+) titration is dominated with a typical photoinduced electron-transfer (PET) process. In contrast, the N(1) atom for PNT can participate in the coordination of Zn(2+) ion, diminishing the electron delocalization of the NDI moiety and resulting in intramolecular charge-transfer (ICT) disturbance. For PNT, the distinct blueshift in both absorbance and fluorescence is indicative of a combination of PET and ICT processes, which unexpectedly decreases the sensitivity to Zn(2+). Due to the differential binding mode caused by the ligand effect, PND shows excellent selectivity to Zn(2+) over other metal ions, with a larger fluorescent enhancement centered at 650 nm. Also both PND and PNT were successfully used to image intracellular Zn(2+) ions in the living KB cells.

Ultrafast responses of dipolar and V-shaped dipicolinate derivatives with potential applications in the labeling of biomolecules

NASA Astrophysics Data System (ADS)

Wang, Yaochuan; Liu, Siyuan; Liu, Dajun; Wang, Guiqiu; Xiao, Haibo

2016-02-01

A dipolar dipicolinate derivative, trans-dimethyl-4-[4'-(N,N-diphenylamino)-styry1]-pyridin-2,6-dicarboxylate (P-1), and a P-1based V-shaped compound, {4-[(E)-2-(2,6-dimethoxycarbonylpyridin-4-yl) vinyl]}-N-phenyl-N-{4-[(E)-2-(2,6-dimethoxycarbonylpyridin-4-yl)vinylphenyl]}aniline (P-2), with intense two-photon fluorescence emission properties were systematically investigated by using steady-state absorption and fluorescence spectroscopy, open-aperture Z-scans, and two-photon excited fluorescence (TPF). The two-photon absorption cross-section of the V-shaped compound P-2 in tetrahydrofuran (THF) was determined to be 208 GM, which represents a 6.5-fold enhancement compared with its dipolar counterpart P-1 (32 GM). Extension of the intramolecular charge transfer (ICT) in the V-shaped dipicolinate derivative has been suggested as the mechanism of enhancement. The excited state dynamics from transient absorption spectroscopy were analyzed and discussed. The formation and relaxation lifetimes of the ICT state for these dipicolinate derivatives in THF solutions were found to be several picoseconds and several hundred picoseconds, respectively. The results show an increased ICT character of the V-shaped compound and a potential application for this compound in two-photon fluorescence imaging fields.

Label-Free Fluorescence Assay of S1 Nuclease and Hydroxyl Radicals Based on Water-Soluble Conjugated Polymers and WS₂ Nanosheets.

PubMed

Li, Junting; Zhao, Qi; Tang, Yanli

2016-06-13

We developed a new method for detecting S1 nuclease and hydroxyl radicals based on the use of water-soluble conjugated poly[9,9-bis(6,6-(N,N,N-trimethylammonium)-fluorene)-2,7-ylenevinylene-co-alt-2,5-dicyano-1,4-phenylene)] (PFVCN) and tungsten disulfide (WS₂) nanosheets. Cationic PFVCN is used as a signal reporter, and single-layer WS₂ is used as a quencher with a negatively charged surface. The ssDNA forms complexes with PFVCN due to much stronger electrostatic interactions between cationic PFVCN and anionic ssDNA, whereas PFVCN emits yellow fluorescence. When ssDNA is hydrolyzed by S1 nuclease or hydroxyl radicals into small fragments, the interactions between the fragmented DNA and PFVCN become weaker, resulting in PFVCN being adsorbed on the surface of WS₂ and the fluorescence being quenched through fluorescence resonance energy transfer. The new method based on PFVCN and WS₂ can sense S1 nuclease with a low detection limit of 5 × 10(-6) U/mL. Additionally, this method is cost-effective by using affordable WS₂ as an energy acceptor without the need for dye-labeled ssDNA. Furthermore, the method provides a new platform for the nuclease assay and reactive oxygen species, and provides promising applications for drug screening.

A Linear Ion Trap with an Expanded Inscribed Diameter to Improve Optical Access for Fluorescence Spectroscopy

NASA Astrophysics Data System (ADS)

Rajagopal, Vaishnavi; Stokes, Chris; Ferzoco, Alessandra

2018-02-01

We report a custom-geometry linear ion trap designed for fluorescence spectroscopy of gas-phase ions at ambient to cryogenic temperatures. Laser-induced fluorescence from trapped ions is collected from between the trapping rods, orthogonal to the excitation laser that runs along the axis of the linear ion trap. To increase optical access to the ion cloud, the diameter of the round trapping rods is 80% of the inscribed diameter, rather than the roughly 110% used to approximate purely quadrupolar electric fields. To encompass as much of the ion cloud as possible, the first collection optic has a 25.4 mm diameter and a numerical aperture of 0.6. The choice of geometry and collection optics yields 107 detected photons/s from trapped rhodamine 6G ions. The trap is coupled to a closed-cycle helium refrigerator, which in combination with two 50 Ohm heaters enables temperature control to below 25 K on the rod electrodes. The purpose of the instrument is to broaden the applicability of fluorescence spectroscopy of gas-phase ions to cases where photon emission is a minority relaxation pathway. Such studies are important to understand how the microenvironment of a chromophore influences excited state charge transfer processes.

Fluorescence probe of polypeptide conformational dynamics in gas phase and in solution

NASA Astrophysics Data System (ADS)

Iavarone, Anthony T.; Meinen, Jan; Schulze, Susanne; Parks, Joel H.

2006-07-01

Fluorescence measurements of polypeptides derivatized with the fluorescent dye BODIPY TMR have been used to probe the polypeptide conformational dynamics as a function of temperature and charge state. Measurements of (BODIPY TMR)-[Pro]n-Arg-Trp and (BODIPY TMR)-[Gly-Ser]m-Arg-Trp have been performed for charge states 1+ and 2+ of n = 4 and 10 and m = 2 and 5. The 2+ charge states of both of these polypeptides exhibit similar temperature dependences for equal chain lengths (n = 4, m = 2 and n = 10, m = 5) and suggest conformations dominated by Coulomb repulsion. In the absence of such Coulomb repulsion, the 1+ charge state conformations appear to be characterized by the flexibility of the polypeptide chain for which [Gly-Ser]m > [Pro]n. Comparisons of these gas phase polypeptide measurements with corresponding measurements in solution provide a direct measure of the effects of solvent on the conformational dynamics. The change in fluorescence as a function of temperature in the gas phase is two orders of magnitude greater than that in solution, a dramatic result we attribute to the restrictions on intramolecular dynamics imposed by diffusion-limited kinetics and the lack of shielding by solvent. Measurements were also made of unsolvated Pron peptides without the tryptophan (Trp) residue to isolate the interaction of the fluorescent dye with charges.

Quantitative Super-Resolution Microscopy of Nanopipette-Deposited Fluorescent Patterns.

PubMed

Hennig, Simon; van de Linde, Sebastian; Bergmann, Stephan; Huser, Thomas; Sauer, Markus

2015-08-25

We describe a method for the deposition of minute amounts of fluorophore-labeled oligonucleotides with high local precision in conductive and transparent solid layers of poly(vinyl alcohol) (PVA) doped with glycerin and cysteamine (PVA-G-C layers). Deposition of negatively charged fluorescent molecules was accomplished with a setup based on a scanning ion conductance microscope (SICM) using nanopipettes with tip diameters of ∼100 nm by using the ion flux flowing between two electrodes through the nanopipette. To investigate the precision of the local deposition process, we performed in situ super-resolution microscopy by direct stochastic optical reconstruction microscopy (dSTORM). Exploiting the single-molecule sensitivity and reliability of dSTORM, we determine the number of fluorescent molecules deposited in single spots. The correlation of applied charge and number of deposited molecules enables the quantification of delivered molecules by measuring the charge during the delivery process. We demonstrate the reproducible deposition of 3-168 fluorescent molecules in single spots and the creation of fluorescent structures. The fluorescent structures are highly stable and can be reused several times.

Charge Transfer Inefficiency in Pinned Photodiode CMOS image sensors: Simple Montecarlo modeling and experimental measurement based on a pulsed storage-gate method

NASA Astrophysics Data System (ADS)

Pelamatti, Alice; Goiffon, Vincent; Chabane, Aziouz; Magnan, Pierre; Virmontois, Cédric; Saint-Pé, Olivier; de Boisanger, Michel Breart

2016-11-01

The charge transfer time represents the bottleneck in terms of temporal resolution in Pinned Photodiode (PPD) CMOS image sensors. This work focuses on the modeling and estimation of this key parameter. A simple numerical model of charge transfer in PPDs is presented. The model is based on a Montecarlo simulation and takes into account both charge diffusion in the PPD and the effect of potential obstacles along the charge transfer path. This work also presents a new experimental approach for the estimation of the charge transfer time, called pulsed Storage Gate (SG) method. This method, which allows reproduction of a ;worst-case; transfer condition, is based on dedicated SG pixel structures and is particularly suitable to compare transfer efficiency performances for different pixel geometries.

Fluorescence energy transfer as a probe for nucleic acid structures and sequences.

PubMed Central

Mergny, J L; Boutorine, A S; Garestier, T; Belloc, F; Rougée, M; Bulychev, N V; Koshkin, A A; Bourson, J; Lebedev, A V; Valeur, B

1994-01-01

The primary or secondary structure of single-stranded nucleic acids has been investigated with fluorescent oligonucleotides, i.e., oligonucleotides covalently linked to a fluorescent dye. Five different chromophores were used: 2-methoxy-6-chloro-9-amino-acridine, coumarin 500, fluorescein, rhodamine and ethidium. The chemical synthesis of derivatized oligonucleotides is described. Hybridization of two fluorescent oligonucleotides to adjacent nucleic acid sequences led to fluorescence excitation energy transfer between the donor and the acceptor dyes. This phenomenon was used to probe primary and secondary structures of DNA fragments and the orientation of oligodeoxynucleotides synthesized with the alpha-anomers of nucleoside units. Fluorescence energy transfer can be used to reveal the formation of hairpin structures and the translocation of genes between two chromosomes. PMID:8152922

Charge transfer efficiency improvement of 4T pixel for high speed CMOS image sensor

NASA Astrophysics Data System (ADS)

Jin, Xiangliang; Liu, Weihui; Yang, Hongjiao; Tang, Lizhen; Yang, Jia

2015-03-01

The charge transfer efficiency improvement method is proposed by optimizing the electrical potential distribution along the transfer path from the PPD to the FD. In this work, we present a non-uniform doped transfer transistor channel, with the adjustments to the overlap length between the CPIA layer and the transfer gate, and the overlap length between the SEN layer and transfer gate. Theory analysis and TCAD simulation results show that the density of the residual charge reduces from 1e11 /cm3 to 1e9 /cm3, and the transfer time reduces from 500 ns to 143 ns, and the charge transfer efficiency is about 77 e-/ns. This optimizing design effectively improves the charge transfer efficiency of 4T pixel and the performance of 4T high speed CMOS image sensor.

Heat transfer assembly for a fluorescent lamp and fixture

DOEpatents

Siminovitch, Michael J.; Rubenstein, Francis M.; Whitman, Richard E.

1992-01-01

In a lighting fixture including a lamp and a housing, a heat transfer structure is disclosed for reducing the minimum lamp wall temperature of a fluorescent light bulb. The heat transfer structure, constructed of thermally conductive material, extends from inside the housing to outside the housing, transferring heat energy generated from a fluorescent light bulb to outside the housing where the heat energy is dissipated to the ambient air outside the housing. Also disclosed is a method for reducing minimum lamp wall temperatures. Further disclosed is an improved lighting fixture including a lamp, a housing and the aforementioned heat transfer structure.

The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures

DOE PAGES

Wang, Han; Bang, Junhyeok; Sun, Yiyang; ...

2016-05-10

Here, the success of van der Waals (vdW) heterostructures, made of graphene, metal dichalcogenides, and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that vdW heterostructues can exhibit ultra-fast charge transfer despite the weak binding of the heterostructure. Using time-dependent density functional theory molecular dynamics, we identify a strong dynamic coupling between the vdW layers associated with charge transfer. This dynamic coupling results in rapid nonlinear coherentmore » charge oscillations which constitute a purely electronic phenomenon and are shown to be a general feature of vdW heterostructures provided they have a critical minimum dipole coupling. Application to MoS2/WS2 heterostructure yields good agreement with experiment, indicating near complete charge transfer within a timescale of 100 fs.The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs.« less

The role of collective motion in the ultrafast charge transfer in van der Waals heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Han; Bang, Junhyeok; Sun, Yiyang

Here, the success of van der Waals (vdW) heterostructures, made of graphene, metal dichalcogenides, and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that vdW heterostructues can exhibit ultra-fast charge transfer despite the weak binding of the heterostructure. Using time-dependent density functional theory molecular dynamics, we identify a strong dynamic coupling between the vdW layers associated with charge transfer. This dynamic coupling results in rapid nonlinear coherentmore » charge oscillations which constitute a purely electronic phenomenon and are shown to be a general feature of vdW heterostructures provided they have a critical minimum dipole coupling. Application to MoS2/WS2 heterostructure yields good agreement with experiment, indicating near complete charge transfer within a timescale of 100 fs.The success of van der Waals heterostructures made of graphene, metal dichalcogenides and other layered materials, hinges on the understanding of charge transfer across the interface as the foundation for new device concepts and applications. In contrast to conventional heterostructures, where a strong interfacial coupling is essential to charge transfer, recent experimental findings indicate that van der Waals heterostructues can exhibit ultrafast charge transfer despite the weak binding of these heterostructures. Here we find, using time-dependent density functional theory molecular dynamics, that the collective motion of excitons at the interface leads to plasma oscillations associated with optical excitation. By constructing a simple model of the van der Waals heterostructure, we show that there exists an unexpected criticality of the oscillations, yielding rapid charge transfer across the interface. Application to the MoS2/WS2 heterostructure yields good agreement with experiments, indicating near complete charge transfer within a timescale of 100 fs.« less

Cell uptake, intracellular distribution, fate and reactive oxygen species generation of polymer brush engineered CeO2-x NPs

NASA Astrophysics Data System (ADS)

Qiu, Yuan; Rojas, Elena; Murray, Richard A.; Irigoyen, Joseba; Gregurec, Danijela; Castro-Hartmann, Pablo; Fledderman, Jana; Estrela-Lopis, Irina; Donath, Edwin; Moya, Sergio E.

2015-04-01

Cerium Oxide nanoparticles (CeO2-x NPs) are modified with polymer brushes of negatively charged poly (3-sulfopropylmethacrylate) (PSPM) and positively charged poly (2-(methacryloyloxy)ethyl-trimethylammonium chloride) (PMETAC) by Atom Transfer Radical Polymerisation (ATRP). CeO2-x NPs are fluorescently labelled by covalently attaching Alexa Fluor® 488/Fluorescein isothiocyanate to the NP surface prior to polymerisation. Cell uptake, intracellular distribution and the impact on the generation of intracellular Reactive Oxygen Species (ROS) with respect to CeO2-x NPs are studied by means of Raman Confocal Microscopy (CRM), Transmission Electron Microscopy (TEM) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). PSPM and PMETAC coated CeO2-x NPs show slower and less uptake compared to uncoated Brush modified NPs display a higher degree of co-localisation with cell endosomes and lysosomes after 24 h of incubation. They also show higher co-localisation with lipid bodies when compared to unmodified CeO2-x NPs. The brush coating does not prevent CeO2-x NPs from displaying antioxidant properties.Cerium Oxide nanoparticles (CeO2-x NPs) are modified with polymer brushes of negatively charged poly (3-sulfopropylmethacrylate) (PSPM) and positively charged poly (2-(methacryloyloxy)ethyl-trimethylammonium chloride) (PMETAC) by Atom Transfer Radical Polymerisation (ATRP). CeO2-x NPs are fluorescently labelled by covalently attaching Alexa Fluor® 488/Fluorescein isothiocyanate to the NP surface prior to polymerisation. Cell uptake, intracellular distribution and the impact on the generation of intracellular Reactive Oxygen Species (ROS) with respect to CeO2-x NPs are studied by means of Raman Confocal Microscopy (CRM), Transmission Electron Microscopy (TEM) and Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). PSPM and PMETAC coated CeO2-x NPs show slower and less uptake compared to uncoated Brush modified NPs display a higher degree of co-localisation with cell endosomes and lysosomes after 24 h of incubation. They also show higher co-localisation with lipid bodies when compared to unmodified CeO2-x NPs. The brush coating does not prevent CeO2-x NPs from displaying antioxidant properties. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00884k

A novel fluorescent biosensor for adrenaline detection and tyrosinase inhibitor screening.

PubMed

Liu, Ziping; Liu, Shasha

2018-04-17

In this work, a novel simple fluorescent biosensor for the highly sensitive and selective detection of adrenaline was established. Firstly, water-soluble CuInS 2 quantum dots (QDs) capped by L-Cys were synthesized via a hydrothermal synthesis method. Then, the positively charged adrenaline was assembled on the surface of CuInS 2 QDs due to the electrostatic interactions and hydrogen bonding, which led to the formation of adrenaline-CuInS 2 QD (Adr-CuInS 2 QD) electrostatic complexes. Tyrosinase (TYR) can catalyze adrenaline to generate H 2 O 2 , and additionally oxidize the adrenaline to adrenaline quinone. Both the H 2 O 2 and the adrenaline quinone can quench the fluorescence of the CuInS 2 QDs through the electron transfer (ET) process. Thus, the determination of adrenaline could be facilely achieved by taking advantage of the fluorescence "turn off" feature of CuInS 2 QDs. Under the optimum conditions, the fluorescence quenching ratio I f /I f0 (I f and I f0 were the fluorescence intensity of Adr-CuInS 2 QDs in the presence and absence of TYR, respectively) was proportional to the logarithm of adrenaline concentration in the range of 1 × 10 -8 -1 × 10 -4  mol L -1 with the detection limit of 3.6 nmol L -1 . The feasibility of the proposed biosensor in real sample assay was also studied and satisfactory results were obtained. Significantly, the proposed fluorescent biosensor can also be utilized to screen TYR inhibitors. Graphical abstract Schematic illustration of the fluorescent biosensor for adrenaline detection (A) and tyrosinase inhibitor screening (B).

A NIR sensor for cyanide detection and its application in cell imaging

NASA Astrophysics Data System (ADS)

Wu, Wei-Na; Wu, Hao; Wang, Yuan; Zhao, Xiao-Lei; Xu, Zhou-Qing; Xu, Zhi-Hong; Fan, Yun-Chang

2018-06-01

A novel 'D-π-A' sensor 1 has been designed and prepared via the condensation reaction of 3‑ethyl‑2‑methyl‑1,3‑benzothiazol‑3‑ium iodide and 5‑nitro‑o‑vanillin. Upon treatment with cyanide, sensor 1 exhibited a significant near-infrared (NIR) fluorescence quenching at 663 nm. The MS, IR, 1H NMR and DFT methods confirmed that the response of 1 to cyanide is due to the nucleophilic addition reaction, which results in the inhibition of the Intramolecular Charge Transfer (ICT) process in the sensor. Furthermore, sensor 1 was used for the determination of CN- in HeLa cells.

The Broken Ring: Reduced Aromaticity in Lys-Trp Cations and High pH Tautomer Correlates with Lower Quantum Yield and Shorter Lifetimes

PubMed Central

2015-01-01

Several nonradiative processes compete with tryptophan fluorescence emission. The difficulty in spectral interpretation lies in associating specific molecular environmental features with these processes and thereby utilizing the fluorescence spectral data to identify the local environment of tryptophan. Here, spectroscopic and molecular modeling study of Lys-Trp dipeptide charged species shows that backbone-ring interactions are undistinguished. Instead, quantum mechanical ground state isosurfaces reveal variations in indole π electron distribution and density that parallel charge (as a function of pK1, pK2, and pKR) on the backbone and residues. A pattern of aromaticity-associated quantum yield and fluorescence lifetime changes emerges. Where quantum yield is high, isosurfaces have a charge distribution similar to the highest occupied molecular orbital (HOMO) of indole, which is the dominant fluorescent ground state of the 1La transition dipole moment. Where quantum yield is low, isosurface charge distribution over the ring is uneven, diminished, and even found off ring. At pH 13, the indole amine is deprotonated, and Lys-Trp quantum yield is extremely low due to tautomer structure that concentrates charge on the indole amine; the isosurface charge distribution bears scant resemblance to the indole HOMO. Such greatly diminished fluorescence has been observed for proteins where the indole nitrogen is hydrogen bonded, lending credence to the association of aromaticity changes with diminished quantum yield in proteins as well. Thus tryptophan ground state isosurfaces are an indicator of indole aromaticity, signaling the partition of excitation energy between radiative and nonradiative processes. PMID:24882092

Ultrafast Intramolecular Electron and Proton Transfer in Bis(imino)isoindole Derivatives.

PubMed

Driscoll, Eric; Sorenson, Shayne; Dawlaty, Jahan M

2015-06-04

Concerted motion of electrons and protons in the excited state is pertinent to a wide range of chemical phenomena, including those relevant for solar-to-fuel light harvesting. The excited state dynamics of small proton-bearing molecules are expected to serve as models for better understanding such phenomena. In particular, for designing the next generation of multielectron and multiproton redox catalysts, understanding the dynamics of more than one proton in the excited state is important. Toward this goal, we have measured the ultrafast dynamics of intramolecular excited state proton transfer in a recently synthesized dye with two equivalent transferable protons. We have used a visible ultrafast pump to initiate the proton transfer in the excited state, and have probed the transient absorption of the molecule over a wide bandwidth in the visible range. The measurement shows that the signal which is characteristic of proton transfer emerges within ∼710 fs. To identify whether both protons were transferred in the excited state, we have measured the ultrafast dynamics of a related derivative, where only a single proton was available for transfer. The measured proton transfer time in that molecule was ∼427 fs. The observed dynamics in both cases were reasonably fit with single exponentials. Supported by the ultrafast observations, steady-state fluorescence, and preliminary computations of the relaxed excited states, we argue that the doubly protonated derivative most likely transfers only one of its two protons in the excited state. We have performed calculations of the frontier molecular orbitals in the Franck-Condon region. The calculations show that in both derivatives, the excitation is primarily from the HOMO to LUMO causing a large rearrangement of the electronic charge density immediately after photoexcitation. In particular, charge density is shifted away from the phenolic protons and toward the proton acceptor nitrogens. The proton transfer is hypothesized to occur both due to enhanced acidity of the phenolic proton and enhanced basicity of the nitrogen in the excited state. We hope this study can provide insight for better understanding of the general class of excited state concerted electron-proton dynamics.

Charge migration and charge transfer in molecular systems

PubMed Central

Wörner, Hans Jakob; Arrell, Christopher A.; Banerji, Natalie; Cannizzo, Andrea; Chergui, Majed; Das, Akshaya K.; Hamm, Peter; Keller, Ursula; Kraus, Peter M.; Liberatore, Elisa; Lopez-Tarifa, Pablo; Lucchini, Matteo; Meuwly, Markus; Milne, Chris; Moser, Jacques-E.; Rothlisberger, Ursula; Smolentsev, Grigory; Teuscher, Joël; van Bokhoven, Jeroen A.; Wenger, Oliver

2017-01-01

The transfer of charge at the molecular level plays a fundamental role in many areas of chemistry, physics, biology and materials science. Today, more than 60 years after the seminal work of R. A. Marcus, charge transfer is still a very active field of research. An important recent impetus comes from the ability to resolve ever faster temporal events, down to the attosecond time scale. Such a high temporal resolution now offers the possibility to unravel the most elementary quantum dynamics of both electrons and nuclei that participate in the complex process of charge transfer. This review covers recent research that addresses the following questions. Can we reconstruct the migration of charge across a molecule on the atomic length and electronic time scales? Can we use strong laser fields to control charge migration? Can we temporally resolve and understand intramolecular charge transfer in dissociative ionization of small molecules, in transition-metal complexes and in conjugated polymers? Can we tailor molecular systems towards specific charge-transfer processes? What are the time scales of the elementary steps of charge transfer in liquids and nanoparticles? Important new insights into each of these topics, obtained from state-of-the-art ultrafast spectroscopy and/or theoretical methods, are summarized in this review. PMID:29333473

Through-Space Ultrafast Photoinduced Electron Transfer Dynamics of a C 70 -Encapsulated Bisporphyrin Covalent Organic Polyhedron in a Low-Dielectric Medium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ortiz, Michael; Cho, Sung; Niklas, Jens

Ultrafast photoinduced electron transfer (PIET) dynamics of a C 70-encapsulated bisporphyrin covalent organic polyhedron hybrid (C 70@COP-5) is studied in a nonpolar toluene medium with fluorescence and transient absorption spectroscopies. This structurally rigid donor (D)-acceptor (A) molecular hybrid offers a new platform featuring conformationally predetermined cofacial D-A orientation with a fixed edge-to-edge separation, R EE (2.8 Å), without the aid of covalent bonds. Sub-picosecond PIET (T ET ≤ 0.4 ps) and very slow charge recombination (T CR ≈ 600 ps) dynamics are observed. The origin of these dynamics is discussed in terms of enhanced D-A coupling (V = 675 cmmore » -1) and extremely small reorganization energy (λ ≈ 0.18 eV), induced by the intrinsic structural rigidity of the C 70@COP-5 complex.« less

Through-Space Ultrafast Photoinduced Electron Transfer Dynamics of a C 70 -Encapsulated Bisporphyrin Covalent Organic Polyhedron in a Low-Dielectric Medium

DOE PAGES

Ortiz, Michael; Cho, Sung; Niklas, Jens; ...

2017-03-13

Ultrafast photoinduced electron transfer (PIET) dynamics of a C 70-encapsulated bisporphyrin covalent organic polyhedron hybrid (C 70@COP-5) is studied in a nonpolar toluene medium with fluorescence and transient absorption spectroscopies. This structurally rigid donor (D)-acceptor (A) molecular hybrid offers a new platform featuring conformationally predetermined cofacial D-A orientation with a fixed edge-to-edge separation, R EE (2.8 Å), without the aid of covalent bonds. Sub-picosecond PIET (T ET ≤ 0.4 ps) and very slow charge recombination (T CR ≈ 600 ps) dynamics are observed. The origin of these dynamics is discussed in terms of enhanced D-A coupling (V = 675 cmmore » -1) and extremely small reorganization energy (λ ≈ 0.18 eV), induced by the intrinsic structural rigidity of the C 70@COP-5 complex.« less

The NEXT-A (N-terminal EXtension with Transferase and ARS) reaction.

PubMed

Taki, Masumi; Kuroiwa, Hiroyuki; Sisido, Masahiko

2009-01-01

L/F-transferase is known to catalyze transfer of hydrophobic amino acids from aminoacyl tRNA to the N-terminus of a protein possessing lysine or arginine as the N-terminus. Combining L/F-transferase with E. coli phenylalanyl-tRNA synthetase (ARS), we achieved non-ribosomal N-terminal-specific introduction of various kinds of nonnatural amino acids to a protein. A nonnatural amino acid is once charged onto an E. coli tRNA(Phe) by a mutant ARS in situ, and successively transferred from the tRNA to a target protein, namely the NEXT-A reaction. Besides alphaA294G mutation on the ARS, alphaT251A, betaG318W, or betaA356W double-mutation were effective to increase the introduction efficiency through the NEXT-A reaction. Protein specific fluorescence labelling via the NEXT-A reaction followed by Huisgen cycloaddition was also demonstrated.

Through-Space Ultrafast Photoinduced Electron Transfer Dynamics of a C70-Encapsulated Bisporphyrin Covalent Organic Polyhedron in a Low-Dielectric Medium.

PubMed

Ortiz, Michael; Cho, Sung; Niklas, Jens; Kim, Seonah; Poluektov, Oleg G; Zhang, Wei; Rumbles, Garry; Park, Jaehong

2017-03-29

Ultrafast photoinduced electron transfer (PIET) dynamics of a C 70 -encapsulated bisporphyrin covalent organic polyhedron hybrid (C 70 @COP-5) is studied in a nonpolar toluene medium with fluorescence and transient absorption spectroscopies. This structurally rigid donor (D)-acceptor (A) molecular hybrid offers a new platform featuring conformationally predetermined cofacial D-A orientation with a fixed edge-to-edge separation, R EE (2.8 Å), without the aid of covalent bonds. Sub-picosecond PIET (τ ET ≤ 0.4 ps) and very slow charge recombination (τ CR ≈ 600 ps) dynamics are observed. The origin of these dynamics is discussed in terms of enhanced D-A coupling (V = 675 cm -1 ) and extremely small reorganization energy (λ ≈ 0.18 eV), induced by the intrinsic structural rigidity of the C 70 @COP-5 complex.

Fluoride anion sensing mechanism of 2-ureido-4[1H]-pyrimidinone quadruple hydrogen-bonded supramolecular assembly: photoinduced electron transfer and partial configuration change.

PubMed

Chen, Jun-Sheng; Zhou, Pan-Wang; Li, Guang-Yue; Chu, Tian-Shu; He, Guo-Zhong

2013-05-02

The fluoride anion sensing mechanism of 6-methyl-5-(9-methylene-anthracene)-(2-butylureido-4[1H]-pyrimidinone) (AnUP) has been investigated using the DFT/TDDFT method. The theoretical results indicate that the proton of the N3-H3 group in pyrimidine moiety is captured by the added fluoride anion and then deprotonated. The calculated vertical excitation energies of AnUP-dimer and its deprotonated form agree well with the experimental results. The molecular orbital analysis demonstrates that the first excited state (S1) of AnUP-dimer is a local excited state with a π-π* transition, whereas for the deprotonated form, S1 is a completely charge-separation state and is responsible for the photoinduced electron transfer (PET) process. The PET process from anthracene to the pyrimidine moiety leads to the fluorescence quenching.

Nonadiabatic coupling reduces the activation energy in thermally activated delayed fluorescence.

PubMed

Gibson, J; Penfold, T J

2017-03-22

The temperature dependent rate of a thermally activated process is given by the Arrhenius equation. The exponential decrease in the rate with activation energy, which this imposes, strongly promotes processes with small activation barriers. This criterion is one of the most challenging during the design of thermally activated delayed fluorescence (TADF) emitters used in organic light emitting diodes. The small activation energy is usually achieved with donor-acceptor charge transfer complexes. However, this sacrifices the radiative rate and is therefore incommensurate with the high luminescence quantum yields required for applications. Herein we demonstrate that the spin-vibronic mechanism, operative for efficient TADF, overcomes this limitation. Nonadiabatic coupling between the lowest two triplet states give rise to a strong enhancement of the rate of reserve intersystem crossing via a second order mechanism and promotes population transfer between the T 1 to T 2 states. Consequently the rISC mechanism is actually operative between initial and final state exhibiting an energy gap that is smaller than between the T 1 and S 1 states. This contributes to the small activation energies for molecules exhibiting a large optical gap, identifies limitations of the present design procedures and provides a basis from which to construct TADF molecules with simultaneous high radiative and rISC rates.

Time-resolved studies of energy transfer from meso-tetrakis(N-methylpyridinium-4-yl)- porphyrin to 3,3'-diethyl-2,2'-thiatricarbocyanine iodide along deoxyribonucleic acid Chain.

PubMed

Kakiuchi, Toshifumi; Ito, Fuyuki; Nagamura, Toshihiko

2008-04-03

The excitation energy transfer from meso-tetrakis(N-methylpyridinium-4-yl)porphyrin (TMPyP) to 3,3'-diethyl-2,2'-thiatricarbocyanine iodide (DTTCI) along the deoxyribonucleic acid (DNA) double strand was investigated by the steady-state absorption and fluorescence measurements and time-resolved fluorescence measurements. The steady-state fluorescence spectra showed that the near-infrared fluorescence of DTTCI was strongly enhanced up to 86 times due to the energy transfer from the excited TMPyP molecule in DNA buffer solution. Furthermore, we elucidated the mechanism of fluorescence quenching and enhancement by the direct observation of energy transfer using the time-resolved measurements. The fluorescence quenching of TMPyP chiefly consists of a static component due to the formation of complex and dynamic components due to the excitation energy transfer. In a heterogeneous one-dimensional system such as a DNA chain, it was proved that the energy transfer process only carries out within the critical distance based on the Förster theory and within a threshold value estimated from the modified Stern-Volmer equation. The present results showed that DNA chain is one of the most powerful tools for nanoassemblies and will give a novel concepts of material design.

DEVELOPMENT OF EVALUATION OF A QUANTITATIVE VIDEO-FLUORESCENCE IMAGING SYSTEM AND FLUORESCENT TRACER FOR MEASURING TRANSFER OF PESTICIDE RESIDUES FROM SURFACES TO HANDS WITH REPEATED CONTACTS

EPA Science Inventory

A video imaging system and the associated quantification methods have been developed for measurement of the transfers of a fluorescent tracer from surfaces to hands. The highly fluorescent compound riboflavin (Vitamin B2), which is also water soluble and non-toxic, was chosen as...

Biometal binding-site mimicry with modular, hetero-bifunctionally modified architecture encompassing a Trp/His motif: insights into spatiotemporal noncovalent interactions from a comparative spectroscopic study.

PubMed

Yang, Chi Ming

2011-03-28

Metal-site Trp/His interactions are crucial to diverse metalloprotein functions. This paper presents a study using metal-motif mimicry to capture and dissect the static and transient components of physicochemical properties underlying the Trp/His aromatic side-chain noncovalent interactions across the first- and second-coordination spheres of biometal ions. Modular biomimetic constructs, EDTA-(L-Trp, L-His) or EWH and DTPA-(L-Trp, L-His) or DWH, featuring a function-significant Trp/His pair, enabled extracting the putative hydrophobic/hydrophilic aromatic interactions surrounding metal centers. Fluorescence, circular dichroism (CD) spectroscopic titrations and ESI mass spectrometry demonstrated that both the constructs stoichiometrically bind to Ca(2+), Co(2+), Cu(2+), Ni(2+), Mn(2+), Zn(2+), Cd(2+), and Fe(2+), and such binding was strongly coupled to stereospecific side-chain structure reorientations of the Trp indole and His imidazole rings. A mechanistic dichotomy corresponding to the participation of the indole unit in the binding event was revealed by a scaffold-platform correlation of steady-state fluorescence-response landscape, illuminating that secondary-coordination-sphere ligand cation-π interactions were immediately followed by subsequent transient physicochemical processes including through-space energy transfer, charge transfer and/or electron transfer, depending on the type of metals. The fluorescence quenching of Trp side chain by 3d metal ions can be ascribed to through-space d-π interactions. While the fluorescence titration was capable of illuminating a two-component energetic model, clean isosbestic/isodichroic points in the CD titration spectra indicated that the metallo-constructs, such as Cu(2+)-EWH complex, fold thermodynamically by means of a two-state equilibrium. Further, the metal-ion dependence of Trp conformational variation in the modular architecture of metal-bound scaffolds was evidenced unambiguously by the CD spectra and supported by MMFF calculations; both were capable of distinguishing between the coordination geometry and the preference for metal binding mode. The study thus helps understand how aromatic rings around metal-sites have unique capabilities through the control of the spatiotemporal distribution of noncovalent interaction elements to achieve diverse chemical functionality.

Detecting RNA/DNA hybridization using double-labeled donor probes with enhanced fluorescence resonance energy transfer signals.

PubMed

Okamura, Yukio; Watanabe, Yuichiro

2006-01-01

Fluorescence resonance energy transfer (FRET) occurs when two fluorophores are in close proximity, and the emission energy of a donor fluorophore is transferred to excite an acceptor fluorophore. Using such fluorescently labeled oligonucleotides as FRET probes, makes possible specific detection of RNA molecules even if similar sequences are present in the environment. A higher ratio of signal to background fluorescence is required for more sensitive probe detection. We found that double-labeled donor probes labeled with BODIPY dye resulted in a remarkable increase in fluorescence intensity compared to single-labeled donor probes used in conventional FRET. Application of this double-labeled donor system can improve a variety of FRET techniques.

Impact of charge-transfer excitons in regioregular polythiophene on the charge separation at polythiophene-fullerene heterojunctions

NASA Astrophysics Data System (ADS)

Polkehn, M.; Tamura, H.; Burghardt, I.

2018-01-01

This study addresses the mechanism of ultrafast charge separation in regioregular oligothiophene-fullerene assemblies representative of poly-3-hexylthiophene (P3HT)-[6,6]-phenyl-C61 butyric acid methyl ester (PCBM) heterojunctions, with special emphasis on the inclusion of charge transfer excitons in the oligothiophene phase. The formation of polaronic inter-chain charge separated species in highly ordered oligothiophene has been demonstrated in recent experiments and could have a significant impact on the net charge transfer to the fullerene acceptor. The present approach combines a first-principles parametrized multi-site Hamiltonian, based on time-dependent density functional theory calculations, with accurate quantum dynamics simulations using the multi-layer multi-configuration time-dependent Hartree method. Quantum dynamical studies are carried out for up to 182 electronic states and 112 phonon modes. The present analysis follows up on our previous study of (Huix-Rotllant et al 2015 J. Phys. Chem. Lett. 6 1702) and significantly expands the scope of this analysis by including the dynamical role of charge transfer excitons. Our investigation highlights the pronounced mixing of photogenerated Frenkel excitons with charge transfer excitons in the oligothiophene domain, and the opening of new transfer channels due the creation of such charge-separated species. As a result, it turns out that the interfacial donor/acceptor charge transfer state can be largely circumvented due to the presence of charge transfer excitons. However, the latter states in turn act as a trap, such that the free carrier yield observed on ultrafast time scales is tangibly reduced. The present analysis underscores the complexity of the transfer pathways at P3HT-PCBM type junctions.

Heat transfer assembly for a fluorescent lamp and fixture

DOEpatents

Siminovitch, M.J.; Rubenstein, F.M.; Whitman, R.E.

1992-12-29

In a lighting fixture including a lamp and a housing, a heat transfer structure is disclosed for reducing the minimum lamp wall temperature of a fluorescent light bulb. The heat transfer structure, constructed of thermally conductive material, extends from inside the housing to outside the housing, transferring heat energy generated from a fluorescent light bulb to outside the housing where the heat energy is dissipated to the ambient air outside the housing. Also disclosed is a method for reducing minimum lamp wall temperatures. Further disclosed is an improved lighting fixture including a lamp, a housing and the aforementioned heat transfer structure. 11 figs.

The effect of gold(I) coordination on the dual fluorescence of 4-(dimethylamino)pyridine.

PubMed

López-de-Luzuriaga, José M; Manso, Elena; Monge, Miguel; Olmos, M Elena; Rodríguez-Castillo, María; Sampedro, Diego

2015-06-28

The reactions of 4(dimethylamino)pyridine (DMAP) with the gold(I) precursors [AuR(tht)] (R = C6F5, C6Cl2F3 or C6Cl5; tht = tetrahydrothiophene) lead to complexes [AuR(DMAP)] (R = C6F5 (1), C6Cl2F3 (2) or C6Cl5 (3)). X-ray diffraction studies of the complexes reveal the presence of discrete molecules in which aurophilic contacts are absent, with π-stacking (1) or hydrogen bond (2) interactions being responsible for the supramolecular arrangements found in the solid state. All complexes display fluorescence in solution in solvents of different polarities such as toluene, chloroform or acetonitrile. In all cases the emission energy is similar to the low-energy Twisted Intramolecular Charge Transfer (TICT) emission of free DMAP. TDDFT calculations confirm that the fluorescence of complexes 1-3 arises from the ICT excited state of bonded DMAP in which a 90° distortion of the pyridine ring and -NMe2 planes is observed. Model calculations based on experimental parameters show a higher degree of polarization of DMAP upon coordination to Au(I) organometallic fragments.

Photochemical and DFT studies on DNA-binding ability and antibacterial activity of lanthanum(III)-phenanthroline complex

NASA Astrophysics Data System (ADS)

Niroomand, Sona; Khorasani-Motlagh, Mozhgan; Noroozifar, Meissam; Jahani, Shohreh; Moodi, Asieh

2017-02-01

The binding of the lanthanum(III) complex containing 1,10-phenanthroline (phen), [La(phen)3Cl3·OH2], to DNA is investigated by absorption and emission methods. This complex shows absorption decreasing in a charge transfer band, and fluorescence decrement when it binds to DNA. Electronic absorption spectroscopy (UV-Vis), fluorescence spectra, iodide quenching experiments, salt effect and viscosity measurements, ethidium bromide (EB) competition test, circular dichroism (CD) spectra as well as variable temperature experiments indicate that the La(III) complex binds to fish salmon (FS) DNA, presumably via groove binding mode. The binding constants (Kb) of the La(III) complex with DNA is (2.55 ± 0.02) × 106 M-1. Furthermore, the binding site size, n, the Stern-Volmer constant KSV and thermodynamic parameters; enthalpy change (ΔH0) and entropy change (ΔS0) and Gibb's free energy (ΔG0), are calculated according to relevant fluorescent data and the Van't Hoff equation. The La(III) complex has been screened for its antibacterial activities by the disc diffusion method. Also, in order to supplement the experimental findings, DFT computation and NBO analysis are carried out.

New styryl phenanthroline derivatives as model D-π-A-π-D materials for non-linear optics.

PubMed

Bonaccorso, Carmela; Cesaretti, Alessio; Elisei, Fausto; Mencaroni, Letizia; Spalletti, Anna; Fortuna, Cosimo Gianluca

2018-04-27

Four novel push-pull systems combining a central phenanthroline acceptor moiety and two substituted benzene rings, as a part of the conjugated π-system between the donor and the acceptor moieties, have been synthetized through a straightforward and efficient one-step synthetic procedure. The chromophores display high fluorescence and a peculiar fluorosolvatochromic behavior. Ultrafast investigation by means of state-of-the-art femtosecond-resolved transient absorption and fluorescence up-conversion spectroscopies allowed the role of intramolecular charge transfer (ICT) states to be evidenced, also revealing the crucial role played by both the polarity and proticity of the medium on the excited state dynamics of the chromophores. The ICT processes, responsible for the solvatochromism, also lead to interesting non-linear optical (NLO) properties: namely great two photon absorption cross-sections (hundreds of GM), investigated by the Two Photon Excited Fluorescence (TPEF) technique, and large second order hyperpolarizability coefficients, estimated through a convenient solvatochromic method. These features thus make the investigated styryl phenanthroline molecules model D-π-A-π-D compounds for non-linear optical applications. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modulation of ICT probability in bi(polyarene)-based O-BODIPYs: towards the development of low-cost bright arene-BODIPY dyads.

PubMed

Gartzia-Rivero, Leire; Sánchez-Carnerero, Esther M; Jiménez, Josue; Bañuelos, Jorge; Moreno, Florencio; Maroto, Beatriz L; López-Arbeloa, Iñigo; de la Moya, Santiago

2017-09-12

We report the synthesis, and spectroscopic and electrochemical properties of a selected library of novel spiranic O-BODIPYs bearing a phenol-based bi(polyarene) unit tethered to the boron center through oxygen atoms. These dyes constitute an interesting family of arene-BODIPY dyads useful for the development of photonic applications due to their synthetic accessibility and tunable photonic properties. It is demonstrated that the electron-donor capability of the involved arene moiety switches on a non-emissive intramolecular charge transfer (ICT) state, which restricts the fluorescence efficiency of the dyad. Interestingly, the influence of this non-radiative deactivation channel can be efficiently modulated by the substitution pattern, either at the dipyrrin ligand or at the polyarene moiety. Thus, dyads featuring electron-rich dipyrrin and electron-poor polyarene show lower or almost negligible ICT probability, and hence display bright fluorescence upon dual excitation at far-away spectral regions. This synthetic approach has allowed the easy development of low-cost efficient ultraviolet-absorbing visible-emitting cassettes by selecting properly the substitution pattern of the involved key units, dipyrrin and bi(polyarene), to modulate not only absorption and emission wavelengths, but also fluorescence efficiencies.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nageswara Rao, B.D.; Kemple, M.D.; Prendergast, F.G.

Aequorin is a protein of low molecular weight (20,000) isolated from the jellyfish Aequorea forskalea which emits blue light upon the binding of Ca/sup 2 +/ ions. This bioluminescence requires neither exogenous oxygen nor any other cofactors. The light emission occurs from an excited state of a chromophore (an imidazolopyrazinone) which is tightly and noncovalently bound to the protein. Apparently the binding of Ca/sup 2 +/ by the protein induces changes in the protein conformation which allow oxygen, already bound or otherwise held by the protein, to react with and therein oxidize the chromophore. The resulting discharged protein remains intact,more » with the Ca/sup 2 +/ and the chromophore still bound, but is incapable of further luminescence. The fluorescence spectrum of this discharged protein and the bioluminescence spectrum of the original charged aequorin are identical. A green fluorescent protein (GFP) of approx. 30,000 mol wt isolated from the same organism, functions in vivo as an acceptor of energy from aequorin and subsequently emits green light. We are applying proton nuclear magnetic resonance (NMR) spectroscopy and fluorescence spectroscopy to examine structural details of, and fluctuations associated with the luminescent reaction of aequorin and the in vivo energy transfer from aequorin to the GFP.« less

Theoretical design and investigation of 1,8-naphthalimide-based two-photon fluorescent probes for detecting cytochrome P450 1A with separated fluorescence signal.

PubMed

Zhang, Chun; Ren, Ai-Min; Guo, Jing-Fu; Wang, Dan; Yu, Li-Ying

2018-05-16

As a type of enzyme with a terminal oxygen, the CYP1A subfamily possesses the ability to catalyze the reactions of many environmental toxins, endogenous substrates and clinical drugs. The development of efficient methods for the rapid and real-time detection of CYP1A enzyme activity in complex biological systems is of considerable significance for identifying potential abnormalities in these cancer-related enzymes. With this goal, we firstly provided a series of 1,8-naphthalimide-based two-photon fluorescent chromophores with large two-photon absorption (TPA) cross-sections (500-7000 GM) and remarkable changes in fluorescence spectra upon recognizing the CYP1A enzyme from its theoretical aspect. Moreover, we have thoroughly studied the effects of cyclic acceptor (dichlorobenzene and benzothiadiazole) and donor (fluorene and carbazole) groups on the one-photon absorption (OPA), TPA, and fluorescence properties of CYP1A enzyme probes and the corresponding reaction products. The connection of a heterocycle as the donor group to a 1,8-naphthalimide-based molecule to form a D-π-A-π-D-type electronic structure can effectively cause red shifts in the absorption and emission wavelengths to facilitate bioimaging in the near infrared (NIR) region, which is attributed to the lower transition energy, larger transition dipole moment and amount of transferred charge. Docking analysis suggests that the two-photon fluorescent probes NCMN-3 and NCMN-5 that were designed will guarantee and achieve excellent selectivity for the CYP1A enzyme.

Laboratory Studies of Thermal Energy Charge Transfer of Silicon and Iron Ions in Astrophysical Plasmas

NASA Technical Reports Server (NTRS)

Kwong, Victor H. S.

1996-01-01

Charge transfer at electron-volt energies between multiply charged atomic ions and neutral atoms and molecules is of considerable importance in astrophysics, plasma physics, and in particular, fusion plasmas. In the year covered by this report, several major tasks were completed. These include: (1) the re-calibration of the ion gauge to measure the absolute particle densities of H2, He, N2, and CO for our current measurements; (2) the analysis of data for charge transfer reactions of N(exp 2 plus) ion and He, H2, N2, and CO; (3) measurement and data analysis of the charge transfer reaction of (Fe(exp 2 plus) ion and H2; (4) charge transfer measurement of Fe(exp 2 plus) ion and H2; and (5) redesign and modification of the ion detection and data acquisition system for the low energy beam facility (reflection time of flight mass spectrometer) dedicated to the study of state select charge transfer.

Different Approaches for Assaying Melanosome Transfer

PubMed Central

Berens, Werner; Van Den Bossche, Karolien; Yoon, Tae-Jin; Westbroek, Wendy; Valencia, Julio C.; Out, Coby J.; Naeyaert, Jean Marie; Hearing, Vincent J.; Lambert, Jo

2006-01-01

Summary Many approaches have been tried to establish assays for melanosome transfer to keratinocytes. In this report we describe and summarize various novel attempts to label melanosomes in search of a reliable, specific, reproducible and quantitative assay system. We tried to fluorescently label melanosomes by transfection of GFP-labeled melanosomal proteins and by incubation of melanocytes with fluorescent melanin intermediates or homologues. In most cases a weak cytoplasmic fluorescence was perceived, which was probably due to incorrect sorting or deficient incorporation of the fluorescent protein and different localisation. We were able to label melanosomes via incorporation of 14C-thiouracil into melanin. Consequently, we tried to develop an assay to separate keratinocytes with transferred radioactivity from melanocytes after co-culture. Differential trypsination and different magnetic bead separation techniques were tested with unsatisfactory results. An attempt was also made to incorporate fluorescent thiouracil, since this would allow cells to be separated by FACS. In conclusion, different methods to measure pigment transfer between donor melanocytes and acceptor keratinocytes were thoroughly examined. This information could give other researchers a head start in the search for a melanosome transfer assay with said qualities to better understand pigment transfer. PMID:16162177

Synergistic electron transfer effect-based signal amplification strategy for the ultrasensitive detection of dopamine.

PubMed

Lu, Qiujun; Chen, Xiaogen; Liu, Dan; Wu, Cuiyan; Liu, Meiling; Li, Haitao; Zhang, Youyu; Yao, Shouzhuo

2018-05-15

The selective and sensitive detection of dopamine (DA) is of great significance for the identification of schizophrenia, Huntington's disease, and Parkinson's disease from the perspective of molecular diagnostics. So far, most of DA fluorescence sensors are based on the electron transfer from the fluorescence nanomaterials to DA-quinone. However, the limited electron transfer ability of the DA-quinone affects the level of detection sensitivity of these sensors. In this work, based on the DA can reduce Ag + into AgNPs followed by oxidized to DA-quinone, we developed a novel silicon nanoparticles-based electron transfer fluorescent sensor for the detection of DA. As electron transfer acceptor, the AgNPs and DA-quinone can quench the fluorescence of silicon nanoparticles effectively through the synergistic electron transfer effect. Compared with traditional fluorescence DA sensors, the proposed synergistic electron transfer-based sensor improves the detection sensitivity to a great extent (at least 10-fold improvement). The proposed sensor shows a low detection limit of DA, which is as low as 0.1 nM under the optimal conditions. This sensor has potential applicability for the detection of DA in practical sample. This work has been demonstrated to contribute to a substantial improvement in the sensitivity of the sensors. It also gives new insight into design electron transfer-based sensors. Copyright © 2018. Published by Elsevier B.V.

Molecular orbital (SCF-Xα-SW) theory of metal-metal charge transfer processes in minerals - II. Application to Fe2+ --> Ti4+ charge transfer transitions in oxides and silicates

USGS Publications Warehouse

Sherman, David M.

1987-01-01

A molecular orbital description, based on Xα-Scattered wave calculations on a (FeTiO10)14− cluster, is given for Fe2+ → Ti4+ charge transfer transitions in minerals. The calculated energy for the lowest Fe2+ → Ti4+ metal-metal charge transfer transition is 18040 cm−1 in reasonable agreement with energies observed in the optical spectra of Fe-Ti oxides and silicates. As in the case of Fe2+ → Fe3+ charge transfer in mixed-valence iron oxides and silicates, Fe2+ → Ti4+ charge transfer is associated with Fe-Ti bonding across shared polyhedral edges. Such bonding results from the overlap of the Fe(t 2g ) and Ti(t 2g ) 3d orbitals.

Charge transfer transitions in optical spectra of NicMg1-cO oxides

NASA Astrophysics Data System (ADS)

Churmanov, V. N.; Sokolov, V. I.; Pustovarov, V. A.; Gruzdev, N. B.; Uimin, M. A.; Byzov, I. V.; Druzhinin, A. V.; Korolyov, A. V.; Kim, G. A.; Zatsepin, A. F.; Kuznetsova, J. A.

2017-04-01

Radiative recombination with charge transfer was observed in NicMg1-cO (c = 0.008) oxides over the 8-300 K temperature range. This recombination occurs as a result of strong hybridization of the Ni2+ ion 3d-states and the band states. The charge transfer radiation excitation spectrum shows vibrational LO repeats of two exciton lines having charge transfer energy intervals of about 35 meV. The NiO nanocrystal absorption spectrum shows two weak peaks with energies of 3.510 and 3.543 eV, which are highly dependent on temperature. They are interpreted as charge transfer excitons at the edge of NiO fundamental absorption. The distance between the charge transfer exciton lines in the NicMg1-cO oxide spectra are caused by spin-orbit splitting of the valence band peak that was formed by the p-states of the oxygen ion.

Optical, Fluorescence with quantum analysis of hydrazine (1, 3- Dinitro Phenyl) by DFT and Ab initio approach

NASA Astrophysics Data System (ADS)

Cecily Mary Glory, D.; Sambathkumar, K.; Madivanane, R.; Velmurugan, G.; Gayathri, R.; Nithiyanantham, S.; Venkatachalapathy, M.; Rajkamal, N.

2018-07-01

Experimental and computational study of molecular structure, vibrational and UV-spectral analysis of Hydrazine (1, 3- Dinitrophenyl) (HDP) derivatives. The crystal was grown by slow cooling method and the crystalline perfection of single crystals was evaluated by high resolution X-ray diffractometry (HRXRD) using a multicrystal X-ray diffractometer. Fluorescence, FT-IR and FT-Raman spectra of HDP crystal were recorded. The assignments of the vibrational spectra have been carried out with the help of normal co-ordinate analysis (NCA) followed by scaled quantum force field methodology (SQMFF). NMR studies have confirmed respectively the crystal structure and functional groups of the grown crystal. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) result complements the experimental findings. The calculated MESP, UV, HOMO-LUMO energies show that charge transfer done within the molecule. And various thermodynamic parameters are studied. Fukui determines the local reactive site of electrophilic, nucleophilic, descriptor.

Red emissive cross-linked chitosan and their nanoparticles for imaging the nucleoli of living cells.

PubMed

Wang, Ke; Yuan, Xun; Guo, Zhenpeng; Xu, Jiying; Chen, Yi

2014-02-15

Biocompatible glutaraldehyde-cross-linked chitosan with new red fluorescence were prepared for the first time and were shaped into nanoparticles via inverse-microemulsion method. They could luminesce at ca. 670 nm either as powders and nanoparticles or in real and gelling solutions or suspensions, having a lifetime of 1.353 ns and a quantum yield of 0.08 in solution or 0.01 in solid state. The new-formed pyridinium structures and the intramolecular charge transfer effect are considered to be responsible for the new red emission, which have been proved by FTIR, (13)C NMR, and some calculation using Gaussian 09, respectively. Strikingly, they are quite inert and anti-photobleaching, with only <3% loss of fluorescent intensity per minute in average under a continuous laser illumination at 633 nm and 50 μW. Especially, their nanoparticles (5.6 nm) could enter into the negative nucleoli of living HeLa cells with low cytotoxicity for high contrast imaging inspections. Copyright © 2013 Elsevier Ltd. All rights reserved.

Effect of Cavity Size of Mesoporous Silica on Short DNA Duplex Stability.

PubMed

Masuda, Tsubasa; Shibuya, Yuuta; Arai, Shota; Kobayashi, Sayaka; Suzuki, Sotaro; Kijima, Jun; Itoh, Tetsuji; Sato, Yusuke; Nishizawa, Seiichi; Yamaguchi, Akira

2018-05-15

We studied the stabilities of short (4- and 3-bp) DNA duplexes within silica mesopores modified with a positively charged trimethyl aminopropyl (TMAP) monolayer (BJH pore diameter 1.6-7.4 nm). The DNA fragments with fluorescent dye were introduced into the pores, and their fluorescence resonance energy transfer (FRET) response was measured to estimate the structuring energies of the short DNA duplexes under cryogenic conditions (temperature 233-323 K). The results confirmed the enthalpic stability gain of the duplex within size-matched pores (1.6 and 2.3 nm). The hybridization equilibrium constants found for the size-matched pores were 2 orders of magnitude larger than those for large pores (≥3.5 nm), and this size-matching effect for the enhanced duplex stability was explained by a tight electrostatic interaction between the duplex and the surface TMAP groups. These results indicate the requirement of the precise regulation of mesopore size to ensure the stabilization of hydrogen-bonded supramolecular assemblies.

Encapsulation of labetalol, pseudoephedrine in β-cyclodextrin cavity: spectral and molecular modeling studies.

PubMed

Prabhu, A Antony Muthu; Rajendiran, N

2012-11-01

The absorption and fluorescence spectra of labetalol and pseudoephedrine have been studied in different polarities of solvents and β-cyclodextrin (β-CD). The inclusion complexation with β-CD is investigated by UV-visible, steady state and time resolved fluorescence spectra and PM3 method. In protic solvents, the normal emission originates from a locally excited state and the longer wavelength emission is due to intramolecular charge transfer (TICT). Labetalol forms a 1:2 complex and pseudoephedrine forms 1:1 complex with β-CD. Nanosecond time-resolved studies indicated that both molecules show triexponential decay. Thermodynamic parameters (ΔG, ΔH, ΔS) and HOMO, LUMO orbital investigations confirm the stability of the inclusion complex. The geometry of the most stable complex shows that the aromatic ring is deeply self included inside the β-CD cavity and intermolecular hydrogen bonds were established between host and guest molecules. This suggests that hydrophobic effect and hydrogen bond play an important role in the inclusion process.

Molecular complexes of L-phenylalanine with substituted 1,4-benzoquinones in aqueous medium: Spectral and theoretical investigations

NASA Astrophysics Data System (ADS)

Ganesh, K.; El-Mossalamy, E. H.; Satheshkumar, A.; Balraj, C.; Elango, K. P.

2013-12-01

Various spectral techniques such as UV-Vis, FT-IR, and fluorescence have been employed to investigate the charge transfer interaction of L-phenylalanine (LPA) with substituted 1,4-benzoquinones (MQ1-4). Kinetic and thermodynamic properties of the complexes were determined in aqueous medium at physiological condition (pH = 7). The interaction of MQ1-4 with L-phenylalanine (LPA) was found to proceed through the formation of donor-acceptor complex, yielding a radical anion. The stoichiometry of the complexes was determined by Jobs continuous variation method and was found to be 1:1 in all the cases. Fluorescence quenching studies showed that the interaction between the donor and the acceptors is spontaneous. The results indicated that the progressive replacement of chlorine atom (-I effect) by methoxy group (+M effect) in the quinone decreased the electron acceptor property of the quinone. The order of the experimentally measured association constant of these complexes was well supported by DFT/B3LYP calculations.

Biochemical investigation of yttrium(III) complex containing 1,10-phenanthroline: DNA binding and antibacterial activity.

PubMed

Khorasani-Motlagh, Mozhgan; Noroozifar, Meissam; Moodi, Asieh; Niroomand, Sona

2013-03-05

Characterization of the interaction between yttrium(III) complex containing 1,10-phenanthroline as ligand, [Y(phen)2Cl(OH2)3]Cl2⋅H2O, and DNA has been carried out by UV absorption, fluorescence spectra and viscosity measurements in order to investigate binding mode. The experimental results indicate that the yttrium(III) complex binds to DNA and absorption is decreasing in charge transfer band with the increase in amount of DNA. The binding constant (Kb) at different temperatures as well as thermodynamic parameters, enthalpy change (ΔH°) and entropy change (ΔS°), were calculated according to relevant fluorescent data and Vant' Hoff equation. The results of interaction mechanism studies, suggested that groove binding plays a major role in the binding of the complex and DNA. The activity of yttrium(III) complex against some bacteria was tested and antimicrobial screening tests shown growth inhibitory activity in the presence of yttrium(III) complex. Copyright © 2013 Elsevier B.V. All rights reserved.

Pyrene-based dyad and triad leading to a reversible chemical and redox optical and magnetic switch.

PubMed

Franco, Carlos; Mas-Torrent, Marta; Caballero, Antonio; Espinosa, Arturo; Molina, Pedro; Veciana, Jaume; Rovira, Concepció

2015-03-27

Two new pyrene-polychlorotriphenylmethyl (PTM) dyads and triads have been synthesized and characterized by optical, magnetic, and electrochemical methods. The interplay between the different electronic states of the PTM moiety in the dyads and triads and the optical and magnetic properties of the molecules have been studied. The electronic spectra of the radicals 5(.) and 6(.) show the intramolecular charge-transfer transition at around 700 nm due to the acceptor character of the PTM radical. In the diamagnetic protonated derivatives 3 and 4 the fluorescence due to the pyrene is maintained, whereas in the radicals 5(.) and 6(.) and the corresponding anions 5(-) and 6(-) there is a clear quenching of the fluorescence, which is more efficient in the case of radicals. The redox activity of PTM radicals that are easily reduced to the corresponding carbanion has been exploited to fabricate electrochemical switches with optical and magnetic response. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Potassium ions intercalated into g-C3N4-modified TiO2 nanobelts for the enhancement of photocatalytic hydrogen evolution activity under visible-light irradiation

NASA Astrophysics Data System (ADS)

Ma, Jian; Zhou, Wei; Tan, Xin; Yu, Tao

2018-05-01

Solar-to-chemical energy conversion is a challenging photochemical reaction for renewable energy storage. In recent decades, photocatalytic H2 evolution has been studied extensively. TiO2 is a well-established semiconductor in the field of photocatalytic H2 production; however, its low efficiency for solar energy utilization, and high photocarrier recombination rate, restrict its photocatalytic efficiency. Here, a series of K-intercalated g-C3N4-modified TiO2 nanobelts (TCN–Kx) with different dosages of K atoms were fabricated using a hydrothermal method followed by a calcination process. XRD, TEM and XPS tests indicate that a tight interfacial connection is formed between K–g-C3N4 and the TiO2 nanobelts. DFT calculations indicated that K dopants prefer to be at the interlayer sites of g-C3N4, suggesting increased charge transfer efficiency. The H2 production efficiency of the TCN–Kx composite materials from water splitting under visible-light irradiation was clearly improved. Steady fluorescence spectroscopy and photocurrent measurements confirmed that the improvement in photocatalytic H2 production activity was due to the superior charge separation and electron transfer efficiency of TCN–Kx composite materials.

Potassium ions intercalated into g-C3N4-modified TiO2 nanobelts for the enhancement of photocatalytic hydrogen evolution activity under visible-light irradiation.

PubMed

Ma, Jian; Zhou, Wei; Tan, Xin; Yu, Tao

2018-05-25

Solar-to-chemical energy conversion is a challenging photochemical reaction for renewable energy storage. In recent decades, photocatalytic H 2 evolution has been studied extensively. TiO 2 is a well-established semiconductor in the field of photocatalytic H 2 production; however, its low efficiency for solar energy utilization, and high photocarrier recombination rate, restrict its photocatalytic efficiency. Here, a series of K-intercalated g-C 3 N 4 -modified TiO 2 nanobelts (TCN-Kx) with different dosages of K atoms were fabricated using a hydrothermal method followed by a calcination process. XRD, TEM and XPS tests indicate that a tight interfacial connection is formed between K-g-C 3 N 4 and the TiO 2 nanobelts. DFT calculations indicated that K dopants prefer to be at the interlayer sites of g-C 3 N 4 , suggesting increased charge transfer efficiency. The H 2 production efficiency of the TCN-Kx composite materials from water splitting under visible-light irradiation was clearly improved. Steady fluorescence spectroscopy and photocurrent measurements confirmed that the improvement in photocatalytic H 2 production activity was due to the superior charge separation and electron transfer efficiency of TCN-Kx composite materials.

Interaction of two overlapped synthetic peptides from GB virus C with charged mono and bilayers.

PubMed

Alay, M; Haro, I; Alsina, M A; Girona, V; Prat, J; Busquets, M A

2013-05-01

The physical chemistry properties and interactions of E2 (125-139) and E2 (120-139) peptide sequences from GB virus C with model cell membranes were investigated by means of several biophysical techniques in order to gain better understanding of the effect of peptide length and lipid charge on membrane binding. The peptides, having one net negative charge at the pH of the assays, interacted with monolayers of all the phospholipids regardless of the charge but with more extent with the cationic DPTAP thus indicating that the interaction had both a hydrophobic and an electrostatic component as has been observed for other peptides of the same family. The peptides were able to leakage contents of liposomes and showed fluorescence energy transfer in vesicles depending on the vesicles lipid composition. On another hand, circular dichroism has shown that the peptides exist mainly as a mixture of disordered structure and β-type conformations in aqueous solution but diminished its unstructured content, folding preferentially into α-helical conformation upon interaction with hydrophobic solvents or positively charged lipid surfaces. Altogether, results of this work indicate that the peptides interact at a surface level, penetrate into bilayers composed of fluid lipids and that conformational changes could be responsible for this effect. Copyright © 2012 Elsevier B.V. All rights reserved.

Calculation of rates of exciton dissociation into hot charge-transfer states in model organic photovoltaic interfaces

NASA Astrophysics Data System (ADS)

Vázquez, Héctor; Troisi, Alessandro

2013-11-01

We investigate the process of exciton dissociation in ordered and disordered model donor/acceptor systems and describe a method to calculate exciton dissociation rates. We consider a one-dimensional system with Frenkel states in the donor material and states where charge transfer has taken place between donor and acceptor. We introduce a Green's function approach to calculate the generation rates of charge-transfer states. For disorder in the Frenkel states we find a clear exponential dependence of charge dissociation rates with exciton-interface distance, with a distance decay constant β that increases linearly with the amount of disorder. Disorder in the parameters that describe (final) charge-transfer states has little effect on the rates. Exciton dissociation invariably leads to partially separated charges. In all cases final states are “hot” charge-transfer states, with electron and hole located far from the interface.

Interaction of the alpha-toxin of Staphylococcus aureus with the liposome membrane.

PubMed

Ikigai, H; Nakae, T

1987-02-15

When the liposome membrane is exposed to the alpha-toxin of Staphylococcus aureus, fluorescence of the tryptophan residue(s) of the toxin molecule increases concomitantly with the degree of toxin-hexamer formation (Ikigai, H., and Nakae, T. (1985) Biochem. Biophys. Res. Commun. 130, 175-181). In the present study, the toxin-membrane interaction was distinguished from the hexamer formation by the fluorescence energy transfer from the tryptophan residue(s) of the toxin molecule to the dansylated phosphatidylethanolamine in phosphatidylcholine liposome. Measurement of these two parameters yielded the following results. The effect of the toxin concentration and phospholipid concentration on these two parameters showed first order kinetics. The effect of liposome size on the energy transfer and the fluorescence increment of the tryptophan residue(s) was only detectable in small liposomes. Under moderately acidic or basic conditions, the fluorescence energy transfer always preceded the fluorescence increment of the tryptophan residue(s). The fluorescence increment at 336 nm at temperatures below 20 degrees C showed a latent period, whereas the fluorescence energy transfer did not. These results were thought to indicate that when alpha-toxin damages the target membrane, the molecule interacts with the membrane first, and then undergoes oligomerization within the membrane.

Lighting the Way to See Inside Two-Photon Absorption Materials: Structure–Property Relationship and Biological Imaging

PubMed Central

Zhang, Qiong; Tian, Xiaohe; Zhou, Hongping; Wu, Jieying; Tian, Yupeng

2017-01-01

The application of two-photon absorption (2PA) materials is a classical research field and has recently attracted increasing interest. It has generated a demand for new dyes with high 2PA cross-sections. In this short review, we briefly cover the structure-2PA property relationships of organic fluorophores, organic-inorganic nanohybrids and metal complexes explored by our group. (1) The two-photon absorption cross-section (δ) of organic fluorophores increases with the extent of charge transfer, which is important to optimize the core, donor-acceptor pair, and conjugation-bridge to obtain a large δ value. Among the various cores, triphenylamine appears to be an efficient core. Lengthening of the conjugation with styryl groups in the D-π-D quadrupoles and D-π-A dipoles increased δ over a long wavelength range than when vinylene groups were used. Large values of δ were observed for extended conjugation length and moderate donor-acceptors in the near-IR wavelengths. The δ value of the three-arm octupole is larger than that of the individual arm, if the core has electron accepting groups that allow significant electronic coupling between the arms; (2) Optical functional organic/inorganic hybrid materials usually show high thermal stability and excellent optical activity; therefore the design of functional organic molecules to build functional organic-inorganic hybrids and optimize the 2PA properties are significant. Advances have been made in the design of organic-inorganic nanohybrid materials of different sizes and shapes for 2PA property, which provide useful examples to illustrate the new features of the 2PA response in comparison to the more thoroughly investigated donor-acceptor based organic compounds and inorganic components; (3) Metal complexes are of particular interest for the design of new materials with large 2PA ability. They offer a wide range of metals with different ligands, which can give rise to tunable electronic and 2PA properties. The metal ions, including transition metals and lanthanides, can serve as an important part of the structure to control the intramolecular charge-transfer process that drives the 2PA process. As templates, transition metal ions can assemble simple to more sophisticated ligands in a variety of multipolar arrangements resulting in interesting and tailorable electronic and optical properties, depending on the nature of the metal center and the energetics of the metal-ligand interactions, such as intraligand charge-transfer (ILCT) and metal-ligand charge-transfer (MLCT) processes. Lanthanide complexes are attractive for a number of reasons: (i) their visible emissions are quite long-lived; (ii) their absorption and emission can be tuned with the aid of appropriate photoactive ligands; (iii) the accessible energy-transfer path between the photo-active ligands and the lanthanide ion can facilitate efficient lanthanide-based 2PA properties. Thus, the above materials with excellent 2PA properties should be applied in two-photon applications, especially two-photon fluorescence microscopy (TPFM) and related emission-based applications. Furthermore, the progress of research into the use of those new 2PA materials with moderate 2PA cross section in the near-infrared region, good biocompatibility, and enhanced two-photon excited fluorescence for two-photon bio-imaging is summarized. In addition, several possible future directions in this field are also discussed (146 references). PMID:28772584

Three-dimensional representations of photo-induced electron transfer rates in pyrene-(CH2)n-N,N'-dimethylaniline systems obtained by three electron transfer theories.

PubMed

Rujkorakarn, Rong; Tanaka, Fumio

2009-01-01

The observed rates of photo-induced electron transfer (ET) from N,N'-dimethylaniline (DMA) to the excited pyrene (Py) in confined systems of pyrene-(CH(2))(n)-N,N'- dimethylaniline (PnD: n=1-3) were studied by molecular dynamic simulation (MD) and three kinds of electron transfer theories. ET parameters contained in Marcus theory (M theory), Bixon and Jortner theory (BJ theory) and Kakitani and Mataga theory (KM theory) were determined so as to fit the calculated fluorescence intensities with those obtained by the observed ET rates, according to a non-linear least squares method. Three-dimensional profiles of logarithm of calculated ET rates depending on two of three ET parameters, R, epsilon(0) and -DeltaG degrees were systematically examined with best-fit ET parameters of P1D. Bell shape dependencies of ET rate were predicted on R and on epsilon(0), and on -DeltaG degrees as well, by M theory and KM theory. The profiles of logarithm of ET rate calculated by BJ theory exhibited oscillatory dependencies not only on -DeltaG degrees , but also on R and on epsilon(0). Relationship between ET state and charge transfer complex was discussed with BJ theory.

Capillary electrophoresis electrospray ionization mass spectrometry interface

DOEpatents

Smith, Richard D.; Severs, Joanne C.

1999-01-01

The present invention is an interface between a capillary electrophoresis separation capillary end and an electrospray ionization mass spectrometry emitter capillary end, for transporting an anolyte sample from a capillary electrophoresis separation capillary to a electrospray ionization mass spectrometry emitter capillary. The interface of the present invention has: (a) a charge transfer fitting enclosing both of the capillary electrophoresis capillary end and the electrospray ionization mass spectrometry emitter capillary end; (b) a reservoir containing an electrolyte surrounding the charge transfer fitting; and (c) an electrode immersed into the electrolyte, the electrode closing a capillary electrophoresis circuit and providing charge transfer across the charge transfer fitting while avoiding substantial bulk fluid transfer across the charge transfer fitting. Advantages of the present invention have been demonstrated as effective in providing high sensitivity and efficient analyses.

Encapsulation of 3-hydroxyflavone and fisetin in β-cyclodextrins: Excited state proton transfer fluorescence and molecular mechanics studies

NASA Astrophysics Data System (ADS)

Banerjee, Anwesha; Sengupta, Pradeep K.

2006-06-01

Excited-state intramolecular proton-transfer (ESIPT) and dual emission properties (emission profile, anisotropy and decay kinetics) of 3-hydroxyflavone (a synthetic, model flavonol) and fisetin (3,7,3',4'-OH-flavone, a therapeutically active plant flavonol) have been exploited to study their encapsulation in nano-cavities comprising of natural and chemically modified β-cyclodextrins. In the presence of β-CDs, both the flavonols show significantly enhanced relative yields (along with changes in other emission parameters) of the tautomer emission. In addition, for fisetin, large blue shifts are observed for the normal emission (which has significant charge transfer character). From these we infer that the flavonols are encaged in predominantly hydrophobic micro-environments, where external hydrogen bonding perturbations (interfering with the intrinsic ESIPT), and dipolar relaxation effects, are minimized. This is further explained from results of molecular mechanics calculations which indicate selectivity in orientation of the encapsulated flavonols. Moreover, chemical modification of the β-CDs is found to profoundly influence the binding affinities of the guest flavonols.

Experimental and quantum chemical studies of a new organic proton transfer compound, 1H-imidazole-3-ium-3-hydroxy-2,4,6-trinitrophenolate

NASA Astrophysics Data System (ADS)

Dhamodharan, P.; Sathya, K.; Dhandapani, M.

2018-02-01

A new proton transfer compound, 1H-imidazole-3-ium-3-hydroxy-2,4,6-trinitrophenolate (IMHTP), was crystallized by slow evaporation-solution growth technique. 1H and 13C NMR spectral studies confirm the molecular structure of the grown crystal. Single crystal X-ray diffraction study confirms that IMHTP crystallizes in monoclinic system with space group P21/c. Thermal curves (TG/DTA) show that the material is thermally stable up to 198 °C. The crystal emits fluorescence at 510 nm, proving its utility in making green light emitting materials in optical applications. The stable molecular structure was optimized by Gaussian 09 program with B3LYP/6-311++G(d,p) level of basis set. The frontier molecular orbital study shows that the charge transfer interaction occurs within the complex. The calculated first-order hyperpolarizability value of IMHTP is 44 times higher than that the reference material, urea. The electrostatic potential map was used to probe into electrophilic and nucleophilic reactive sites present in the molecule.

Ground-State Charge-Density Distribution in a Crystal of the Luminescent ortho-Phenylenediboronic Acid Complex with 8-Hydroxyquinoline.

PubMed

Jarzembska, Katarzyna N; Kamiński, Radosław; Durka, Krzysztof; Woźniak, Krzysztof

2018-05-10

This contribution is devoted to the first electron density studies of a luminescent oxyquinolinato boron complex in the solid state. ortho-Phenylenediboronic acid mixed with 8-hydroxyquinoline in dioxane forms high-quality single crystals via slow solvent evaporation, which allows successful high resolution data collection (sin θ/λ = 1.2 Å -1 ) and charge density distribution modeling. Particular attention has been paid to the boron-oxygen fragment connecting the two parts of the complex, and to the solvent species exhibiting anharmonic thermal motion. The experiment and theory compared rather well in terms of atomic charges and volumes, except for the boron centers. Boron atoms, as expected, constitute the most electron-deficient species in the complex molecule, whereas the neighboring oxygen and carbon atoms are the most significantly negatively charged ones. This part of the molecule appears to be very much involved in the charge transfer occurring between the acid fragment and oxyquinoline moiety leading to the observed fluorescence, as supported by the time-dependent density functional theory (TDDFT) results and the generated transition density maps. TDDFT calculations indicated that p-type atomic orbitals contributing to the HOMO-1, HOMO, and LUMO play the major role in the lowest energy transitions, and enabled further comparison with the charge density features, which is discussed in details. Furthermore, the results confirmed the known fact the Q ligand character is most important for the spectroscopic properties of this class of complexes.

Time-resolved and steady-state fluorescence studies of excited-state proton-transfer reactions of proflavine

NASA Astrophysics Data System (ADS)

De Silvestri, S.; Laporta, P.

1984-01-01

Time-resolved and steady-state fluorescence studies of proflavine in aqueous solution are presented. The observation of a monoexponential fluorescence decay with a time constant decreasing with increasing pH and the presence of an anomalous red-shift in the fluorescence spectrum as a function of pH indicate the existence of a complex proton-transfer mechanism in the excited state. A reaction scheme is proposed and the corresponding proton-transfer rates are evaluated. An excited-state pK value of 12.85 is obtained for the equilibrium between the cationic form of proflavine and the same form dissociated at an amino group.

Bacterial attachment to RO membranes surface-modified by concentration-polarization-enhanced graft polymerization.

PubMed

Bernstein, Roy; Belfer, Sofia; Freger, Viatcheslav

2011-07-15

Concentration polarization-enhanced radical graft polymerization, a facile surface modification technique, was examined as an approach to reduce bacterial deposition onto RO membranes and thus contribute to mitigation of biofouling. For this purpose an RO membrane ESPA-1 was surface-grafted with a zwitterionic and negatively and positively charged monomers. The low monomer concentrations and low degrees of grafting employed in modifications moderately reduced flux (by 20-40%) and did not affect salt rejection, yet produced substantial changes in surface chemistry, charge and hydrophilicity. The propensity to bacterial attachment of original and modified membranes was assessed using bacterial deposition tests carried out in a parallel plate flow setup using a fluorescent strain of Pseudomonas fluorescens. Compared to unmodified ESPA-1 the deposition (mass transfer) coefficient was significantly increased for modification with the positively charged monomer. On the other hand, a substantial reduction in bacterial deposition rates was observed for membranes modified with zwitterionic monomer and, still more, with very hydrophilic negatively charged monomers. This trend is well explained by the effects of surface charge (as measured by ζ-potential) and hydrophilicity (contact angle). It also well correlated with force distance measurements by AFM using surrogate spherical probes with a negative surface charge mimicking the bacterial surface. The positively charged surface showed a strong hysteresis with a large adhesion force, which was weaker for unmodified ESPA-1 and still weaker for zwitterionic surface, while negatively charged surface showed a long-range repulsion and negligible hysteresis. These results demonstrate the potential of using the proposed surface- modification approach for varying surface characteristics, charge and hydrophilicity, and thus minimizing bacterial deposition and potentially reducing propensity biofouling.

A new visible-light-excitable ICT-CHEF-mediated fluorescence 'turn-on' probe for the selective detection of Cd(2+) in a mixed aqueous system with live-cell imaging.

PubMed

Goswami, Shyamaprosad; Aich, Krishnendu; Das, Sangita; Das Mukhopadhyay, Chitrangada; Sarkar, Deblina; Mondal, Tapan Kumar

2015-03-28

A new quinoline based sensor was developed and applied for the selective detection of Cd(2+) both in vitro and in vivo. The designed probe displays a straightforward approach for the selective detection of Cd(2+) with a prominent fluorescence enhancement along with a large red shift (∼38 nm), which may be because of the CHEF (chelation-enhanced fluorescence) and ICT (internal charge transfer) processes after interaction with Cd(2+). The interference from other biologically important competing metal ions, particularly Zn(2+), has not been observed. The visible-light excitability of the probe merits in the viewpoint of its biological application. The probe enables the detection of intracellular Cd(2+) with non-cytotoxic effects, which was demonstrated with the live RAW cells. The experimentally observed change in the structure and electronic properties of the sensor after the addition of Cd(2+) were modelled by the density functional theory (DFT) and time-dependent density functional theory (TDDFT) computational calculations, respectively. Moreover, the test strip experiment with this sensor exhibits both absorption and fluorescence color changes when exposed to Cd(2+) in a mixed aqueous solution, which also makes the probe more useful. The minimum limit of detection of Cd(2+) by the probe was in the range of 9.9 × 10(-8) M level.

A highly sensitive fluorescent probe for fast recognization of DTT and its application in one- and two-photon imaging.

PubMed

Sun, Tong; Xia, Lili; Huang, Jinxin; Gu, Yueqing; Wang, Peng

2018-09-01

As a widely used reducing agent, 1, 4-dithiothreitol (DTT) plays important roles in the fields of biology, biochemistry, and biomedicine. The development of facile and fast methods for DTT detection is urgent and necessary. In this article, we rationally constructed a novel two-photon fluorescent probe 6-(methylsulfinyl)-2-phenyl-1H-benzo[de]isoquinoline-1,3(2 H)-dione (NC-DTT) for detecting DTT, which employed the 1,8-naphthalimide and sulfoxide as the fluorophore and receptor unit respectively. The sulfoxide group in probe NC-DTT can be reduced by DTT to compound 6-(methylthio)-2-phenyl-1H-benzo[de]isoquinoline-1,3(2 H)-dione (NC), which could emit strong fluorescence with large Stokes shift presumably due to the enhanced intramolecular charge transfer (ICT). This probe responded to DTT quickly (within 1000 s) and showed satisfactory selectivity. A good linearity between fluorescence intensity and the concentration of DTT in the range of 0 - 700 μM was observed, and the detection limit towards DTT was 1.4 × 10 -7 M. Furthermore, the probe was successfully employed in one- and two-photon imaging of DTT in HepG2 cells with low cytotoxicity. Copyright © 2018 Elsevier B.V. All rights reserved.

Optical tracking of organically modified silica nanoparticles as DNA carriers: A nonviral, nanomedicine approach for gene delivery

NASA Astrophysics Data System (ADS)

Roy, Indrajit; Ohulchanskyy, Tymish Y.; Bharali, Dhruba J.; Pudavar, Haridas E.; Mistretta, Ruth A.; Kaur, Navjot; Prasad, Paras N.

2005-01-01

This article reports a multidisciplinary approach to produce fluorescently labeled organically modified silica nanoparticles as a nonviral vector for gene delivery and biophotonics methods to optically monitor intracellular trafficking and gene transfection. Highly monodispersed, stable aqueous suspensions of organically modified silica nanoparticles, encapsulating fluorescent dyes and surface functionalized by cationic-amino groups, are produced by micellar nanochemistry. Gel-electrophoresis studies reveal that the particles efficiently complex with DNA and protect it from enzymatic digestion of DNase 1. The electrostatic binding of DNA onto the surface of the nanoparticles, due to positively charged amino groups, is also shown by intercalating an appropriate dye into the DNA and observing the Förster (fluorescence) resonance energy transfer between the dye (energy donor) intercalated in DNA on the surface of nanoparticles and a second dye (energy acceptor) inside the nanoparticles. Imaging by fluorescence confocal microscopy shows that cells efficiently take up the nanoparticles in vitro in the cytoplasm, and the nanoparticles deliver DNA to the nucleus. The use of plasmid encoding enhanced GFP allowed us to demonstrate the process of gene transfection in cultured cells. Our work shows that the nanomedicine approach, with nanoparticles acting as a drug-delivery platform combining multiple optical and other types of probes, provides a promising direction for targeted therapy with enhanced efficacy as well as for real-time monitoring of drug action. nonviral vector | ORMOSIL nanoparticles | confocal microscopy

[Photophysical properties of poly (2-methoxy-5-octyloxy)-p-phenylene vinylene/TiO2 nano-composites].

PubMed

Sun, Jian-ping; Weng, Jia-bao; Cheng, Yun-tao; Lin, Ting; Huang, Xiao-zhu

2008-12-01

The photoelectric composites of poly (2-methoxy-5-octyloxy)-p-phenylene vinylene/nanometer TiO2 (PMOCOPV/ TiO2) with different nanometer TiOz amount were synthesized through dehydrochlorination in-situ polymerization. The results of Fourier transform infrared spectroscopy and Raman spectroscopy indicated that the surface of nanometer TiO2 was coated with PMOCOPV. UV-Vis spectrum showed that the absorption of PMOCOPV/TiO2 nano-composites was strengthened in the range of violet and visible light with the contents of TiO2 increasing. The composite dimensions were observed by highly resolution transmission electron microscope, PMOCOPV/TiO2 nano-composites dispersed uniformly and possessed core-shell structure, the diameter of PMOCOPV/TiO2 was measured to be about 30 nm, and the thickness of the PMOCOPV coating was about 8-10 nm. Photoluminescence spectroscopy indicated that the maximum emission wavelength of the PMOCOPV/TiO2 was red-shifted with increasing TiO2 concentration. The fluorescence lifetime of PMOCOPV/TiO2 was about 1 ns. The intensity and lifetime of fluorescence was increased remarkably with the contents of TiO2 increasing. The mechanism of the strengthened fluorescence quantum efficiency and fluorescence intensity of PMOCOPV/TiO2 was investigated through the charge transfer, exciton dissociation and potential energy in PMOCOPV/TiO2 nano-composites.

Site energies and charge transfer rates near pentacene grain boundaries from first-principles calculations

NASA Astrophysics Data System (ADS)

Kobayashi, Hajime; Tokita, Yuichi

2015-03-01

Charge transfer rates near pentacene grain boundaries are derived by calculating the site energies and transfer integrals of 37 pentacene molecules using first-principles calculations. The site energies decrease considerably near the grain boundaries, and electron traps of up to 300 meV and hole barriers of up to 400 meV are generated. The charge transfer rates across the grain boundaries are found to be reduced by three to five orders of magnitude with a grain boundary gap of 4 Å because of the reduction in the transfer integrals. The electron traps and hole barriers also reduce the electron and hole transfer rates by factors of up to 10 and 50, respectively. It is essential to take the site energies into consideration to determine charge transport near the grain boundaries. We show that the complex site energy distributions near the grain boundaries can be represented by an equivalent site energy difference, which is a constant for any charge transfer pass. When equivalent site energy differences are obtained for various grain boundary structures by first-principles calculations, the effects of the grain boundaries on the charge transfer rates are introduced exactly into charge transport simulations, such as the kinetic Monte Carlo method.

A gold nanocluster-based fluorescent probe for simultaneous pH and temperature sensing and its application to cellular imaging and logic gates

NASA Astrophysics Data System (ADS)

Wu, Yun-Tse; Shanmugam, Chandirasekar; Tseng, Wei-Bin; Hiseh, Ming-Mu; Tseng, Wei-Lung

2016-05-01

Metal nanocluster-based nanomaterials for the simultaneous determination of temperature and pH variations in micro-environments are still a challenge. In this study, we develop a dual-emission fluorescent probe consisting of bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs) and fluorescein-5-isothiocyanate (FITC) as temperature- and pH-responsive fluorescence signals. Under single wavelength excitation the FITC/BSA-AuNCs exhibited well-separated dual emission bands at 525 and 670 nm. When FITC was used as a reference fluorophore, FITC/BSA-AuNCs showed a good linear response over the temperature range 1-71 °C and offered temperature-independent spectral shifts, temperature accuracy, activation energy, and reusability. The possible mechanism for high temperature-induced fluorescence quenching of FITC/BSA-AuNCs could be attributed to a weakening of the Au-S bond, thereby lowering the charge transfer from BSA to AuNCs. Additionally, the pH- and temperature-responsive properties of FITC/BSA-AuNCs allow simultaneous temperature sensing from 21 to 41 °C (at intervals of 5 °C) and pH from 6.0 to 8.0 (at intervals of 0.5 pH unit), facilitating the construction of two-input AND logic gates. Three-input AND logic gates were also designed using temperature, pH, and trypsin as inputs. The practicality of using FITC/BSA-AuNCs to determine the temperature and pH changes in HeLa cells is also validated.Metal nanocluster-based nanomaterials for the simultaneous determination of temperature and pH variations in micro-environments are still a challenge. In this study, we develop a dual-emission fluorescent probe consisting of bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs) and fluorescein-5-isothiocyanate (FITC) as temperature- and pH-responsive fluorescence signals. Under single wavelength excitation the FITC/BSA-AuNCs exhibited well-separated dual emission bands at 525 and 670 nm. When FITC was used as a reference fluorophore, FITC/BSA-AuNCs showed a good linear response over the temperature range 1-71 °C and offered temperature-independent spectral shifts, temperature accuracy, activation energy, and reusability. The possible mechanism for high temperature-induced fluorescence quenching of FITC/BSA-AuNCs could be attributed to a weakening of the Au-S bond, thereby lowering the charge transfer from BSA to AuNCs. Additionally, the pH- and temperature-responsive properties of FITC/BSA-AuNCs allow simultaneous temperature sensing from 21 to 41 °C (at intervals of 5 °C) and pH from 6.0 to 8.0 (at intervals of 0.5 pH unit), facilitating the construction of two-input AND logic gates. Three-input AND logic gates were also designed using temperature, pH, and trypsin as inputs. The practicality of using FITC/BSA-AuNCs to determine the temperature and pH changes in HeLa cells is also validated. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr02341j

Charge Transfer and Orbital Level Alignment at Inorganic/Organic Interfaces: The Role of Dielectric Interlayers.

PubMed

Hollerer, Michael; Lüftner, Daniel; Hurdax, Philipp; Ules, Thomas; Soubatch, Serguei; Tautz, Frank Stefan; Koller, Georg; Puschnig, Peter; Sterrer, Martin; Ramsey, Michael G

2017-06-27

It is becoming accepted that ultrathin dielectric layers on metals are not merely passive decoupling layers, but can actively influence orbital energy level alignment and charge transfer at interfaces. As such, they can be important in applications ranging from catalysis to organic electronics. However, the details at the molecular level are still under debate. In this study, we present a comprehensive analysis of the phenomenon of charge transfer promoted by a dielectric interlayer with a comparative study of pentacene adsorbed on Ag(001) with and without an ultrathin MgO interlayer. Using scanning tunneling microscopy and photoemission tomography supported by density functional theory, we are able to identify the orbitals involved and quantify the degree of charge transfer in both cases. Fractional charge transfer occurs for pentacene adsorbed on Ag(001), while the presence of the ultrathin MgO interlayer promotes integer charge transfer with the lowest unoccupied molecular orbital transforming into a singly occupied and singly unoccupied state separated by a large gap around the Fermi energy. Our experimental approach allows a direct access to the individual factors governing the energy level alignment and charge-transfer processes for molecular adsorbates on inorganic substrates.

Intrinsic Tryptophan Fluorescence in the Detection and Analysis of Proteins: A Focus on Förster Resonance Energy Transfer Techniques

PubMed Central

Ghisaidoobe, Amar B. T.; Chung, Sang J.

2014-01-01

Förster resonance energy transfer (FRET) occurs when the distance between a donor fluorophore and an acceptor is within 10 nm, and its application often necessitates fluorescent labeling of biological targets. However, covalent modification of biomolecules can inadvertently give rise to conformational and/or functional changes. This review describes the application of intrinsic protein fluorescence, predominantly derived from tryptophan (λEX ∼ 280 nm, λEM ∼ 350 nm), in protein-related research and mainly focuses on label-free FRET techniques. In terms of wavelength and intensity, tryptophan fluorescence is strongly influenced by its (or the protein’s) local environment, which, in addition to fluorescence quenching, has been applied to study protein conformational changes. Intrinsic Förster resonance energy transfer (iFRET), a recently developed technique, utilizes the intrinsic fluorescence of tryptophan in conjunction with target-specific fluorescent probes as FRET donors and acceptors, respectively, for real time detection of native proteins. PMID:25490136

Migration of CT triplet excitons in TCNB-biphenyl and TCNB-HMB crystals

NASA Astrophysics Data System (ADS)

Kozankiewicz, BolesAw

1994-01-01

Delayed fluorescence decay curves of charge transfer (CT) crystals of tetracyanobenzene with biphenyl (TCNB-B) and with hexamethylbenzene (TCNB-HMB) have been studied over a wide temperature range (5-200 K). The decay curves have been adequately described by decay expressions derived for different mechanisms of triplet-triplet annihilation. This analysis points to one-dimensional, thermally activated motion of CT triplet excitons. The estimated activation energies for the exciton hopping are 360±60 and 650±100 cm -1 (or 550±150 cm -1 depending on the applied model) for the TCNB-B and TCNB-HMB crystals, respectively. The results seem to confirm the self-trapping of triplet CT excitons.

Membrane-spanning lipids for an uncompromised monitoring of membrane fusion and intermembrane lipid transfer

PubMed Central

Schwarzmann, Günter; Breiden, Bernadette; Sandhoff, Konrad

2015-01-01

A Förster resonance energy transfer-based fusion and transfer assay was developed to study, in model membranes, protein-mediated membrane fusion and intermembrane lipid transfer of fluorescent sphingolipid analogs. For this assay, it became necessary to apply labeled reporter molecules that are resistant to spontaneous as well as protein-mediated intermembrane transfer. The novelty of this assay is the use of nonextractable fluorescent membrane-spanning bipolar lipids. Starting from the tetraether lipid caldarchaeol, we synthesized fluorescent analogs with fluorophores at both polar ends. In addition, we synthesized radioactive glycosylated caldarchaeols. These labeled lipids were shown to stretch through bilayer membranes rather than to loop within a single lipid layer of liposomes. More important, the membrane-spanning lipids (MSLs) in contrast to phosphoglycerides proved to be nonextractable by proteins. We could show that the GM2 activator protein (GM2AP) is promiscuous with respect to glycero- and sphingolipid transfer. Saposin (Sap) B also transferred sphingolipids albeit with kinetics different from GM2AP. In addition, we could unambiguously show that the recombinant activator protein Sap C x His6 induced membrane fusion rather than intermembrane lipid transfer. These findings showed that these novel MSLs, in contrast with fluorescent phosphoglycerolipids, are well suited for an uncompromised monitoring of membrane fusion and intermembrane lipid transfer. PMID:26269359

Bio-Inspired Photon Absorption and Energy Transfer for Next Generation Photovoltaic Devices

NASA Astrophysics Data System (ADS)

Magsi, Komal

Nature's solar energy harvesting system, photosynthesis, serves as a model for photon absorption, spectra broadening, and energy transfer. Photosynthesis harvests light far differently than photovoltaic cells. These differences offer both engineering opportunity and scientific challenges since not all of the natural photon absorption mechanisms have been understood. In return, solar cells can be a very sensitive probe for the absorption characteristics of molecules capable of transferring charge to a conductive interface. The objective of this scientific work is the advancement of next generation photovoltaics through the development and application of natural photo-energy transfer processes. Two scientific methods were used in the development and application of enhancing photon absorption and transfer. First, a detailed analysis of photovoltaic front surface fluorescent spectral modification and light scattering by hetero-structure was conducted. Phosphor based spectral down-conversion is a well-known laser technology. The theoretical calculations presented here indicate that parasitic losses and light scattering within the spectral range are large enough to offset any expected gains. The second approach for enhancing photon absorption is based on bio-inspired mechanisms. Key to the utilization of these natural processes is the development of a detailed scientific understanding and the application of these processes to cost effective systems and devices. In this work both aspects are investigated. Dye type solar cells were prepared and tested as a function of Chlorophyll (or Sodium-Copper Chlorophyllin) and accessory dyes. Forster has shown that the fluorescence ratio of Chlorophyll is modified and broadened by separate photon absorption (sensitized absorption) through interaction with nearby accessory pigments. This work used the dye type solar cell as a diagnostic tool by which to investigate photon absorption and photon energy transfer. These experiments shed some doubt on the Foster Resonant Energy Transfer mechanism since energy relay dye architecture-photosensitizer mixtures do not broaden the response of solar cells. Spectral absorption characterization of chromophore-Chlorophyll solutions in varying solvent polarity confirm the lack of cooperative absorption via a Foster-like mechanism and point the way to new concepts of cooperative absorption in natural systems and the development of a new photovoltaic paradigm.

Azophenine as Central Core for Efficient Light Harvesting Devices.

PubMed

Lei, Hu; Karsenti, Paul-Ludovic; Harvey, Pierre D

2018-03-05

The notoriously non-luminescent uncycled azophenine (Q) was harnessed with Bodipy and zinc(II)porphyrin antennas to probe its fluorescence properties, its ability to act as a singlet excited state energy acceptor and to mediate the transfer. Two near-IR emissions are depicted from time-resolved fluorescence spectroscopy, which are most likely due to the presence of tautomers of very similar calculated total energies (350 cm -1 ; DFT; B3LYP). The rates for energy transfer, k ET (S 1 ), for 1 Bodipy*→Q are in the order of 10 10 -10 11  s -1 and are surprisingly fast when considering the low absorptivity properties of the lowest energy charge transfer excited state of azophenine. The rational is provided by the calculated frontier molecular orbitals (MOs) which show atomic contributions in the C 6 H 4 C≡CC 6 H 4 arms, thus favoring the double electron exchange mechanism. In the mixed-antenna Bodipy-porphyrin star molecule, the rate for 1 Bodipy*→porphyrin has also been evaluated (≈16×10 10  s -1 ) and is among the fastest rates reported for Bodipy-zinc(II)porphyrin pairs. This astonishing result is again explained from the atomic contributions of the C 6 H 4 C≡CC 6 H 4 and C≡CC 6 H 4 arms thus favouring the Dexter process. Here, for the first time, this process is found to be sensitively temperature-dependent. The azophenine turns out to be excellent for electronic communication. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Improvement of the Mutation-Discrimination Threshold for Rare Point Mutations by a Separation-Free Ligase Detection Reaction Assay Based on Fluorescence Resonance Energy Transfer.

PubMed

Hagihara, Kenta; Tsukagoshi, Kazuhiko; Nakajima, Chinami; Esaki, Shinsuke; Hashimoto, Masahiko

2016-01-01

We previously developed a separation-free ligase detection reaction assay based on fluorescence resonance energy transfer from a donor quantum dot to an acceptor fluorescent dye. This assay could successfully detect one cancer mutation among 10 wild-type templates. In the current study, the mutation-discrimination threshold was improved by one order of magnitude by replacing the original acceptor dye (Alexa Fluor 647) with another fluorescent dye (Cyanine 5) that was spectrally similar but more fluorescent.

Multiconfiguration Pair-Density Functional Theory Outperforms Kohn-Sham Density Functional Theory and Multireference Perturbation Theory for Ground-State and Excited-State Charge Transfer.

PubMed

Ghosh, Soumen; Sonnenberger, Andrew L; Hoyer, Chad E; Truhlar, Donald G; Gagliardi, Laura

2015-08-11

The correct description of charge transfer in ground and excited states is very important for molecular interactions, photochemistry, electrochemistry, and charge transport, but it is very challenging for Kohn-Sham (KS) density functional theory (DFT). KS-DFT exchange-correlation functionals without nonlocal exchange fail to describe both ground- and excited-state charge transfer properly. We have recently proposed a theory called multiconfiguration pair-density functional theory (MC-PDFT), which is based on a combination of multiconfiguration wave function theory with a new type of density functional called an on-top density functional. Here we have used MC-PDFT to study challenging ground- and excited-state charge-transfer processes by using on-top density functionals obtained by translating KS exchange-correlation functionals. For ground-state charge transfer, MC-PDFT performs better than either the PBE exchange-correlation functional or CASPT2 wave function theory. For excited-state charge transfer, MC-PDFT (unlike KS-DFT) shows qualitatively correct behavior at long-range with great improvement in predicted excitation energies.

Review on charge transfer and chemical activity of TiO2: Mechanism and applications

NASA Astrophysics Data System (ADS)

Cai, Yongqing; Feng, Yuan Ping

2016-12-01

Charge separation and transfer at the interface between two materials play a significant role in various atomic-scale processes and energy conversion systems. In this review, we present the mechanism and outcome of charge transfer in TiO2, which is extensively explored for photocatalytic applications in the field of environmental science. We list several experimental and computational methods to estimate the amount of charge transfer. The effects of the work function, defects and doping, and employment of external electric field on modulating the charge transfer are presented. The interplay between the band bending and carrier transport across the surface and interface consisting of TiO2 is discussed. We show that the charge transfer can also strongly affect the behavior of deposited nanoparticles on TiO2 through built-in electric field that it creates. This review encompasses several advances of composite materials where TiO2 is combined with two-dimensional materials like graphene, MoS2, phosphorene, etc. The charge transport in the TiO2-organohalide perovskite with respect to the electron-hole separation at the interface is also discussed.

What Controls the Rate of Ultrafast Charge Transfer and Charge Separation Efficiency in Organic Photovoltaic Blends.

PubMed

Jakowetz, Andreas C; Böhm, Marcus L; Zhang, Jiangbin; Sadhanala, Aditya; Huettner, Sven; Bakulin, Artem A; Rao, Akshay; Friend, Richard H

2016-09-14

In solar energy harvesting devices based on molecular semiconductors, such as organic photovoltaics (OPVs) and artificial photosynthetic systems, Frenkel excitons must be dissociated via charge transfer at heterojunctions to yield free charges. What controls the rate and efficiency of charge transfer and charge separation is an important question, as it determines the overall power conversion efficiency (PCE) of these systems. In bulk heterojunctions between polymer donor and fullerene acceptors, which provide a model system to understand the fundamental dynamics of electron transfer in molecular systems, it has been established that the first step of photoinduced electron transfer can be fast, of order 100 fs. But here we report the first study which correlates differences in the electron transfer rate with electronic structure and morphology, achieved with sub-20 fs time resolution pump-probe spectroscopy. We vary both the fullerene substitution and donor/fullerene ratio which allow us to control both aggregate size and the energetic driving force for charge transfer. We observe a range of electron transfer times from polymer to fullerene, from 240 fs to as short as 37 fs. Using ultrafast electro-optical pump-push-photocurrent spectroscopy, we find the yield of free versus bound charges to be weakly dependent on the energetic driving force, but to be very strongly dependent on fullerene aggregate size and packing. Our results point toward the importance of state accessibility and charge delocalization and suggest that energetic offsets between donor and acceptor levels are not an important criterion for efficient charge generation. This provides design rules for next-generation materials to minimize losses related to driving energy and boost PCE.

Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory.

PubMed

Isegawa, Miho; Gao, Jiali; Truhlar, Donald G

2011-08-28

Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi-Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi-Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred. © 2011 American Institute of Physics

Incorporation of charge transfer into the explicit polarization fragment method by grand canonical density functional theory

PubMed Central

Isegawa, Miho; Gao, Jiali; Truhlar, Donald G.

2011-01-01

Molecular fragmentation algorithms provide a powerful approach to extending electronic structure methods to very large systems. Here we present a method for including charge transfer between molecular fragments in the explicit polarization (X-Pol) fragment method for calculating potential energy surfaces. In the conventional X-Pol method, the total charge of each fragment is preserved, and charge transfer between fragments is not allowed. The description of charge transfer is made possible by treating each fragment as an open system with respect to the number of electrons. To achieve this, we applied Mermin's finite temperature method to the X-Pol wave function. In the application of this method to X-Pol, the fragments are open systems that partially equilibrate their number of electrons through a quasithermodynamics electron reservoir. The number of electrons in a given fragment can take a fractional value, and the electrons of each fragment obey the Fermi–Dirac distribution. The equilibrium state for the electrons is determined by electronegativity equalization with conservation of the total number of electrons. The amount of charge transfer is controlled by re-interpreting the temperature parameter in the Fermi–Dirac distribution function as a coupling strength parameter. We determined this coupling parameter so as to reproduce the charge transfer energy obtained by block localized energy decomposition analysis. We apply the new method to ten systems, and we show that it can yield reasonable approximations to potential energy profiles, to charge transfer stabilization energies, and to the direction and amount of charge transferred. PMID:21895159

Time-resolved UV-excited microarray reader for fluorescence energy transfer (FRET) measurements

NASA Astrophysics Data System (ADS)

Orellana, Adelina; Hokkanen, Ari P.; Pastinen, Tomi; Takkinen, Kristina; Soderlund, Hans

2001-05-01

Analytical systems based on immunochemistry are largely used in medical diagnostics and in biotechnology. There is a significant pressure to develop the present assay formats to become easier to use, faster, and less reagent consuming. Further developments towards high density array--like multianalyte measurement systems would be valuable. To this aim we have studied the applicability of fluorescence resonance energy transfer and time-resolved fluorescence resonance energy transfer in immunoassays on microspots and in microwells. We have used engineered recombinant antibodies detecting the pentameric protein CRP as a model analyte system, and tested different assay formats. We describe also the construction of a time-resolved scanning epifluorometer with which we could measure the FRET interaction between the slow fluorescence decay from europium chelates and its energy transfer to the rapidly decaying fluorophore Cy5.

Highly Efficient Full-Color Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes: Extremely Low Efficiency Roll-Off Utilizing a Host with Small Singlet-Triplet Splitting.

PubMed

Zhang, Dongdong; Zhao, Chongguang; Zhang, Yunge; Song, Xiaozeng; Wei, Pengcheng; Cai, Minghan; Duan, Lian

2017-02-08

Numerous efforts have been devoted to boost the efficiency of thermally activated delayed fluorescence (TADF) devices; however, strategies to suppress the device efficiency roll-off are still in urgent need. Here, a general and effective approach to suppress the efficiency roll-off of TADF devices is proposed, that is, utilizing TADF materials as the hosts for TADF emitters. Bearing small singlet-triplet splitting (ΔE ST ) with donor and acceptor units, TADF materials as the hosts possess the potential to achieve matched frontier energy levels with the adjacent transporting layers, facilitating balanced charge injection as well as bipolar charge transport mobilities beneficial to the balanced charges transportation. Furthermore, an enhanced Förster energy transfer from the host to the dopant can be anticipated, helpful to reduce the exciton concentration. Based on the principles, a new TADF material based on indeno[2,1-b]carbazole/1,3,5-triazin derivation is synthesized and used as the universal host for the full-color TADF devices. Remarkable low efficiency roll-off was achieved with above 90% of the maximum external quantum efficiencies (EQE max 's) maintained even at a brightness of 2000 cd/m 2 , along with EQE max 's of 23.2, 21.0, and 19.2% for orange, green, and sky-blue TADF devices, respectively. Through computational simulation, we identified the suppressed exciton annihilation rates compared with devices adopting conventional hosts. The state-of-the-art low efficiency roll-off of those TADF devices manifests the great potential of such host design strategy, paving an efficient strategy toward their practical application.

Performing the Millikan experiment at the molecular scale: Determination of atomic Millikan-Thomson charges by computationally measuring atomic forces.

PubMed

Rogers, T Ryan; Wang, Feng

2017-10-28

An atomic version of the Millikan oil drop experiment is performed computationally. It is shown that for planar molecules, the atomic version of the Millikan experiment can be used to define an atomic partial charge that is free from charge flow contributions. We refer to this charge as the Millikan-Thomson (MT) charge. Since the MT charge is directly proportional to the atomic forces under a uniform electric field, it is the most relevant charge for force field developments. The MT charge shows good stability with respect to different choices of the basis set. In addition, the MT charge can be easily calculated even at post-Hartree-Fock levels of theory. With the MT charge, it is shown that for a planar water dimer, the charge transfer from the proton acceptor to the proton donor is about -0.052 e. While both planar hydrated cations and anions show signs of charge transfer, anions show a much more significant charge transfer to the hydration water than the corresponding cations. It might be important to explicitly model the ion charge transfer to water in a force field at least for the anions.

Fluorescence quenching of human orosomucoid. Accessibility to drugs and small quenching agents.

PubMed Central

Friedman, M L; Schlueter, K T; Kirley, T L; Halsall, H B

1985-01-01

The fluorescence behaviour of human orosomucoid was investigated. The intrinsic fluorescence was more accessible to acrylamide than to the slightly larger succinimide, indicating limited accessibility to part of the tryptophan population. Although I- showed almost no quenching, that of Cs+ was enhanced, and suggested a region of negative charge proximal to an emitting tryptophan residue. Removal of more than 90% of sialic acid from the glycan chains led to no change in the Cs+, I-, succinimide or acrylamide quenching, indicating that the negatively charged region originates with the protein core. Quenching as a function of pH and temperature supported this view. The binding of chlorpromazine monitored by fluorescence quenching, in the presence and in the absence of the small quenching probes (above), led to a model of its binding domain on orosomucoid that includes two tryptophan residues relatively shielded from the bulk solvent, with the third tryptophan residue being on the periphery of the domain, or affected allotopically and near the negatively charged field. PMID:4091825

Time-resolved spectroscopic studies of photosynthetic reaction centers and tetrapyrrole chromophores for biomedical and solar-energy applications

NASA Astrophysics Data System (ADS)

Kee, Hooi Ling

2008-10-01

The photophysical properties of diverse tetrapyrrole chromophores as well as energy and electron transfer processes in tetrapyrrole dyads are investigated using static and time-resolved (femtoseconds to seconds) absorption and fluorescence spectroscopy. The goal of these studies is to elucidate the molecular design principals necessary to construct chromophores with the specific and tunable properties that will enhance applications in optical molecular imaging, photodynamic therapy, and solar-energy conversion. The kinetic properties of the transient intermediate P+H B- involving the bacteriopheophytin molecule HB on the normally inactive (B) cofactor branch of the bacterial photosynthetic reaction center are examined in Rhodobacter capsulatus mutants. Using nanosecond flash photolysis and F(L181)Y/Y(M208)F/L(M212)H mutant, the decay pathways and yields of P+HB- were measured, giving an overall yield of 13% for B-side charge separation P* → P+HB- → P+ QB- in this mutant. The goal of these studies is to understand the fundamental differences in the rates, yields, and mechanisms of charge separation and charge recombination along the two parallel electron-transport chains in the bacterial reaction center.

Effects of Charge-Transfer Excitons on the Photophysics of Organic Semiconductors

NASA Astrophysics Data System (ADS)

Hestand, Nicholas J.

The field of organic electronics has received considerable attention over the past several years due to the promise of novel electronic materials that are cheap, flexible and light weight. While some devices based on organic materials have already emerged on the market (e.g. organic light emitting diodes), a deeper understanding of the excited states within the condensed phase is necessary both to improve current commercial products and to develop new materials for applications that are currently in the commercial pipeline (e.g. organic photovoltaics, wearable displays, and field effect transistors). To this end, a model for pi-conjugated molecular aggregates and crystals is developed and analyzed. The model considers two types of electronic excitations, namely Frenkel and charge-transfer excitons, both of which play a prominent role in determining the nature of the excited states within tightly-packed organic systems. The former consist of an electron-hole pair bound to the same molecule while in the later the electron and hole are located on different molecules. The model also considers the important nuclear reorganization that occurs when the system switches between electronic states. This is achieved using a Holstein-style Hamiltonian that includes linear vibronic coupling of the electronic states to the nuclear motion associated with the high frequency vinyl-stretching and ring-breathing modes. Analysis of the model reveals spectroscopic signatures of charge-transfer mediated J- and H-aggregation in systems where the photophysical properties are determined primarily by charge-transfer interactions. Importantly, such signatures are found to be sensitive to the relative phase of the intermolecular electron and hole transfer integrals, and the relative energy of the Frenkel and charge-transfer states. When the charge-transfer integrals are in phase and the energy of the charge-transfer state is higher than the Frenkel state, the system exhibits J-aggregate characteristics including a positive band curvature, a red shifted main absorption peak, and an increase in the ratio of the first two vibronic peaks relative to the monomer. On the other hand, when the charge-transfer integrals are out of phase and the energy of the charge-transfer state is higher than the Frenkel state, the system exhibits H-aggregate characteristics including a negative band curvature, a blue shifted main absorption peak, and a decrease in the ratio of the first two vibronic peaks relative to the monomer. Notably, these signatures are consistent with those exhibited by Coulombically coupled J- and H-aggregates. Additional signatures of charge-transfer J- and H-aggregation are also discovered, the most notable of which is the appearance of a second absorption band when the charge-transfer integrals are in phase and the charge-transfer and Frenkel excitons are near resonance. In such instances, the peak-to-peak spacing is found to be proportional to the sum of the electron and hole transfer integrals. Further analysis of the charge-transfer interactions within the context of an effective Frenkel exciton coupling reveals that the charge-transfer interactions interfere directly with the intermolecular Coulombic coupling. The interference can be either constructive or destructive resulting in either enhanced or suppressed J- or H- aggregate behavior relative to what is expected based on Coulombic coupling alone. Such interferences result in four new aggregate types, namely HH-, HJ-, JH-, and JJ-aggregates, where the first letter indicates the nature of the Coulombic coupling and the second indicates the nature of the charge-transfer coupling. Vibronic signatures of such aggregates are developed and provide a means by which to rapidly screen materials for certain electronic characteristics. Notably, a large total (Coulombic plus charge-transfer) exciton coupling is associated with an absorption spectrum in which the ratio of the first two vibronic peaks deviates significantly from that of the unaggregated monomer. Hence, strongly coupled, high exciton mobility aggregates can be readily distinguished from low mobility aggregates by the ratio of their first two vibronic peaks. (Abstract shortened by ProQuest.).

Creating and optimizing interfaces for electric-field and photon-induced charge transfer.

PubMed

Park, Byoungnam; Whitham, Kevin; Cho, Jiung; Reichmanis, Elsa

2012-11-27

We create and optimize a structurally well-defined electron donor-acceptor planar heterojunction interface in which electric-field and/or photon-induced charge transfer occurs. Electric-field-induced charge transfer in the dark and exciton dissociation at a pentacene/PCBM interface were probed by in situ thickness-dependent threshold voltage shift measurements in field-effect transistor devices during the formation of the interface. Electric-field-induced charge transfer at the interface in the dark is correlated with development of the pentacene accumulation layer close to PCBM, that is, including interface area, and dielectric relaxation time in PCBM. Further, we demonstrate an in situ test structure that allows probing of both exciton diffusion length and charge transport properties, crucial for optimizing optoelectronic devices. Competition between the optical absorption length and the exciton diffusion length in pentacene governs exciton dissociation at the interface. Charge transfer mechanisms in the dark and under illumination are detailed.

Phototolerance of lichens, mosses and higher plants in an alpine environment: analysis of photoreactions.

PubMed

Heber, U; Bilger, W; Bligny, R; Lange, O L

2000-11-01

Adaptation to excessive light is one of the requirements of survival in an alpine environment particularly for poikilohydric organisms which in contrast to the leaves of higher plants tolerate full dehydration. Changes in modulated chlorophyll fluorescence and 820-nm absorption were investigated in the lichens Xanthoria elegans (Link) Th. Fr. and Rhizocarpon geographicum (L.) DC, in the moss Grimmia alpestris Limpr. and the higher plants Geum montanum L., Gentiana lutea L. and Pisum sativum L., all collected at altitudes higher than 2000 m above sea level. In the dehydrated state, chlorophyll fluorescence was very low in the lichens and the moss, but high in the higher plants. It increased on rehydration in the lichens and the moss, but decreased in the higher plants. Light-induced charge separation in photosystem II was indicated by pulse-induced fluorescence increases only in dried leaves, not in the dry moss and dry lichens. Strong illumination caused photodamage in the dried leaves, but not in the dry moss and dry lichens. Light-dependent increases in 820-nm absorption revealed formation of potential quenchers of chlorophyll fluorescence in all dehydrated plants, but energy transfer to quenchers decreased chlorophyll fluorescence only in the moss and the lichens, not in the higher plants. In hydrated systems, coupled cyclic electron transport is suggested to occur concurrently with linear electron transport under strong actinic illumination particularly in the lichens because far more electrons became available after actinic illumination for the reduction of photo-oxidized P700 than were available in the pool of electron carriers between photosystems II and I. In the moss Grimmia, but not in the lichens or in leaves, light-dependent quenching of chlorophyll fluorescence was extensive even under nitrogen, indicating anaerobic thylakoid acidification by persistent cyclic electron transport. In the absence of actinic illumination, acidification by ca. 8% CO2 in air quenched the initial chlorophyll fluorescence yield Fo only in the hydrated moss and the lichens, not in leaves of the higher plants. Under the same conditions, 8% CO2 reduced the maximal fluorescence yield Fm strongly in the poikilohydric organisms, but only weakly or not at all in leaves. The data indicate the existence of deactivation pathways which enable poikilohydric organisms to avoid photodamage not only in the hydrated but also in the dehydrated state. In the hydrated state, strong nonphotochemical quenching of chlorophyll fluorescence indicated highly sensitive responses to excess light which facilitated the harmless dissipation of absorbed excitation energy into heat. Protonation-dependent fluorescence quenching by cyclic electron transport, P700 oxidation and, possibly, excitation transfer between the photosystems were effectively combined to produce phototolerance.

Robust Stacking-Independent Ultrafast Charge Transfer in MoS2/WS2 Bilayers.

PubMed

Ji, Ziheng; Hong, Hao; Zhang, Jin; Zhang, Qi; Huang, Wei; Cao, Ting; Qiao, Ruixi; Liu, Can; Liang, Jing; Jin, Chuanhong; Jiao, Liying; Shi, Kebin; Meng, Sheng; Liu, Kaihui

2017-12-26

Van der Waals-coupled two-dimensional (2D) heterostructures have attracted great attention recently due to their high potential in the next-generation photodetectors and solar cells. The understanding of charge-transfer process between adjacent atomic layers is the key to design optimal devices as it directly determines the fundamental response speed and photon-electron conversion efficiency. However, general belief and theoretical studies have shown that the charge transfer behavior depends sensitively on interlayer configurations, which is difficult to control accurately, bringing great uncertainties in device designing. Here we investigate the ultrafast dynamics of interlayer charge transfer in a prototype heterostructure, the MoS 2 /WS 2 bilayer with various stacking configurations, by optical two-color ultrafast pump-probe spectroscopy. Surprisingly, we found that the charge transfer is robust against varying interlayer twist angles and interlayer coupling strength, in time scale of ∼90 fs. Our observation, together with atomic-resolved transmission electron characterization and time-dependent density functional theory simulations, reveals that the robust ultrafast charge transfer is attributed to the heterogeneous interlayer stretching/sliding, which provides additional channels for efficient charge transfer previously unknown. Our results elucidate the origin of transfer rate robustness against interlayer stacking configurations in optical devices based on 2D heterostructures, facilitating their applications in ultrafast and high-efficient optoelectronic and photovoltaic devices in the near future.

Quantum Dot-Fullerene Based Molecular Beacon Nanosensors for Rapid, Highly Sensitive Nucleic Acid Detection.

PubMed

Liu, Ye; Kannegulla, Akash; Wu, Bo; Cheng, Li-Jing

2018-05-15

Spherical fullerene (C 60 ) can quench the fluorescence of a quantum dot (QD) through energy transfer and charge transfer processes, with the quenching efficiency regulated by the number of proximate C 60 on each QD. With the quenching property and its small size compared with other nanoparticle-based quenchers, it is advantageous to group a QD reporter and multiple C 60 -labeled oligonucleotide probes to construct a molecular beacon (MB) probe for sensitive, robust nucleic acid detection. We demonstrated a rapid, high-sensitivity DNA detection method using the nanosensors composed of QD-C 60 based MBs carried by magnetic nanoparticles (MNPs). The assay was accelerated by first dispersing the nanosensors in analytes for highly efficient DNA capture resulting from short-distance 3-dimensional diffusion of targets to the sensor surface and then concentrating the nanosensors to a substrate by magnetic force to amplify the fluorescence signal for target quantification. The enhanced mass transport enabled a rapid detection (< 10 min) with a small sample volume (1-10 µl). The high signal-to-noise ratio produced by the QD-C 60 pairs and magnetic concentration yielded a detection limit of 100 fM (~106 target DNA copies for a 10 µl analyte). The rapid, sensitive, label-free detection method will benefit the applications in point-of-care molecular diagnostic technologies.

Development of Eu3+ activated monoclinic, perovskite, and garnet compounds in the Gd2O3-Al2O3 phase diagram as efficient red-emitting phosphors

NASA Astrophysics Data System (ADS)

Li, Jinkai; Li, Ji-Guang; Li, Jing; Liu, Shaohong; Li, Xiaodong; Sun, Xudong; Sakka, Yoshio

2013-10-01

Eu3+ doped Gd4Al2O9 (GdAM), GdAlO3 (GdAP), and Gd3Al5O12 (GdAG, containing 10 at% of Lu3+ for lattice stabilization) have been developed in this work as efficient red-emitting phosphors. With coprecipitated carbonate precursors, phase evolution studies found minimum processing temperatures of ~1000, 1100, and 1300 °C for the three phosphors to crystallize as pure phases, respectively. Compared with their yttrium aluminate counterparts, the gadolinium-based phosphors exhibit red-shifted O2--Eu3+ charge transfer excitation band (CTB) centers due to the lower electronegativity of Gd3+ and appreciably higher quantum yields of photoluminescence owing to the occurrence of efficient Gd3+→Eu3+energy transfer. The optimal Eu3+ contents were determined to be ~7.5 at% for GdAM and 5.0 at% for both GdAP and GdAG, and concentration quenching of luminescence was suggested to be due to exchange interactions. Fluorescence decay analysis found a shorter lifetime for the phosphor powder processed at a higher temperature or with a higher Eu3+ content, and the underlying mechanism was discussed. Fluorescence lifetimes were also compared between the yttrium and gadolinium phosphor systems for the dominant emissions.

Supramolecular networks with electron transfer in two dimensions

DOEpatents

Stupp, Samuel I.; Stoddart, J. Fraser; Shveyd, Alexander K.; Tayi, Alok S.; Sue, Chi-Hau; Narayanan, Ashwin

2016-09-13

Organic charge-transfer (CT) co-crystals in a crossed stack system are disclosed. The co-crystals exhibit bidirectional charge transfer interactions where one donor molecule shares electrons with two different acceptors, one acceptor face-to-face and the other edge-to-face. The assembly and charge transfer interaction results in a pleochroic material whereby the optical absorption continuously changes depending on the polarization angle of incident light.

Charge transfer polarisation wave and carrier pairing in the high T(sub c) copper oxides

NASA Technical Reports Server (NTRS)

Chakraverty, B. K.

1990-01-01

The High T(sub c) oxides are highly polarizable materials and are charge transfer insulators. The charge transfer polarization wave formalism is developed in these oxides. The dispersion relationships due to long range dipole-dipole interaction of a charge transfer dipole lattice are obtained in 3-D and 2-D. These are high frequency bosons and their coupling with carriers is weak and antiadiabatic in nature. As a result, the mass renormalization of the carriers is negligible in complete contrast to conventional electron-phonon interaction, that give polarons and bipolarons. Both bound and superconducting pairing is discussed for a model Hamiltonian valid in the antiadiabatic regime, both in 3-D and 2-D. The stability of the charge transfer dipole lattice has interesting consequences that are discussed.

Fluorescence from graphene oxide and the influence of ionic, π-π interactions and heterointerfaces: electron or energy transfer dynamics.

PubMed

Vempati, Sesha; Uyar, Tamer

2014-10-21

2D crystals such as graphene and its oxide counterpart have sought good research attention for their application as well as fundamental interest. Especially graphene oxide (GO) is quite interesting because of its versatility and diverse application potential. However the mechanism of fluorescence from GO is under severe discussion. To explain the emission in general two interpretations were suggested, viz localization of sp(2) clusters and involvement of oxygeneous functional groups. Despite this disagreement, it should be acknowledged that the heterogeneous atomic structure, synthesis dependent and uncontrollable implantation of oxygen functional groups on the basal plane make such explanations more difficult. Nevertheless, a suitable explanation enhances the applicability of the material which also enables the design of novel materials. At this juncture we believe that given the complexity in understanding the emission mechanism it would be very useful to review the literature. In this perspective we juxtapose various results related to fluorescence and influencing factors so that a conclusive interpretation may be unveiled. Apparently, the existing interpretations have largely ignored the factors such as self-rolling, byproduct formation etc. Vis-a-vis previous reviews did not discuss the interfacial charge transfer across heterostructures and the implication on the optical properties of GO or reduced graphene oxide (rGO). Such analysis would be very insightful to determine the energetic location of sub band gap states. Moreover, ionic and π-π type interactions are also considered for their influence on emission properties. Apart from these, quantum dots, covalent modifications and nonlinear optical properties of GO and rGO were discussed for completeness. Finally we made concluding remarks with outlook.

Halobenzoquinone-mediated assembly of amino acid modified Mn-doped ZnS quantum dots for halobenzoquinones detection in drinking water.

PubMed

Jiao, Zhe; Zhang, Pengfei; Chen, Hongwei; Li, Jingwen; Zhong, Zhengquan; Fan, Hongbo; Cheng, Faliang

2018-10-05

Halobenzoquinones (HBQs) were reported as disinfection byproducts (DBPs) which had potential risk of bladder cancer. In this paper, a highly selective analytical method for HBQs was developed by HBQs-mediated assembly of amino acid modified Mn-doped ZnS/Quantum Dots (Mn: ZnS QDs). In the presence HBQs, a charge-transfer complex (CTC) was formed between aromatic rings of HBQs and the primary amino groups on the surface of the QDs. The formation of CTC led to the aggregation of QDs, as a result fluorescence decreasing occurred. The decrease was correlated with the concentration of HBQs. Then a fluorescence sensor array for discrimination of three kinds of HBQs including 2,6-Dichloro-1,4-benzoquinone (DCBQ), 2,6-Dibromo-1,4-benzoquinone (DBBQ) and 2,3,6-trichloro-1,4-benzoquinone (TCBQ) was developed. Four kinds of amino acids including cysteine, threonine, tyrosine and tryptophan were embellished on the Mn: ZnS QDs. The different extents of aggregation led to different fluorescence decreasing effect, thus distinct fluorescence patterns were created. It showed that three kinds of HBQs could be discriminated successfully by fluorescence sensor array at a range of concentrations through principal component analysis (PCA). The unknown samples were predicted by with a stepwise linear discriminant analysis (SLDA) using Mahalanobis distance as a selection criterion with accuracy of 100%. Remarkably, the practicability of the proposed sensor array was further validated by identification of three kinds of HBQs at different concentrations in real drinking water samples. Compared to LC/MS/MS, this fluorescent sensor array-based method was proved to be more convenient since the nanoparticles can be prepared flexibly according to the property of the target. Copyright © 2018 Elsevier B.V. All rights reserved.

Time-Lapse Monitoring of DNA Damage Colocalized With Particle Tracks in Single Living Cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

McFadden, Conor H.; Hallacy, Timothy M.; Department of Physics and Astronomy, Rice University, Houston, Texas

2016-09-01

Purpose: Understanding the DNA damage and repair induced by hadron therapy (HT) beams is crucial for developing novel strategies to maximize the use of HT beams to treat cancer patients. However, spatiotemporal studies of DNA damage and repair for beam energies relevant to HT have been challenging. We report a technique that enables spatiotemporal measurement of radiation-induced damage in live cells and colocalization of this damage with charged particle tracks over a broad range of clinically relevant beam energies. The technique uses novel fluorescence nuclear track detectors with fluorescence confocal laser scanning microscopy in the beam line to visualize particlemore » track traversals within the subcellular compartments of live cells within seconds after injury. Methods and Materials: We designed and built a portable fluorescence confocal laser scanning microscope for use in the beam path, coated fluorescence nuclear track detectors with fluorescent-tagged live cells (HT1080 expressing enhanced green fluorescent protein tagged to XRCC1, a single-strand break repair protein), placed the entire assembly into a proton therapy beam line, and irradiated the cells with a fluence of ∼1 × 10{sup 6} protons/cm{sup 2}. Results: We successfully obtained confocal images of proton tracks and foci of DNA single-strand breaks immediately after irradiation. Conclusions: This technique represents an innovative method for analyzing biological responses in any HT beam line at energies and dose rates relevant to therapy. It allows precise determination of the number of tracks traversing a subcellular compartment and monitoring the cellular damage therein, and has the potential to measure the linear energy transfer of each track from therapeutic beams.« less

Environment-sensitive fluorophores with benzothiadiazole and benzoselenadiazole structures as candidate components of a fluorescent polymeric thermometer.

PubMed

Uchiyama, Seiichi; Kimura, Kohki; Gota, Chie; Okabe, Kohki; Kawamoto, Kyoko; Inada, Noriko; Yoshihara, Toshitada; Tobita, Seiji

2012-07-27

An environment-sensitive fluorophore can change its maximum emission wavelength (λ(em)), fluorescence quantum yield (Φ(f)), and fluorescence lifetime in response to the surrounding environment. We have developed two new intramolecular charge-transfer-type environment-sensitive fluorophores, DBThD-IA and DBSeD-IA, in which the oxygen atom of a well-established 2,1,3-benzoxadiazole environment-sensitive fluorophore, DBD-IA, has been replaced by a sulfur and selenium atom, respectively. DBThD-IA is highly fluorescent in n-hexane (Φ(f) =0.81, λ(em) =537 nm) with excitation at 449 nm, but is almost nonfluorescent in water (Φ(f) =0.037, λ(em) =616 nm), similarly to DBD-IA (Φ(f) =0.91, λ(em) =520 nm in n-hexane; Φ(f) =0.027, λ(em) =616 nm in water). A similar variation in fluorescence properties was also observed for DBSeD-IA (Φ(f) =0.24, λ(em) =591 nm in n-hexane; Φ(f) =0.0046, λ(em) =672 nm in water). An intensive study of the solvent effects on the fluorescence properties of these fluorophores revealed that both the polarity of the environment and hydrogen bonding with solvent molecules accelerate the nonradiative relaxation of the excited fluorophores. Time-resolved optoacoustic and phosphorescence measurements clarified that both intersystem crossing and internal conversion are involved in the nonradiative relaxation processes of DBThD-IA and DBSeD-IA. In addition, DBThD-IA exhibits a 10-fold higher photostability in aqueous solution than the original fluorophore DBD-IA, which allowed us to create a new robust molecular nanogel thermometer for intracellular thermometry. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Detection of Subclinical Arthritis in Mice by a Thrombin Receptor-Derived Imaging Agent.

PubMed

Friedman, Beth; Whitney, Michael A; Savariar, Elamprakash N; Caneda, Christa; Steinbach, Paul; Xiong, Qing; Hingorani, Dina V; Crisp, Jessica; Adams, Stephen R; Kenner, Michael; Lippert, Csilla N; Nguyen, Quyen T; Guma, Monica; Tsien, Roger Y; Corr, Maripat

2018-01-01

Functional imaging of synovitis could improve both early detection of rheumatoid arthritis (RA) and long-term outcomes. Given the intersection of inflammation with coagulation protease activation, this study was undertaken to examine coagulation protease activities in arthritic mice with a dual-fluorescence ratiometric activatable cell-penetrating peptide (RACPP) that has a linker, norleucine (Nle)-TPRSFL, with a cleavage site for thrombin. K/BxN-transgenic mice with chronic arthritis and mice with day 1 passive serum-transfer arthritis were imaged in vivo for Cy5:Cy7 emission ratiometric fluorescence from proteolytic cleavage and activation of RACPP NleTPRSFL . Joint thickness in mice with serum-transfer arthritis was measured from days 0 to 10. The cleavage-evoked release of Cy5-tagged tissue-adhesive fragments enabled microscopic correlation with immunohistochemistry for inflammatory markers. Thrombin dependence of ratiometric fluorescence was tested by ex vivo application of RACPP NleTPRSFL and argatroban to cryosections obtained from mouse hind paws on day 1 of serum-transfer arthritis. In chronic arthritis, RACPP NleTPRSFL fluorescence ratios of Cy5:Cy7 emission were significantly higher in diseased swollen ankles of K/BxN-transgenic mice than in normal mouse ankles. A high ratio of RACPP NleTPRSFL fluorescence in mouse ankles and toes on day 1 of serum-transfer arthritis correlated with subsequent joint swelling. Foci of high ratiometric fluorescence localized to inflammation, as demarcated by immune reactivity for citrullinated histones, macrophages, mast cells, and neutrophils, in soft tissue on day 1 of serum-transfer arthritis. Ex vivo application of RACPP NleTPRSFL to cryosections obtained from mice on day 1 of serum-transfer arthritis produced ratiometric fluorescence that was inhibited by argatroban. RACPP NleTPRSFL activation detects established experimental arthritis, and the detection of inflammation by RACPP NleTPRSFL on day 1 of serum-transfer arthritis correlates with disease progression. © 2017, American College of Rheumatology.

Two-phase charge-coupled device

NASA Technical Reports Server (NTRS)

Kosonocky, W. F.; Carnes, J. E.

1973-01-01

A charge-transfer efficiency of 99.99% per stage was achieved in the fat-zero mode of operation of 64- and 128-stage two-phase charge-coupled shift registers at 1.0-MHz clock frequency. The experimental two-phase charge-coupled shift registers were constructed in the form of polysilicon gates overlapped by aluminum gates. The unidirectional signal flow was accomplished by using n-type substrates with 0.5 to 1.0 ohm-cm resistivity in conjunction with a channel oxide thickness of 1000 A for the polysilicon gates and 3000 A for the aluminum gates. The operation of the tested shift registers with fat zero is in good agreement with the free-charge transfer characteristics expected for the tested structures. The charge-transfer losses observed when operating the experimental shift registers without the fat zero are attributed to fast interface state trapping. The analytical part of the report contains a review backed up by an extensive appendix of the free-charge transfer characteristics of CCD's in terms of thermal diffusion, self-induced drift, and fringing field drift. Also, a model was developed for the charge-transfer losses resulting from charge trapping by fast interface states. The proposed model was verified by the operation of the experimental two-phase charge-coupled shift registers.

A quantum mechanical-Poisson-Boltzmann equation approach for studying charge flow between ions and a dielectric continuum

NASA Astrophysics Data System (ADS)

Gogonea, Valentin; Merz, Kenneth M.

2000-02-01

This paper presents a theoretical model for the investigation of charge transfer between ions and a solvent treated as a dielectric continuum media. The method is a combination of a semiempirical effective Hamiltonian with a modified Poisson-Boltzmann equation which includes charge transfer in the form of a surface charge density positioned at the dielectric interface. The new Poisson-Boltzmann equation together with new boundary conditions results in a new set of equations for the electrostatic potential (or polarization charge densities). Charge transfer adds a new free energy component to the solvation free energy term, which accounts for all interactions between the transferred charge at the dielectric interface, the solute wave function and the solvent polarization charges. Practical calculations on a set of 19 anions and 17 cations demonstrate that charge exchange with a dielectric is present and it is in the range of 0.06-0.4 eu. Furthermore, the pattern of the magnitudes of charge transfer can be related to the acid-base properties of the ions in many cases, but exceptions are also found. Finally, we show that the method leads to an energy decomposition scheme of the total electrostatic energy, which can be used in mechanistic studies on protein and DNA interaction with water.

a Computational Tddft Study on Intramolecular Charge Transfer in Di-Tert and 2,4,6-TRICYANOANILINES.

NASA Astrophysics Data System (ADS)

Fujiwara, Takashige; Zgierski, Marek Z.

2014-06-01

We have carried out TDDFT computational studies on the low-lying excited states of di-tert-butylaminobenzonitrile and 2,4,6-tricyanoaniline compounds that exhibit unusual photophysical behaviors associated with the intramolecular charge transfer (ICT). For both 3- and 4-di-tert-butylamino)benzonitriles (m-DTBABN and p-DTBABN, respectively) show the ICT formation, and p-DTBABN appears to be the only meta-substituted aminobenzonitrile that exhibits the ICT formation. The TDDFT calculations indicate evidence that the ultrafast ICT formation in p-DTBABN and m-DTBABN is due to the sequential state switches: ππ*(La)→ πσ*→ ICT in the presence of conical intersections among the three closely-lying excited-states. On the other hand, 2,4,6-tricyanoaniline does not show clear evidence for the LE (locally excited) state → ICT state formation from steady-state fluorescence studies, despite the greater electron acceptor strength of tricycanobenzene as compared to monocyanobenzene, which is part of a 4-(dimethylamino)benzonitrile (p-DMABN) compound. However, it is predicted that 2,4,6-tricyano-N,N-dimethylaniline (TCDMA), but not 2,4,6-tricyanoaniline (TCA), possesses two ICT states, which show the ICT-characterized quinoidal structures and lie below the initially photo-excited S1(ππ*) state. The CC2 calculations further predict two conformers as labeled with quinoidal (ICT--Q) and anti-quinoidal (ICT--AQ) structures are rapidly interconnecting with each other. The lower energy ICT--Q structure tends to be populated from the unstable ICT--AQ structure, which is responsible for the observed time-resolved fluorescence as well as the excited-state absorption from the mixed S1(ππ*)/ICT state of TCDMA. In both cases for TCDMA and TCA, the πσ* state locates significantly higher in energy than the S1(ππ*) state (and the ICT state for TCA), thus precluding the πσ*→ ICT formation, which is believed to occur in a p-DMABN in polar environments.

Convergent synthesis and photoinduced processes in multi-chromophoric rotaxanes.

PubMed

Megiatto, Jackson D; Li, Ke; Schuster, David I; Palkar, Amit; Herranz, M Ángeles; Echegoyen, Luis; Abwandner, Silke; de Miguel, Gustavo; Guldi, Dirk M

2010-11-18

A series of [2]rotaxane materials, in which [60]fullerene is linked to a macrocycle and ferrocene (Fc) moieties are placed at the termini of a thread, both of which possess a central Cu(I)-1,10-phenanthroline [Cu(phen)(2)](+) complex, were synthesized by self-assembly using Sauvage metal template methodology. Two types of threads were constructed, one with terminal ester linkages, and a second with terminal 1,2,3-triazole linkages derived from Cu(I)-catalyzed "click" 1,3-cycloaddition reactions. Model compounds lacking the fullerene moiety were prepared in an analogous manner. The ability of the interlocked Fc-[Cu(phen)(2)](+)-C(60) hybrids to undergo electron transfer upon photoexcitation in benzonitrile, dichloromethane, and ortho-dichlorobenzene was investigated by means of time-resolved fluorescence and transient absorption spectroscopy, using excitation wavelengths directed at the fullerene and [Cu(phen)(2)](+) subunits. The energies of the electronic excited states and charge separated (CS) states that might be formed upon photoexcitation were determined from spectroscopic and electrochemical data. These studies showed that MLCT excited states of the copper complex in the fullerenerotaxanes were quenched by electron transfer to the fullerene in benzonitrile, resulting in charge separated states with oxidized copper and reduced fullerene moieties, (Fc)(2)-[Cu(phen)(2)](2+)-C(60)(•-). Even though electron transfer from Fc to the oxidized copper complex is predicted to be exergonic by 0.16 to 0.20 eV, no unequivocal evidence in support of such a process was obtained. The conclusion that Fc plays no role in the photoinduced processes in our systems rests on the lack of enhancement of the lifetime of the charge separated state, as measured by decay of C(60)(•-) at ∼1000 nm, since one-electron oxidized Fc is very difficult to detect spectroscopically in the 500-800 nm spectral region.

Charge-transfer potentials for ionic crystals: Cauchy violation, LO-TO splitting, and the necessity of an ionic reference state.

PubMed

Sukhomlinov, Sergey V; Müser, Martin H

2015-12-14

In this work, we study how including charge transfer into force fields affects the predicted elastic and vibrational Γ-point properties of ionic crystals, in particular those of rock salt. In both analytical and numerical calculations, we find that charge transfer generally leads to a negative contribution to the Cauchy pressure, P(C) ≡ C12 - C66, where C12 and C66 are elements of the elastic tensor. This contribution increases in magnitude with pressure for different charge-transfer approaches in agreement with results obtained with density functional theory (DFT). However, details of the charge-transfer models determine the pressure dependence of the longitudinal optical-transverse optical splitting and that for partial charges. These last two quantities increase with density as long as the chemical hardness depends at most weakly on the environment while experiments and DFT find a decrease. In order to reflect the correct trends, the charge-transfer expansion has to be made around ions and the chemical (bond) hardness has to increase roughly exponentially with inverse density or bond lengths. Finally, the adjustable force-field parameters only turn out meaningful, when the expansion is made around ions.

Charge-transfer potentials for ionic crystals: Cauchy violation, LO-TO splitting, and the necessity of an ionic reference state

NASA Astrophysics Data System (ADS)

Sukhomlinov, Sergey V.; Müser, Martin H.

2015-12-01

In this work, we study how including charge transfer into force fields affects the predicted elastic and vibrational Γ-point properties of ionic crystals, in particular those of rock salt. In both analytical and numerical calculations, we find that charge transfer generally leads to a negative contribution to the Cauchy pressure, PC ≡ C12 - C66, where C12 and C66 are elements of the elastic tensor. This contribution increases in magnitude with pressure for different charge-transfer approaches in agreement with results obtained with density functional theory (DFT). However, details of the charge-transfer models determine the pressure dependence of the longitudinal optical-transverse optical splitting and that for partial charges. These last two quantities increase with density as long as the chemical hardness depends at most weakly on the environment while experiments and DFT find a decrease. In order to reflect the correct trends, the charge-transfer expansion has to be made around ions and the chemical (bond) hardness has to increase roughly exponentially with inverse density or bond lengths. Finally, the adjustable force-field parameters only turn out meaningful, when the expansion is made around ions.

Membrane-spanning lipids for an uncompromised monitoring of membrane fusion and intermembrane lipid transfer.

PubMed

Schwarzmann, Günter; Breiden, Bernadette; Sandhoff, Konrad

2015-10-01

A Förster resonance energy transfer-based fusion and transfer assay was developed to study, in model membranes, protein-mediated membrane fusion and intermembrane lipid transfer of fluorescent sphingolipid analogs. For this assay, it became necessary to apply labeled reporter molecules that are resistant to spontaneous as well as protein-mediated intermembrane transfer. The novelty of this assay is the use of nonextractable fluorescent membrane-spanning bipolar lipids. Starting from the tetraether lipid caldarchaeol, we synthesized fluorescent analogs with fluorophores at both polar ends. In addition, we synthesized radioactive glycosylated caldarchaeols. These labeled lipids were shown to stretch through bilayer membranes rather than to loop within a single lipid layer of liposomes. More important, the membrane-spanning lipids (MSLs) in contrast to phosphoglycerides proved to be nonextractable by proteins. We could show that the GM2 activator protein (GM2AP) is promiscuous with respect to glycero- and sphingolipid transfer. Saposin (Sap) B also transferred sphingolipids albeit with kinetics different from GM2AP. In addition, we could unambiguously show that the recombinant activator protein Sap C x His6 induced membrane fusion rather than intermembrane lipid transfer. These findings showed that these novel MSLs, in contrast with fluorescent phosphoglycerolipids, are well suited for an uncompromised monitoring of membrane fusion and intermembrane lipid transfer. Copyright © 2015 by the American Society for Biochemistry and Molecular Biology, Inc.

Charge Transfer from n-Doped Nanocrystals: Mimicking Intermediate Events in Multielectron Photocatalysis.

PubMed

Wang, Junhui; Ding, Tao; Wu, Kaifeng

2018-06-12

In multielectron photocatalytic reactions, an absorbed photon triggers charge transfer from the light-harvester to the attached catalyst, leaving behind a charge of the opposite sign in the light-harvester. If this charge is not scavenged before the absorption of the following photons, photoexcitation generates not neutral but charged excitons from which the extraction of charges should become more difficult. This is potentially an efficiency-limiting intermediate event in multielectron photocatalysis. To study the charge dynamics in this event, we doped CdS nanocrystal quantum dots (QDs) with an extra electron and measured hole transfer from n-doped QDs to attached acceptors. We find that the Auger decay of charged excitons lowers the charge separation yield to 68.6% from 98.4% for neutral excitons. In addition, the hole transfer rate in the presence of two electrons (1290 ps) is slower than that in the presence one electron (776 ps), and the recombination rate of charge separated states is about 2 times faster in the former case. This model study provides important insights into possible efficiency-limiting intermediate events involved in photocatalysis.

Artificial Neural Network with Hardware Training and Hardware Refresh

NASA Technical Reports Server (NTRS)

Duong, Tuan A. (Inventor)

2003-01-01

A neural network circuit is provided having a plurality of circuits capable of charge storage. Also provided is a plurality of circuits each coupled to at least one of the plurality of charge storage circuits and constructed to generate an output in accordance with a neuron transfer function. Each of a plurality of circuits is coupled to one of the plurality of neuron transfer function circuits and constructed to generate a derivative of the output. A weight update circuit updates the charge storage circuits based upon output from the plurality of transfer function circuits and output from the plurality of derivative circuits. In preferred embodiments, separate training and validation networks share the same set of charge storage circuits and may operate concurrently. The validation network has a separate transfer function circuits each being coupled to the charge storage circuits so as to replicate the training network s coupling of the plurality of charge storage to the plurality of transfer function circuits. The plurality of transfer function circuits may be constructed each having a transconductance amplifier providing differential currents combined to provide an output in accordance with a transfer function. The derivative circuits may have a circuit constructed to generate a biased differential currents combined so as to provide the derivative of the transfer function.

[Spectrofluorometric detection of protein with a novel hydrophilic cyanine dye].

PubMed

Lin, Xu-Cong; Guo, Liang-Qia; Lin, Yan-Xia; Xie, Zeng-Hong

2007-09-01

A sensitive fluorescence quantitative determination for bovine serum albumin (BSA) or human serum albumin (HSA) has been developed by using a new hydrophilic cyanine dye 1, 1'-sulfonopropyl-3,3,3', 3'-tetramethylindolium-5,5'-disulfonic potassium (STDP) as a fluorescence probe. Using BSA as a representative protein, characteristics of the fluorescence reaction of STDP with protein were investigated. Effects of the concentration of the hydrophilic cyanine dye, pH value of the buffer solution, and ion-intensity of NaCl were also studied as well as the ratio of ethanol. In the citrate-HCl buffer solution, the fluorescence emission wavelength of BSA-STDP system was 562 nm with the maximum excitation wavelength of 548 nm, and the Stokes displacement was 14 nm. With the pH ranging from 1.0 to 2.0, the fluorescence was increasing and up to the maximum at pH 2.0. However, in the pH range of 3.0-5.0, the interaction of BSA and STDP was weakened due to the decrease in positive charge on the BSA chain, which resulted in an observable decrease of the enhancement of the fluorescence intensity. At the optimum pH of 2.0, electrostatic interactions of positive charges of the BSA chain and negative charges on the sulfonic groups of STDP were carried out. The interactions of the indole group of STDP and some active groups of BSA (viz. amido, carboxyl or sulfhydryl) were also achieved, and resulted in the combination of indole group of cyanine dye into the chain of BSA. So the hydrophobic effect and the protection provided by the skeleton chain of BSA were both improved to prevent the fluorescent energy of STDP from losing in the solution, which caused a notable fluorescence increase with an observable shift to the longer emission wavelength. Furthermore, with the augmentation of BSA, the alpha-helix structure of BSA molecular turned from the unwrapped state to the enfolded state, in favor of restraining free-oscillation of fluorescence probe in the solution and maintaining a high energy transfer efficiency. Such a fact fueled a highly enhancement of the fluorescence too. Besides, effects of the concentration of cyanine dye on the determination of BSA were also investigated. The fluorescence intensity (DeltaF) was enhanced with the increase in the quantity of STDP and gained the peak at 1.00 micromol x L(-1). However, when STDP ranged from 1.50 to 5.00 micromol x L(-1), some negative congregate effects on the nature of cyanine dye might happen and resulted in a too high fluorescence background. A rapid decrease of the fluorescence intensity was observed. The effects of ion-intensity of NaCl and ethanol on the fluorescence of BSA-STDP system were obvious. Though the fluorescence still remained high at the level of NaCl of 0.025 mol x L(-1), a rapid decrease happen at the level of NaCl from 0.05 to 0.15 mol x L(-1). With the addition of ethanol, the dissolvation capacity of both STDP and BSA was improved and their interactions were accelerated. An increasing fluorescence with the augment of ethanol was obtained and the maximum was achieved with the ratio of ethanol at 10%. Influences of coexistent substances such as amino acid, metal ions such as Cu2+, Na+, Ca2+, Mg2+, Al3+ and Fe3+ were also investigated. Most substances had no notable influences on the determination of BSA except Fe3+ and Cu2+ ions. Under the optimum conditions, the fluorescence of STDP was enhanced markedly with the addition of the BSA or HSA protein. Good calibration curves of the proteins were obtained in the range of 0.20-15.00 microg x mL(-1) for BSA and 0.20-12.00 microg x mL(-1) for HSA with detection limits (3sigma/K) of 0.01 microg x mL(-1). Applied to simulant BSA samples, this method was adaptable. And the results were satisfied with good recoveries ranging from 94.5% to 103.3% at the revels of 4.00, 6.00 and 8.00 microg x mL(-1) respectively.

Study of excitation transfer in laser dye mixtures by direct measurement of fluorescence lifetime

NASA Technical Reports Server (NTRS)

Lin, C.; Dienes, A.

1973-01-01

By directly measuring the donor fluorescence lifetime as a function of acceptor concentration in the laser dye mixture Rhodamine 6G-Cresyl violet, we found that the Stern-Volmer relation is obeyed, from which the rate of excitation transfer is determined. The experimental results indicate that the dominant mechanism responsible for the efficient excitation transfer is that of resonance transfer due to long range dipole-dipole interaction.

Tuning charge transfer in the LaTiO3/RO/LaNiO3 (R = rare-earth) superlattices by the rare-earth oxides interfaces from a first-principles calculation

NASA Astrophysics Data System (ADS)

Yao, Fen; Zhang, Lifang; Meng, Junling; Liu, Xiaojuan; Zhang, Xiong; Zhang, Wenwen; Meng, Jian; Zhang, Hongjie

2018-03-01

We investigate the internal charge transfer at the isopolar interfaces in LaTiO3/RO/LaNiO3 (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) superlattices by means of density functional theory calculations. The charge transfer from Ti sites to Ni sites in all superlattices is induced by the electronegativity difference between the elements Ti and Ni, and the lanthanide oxides interfaces can modulate the amount of charge transfer. Comparison of the perovskite heterostructures with the different rare-earth interfaces shows that increasing the deviations of bond angles from 180.0° and the oxygen motions near the interfaces enhance charge transfer. The 4f electrons themselves of rare-earth elements have faint influences on charge transfer. In addition, the reasons why our calculated 4f states of Sm and Tm elements disagree with the experimental systems have been provided. It is hoped that all the calculated results could be used to design new functional nanoelectronic devices in perovskite oxides.

An Ab Initio Exciton Model Including Charge-Transfer Excited States

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xin; Parrish, Robert M.; Liu, Fang

Here, the Frenkel exciton model is a useful tool for theoretical studies of multichromophore systems. We recently showed that the exciton model could be used to coarse-grain electronic structure in multichromophoric systems, focusing on singly excited exciton states. However, our previous implementation excluded charge-transfer excited states, which can play an important role in light-harvesting systems and near-infrared optoelectronic materials. Recent studies have also emphasized the significance of charge-transfer in singlet fission, which mediates the coupling between the locally excited states and the multiexcitonic states. In this work, we report on an ab initio exciton model that incorporates charge-transfer excited statesmore » and demonstrate that the model provides correct charge-transfer excitation energies and asymptotic behavior. Comparison with TDDFT and EOM-CC2 calculations shows that our exciton model is robust with respect to system size, screening parameter, and different density functionals. Inclusion of charge-transfer excited states makes the exciton model more useful for studies of singly excited states and provides a starting point for future construction of a model that also includes double-exciton states.« less

An Ab Initio Exciton Model Including Charge-Transfer Excited States

DOE PAGES

Li, Xin; Parrish, Robert M.; Liu, Fang; ...

2017-06-15

Here, the Frenkel exciton model is a useful tool for theoretical studies of multichromophore systems. We recently showed that the exciton model could be used to coarse-grain electronic structure in multichromophoric systems, focusing on singly excited exciton states. However, our previous implementation excluded charge-transfer excited states, which can play an important role in light-harvesting systems and near-infrared optoelectronic materials. Recent studies have also emphasized the significance of charge-transfer in singlet fission, which mediates the coupling between the locally excited states and the multiexcitonic states. In this work, we report on an ab initio exciton model that incorporates charge-transfer excited statesmore » and demonstrate that the model provides correct charge-transfer excitation energies and asymptotic behavior. Comparison with TDDFT and EOM-CC2 calculations shows that our exciton model is robust with respect to system size, screening parameter, and different density functionals. Inclusion of charge-transfer excited states makes the exciton model more useful for studies of singly excited states and provides a starting point for future construction of a model that also includes double-exciton states.« less

Interlayer‐State‐Coupling Dependent Ultrafast Charge Transfer in MoS2/WS2 Bilayers

PubMed Central

Zhang, Jin; Hong, Hao; Lian, Chao; Ma, Wei; Xu, Xiaozhi; Zhou, Xu; Fu, Huixia

2017-01-01

Light‐induced interlayer ultrafast charge transfer in 2D heterostructures provides a new platform for optoelectronic and photovoltaic applications. The charge separation process is generally hypothesized to be dependent on the interlayer stackings and interactions, however, the quantitative characteristic and detailed mechanism remain elusive. Here, a systematical study on the interlayer charge transfer in model MoS2/WS2 bilayer system with variable stacking configurations by time‐dependent density functional theory methods is demonstrated. The results show that the slight change of interlayer geometry can significantly modulate the charge transfer time from 100 fs to 1 ps scale. Detailed analysis further reveals that the transfer rate in MoS2/WS2 bilayers is governed by the electronic coupling between specific interlayer states, rather than the interlayer distances, and follows a universal dependence on the state‐coupling strength. The results establish the interlayer stacking as an effective freedom to control ultrafast charge transfer dynamics in 2D heterostructures and facilitate their future applications in optoelectronics and light harvesting. PMID:28932669

An Ab Initio Exciton Model Including Charge-Transfer Excited States.

PubMed

Li, Xin; Parrish, Robert M; Liu, Fang; Kokkila Schumacher, Sara I L; Martínez, Todd J

2017-08-08

The Frenkel exciton model is a useful tool for theoretical studies of multichromophore systems. We recently showed that the exciton model could be used to coarse-grain electronic structure in multichromophoric systems, focusing on singly excited exciton states [ Acc. Chem. Res. 2014 , 47 , 2857 - 2866 ]. However, our previous implementation excluded charge-transfer excited states, which can play an important role in light-harvesting systems and near-infrared optoelectronic materials. Recent studies have also emphasized the significance of charge-transfer in singlet fission, which mediates the coupling between the locally excited states and the multiexcitonic states. In this work, we report on an ab initio exciton model that incorporates charge-transfer excited states and demonstrate that the model provides correct charge-transfer excitation energies and asymptotic behavior. Comparison with TDDFT and EOM-CC2 calculations shows that our exciton model is robust with respect to system size, screening parameter, and different density functionals. Inclusion of charge-transfer excited states makes the exciton model more useful for studies of singly excited states and provides a starting point for future construction of a model that also includes double-exciton states.

Nanoscale charge transfer and diffusion at the MoS2/SiO2 interface by atomic force microscopy: contact injection versus triboelectrification.

PubMed

Xu, Rui; Ye, Shili; Xu, Kunqi; Lei, Le; Hussain, Sabir; Zheng, Zhiyue; Pang, Fei; Xing, Shuya; Liu, Xinmeng; Ji, Wei; Cheng, Zhihai

2018-08-31

Understanding the process of charge generation, transfer, and diffusion between two-dimensional (2D) materials and their supporting substrates is very important for potential applications of 2D materials. Compared with the systematic studies of triboelectric charging in a bulk sample, a fundamental understanding of the triboelectrification of the 2D material/insulator system is rather limited. Here, the charge transfer and diffusion of both the SiO 2 surface and MoS 2 /SiO 2 interface through contact electrification and frictional electrification are investigated systematically in situ by scanning Kelvin probe microscopy and dual-harmonic electrostatic force microscopy. Different from the simple static charge transfer between SiO 2 and the PtSi alloy atomic force microscope (AFM) tip, the charge transfer between the tip and the MoS 2 /SiO 2 system is complicated. Triboelectric charges, generated by contact or frictional electrification with the AFM tip, are trapped at the MoS 2 /SiO 2 interface and act as floating gates. The local charge discharge processes can be obtained by monitoring the surface potential. The charge decay time (τ) of the MoS 2 /SiO 2 interface is one (or two) orders of magnitude larger than the decay time τ of the SiO 2 surface. This work facilitates an understanding of the triboelectric and de-electrification of the interface between 2D materials and substrates. In addition to the charge transfer and diffusion, we demonstrate the nanopatterns of surface and interfacial charges, which have great potential for the application of self-assembly of charged nanostructures.

Analyte interactions with a new ditopic dansylamide-nitrobenzoxadiazole dyad: a combined photophysical, NMR, and theoretical (DFT) study.

PubMed

Bhoi, Abhas Kumar; Das, Sudhir Kumar; Majhi, Debashis; Sahu, Prabhat Kumar; Nijamudheen, A; N, Anoop; Rahaman, Abdur; Sarkar, Moloy

2014-08-21

We report herein the synthesis and photophysical studies on a new multicomponent chemosensor dyad comprising two fluorescing units, dansylamide (DANS) and nitrobenzoxadiazole (NBD). The system has been developed to investigate receptor-analyte binding interactions in the presence of both cations and anions in a single molecular system. A dimethyl amino (in the DANS unit) group is used as a receptor for cations, and acidic hydrogens of sulfonamide and the NBD group are used as receptors for anions. The system is characterized by conventional analytical techniques. The photophysical properties of this supramolecular system in the absence and presence of various metal ions and nonmetal ions as additives are investigated in an acetonitrile medium. Utility of this system in an aqueous medium has also been demonstrated. The absorption and fluorescence spectrum of the molecular system consists of a broad band typical of an intramolecular charge-transfer (ICT) transition. A low quantum yield and lifetime of the NBD moiety in the present dyad indicates photoinduced electron transfer (PET) between DANS and the NBD moiety. The fluorescence intensity of the system is found to decrease in the presence of fluoride and acetate anions; however, the quenching is found to be much higher for fluoride. This quenching behavior is attributed to the enhanced PET from the anion receptor to the fluorophore moiety. The mechanistic aspect of the fluoride ion signaling behavior has also been studied by infrared (IR) and (1)H NMR experiments. The hydrogen bonding interaction between the acidic NH protons of the DPN moiety and F(-) is found to be primarily responsible for the fluoride selective signaling behavior. While investigating the cation signaling behavior, contrary to anions, significant fluorescence enhancement has been observed only in the presence of transition-metal ions. This behavior is rationalized by considering the disruption of PET communication between DANS and the NBD moiety due to transition-metal ion binding. Theoretical (density functional theory) studies are also performed for the better understanding of the receptor-analyte interaction. Interestingly, negative cooperativity in binding is observed when the interaction of this system is studied in the presence of both Zn(2+) and F(-). Fluorescence microscopy studies also revealed that the newly developed fluorescent sensor system can be employed as an imaging probe in live cells.

Lowest energy Frenkel and charge transfer exciton intermixing in one-dimensional copper phthalocyanine molecular lattice

NASA Astrophysics Data System (ADS)

Bondarev, I. V.; Popescu, A.; Younts, R. A.; Hoffman, B.; McAfee, T.; Dougherty, D. B.; Gundogdu, K.; Ade, H. W.

2016-11-01

We report the results of the combined experimental and theoretical studies of the low-lying exciton states in crystalline copper phthalocyanine. We derive the eigen energy spectrum for the two lowest intramolecular Frenkel excitons coupled to the intermolecular charge transfer exciton state and compare it with temperature dependent optical absorption spectra measured experimentally, to obtain the parameters of the Frenkel-charge-transfer exciton intermixing. The two Frenkel exciton states are spaced apart by 0.26 eV, and the charge transfer exciton state is 50 meV above the lowest Frenkel exciton. Both Frenkel excitons are strongly mixed with the charge transfer exciton, showing the coupling constant 0.17 eV which agrees with earlier experimental measurements. These results can be used for the proper interpretation of the physical properties of crystalline phthalocyanines.

Experimental and theoretical studies of the He(2+)-He system - Differential cross sections for direct, single-, and double-charge-transfer scattering at keV energies

NASA Technical Reports Server (NTRS)

Gao, R. S.; Dutta, C. M.; Lane, N. F.; Smith, K. A.; Stebbings, R. F.; Kimura, M.

1992-01-01

Measurements and calculations of differential cross sections for direct scattering, single-charge transfer, and double-charge transfer in collisions of 1.5-, 2.0-, 6.0-, and 10.0-keV (He-3)2+ with an He-4 target are reported. The measurements cover laboratory scattering angles below 1.5 deg with an angular resolution of about 0.03 deg. A quantum-mechanical molecular-state representation is employed in the calculations; in the case of single-charge transfer a two-state close-coupling calculation is carried out taking into account electron-translation effects. The theoretical calculations agree well with the experimental results for direct scattering and double-charge transfer. The present calculation identifies the origins of oscillatory structures observed in the differential cross sections.

Exciplex mediated photoinduced electron transfer reactions of phthalocyanine-fullerene dyads.

PubMed

Niemi, Marja; Tkachenko, Nikolai V; Efimov, Alexander; Lehtivuori, Heli; Ohkubo, Kei; Fukuzumi, Shunichi; Lemmetyinen, Helge

2008-07-31

Evidences of an intramolecular exciplex intermediate in a photoinduced electron transfer (ET) reaction of double-linked free-base and zinc phthalocyanine-C60 dyads were found. This was the first time for a dyad with phthalocyanine donor. Excitation of the phthalocyanine moiety of the dyads results in rapid ET from phthalocyanine to fullerene via an exciplex state in both polar and nonpolar solvents. Relaxation of the charge-separated (CS) state Pc(*+)-C60(*-) in a polar solvent occurs directly to the ground state in 30-70 ps. In a nonpolar solvent, roughly 20% of the molecules undergo transition from the CS state to phthalocyanine triplet state (3)Pc*-C60 before relaxation to the ground state. Formation of the CS state was confirmed with electron spin resonance measurements at low temperature in both polar and nonpolar solvent. Reaction schemes for the photoinduced ET reactions of the dyads were completed with rate constants obtained from the time-resolved absorption and emission measurements and with state energies obtained from the fluorescence, phosphorescence, and voltammetric measurements.

Radiation resistance of biological reagents for in situ life detection.

PubMed

Carr, Christopher E; Rowedder, Holli; Vafadari, Cyrus; Lui, Clarissa S; Cascio, Ethan; Zuber, Maria T; Ruvkun, Gary

2013-01-01

Life on Mars, if it exists, may share a common ancestry with life on Earth derived from meteoritic transfer of microbes between the planets. One means to test this hypothesis is to isolate, detect, and sequence nucleic acids in situ on Mars, then search for similarities to known common features of life on Earth. Such an instrument would require biological and chemical components, such as polymerase and fluorescent dye molecules. We show that reagents necessary for detection and sequencing of DNA survive several analogues of the radiation expected during a 2-year mission to Mars, including proton (H-1), heavy ion (Fe-56, O-18), and neutron bombardment. Some reagents have reduced performance or fail at higher doses. Overall, our findings suggest it is feasible to utilize space instruments with biological components, particularly for mission durations of up to several years in environments without large accumulations of charged particles, such as the surface of Mars, and have implications for the meteoritic transfer of microbes between planets.

Asymmetrically Substituted and π-Conjugated 2,2'-Bipyridine Derivatives: Synthesis, Spectroscopy, Computation, and Crystallography.

PubMed

Bodapati, Ramakrishna; Sarma, Monima; Kanakati, Arunkumar; Das, Samar K

2015-12-18

A new series of monosubstituted styryl- and bistyryl-2,2'-bipyridine luminophores (compounds 16-23) have been synthesized via Horner-Wadsworth-Emmons reaction involving a monophosphonate and donor aromatic aldehydes. In the title chromophores, the amino donors are varied between acyclic and cyclic while the alkoxy donors are varied in terms of their number and position. The absorption maxima of these chromophores shift predominantly due to intramolecular charge transfer (ICT) between different donor and acceptor moieties. The title donor-acceptor molecules exhibit intense fluorescence in solution at room temperature, and their emissive behavior has been found to be highly sensitive to solvent polarity. The fluorescence spectra and quantum yields of all the chromophores were recorded in four different solvent media, and the chromophores 16, 17, 19, and 21 exhibit fluorescence in the solid state too. The influence of the nature and position of the donor functionalities in the conjugated backbone of the bipyridine moiety on the electronic absorption properties of the title chromophores (16-23) has been demonstrated, which has further been corroborated by DFT and TD-DFT computation both in gas phase and in solution phase. The crystal structure of compound 18 has been described as a representative member of the family (16-23).

Picosecond fluorescence of intact and dissolved PSI-LHCI crystals.

PubMed

van Oort, Bart; Amunts, Alexey; Borst, Jan Willem; van Hoek, Arie; Nelson, Nathan; van Amerongen, Herbert; Croce, Roberta

2008-12-15

Over the past several years, many crystal structures of photosynthetic pigment-protein complexes have been determined, and these have been used extensively to model spectroscopic results obtained on the same proteins in solution. However, the crystal structure is not necessarily identical to the structure of the protein in solution. Here, we studied picosecond fluorescence of photosystem I light-harvesting complex I (PSI-LHCI), a multisubunit pigment-protein complex that catalyzes the first steps of photosynthesis. The ultrafast fluorescence of PSI-LHCI crystals is identical to that of dissolved crystals, but differs considerably from most kinetics presented in the literature. In contrast to most studies, the data presented here can be modeled quantitatively with only two compartments: PSI core and LHCI. This yields the rate of charge separation from an equilibrated core (22.5 +/- 2.5 ps) and rates of excitation energy transfer from LHCI to core (k(LC)) and vice versa (k(CL)). The ratio between these rates, R = k(CL)/k(LC), appears to be wavelength-dependent and scales with the ratio of the absorption spectra of LHCI and core, indicating the validity of a detailed balance relation between both compartments. k(LC) depends slightly but nonsystematically on detection wavelength, averaging (9.4 +/- 4.9 ps)(-1). R ranges from 0.5 (<690 nm) to approximately 1.3 above 720 nm.

Manipulating the alkali metal charge compensation and tungsten oxide to continuously enhance the red fluorescence in (Li,Na,K)Ca(Mo,W)O4:Eu3+ solid solution compounds

NASA Astrophysics Data System (ADS)

Xie, Wei; Li, Jiaxin; Tian, Canxin; Wang, Zesong; Xie, Mubiao; Zou, Changwei; Sun, Guohuan; Kang, Fengwen

2018-02-01

When compared to other phosphors typically the blue and green phosphors, red phosphors, which can be used for white light-emitting diodes (wLEDs), always suffer from various problems such as higher cost, lower luminescence efficiency and bad thermal stability. And thus, great interests have been paid to how to enhance the red fluorescence intensity in the recent years. Here we report on a red-emitting solid solutions, (Li,Na,K)Ca(Mo,W)O4:Eu3+, which enable exhibiting continuous Eu3+ emission enhancement through manipulating the alkali metal ions and the relative content ratios between tungsten and molybdenum oxides. X-ray powder diffraction (XRD) has been employed to check the phase purity, and results show that all samples crystallize in a scheelite structure with space group of I41/a (No.88). A regular blue-shifting of XRD peaks, which indicates the increase of crystal plane spacing, appears as the alkali cationic radius increases from 0.92 Å (for Li), 1.18 Å (for Na) and to 1.38 Å (for K). Replacing Mo ion (0.41 Å) by W ion (0.42 Å) enables not only forming the solid solution compounds (Li,Na,K)Ca(Mo,W)O4:Eu3+, but also blue-shifting the XRD position. Similar to the XRD position shifting, our samples also exhibit the regular change in the photoluminescence (PL) spectra, in which the charge transfer (CT) band position as the alkali cationic radii increase from Li, Na and to K and further from Mo to W shows a continuous red-shifting behavior. As for the CT and Eu3+ intensity, our experimental results show that the alkali ion that corresponds to the maximum intensity is Li, and this intensity can be further enhanced by adding W. In coincidence with the change in the excitation spectral intensity, the continuous enhanced Eu3+ emission intensity can be observed up excitation at the CT band and Eu3+ lines. We have discussed the above CT band shifting and Eu3+ fluorescence enhancement and give a feasible mechanism profile that base on the energy transfer from CT band to Eu3+ dopant.

33 CFR 156.115 - Person in charge: Limitations.

Code of Federal Regulations, 2011 CFR

2011-07-01

... transfer operations on more than one vessel at a time during transfers between vessels or between two or... (CONTINUED) POLLUTION OIL AND HAZARDOUS MATERIAL TRANSFER OPERATIONS Oil and Hazardous Material Transfer... charge of both a vessel and a facility during transfer operations unless authorized by the COTP. [CGD 75...

33 CFR 156.115 - Person in charge: Limitations.

Code of Federal Regulations, 2012 CFR

2012-07-01

... transfer operations on more than one vessel at a time during transfers between vessels or between two or... (CONTINUED) POLLUTION OIL AND HAZARDOUS MATERIAL TRANSFER OPERATIONS Oil and Hazardous Material Transfer... charge of both a vessel and a facility during transfer operations unless authorized by the COTP. [CGD 75...

33 CFR 156.115 - Person in charge: Limitations.

Code of Federal Regulations, 2010 CFR

2010-07-01

... transfer operations on more than one vessel at a time during transfers between vessels or between two or... (CONTINUED) POLLUTION OIL AND HAZARDOUS MATERIAL TRANSFER OPERATIONS Oil and Hazardous Material Transfer... charge of both a vessel and a facility during transfer operations unless authorized by the COTP. [CGD 75...

33 CFR 156.115 - Person in charge: Limitations.

Code of Federal Regulations, 2013 CFR

2013-07-01

... transfer operations on more than one vessel at a time during transfers between vessels or between two or... (CONTINUED) POLLUTION OIL AND HAZARDOUS MATERIAL TRANSFER OPERATIONS Oil and Hazardous Material Transfer... charge of both a vessel and a facility during transfer operations unless authorized by the COTP. [CGD 75...

33 CFR 156.115 - Person in charge: Limitations.

Code of Federal Regulations, 2014 CFR

2014-07-01

... transfer operations on more than one vessel at a time during transfers between vessels or between two or... (CONTINUED) POLLUTION OIL AND HAZARDOUS MATERIAL TRANSFER OPERATIONS Oil and Hazardous Material Transfer... charge of both a vessel and a facility during transfer operations unless authorized by the COTP. [CGD 75...

High Pressure Optical Studies of the Thallous Halides and of Charge-Transfer Complexes

NASA Astrophysics Data System (ADS)

Jurgensen, Charles Willard

High pressure was used to study the insulator -to-metal transition in sulfur and the thallous halides and to study the intermolecular interactions in charge -transfer complexes. The approach to the band overlap insulator -to-metal transition was studied in three thallous halides and sulfur by optical absorption measurements of the band gap as a function of pressure. The band gap of sulfur continuously decreases with pressure up to the insulator -to-metal transition which occurs between 450 and 485 kbars. The results on the thallous halides indicate that the indirect gap decreases more rapidly than the direct gap; the closing of the indirect gap is responsible for the observed insulator -to-metal transitions. High pressure electronic and vibrational spectroscopic measurements on the solid-state complexes of HMB-TCNE were used to study the intermolecular interactions of charge -transfer complexes. The vibrational frequency shifts indicate that the degree of charge transfer increases with pressure which is independently confirmed by an increase in the molar absorptivity of the electronic charge-transfer peak. Induction and dispersion forces contribute towards a red shift of the charge-transfer peak; however, charge-transfer resonance contributes toward a blue shift and this effect is dominant for the HMB-TCNE complexes. High pressure electronic spectra were used to study the effect of intermolecular interactions on the electronic states of TCNQ and its complexes. The red shifts with pressure of the electronic spectra of TCNQ and (TCNQ)(' -) in polymer media and of crystalline TCNQ can be understood in terms of Van der Waals interactions. None of the calculations which considered intradimer distance obtained the proper behavior for either the charge-transfer of the locally excited states of the complexes. The qualitative behavior of both states can be interpreted as the effect of increased mixing of the locally excited and charge transfer states.

Investigations on the charge transfer mechanism at donor/acceptor interfaces in the quest for descriptors of organic solar cell performance.

PubMed

Muraoka, Azusa; Fujii, Mikiya; Mishima, Kenji; Matsunaga, Hiroki; Benten, Hiroaki; Ohkita, Hideo; Ito, Shinzaburo; Yamashita, Koichi

2018-05-07

Herein, we theoretically and experimentally investigated the mechanisms of charge separation processes of organic thin-film solar cells. PTB7, PTB1, and PTBF2 have been chosen as donors and PC 71 BM has been chosen as an acceptor considering that effective charge generation depends on the difference between the material combinations. Experimental results of transient absorption spectroscopy show that the hot process is a key step for determining external quantum efficiency (EQE) in these systems. From the quantum chemistry calculations, it has been found that EQE tends to increase as the transferred charge, charge transfer distance, and variation of dipole moments between the ground and excited states of the donor/acceptor complexes increase; this indicates that these physical quantities are a good descriptor to assess the donor-acceptor charge transfer quality contributing to the solar cell performance. We propose that designing donor/acceptor interfaces with large values of charge transfer distance and variation of dipole moments of the donor/acceptor complexes is a prerequisite for developing high-efficiency polymer/PCBM solar cells.

Fluorescence excitation and excited state intramolecular relaxation dynamics of jet-cooled methyl-2-hydroxy-3-naphthoate

NASA Astrophysics Data System (ADS)

McCarthy, Annemarie; Ruth, Albert A.

2013-11-01

Two distinct S0 → S1 fluorescence excitation spectra of methyl-2-hydroxy-3-napthoate (MHN23) have been obtained by monitoring fluorescence separately in the short (˜410 nm) and long (˜650 nm) wavelength emission bands. The short wavelength fluorescence is assigned to two MHN23 conformers which do not undergo excited state intramolecular proton transfer (ESIPT). Analysis of the 'long wavelength' fluorescence excitation spectrum, which arises from the proton transfer tautomer of MHN23 indicates an average lifetime of τ ⩾ 18 ± 2 fs for the initially excited states. Invoking the results of Catalan et al. [J. Phys. Chem. A, 1999, 103, 10921], who determined the N tautomer to decay predominantly via a fast non-radiative process, the limit of the rate of intramolecular excited proton transfer in MHN23 is calculated as, kpt ⩽ 1 × 1012 s-1.

Reduced Charge Transfer Exciton Recombination in Organic Semiconductor Heterojunctions by Molecular Doping

NASA Astrophysics Data System (ADS)

Deschler, Felix; da Como, Enrico; Limmer, Thomas; Tautz, Raphael; Godde, Tillmann; Bayer, Manfred; von Hauff, Elizabeth; Yilmaz, Seyfullah; Allard, Sybille; Scherf, Ullrich; Feldmann, Jochen

2011-09-01

We investigate the effect of molecular doping on the recombination of electrons and holes localized at conjugated-polymer-fullerene interfaces. We demonstrate that a low concentration of p-type dopant molecules (<4% weight) reduces the interfacial recombination via charge transfer excitons and results in a favored formation of separated carriers. This is observed by the ultrafast quenching of photoluminescence from charge transfer excitons and the increase in photoinduced polaron density by ˜70%. The results are consistent with a reduced formation of emissive charge transfer excitons, induced by state filling of tail states.

An Enzyme-Responsive "Turn-on" Fluorescence Polymeric Superamphiphile as a Potential Visualizable Phosphate Prodrug Delivery Vehicle.

PubMed

Yang, Xi; Shen, Shihong; Guo, Li; Tan, Jidong; Lei, Henxin; Wu, Jianghan; Zhao, Lei; Xiong, Tao; Wu, Youshen; Cheng, Yilong; Zhang, Yanfeng

2018-06-01

The development of inexpensive and highly efficient enzyme-responsive polymers has significantly contributed to targeted drug delivery systems. Here, a superamphiphile with a capability of fluorescent dissociation sensing is designed. It is constructed with negatively charged adenosine 5'-triphosphate (ATP) and negatively charged fluorescein diphosphate (FDP), which are used as fluorescence detection, and a cationic diblock copolymer methoxy-poly(ethylene glycol) 113 -b-poly(2-dimethyl-aminoethyl methacrylate) 70 . Upon addition of calf intestinal alkaline phosphatase, the superamphiphile disintegrates, presumably due to the enzymatic hydrolysis of ATP. This process is accompanied by an increase in the fluorescence emission intensity of fluorescein owing to the hydrolysis of FDP. The in vitro application of the superamphiphile is also proven. Thus, the "turn-on" fluorescence of the superamphiphile serves as a real-time module for detection of the disintegration of superamphiphile. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Scientific Computation Application Partnerships in Materials and Chemical Sciences, Charge Transfer and Charge Transport in Photoactivated Systems, Developing Electron-Correlated Methods for Excited State Structure and Dynamics in the NWChem Software Suite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cramer, Christopher J.

Charge transfer and charge transport in photoactivated systems are fundamental processes that underlie solar energy capture, solar energy conversion, and photoactivated catalysis, both organometallic and enzymatic. We developed methods, algorithms, and software tools needed for reliable treatment of the underlying physics for charge transfer and charge transport, an undertaking with broad applicability to the goals of the fundamental-interaction component of the Department of Energy Office of Basic Energy Sciences and the exascale initiative of the Office of Advanced Scientific Computing Research.

Fluorescent Polymer-Single-Walled Carbon Nanotube Complexes with Charged and Noncharged Dendronized Perylene Bisimides for Bioimaging Studies.

PubMed

Huth, Katharina; Glaeske, Mareen; Achazi, Katharina; Gordeev, Georgy; Kumar, Shiv; Arenal, Raúl; Sharma, Sunil K; Adeli, Mohsen; Setaro, Antonio; Reich, Stephanie; Haag, Rainer

2018-06-05

Fluorescent nanomaterials are expected to revolutionize medical diagnostic, imaging, and therapeutic tools due to their superior optical and structural properties. Their inefficient water solubility, cell permeability, biodistribution, and high toxicity, however, limit the full potential of their application. To overcome these obstacles, a water-soluble, fluorescent, cytocompatible polymer-single-walled carbon nanotube (SWNT) complex is introduced for bioimaging applications. The supramolecular complex consists of an alkylated polymer conjugated with neutral hydroxylated or charged sulfated dendronized perylene bisimides (PBIs) and SWNTs as a general immobilization platform. The polymer backbone solubilizes the SWNTs, decorates them with fluorescent PBIs, and strongly improves their cytocompatibility by wrapping around the SWNT scaffold. In photophysical measurements and biological in vitro studies, sulfated complexes exhibit superior optical properties, cellular uptake, and intracellular staining over their hydroxylated analogs. A toxicity assay confirms the highly improved cytocompatibility of the polymer-wrapped SWNTs toward surfactant-solubilized SWNTs. In microscopy studies the complexes allow for the direct imaging of the SWNTs' cellular uptake via the PBI and SWNT emission using the 1st and 2nd optical window for bioimaging. These findings render the polymer-SWNT complexes with nanometer size, dual fluorescence, multiple charges, and high cytocompatibility as valuable systems for a broad range of fluorescence bioimaging studies. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Topological Effects of Charge Transfer in Telomere G-Quadruplex Mechanism on Telomerase Activation and Inhibition

NASA Astrophysics Data System (ADS)

Wang, Xin; Liang, Shi-Dong

2013-02-01

We explore the charge transfer in the telomere G-Quadruplex (TG4) DNA theoretically by the nonequilibrium Green's function method, and reveal the topological effect of the charge transport in TG4 DNA. The consecutive TG4 (CTG4) is semiconducting with 0.2 0.3 eV energy gap. Charges transfer favorably in the CTG4, but are trapped in the nonconsecutive TG4 (NCTG4). The global conductance is inversely proportional to the local conductance for NCTG4. The topological structure transition from NCTG4 to CTG4 induces abruptly 3nA charge current, which provide a microscopic clue to understand the telomerase activated or inhibited by TG4. Our findings reveal the fundamental property of charge transfer in TG4 and its relationship with the topological structure of TG4.

Compatible validated spectrofluorimetric and spectrophotometric methods for determination of vildagliptin and saxagliptin by factorial design experiments.

PubMed

Abdel-Aziz, Omar; Ayad, Miriam F; Tadros, Mariam M

2015-04-05

Simple, selective and reproducible spectrofluorimetric and spectrophotometric methods have been developed for the determination of vildagliptin and saxagliptin in bulk and their pharmaceutical dosage forms. The first proposed spectrofluorimetric method is based on the dansylation reaction of the amino group of vildagliptin with dansyl chloride to form a highly fluorescent product. The formed product was measured spectrofluorimetrically at 455 nm after excitation at 345 nm. Beer's law was obeyed in a concentration range of 100-600 μg ml(-1). The second proposed spectrophotometric method is based on the charge transfer complex of saxagliptin with tetrachloro-1,4-benzoquinone (p-chloranil). The formed charge transfer complex was measured spectrophotometrically at 530 nm. Beer's law was obeyed in a concentration range of 100-850 μg ml(-1). The third proposed spectrophotometric method is based on the condensation reaction of the primary amino group of saxagliptin with formaldehyde and acetyl acetone to form a yellow colored product known as Hantzsch reaction, measured at 342.5 nm. Beer's law was obeyed in a concentration range of 50-300 μg ml(-1). All the variables were studied to optimize the reactions' conditions using factorial design. The developed methods were validated and proved to be specific and accurate for quality control of vildagliptin and saxagliptin in their pharmaceutical dosage forms. Copyright © 2015. Published by Elsevier B.V.

Compatible validated spectrofluorimetric and spectrophotometric methods for determination of vildagliptin and saxagliptin by factorial design experiments

NASA Astrophysics Data System (ADS)

Abdel-Aziz, Omar; Ayad, Miriam F.; Tadros, Mariam M.

2015-04-01

Simple, selective and reproducible spectrofluorimetric and spectrophotometric methods have been developed for the determination of vildagliptin and saxagliptin in bulk and their pharmaceutical dosage forms. The first proposed spectrofluorimetric method is based on the dansylation reaction of the amino group of vildagliptin with dansyl chloride to form a highly fluorescent product. The formed product was measured spectrofluorimetrically at 455 nm after excitation at 345 nm. Beer's law was obeyed in a concentration range of 100-600 μg ml-1. The second proposed spectrophotometric method is based on the charge transfer complex of saxagliptin with tetrachloro-1,4-benzoquinone (p-chloranil). The formed charge transfer complex was measured spectrophotometrically at 530 nm. Beer's law was obeyed in a concentration range of 100-850 μg ml-1. The third proposed spectrophotometric method is based on the condensation reaction of the primary amino group of saxagliptin with formaldehyde and acetyl acetone to form a yellow colored product known as Hantzsch reaction, measured at 342.5 nm. Beer's law was obeyed in a concentration range of 50-300 μg ml-1. All the variables were studied to optimize the reactions' conditions using factorial design. The developed methods were validated and proved to be specific and accurate for quality control of vildagliptin and saxagliptin in their pharmaceutical dosage forms.

Effect of the LHCII pigment-protein complex aggregation on photovoltaic properties of sensitized TiO2 solar cells.

PubMed

Yang, Yiqun; Jankowiak, Ryszard; Lin, Chen; Pawlak, Krzysztof; Reus, Michael; Holzwarth, Alfred R; Li, Jun

2014-10-14

A modified dye-sensitized solar cell consisting of a thin TiO2 barrier layer sensitized with natural trimeric light-harvesting complex II (LHCII) from spinach was used as a biomimetic model to study the effects of LHCII aggregation on the photovoltaic properties. The aggregation of individual trimers induced molecular reorganization, which dramatically increased the photocurrent. The morphology of small- and large-size LHCII aggregates deposited on a surface was confirmed by atomic force microscopy. Enhanced LHCII immobilization was accomplished via electrostatic interaction with amine-functionalized photoanodes. The photocurrent responses of the assembled solar cells under illumination at three characteristic wavelength bands in the UV-Vis absorption spectra of LHCII solutions confirmed that a significant photocurrent was generated by LHCII photosensitizers. The enhanced photocurrent by large aggregated LHCII is shown to correlate with the quenching in the far-red fluorescence deriving from chlorophyll-chlorophyll charge transfer states that are effectively coupled with the TiO2 surface and thus inject electrons into the TiO2 conduction band. The large aggregated LHCII with more chlorophyll-chlorophyll charge transfer states is a much better sensitizer since it injects electrons more efficiently into the conduction band of TiO2 than the small aggregated LHCII mostly consisting of unquenched chlorophyll excited state. The assembled solar cells demonstrated remarkable stability in both aqueous buffer and acetonitrile electrolytes over 30 days.

Amperometric cholesterol biosensor based on in situ reconstituted cholesterol oxidase on an immobilized monolayer of flavin adenine dinucleotide cofactor.

PubMed

Vidal, Juan-C; Espuelas, Javier; Castillo, Juan-R

2004-10-01

A new amperometric biosensor for determining cholesterol based on deflavination of the enzyme cholesterol oxidase (ChOx) and subsequent reconstitution of the apo-protein with a complexed flavin adenine dinucleotide (FAD) monolayer is described. The charge transfer mediator pyrroquinoline quinone (PQQ) was covalently bound to a cystamine self-assembled monolayer (SAM) on an Au electrode. Boronic acid (BA) was then bound to PQQ using the carbodiimide procedure, and the BA ligand was complexed to the FAD molecules on which the apo-ChOx was subsequently reconstituted. The effective release of the FAD from the enzyme and the successful reconstitution were verified using molecular fluorescence and cyclic voltammetry. The optimal orientation of FAD toward the PQQ mediator and the distances between FAD and PQQ and between PQQ and electrode enhance the charge transfer, very high sensitivity (about 2,500 nAmM(-1)cm(-2)) being obtained for cholesterol determination. The biosensor is selective toward electroactive interferents (ascorbic acid and uric acid) and was tested in reference serum samples, demonstrating excellent accuracy (relative errors below 3% in all cases). The biosensor activity can be successfully regenerated in a simple process by successive reconstitution with batches of recently prepared apo-ChOx on the same immobilized Au/SAM-PQQ-BA-FAD monolayer (it was tested five times); the lifetime of the biosensor is about 45-60 days.

Transfer of ultraviolet photon energy into fluorescent light in the visible path represents a new and efficient protection mechanism of sunscreens

NASA Astrophysics Data System (ADS)

Vergou, Theognosia; Patzelt, Alexa; Richter, Heike; Schanzer, Sabine; Zastrow, Leonhard; Golz, Karin; Doucet, Olivier; Antoniou, Christina; Sterry, Wolfram; Lademann, Juergen

2011-10-01

The development of sunscreens with high sun protection factor (SPF) values but low filter concentrations is the ultimate goal. The purpose of the present study was to investigate why a sunscreen spray and cream with different concentrations of the same UV-filters provided the same SPF. Therefore, the homogeneity of the distribution of both sunscreens was investigated by laser scanning microscopy (LSM) and tape stripping (TS). Additionally, the energy transfer mechanisms of the sunscreens on the skin were analyzed. The TS and LSM showed a better homogeneity of the distribution of the spray. With Wood's light, a total absorption of the irradiation was detected in the spray area. In contrast, after cream treatment, an intensive fluorescent signal was observed. It was demonstrated that this fluorescent signal was caused by nonthermal energy transferred from the UV-filters to one compound of the cream releasing its excitation energy by fluorescence. This nonthermal energy transfer seemed to be the reason for the high efficiency of the cream, which is subjected to thermal relaxation. The transfer of UV photon energy into fluorescent light represents a new approach to increase the efficiency of sunscreens and could form the basis for a new generation of sunscreens.

Blinking fluorescence of single donor-acceptor pairs: important role of "dark'' states in resonance energy transfer via singlet levels.

PubMed

Osad'ko, I S; Shchukina, A L

2012-06-01

The influence of triplet levels on Förster resonance energy transfer via singlet levels in donor-acceptor (D-A) pairs is studied. Four types of D-A pair are considered: (i) two-level donor and two-level acceptor, (ii) three-level donor and two-level acceptor, (iii) two-level donor and three-level acceptor, and (iv) three-level donor and three-level acceptor. If singlet-triplet transitions in a three-level acceptor molecule are ineffective, the energy transfer efficiency E=I_{A}/(I_{A}+I_{D}), where I_{D} and I_{A} are the average intensities of donor and acceptor fluorescence, can be described by the simple theoretical equation E(F)=FT_{D}/(1+FT_{D}). Here F is the rate of energy transfer, and T_{D} is the donor fluorescence lifetime. In accordance with the last equation, 100% of the donor electronic energy can be transferred to an acceptor molecule at FT_{D}≫1. However, if singlet-triplet transitions in a three-level acceptor molecule are effective, the energy transfer efficiency is described by another theoretical equation, E(F)=F[over ¯](F)T_{D}/[1+F[over ¯](F)T_{D}]. Here F[over ¯](F) is a function of F depending on singlet-triplet transitions in both donor and acceptor molecules. Expressions for the functions F[over ¯](F) are derived. In this case the energy transfer efficiency will be far from 100% even at FT_{D}≫1. The character of the intensity fluctuations of donor and acceptor fluorescence indicates which of the two equations for E(F) should be used to find the value of the rate F. Therefore, random time instants of photon emission in both donor and acceptor fluorescence are calculated by the Monte Carlo method for all four types of D-A pair. Theoretical expressions for start-stop correlators (waiting time distributions) in donor and acceptor fluorescence are derived. The probabilities w_{N}^{D}(t) and w_{N}^{A}(t) of finding N photons of donor and acceptor fluorescence in the time interval t are calculated for various values of the energy transfer rate F and for all four types of D-A pair. Comparison of the calculated D and A fluorescence trajectories with those measured by Weiss and co-workers proves the important role of triplet levels in energy transfer via singlet levels.

78 FR 63268 - Self-Regulatory Organizations; Financial Industry Regulatory Authority, Inc.; Notice of Filing...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-23

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33 CFR 155.710 - Qualifications of person in charge.

Code of Federal Regulations, 2010 CFR

2010-07-01

... available to the PIC on the tankship at all times during the transfer or cargo-tank cleaning; and (iii) Is... Transfer Personnel, Procedures, Equipment, and Records § 155.710 Qualifications of person in charge. (a) On... the vessel, or the person who arranges and hires a person to be in charge either of a transfer of...

Charge transfer in model peptides: obtaining Marcus parameters from molecular simulation.

PubMed

Heck, Alexander; Woiczikowski, P Benjamin; Kubař, Tomáš; Giese, Bernd; Elstner, Marcus; Steinbrecher, Thomas B

2012-02-23

Charge transfer within and between biomolecules remains a highly active field of biophysics. Due to the complexities of real systems, model compounds are a useful alternative to study the mechanistic fundamentals of charge transfer. In recent years, such model experiments have been underpinned by molecular simulation methods as well. In this work, we study electron hole transfer in helical model peptides by means of molecular dynamics simulations. A theoretical framework to extract Marcus parameters of charge transfer from simulations is presented. We find that the peptides form stable helical structures with sequence dependent small deviations from ideal PPII helices. We identify direct exposure of charged side chains to solvent as a cause of high reorganization energies, significantly larger than typical for electron transfer in proteins. This, together with small direct couplings, makes long-range superexchange electron transport in this system very slow. In good agreement with experiment, direct transfer between the terminal amino acid side chains can be dicounted in favor of a two-step hopping process if appropriate bridging groups exist. © 2012 American Chemical Society

NIR-Mediated Nanohybrids of Upconversion Nanophosphors and Fluorescent Conjugated Polymers for High-Efficiency Antibacterial Performance Based on Fluorescence Resonance Energy Transfer.

PubMed

Li, Junting; Zhao, Qi; Shi, Feng; Liu, Chenghui; Tang, Yanli

2016-12-01

A novel nanohybrid comprised of upconversion nanophosphors (UCNPs) and fluorescent conjugated polymers (PFVCN) is rationally fabricated. The new UCNP/PFVCN nanohybrids combine the excellent antibacterial ability of PFVCN and the near IR (NIR) absorbing property of UCNPs, which allows for NIR-mediated antibacterial through the effective fluorescence resonance energy transfer from UCNPs to PFVCN accompanied with generation of reactive oxygen species to kill bacteria. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cerium Ion Mobility and Diffusivity Rates in Perfluorosulfonic Acid Membranes Measured via Hydrogen Pump Operation

DOE PAGES

Baker, Andrew M.; Babu, Siddharth Komini; Mukundan, Rangachary; ...

2017-09-21

Ion mobility and diffusivity coefficients were determined for cerium ions in Nafion XL perfluorosulfonic acid ionomer membranes at 100% and 50% relative humidity in a conductivity cell using a hydrogen pump. We quantified Ce ion migration profiles as a function of charge transfer through the cell using X-ray fluorescence (XRF). To decouple simultaneous effects of Ce ion mobility and back-diffusion which occur due to potential and concentration gradients, respectively, a one-dimensional model was developed and fit to these intermittent XRF profiles. The resulting mobility and diffusivity coefficients demonstrate the dramatic effects of potential and concentration gradients on Ce ion migrationmore » during PEM fuel cell operation.« less

A NIR sensor for cyanide detection and its application in cell imaging.

PubMed

Wu, Wei-Na; Wu, Hao; Wang, Yuan; Zhao, Xiao-Lei; Xu, Zhou-Qing; Xu, Zhi-Hong; Fan, Yun-Chang

2018-06-15

A novel 'D-π-A' sensor 1 has been designed and prepared via the condensation reaction of 3‑ethyl‑2‑methyl‑1,3‑benzothiazol‑3‑ium iodide and 5‑nitro‑o‑vanillin. Upon treatment with cyanide, sensor 1 exhibited a significant near-infrared (NIR) fluorescence quenching at 663nm. The MS, IR, 1 H NMR and DFT methods confirmed that the response of 1 to cyanide is due to the nucleophilic addition reaction, which results in the inhibition of the Intramolecular Charge Transfer (ICT) process in the sensor. Furthermore, sensor 1 was used for the determination of CN - in HeLa cells. Copyright © 2018 Elsevier B.V. All rights reserved.

The binding domain of the HMGB1 inhibitor carbenoxolone: Theory and experiment

NASA Astrophysics Data System (ADS)

Mollica, Luca; Curioni, Alessandro; Andreoni, Wanda; Bianchi, Marco E.; Musco, Giovanna

2008-05-01

We present a combined computational and experimental study of the interaction of the Box A of the HMGB1 protein and carbenoxolone, an inhibitor of its pro-inflammatory activity. The computational approach consists of classical molecular dynamics (MD) simulations based on the GROMOS force field with quantum-refined (QRFF) atomic charges for the ligand. Experimental data consist of fluorescence intensities, chemical shift displacements, saturation transfer differences and intermolecular Nuclear Overhauser Enhancement signals. Good agreement is found between observations and the conformation of the ligand-protein complex resulting from QRFF-MD. In contrast, simple docking procedures and MD based on the unrefined force field provide models inconsistent with experiment. The ligand-protein binding is dominated by non-directional interactions.

Cerium Ion Mobility and Diffusivity Rates in Perfluorosulfonic Acid Membranes Measured via Hydrogen Pump Operation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, Andrew M.; Babu, Siddharth Komini; Mukundan, Rangachary

Ion mobility and diffusivity coefficients were determined for cerium ions in Nafion XL perfluorosulfonic acid ionomer membranes at 100% and 50% relative humidity in a conductivity cell using a hydrogen pump. We quantified Ce ion migration profiles as a function of charge transfer through the cell using X-ray fluorescence (XRF). To decouple simultaneous effects of Ce ion mobility and back-diffusion which occur due to potential and concentration gradients, respectively, a one-dimensional model was developed and fit to these intermittent XRF profiles. The resulting mobility and diffusivity coefficients demonstrate the dramatic effects of potential and concentration gradients on Ce ion migrationmore » during PEM fuel cell operation.« less

Lifetimes of bacteriochlorophyll fluorescence in Rhodopseudomonas viridis and Heliobacterium chlorum at low temperatures

NASA Technical Reports Server (NTRS)

Kleinherenbrink, F. A.; Cheng, P.; Amesz, J.; Blankenship, R. E.

1993-01-01

Fluorescence lifetimes of isolated membranes of Rhodopseudomonas viridis were measured in the temperature range of 77 K to 25 K. At room temperature, the main component of the fluorescence decay of bacteriochlorophyll (BChl) b had a time constant of 50 ps. In contrast to other purple bacteria, the emission at low temperature was spectrally homogeneous and showed essentially single lifetimes of 140 ps at 77 K and 180 ps at 25 K, with the primary electron donor in the oxidized state. Taking into account the relative fluorescence yields with open and closed reaction centers, we arrive at numbers of 125 ps and 215 ps, respectively, for open reaction centers. These numbers are significantly smaller than expected on the basis of measurements of the efficiency of charge separation, perhaps suggesting that the excitation decay in the absence of reaction centers is considerably faster at low temperature than at room temperature. At least four different spectral components with different lifetimes were observed at 25 K in the emission of Heliobacterium chlorum, a short-wavelength component of about 30 ps and three longer-wavelength components of about 100 ps, 300 ps, and 900 ps. This indicates a strong heterogeneity in the emitting pigment, BChl g-808. The component with the shortest lifetime does not appear to be affected by the redox state of the reaction center and might reflect energy transfer to BChl g species which are connected to the reaction center.

[Stimulation of DNA molecules association with amphiphilic derivatives of 1,3-diazaadamantane containing hydrophobic side chanins].

PubMed

Mamaeva, O K; Gabrielian, A G; Arutiunian, G L; Bocharova, T N; Smirnova, E A; Volodin, A A; Shchelkina, A K; Kaliuzhnyĭ, D N

2014-01-01

Earlier, a new class of compounds--amphiphilic derivatives of 1,3-diazaadamantanes, capable of facilitating the strand exchange in the system of short oligonucleotides was revealed. Longer hydrophobic side chains of 1,3-diazaadamantanes promoted stronger acceleration of the reaction. In this study, interaction with DNA of two 1,3-diazaadamantane derivatives containing different side chains was investigated by use of optical methods. Concentration of the investigated 1,3-diazaadamantans micelles formation were determined by the means of monitoring fluorescence intensity enhancement of 1-anilinonaphtalene-8-sulphonate probe; as well as the ranges of concentrations where the compounds/water mixtures existed as true solutions. 1,3-diazaadamantanes affinity to DNA was determined with Fluorescent Intercalator Displacement (FID) approach. Significant increase in hydrodynamic volume of short DNA hairpins in the complexes with 1,3-diazaadamantanes was revealed by estimation of the fluorescence polarization of ethidium bromide probe bound to the hairpins. Intermolecular association of DNA hairpins upon binding with 1,3-diazaadamantans was confirmed by Förster resonance energy transfer in system of an equimolar mixture of fluorescently labeled with Cy-3 and Cy-5 hairpins. In this study, the number of positive charges at 1,3-diazaadamantane derivatives containing side chains of different lengths was demonstrated to affect their affinity to DNA, whereas longer length of the hydrophobic side chains ensured more efficient interaction between the DNA duplexes that may facilitate, in particular, DNA strand exchange.

A gold nanocluster-based fluorescent probe for simultaneous pH and temperature sensing and its application to cellular imaging and logic gates.

PubMed

Wu, Yun-Tse; Shanmugam, Chandirasekar; Tseng, Wei-Bin; Hiseh, Ming-Mu; Tseng, Wei-Lung

2016-06-07

Metal nanocluster-based nanomaterials for the simultaneous determination of temperature and pH variations in micro-environments are still a challenge. In this study, we develop a dual-emission fluorescent probe consisting of bovine serum albumin-stabilized gold nanoclusters (BSA-AuNCs) and fluorescein-5-isothiocyanate (FITC) as temperature- and pH-responsive fluorescence signals. Under single wavelength excitation the FITC/BSA-AuNCs exhibited well-separated dual emission bands at 525 and 670 nm. When FITC was used as a reference fluorophore, FITC/BSA-AuNCs showed a good linear response over the temperature range 1-71 °C and offered temperature-independent spectral shifts, temperature accuracy, activation energy, and reusability. The possible mechanism for high temperature-induced fluorescence quenching of FITC/BSA-AuNCs could be attributed to a weakening of the Au-S bond, thereby lowering the charge transfer from BSA to AuNCs. Additionally, the pH- and temperature-responsive properties of FITC/BSA-AuNCs allow simultaneous temperature sensing from 21 to 41 °C (at intervals of 5 °C) and pH from 6.0 to 8.0 (at intervals of 0.5 pH unit), facilitating the construction of two-input AND logic gates. Three-input AND logic gates were also designed using temperature, pH, and trypsin as inputs. The practicality of using FITC/BSA-AuNCs to determine the temperature and pH changes in HeLa cells is also validated.

Charge transfer induced by MoO3 at boron subphthalocyanine chloride/α-sexithiophene heterojunction interface

NASA Astrophysics Data System (ADS)

Foggiatto, Alexandre L.; Sakurai, Takeaki

2018-03-01

The energy-level alignment of boron subphthalocyanine chloride (SubPc)/α-sexithiophene (6T) grown on MoO3 was investigated using ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS). We demonstrated that the p-doping effect generated by the MoO3 layer can induce charge transfer at the organic-organic heterojunction interface. After the deposition of 6T on MoO3, the fermi level becomes pinned close to the 6T highest occupied molecular orbital (HOMO) level and when SubPc is deposited, owing to its tail states, charge transfer occurs in order to achieve thermodynamic equilibrium. We also demonstrated that the charge transfer can be reduced by annealing the film. We suggested that the reduction of the misalignment on the film induces a reduction in the density of gap states, which controls the charge transfer.

Understanding the Charge Transfer at the Interface of Electron Donors and Acceptors: TTF–TCNQ as an Example

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Changwon; Atalla, Viktor; Smith, Sean

Charge transfer between an electron donor and an electron acceptor is widely accepted as being independent of their relative configurations if the interaction between them is weak; however, the limit of this concept for an interacting system has not yet been well established. Our study of prototypical electron donor–acceptor molecules, tetrathiafulvalene–tetracyanoquinodimethane, using density functional theory based on an advanced functional, clearly demonstrates that for interacting molecules, their configurational arrangement is as important as their individual electronic properties in the asymptotic limit to determine the charge transfer direction. For the first time, we demonstrate that by changing their relative orientation, onemore » can reverse the charge transfer direction of the pair, causing the molecules to exchange roles as donor and acceptor. In conclusion, our theory has important implications for understanding the interfacial charge-transfer mechanism of hybrid systems and related phenomena.« less

Interfacial charge transfer absorption: Application to metal molecule assemblies

NASA Astrophysics Data System (ADS)

Creutz, Carol; Brunschwig, Bruce S.; Sutin, Norman

2006-05-01

Optically induced charge transfer between adsorbed molecules and a metal electrode was predicted by Hush to lead to new electronic absorption features, but has been only rarely observed experimentally. Interfacial charge transfer absorption (IFCTA) provides information concerning the barriers to charge transfer between molecules and the metal/semiconductor and the magnitude of the electronic coupling and could thus provide a powerful tool for understanding interfacial charge-transfer kinetics. Here, we utilize a previously published model [C. Creutz, B.S. Brunschwig, N. Sutin, J. Phys. Chem. B 109 (2005) 10251] to predict IFCTA spectra of metal-molecule assemblies and compare the literature observations to these predictions. We conclude that, in general, the electronic coupling between molecular adsorbates and the metal levels is so small that IFCTA is not detectable. However, few experiments designed to detect IFCTA have been done. We suggest approaches to optimizing the conditions for observing the process.

Understanding the Charge Transfer at the Interface of Electron Donors and Acceptors: TTF–TCNQ as an Example

DOE PAGES

Park, Changwon; Atalla, Viktor; Smith, Sean; ...

2017-06-16

Charge transfer between an electron donor and an electron acceptor is widely accepted as being independent of their relative configurations if the interaction between them is weak; however, the limit of this concept for an interacting system has not yet been well established. Our study of prototypical electron donor–acceptor molecules, tetrathiafulvalene–tetracyanoquinodimethane, using density functional theory based on an advanced functional, clearly demonstrates that for interacting molecules, their configurational arrangement is as important as their individual electronic properties in the asymptotic limit to determine the charge transfer direction. For the first time, we demonstrate that by changing their relative orientation, onemore » can reverse the charge transfer direction of the pair, causing the molecules to exchange roles as donor and acceptor. In conclusion, our theory has important implications for understanding the interfacial charge-transfer mechanism of hybrid systems and related phenomena.« less

Collisional charging of individual submillimeter particles: Using ultrasonic levitation to initiate and track charge transfer

NASA Astrophysics Data System (ADS)

Lee, Victor; James, Nicole M.; Waitukaitis, Scott R.; Jaeger, Heinrich M.

2018-03-01

Electrostatic charging of insulating fine particles can be responsible for numerous phenomena ranging from lightning in volcanic plumes to dust explosions. However, even basic aspects of how fine particles become charged are still unclear. Studying particle charging is challenging because it usually involves the complexities associated with many-particle collisions. To address these issues, we introduce a method based on acoustic levitation, which makes it possible to initiate sequences of repeated collisions of a single submillimeter particle with a flat plate, and to precisely measure the particle charge in situ after each collision. We show that collisional charge transfer between insulators is dependent on the hydrophobicity of the contacting surfaces. We use glass, which we modify by attaching nonpolar molecules to the particle, the plate, or both. We find that hydrophilic surfaces develop significant positive charges after contacting hydrophobic surfaces. Moreover, we demonstrate that charging between a hydrophilic and a hydrophobic surface is suppressed in an acidic environment and enhanced in a basic one. Application of an electric field during each collision is found to modify the charge transfer, again depending on surface hydrophobicity. We discuss these results within the context of contact charging due to ion transfer, and we show that they lend strong support to O H- ions as the charge carriers.

Electron Transfer Dissociation: Effects of Cation Charge State on Product Partitioning in Ion/Ion Electron Transfer to Multiply Protonated Polypeptides

PubMed Central

Liu, Jian; McLuckey, Scott A.

2012-01-01

The effect of cation charge state on product partitioning in the gas-phase ion/ion electron transfer reactions of multiply protonated tryptic peptides, model peptides, and relatively large peptides with singly charged radical anions has been examined. In particular, partitioning into various competing channels, such as proton transfer (PT) versus electron transfer (ET), electron transfer with subsequent dissociation (ETD) versus electron transfer with no dissociation (ET,noD), and fragmentation of backbone bonds versus fragmentation of side chains, was measured quantitatively as a function of peptide charge state to allow insights to be drawn about the fundamental aspects of ion/ion reactions that lead to ETD. The ET channel increases relative to the PT channel, ETD increases relative to ET,noD, and fragmentation at backbone bonds increases relative to side-chain cleavages as cation charge state increases. The increase in ET versus PT with charge state is consistent with a Landau-Zener based curve-crossing model. An optimum charge state for ET is predicted by the model for the ground state-to-ground state reaction. However, when the population of excited product ion states is considered, it is possible that a decrease in ET efficiency as charge state increases will not be observed due to the possibility of the population of excited electronic states of the products. Several factors can contribute to the increase in ETD versus ET,noD and backbone cleavage versus side-chain losses. These factors include an increase in reaction exothermicity and charge state dependent differences in precursor and product ion structures, stabilities, and sites of protonation. PMID:23264749

Proton Transfer in Perfluorosulfonic Acid Fuel Cell Membranes with Differing Pendant Chains and Equivalent Weights.

PubMed

Thomaz, Joseph E; Lawler, Christian M; Fayer, Michael D

2017-05-04

Proton transfer in the nanoscopic water channels of polyelectrolyte fuel cell membranes was studied using a photoacid, 8-hydroxypyrene-1,3,6-trisulfonic acid sodium salt (HPTS), in the channels. The local environment of the probe was determined using 8-methoxypyrene-1,3,6-trisulfonic acid sodium salt (MPTS), which is not a photoacid. Three fully hydrated membranes, Nafion (DuPont) and two 3M membranes, were studied to determine the impact of different pendant chains and equivalent weights on proton transfer. Fluorescence anisotropy and excited state population decay data that characterize the local environment of the fluorescent probes and proton transfer dynamics were measured. The MPTS lifetime and anisotropy results show that most of the fluorescent probes have a bulk-like water environment with a relatively small fraction interacting with the channel wall. Measurements of the HPTS protonated and deprotonated fluorescent bands' population decays provided information on the proton transport dynamics. The decay of the protonated band from ∼0.5 ns to tens of nanoseconds is in part determined by dissociation and recombination with the HPTS, providing information on the ability of protons to move in the channels. The dissociation and recombination is manifested as a power law component in the protonated band fluorescence decay. The results show that equivalent weight differences between two 3M membranes resulted in a small difference in proton transfer. However, differences in pendant chain structure did significantly influence the proton transfer ability, with the 3M membranes displaying more facile transfer than Nafion.

Modulation of protein stability and aggregation properties by surface charge engineering.

PubMed

Raghunathan, Govindan; Sokalingam, Sriram; Soundrarajan, Nagasundarapandian; Madan, Bharat; Munussami, Ganapathiraman; Lee, Sun-Gu

2013-09-01

An attempt to alter protein surface charges through traditional protein engineering approaches often affects the native protein structure significantly and induces misfolding. This limitation is a major hindrance in modulating protein properties through surface charge variations. In this study, as a strategy to overcome such a limitation, we attempted to co-introduce stabilizing mutations that can neutralize the destabilizing effect of protein surface charge variation. Two sets of rational mutations were designed; one to increase the number of surface charged amino acids and the other to decrease the number of surface charged amino acids by mutating surface polar uncharged amino acids and charged amino acids, respectively. These two sets of mutations were introduced into Green Fluorescent Protein (GFP) together with or without stabilizing mutations. The co-introduction of stabilizing mutations along with mutations for surface charge modification allowed us to obtain functionally active protein variants (s-GFP(+15-17) and s-GFP(+5-6)). When the protein properties such as fluorescent activity, folding rate and kinetic stability were assessed, we found the possibility that the protein stability can be modulated independently of activity and folding by engineering protein surface charges. The aggregation properties of GFP could also be altered through the surface charge engineering.

Spectral and theoretical study on complexation of sulfamethoxazole with β- and HPβ-cyclodextrins in binary and ternary systems

NASA Astrophysics Data System (ADS)

Varghese, Beena; Suliman, FakhrEldin O.; Al-Hajri, Aalia; Al Bishri, Nahed Surur S.; Al-Rwashda, Nathir

2018-02-01

The inclusion complexes of sulfamethoxazole (SMX) with β-cyclodextrin (βCD) and (2-hydroxypropyl) β-cyclodextrin (HPβCD) were prepared. Fluorescence spectroscopy and electrospray mass spectrometry, ESI-MS, were used to investigate and characterize the inclusion complexation of SMX with cyclodextrins in solutions. Whereas in the solid state the complexes were characterized by Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD) and Raman techniques. Enhanced twisted intramolecular charge transfer (TICT), emission as well as local excited (LE) bands were observed upon addition of HPβCD indicate that SMX enters deeper into the cyclodextrins cavity. The stoichiometries and association constants of these complexes have been determined by monitoring the fluorescence data. The effect of presence of ternary components like arginine and cysteine on the complexation efficiency of SMX with cyclodextrins was investigated. Molecular Dynamic simulations were also performed to shed an atomistic insight into the complexation mechanism. The results obtained showed that complexes of SMX with both cyclodextrins are stabilized in aqueous media by strong hydrogen bonding interactions.

Screening and structural elucidation of the zwitterionic cocrystal o-picolinic acid with p-nitro aniline

NASA Astrophysics Data System (ADS)

Mekala, R.; Jagdish, P.; Mathammal, R.; Sangeetha, K.

2017-04-01

The cocrystal was screened by solvent drop grinding method and the crystals were grown by slow evaporation method at ambient conditions. The cocrystal formation of o-picolinic acid with p-nitro aniline was initially analysed by powder X-ray diffraction. Further the structural properties of the grown crystal were confirmed by the single X-ray diffraction which indicates that the cocrystal were connected by the strong N+sbnd H-⋯O hydrogen bond interaction. The cell parameters of the grown crystal were a = 14.2144(5) Å, b = 5.7558(2) Å, c = 16.0539(6) Å. The functional groups were identified using Fourier transform infrared and Raman spectral analysis. The excitation and emission state of the sample was analysed by the UV-Visible and Fluorescence studies. The red emission was observed from the Fluorescence studies. NMR studies revealed the chemical shift of the cocrystal. Thermal stability and its melting behaviour were studied by TGA and DSC analytical techniques. Electrical behaviour was studied using the dielectric studies. The intermolecular charge transfer within the molecule were analysed using HOMO- LUMO plots.

Synthesis and fluorescent properties of poly(arylpyrazoline)'s for organic-electronics

NASA Astrophysics Data System (ADS)

Vandana, T.; Ramkumar, V.; Kannan, P.

2016-08-01

The present work focuses on the synthesis and characterization of poly(arylchalcone)'s (PCH I-IV) by reacting acetone with various dialdehydes for the first time at below ambient temperature followed by cyclization with phenylhydrazinehydrochloride to yield luminescent poly(arylpyrazoline)'s (PPY I-IV). The synthesized polymers were characterized by standard techniques such as, GPC, SEM, TGA, FT-IR, 1H NMR, UV-Vis absorption and fluorescence spectroscopy, and electrochemical studies by cyclic voltammetry analyses. The Pyrazoline group hooked with different aryl donors such as benzene, thiophene, carbazole, triphenylamine, thus results a series of blue and green emitting materials. The obtained optical bandgap energy of the polymers (PPY I-IV) were 2.53, 3.41, 3.07, 3.10 eV respectively, suggest that all the polymers belongs to semiconducting category. The solvent effect of polymers was thoroughly studied and explained by Lippert-Mataga equation. The polymers I & IV display large degree of intra-molecular charge transfer in excited state evidenced from solvatochromic shift on the emission spectra. The obtained results demonstrate that they are promising materials for organic electronics applications.

Molecular complexes of l-phenylalanine with substituted 1,4-benzoquinones in aqueous medium: spectral and theoretical investigations.

PubMed

Ganesh, K; El-Mossalamy, E H; Satheshkumar, A; Balraj, C; Elango, K P

2013-12-01

Various spectral techniques such as UV-Vis, FT-IR, and fluorescence have been employed to investigate the charge transfer interaction of L-phenylalanine (LPA) with substituted 1,4-benzoquinones (MQ(1-4)). Kinetic and thermodynamic properties of the complexes were determined in aqueous medium at physiological condition (pH=7). The interaction of MQ(1-4) with L-phenylalanine (LPA) was found to proceed through the formation of donor-acceptor complex, yielding a radical anion. The stoichiometry of the complexes was determined by Jobs continuous variation method and was found to be 1:1 in all the cases. Fluorescence quenching studies showed that the interaction between the donor and the acceptors is spontaneous. The results indicated that the progressive replacement of chlorine atom (-I effect) by methoxy group (+M effect) in the quinone decreased the electron acceptor property of the quinone. The order of the experimentally measured association constant of these complexes was well supported by DFT/B3LYP calculations. Copyright © 2013 Elsevier B.V. All rights reserved.

Through-Space Intervalence Charge Transfer as a Mechanism for Charge Delocalisation in Metal-Organic Frameworks.

PubMed

Hua, Carol; Doheny, Patrick William; Ding, Bowen; Chan, Bun; Yu, Michelle; Kepert, Cameron J; D'Alessandro, Deanna M

2018-05-04

Understanding the nature of charge transfer mechanisms in 3-dimensional Metal-Organic Frameworks (MOFs) is an important goal owing to the possibility of harnessing this knowledge to design conductive frameworks. These materials have been implicated as the basis for the next generation of technological devices for applications in energy storage and conversion, including electrochromic devices, electrocatalysts, and battery materials. After nearly two decades of intense research into MOFs, the mechanisms of charge transfer remain relatively poorly understood, and new strategies to achieve charge mobility remain elusive and challenging to experimentally explore, validate and model. We now demonstrate that aromatic stacking interactions in Zn(II) frameworks containing cofacial thiazolo[5,4-d]thiazole units lead to a mixed-valence state upon electrochemical or chemical reduction. This through-space Intervalence Charge Transfer (IVCT) phenomenon represents a new mechanism for charge delocalisation in MOFs. Computational modelling of the optical data combined with application of Marcus-Hush theory to the IVCT bands for the mixed-valence framework has enabled quantification of the degree of delocalisation using both in situ and ex situ electro- and spectro-electrochemical methods. A distance dependence for the through-space electron transfer has also been identified on the basis of experimental studies and computational calculations. This work provides a new window into electron transfer phenomena in 3-dimensional coordination space, of relevance to electroactive MOFs where new mechanisms for charge transfer are highly sought after, and to understanding biological light harvesting systems where through-space mixed-valence interactions are operative.

[Fluorescence Resonance Energy Transfer Detection of Cobalt Ions by Silver Triangular Nanoplates and Rhodamine 6G].

PubMed

Zhang, Xiu-qing; Peng, Jun; Ling, Jian; Liu, Chao-juan; Cao, Qiu-e; Ding, Zhong-tao

2015-04-01

In the present paper, the authors studied fluorescence resonance energy transfer (FRET) phenomenon between silver triangular nanoplates and bovine serum albumin (BSA)/Rhodamine 6G fluorescence complex, and established a fluorescence method for the detection of cobalt ions. We found that when increasing the silver triangular nanoplates added to certain concentrations of fluorescent bovine serum albumin (BSA)/Rhodamine 6G complex, the fluorescence of Rhodamine 6G would be quenched up to 80% due to the FRET between the quencher and donor. However, in the presence of cobalt ions, the disassociation of the fluorescent complex from silver triangular nanoplates occurred and the fluorescence of the Rhodamine 6G recovered. The recovery of fluorescence intensity rate (I/I0) has a good relationship with the cobalt ion concentration (cCO2+) added. Thus, the authors developed a fluorescence method for the detection of cobalt ions based on the FRET of silver triangular nanoplates and Rhodamine 6G.

Photoinduced energy and electron transfer processes in hexapyropheophorbide a- fullerene [C(60)] molecular systems.

PubMed

Regehly, Martin; Ermilov, Eugeny A; Helmreich, Matthias; Hirsch, Andreas; Jux, Norbert; Röder, Beate

2007-02-08

The photophysical properties of the novel hexapyropheophorbide a (P6), and hexakis (pyropheophorbide a)-C60 (FP6) were studied and compared with those of hexakis (pyropheophorbide a)-fullerene [5:1] hexaadduct (FHP6). It was found that after light absorption the pyropheophorbide a molecules in all three compounds undergo very efficient energy transfer as well as partly excitonic interactions. The last process results in the formation of energy traps, which could be resolved experimentally. For P6, due to shorter distances between neighboring dye molecules, stronger interactions between pyropheophorbide a units than for FHP6 were observed. As a consequence, the excitation energy is delivered rapidly to traps formed by stacked pyropheophorbide a molecules resulting in the reduction of fluorescence, intersystem crossing, and singlet oxygen quantum yields compared to the values of FHP6. For FP6 the reduction of these values is much stronger due to an additional fast and efficient deactivation process, namely photoinduced electron transfer from pyropheophorbide a to the fullerene moiety. Consequently, FP6 can be considered as a combination of a light-harvesting system consisting of several separate pyropheophorbide a molecules and a charge-separating center.

Optical properties of humic substances and CDOM: relation to structure.

PubMed

Boyle, Erin S; Guerriero, Nicolas; Thiallet, Anthony; Del Vecchio, Rossana; Blough, Neil V

2009-04-01

The spectral dependencies of absorption and fluorescence emission (emission maxima (lamdamax), quantum yields (phi), and mean lifetimes (taum)) were acquired for a commercial lignin, Suwannee River humic (SRHA) and fulvic (SRFA) acids, and a series solid phase extracts (C18) from the Middle Atlantic Bight (MAB extracts). These parameters were compared with the relative average size and total lignin phenol content (TLP). TLP was strongly correlated with absorption at 280 and 355 nm for the MAB extracts, SRHA, and SRFA. The spectral dependence of lamdamax, phi), and taum was very similar for all samples, suggesting a common photophysical and thus structural basis. A strong decrease of phi and taum with increasing average size indicates that intramolecular interactions must be important. When combined with previous work, the results lead us to conclude that the optical properties commonly associated with terrestrial humic substances and chromophoric dissolved organic matter arise primarily from an ensemble of partially oxidized lignins derived from vascular plant sources. Theyfurther provide additional support for an electronic interaction model in which intramolecular energy transfer, excited-state electron transfer, as well as charge transfer likely play important roles in producing the observed optical and photochemical properties of these materials.

Investigation of polar and stereoelectronic effects on pure excited-state hydrogen atom abstractions from phenols and alkylbenzenes.

PubMed

Pischel, Uwe; Patra, Digambara; Koner, Apurba L; Nau, Werner M

2006-01-01

The fluorescence quenching of singlet-excited 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by 22 phenols and 12 alkylbenzenes has been investigated. Quenching rate constants in acetonitrile are in the range of 10(8)-10(9) M(-1)s(-1) for phenols and 10(5)-10(6) M(-1)s(-1) for alkylbenzenes. In contrast to the quenching of triplet-excited benzophenone, no exciplexes are involved, so that a pure hydrogen atom transfer is proposed as quenching mechanism. This is supported by (1) pronounced deuterium isotope effects (kH/kD ca 4-6), which were observed for phenols and alkylbenzenes, and (2) a strongly endergonic thermodynamics for charge transfer processes (electron transfer, exciplex formation). In the case of phenols, linear free energy relationships applied, which led to a reaction constant of rho = -0.40, suggesting a lower electrophilicity of singlet-excited DBO than that of triplet-excited ketones and alkoxyl radicals. The reactivity of singlet-excited DBO exposes statistical, steric, polar and stereoelectronic effects on the hydrogen atom abstraction process in the absence of complications because of competitive exciplex formation.

Proton transfer complexes based on some π-acceptors having acidic protons with 3-amino-6-[2-(2-thienyl)vinyl]-1,2,4-triazin-5(4 H)-one donor: Synthesis and spectroscopic characterizations

NASA Astrophysics Data System (ADS)

Refat, Moamen S.; Saad, Hosam A.; Adam, Abdel Majid A.

2011-05-01

Charge transfer complexes based on 3-amino-6-[2-(2-thienyl)vinyl]-1,2,4-triazin-5(4 H)-one (ArNH 2) organic basic donor and pi-acceptors having acidic protons such as picric acid (PiA), hydroquinone (Q(OH) 2) and 3,5-dinitrobenzene (DNB) have been synthesized and spectroscopically studied. The sbnd NH3+ ammonium ion was formed under the acid-base theory through proton transfer from an acidic to basic centers in all charge transfer complexes resulted. The values of formation constant ( KCT) and molar extinction coefficient ( ɛCT) which were estimated from the spectrophotometric studies have a dramatic effect for the charge transfer complexes with differentiation of pi-acceptors. For further studies the vibrational spectroscopy of the [( ArNH3+)(PiA -)] (1), [( ArNH3+)(Q (OH)2-)] (2) and [( ArNH3+)(DNB -)] (3) of (1:1) charge transfer complexes of (donor: acceptor) were characterized by elemental analysis, infrared spectra, Raman spectra, 1H and 13CNMR spectra. The experimental data of elemental analyses of the charge transfer complexes (1), (2) and (3) were in agreement with calculated data. The IR and Raman spectra of (1), (2) and (3) are indicated to the presence of bands around 3100 and 1600 cm -1 distinguish to sbnd NH3+. The thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) techniques were performed to give knowledge about thermal stability behavior of the synthesized charge transfer complexes. The morphological features of start materials and charge transfer complexes were investigated using scanning electron microscopy (SEM) and optical microscopy.

Process techniques of charge transfer time reduction for high speed CMOS image sensors

NASA Astrophysics Data System (ADS)

Zhongxiang, Cao; Quanliang, Li; Ye, Han; Qi, Qin; Peng, Feng; Liyuan, Liu; Nanjian, Wu

2014-11-01

This paper proposes pixel process techniques to reduce the charge transfer time in high speed CMOS image sensors. These techniques increase the lateral conductivity of the photo-generated carriers in a pinned photodiode (PPD) and the voltage difference between the PPD and the floating diffusion (FD) node by controlling and optimizing the N doping concentration in the PPD and the threshold voltage of the reset transistor, respectively. The techniques shorten the charge transfer time from the PPD diode to the FD node effectively. The proposed process techniques do not need extra masks and do not cause harm to the fill factor. A sub array of 32 × 64 pixels was designed and implemented in the 0.18 μm CIS process with five implantation conditions splitting the N region in the PPD. The simulation and measured results demonstrate that the charge transfer time can be decreased by using the proposed techniques. Comparing the charge transfer time of the pixel with the different implantation conditions of the N region, the charge transfer time of 0.32 μs is achieved and 31% of image lag was reduced by using the proposed process techniques.

Photoinduced electron transfer in a molecular dyad by nanosecond pump-pump-probe spectroscopy.

PubMed

Ha-Thi, M-H; Pham, V-T; Pino, T; Maslova, V; Quaranta, A; Lefumeux, C; Leibl, W; Aukauloo, A

2018-06-01

The design of robust and inexpensive molecular photocatalysts for the conversion of abundant stable molecules like H2O and CO2 into an energetic carrier is one of the major fundamental questions for scientists nowadays. The outstanding challenge is to couple single photoinduced charge separation events with the sequential accumulation of redox equivalents at the catalytic unit for performing multielectronic catalytic reactions. Herein, double excitation by nanosecond pump-pump-probe experiments was used to interrogate the photoinduced charge transfer and charge accumulation on a molecular dyad composed of a porphyrin chromophore and a ruthenium-based catalyst in the presence of a reversible electron acceptor. An accumulative charge transfer state is unattainable because of rapid reverse electron transfer to the photosensitizer upon the second excitation and the low driving force of the forward photodriven electron transfer reaction. Such a method allows the fundamental understanding of the relaxation mechanism after two sequential photon absorptions, deciphering the undesired electron transfer reactions that limit the charge accumulation efficiency. This study is a step toward the improvement of synthetic strategies of molecular photocatalysts for light-induced charge accumulation and more generally, for solar energy conversion.