Chromium complexes for luminescence, solar cells, photoredox catalysis, upconversion, and phototriggered NO release.

PubMed

Büldt, Laura A; Wenger, Oliver S

2017-11-01

Some complexes of Cr(iii) and Cr(0) have long been known to exhibit interesting photophysical and photochemical properties, but in the past few years important conceptual progress was made. This Perspective focuses on the recent developments of Cr(iii) complexes as luminophores and dyes for solar cells, their application in photoredox catalysis, their use as sensitizers in upconversion processes, and their performance as photochemical nitric oxide sources. The example of a luminescent Cr(0) isocyanide complex illustrates the possibility of obtaining photoactive analogues of d 6 metal complexes that are commonly made from precious metals such as Ru(ii) or Ir(iii). The studies highlighted herein illustrate the favorable excited-state properties of robust first-row transition metal complexes with broad application potential.

Photophysics of N,N-Dimethyldihydrophenazine and Benzoannelated Analogues. Structurally Dependent Excited State Hierarchy,

DTIC Science & Technology

1980-02-26

phenazine (DrOIAC), 9,14-dimethyl-9,14-dihydrophenanthro[4,5-J] phenazine -(D!IPP) L.A- and 6,13-dimethyl-6,13-dihydrobibenzo[b,i] phenazine (DMBI) hie been...electrochemical oxidation,3 photochemical oxidation,4 and photoionization5 of 5,10-dlmethyl-5,10-dihydro- phenazine (DMP)’ have been studied. Our initial interest...dihydrodibenzo[a,c] phenazine (DMAC) 9,14-dlmethyl-9,14-dihydrophenanthro[4,5-abcphenazine (DMPP) and 6,13-di- methyl-6,13-dihydrodibenzo[b,ilphenazine

Photophysics and Photochemistry of 2-Aminobenzoic Acid Anion in Aqueous Solution

NASA Astrophysics Data System (ADS)

Pozdnyakov, Ivan P.; Plyusnin, Victor F.; Grivin, Vjacheslav P.

2009-11-01

Nanosecond laser flash photolysis and absorption and fluorescence spectroscopy were used to study photochemical processes of 2-aminobenzoic acid anion (ABA-) in aqueous solutions. Excitation of this species gives rise to the ABA- triplet state to the ABA• radical and to the hydrated electron (eaq-). The last two species result from two-photon processes. In a neutral medium, the main decay channels of ABA- triplet state, the ABA• radical, and eaq- are T-T annihilation, recombination, and capture by the ABA- anion, respectively.

Efficiency of photochemical stages of photosynthesis in purple bacteria (a critical survey).

PubMed

Borisov, A Yu

2014-03-01

Based on currently available data, the energy transfer efficiency in the successive photophysical and photochemical stages has been analyzed for purple bacteria. This analysis covers the stages starting from migration of the light-induced electronic excitations from the bulk antenna pigments to the reaction centers up to irreversible stage of the electron transport along the transmembrane chain of cofactors-carriers. Some natural factors are revealed that significantly increase the rates of efficient processes in these stages. The influence on their efficiency by the "bottleneck" in the energy migration chain is established. The overall quantum yield of photosynthesis in these stages is determined.

Visible light photocatalysis as a greener approach to photochemical synthesis.

PubMed

Yoon, Tehshik P; Ischay, Michael A; Du, Juana

2010-07-01

Light can be considered an ideal reagent for environmentally friendly, 'green' chemical synthesis; unlike many conventional reagents, light is non-toxic, generates no waste, and can be obtained from renewable sources. Nevertheless, the need for high-energy ultraviolet radiation in most organic photochemical processes has limited both the practicality and environmental benefits of photochemical synthesis on industrially relevant scales. This perspective describes recent approaches to the use of metal polypyridyl photocatalysts in synthetic organic transformations. Given the remarkable photophysical properties of these complexes, these new transformations, which use Ru(bpy)(3)(2+) and related photocatalysts, can be conducted using almost any source of visible light, including both store-bought fluorescent light bulbs and ambient sunlight. Transition metal photocatalysis thus represents a promising strategy towards the development of practical, scalable industrial processes with great environmental benefits.

Aldehyde Substituted Phthalocyanines: Synthesis, Characterization and Investigation of Photophysical and Photochemical Properties.

PubMed

Sen, Pinar; Yildiz, S Zeki; Erdoğmuş, Ali; Dege, Necmi; Atalay, Yusuf

2016-07-01

The new free and nickel phthalocyanine derivatives, tetrakis [(2-formylphenoxy)-phthalocyanine (4), tetrakis [(2-formylphenoxy)-phthalocyaninato]nickel(II) (5) have been synthesized via de-protection of tetra acetal-substituted phthalocyanines in acetic acid/FeCl3 system. The starting phthalocyanines, tetrakis [(2-(1,3-dioxolan-2-yl)phenoxy)-phthalocyanine (2) and tetrakis [(2-(1,3-dioxolan-2-yl)phenoxy)-phthalocyaninato]nickel (3), were prepared by the tetramerization of 4-(2-(1,3-dioxolan-2-yl) phenoxy) phthalonitrile (1). The new compounds have been characterized by the combination of FT-IR, (1)H NMR, UV-Vis, Mass spectra and elemental analysis. Compound 1 crystallizes in the Orthorhombic, space group Pbca with a = 9.2542 (4) Å, b = 13.3299 (5) Å, c = 23.2333 (11) Å, and Z = 8. Compound 1 is built up from two planar groups (phthalonitrile and phenoxy), with a dihedral angle of 69.693(36)° between them and non-planar dioxolane group. We report a combined experimental and theoretical study on molecule 1, as well. Geometric, spectroscopic and electronic properties of compound 1 has been calculated using B3LYP method and 6-311++G(dp) basis set. Fluorescence spectroscopy was applied to record the photoluminescence spectra of the prepared phthalocyanines and the photophysical and photochemical properties were examined in DMSO.

Photoactive High Explosives: Substituents Effects on Tetrazine Photochemistry and Photophysics

DOE PAGES

McGrane, Shawn David; Bolme, Cynthia Anne; Greenfield, Margo Torello; ...

2016-01-21

High explosives that are photoactive, i.e., can be initiated with light, offer significant advantages in reduced potential for accidental electrical initiation. In this study, we examined a series of structurally related tetrazine based photoactive high explosive materials to detail their photochemical and photophysical properties. Using photobleaching infrared absorption, we determined quantum yields of photochemistry for nanosecond pulsed excitation at 355 and 532 nm. Changes in mass spectrometry during laser irradiation in vacuum measured the evolution of gaseous products. Fluorescence spectra, quantum yields, and lifetimes were measured to observe radiative channels of energy decay that compete with photochemistry. For the 6more » materials studied, quantum yields of photochemistry ranged from <10 –5 to 0.03 and quantum yield of fluorescence ranged from <10 –3 to 0.33. In all cases, the photoexcitation nonradiatively relaxed primarily to heat, appropriate for supporting photothermal initiation processes. Lastly, the photochemistry observed was dominated by ring scission of the tetrazine, but there was evidence of more extensive multistep reactions as well.« less

Amphiphilic zinc phthalocyanine photosensitizers: synthesis, photophysicochemical properties and in vitro studies for photodynamic therapy.

PubMed

Çakır, Dilek; Göksel, Meltem; Çakır, Volkan; Durmuş, Mahmut; Biyiklioglu, Zekeriya; Kantekin, Halit

2015-05-28

Peripherally and non-peripherally tetra-substituted zinc(ii) phthalocyanines bearing 2-(2-{2-[3-(dimethylamino)phenoxy]ethoxy}ethoxy)ethoxy and 2-(2-{2-[3-(diethylamino)phenoxy]ethoxy}ethoxy)ethoxy groups (, , and ) were synthesized by cyclotetramerization of the corresponding phthalonitriles (, , and ). Their quaternized ionic derivatives (, , and ) were also synthesized by the reaction of them with methyl iodide. The novel compounds were characterized by using standard spectroscopic techniques such as FT-IR, (1)H NMR, (13)C NMR, UV-vis, mass and elemental analyses. The obtained quaternized phthalocyanines (, , and ) showed amphiphilic behaviour with excellent solubility in both organic and aqueous solutions, which makes them potential photosensitizers for use in photodynamic therapy (PDT) of cancer. The photophysical (fluorescence quantum yields and lifetimes) and photochemical (singlet oxygen and photodegradation quantum yields) properties of these novel phthalocyanines were studied in DMSO for both non-ionic and ionic quaternized derivatives. However, these properties were examined in both DMSO and phosphate buffer solution (PBS) for quaternized ionic phthalocyanines. The effects of the positions of substituents (peripheral or non-peripheral) and the quaternization of the nitrogen atoms on the substituents about their photophysical and photochemical properties were also compared in this study. The bovine serum albumin (BSA) binding behaviours of the studied quaternized ionic zinc(ii) phthalocyanines were also described in PBS solutions. The quaternized phthalocyanines (, , and ) successfully displayed light-dependent photodamage in HeLa and HuH-7 cancer cells in photodynamic therapy treatment. The photosensitivity and the intensity of damage were found directly related to the concentration of the photosensitizers.

Photophysics and photochemistry of 2-aminobenzoic acid anion in aqueous solution.

PubMed

Pozdnyakov, Ivan P; Plyusnin, Victor F; Grivin, Vjacheslav P

2009-12-24

Nanosecond laser flash photolysis and absorption and fluorescence spectroscopy were used to study photochemical processes of 2-aminobenzoic acid anion (ABA(-)) in aqueous solutions. Excitation of this species gives rise to the ABA(-) triplet state to the ABA* radical and to the hydrated electron (e(aq)(-)). The last two species result from two-photon processes. In a neutral medium, the main decay channels of ABA(-) triplet state, the ABA* radical, and e(aq)(-) are T-T annihilation, recombination, and capture by the ABA(-) anion, respectively.

Photophysical and Photochemical Properties of Some Fluorescent Derivatives of Vitamin B1

NASA Astrophysics Data System (ADS)

Marciniak, B.

1987-05-01

Absorption and emission spectra, depopulation kinetics of the lowest excited singlet and triplet states and acid-base equilibria of two fluorescent vitamin B, derivatives, the products I and II of the reaction of N-methylated vitamine B, with cytidine and adenosine, respectively, were investigated. Analysis of the lifetime and quantum yield data indicate that at 77 K emissions are the main processes of deactivation of the S1 and T1 states for the free ion and protonated forms. The pKa values indicate a much higher acidity in the excited singlet and triplet states than in the ground state. I and II undergo very slow photochemical reactions in solution in the presence of oxygen (Φ ~ 10-4).

Photochemistry of fac-[Re(CO)3(dcbH2)( trans-stpy)]+: New Insights on the Isomerization Mechanism of Coordinated Stilbene-like Ligands.

PubMed

Faustino, Leandro A; Hora Machado, Antonio Eduardo; Patrocinio, Antonio Otavio T

2018-03-05

In this work, a novel complex fac-[Re(CO) 3 (dcbH 2 )( trans-stpy)] + , (dcbH 2 = 4,4'-dicarboxylic acid-2,2'-bipyridine; trans-stpy = trans-4-styrylpyridine) was synthesized and characterized toward its spectroscopic, photochemical, and photophysical properties. The experimental data provide new insights on the mechanism of photochemical trans-to- cis isomerization of the stilbene-like ligand coordinated to Re(I) polypyridyl complexes. The new complex exhibits an unusual and strong dependence of the isomerization quantum yield (Φ t →c ) on the irradiation wavelength. Φ t →c was 0.81 ± 0.08 for irradiation at 365 nm and continuously decreased as the irradiation wavelength is shifted to the visible. At 405 nm irradiation Φ t →c is almost 2 orders of magnitude lower (0.010 ± 0.005) than that observed at 365 nm excitation. This behavior can be explained by the low-lying triplet metal-to-ligand charge-transfer excited state ( 3 MLCT) that hinders the triplet photoreaction mechanism under visible light absorption. Under UV irradiation, direct population of styrylpyridine-centered excited state ( 1 IL) leads to the occurrence of the photoisomerization via a singlet mechanism. Further experiments were performed with the complex immobilized on the surface of TiO 2 and Al 2 O 3 films. The nonoccurrence of isomerization at the oxide surfaces even under UV excitation evidences the role of energy gap between the 1 IL/ 1 MLCT states on the photochemical/photophysical processes. The results establish important relationships between the molecular structure and the photoelectrochemical behavior, which can further contribute to the development of solid-state molecular switches based on Re(I) polypyridyl complexes.

Photooxidative degradation of clear ultraviolet absorbing acrylic copolymer surfaces

NASA Technical Reports Server (NTRS)

Gupta, A.; Liang, R. H.; Vogl, O.; Pradellok, W.; Huston, A. L.; Scott, G. W.

1983-01-01

Photodegradation of copolymer of methyl methacrylate and 2(2'-hydroxy 5'vinyl-phenyl) 2H-benzotriazole has been investigated in order to determine the changes in the chemical composition of the surface of the copolymer on photooxidation. An electronic energy transfer mechanism has been postulated in order to interpret the observed photochemical changes in the polymer. Preliminary examination of the photophysical properties of the chromophore provides support for such a mechanism.

pHP-Tethered N-Acyl Carbamate: A Photocage for Nicotinamide.

PubMed

Salahi, Farbod; Purohit, Vatsal; Ferraudi, Guillermo; Stauffacher, Cynthia; Wiest, Olaf; Helquist, Paul

2018-05-04

The synthesis of a new photocaged nicotinamide having an N-acyl carbamate linker and a p-hydroxyphenacyl (pHP) chromophore is described. The photophysical and photochemical studies showed an absorption maximum at λ = 330 nm and a quantum yield for release of 11% that are dependent upon both pH and solvent. While the acyl carbamate releases nicotinamide efficiently, a simpler amide linker was inert to photocleavage. This photocaged nicotinamide has significant advantages with respect to quantum yield, absorbance wavelength, rate of release, and solubility that make it the first practical example of a photocaged amide.

Multistate photo-induced relaxation and photoisomerization ability of fumaramide threads: a computational and experimental study.

PubMed

Altoè, Piero; Haraszkiewicz, Natalia; Gatti, Francesco G; Wiering, Piet G; Frochot, Céline; Brouwer, Albert M; Balkowski, Grzegorz; Shaw, Daniel; Woutersen, Sander; Buma, Wybren Jan; Zerbetto, Francesco; Orlandi, Giorgio; Leigh, David A; Garavelli, Marco

2009-01-14

Fumaric and maleic amides are the photoactive units of an important and widely investigated class of photocontrollable rotaxanes as they trigger ring shuttling via a cis-trans photoisomerization. Here, ultrafast decay and photoinduced isomerization in isolated fumaramide and solvated nitrogen-substituted fumaramides (that are employed as threads in those rotaxanes) have been investigated by means of CASPT2//CASSCF computational and time-resolved spectroscopic techniques, respectively. A complex multistate network of competitive deactivation channels, involving both internal conversion and intersystem crossing (ISC) processes, has been detected and characterized that accounts for the picosecond decay and photochemical/photophysical properties observed in the singlet as well as triplet (photosensitized) photochemistry of fumaramides threads. Interestingly, singlet photochemistry appears to follow a non-Kasha rule model, where nonequilibrium dynamical factors control the outcome of the photochemical process: accessible high energy portions of extended crossing seams turn out to drive the deactivation process and ground-state recovery. Concurrently, extended singlet/triplet degenerate regions of twisted molecular structures with significant spin-orbit-coupling values account for ultrafast (picosecond time scale) ISC processes that lead to higher photoisomerization efficiencies. This model discloses the principles behind the intrinsic photochemical reactivity of fumaramide and its control.

A metal-organic cage incorporating multiple light harvesting and catalytic centres for photochemical hydrogen production

NASA Astrophysics Data System (ADS)

Chen, Sha; Li, Kang; Zhao, Fang; Zhang, Lei; Pan, Mei; Fan, Yan-Zhong; Guo, Jing; Shi, Jianying; Su, Cheng-Yong

2016-11-01

Photocatalytic water splitting is a natural but challenging chemical way of harnessing renewable solar power to generate clean hydrogen energy. Here we report a potential hydrogen-evolving photochemical molecular device based on a self-assembled ruthenium-palladium heterometallic coordination cage, incorporating multiple photo- and catalytic metal centres. The photophysical properties are investigated by absorption/emission spectroscopy, electrochemical measurements and preliminary DFT calculations and the stepwise electron transfer processes from ruthenium-photocentres to catalytic palladium-centres is probed by ultrafast transient absorption spectroscopy. The photocatalytic hydrogen production assessments reveal an initial reaction rate of 380 μmol h-1 and a turnover number of 635 after 48 h. The efficient hydrogen production may derive from the directional electron transfers through multiple channels owing to proper organization of the photo- and catalytic multi-units within the octahedral cage, which may open a new door to design photochemical molecular devices with well-organized metallosupramolecules for homogenous photocatalytic applications.

Ligand-Sensitized Lanthanide Nanocrystals: Merging Solid-State Photophysics and Molecular Solution Chemistry

DOE PAGES

Agbo, Peter; Abergel, Rebecca J.

2016-06-30

To date, the breadth of scientific research that has been devoted to investigating the photochemical and photophysical behavior of the lanthanide elements has generally fallen into one of two camps: solution studies of luminescent lanthanide metal-ligand complexes or investigations of solid-state nanoparticles, composed primarily of, or doped with, lanthan ide lumiphores. In the latter case, most research of lanthanide nanocolloids has precluded any investigations regarding the use of organic ligands to overcome the difficulties associated with f-f excitation of lanthanides. Instead, most work on condensed-phase lanthanide luminescence has centered on strategies such as d-f charge separation in divalent lanthanides andmore » the sensitization of lanthanide excited states using quantum dots. Current work now aims at bridging the camps of condensed-phase lanthanide photophysics and the solution chemistry of ligand-lanthanide molecular complexes. Some recent efforts have partly focused on the fundamental characterization of NaGd 1-x Ln x F 4 nanoparticles featuring surface display of the sensitizer ligand 3,4,3-LI(1,2-HOPO), showing these structures to be capable of converting absorbed UV light into luminescence from Eu 3+ and Tb 3+ ions. Our results suggest such a use of the ligand sensitization as a tool of choice to overcome the constraints of UV solar spectrum/semiconductor band-gap mismatch and low absorption cross sections in solid-state lanthanide systems.« less

Photoinitiated Electron Collection in Mixed-Metal Supramolecular Complexes: Development of Photocatalysts for Hydrogen Production. Final Report of Progress August 2017

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

Tanko, James M.

Mixed-metal supramolecular complexes containing one or two RuII light absorbing subunits coupled through polyazine bridging ligands to a RhIII reactive metal center were prepared for use as photocatalysts for the production of solar H 2 fuel from H 2O. The electrochemical, photophysical, and photochemical properties upon variation of the monodentate, labile ligands coordinated to the Rh reactive metal center were investigated.

Photodynamic evaluation of tetracarboxy-phthalocyanines in model systems.

PubMed

Alonso, Lais; Sampaio, Renato N; Souza, Thalita F M; Silva, Rodrigo C; Neto, Newton M Barbosa; Ribeiro, Anderson O; Alonso, Antonio; Gonçalves, Pablo J

2016-08-01

The present work reports the synthesis, photophysical and photochemical characterization and photodynamic evaluation of zinc, aluminum and metal free-base tetracarboxy-phthalocyanines (ZnPc, AlPc and FbPc, respectively). To evaluate the possible application of phthalocyanines as a potential photosensitizer the photophysical and photochemical characterization were performed using aqueous (phosphate-buffered solution, PBS) and organic (dimethyl sulfoxide, DMSO) solvents. The relative lipophilicity of the compounds was estimated by the octanol-water partition coefficient and the photodynamic activity evaluated through the photooxidation of a protein and photohemolysis. The photooxidation rate constants (k) were obtained and the hemolytic potential was evaluated by the maximum percentage of hemolysis achieved (Hmax) and the time (t50) to reach 50% of the Hmax. Although these phthalocyanines are all hydrophilic and possess very low affinity for membranes (log PO/W=-2.0), they led to significant photooxidation of bovine serum albumin (BSA) and photohemolysis. Our results show that ZnPc was the most efficient photosensitizer, followed by AlPc and FbPc; this order is the same as the order of the triplet and singlet oxygen quantum yields (ZnPc>AlPc>FbPc). Furthermore, together, the triplet, fluorescence and singlet oxygen quantum yields of zinc tetracarboxy-phthalocyanines suggest their potential for use in theranostic applications, which simultaneously combines photodiagnosis and phototherapy. Copyright © 2016 Elsevier B.V. All rights reserved.

Organic photochemical storage of solar energy. Progress report, July 1, 1977--Feburary 28, 1978

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

Jones, G. II

1978-03-01

The prospects for driving endoergic reactions of simple, relatively abundant organic chemicals by photochemical means have been examined. Strategies for utilization of light of varying wavelength involve sensitization mechanisms which depend on the redox properties of energy storing substrates and photosensitizers. Of principal interest is valence isomerization which can be induced by electron donor-acceptor interaction between substrate and sensitizer in an excited complex or exciplex. Photophysical studies show that potentially isomerizable substrates efficiently intercept redox photosensitizers. The quenching of emission of electron acceptor sensitizers by non conjugated hydrocarbon dienes is indeed a function of the reduction potential of the acceptorsmore » (a series of aromatics with varying absorption characteristics) and the oxidation potentials of the substrates. Electron deficient dienes have been shown alternatively to be efficient quenchers of excited donor sensitizers. That exciplexes are formed between isomerizable substrates and donor or acceptor sensitizers has been confirmed by emission spectroscopy. The rearrangement of hexamethyldewarbenzene, a model exciplex isomerization has been examined in some detail.« less

A Comparative Study on the Photophysics and Photochemistry of Xanthene Dyes in the Presence of Polyamidoamine (PAMAM) Dendrimers.

PubMed

Arbeloa, Ernesto Maximiliano; Previtali, Carlos Mario; Bertolotti, Sonia Graciela

2018-04-17

The photophysical and photochemical properties of the xanthene dyes Eosin Y, Erythrosin B, and Rose Bengal are evaluated in the presence of amino-terminated polyamidoamine (PAMAM) dendrimers of relatively high generation (G3-G5) in alkaline aqueous solution. UV/Vis absorption and fluorescence spectra of the dyes show bathochromic shifts, which correlate with the size of the dendrimer. Binding constants (K bind ) are calculated from absorption data. The resulting high K bind values indicate strong interactions between both molecules. Triplet-triplet absorption spectra of the dyes are recorded by laser flash photolysis, and a decrease in the triplet lifetimes is observed in the presence of dendrimers. At the same time, an increase in the absorption of the semireduced form of the dyes is observed. Rate constants for triplet quenching ( 3 k q ) and radical quantum yields (Φ R ) are obtained. The results are explained by a very efficient electron-transfer process from PAMAM to xanthene dyes for all of the dye/dendrimer couples that are evaluated. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Optical and Photophysical Investigation of (2E)-1-(2,5-Dimethylfuran-3-Yl)-3-(9-Ethyl-9H-Carbazol-3-Yl)Prop-2-en-1-One (DEPO) by Spectrofluorometer in Organized Medium.

PubMed

Asiri, Abdullah M; Al-Dies, Al-Anood M; Khan, Salman A

2017-07-01

(2E)-1-(2,5-dimethylfuran-3-yl)-3-(9-ethyl-9H-carbazol-3-yl)prop-2-en-1-one (DEPO) was prepared by the reaction of 9-ethyl-9H-carbazole-3-carbaldehyde with 1-(2,5-dimethylfuran-3-yl)ethanone under microwave irradiation. The structure of DEPO was established experimentally by EI-MS, FT-IR, 1 H and 13 C NMR spectral studies. Electronic absorption and emission spectra of DEPO were studied in different solvents on the basis of polarities, and the obtain data were used to determine the solvatochromic properties such as extinction coefficient, oscillator strength, transition dipole moment, stokes shift, fluorescence quantum yield and photochemical quantum yield. Photochemical quantum yield (Φ c ) of DEPO dye was determined in different solvent. The dye comparatively photostable in DMSO but undergoes photodecomposition in chloro methane solvents. The DEPO dye may be use as probe or quencher to determine critical micelle concentration (CMC) of cetyltri methyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS).

An explanation of the very low fluorescence and phosphorescence in pyridine: a CASSCF/CASMP2 study

NASA Astrophysics Data System (ADS)

Varras, Panayiotis C.; Gritzapis, Panagiotis S.; Fylaktakidou, Konstantina C.

2018-01-01

In this work, we applied the multiconfigurational complete active space self-consistent field method and the multiconfigurational second-order perturbation theory CASMP2 to study the fundamental excited states of pyridine and its possible photophysical and photochemical transformations. Our calculations, which are in agreement with the experimental results corresponding to excitations around the 0-0 transition, showed that the very low experimentally observed fluorescence of pyridine is due to the presence of two almost isoenergetic crossings, one of triple character, S1/T1/S0 and the other of S1/S0 character. Both crossings are below the minimum of S1(nπ*) and have a common transition state (S1(TS)) with a very low energy barrier (1.85 kcal/mol or 0.08 eV at the CASMP2 level of theory) separating them. A third triple crossing of the type S1/T1/S0 lying lower with respect to the other two elucidates the observed T1→S0 radiationless transition. This explains not only pyridine's very low fluorescence and phosphorescence but also its almost negligible photochemistry, showing that photophysics is the prevalent process in this molecule.

Photochemical and Photophysical Properties of Phthalocyanines Modified with Optically Active Alcohols.

PubMed

Ramos, Aline A; Nascimento, Francisco B; de Souza, Thaiza F M; Omori, Alvaro T; Manieri, Tânia M; Cerchiaro, Giselle; Ribeiro, Anderson O

2015-07-24

Three phthalocyanine derivatives were synthesized and characterized: one modified with a racemic mixture of 1-(4-bromophenyl)ethanol and two other macrocycles modified with each one of the enantioenriched isomers (R)-1-(4-bromophenyl)ethanol and (S)-1-(4-bromophenyl)ethanol. The compounds were characterized by 1H-NMR spectroscopy, mass spectrometry, UV-Vis absorption, and excitation and emission spectra. Additionally, partition coefficient values and the quantum yield of the generation of oxygen reactive species were determined. Interestingly, the phthalocyanine containing a (R)-1-(4-bromophenyl)ethoxy moiety showed higher quantum yield of reactive oxygen species generation than other compounds under the same conditions. In addition, the obtained fluorescence microscopy and cell viability results have shown that these phthalocyanines have different interactions with mammary MCF-7 cells. Therefore, our results indicate that the photochemical and biological properties of phthalocyanines with chiral ligands should be evaluated separately for each enantiomeric species.

Exciplex ensemble modulated by excitation mode in intramolecular charge-transfer dyad: effects of temperature, solvent polarity, and wavelength on photochemistry and photophysics of tethered naphthalene-dicyanoethene system.

PubMed

Aoki, Yoshiaki; Matsuki, Nobuo; Mori, Tadashi; Ikeda, Hiroshi; Inoue, Yoshihisa

2014-09-19

Solvent, temperature, and excitation wavelength significantly affected the photochemical outcomes of a naphthalene-dicyanoethene system tethered by different number (n) of methylene groups (1-3). The effect of irradiation wavelength was almost negligible for 2a but pronounced for 3a. The temperature dependence and theoretical calculations indicated the diversity of exciplex conformations, an ensemble of which can be effectively altered by changing excitation wavelength to eventually switch the regioselectivity of photoreactions.

Photocatalytic Conversion of CO2 to CO using Rhenium Bipyridine Platforms Containing Ancillary Phenyl or BODIPY Moieties

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

Andrade, Gabriel; Pistner, Allen; Yapp, Glenn P. A.

2013-01-01

Harnessing of solar energy to drive the reduction of carbon dioxide to fuels requires the development of efficient catalysts that absorb sunlight. In this work, we detail the synthesis, electrochemistry and photophysical properties of a set of homologous fac-ReI(CO)3 complexes containing either an ancillary phenyl (8) or BODIPY (12) substituent. These studies demonstrate that both the electronic properties of the rhenium center and BODIPY chromophore are maintained for these systems. Photolysis studies demonstrate that both assemblies 8 and 12 are competent catalysts for the photochemical reduction of CO2 to CO in DMF using triethanolamine (TEOA) as a sacrificial reductant. Bothmore » these systems display TOFs for photocatalytic CO production upon irradiation with light ( ex 400 nm) of ~5 hr 1 with TON values of approximately 20. Although structural and photophysical measurements demonstrate that electronic coupling between the BODIPY and fac-ReI(CO)3 units is limited for complex 12, this work clearly shows that the photoactive BODIPY moiety is tolerated during catalysis and does not interfere with the observed photochemistry. When taken together, these results provide a clear roadmap for the development of advanced rhenium bipyridine complexes bearing ancillary BODIPY groups for the efficient photocatalytic reduction of CO2 using visible light.« less

Photophysics and photochemistry of dyes bound to human serum albumin are determined by the dye localization.

PubMed

Alarcón, Emilio; Edwards, Ana Maria; Aspee, Alexis; Moran, Faustino E; Borsarelli, Claudio D; Lissi, Eduardo A; Gonzalez-Nilo, Danilo; Poblete, Horacio; Scaiano, J C

2010-01-01

The photophysics and photochemistry of rose bengal (RB) and methylene blue (MB) bound to human serum albumin (HSA) have been investigated under a variety of experimental conditions. Distribution of the dyes between the external solvent and the protein has been estimated by physical separation and fluorescence measurements. The main localization of protein-bound dye molecules was estimated by the intrinsic fluorescence quenching, displacement of fluorescent probes bound to specific protein sites, and by docking modelling. All the data indicate that, at low occupation numbers, RB binds strongly to the HSA site I, while MB localizes predominantly in the protein binding site II. This different localization explains the observed differences in the dyes' photochemical behaviour. In particular, the environment provided by site I is less polar and considerably less accessible to oxygen. The localization of RB in site I also leads to an efficient quenching of the intrinsic protein fluorescence (ascribed to the nearby Trp residue) and the generation of intra-protein singlet oxygen, whose behaviour is different to that observed in the external solvent or when it is generated by bound MB.

Impact of charge carrier injection on single-chain photophysics of conjugated polymers

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

Hofmann, Felix J.; Vogelsang, Jan, E-mail: jan.vogelsang@physik.uni-regensburg.de; Lupton, John M.

Charges in conjugated polymer materials have a strong impact on the photophysics and their interaction with the primary excited state species has to be taken into account in understanding device properties. Here, we employ single-molecule spectroscopy to unravel the influence of charges on several photoluminescence (PL) observables. The charges are injected either stochastically by a photochemical process or deterministically in a hole-injection sandwich device configuration. We find that upon charge injection, besides a blue-shift of the PL emission and a shortening of the PL lifetime due to quenching and blocking of the lowest-energy chromophores, the non-classical photon arrival time distributionmore » of the multichromophoric chain is modified towards a more classical distribution. Surprisingly, the fidelity of photon antibunching deteriorates upon charging, whereas one would actually expect the opposite: the number of chromophores to be reduced. A qualitative model is presented to explain the observed PL changes. The results are of interest to developing a microscopic understanding of the intrinsic charge-exciton quenching interaction in devices.« less

Calculation of singlet oxygen formation from one photon absorbing photosensitizers used in PDT

NASA Astrophysics Data System (ADS)

Potasek, M.; Parilov, Evgueni; Beeson, K.

2013-03-01

Advances in biophotonic medicine require new information on photodynamic mechanisms. In photodynamic therapy (PDT), a photosensitizer (PS) is injected into the body and accumulates at higher concentrations in diseased tissue compared to normal tissue. The PS absorbs light from a light source and generates excited-state triplet states of the PS. The excited triplet states of the PS can then react with ground state molecular oxygen to form excited singlet - state oxygen or form other highly reactive species. The reactive species react with living cells, resulting in cel l death. This treatment is used in many forms of cancer including those in the prostrate, head and neck, lungs, bladder, esophagus and certain skin cancers. We developed a novel numerical method to model the photophysical and photochemical processes in the PS and the subsequent energy transfer to O2, improving the understanding of these processes at a molecular level. Our numerical method simulates light propagation and photo-physics in PS using methods that build on techniques previously developed for optical communications and nonlinear optics applications.

Axially substituted silicon(IV) phthalocyanine and its quaternized derivative as photosensitizers towards tumor cells and bacterial pathogens.

PubMed

Ömeroğlu, İpek; Kaya, Esra Nur; Göksel, Meltem; Kussovski, Vesselin; Mantareva, Vanya; Durmuş, Mahmut

2017-10-15

Axially di-(alpha,alpha-diphenyl-4-pyridylmethoxy) silicon(IV) phthalocyanine (3) and its quaternized derivative (3Q) were synthesized and tested as photosensitizers against tumor and bacterial cells. These new phthalocyanines were characterized by elemental analysis, and different spectroscopic methods such as FT-IR, UV-Vis, MALDI-TOF and 1 H NMR. The photophysical properties such as absorption and fluorescence, and the photochemical properties such as singlet oxygen generation of both phthalocyanines were investigated in solutions. The obtained values were compared to the values obtained with unsubstituted silicon(IV) phthalocyanine dichloride (SiPcCl 2 ). The addition of two di-(alpha,alpha-diphenyl-4-pyridylmethanol) groups as axial ligands showed an improvement of the photophysical and photochemical properties and an increasement of the singlet oxygen quantum yield (Φ Δ ) from 0.15 to 0.33 was determined. The photodynamic efficacy of synthesized photosensitizers (3 and 3Q) were evaluated with promising photocytotoxicity (17% cell survival for 3 and 28% for 3Q) against the cervical cancer cell line (HeLa). The photodynamic inactivation of pathogenic bacterial strains Streptococcus mutans, Staphylococcus aureus, and Pseudomonas aeruginosa suggested a high susceptibility with quaternized derivative (3Q). The both Gram-positive bacterial strains were fully photoinactivated with 11μM 3Q and mild light dose 50J.cm -2 . In case of P. aeruginosa the effect was negligible for concentrations up to 22μM 3Q and light dose 100J.cm -2 . The results suggested that the novel axially substituted silicon(IV) phthalocyanines have promising characteristic as photosensitizer towards tumor cells. The quaternized derivative 3Q has high potential for photoinactivation of pathogenic bacterial species. Copyright © 2017 Elsevier Ltd. All rights reserved.

Semiconductor Quantum Dots with Photoresponsive Ligands.

PubMed

Sansalone, Lorenzo; Tang, Sicheng; Zhang, Yang; Thapaliya, Ek Raj; Raymo, Françisco M; Garcia-Amorós, Jaume

2016-10-01

Photochromic or photocaged ligands can be anchored to the outer shell of semiconductor quantum dots in order to control the photophysical properties of these inorganic nanocrystals with optical stimulations. One of the two interconvertible states of the photoresponsive ligands can be designed to accept either an electron or energy from the excited quantum dots and quench their luminescence. Under these conditions, the reversible transformations of photochromic ligands or the irreversible cleavage of photocaged counterparts translates into the possibility to switch luminescence with external control. As an alternative to regulating the photophysics of a quantum dot via the photochemistry of its ligands, the photochemistry of the latter can be controlled by relying on the photophysics of the former. The transfer of excitation energy from a quantum dot to a photocaged ligand populates the excited state of the species adsorbed on the nanocrystal to induce a photochemical reaction. This mechanism, in conjunction with the large two-photon absorption cross section of quantum dots, can be exploited to release nitric oxide or to generate singlet oxygen under near-infrared irradiation. Thus, the combination of semiconductor quantum dots and photoresponsive ligands offers the opportunity to assemble nanostructured constructs with specific functions on the basis of electron or energy transfer processes. The photoswitchable luminescence and ability to photoinduce the release of reactive chemicals, associated with the resulting systems, can be particularly valuable in biomedical research and can, ultimately, lead to the realization of imaging probes for diagnostic applications as well as to therapeutic agents for the treatment of cancer.

Photooxidation of Diimine Dithiolate Platinium(II) Complexes Induced by Charge Transfer to Diimine Excitation.

PubMed

Zhang, Yin; Ley, Kevin D.; Schanze, Kirk S.

1996-11-20

A photochemical and photophysical investigation was carried out on (tbubpy)Pt(II)(dpdt) and (tbubpy)Pt(II)(edt) (1 and 2, respectively, where tbubpy = 4,4'-di-tert-butyl-2,2'-bipyridine, dpdt = meso-1,2-diphenyl-1,2-ethanedithiolate and edt = 1,2-ethanedithiolate). Luminescence and transient absorption studies reveal that these complexes feature a lowest excited state with Pt(S)(2) --> tbubpy charge transfer to diimine character. Both complexes are photostable in deoxygenated solution; however, photolysis into the visible charge transfer band in air-saturated solution induces moderately efficient photooxidation. Photooxidation of 1 produces the dehydrogenation product (tbubpy)Pt(II)(1,2-diphenyl-1,2-ethenedithiolate) (4). By contrast, photooxidation of 2 produces S-oxygenated complexes in which one or both thiolate ligands are converted to sulfinate (-SO(2)R) ligands. Mechanistic photochemical studies and transient absorption spectroscopy reveal that photooxidation occurs by (1) energy transfer from the charge transfer to diimine excited state of 1 to (3)O(2) to produce (1)O(2) and (2) reaction between (1)O(2) and the ground state 1. Kinetic data indicates that excited state 1 produces (1)O(2) efficiently and that reaction between ground state 1 and (1)O(2) occurs with k approximately 3 x 10(8) M(-)(1) s(-)(1).

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.

Synthesis of asymmetric zinc(II) phthalocyanines with two different functional groups & spectroscopic properties and photodynamic activity for photodynamic therapy.

PubMed

Göksel, Meltem

2016-09-15

Zinc(II) phthalocyanine containing [2-(tert-butoxycarbonyl)amino]ethoxy and iodine groups (A and B), as well as their deprotected mono-amino and tri-iodine zinc(II) phthalocyanine (2) were obtained. This structure surrounds by substituents with functional groups. From this perspective it can be used a starting material for many reactions and applications, such as sonogashira coupling, carbodiimide coupling. An example of a first diversification reaction of this compound was obtained with conjugation of a biotin. Asymmetrically biotin conjugated and heavy atom bearing zinc(II) phthalocyanine (3) were synthesized characterized for the first time and photophysical, photochemical and photobiological properties of these phthalocyanines were compared in this study. Copyright © 2016 Elsevier Ltd. All rights reserved.

Photophysical and photochemical effects of UV and VUV photo-oxidation and photolysis on PET and PEN

NASA Astrophysics Data System (ADS)

Morgan, Andrew

Polyethylene Terephthalate (PET) is a widely used polymer in the bottling, packaging, and clothing industry. In recent years an increasing global demand for PET has taken place due to the Solar Disinfection (SODIS) process. SODIS is a method of sterilizing fresh water into drinkable water. The PET bottles are used in the process to contain the water during solar irradiation due to its highly transparent optical property. Alongside PET, polyethylene 2,6-napthalate (PEN) is used in bottling and flexible electronic applications. The surface of PEN would need to be modified to control the hydrophilicity and the interaction it exudes as a substrate. The UV light absorption properties of PET and PEN are of great importance for many applications, and thus needs to be studied along with its photochemical resistance. The optical and chemical nature of PET was studied as it was treated by UV photo-oxidation, photo-ozonation, and photolysis under atmospheric pressure. Another investigation was also used to study PEN and PET as they are treated by vacuum UV (VUV) photo-oxidation, VUV photolysis, and remote oxygen reactions. The extent of the photoreactions' effect into the depth of the polymers is examined as treatment conditions are changed. The different experimental methods established the rate of several competing photoreactions on PET and PEN during irradiance, and their effect on the optical quality of the polymers.

Fluorescence correlation spectroscopy: novel variations of an established technique.

PubMed

Haustein, Elke; Schwille, Petra

2007-01-01

Fluorescence correlation spectroscopy (FCS) is one of the major biophysical techniques used for unraveling molecular interactions in vitro and in vivo. It allows minimally invasive study of dynamic processes in biological specimens with extremely high temporal and spatial resolution. By recording and correlating the fluorescence fluctuations of single labeled molecules through the exciting laser beam, FCS gives information on molecular mobility and photophysical and photochemical reactions. By using dual-color fluorescence cross-correlation, highly specific binding studies can be performed. These have been extended to four reaction partners accessible by multicolor applications. Alternative detection schemes shift accessible time frames to slower processes (e.g., scanning FCS) or higher concentrations (e.g., TIR-FCS). Despite its long tradition, FCS is by no means dated. Rather, it has proven to be a highly versatile technique that can easily be adapted to solve specific biological questions, and it continues to find exciting applications in biology and medicine.

The water soluble axially disubstituted silicon phthalocyanines: photophysicochemical properties and in vitro studies.

PubMed

Göksel, Meltem; Biyiklioglu, Zekeriya; Durmuş, Mahmut

2017-08-01

Two novel silicon(IV) phthalocyanines bearing 1,3-bis[3(dimethylamino)phenoxy]propan-2-ol or 1,3-bis[3(diethylamino)phenoxy]propan-2-ol groups at their axial positions were synthesized. These phthalocyanines were converted into their water soluble derivatives by the quaternization reaction with methyl iodide. The quaternized phthalocyanines show excellent solubility aqueous solutions without any aggregation which makes them potential photosensitizers for use in photodynamic therapy (PDT). For this reason, the photophysical and photochemical properties such as fluorescence quantum yields, lifetimes, singlet oxygen generation and photodegradation of both non-ionic (3 and 5) and quaternized cationic silicon(IV) phthalocyanines were investigated. Furthermore, the cytotoxicity of PDT was determined by colorimetric proliferation assay against to hepatocellular carcinoma (HuH-7) cancer cells. In this study, the cells were incubated with a novel water soluble silicon(IV) phthalocyanine derivatives and thereafter the cells were illuminated using broad-band incoherent light source.

Spatial photosensitizer fluorescence emission predictive analysis for photodynamic therapy monitoring applied to a skin disease

NASA Astrophysics Data System (ADS)

Salas-García, Irene; Fanjul-Vélez, Félix; Arce-Diego, José Luis

2012-03-01

The development of Photodynamic Therapy (PDT) predictive models has become a valuable tool for an optimal treatment planning, monitoring and dosimetry adjustment. A few attempts have achieved a quite complete characterization of the complex photochemical and photophysical processes involved, even taking into account superficial fluorescence in the target tissue. The present work is devoted to the application of a predictive PDT model to obtain fluorescence tomography information during PDT when applied to a skin disease. The model takes into account the optical radiation distribution, a non-homogeneous topical photosensitizer distribution, the time dependent photochemical interaction and the photosensitizer fluorescence emission. The results show the spatial evolution of the photosensitizer fluorescence emission and the amount of singlet oxygen produced during PDT. The depth dependent photosensitizer fluorescence emission obtained is essential to estimate the spatial photosensitizer concentration and its degradation due to photobleaching. As a consequence the proposed approach could be used to predict the photosensitizer fluorescence tomographic measurements during PDT. The singlet oxygen prediction could also be employed as a valuable tool to predict the short term treatment outcome.

Synthesis and Photophysical Characterization of an Artificial Photosynthetic Reaction Center Exhibiting Acid-Responsive Regulation of Charge Separation

NASA Astrophysics Data System (ADS)

Pahk, Ian

Non-photochemical quenching (NPQ) is a photoprotective regulatory mechanism essential to the robustness of the photosynthetic apparatus of green plants. Energy flow within the low-light adapted reaction centers is dynamically optimized to match the continuously fluctuating light conditions found in nature. Activated by compartmentalized decreases in pH resulting from photosynthetic activity during periods of elevated photon flux, NPQ induces rapid thermal dissipation of excess excitation energy that would otherwise overwhelm the apparatus's ability to consume it. Consequently, the frequency of charge separation decreases and the formation of potentially deleterious, high-energy intermediates slows, thereby reducing the threat of photodamage by disallowing their accumulation. Herein is described the synthesis and photophysical analysis of a molecular triad that mimics the effects of NPQ on charge separation within the photosynthetic reaction centers. Steady-state absorption and emission, time-resolved fluorescence, and transient absorption spectroscopies were used to demonstrate reversible quenching of the first singlet excited state affecting the quantum yield of charge separation by approximately one order of magnitude. As in the natural system, the populations of unquenched and quenched states and, therefore, the overall yields of charge separation were found to be dependent upon acid concentration.

Photophysical and photochemical properties of Bauhinia megalandra (Caesalpinaceae) extracts as new PDT photosensitizer

NASA Astrophysics Data System (ADS)

Vargas Tovar, Franklin R.; Rivas, C.; Estrada, O.; Marcano O., Aristides A.; Echevarria, Lorenzo; Diaz, Yrene; Alexander, I.; Rodriguez, L.; Padron, L.; Rivera, I. R.

2004-10-01

Recently new photosensitizers, chlorophyll "a and b" derivatives, for photodynamic therapy (PDT) have been presented. It already passed complete pre-clinical investigations. This prompted us to carry out an extensive study of photophysical properties of chlorine derivatives, important both for optimization of their clinic applications and for study of mechanisms of chlorine PDT&. The fresh leaves of Bauhinia megalandra (Caesalpinaceae) were extracted with methanol by percolation, and re-extract with a mixture of methanol-water (1:1), the insoluble fraction was then separated by column chromatography [RP18/hexane-ethylacetate (9:1)] to obtain four fractions named 1 to 4. These compounds were identified by NMR data. We found that 3 and 4 efficiently generates singlet oxygen when irradiated with visible light. Detection of the singlet oxygen was fulfilled by its reaction with histidine and detected by bleaching p-nitrosodimethylaniline under 440 nm irradiation. The quantum yields of singlet oxygen determined by us were 0.088 (1), 0.151 (2), 0.219 (3) and 0.301 (4). We measured absorption and fluorescence spectra of compounds 1 to 4 (Mg-chlorophyll-a, Pheophytin, Mg-chlorophyll-b and chlorophyll-b respectively) in different media and in aqueous solutions of human serum albumin. The association constant of the compounds 1, 2, 3 and 4 in the presence of HSA were estimated. The binding and quenching studies suggest that only 1 and 3 may serve as a useful fluorescence probe for structure/function studies of different chlorophyll binding proteins. No photoinduced binding was observed after irradiation by all the studied compounds in presence of human serum albumin.

Synthesis and biological evaluation of 173-dicarboxylethyl-pyropheophorbide-a amide derivatives for photodynamic therapy.

PubMed

Zhu, Wei; Wang, Lai-Xing; Chen, Dan-Ye; Gao, Ying-Hua; Yan, Yi-Jia; Wu, Xiao-Feng; Wang, Mi; Han, Yi-Ping; Chen, Zhi-Long

2017-12-19

Three novel 17 3 -dicarboxylethyl-pyropheophorbide-a amide derivatives as photosensitizers for photodynamic therapy (PDT) were synthesized from pyropheophorbide-a (Ppa). Their photophysical and photochemical properties, intracellular localization, photocytotoxicity in vitro and in vivo were investigated. All target compounds exhibited low cytotoxicity in the dark and remarkable photocytotoxicity against human esophageal cancer cells. Among them, 1a showed highest singlet oxygen quantum yield. Upon light activation, 1a exhibited significant photocytotoxicity. After PDT treatment, the growth of Eca-109 tumor in nude mice was significantly inhibited. Therefore, 1a is a powerful and promising antitumor photosensitizer for PDT. Copyright © 2017 Elsevier Ltd. All rights reserved.

Preparation, characterization, and cellular studies of photosensitizer-loaded lipid nanoparticles for photodynamic therapy

NASA Astrophysics Data System (ADS)

Navarro, Fabrice P.; Bechet, Denise; Delmas, Thomas; Couleaud, Pierre; Frochot, Céline; Verhille, Marc; Kamarulzaman, Ezatul; Vanderesse, Régis; Boisseau, Patrick; Texier, Isabelle; Gravier, Julien; Vinet, Françoise; Barberi-Heyob, Muriel; Couffin, Anne Claude

2011-02-01

PhotoDynamic Therapy (PDT) has been established as a potent and less invasive treatment for different kinds of cancer. Among various attempts to enhance the therapeutics efficacy of PDT, the specific delivery of the PhotoSensitizer (PS) in the tumor is expected to increase its clinical applications, since unwanted accumulation, especially in the skin, impairs the patients' quality of life (prolonged cutaneous photosensitivity). The aim of this study was to engineer Lipid Nanoparticles (LNP) with different sizes and various PS contents, using simple, solvent-free and easily scale up manufacturing processes. Meso-tetra (hydroxyphenyl) chlorin (mTHPC) is one of the most potent photoactive compounds for clinical use and it has been successfully applied in the treatment of various indications, such as the head and neck, prostate and pancreatic cancers. Here, a derivative of mTHPC was efficiently incorporated into the lipid core of LNP, leading to a large range of stable and reproducible mTHPC-loaded LNP with narrow size distribution. The photophysical and photochemical properties of mTHPC-loaded LNP were studied by measuring absorbance and fluorescence spectra, colloidal stability, particle size and zeta potential, as well as singlet oxygen luminescence. The photocytotoxicity of three selected mTHPC-loaded LNP (25 nm, 45 nm and 95 nm of diameter, respectively) was evaluated on MCF-7 cells, in comparison to free mTHPC, under irradiation at 652 nm with a range of light fluence from 1 to 5 J/cm2. All the physico-chemical, photophysical and biological measurements allow us to conclude that LNP is a promising nano-drug delivery system for PDT.

Photochemical studies of a fluorescent chlorophyll catabolite--source of bright blue fluorescence in plant tissue and efficient sensitizer of singlet oxygen.

PubMed

Jockusch, Steffen; Turro, Nicholas J; Banala, Srinivas; Kräutler, Bernhard

2014-02-01

Fluorescent chlorophyll catabolites (FCCs) are fleeting intermediates of chlorophyll breakdown, which is seen as an enzyme controlled detoxification process of the chlorophylls in plants. However, some plants accumulate large amounts of persistent FCCs, such as in senescent leaves and in peels of yellow bananas. The photophysical properties of such a persistent FCC (Me-sFCC) were investigated in detail. FCCs absorb in the near UV spectral region and show blue fluorescence (max at 437 nm). The Me-sFCC fluorescence had a quantum yield of 0.21 (lifetime 1.6 ns). Photoexcited Me-sFCC intersystem crosses into the triplet state (quantum yield 0.6) and generates efficiently singlet oxygen (quantum yield 0.59). The efficient generation of singlet oxygen makes fluorescent chlorophyll catabolites phototoxic, but might also be useful as a (stress) signal and for defense of the plant tissue against infection by pathogens.

Micro sculpting technology using DPSSL

NASA Astrophysics Data System (ADS)

Chang, Won-Seok; Shin, Bosung; Kim, Jae-gu; Whang, Kyung-Hyun

2003-11-01

Multiple pulse laser ablation of polymer is performed with DPSS (Diode Pumped Solid State) 3rd harmonic Nd:YVO4 laser (355 nm) in order to fabricate three-dimensional micro components. Here we considered mechanistic aspects of the interaction between UV laser and polymer to obtain optimum process conditions for maskless photomachining using DPSSL. The photo-physical and photochemical parameters such as laser wavelength and optical characteristics of polymers are investigated by experiments to reduce plume effect, which induce the re-deposited debris on the surface of substrate. In this study, LDST (laser direct sculpting technique) are developed to gain various three-dimensional shape with size less than 500 micrometer. Main process sequences are from rapid prototyping technology such as CAD/CAM modeling of products, machining path generation, layer-by-layer machining, and so on. This method can be applied to manufacture the prototype of micro device and the polymer mould for mass production without expensive mask fabrication.

Molecular Engineering of UV/Vis Light-Emitting Diode (LED)-Sensitive Donor-π-Acceptor-Type Sulfonium Salt Photoacid Generators: Design, Synthesis, and Study of Photochemical and Photophysical Properties.

PubMed

Wu, Xingyu; Jin, Ming; Xie, Jianchao; Malval, Jean-Pierre; Wan, Decheng

2017-11-07

A series of donor-π-acceptor-type sulfonium salt photoacid generators (PAGs) were designed and synthesized by systematically changing electron-donating groups, π-conjugated systems, electron-withdrawing groups, and the number of branches through molecular engineering. These PAGs can effectively decompose under UV/Vis irradiation from a light-emitting diode (LED) light source because of the matching absorption and emitting spectra of the LEDs. The absorption and acid-generation properties of these sulfonium salts were elucidated by UV/Vis spectroscopy and so forth. Results indicated that the PAG performance benefited from the introduction of strong electron-donating groups, specific π-conjugated structures, certain electron-withdrawing groups, or two-branched structures. Most sulfonium salts showed potential as photoinitiators under irradiation by a wide variety of UV and visible LEDs. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Photoisomerization of ruthenium(ii) aquo complexes: mechanistic insights and application development.

PubMed

Hirahara, Masanari; Yagi, Masayuki

2017-03-21

Ruthenium(ii) complexes with polypyridyl ligands have been extensively studied as promising functional molecules due to their unique photochemical and photophysical properties as well as redox properties. In this context, we report the photoisomerization of distal-[Ru(tpy)(pynp)OH 2 ] 2+ (d-1) (tpy = 2,2';6',2''-terpyridine, pynp = 2-(2-pyridyl)-1,8-naphthyridine) to proximal-[Ru(tpy)(pynp)OH 2 ] 2+ (p-1), which has not been previously characterized for polypyridyl ruthenium(ii) aquo complexes. Herein, we review recent progress made by our group on the mechanistic insights and application developments related to the photoisomerization of polypyridyl ruthenium(ii) aquo complexes. We report a new strategic synthesis of dinuclear ruthenium(ii) complexes that can act as an active water oxidation catalyst, as well as the development of unique visible-light-responsive giant vesicles, both of which were achieved based on photoisomerization.

Triplet state dissolved organic matter in aquatic photochemistry: reaction mechanisms, substrate scope, and photophysical properties.

PubMed

McNeill, Kristopher; Canonica, Silvio

2016-11-09

Excited triplet states of chromophoric dissolved organic matter ( 3 CDOM*) play a major role among the reactive intermediates produced upon absorption of sunlight by surface waters. After more than two decades of research on the aquatic photochemistry of 3 CDOM*, the need for improving the knowledge about the photophysical and photochemical properties of these elusive reactive species remains considerable. This critical review examines the efforts to date to characterize 3 CDOM*. Information on 3 CDOM* relies mainly on the use of probe compounds because of the difficulties associated with directly observing 3 CDOM* using transient spectroscopic methods. Singlet molecular oxygen ( 1 O 2 ), which is a product of the reaction between 3 CDOM* and dissolved oxygen, is probably the simplest indicator that can be used to estimate steady-state concentrations of 3 CDOM*. There are two major modes of reaction of 3 CDOM* with substrates, namely triplet energy transfer or oxidation (via electron transfer, proton-coupled electron transfer or related mechanisms). Organic molecules, including several environmental contaminants, that are susceptible to degradation by these two different reaction modes are reviewed. It is proposed that through the use of appropriate sets of probe compounds and model photosensitizers an improved estimation of the distribution of triplet energies and one-electron reduction potentials of 3 CDOM* can be achieved.

Photophysical and Photochemical Properties of 3-methylpterin as a New and More Stable Pterin-type Photosensitizer.

PubMed

Estébanez, Sandra; Lorente, Carolina; Kaufman, Teodoro S; Larghi, Enrique L; Thomas, Andrés H; Serrano, Mariana P

2018-05-04

Pterin derivatives are heterocyclic compounds which are present in different biological systems. Neutral aqueous solutions of pterins presents acid-base and keto-enol equilibria. These compounds under UV-A radiation fluoresce, undergo photooxidation, generate reactive oxygen species, and photoinduce the oxidation of biological substrates. As photosensitizers, they may act through different mechanisms; mainly through an electron-transfer initiated process (type I mechanism), but they also produce singlet molecular oxygen ( 1 O 2 ) upon irradiation (type II mechanism). In general, upon UV-A excitation two triplet states, corresponding to the lactim and lactam tautomers, are formed, but only the last one is the responsible for the photosensitized reactions of biomolecules. We present a study of the photochemical properties of 3-methylpterin (3-Mep) which, in contrast to most pterin derivatives, exists only in the lactam form. Also an improvement in the synthesis of 3-Mep is reported. The spectroscopic properties 3-Mep in aqueous solution were similar to those of the unsubstituted pterin derivative (Ptr) in its acid form, such as absorption, fluorescent and phosphorescent emission spectra. Experiments using 2'-deoxyguanosine 5'-monophosphate (dGMP) as oxidizable target, demonstrated that methylation at C-3 position of the pterin moiety does not affect significantly the efficiency of photosensitization, but results in a more photostable sensitizer. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.

Novel axially carborane-cage substituted silicon phthalocyanine photosensitizer; synthesis, characterization and photophysicochemical properties

NASA Astrophysics Data System (ADS)

Atmaca, Göknur Yaşa; Dizman, Cemil; Eren, Tarık; Erdoğmuş, Ali

2015-02-01

The novel axially dicarborane substituted silicon (IV) (SiPc-DC) phthalocyanine was synthesized by treating silicon phthalocyanine dichloride SiPc(Cl)2 (SiPc) with o-Carborane monool. The compound was characterized by mass spectrometry, UV-Vis, FT-IR, 1H and 11B Nuclear Magnetic Resonance Spectroscopy (NMR). Spectral, photophysical (fluorescence quantum yield) and photochemical (singlet oxygen (ΦΔ) and photodegradation quantum yield (Φd)) properties of the complex were reported in different solutions (Dimethyl sulfoxide (DMSO), Dimethylformamide (DMF) and Toluene). The results of spectral measurements showed that both SiPc and carborane cage can have potential to be used as sensitizers in photodynamic therapy (PDT) and boron neutron capture therapy (BNCT) by their singlet oxygen efficiencies (ΦΔ = 0.41, 0.39).

Conjugated Polymers: Catalysts for Photocatalytic Hydrogen Evolution.

PubMed

Zhang, Guigang; Lan, Zhi-An; Wang, Xinchen

2016-12-19

Conjugated polymers, comprising fully π-conjugated systems, present a new generation of heterogeneous photocatalysts for solar-energy utilization. They have three key features, namely robustness, nontoxicity, and visible-light activity, for photocatalytic processes, thus making them appealing candidates for scale-up. Presented in this Minireview, is a brief summary on the recent development of various promising polymer photocatalysts for hydrogen evolution from aqueous solutions, including linear polymers, planarized polymers, triazine/heptazine polymers, and other related organic conjugated semiconductors, with a particular focus on the rational manipulation in the composition, architectures, and optical and electronic properties that are relevant to photophysical and photochemical properties. Some future trends and prospects for organic conjugated photocatalysts in artificial photosynthesis, by water splitting, are also envisaged. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Superresolution microscopy with transient binding.

PubMed

Molle, Julia; Raab, Mario; Holzmeister, Susanne; Schmitt-Monreal, Daniel; Grohmann, Dina; He, Zhike; Tinnefeld, Philip

2016-06-01

For single-molecule localization based superresolution, the concentration of fluorescent labels has to be thinned out. This is commonly achieved by photophysically or photochemically deactivating subsets of molecules. Alternatively, apparent switching of molecules can be achieved by transient binding of fluorescent labels. Here, a diffusing dye yields bright fluorescent spots when binding to the structure of interest. As the binding interaction is weak, the labeling is reversible and the dye ligand construct diffuses back into solution. This approach of achieving superresolution by transient binding (STB) is reviewed in this manuscript. Different realizations of STB are discussed and compared to other localization-based superresolution modalities. We propose the development of labeling strategies that will make STB a highly versatile tool for superresolution microscopy at highest resolution. Copyright © 2015 Elsevier Ltd. All rights reserved.

Coherent Multidimensional Core Spectroscopy of Molecules with Multiple X-ray pulses

NASA Astrophysics Data System (ADS)

Mukamel, Shaul

2017-04-01

Multidimensional spectroscopy uses sequences of optical pulses to study dynamical processes in complex molecules through correlation plots involving several time delay periods. Extensions of these techniques to the x-ray regime will be discussed. Ultrafast nonlinear x-ray spectroscopy is made possible by newly developed free electron laser and high harmonic generation sources. The attosecond duration of X-ray pulses and the atomic selectivity of core X-ray excitations offer a uniquely high spatial and temporal resolution. We demonstrate how stimulated Raman detection of an X-ray probe may be used to monitor the phase and dynamics of the nonequilibrium valence electronic state wavepacket created by e.g. photoexcitation, photoionization and Auger processes. Spectroscopy of multiplecore excitations provides a new window into electron correlations. Applications will be presented to long-range charge transfer in proteins and to excitation energy transfer in porphyrin arrays. Conical intersections (CoIn) dominate the pathways and outcomes of virtually all photophysical and photochemical molecular processes. Despite extensive experimental and theoretical effort CoIns have not been directly observed yet and the experimental evidence is being inferred from fast reaction rates and some vibrational signatures. Novel ultrafast X ray probes for these processes will be presented. Short X-ray pulses can directly detect the passage through a CoIn with the adequate temporal and spectral sensitivity. The technique is based on a coherent Raman process that employs a composite femtosecond/attosecond X-ray pulse to directly detect the electronic coherences (rather than populations) that are generated as the system passes through the CoIn. Streaking of time-resolved photoelectron spectroscopy (TRPES) signals offers another powerful window into the joint electronic/vibrational dynamics at concial intersections. Strong coupling of molecules to the vacuum field of micro cavities can modify the potential energy surfaces thereby manipulating the photophysical and photochemical reaction pathways. The photonic vacuum state of a localized cavity mode can be strongly mixed with the molecular degrees of freedom to create hybrid field-matter states known as polaritons. Simulations of the avoided crossing of sodium iodide in a cavity which incorporate the quantized cavity field into the nuclear wave packet dynamics will be presented. Numerical results show how the branching ratio between the covalent and ionic dissociation channels can be strongly manipulated by the optical cavity.

Synthesis of new porphyrinoids for biomedical and materials applications

NASA Astrophysics Data System (ADS)

Stewart, Fraser

The facile synthesis of three non-hydrolysable thioglycosylated porphyrinoids is reported. Starting from meso perfluorophenylporphyrin (TPPF20), the non-hydrolysable thioglycosylated porphyrin (PGlc4), chlorin (CGlc4), isobacteriochlorin (IGlc4), and bacteriochlorin (BGlc4) can be made in 2-3 steps. The ability to append a wide range of targeting agents onto the perfluorophenyl moieties, the chemical stability, and the ability to fine-tune the photophysical properties of the chromophores make this a suitable platform for development of biochemical tags, diagnostics, or as photodynamic therapeutic agents. With reduction of one or two pyrrole double bonds, there is a red shift in the lowest energy absorption band and a significant increase in intensity. The fluorescence of these porphyrinoids is in the order PGlc4 = BGlc4 < CGlc4 < IGlc4 and there is a corresponding decrease in the amount of triplet formed. Fluorescence micrographs of cells after treatment with these four porphyrinoids indicate they are taken up. The CGlc4 and IGlc4 may be dual function agents that can detect cancer by luminescence, and treat cancer by photodynamic therapy (PDT). Porphyrins appended with four rigid hydrogen bonding motifs on the meso positions were synthesized and self-assembled into a cofacial cage with four complementary bis- (decyl)melamine units in dry solvents, these hydrogen-bonded cages were analysed by diffusion-ordered spectroscopy (DOSY) in solution. The hydrocarbon chains on the melamine mediate the formation of nanofilms on surfaces as the solvent slowly evaporates. A water soluble zinc (II) phthalocyanine symmetrically appended with eight thioglucose units was synthesized from commercially available hexadecafluoro-phthalocyaninato zinc(II) by controlled nucleophilic substitution of the peripheral fluoro groups by thio-sugars. The photophysical properties and cancer cell uptake studies of this nonhydrolyzable thioglycosylated phthalocyanine are reported. The new compound has amphiphilic character, is chemically and photochemically stable, and can potentially be used as a photosensitizer in photodynamic therapy. A porphyrin bearing pyridyl groups at the meso positions was synthesized using 2,6-diacetamido-4-formylpyridine. A new method has been developed for the synthesis of the precursor aldehyde that avoid much of the problems associated with the earlier synthesis. With this porphyrin it is possible to build hetero-complementary rigid, multi-porphyrin supramolecular arrays via hydrogen bonds. For example, when using naphthalenediimide (NDI) units a checkerboard pattern is expected to be formed using this porphyrin as a donor and NDI as an acceptor where triple hydrogen bond is formed between the diimide and pyridyl units. Energy transfer can be studied through this hydrogen bonded supramolecular assembly. The synthesis of a triply bridged diporphyrin appended with six thioglucose units is reported. The electronic spectrum of this triply bridged porphyrin has enhanced intensity at low-energy wavelengths that reaches the near infrared region. The goal of this project is to create tumor targeting dyes that can be activated with red wavelengths of light that penetrate deeper into tissues. This new compound is amphiphilic in nature, chemically and photochemically stable, expected to have unusual photophysical and electrochemical properties, and can potentially be used as a photosensitizer in photodynamic therapy.

On the mechanism of non-radiative decay of blue fluorescent protein chromophore: New insight from the excited-state molecular dynamics simulations and potential energy calculations

NASA Astrophysics Data System (ADS)

Zhao, Li; Liu, Jian-Yong; Zhou, Pan-Wang

2017-11-01

A detailed theoretical investigation based on the ab initio on-the-fly surface hopping dynamics simulations and potential energy surfaces calculations has been performed to unveil the mechanism of the photoinduced non-adiabatic relaxation process of the isolated blue fluorescent protein (BFP) chromophore in gas phase. The data analysis presents that the dominant reaction coordinate of the BFP chromophore is driven by a rotation motion around the CC double bridging bond, which is in remarkable difference with a previous result which supports a Hula-Twist rotation pattern. Such behavior is consistent with the double bond rotation pattern of the GFP neutral chromophore. In addition, the dynamics simulations give an estimated decay time of 1.1 ps for the S1 state, which is agrees well with the experimental values measured in proteins. The present work offers a straightforward understanding for the decay mechanism of the BFP chromophore and suggestions of the photochemical properties of analogous protein chromophores. We hope the current work would be helpful for further exploration of the BFP photochemical and photophysical properties in various environments, and can provide guidance and prediction for rational design of the fluorescent proteins catering for different demands.

Effect of donor-acceptor chromophores on photophysical properties of newly synthesized pyrazolo-pyrrolo-pyrimidines (PPP).

PubMed

Rote, Ramhari V; Shelar, Deepak P; Patil, Sandeep R; Shinde, Santosh S; Toche, Raghunath B; Jachak, Madhukar N

2011-01-01

Novel pyrazolo-pyrrolo-pyrimidine (PPP) derivatives having remarkable photophysical properties are designed with the help of theoretical semiempirical calculations. These compounds then synthesized successfully and studied effect of substituents on its photophysical properties.

Non-adiabatic dynamics of molecules in optical cavities

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

Kowalewski, Markus, E-mail: mkowalew@uci.edu; Bennett, Kochise; Mukamel, Shaul, E-mail: smukamel@uci.edu

2016-02-07

Strong coupling of molecules to the vacuum field of micro cavities can modify the potential energy surfaces thereby opening new photophysical and photochemical reaction pathways. While the influence of laser fields is usually described in terms of classical field, coupling to the vacuum state of a cavity has to be described in terms of dressed photon-matter states (polaritons) which require quantized fields. We present a derivation of the non-adiabatic couplings for single molecules in the strong coupling regime suitable for the calculation of the dressed state dynamics. The formalism allows to use quantities readily accessible from quantum chemistry codes likemore » the adiabatic potential energy surfaces and dipole moments to carry out wave packet simulations in the dressed basis. The implications for photochemistry are demonstrated for a set of model systems representing typical situations found in molecules.« less

Novel fully-BODIPY functionalized cyclotetraphosphazene photosensitizers having high singlet oxygen quantum yields

NASA Astrophysics Data System (ADS)

Şenkuytu, Elif; Eçik, Esra Tanrıverdi

2017-07-01

Novel fully-BODIPY functionalized dendrimeric cyclotetraphosphazenes (FBCP 1 and 2) have been synthesized and characterized by 1H, 13C and 31P NMR spectroscopies. The photophysical and photochemical properties of FBCP 1 and 2 are investigated in dichloromethane solution. The effectiveness of singlet oxygen generation was measured for FBCP 1 and 2 by UV-Vis spectra monitoring of the solution of 1,3-diphenylisobenzofuran (DPBF), which is a well-known trapping molecule used in detection of singlet oxygen. FBCP 1 and 2 show high molar extinction coefficients in the NIR region, good singlet oxygen quantum yields and appropriate photo degradation. The data presented in the work indicate that the dendrimeric cyclotetraphosphazenes are effective singlet oxygen photosensitizers that might be used for various areas of applications such as photodynamic therapy and photocatalysis.

Two-photon or higher-order absorbing optical materials for generation of reactive species

NASA Technical Reports Server (NTRS)

Marder, Seth R. (Inventor); Cumpston, Brian (Inventor); Lipson, Matthew (Inventor); Perry, Joseph W. (Inventor)

2003-01-01

Disclosed are highly efficient multiphoton absorbing compounds and methods of their use. The compounds generally include a bridge of pi-conjugated bonds connecting electron donating groups or electron accepting groups. The bridge may be substituted with a variety of substituents as well. Solubility, lipophilicity, absorption maxima and other characteristics of the compounds may be tailored by changing the electron donating groups or electron accepting groups, the substituents attached to or the length of the pi-conjugated bridge. Numerous photophysical and photochemical methods are enabled by converting these compounds to electronically excited states upon simultaneous absorption of at least two photons of radiation. The compounds have large two-photon or higher-order absorptivities such that upon absorption, one or more Lewis acidic species, Lewis basic species, radical species or ionic species are formed.

Two-photon or higher-order absorbing optical materials for generation of reactive species

NASA Technical Reports Server (NTRS)

Perry, Joseph W (Inventor); Cumpston, Brian (Inventor); Lipson, Matthew (Inventor); Marder, Seth R (Inventor)

2007-01-01

Disclosed are highly efficient multiphoton absorbing compounds and methods of their use. The compounds generally include a bridge of pi-conjugated bonds connecting electron donating groups or electron accepting groups. The bridge may be substituted with a variety of substituents as well. Solubility, lipophilicity, absorption maxima and other characteristics of the compounds may be tailored by changing the electron donating groups or electron accepting groups, the substituents attached to or the length of the pi-conjugated bridge. Numerous photophysical and photochemical methods are enabled by converting these compounds to electronically excited states upon simultaneous absorption of at least two photons of radiation. The compounds have large two-photon or higher-order absorptivities such that upon absorption, one or more Lewis acidic species, Lewis basic species, radical species or ionic species are formed.

Two-Photon or Higher-Order Absorbing Optical Materials for Generation of Reactive Species

NASA Technical Reports Server (NTRS)

Perry, Joseph W. (Inventor); Cumpston, Brian (Inventor); Lipson, Matthew (Inventor); Marder, Seth R. (Inventor)

2013-01-01

Disclosed are highly efficient multiphoton absorbing compounds and methods of their use. The compounds generally include a bridge of pi-conjugated bonds connecting electron donating groups or electron accepting groups. The bridge may be substituted with a variety of substituents as well. Solubility, lipophilicity, absorption maxima and other characteristics of the compounds may be tailored by changing the electron donating groups or electron accepting groups, the substituents attached to or the length of the pi-conjugated bridge. Numerous photophysical and photochemical methods are enabled by converting these compounds to electronically excited states upon simultaneous absorption of at least two photons of radiation. The compounds have large two-photon or higher-order absorptivities such that upon absorption, one or more Lewis acidic species, Lewis basic species, radical species or ionic species are formed.

Experimenting with cameraless photography using turmeric and borax: an introduction to photophysics

NASA Astrophysics Data System (ADS)

Appleyard, S. J.

2012-07-01

An alcoholic extract of the spice turmeric can be used to create a light-sensitive dye that can be used to stain paper. On exposure to sunlight, the dyed paper can be used to capture photographic images of flat objects or reproduce existing images through the preferential degradation of the dye in light-exposed areas over a time period of a few hours. The images can be developed and preserved by spraying the exposed paper with a dilute solution of borax, which forms coloured organo-boron complexes that limit further degradation of the dye and enhance the colour of the image. Similar photochemical reactions that lead to the degradation of the turmeric dye can also be used for reducing the organic pollution load in wastewater produced by many industrial processes and in dye-sensitized solar cells for producing electricity.

Interstellar problems and matrix solutions

NASA Technical Reports Server (NTRS)

Allamandola, Louis J.

1987-01-01

The application of the matrix isolation technique to interstellar problems is described. Following a brief discussion of the interstellar medium (ISM), three areas are reviewed in which matrix experiments are particularly well suited to contribute the information which is sorely needed to further understanding of the ISM. The first involves the measurement of the spectroscopic properties of reactive species. The second is the determination of reaction rates and the elucidation of reaction pathways involving atoms, radicals, and ions which are likely to interact on grain surfaces and in grain mantles. The third entails the determiantion of the spectroscopic, photochemical, and photophysical properties of interstellar and cometary ice analogs. Significant, but limited, progress has been made in these three areas, and a tremendous amount of work is required to fully address the variety of unique chemical and spectroscopic questions posed by the astronomical observations.

Orbital nature of electronic states and elementary acts of their deactivation in a homologous series of phenylmethane molecules

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

Pak, M.A.; Shigorin, D.N.; Konoplev, G.G.

1986-11-01

The aim of this work is to establish the mechanisms of the elementary acts of photophysical and photochemical processes in an homologous series of phenylmethane molecules Ph/sub n/C-H/sub m-n/, where m = 4, n = 1,...,4, and pH is a phenyl radical. The molecules that form the homologous series belong to the same orbital class (in this case sigma..pi..) and the same spectral-luminescence systematization group (SLG). In the studied series of molecules, as a result of the change of the number of the (Ph) and (C-H) systems, an evolution of the orbital nature of the states occurs (in the givenmore » orbital class) on insignificant change of their relative position. As a result of this a considerable redistribution of the relaxation channels of the electron-excitation energy and the rate constants of the radiation and radiationless processes takes place. To establish the character of these changes they performed experimental and theoretical studies of the mentioned series of molecules.« less

A diffuse reflectance comparative study of benzil inclusion within microcrystalline cellulose and beta-cyclodextrin.

PubMed

Vieira Ferreira, Luis F; Ferreira Machado, Isabel; Da Silva, José P; Oliveira, Anabela S

2004-02-01

Diffuse reflectance and laser-induced techniques were used to study photochemical and photophysical processes of benzil adsorbed on two solid powdered supports, microcrystalline cellulose and [small beta]-cyclodextrin. In both substrates, a distribution of ground-state benzil conformers exists, largely dominated by skew conformations where the carbonyl groups are twisted one to the other. Room temperature phosphorescence was observed in air-equilibrated samples in both cases. The decay times vary greatly and the largest lifetime was obtained for benzil/[small beta]-cyclodextrin, showing that this host's cavity accommodates benzil well, enhancing its room temperature phosphorescence. Triplet-triplet absorption of benzil entrapped in cellulose was detected and benzil ketyl radical formation also occurred. With benzil included into [small beta]-cyclodextrin, and following laser excitation, benzoyl radicals were detected on the millisecond timescale. Product analysis and identification of laser-irradiated benzil samples in the two hosts clearly showed that the main degradation photoproducts were benzoic acid and benzaldehyde. The main differences were a larger benzoic acid/benzaldehyde ratio in the case of cellulose and the formation of benzyl alcohol in this support.

An On-the-Fly Surface-Hopping Program JADE for Nonadiabatic Molecular Dynamics of Polyatomic Systems: Implementation and Applications.

PubMed

Du, Likai; Lan, Zhenggang

2015-04-14

Nonadiabatic dynamics simulations have rapidly become an indispensable tool for understanding ultrafast photochemical processes in complex systems. Here, we present our recently developed on-the-fly nonadiabatic dynamics package, JADE, which allows researchers to perform nonadiabatic excited-state dynamics simulations of polyatomic systems at an all-atomic level. The nonadiabatic dynamics is based on Tully's surface-hopping approach. Currently, several electronic structure methods (CIS, TDHF, TDDFT(RPA/TDA), and ADC(2)) are supported, especially TDDFT, aiming at performing nonadiabatic dynamics on medium- to large-sized molecules. The JADE package has been interfaced with several quantum chemistry codes, including Turbomole, Gaussian, and Gamess (US). To consider environmental effects, the Langevin dynamics was introduced as an easy-to-use scheme into the standard surface-hopping dynamics. The JADE package is mainly written in Fortran for greater numerical performance and Python for flexible interface construction, with the intent of providing open-source, easy-to-use, well-modularized, and intuitive software in the field of simulations of photochemical and photophysical processes. To illustrate the possible applications of the JADE package, we present a few applications of excited-state dynamics for various polyatomic systems, such as the methaniminium cation, fullerene (C20), p-dimethylaminobenzonitrile (DMABN) and its primary amino derivative aminobenzonitrile (ABN), and 10-hydroxybenzo[h]quinoline (10-HBQ).

The molecular mechanism of excitation in visual transduction and bacteriorhodopsin

PubMed Central

Lewis, Aaron

1978-01-01

An electronic theory of excitation is proposed and described in terms of a three-dimensional excited/ground-state energy surface which elucidates the photochemical and excited-state dynamics of rhodopsins. In this theory the primary action of light is to produce significant electron redistribution in the retinal, thereby generating new interactions that vibrationally excite and perturb the ground-state protein conformation. Thus, light energy causes charge redistribution in the retinal and induces transient charge-density assisted bond rearrangements (such as proton translocation) in the protein structure which is stabilized by subsequent retinal structural alteration. In this theory the isoprenoid chain of the retinal is considered a structurally pliable molecular entity that can generate charge redistributions and can be subsequently achieve intermediate conformations or various isomeric states to minimize the energy of the new protein structure generated by light. Thus, the 11-cis to all trans isomerization of the retinylidene chromophore is not considered a primary mechanism of excitation. An alternate biological role for this molecular process (which is eventually completed in all photoreceptors but not in bacterial rhodopsins) is to provide the irreversibility needed for effective quantum detection on the time scale of a neural response. Finally, it will be demonstrated that this mechanism, which readily accounts for the photophysical and photochemical data, can also be restated in terms of the Monod, Wyman, and Changeux terminology suggesting that aggregates of these pigments may function allosterically. PMID:273216

A Review of Luminescent Anionic Nano System: d10 Metallocyanide Excimers and Exciplexes in Alkali Halide Hosts

PubMed Central

Li, Xiaobo; Patterson, Howard H.

2013-01-01

Dicyanoaurate, dicyanoargentate, and dicyanocuprate ions in solution and doped in different alkali halide hosts exhibit interesting photophysical and photochemical behavior, such as multiple emission bands, exciplex tuning, optical memory, and thermochromism. This is attributed to the formation of different sizes of nanoclusters in solution and in doped hosts. A series of spectroscopic methods (luminescence, UV-reflectance, IR, and Raman) as well as theoretical calculations have confirmed the existence of excimers and exciplexes. This leads to the tunability of these nano systems over a wide wavelength interval. The population of these nanoclusters varies with temperature and external laser irradiation, which explains the thermochromism and optical memory. DFT calculations indicate an MLCT transition for each nanocluster and the emission energy decreases with increasing cluster size. This is in agreement with the relatively long life-time for the emission peaks and the multiple emission peaks dependence upon cluster concentration. PMID:28811397

From Computational Photobiology to the Design of Vibrationally Coherent Molecular Devices and Motors

NASA Astrophysics Data System (ADS)

Olivucci, Massimo

2014-03-01

In the past multi-configurational quantum chemical computations coupled with molecular mechanics force fields have been employed to investigate spectroscopic, thermal and photochemical properties of visual pigments. Here we show how the same computational technology can nowadays be used to design, characterize and ultimately, prepare light-driven molecular switches which mimics the photophysics of the visual pigment bovine rhodopsin (Rh). When embedded in the protein cavity the chromophore of Rh undergoes an ultrafast and coherent photoisomerization. In order to design a synthetic chromophore displaying similar properties in common solvents, we recently focused on indanylidene-pyrroline (NAIP) systems. We found that these systems display light-induced ground state coherent vibrational motion similar to the one detected in Rh. Semi-classical trajectories provide a mechanistic description of the structural changes associated to the observed coherent motion which is shown to be ultimately due to periodic changes in the π-conjugation.

High contrast two-photon imaging of fingermarks

NASA Astrophysics Data System (ADS)

Stoltzfus, Caleb R.; Rebane, Aleksander

2016-04-01

Optically-acquired fingermarks are widely used as evidence across law enforcement agencies as well as in the courts of law. A common technique for visualizing latent fingermarks on nonporous surfaces consists of cyanoacrylate fuming of the fingerprint material, followed by impregnation with a fluorescent dye, which under ultra violet (UV) illumination makes the fingermarks visible and thus accessible for digital recording. However, there exist critical circumstances, when the image quality is compromised due to high background scattering, high auto-fluorescence of the substrate material, or other detrimental photo-physical and photo-chemical effects such as light-induced damage to the sample. Here we present a novel near-infrared (NIR), two-photon induced fluorescence imaging modality, which significantly enhances the quality of the fingermark images, especially when obtained from highly reflective and/or scattering surfaces, while at the same time reducing photo-damage to sensitive forensic samples.

Photophysical study of meso-phenothiazinyl-porphyrins metallocomplexes

NASA Astrophysics Data System (ADS)

Starukhin, Aleksander; Gorski, Aleksander; Knyukshto, Valery; Panarin, Andrei; Pavich, Tatiana; Gaina, Luiza; Gal, Emese

2017-10-01

Photophysical parameters of a set of metallocomplexes of meso-phenylthiazinylporphyrins with Zn (II), Pd (II) and Cu (II) ions were studied in different organic solvents, solid solutions and polymeric matrices at room and liquid nitrogen temperatures. The dependence of the spectral and photophysical parameters on changing the molecular structure with increasing number of branched substituents attached to aryl groups in different positions of the porphyrin macrocycle has been established.

Experimental and theoretical study of the absorption properties of thiolated diamondoids

NASA Astrophysics Data System (ADS)

Landt, Lasse; Bostedt, Christoph; Wolter, David; Möller, Thomas; Dahl, Jeremy E. P.; Carlson, Robert M. K.; Tkachenko, Boryslav A.; Fokin, Andrey A.; Schreiner, Peter R.; Kulesza, Alexander; Mitrić, Roland; Bonačić-Koutecký, Vlasta

2010-04-01

Nanoscale hybrid systems are a new class of molecular aggregates that offer numerous new possibilities in materials design. Diamondoid thiols are promising nanoscale building blocks for such hybrid systems. They allow the incorporation of functional groups and the investigation of their effects on the unique materials' properties of diamondoids. Here we combine experimental data with ab initio theory to explore the optical properties of diamondoid thiols and their dependence on size and shape. Agreement between theoretically and experimentally obtained absorption spectra allows the identification of the nature of the optical transitions that are responsible for some photophysical and photochemical processes. We show that the optical properties of diamondoid thiols in the deep UV regime depend on the functionalization site but are largely size independent. Our findings provide an explanation for the disappearance of diamondoid UV photoluminescence upon thiolation for smaller diamondoids. However, our theoretical results indicate that for larger diamondoid thiols beyond the critical size of six diamondoid cages the lowest energy transitions are characterized by diamondoidlike states suggesting that UV luminescence may be regained.

Photophysicochemical properties and photodynamic therapy activity of highly water-soluble Zn(II) phthalocyanines.

PubMed

Oluwole, David O; Sarı, Fatma Aslıhan; Prinsloo, Earl; Dube, Edith; Yuzer, Abdulcelil; Nyokong, Tebello; Ince, Mine

2018-05-29

The syntheses of two zinc(II) phthalocyanines (ZnPcs) having either imidazole (ZnPc 1) or pyridiloxy (ZnPc 2) moieties as their macrocycle substituents are reported. Quaternization of the ZnPcs with methyl iodide afforded water soluble cationic phthalocyanines. The photophysical, photochemical properties and photodynamic therapy (PDT) activity of the ZnPcs were studied in solution. The fluorescence quantum yield and lifetime of ZnPc 1 were higher as compared to ZnPc 2. ZnPc 2 afforded higher triplet state (Φ T ) and singlet oxygen quantum yields (Φ Δ ) in comparison to ZnPc 1. The PDT activity of ZnPcs was investigated against human breast adenocarcinoma cells (MCF-7). The two compounds afforded a very minimal in vitro dark cytotoxicity with 85% viable cells at concentration ≤80 μM. On irradiation of the cells having the ZnPcs, ≥50% cell death was recorded for ZnPc 1 which was also evidenced by the cells photo-micrograph. Copyright © 2018 Elsevier B.V. All rights reserved.

Light activated compounds as antimicrobial agents - patently obvious?

PubMed

Phoenix, D A; Harris, F

2006-06-01

Microbial pathogens with resistance to conventional drugs are a problem of global proportions and may be viral such as HIV, bacterial as in the case of MRSA or eukaryotic as seen with the malarial parasite Plasmodium falciparum. In response, photodynamic antimicrobial chemotherapy (PACT) has been developed, which is the delivery of a non-toxic photosensitiser (PS) to the site of a microbial infection. When taken up by the pathogen, illumination of the PS by light at an appropriate wavelength can lead to inactivation of the pathogen through the production of highly reactive free radical species, which induce oxidative damage to lipid, proteins and DNA / RNA, and / or adduct formation between the PS and these microbial biomolecules. Here the photochemical and photophysical steps underlying PS antimicrobial action along with the desirable electronic and physiochemical properties of PS are briefly reviewed. The therapeutic uses of PS are then illustrated with reference to a number that have featured in recent patents, including: The induction of endogenous PS by aminolevulinic acid; phenothiazinium based PS, which are the most studied of PACT agents, psoralens and organorhodium complexes.

Preparation and In Vitro Photodynamic Activity of Glucosylated Zinc(II) Phthalocyanines as Underlying Targeting Photosensitizers.

PubMed

Liu, Jian-Yong; Wang, Chen; Zhu, Chun-Hui; Zhang, Zhi-Hong; Xue, Jin-Ping

2017-05-19

Two novel glucosylated zinc(ІІ) phthalocyanines 7a-7b, as well as the acetyl-protected counterparts 6a-6b, have been synthesized by the Cu(I)-catalyzed 1,3-dipolar cycloaddition between the propargylated phthalocyanine and azide-substituted glucoses. All of these phthalocyanines were characterized with various spectroscopic methods and studied for their photo-physical, photo-chemical, and photo-biological properties. With glucose as the targeting unit, phthalocyanines 7a-7b exhibit a specific affinity to MCF-7 breast cancer cells over human embryonic lung fibroblast (HELF) cells, showing higher cellular uptake. Upon illumination, both photosensitizers show high cytotoxicity with IC 50 as low as 0.032 µM toward MCF-7 cells, which are attributed to their high cellular uptake and low aggregation tendency in the biological media, promoting the generation of intracellular reactive oxygen species (ROS). Confocal laser fluorescence microscopic studies have also revealed that they have high and selective affinities to the lysosomes, but not the mitochondria, of MCF-7 cells. The results show that these two glucosylated zinc(II) phthalocyanines are potential anticancer agents for targeting photodynamic therapy.

Physiological considerations acting on triplet oxygen for explicit dosimetry in photodynamic therapy.

PubMed

Sánchez, Víctor; Romero, María Paulina; Pratavieira, Sebastião; Costa, César

2017-09-01

The aims of this study were to determine the spatial and temporal theoretical distribution of the concentrations of Protoporphyrin IX, 3 O 2 and doses of 1 O 2 . The type II mechanism and explicit dosimetry in photodynamic therapy were used. Furthermore, the mechanism of respiration and cellular metabolism acting on 3 O 2 were taken into account. The dermis was considered as an absorbing and a scattering medium. An analytical solution was used for light diffusion in the skin. The photophysical, photochemical and biological effects caused by PDT with the initial irradiances of 20, 60 and 150mW/cm 2 were studied for a time of exposure of 20min and a maximum depth of 0.5cm. We found that the initial irradiance triples its value in 0.02cm and that almost 100% of PpIX is part of the dynamics of reactions in photodynamic therapy. Additionally, with about 40μMof 3 O 2 there is a balance between the consumed and supplied oxygen. Finally, we determined that with 60mW/cm 2 , the highest dose of 1 O 2 is obtained. Copyright © 2017 Elsevier B.V. All rights reserved.

Judicious Design of Cationic, Cyclometalated Ir(III) Complexes for Photochemical Energy Conversion and Optoelectronics.

PubMed

Mills, Isaac N; Porras, Jonathan A; Bernhard, Stefan

2018-02-20

The exponential growth in published studies on phosphorescent metal complexes has been triggered by their utilization in optoelectronics, solar energy conversion, and biological labeling applications. Very recent breakthroughs in organic photoredox transformations have further increased the research efforts dedicated to discerning the inner workings and structure-property relationships of these chromophores. Initially, the principal focus was on the Ru(II)-tris-diimine complex family. However, the limited photostability and lack of luminescence tunability discovered in these complexes prompted a broadening of the research to include 5d transition metal ions. The resulting increase in ligand field splitting prevents the population of antibonding e g * orbitals and widens the energy range available for color tuning. Particular attention was given to Ir(III), and its cyclometalated, cationic complexes have now replaced Ru(II) in the vast majority of applications. At the start, this Account documents the initial efforts dedicated to the color tuning of these complexes for their application in light emitting electrochemical cells, an easy to fabricate single-layer organic light emitting device (OLED). Systematic modifications of the ligand sphere of [Ir(ppy) 2 bpy] + (ppy: 2-phenylpyridine, bpy: 2,2'-bipyridine) with electron withdrawing and donating substituents allowed access to complexes with luminescence emission maxima throughout the visible spectrum exhibiting room temperature excited state lifetimes ranging from nanoseconds to dozens of microseconds and quantum yields up to 15 times that of [Ru(bpy) 3 ] 2+ . The diverse photophysical properties were also beneficial when using these Ir(III) complexes for driving solar fuel-producing reactions. For instance, photocatalytic water-reduction systems were explored to gain access to efficient water splitting systems. For this purpose, a variety of water reduction catalysts were paired with libraries of Ir(III) photosensitizers in high-throughput photoreactors. This parallelized approach allowed exploration of the interplay between the diverse photophysical properties of the Ir compounds and the electron-accepting catalysts. Further work enhanced and simplified the critical electron transfer processes between these two species through the use of bridging functional groups installed on the photosensitizer. Later, a novel approach summarized in this Account explores the possibility of using Zn metal as a solar fuel. Structure-activity relationships of the light-driven reduction of Zn 2+ to Zn metal are described. DFT calculations along with cyclic voltammetry were utilized to gain clear insights into the complexes' electronic structures responsible for the effective photochemical properties observed in these dyes. While [Ir(ppy) 2 bpy] + and its derivatives were found to be much more photostable than the Ru(II)-tris-diimine complex family, mass spectrometry indicated that the bpy ligand still photodissociated under extensive illumination. An interesting new approach involved the substitution of the bidentate 2,2'-bipyridine with a stronger chelating terpyridine ligand. This approach leaves room for one 2-phenylpyridine ligand and a third, anionic ligand, either Cl - or CN - . This Account reviews the effect of structural modifications on the photophysical properties of these [Ir(tpy)(ppy)X] + complexes and corroborates the findings with the results obtained through DFT modeling. These complexes found application in photocatalytic CO 2 reductions as well as a solvent tolerant light-absorber for the photogeneration of hydrogen. It was also documented that the robustness of these dyes in photoredox processes supersedes those of the commercially available [Ir(ppy) 2 (dtbbpy)]PF 6 and [Ir(dF(CF 3 )ppy) 2 (dtbbpy)]PF 6 complexes pioneered in the Bernhard laboratory.

Near-Infrared Emitting Squaraine Dyes with High 2PA Cross Sections for Multiphoton Fluorescence Imaging

PubMed Central

Ahn, Hyo-Yang; Yao, Sheng; Wang, Xuhua; Belfield, Kevin D.

2012-01-01

Designed to achieve high two-photon absorptivity, new near infrared (NIR) emitting squaraine dyes, (E)-2-(1-(2-(2-methoxyethoxy)ethyl)-5-(3,4,5-trimethoxystyryl)-1H-pyrrol-2-yl)-4-(1-(2-(2-methoxyethoxy)ethyl)-5-(3,4,5-trimethoxystyryl)-2H-pyrrolium-2-ylidene)-3-oxocyclobut-1-enolate (1) and (Z)-2-(4-(dibutylamino)-2-hydroxyphenyl)-4-(4-(dibutyliminio)-2-hydroxycyclohexa-2,5-dienylidene)-3-oxocyclobut-1-enolate (2) were synthesized and characterized. Their linear photophysical properties were investigated via UV-visible absorption spectroscopy and fluorescence spectroscopy in various solvents, while their nonlinear photophysical properties were investigated using a combination of two-photon induced fluorescence and open aperture z-scan methods. Squaraine 1 exhibited a high two-photon absorption (2PA) cross section (δ2PA), ~ 20,000 GM at 800 nm, and high photostability with the photochemical decomposition quantum yield one order of magnitude lower than Cy 5, a commercially available pentamethine cyanine NIR dye. The cytotoxicity of the squaraine dyes were evaluated in HCT 116 and COS 7 cell lines to assess the potential of these probes for biomedical imaging. The viability of both cell lines was maintained above 80% at dye concentrations up to 30 μM, indicating good biocompatibility of the probes. Finally, one-photon fluorescence microscopy (1PFM) and two-photon fluorescence microscopy (2PFM) imaging was accomplished after incubation of micelle-encapsulated squaraine probes with HCT 116 and COS 7 cells, demonstrating their potential in 2PFM bioimaging. PMID:22591003

Probing the structural dependency of photoinduced properties of colloidal quantum dots using metal-oxide photo-active substrates.

PubMed

Patty, Kira; Sadeghi, Seyed M; Campbell, Quinn; Hamilton, Nathan; West, Robert G; Mao, Chuanbin

2014-09-21

We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggests the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide.

Probing the structural dependency of photoinduced properties of colloidal quantum dots using metal-oxide photo-active substrates

PubMed Central

Patty, Kira; Sadeghi, Seyed M.; Campbell, Quinn; Hamilton, Nathan; West, Robert G.; Mao, Chuanbin

2014-01-01

We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggests the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide. PMID:25316953

Carbon-doped SnS2 nanostructure as a high-efficiency solar fuel catalyst under visible light.

PubMed

Shown, Indrajit; Samireddi, Satyanarayana; Chang, Yu-Chung; Putikam, Raghunath; Chang, Po-Han; Sabbah, Amr; Fu, Fang-Yu; Chen, Wei-Fu; Wu, Chih-I; Yu, Tsyr-Yan; Chung, Po-Wen; Lin, M C; Chen, Li-Chyong; Chen, Kuei-Hsien

2018-01-12

Photocatalytic formation of hydrocarbons using solar energy via artificial photosynthesis is a highly desirable renewable-energy source for replacing conventional fossil fuels. Using an L-cysteine-based hydrothermal process, here we synthesize a carbon-doped SnS 2 (SnS 2 -C) metal dichalcogenide nanostructure, which exhibits a highly active and selective photocatalytic conversion of CO 2 to hydrocarbons under visible-light. The interstitial carbon doping induced microstrain in the SnS 2 lattice, resulting in different photophysical properties as compared with undoped SnS 2 . This SnS 2 -C photocatalyst significantly enhances the CO 2 reduction activity under visible light, attaining a photochemical quantum efficiency of above 0.7%. The SnS 2 -C photocatalyst represents an important contribution towards high quantum efficiency artificial photosynthesis based on gas phase photocatalytic CO 2 reduction under visible light, where the in situ carbon-doped SnS 2 nanostructure improves the stability and the light harvesting and charge separation efficiency, and significantly enhances the photocatalytic activity.

Silicon Phthalocyanines Axially Disubstituted with Erlotinib toward Small-Molecular-Target-Based Photodynamic Therapy.

PubMed

Chen, Juan-Juan; Huang, Yi-Zhen; Song, Mei-Ru; Zhang, Zhi-Hong; Xue, Jin-Ping

2017-09-21

Small-molecular-target-based photodynamic therapy-a promising targeted anticancer strategy-was developed by conjugating zinc(II) phthalocyanine with a small-molecular-target-based anticancer drug. To prevent self-aggregation and avoid problems of phthalocyanine isomerization, two silicon phthalocyanines di-substituted axially with erlotinib have been synthesized and fully characterized. These conjugates are present in monomeric form in various solvents as well as culture media. Cell-based experiments showed that these conjugates localize in lysosomes and mitochondria, while maintaining high photodynamic activities (IC 50 values as low as 8 nm under a light dose of 1.5 J cm -2 ). With erlotinib as the targeting moiety, two conjugates were found to exhibit high specificity for EGFR-overexpressing cancer cells. Various poly(ethylene glycol) (PEG) linker lengths were shown to have an effect on the photophysical/photochemical properties and on in vitro phototoxicity. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Fourier transform spectra of quantum dots

NASA Astrophysics Data System (ADS)

Damian, V.; Ardelean, I.; Armăşelu, Anca; Apostol, D.

2009-09-01

Semiconductor quantum dots are nanometer-sized crystals with unique photochemical and photophysical properties that are not available from either isolated molecules or bulk solids. These nanocrystals absorb light over a very broad spectral range as compared to molecular fluorophores which have very narrow excitation spectra. High-quality QDs are proper to be use in different biological and medical applications (as fluorescent labels, the cancer treatment and the drug delivery). In this article, we discuss Fourier transform visible spectroscopy of commercial quantum dots. We reveal that QDs produced by Evident Technologies when are enlightened by laser or luminescent diode light provides a spectral shift of their fluorescence spectra correlated to exciting emission wavelengths, as shown by the ARCspectroNIR Fourier Transform Spectrometer. In the final part of this paper we show an important biological application of CdSe/ZnS core-shell ODs as microbial labeling both for pure cultures of cyanobacteria (Synechocystis PCC 6803) and for mixed cultures of phototrophic and heterotrophic microorganisms.

Fourier transform spectra of quantum dots

NASA Astrophysics Data System (ADS)

Damian, V.; Ardelean, I.; Armăşelu, Anca; Apostol, D.

2010-05-01

Semiconductor quantum dots are nanometer-sized crystals with unique photochemical and photophysical properties that are not available from either isolated molecules or bulk solids. These nanocrystals absorb light over a very broad spectral range as compared to molecular fluorophores which have very narrow excitation spectra. High-quality QDs are proper to be use in different biological and medical applications (as fluorescent labels, the cancer treatment and the drug delivery). In this article, we discuss Fourier transform visible spectroscopy of commercial quantum dots. We reveal that QDs produced by Evident Technologies when are enlightened by laser or luminescent diode light provides a spectral shift of their fluorescence spectra correlated to exciting emission wavelengths, as shown by the ARCspectroNIR Fourier Transform Spectrometer. In the final part of this paper we show an important biological application of CdSe/ZnS core-shell ODs as microbial labeling both for pure cultures of cyanobacteria (Synechocystis PCC 6803) and for mixed cultures of phototrophic and heterotrophic microorganisms.

Photophysical behavior of new acridine(1,8)dione dyes.

PubMed

Cabanzo Hernández, Rafael; David Gara, Pedro M; Velasco, Daniel Molina; Erra-Balsells, Rosa; Bilmes, Gabriel M

2013-11-01

The photophysical behavior of five acridine(1,8)dione dyes of biological interest was studied by absorption and fluorescence spectroscopy, photoacoustics and time resolved phosphorescence techniques. The results obtained in ethanol and acetonitrile solutions show that the main spectroscopic and photophysical parameters of these compounds depend strongly on both the solvent and oxygen concentrations. Oxygen completely quenched the triplet state of all dyes. In nitrogen-saturated solutions, quantum efficiencies of triplet formation in ethanol were lower than those in acetonitrile.

Non-adiabatic Excited State Molecule Dynamics Modeling of Photochemistry and Photophysics of Materials

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

Nelson, Tammie Renee; Tretiak, Sergei

2017-01-06

Understanding and controlling excited state dynamics lies at the heart of all our efforts to design photoactive materials with desired functionality. This tailor-design approach has become the standard for many technological applications (e.g., solar energy harvesting) including the design of organic conjugated electronic materials with applications in photovoltaic and light-emitting devices. Over the years, our team has developed efficient LANL-based codes to model the relevant photophysical processes following photoexcitation (spatial energy transfer, excitation localization/delocalization, and/or charge separation). The developed approach allows the non-radiative relaxation to be followed on up to ~10 ps timescales for large realistic molecules (hundreds of atomsmore » in size) in the realistic solvent dielectric environment. The Collective Electronic Oscillator (CEO) code is used to compute electronic excited states, and the Non-adiabatic Excited State Molecular Dynamics (NA-ESMD) code is used to follow the non-adiabatic dynamics on multiple coupled Born-Oppenheimer potential energy surfaces. Our preliminary NA-ESMD simulations have revealed key photoinduced mechanisms controlling competing interactions and relaxation pathways in complex materials, including organic conjugated polymer materials, and have provided a detailed understanding of photochemical products and intermediates and the internal conversion process during the initiation of energetic materials. This project will be using LANL-based CEO and NA-ESMD codes to model nonradiative relaxation in organic and energetic materials. The NA-ESMD and CEO codes belong to a class of electronic structure/quantum chemistry codes that require large memory, “long-queue-few-core” distribution of resources in order to make useful progress. The NA-ESMD simulations are trivially parallelizable requiring ~300 processors for up to one week runtime to reach a meaningful restart point.« less

The use of dendrimers as high-performance shells for round-trip energy transfer: efficient trans-cis photoisomerization from an excited triplet state produced within a dendrimer shell.

PubMed

Miura, Yousuke; Momotake, Atsuya; Takeuchi, Keiichirou; Arai, Tatsuo

2011-01-01

A series of stilbene-cored poly(benzyl ether) dendrimers with benzophenone peripheries were synthesized and their photophysical and photochemical properties were studied. Fluorescence studies revealed that singlet-singlet energy transfer (SSET) from the stilbene core to the benzophenone units took place efficiently in dendrimers of all generations. Similarly, phosphorescence and time-resolved spectroscopic measurements indicated efficient triplet-triplet energy transfer (TTET) from the benzophenone periphery to the stilbene core. Upon excitation at 310 nm, the stilbene core isomerizes via an energy round trip within the dendrimer shell. The quantum yields for the energy round trip (Φ(ERT)), defined as the product of the quantum yields of SSET, intersystem crossing, and TTET (Φ(ERT) = Φ(SS)Φ(isc)Φ(TT)), were extremely high for all generations--99%, 95% and 94% for G1, G2, and G3, respectively--which means that the excitation energy of the dendrimer core was transferred to the dendrimer periphery and back to the core almost quantitatively. The quantum yield for photoisomerization of G1-G3 via an energy round trip was higher than for other stilbene-cored dendrimers, which mainly isomerize from the excited singlet state. Photostability in the dendrimers was also demonstrated and discussed.

Attaching the NorA Efflux Pump Inhibitor INF55 to Methylene Blue Enhances Antimicrobial Photodynamic Inactivation of Methicillin-Resistant Staphylococcus aureus in Vitro and in Vivo.

PubMed

Rineh, Ardeshir; Dolla, Naveen K; Ball, Anthony R; Magana, Maria; Bremner, John B; Hamblin, Michael R; Tegos, George P; Kelso, Michael J

2017-10-13

Antimicrobial photodynamic inactivation (aPDI) uses photosensitizers (PSs) and harmless visible light to generate reactive oxygen species (ROS) and kill microbes. Multidrug efflux systems can moderate the phototoxic effects of PSs by expelling the compounds from cells. We hypothesized that increasing intracellular concentrations of PSs by inhibiting efflux with a covalently attached efflux pump inhibitor (EPI) would enhance bacterial cell phototoxicity and reduce exposure of neighboring host cells to damaging ROS. In this study, we tested the hypothesis by linking NorA EPIs to methylene blue (MB) and examining the photoantimicrobial activity of the EPI-MB hybrids against the human pathogen methicillin-resistant Staphylococcus aureus (MRSA). Photochemical/photophysical and in vitro microbiological evaluation of 16 hybrids carrying four different NorA EPIs attached to MB via four linker types identified INF55-(Ac)en-MB 12 as a lead. Compound 12 showed increased uptake into S. aureus cells and enhanced aPDI activity and wound healing effects (relative to MB) in a murine model of an abrasion wound infected by MRSA. The study supports a new approach for treating localized multidrug-resistant MRSA infections and paves the way for wider exploration of the EPI-PS hybrid strategy in aPDI.

Theoretical study on the photolysis mechanism of 2,3-diazabicyclo[2.2.2]oct-2-ene.

PubMed

Chen, Hui; Li, Shuhua

2005-09-28

A CASPT2/CASSCF study has been carried out to investigate the mechanism of the photolysis of 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) under direct and triplet-sensitized irradiation. By exploring the detailed potential energy surfaces including intermediates, transition states, conical intersections, and singlet/triplet crossing points, for the first excited singlet (S(1)) and the low-lying triplet states (T(1), T(2), and T(3)), we provide satisfactory explanations of many experimental findings associated with the photophysical and photochemical processes of DBO. A key finding of this work is the existence of a significantly twisted S(1) minimum, which can satisfactorily explain the envelope of the broad emission band of DBO. It is demonstrated that the S(1) (n-pi*) intermediate can decay to the T(1) (n-pi*) state by undergoing intersystem crossing (rather inefficient) to the T(2) (pi-pi*) state followed by internal conversion to the T(1) state. The high fluorescence yield and the extraordinarily long lifetime of the singlet excited DBO are due to the presence of relatively high barriers, both for intersystem crossing and for C-N cleavage. The short lifetime of the triplet DBO is caused by fast radiationless decay to the ground state.

Triplet-State Dissolved Organic Matter Quantum Yields and Lifetimes from Direct Observation of Aromatic Amine Oxidation.

PubMed

Schmitt, Markus; Erickson, Paul R; McNeill, Kristopher

2017-11-21

Excited triplet state chromophoric dissolved organic matter ( 3 CDOM*) is a short-lived mixture of excited-state species that plays important roles in aquatic photochemical processes. Unlike the study of the triplet states of well-defined molecules, which are amenable to transient absorbance spectroscopy, the study of 3 CDOM* is hampered by it being a complex mixture and its low average intersystem crossing quantum yield (Φ ISC ). This study is an alternative approach to investigating 3 CDOM* using transient absorption laser spectroscopy. The radical cation of N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD), formed through oxidation by 3 CDOM*, was directly observable by transient absorption spectroscopy and was used to probe basic photophysical properties of 3 CDOM*. Quenching and control experiments verified that TMPD •+ was formed from 3 CDOM* under anoxic conditions. Model triplet sensitizers with a wide range of excited triplet state reduction potentials and CDOM oxidized TMPD at near diffusion-controlled rates. This gives support to the idea that a large cross-section of 3 CDOM* moieties are able to oxidize TMPD and that the complex mixture of 3 CDOM* can be simplified to a single signal. Using the TMPD •+ transient, the natural triplet lifetime and Φ ISC for different DOM isolates and natural waters were quantified; values ranged from 12 to 26 μs and 4.1-7.8%, respectively.

Selective synthesis and characterization of chlorins as sensitizers for photodynamic therapy

NASA Astrophysics Data System (ADS)

Montforts, Franz-Peter; Kusch, Dirk; Hoper, Frank; Braun, Stefan; Gerlach, Benjamin; Brauer, Hans-Dieter; Schermann, Guido; Moser, Joerg G.

1996-04-01

Chlorin type sensitizers have ideal photophysical properties for an application in PDT. The basic chlorin framework of these sensitizers has to be modified by attachment of lipophilic and hydrophilic residues to achieve a good cell uptake and tumor enrichment. In the present study we describe the selective synthesis of amphiphilic chlorins starting from the readily accessible red blood pigment heme. The photophysical properties of the well defined synthetic chlorins are characterized by photophysical investigations. The kinetic of cell uptake, the localization in the cell and the photodynamic behavior of the amphiphilic sensitizers are demonstrated by incubation of A 375 cancer cell lines with structurally different chlorins.

Probing the structural dependency of photoinduced properties of colloidal quantum dots using metal-oxide photo-active substrates

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

Patty, Kira; Campbell, Quinn; Hamilton, Nathan

We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggestsmore » the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide.« less

Aluminum–phthalocyanine chloride associated to poly(methyl vinyl ether-co-maleic anhydride) nanoparticles as a new third-generation photosensitizer for anticancer photodynamic therapy

PubMed Central

Muehlmann, Luis Alexandre; Ma, Beatriz Chiyin; Longo, João Paulo Figueiró; Almeida Santos, Maria de Fátima Menezes; Azevedo, Ricardo Bentes

2014-01-01

Photodynamic therapy is generally considered to be safer than conventional anticancer therapies, and it is effective against different kinds of cancer. However, its clinical application has been significantly limited by the hydrophobicity of photosensitizers. In this work, a system composed of the hydrophobic photosensitizer aluminum–phthalocyanine chloride (AlPc) associated with water dispersible poly(methyl vinyl ether-co-maleic anhydride) nanoparticles is described. AlPc was associated with nanoparticles produced by a method of solvent displacement. This system was analyzed for its physicochemical characteristics, and for its photodynamic activity in vitro in cancerous (murine mammary carcinoma cell lineage 4T1, and human mammary adenocarcinoma cells MCF-7) and noncancerous (murine fibroblast cell lineage NIH/3T3, and human mammary epithelial cell lineage MCF-10A) cell lines. Cell viability and the elicited mechanisms of cell death were evaluated after the application of photodynamic therapy. This system showed improved photophysical and photochemical properties in aqueous media in comparison to the free photosensitizer, and it was effective against cancerous cells in vitro. PMID:24634582

Direct induction of molecular alignment in liquid crystal polymer network film by photopolymerization

NASA Astrophysics Data System (ADS)

Hisano, K.; Aizawa, M.; Ishizu, M.; Kurata, Y.; Shishido, A.

2016-09-01

Liquid crystal (LC) is the promising material for the fabrication of high-performance soft, flexible devices. The fascinating and useful properties arise from their cooperative effect that inherently allows the macroscopic integration and control of molecular alignment through various external stimuli. To date, light-matter interaction is the most attractive stimuli and researchers developed photoalignment through photochemical or photophysical reactions triggered by linearly polarized light. Here we show the new choice based on molecular diffusion by photopolymerization. We found that photopolymerization of a LC monomer and a crosslinker through a photomask enables to direct molecular alignment in the resultant LC polymer network film. The key generating the molecular alignment is molecular diffusion due to the difference of chemical potentials between irradiated and unirradiated regions. This concept is applicable to various shapes of photomask and two-dimensional molecular alignments can be fabricated depending on the spatial design of photomask. By virtue of the inherent versatility of molecular diffusion in materials, the process would shed light on the fabrication of various high-performance flexible materials with molecular alignment having controlled patterns.

A Comprehensive Tutorial on In Vitro Characterization of New Photosensitizers for Photodynamic Antitumor Therapy and Photodynamic Inactivation of Microorganisms

PubMed Central

Maisch, Tim; Berneburg, Mark; Plaetzer, Kristjan

2013-01-01

In vitro research performed on eukaryotic or prokaryotic cell cultures usually represents the initial step for characterization of a novel photosensitizer (PS) intended for application in photodynamic therapy (PDT) of cancer or photodynamic inactivation (PDI) of microorganisms. Although many experimental steps of PS testing make use of the wide spectrum of methods readily employed in cell biology, special aspects of working with photoactive substances, such as the autofluorescence of the PS molecule or the requirement of light protection, need to be considered when performing in vitro experiments in PDT/PDI. This tutorial represents a comprehensive collection of operative instructions, by which, based on photochemical and photophysical properties of a PS, its uptake into cells, the intracellular localization and photodynamic action in both tumor cells and microorganisms novel photoactive molecules may be characterized for their suitability for PDT/PDI. Furthermore, it shall stimulate the efforts to expand the convincing benefits of photodynamic therapy and photodynamic inactivation within both established and new fields of applications and motivate scientists of all disciplines to get involved in photodynamic research. PMID:23762860

Strong impact of the solvent on the photokinetics of a 2(1H)-pyrimidinone.

PubMed

Ryseck, G; Villnow, T; Hugenbruch, S; Schaper, K; Gilch, P

2013-08-01

Pyrimidinones are part of the (6-4) photolesions which may be formed from two pyrimidine bases adjacent on a DNA strand. In relation to the secondary photochemistry of the (6-4) lesion, i.e. its transformation into a Dewar valence isomer, photophysical and photochemical properties of 1-methyl-2(1H)-pyrimidinone (1MP) in water, acetonitrile, methanol, and 1,4-dioxane are reported here. As deduced from steady state fluorescence and femtosecond transient absorption spectroscopy the S1 lifetime of 1MP is strongly affected by the solvent. The lifetimes range from 400 ps for water to 40 ps for 1,4-dioxane. Internal conversion (IC) and intersystem crossing (ISC) contribute to the S1 decay. The solvent effect on the IC rate constant is more pronounced than on the ISC constant. The quantum yields for the consumption of 1MP (values for nitrogen purged solvents) are large for methanol (0.35) and 1,4-dioxane (0.24) and small for acetonitrile (0.02) and water (0.003). Hydrogen abstraction from the solvent by the triplet state of 1MP may rationalize this.

Metal bacteriochlorins which act as dual singlet oxygen and superoxide generators.

PubMed

Fukuzumi, Shunichi; Ohkubo, Kei; Zheng, Xiang; Chen, Yihui; Pandey, Ravindra K; Zhan, Riqiang; Kadish, Karl M

2008-03-06

A series of stable free-base, Zn(II) and Pd(II) bacteriochlorins containing a fused six- or five-member diketo- or imide ring have been synthesized as good candidates for photodynamic therapy sensitizers, and their electrochemical, photophysical, and photochemical properties were examined. Photoexcitation of the palladium bacteriochlorin affords the triplet excited state without fluorescence emission, resulting in formation of singlet oxygen with a high quantum yield due to the heavy atom effect of palladium. Electrochemical studies revealed that the zinc bacteriochlorin has the smallest HOMO-LUMO gap of the investigated compounds, and this value is significantly lower than the triplet excited-state energy of the compound in benzonitrile. Such a small HOMO-LUMO gap of the zinc bacteriochlorin enables intermolecular photoinduced electron transfer from the triplet excited state to the ground state to produce both the radical cation and the radical anion. The radical anion thus produced can transfer an electron to molecular oxygen to produce superoxide anion which was detected by electron spin resonance. The same photosensitizer can also act as an efficient singlet oxygen generator. Thus, the same zinc bacteriochlorin can function as a sensitizer with a dual role in that it produces both singlet oxygen and superoxide anion in an aprotic solvent (benzonitrile).

Photophysical parameters and laser performance of 3-(4‧-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one (DMAFP): A new laser dye

NASA Astrophysics Data System (ADS)

El-Daly, S. A.; Gaber, M.; El-Sayed, Y. S.

2009-09-01

The spectral properties such as singlet absorption, molar absorptivity, emission spectra, fluorescence quantum yield and excited state lifetime of 3-(4'-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one (DMAFP) have been determined in different solvents. DMAFP dye exhibits a large red shift in both electronic absorption and emission spectra as the solvent polarity increases, indicating a large change in the dipole moment of molecules upon excitation. A crystalline solid of DMAFP gives an excimer like emission at 566 nm due to the excitation of molecular aggregates. This is expected from the idealized crystal structure of the dye that belongs to the B-type class of Steven's classification. The ground and excited state protonation constants of DMAFP are calculated and amounted to 1.71 and 8.3, respectively. DMAFP acts as a good laser dye upon pumping with nitrogen laser ( λex=337.1 nm) in chloroform, methylene chloride and dioxane and gives laser emission in the range 460-590 nm. The laser parameters such as the tuning range, gain coefficient ( α), emission cross section ( σ e) and half-life energy ( E1/2) are calculated. The photoreactivity and net photochemical quantum yield of DMAFP in chloromethane solvents are also studied.

Ultrafast dynamics and Raman imaging of metal complexes of tetrasulphonated phthalocyanines in human cancerous and noncancerous breast tissues

NASA Astrophysics Data System (ADS)

Abramczyk, H.; Jarota, A.; Brozek-Pluska, B.; Tondusson, M.; Freysz, E.; Musial, J.; Kordek, R.

2013-03-01

A promising material in medicine, electronics, optoelectronics, electrochemistry, catalysis and photophysics, Al(III) phthalocyanine chloride tetrasulfonic acid (AlPcS4) is investigated at biological interfaces of human breast tissue by means of time-resolved spectroscopy. The nature of fast processes and pathways of the competing relaxation mechanisms from the initially excited electronic states of a photosensitizer at biological interfaces have been studied. Comparison between the results in the biological environment of the breast tissues and in aqueous solutions demonstrates that the photochemical mechanisms become dramatically different. The presented results provide a basis for a substantial revision of the commonly accepted assumption that photochemistry of the bulk properties of photosensitizers in solutions can be translated to the interfacial region. First, in solution the dynamics of the photosensitizer is much slower than that at the biological interface. Second, the dynamics of the photosensitizer in the cancerous tissue is dramatically slower than that in noncancerous tissue. Our results provide evidence that molecular structures responsible for harvesting of the light energy in biological tissue find their ways for a recovery through some special features of the potential energy surfaces such as conical intersections, which facilitate the rate of radiationless transitions and maintain the photostability in the biological systems.

Making waves in a photoactive polymer film

NASA Astrophysics Data System (ADS)

Gelebart, Anne Helene; Jan Mulder, Dirk; Varga, Michael; Konya, Andrew; Vantomme, Ghislaine; Meijer, E. W.; Selinger, Robin L. B.; Broer, Dirk J.

2017-06-01

Oscillating materials that adapt their shapes in response to external stimuli are of interest for emerging applications in medicine and robotics. For example, liquid-crystal networks can be programmed to undergo stimulus-induced deformations in various geometries, including in response to light. Azobenzene molecules are often incorporated into liquid-crystal polymer films to make them photoresponsive; however, in most cases only the bending responses of these films have been studied, and relaxation after photo-isomerization is rather slow. Modifying the core or adding substituents to the azobenzene moiety can lead to marked changes in photophysical and photochemical properties, providing an opportunity to circumvent the use of a complex set-up that involves multiple light sources, lenses or mirrors. Here, by incorporating azobenzene derivatives with fast cis-to-trans thermal relaxation into liquid-crystal networks, we generate photoactive polymer films that exhibit continuous, directional, macroscopic mechanical waves under constant light illumination, with a feedback loop that is driven by self-shadowing. We explain the mechanism of wave generation using a theoretical model and numerical simulations, which show good qualitative agreement with our experiments. We also demonstrate the potential application of our photoactive films in light-driven locomotion and self-cleaning surfaces, and anticipate further applications in fields such as photomechanical energy harvesting and miniaturized transport.

New photocycle intermediates in the photoactive yellow protein from Ectothiorhodospira halophila: picosecond transient absorption spectroscopy.

PubMed

Ujj, L; Devanathan, S; Meyer, T E; Cusanovich, M A; Tollin, G; Atkinson, G H

1998-07-01

Previous studies have shown that the room temperature photocycle of the photoactive yellow protein (PYP) from Ectothiorhodospira halophila involves at least two intermediate species: I1, which forms in <10 ns and decays with a 200-micros lifetime to I2, which itself subsequently returns to the ground state with a 140-ms time constant at pH 7 (Genick et al. 1997. Biochemistry. 36:8-14). Picosecond transient absorption spectroscopy has been used here to reveal a photophysical relaxation process (stimulated emission) and photochemical intermediates in the PYP photocycle that have not been reported previously. The first new intermediate (I0) exhibits maximum absorption at approximately 510 nm and appears in

Localized surface plasmon behavior of Ag-Cu alloy nanoparticles stabilized by rice-starch and gelatin

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

Singh, Manish Kumar; Mandal, R. K., E-mail: rkmandal.met@itbhu.ac.in; Manda, Premkumar

The purpose of this communication was to understand localized surface plasmon behavior of a series of Ag-Cu alloy nanoparticles capped by rice-starch and gelatin. The structures of dried powders were investigated with the help of X-ray diffraction. The analysis revealed Ag-rich and Cu-rich phases with maximum solid solubility of Cu ∼9 atom per cent; 8 atom per cent and Ag ∼ 16 atom per cent; 14 atom per cent in rice-starch and gelatin capped samples respectively. Transmission electron microscope was used for knowing the particle size as well as to supplement FCC phase formations of Ag-rich and Cu-rich solid phasesmore » arrived at based on X-ray diffraction studies. The UV-Vis spectra of sols were examined for the formation and stability of alloy nanoparticles. The temporal evolution of LSPR curves gave us to assert that the sol is stable for more than two months. Small angle X-ray scattering in the sol state was extensively utilized to understand nature of suspensions in terms of fractals. Such a study is important for having a correlation between LSPR behaviors with those of nanoparticle dispersion in aqueous media. It is believed that this work will be a contribution to the emerging field of plasmonics that include applications in the area of photophysical processes and photochemical reactions.« less

Localized surface plasmon behavior of Ag-Cu alloy nanoparticles stabilized by rice-starch and gelatin

NASA Astrophysics Data System (ADS)

Singh, Manish Kumar; Manda, Premkumar; Singh, A. K.; Mandal, R. K.

2015-10-01

The purpose of this communication was to understand localized surface plasmon behavior of a series of Ag-Cu alloy nanoparticles capped by rice-starch and gelatin. The structures of dried powders were investigated with the help of X-ray diffraction. The analysis revealed Ag-rich and Cu-rich phases with maximum solid solubility of Cu ˜9 atom per cent; 8 atom per cent and Ag ˜ 16 atom per cent; 14 atom per cent in rice-starch and gelatin capped samples respectively. Transmission electron microscope was used for knowing the particle size as well as to supplement FCC phase formations of Ag-rich and Cu-rich solid phases arrived at based on X-ray diffraction studies. The UV-Vis spectra of sols were examined for the formation and stability of alloy nanoparticles. The temporal evolution of LSPR curves gave us to assert that the sol is stable for more than two months. Small angle X-ray scattering in the sol state was extensively utilized to understand nature of suspensions in terms of fractals. Such a study is important for having a correlation between LSPR behaviors with those of nanoparticle dispersion in aqueous media. It is believed that this work will be a contribution to the emerging field of plasmonics that include applications in the area of photophysical processes and photochemical reactions.

Synthesis, spectral behaviour and photophysics of donor-acceptor kind of chalcones: Excited state intramolecular charge transfer and fluorescence quenching studies

NASA Astrophysics Data System (ADS)

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

2015-02-01

The spectral and photophysical properties of two chalcones containing electron donating and accepting groups with intramolecular charge transfer characteristics were synthesized and characterized by 1H NMR, 13C NMR and X-ray crystallography. Both compounds show very strong solvent polarity dependent changes in their photophysical characteristics, namely, remarkable red shift in the emission spectra with increasing solvent polarity, large change in Stokes shift, significant reduction in the fluorescence quantum yield; indicating that the fluorescence states of these compounds are of intramolecular charge transfer (ICT) character. The solvent effect on the photophysical parameters such as singlet absorption, molar absorptivity, oscillator strength, dipole moment, fluorescence spectra, and fluorescence quantum yield of both compounds have been investigated comprehensively. For both dyes, Lippert-Mataga and Reichardt's correlations were used to estimate the difference between the excited and ground state dipole moments (Δμ). The interactions of dyes with colloidal silver nanoparticles (Ag NPs) were also studied in ethanol using steady state fluorescence quenching measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of dyes by Ag NPs.

Photophysical studies of newly derivatized mono substituted phthalocyanines grafted onto silica nanoparticles via click chemistry.

PubMed

Fashina, Adedayo; Amuhaya, Edith; Nyokong, Tebello

2015-04-05

This work reports on the synthesis, characterization and photophysical studies of newly derived phthalocyanine complexes and the phthalocyanine-silica nanoparticles conjugates. The derived phthalocyanine complexes have one terminal alkyne group. The derived phthalocyanine complexes showed improved photophysical properties (ФF, ФT, ΦΔ and τT) compared to the respective phthalocyanine complexes from which they were derived. The derived phthalocyanine complexes were conjugated to the surface of an azide functionalized silica nanoparticles via copper (1) catalyzed cyclo-addition reaction. All the conjugates showed lower triplet quantum yields ranging from 0.37 to 0.44 compared to the free phthalocyanine complexes. The triplet lifetimes ranged from 352 to 484 μs for the conjugates and from 341 to 366 μs for the free phthalocyanine complexes. Copyright © 2014 Elsevier B.V. All rights reserved.

Recent development in deciphering the structure of luminescent silver nanodots

NASA Astrophysics Data System (ADS)

Choi, Sungmoon; Yu, Junhua

2017-05-01

Matrix-stabilized silver clusters and stable luminescent few-atom silver clusters, referred to as silver nanodots, show notable difference in their photophysical properties. We present recent research on deciphering the nature of silver clusters and nanodots and understanding the factors that lead to variations in luminescent mechanisms. Due to their relatively simple structure, the matrix-stabilized clusters have been well studied. However, the single-stranded DNA (ssDNA)-stabilized silver nanodots that show the most diverse emission wavelengths and the best photophysical properties remain mysterious species. It is clear that their photophysical properties highly depend on their protection scaffolds. Analyses from combinations of high-performance liquid chromatography, inductively coupled plasma-atomic emission spectroscopy, electrophoresis, and mass spectrometry indicate that about 10 to 20 silver atoms form emissive complexes with ssDNA. However, it is possible that not all of the silver atoms in the complex form effective emission centers. Investigation of the nanodot structure will help us understand why luminescent silver nanodots are stable in aqueous solution and how to further improve their chemical and photophysical properties.

Synthesis and photophysical properties of a series of cyclopenta[b]naphthalene solvatochromic fluorophores.

PubMed

Benedetti, Erica; Kocsis, Laura S; Brummond, Kay M

2012-08-01

The synthesis and photophysical properties of a series of naphthalene-containing solvatochromic fluorophores are described within. These novel fluorophores are prepared using a microwave-assisted dehydrogenative Diels-Alder reaction of styrene, followed by a palladium-catalyzed cross coupling reaction to install an electron donating amine group. The new fluorophores are structurally related to Prodan. Photophysical properties of the new fluorophores were studied and intriguing solvatochromic behavior was observed. For most of these fluorophores, high quantum yields (60-99%) were observed in methylene chloride in addition to large Stokes shifts (95-226 nm) in this same solvent. As the solvent polarity increased, so did the observed Stokes shift with one derivative displaying a Stokes shift of ~300 nm in ethanol. All fluorophore emission maxima, and nearly all absorption maxima were significantly red-shifted when compared to Prodan. Shifting the absorption and emission maxima of a fluorophore into the visible region increases its utility in biological applications. Moreover, the cyclopentane portion of the fluorophore structure provides an attachment point for biomolecules that will minimize disruptions of the photophysical properties.

Photophysical Study of Novel Perylene Analogues for Biophysical Applications

NASA Astrophysics Data System (ADS)

Palos-Chávez, Jorge; Penick, Mark; Negrete, George; Brancaleon, Lorenzo

2011-03-01

Perylene and perylene derivatives have been shown to be useful in a variety of photoinitiated applications, such as molecular dyes, organic solar cells, etc. Recently we started the characterization of novel 3,9-perylene analogues which could potentially lead to the synthesis of novel molecules with improved ability to separate charges. We have characterized the basic photophysical properties of these molecules, and we are currently investigating the photochemistry that leads to photoproducts in chlorinated compounds. Spectroscopic measurements show the substantial changes in photophysical parameters consistent with the conversion of the original compounds into photoproducts. SEM and AFM imaging show that these photoproducts form ordered particles. Mass spectrometry studies have confirmed the presence of these photoproducts as well. Additional studies are underway concerning the use of these novel perylene analogues in binding to biological structures such as proteins. It is hoped that these compounds will prove useful for biophysical applications, specifically in studying the manipulation of protein conformation via physical methods. Supported by NIH/NIGMS MBRS RISE GM-60655.

Acetone photophysics at 282 nm excitation at elevated pressure and temperature. II: Fluorescence modeling

NASA Astrophysics Data System (ADS)

Hartwig, Jason; Raju, Mandhapati; Sung, Chih-Jen

2017-07-01

This is the second in a series of two papers that presents an updated fluorescence model and compares with the new experimental data reported in the first paper, as well as the available literature data, to extend the range of acetone photophysics to elevated pressure and temperature conditions. This work elucidates the complete acetone photophysical model in terms of each and every competing radiative and non-radiative rate. The acetone fluorescence model is then thoroughly examined and optimized based on disparity with recently conducted elevated pressure and temperature photophysical calibration experiments. The current work offers insight into the competition between non-radiative and vibrational energy decay rates at elevated temperature and pressure and proposes a global optimization of model parameters from the photophysical model developed by Thurber (Acetone Laser-Induced Fluorescence for Temperature and Multiparameter Imaging in Gaseous Flows. PhD thesis, Stanford University Mechanical Engineering Department, 1999). The collisional constants of proportionality, which govern vibrational relaxation, are shown to be temperature dependent at elevated pressures. A new oxygen quenching rate is proposed which takes into account collisions with oxygen as well as the oxygen-assisted intersystem crossing component. Additionally, global trends in ketone photophysics are presented and discussed.

PHOTOCHEMICAL MODELING APPLIED TO NATURAL WATERS

EPA Science Inventory

The study examines the application of modeling photochemical processes in natural water systems. For many photochemical reactions occurring in natural waters, a simple photochemical model describing reaction rate as a function of intensity, radiation attenuation, reactant absorpt...

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.

The Unique Photophysical Properties of the Peridinin-Chlorophyll-a-Protein

PubMed Central

Carbonera, Donatella; Valentin, Marilena Di; Spezia, Riccardo; Mezzetti, Alberto

2014-01-01

Peridinin-Chlorophyll-a-Proteins (PCPs) are water-soluble light harvesting complexes from dinoflagellates. They have unique light-harvesting and energy transfer properties which have been studied in details in the last 15 years. This review aims to give an overview on all the main aspects of PCPs photophysics, with an emphasis on some aspects which have not been reviewed in details so far, such as vibrational spectroscopy studies, theoretical calculations, and magnetic resonance studies. A paragraph on the present development of PCPs towards technological applications is also included. PMID:24678668

Synthesis and photophysical characterizations of thermal-stable naphthalene benzimidazoles.

PubMed

Erten-Ela, Sule; Ozcelik, Serdar; Eren, Esin

2011-07-01

Microwave-assisted synthesis, photophysical and electrochemical properties of thermal-stable naphthalene benzimidazoles and naphthalimides are studied in this paper. Microwave-assisted synthesis of naphthalene benzimidazoles provide higher yields than the conventional thermal synthesis. Comparative photophysical properties of naphthalene benzimidazoles and naphthalimides are revealed that conjugation of electron-donating group onto naphthalimide moiety increases fluorescence quantum yields. Fluorophore-solvent interactions are also investigated using Lippert-Mataga equation for naphthalimides and naphthalene benzimidazoles. Thermal stabilities of naphthalene benzimidazoles are better than naphthalimides due to increased aromaticity. The experimental E(LUMO) levels of naphthalene benzimidazoles are found to be between 3.15 and 3.28 eV. Therefore, naphthalene benzimidazole derivatives consisting of anchoring groups are promising materials in organic dye sensitized solar cells. © Springer Science+Business Media, LLC 2011

Direct single-molecule measurements of phycocyanobilin photophysics in monomeric C-phycocyanin

DOE PAGES

Squires, Allison H.; Moerner, W. E.

2017-08-28

Phycobilisomes are highly organized pigment-protein antenna complexes found in the photosynthetic apparatus of cyanobacteria and rhodophyta that harvest solar energy and transport it to the reaction center. A detailed bottom-up model of pigment organization and energy transfer in phycobilisomes is essential to understanding photosynthesis in these organisms, and informing rational design of artificial light-harvesting systems. Particularly, heterogeneous photophysical behaviors of these proteins, which cannot be predicted de novo, may play an essential role in rapid light adaptation and photoprotection. Furthermore, the delicate architecture of these pigment-protein scaffolds sensitizes them to external perturbations, e.g: surface attachment, which can be avoided bymore » study in free solution or in vivo. We present the first single-molecule characterization of C-phycocyanin (C-PC), a three-pigment biliprotein that self-assembles to form the mid-antenna rods of cyanobacterial phycobilisomes. Using the Anti-Brownian Electrokinetic (ABEL) trap to counteract Brownian motion of single particles in real-time, we directly monitor the changing photophysical states of individual C-PC monomers from Spirulina platensis in free solution by simultaneous readout of their brightness, fluorescence anisotropy, fluorescence lifetime, and emission spectra. These include single-chromophore emission states for each of the three covalently bound phycocyanobilins, providing the first direct measurement of the spectra and photophysics of these chemically identical molecules in their native protein environment. We also further show that a simple Förster Resonant Energy Transfer (FRET) network model accurately predicts the observed photophysical states of C-PC, and suggests highly variable quenching behavior of one of the chromophores, which should inform future studies of higher-order complexes.« less

Visual pigments. 11. Spectroscopy and photophysics of retinoic acids and all-trans-methyl retinoate. [Photophysical properties at 77/sup 0/K

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

Takemura, T.; Chihara, K.; Becker, R.S.

1980-04-09

The photophysics of hydrogen-bonded complexes of retinoic acid and its 9-cis and 13-cis isomers and the photophysics of the dimers of these isomers of retinoic acid were studied. The investigation indicated that complexes of retinoic acid and molecules that form hydrogen bonds with the carbonyl oxygen of retinoic acid (type I complexes) have both higher radiative and nonradiative rate constants than do hydrogen-bonded complexes of retinoic acid and molecules that form hydrogen bonds only with the hydroxyl oxygen of retinoic acid (type II complexes). For all-trans-retinoic acid in 3-methylpentane at 77 K, the type I complexes have radiative rate constantsmore » approximately equal to or greater than 2 x 10/sup 8/ s/sup -1/ and nonradiative rate constants greater than 3 x 10/sup 8/ s/sup -1/. Both the radiative and nonradiative rate constants of the type II complexes of all-trans-retinoic acid at 77 K in 3-methylpentane are less than 1 x 10/sup 8/ s/sup -1/. The dimer of retinoic acid (K(association) = 1 x 10/sup 4/ M/sup -1/ at room temperature for the all-trans isomer) behaves like a type I complex, and its excited-state properties are better understood in terms of hydrogen bonding than in terms of an exciton model. The photophysical properties and triplet-triplet absorption spectrum of methyl retinoate were measured. The study concluded with an examination of some of the implications of this work for the role of hydrogen bonding in the dimers and monomers of retinal and retinol.« less

Direct single-molecule measurements of phycocyanobilin photophysics in monomeric C-phycocyanin

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

Squires, Allison H.; Moerner, W. E.

Phycobilisomes are highly organized pigment-protein antenna complexes found in the photosynthetic apparatus of cyanobacteria and rhodophyta that harvest solar energy and transport it to the reaction center. A detailed bottom-up model of pigment organization and energy transfer in phycobilisomes is essential to understanding photosynthesis in these organisms, and informing rational design of artificial light-harvesting systems. Particularly, heterogeneous photophysical behaviors of these proteins, which cannot be predicted de novo, may play an essential role in rapid light adaptation and photoprotection. Furthermore, the delicate architecture of these pigment-protein scaffolds sensitizes them to external perturbations, e.g: surface attachment, which can be avoided bymore » study in free solution or in vivo. We present the first single-molecule characterization of C-phycocyanin (C-PC), a three-pigment biliprotein that self-assembles to form the mid-antenna rods of cyanobacterial phycobilisomes. Using the Anti-Brownian Electrokinetic (ABEL) trap to counteract Brownian motion of single particles in real-time, we directly monitor the changing photophysical states of individual C-PC monomers from Spirulina platensis in free solution by simultaneous readout of their brightness, fluorescence anisotropy, fluorescence lifetime, and emission spectra. These include single-chromophore emission states for each of the three covalently bound phycocyanobilins, providing the first direct measurement of the spectra and photophysics of these chemically identical molecules in their native protein environment. We also further show that a simple Förster Resonant Energy Transfer (FRET) network model accurately predicts the observed photophysical states of C-PC, and suggests highly variable quenching behavior of one of the chromophores, which should inform future studies of higher-order complexes.« less

Global Analysis of Perovskite Photophysics Reveals Importance of Geminate Pathways

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

Manger, Lydia H.; Rowley, Matthew B.; Fu, Yongping

Hybrid organic-inorganic perovskites demonstrate desirable photophysical behaviors and promising applications from efficient photovoltaics to lasing, but the fundamental nature of excited state species is still under debate. We also collected time-resolved photoluminescence of single-crystal nanoplates of methylammonium lead iodide perovskite (MAPbI3), with excitation over a range of fluences and repetition rates, to provide a more complete photophysical picture. A fundamentally different way of simulating the photophysics is developed that relies on unnormalized decays, global analysis over a large array of conditions, and inclusion of steady-state behavior; these details are critical to capturing observed behaviors. These additional constraints require inclusion ofmore » spatially-correlated pairs, along with free carriers and traps, demonstrating the importance of our comprehensive analysis. Modeling geminate and non-geminate pathways shows geminate processes are dominant at high carrier densities and early times. This combination of data and simulation provides a detailed picture of perovskite photophysics across multiple excitation regimes that was not previously available.« less

Global Analysis of Perovskite Photophysics Reveals Importance of Geminate Pathways

DOE PAGES

Manger, Lydia H.; Rowley, Matthew B.; Fu, Yongping; ...

2016-12-20

Hybrid organic-inorganic perovskites demonstrate desirable photophysical behaviors and promising applications from efficient photovoltaics to lasing, but the fundamental nature of excited state species is still under debate. We also collected time-resolved photoluminescence of single-crystal nanoplates of methylammonium lead iodide perovskite (MAPbI3), with excitation over a range of fluences and repetition rates, to provide a more complete photophysical picture. A fundamentally different way of simulating the photophysics is developed that relies on unnormalized decays, global analysis over a large array of conditions, and inclusion of steady-state behavior; these details are critical to capturing observed behaviors. These additional constraints require inclusion ofmore » spatially-correlated pairs, along with free carriers and traps, demonstrating the importance of our comprehensive analysis. Modeling geminate and non-geminate pathways shows geminate processes are dominant at high carrier densities and early times. This combination of data and simulation provides a detailed picture of perovskite photophysics across multiple excitation regimes that was not previously available.« less

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

Mumin, Md Abdul, E-mail: pcharpentier@eng.uwo.ca; Akhter, Kazi Farida, E-mail: pcharpentier@eng.uwo.ca; Charpentier, Paul A., E-mail: pcharpentier@eng.uwo.ca

Semiconductor nanocrystals (NCs) (also known as quantum dots, QDs) have attracted immense attention for their size-tunable optical properties that makes them impressive candidates for solar cells, light emitting devices, lasers, as well as biomedical imaging. However monodispersity, high and consistent photoluminescence, photostability, and biocompatibility are still major challenges. This work focuses on optimizing the photophysical properties and biocompatibility of QDs by forming core-shell nanostructures and their encapsulation by a carrier. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm sizes were synthesized using a facile approach based on pyrolysis of the single molecule precursors. After capping the CdS QDsmore » with a thin layer of ZnS to reduce toxicity, the photoluminescence and photostability of the core-shell QDs was significantly enhanced. To make both the bare and core/shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interaction. This encapsulation enhanced the quantum yield and photostability compared to the bare QDs by providing much stronger resistance to oxidation and Oswald ripening of QDs. Encapsulation also improved biocompatibility of QDs that was evaluated with human umbilical vein endothelial cell lines (HUVEC)« less

Fluorination of phthalocyanine substituents: Improved photoproperties and enhanced photodynamic efficacy after optimal micellar formulations.

PubMed

Pucelik, Barbara; Gürol, Ilke; Ahsen, Vefa; Dumoulin, Fabienne; Dąbrowski, Janusz M

2016-11-29

A fluorinated phthalocyanine and its non-fluorinated analogue were selected to evaluate the potential enhancement of fluorination on photophysical, photochemical and redox properties as well as on biological activity in cellular and animal models. Due to the pharmacological relevance, the affinity of these phthalocyanines towards biological membranes (logP ow ) as well as their primary interaction with human serum albumin (HSA) or low-density lipoprotein (LDL) were determined. Water-dispersible drug formulation of phthalocyanines via Pluronic ® -based triblock copolymer micelles was prepared to avoid self-aggregation effects and to improve their delivery. The obtained results demonstrate that phthalocyanines incorporation into tunable-polymeric micelles significantly enhanced their cellular uptake and their photocytotoxicity. The improved biodistribution and photodynamic efficacy of the phthalocyanines-triblock copolymer conjugates was also confirmed in vivo in CT26 bearing BALB/c mice. PDT with both compounds led to tumor growth inhibition in all treated animals. Fluorinated phthalocyanine 2 turned out to be the most effective anticancer agent as the tumors of 20% of mice treated regressed completely and did not appear for over one year after treatment. Copyright © 2016 Elsevier Masson SAS. All rights reserved.

The role of different structural motifs in the ultrafast dynamics of second generation protein stains.

PubMed

Chatterjee, Soumit; Karuso, Peter; Boulangé, Agathe; Peixoto, Philippe A; Franck, Xavier; Datta, Anindya

2013-12-05

Engineering the properties of fluorescent probes through modifications of the fluorophore structure has become a subject of interest in recent times. By doing this, the photophysical and photochemical properties of the modified fluorophore can be understood and this can guide the design and synthesis of better fluorophores for use in biotechnology. In this work, the electronic spectra and fluorescence decay kinetics of four analogues of the fluorescent natural product epicocconone were investigated. Epicocconone is unique in that the native state is weakly green fluorescent, whereas the enamine formed reversibly with proteins is highly emissive in the red. It was found that the ultrafast dynamics of the analogues depends profoundly on the H-bonding effect of solvents and solvent viscosity though solvent polarity also plays a role. Comparing the steady state and time-resolved data, the weak fluorescence of epicocconone in its native state is most likely due to the photoisomerization of the hydrocarbon side chain, while the keto enol moiety also has a role to play in determining the fluorescence quantum yield. This understanding is expected to aid the design of better protein stains from the same family.

Two-photon absorption and transient photothermal imaging of pigments in tissues

NASA Astrophysics Data System (ADS)

Ye, Tong; Fu, Dan; Matthews, Thomas E.; Hong, Lian; Simon, John D.; Warren, Warren S.

2008-02-01

As a main pigment in skin tissues, melanin plays an important role in photo-protecting skin from UV radiation. However, melanogenesis may be altered due to disease or environmental factors; for example, sun exposure may cause damage and mutation of melanocytes and induce melanoma. Imaging pigmentation changes may provide invaluable information to catch the malignant transformation in its early stage and in turn improve the prognosis of patients. We have demonstrated previously that transmission mode, two-photon, one- or two-color absorption microscopy could provide remarkable contrast in imaging melanin in skin. In this report we demonstrate significantly improved sensitivity, so that we are now able to image in epi-mode (or back reflection) in two-photon absorption. This improvement makes possible for us to characterize the different types of pigmentation on the skin in vivo at virtually any location. Another finding is that we can also image transient photothermal dynamics due to the light absorption of melanin. By carefully choosing excitation and probe wavelengths, we might be able to image melanin in different structures under different micro-environments in skin, which could provide useful photochemical and photophysical insights in understanding how pigments are involved in photoprotection and photodamage of cells.

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.

Advanced Photonic Processes for Photovoltaic and Energy Storage Systems.

PubMed

Sygletou, Maria; Petridis, Constantinos; Kymakis, Emmanuel; Stratakis, Emmanuel

2017-10-01

Solar-energy harvesting through photovoltaic (PV) conversion is the most promising technology for long-term renewable energy production. At the same time, significant progress has been made in the development of energy-storage (ES) systems, which are essential components within the cycle of energy generation, transmission, and usage. Toward commercial applications, the enhancement of the performance and competitiveness of PV and ES systems requires the adoption of precise, but simple and low-cost manufacturing solutions, compatible with large-scale and high-throughput production lines. Photonic processes enable cost-efficient, noncontact, highly precise, and selective engineering of materials via photothermal, photochemical, or photophysical routes. Laser-based processes, in particular, provide access to a plethora of processing parameters that can be tuned with a remarkably high degree of precision to enable innovative processing routes that cannot be attained by conventional approaches. The focus here is on the application of advanced light-driven approaches for the fabrication, as well as the synthesis, of materials and components relevant to PV and ES systems. Besides presenting recent advances on recent achievements, the existing limitations are outlined and future possibilities and emerging prospects discussed. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Validation of photodynamic action via photobleaching of a new curcumin-based composite with enhanced water solubility.

PubMed

Rego-Filho, Francisco G; de Araujo, Maria T; de Oliveira, Kleber T; Bagnato, Vanderlei S

2014-09-01

Motivated by the photochemical and photophysical properties of curcumin-based composites, the characteristics of a new curcumin-based water-soluble salt were investigated via absorption and fluorescence spectroscopy. Photobleaching was investigated using a set of LEDs in three different wavelengths (405 nm, 450 nm and 470 nm) to illuminate an aqueous solution of curcumin, evaluating its degradation for five different exposure times (0, 5, 15, 45 and 105 minutes). The results were compared with equivalent measurements of dark degradation and illumination in the presence of a singlet-oxygen quencher. Three solution concentrations (50, 100 and 150 μg/ml) were studied. To measure the fluorescence, it was used low power 405 nm excitation laser source. Time dependent photodegradation of curcumin was observed, as compared to the natural degradation of samples maintained on a dark environment. Two main absorption peaks were detected and their relation responded to both concentration and wavelength of the illumination source. A spectral correlation between absorption of curcumin and the emission bands of the sources showed an optimal spectral overlap for the 450 nm LED. For this source, photobleaching showed a less intense degradation on the presence of singlet oxygen quencher. This last result confirmed singlet oxygen production in vitro, indicating a strong potential of this composite to be used as a blue-light-activated photosensitizer.

Uncovering the Roles of Oxygen in Cr(III) Photoredox Catalysis.

PubMed

Higgins, Robert F; Fatur, Steven M; Shepard, Samuel G; Stevenson, Susan M; Boston, David J; Ferreira, Eric M; Damrauer, Niels H; Rappé, Anthony K; Shores, Matthew P

2016-04-27

A combined experimental and theoretical investigation aims to elucidate the necessary roles of oxygen in photoredox catalysis of radical cation based Diels-Alder cycloadditions mediated by the first-row transition metal complex [Cr(Ph2phen)3](3+), where Ph2phen = bathophenanthroline. We employ a diverse array of techniques, including catalysis screening, electrochemistry, time-resolved spectroscopy, and computational analyses of reaction thermodynamics. Our key finding is that oxygen acts as a renewable energy and electron shuttle following photoexcitation of the Cr(III) catalyst. First, oxygen quenches the excited Cr(3+)* complex; this energy transfer process protects the catalyst from decomposition while preserving a synthetically useful 13 μs excited state and produces singlet oxygen. Second, singlet oxygen returns the reduced catalyst to the Cr(III) ground state, forming superoxide. Third, the superoxide species reduces the Diels-Alder cycloadduct radical cation to the final product and reforms oxygen. We compare the results of these studies with those from cycloadditions mediated by related Ru(II)-containing complexes and find that the distinct reaction pathways are likely part of a unified mechanistic framework where the photophysical and photochemical properties of the catalyst species lead to oxygen-mediated photocatalysis for the Cr-containing complex but radical chain initiation for the Ru congener. These results provide insight into how oxygen can participate as a sustainable reagent in photocatalysis.

Photophysical investigaions and the bioimaings of α-, β-, γ-pyridine-based terpyridine derivatives

NASA Astrophysics Data System (ADS)

Zhang, Jun; Wang, Hui

2018-04-01

Three unprecedented triphenylamine-based D-A type terpyridine derivatives (TriphenL1-TriphenL3) with different positions of nitrogen atom in the terpyridine moiety were carefully designed and fully characterized, which was further confirmed via single-crystal X-ray diffraction determination. The photophysical properties of all the three compounds were comprehensively studied by both theoretical calculations and experimental techniques, which revealed that TriphenL3 with γ-pyridine in the NIR region possessed large two-photon absorption cross-section. Experiments including photophysical tests and cytotoxicity demonstrated these dyes were characterized with larger Stokes shifts, longer fluorescence lifetime, low toxicity and good cell penetrability, thus TriphenL1-TriphenL3 were succeed to be devoted as cell stains, suggesting a prospect for applications of in vitro and vivo cellular imaging.

Photophysics of GaN single-photon emitters in the visible spectral range

NASA Astrophysics Data System (ADS)

Berhane, Amanuel M.; Jeong, Kwang-Yong; Bradac, Carlo; Walsh, Michael; Englund, Dirk; Toth, Milos; Aharonovich, Igor

2018-04-01

In this work, we present a detailed photophysical analysis of recently discovered, optically stable single-photon emitters (SPEs) in gallium nitride (GaN). Temperature-resolved photoluminescence measurements reveal that the emission lines at 4 K are three orders of magnitude broader than the transform-limited width expected from excited-state lifetime measurements. The broadening is ascribed to ultrafast spectral diffusion. The photophysical study on several emitters at room temperature (RT) reveals an average brightness of (427 ±215 )kCounts /s . Finally, polarization measurements from 14 emitters are used to determine visibility as well as dipole orientation of defect systems within the GaN crystal. Our results underpin some of the fundamental properties of SPEs in GaN both at cryogenic and RT, and define the benchmark for future work in GaN-based single-photon technologies.

An electrochemical and photophysical study of a covalently linked inorganic-organic dyad.

PubMed

Kahnt, Axel; Heiniger, Leo-Philipp; Liu, Shi-Xia; Tu, Xiaoyan; Zheng, Zhiping; Hauser, Andreas; Decurtins, Silvio; Guldi, Dirk M

2010-02-22

A molecular donor-acceptor dyad comprising a hexarhenium cluster core, [Re(6)(mu(3)-Se)(8)](2+), and a fullerene moiety which are covalently linked through a pyridine ligand was synthesized and fully characterized. The electrochemical and photophysical properties are reported. The detailed study includes cyclic voltammetry, steady-state absorption and fluorescence spectroscopy, radiation chemistry and transient absorption spectroscopy. A light-induced electron transfer between the inorganic cluster moiety and the fullerene can be excluded. However, a light-induced energy transfer from the rhenium cluster to the fullerene is proposed.

A Simple Parallel Photochemical Reactor for Photodecomposition Studies

ERIC Educational Resources Information Center

Xiaobo Chen; Halasz, Sarah M.; Giles, Eric C.; Mankus, Jessica V.; Johnson, Joseph C.; Burda, Clemens

2006-01-01

A simple and useful parallel photochemical reactor intended to study the photodecomposition of dyes using semiconductor photocatalysis is presented. The photochemical reactions are followed through time-dependent changes in the ground-state absorption spectra of the dyes.

Highly efficient destruction of squamous carcinoma cells of the head and neck by photochemical internalization of Ranpirnase.

PubMed

Liebers, Nora; Holland-Letz, Tim; Welschof, Mona; Høgset, Anders; Jäger, Dirk; Arndt, Michaela A E; Krauss, Jürgen

2017-11-01

Photochemical Internalization is a novel drug delivery technology for cancer treatment based on the principle of Photodynamic Treatment. Using a photosensitizer that locates in endocytic vesicles membranes of tumor cells, Photochemical internalization enables cytosolic release of endocytosed antitumor agents in a site-specific manner. The purpose of the present in-vitro study was to explore whether Photochemical Internalization is able to enhance the efficacy of Ranpirnase, a cytotoxic amphibian ribonuclease, for eradication of squamous cell carcinoma of the head and neck. Cell viability was measured in 8 primary human cell lines of squamous cell carcinoma of the head and neck after treatment with Ranpirnase and Photochemical Internalization. For Photochemical Internalization the photosensitizer disulfonated tetraphenyl porphine was incubated with tumor cells followed by exposure to blue light (435 nm). Our study demonstrates significant enhancement of antitumor activity of Ranpirnase by Photochemical Internalization. Treatment responses were heterogeneous between the primary cancer cell lines. Combining Photochemical Internalization with Ranpirnase resulted in 4.6 to 1,940-fold increased cytotoxicity when compared with the ribonuclease alone (P < 0.05). Cytotoxicity of Ranpirnase can be markedly enhanced by Photochemical Internalization in squamous cell carcinoma of the head and neck.

Application of spectroscopy and super-resolution microscopy: Excited state

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

Bhattacharjee, Ujjal

Photophysics of inorganic materials and organic molecules in complex systems have been extensively studied with absorption and emission spectroscopy.1-4 Steady-state and time-resolved fluorescence studies are commonly carried out to characterize excited-state properties of fluorophores. Although steady-state fluorescence measurements are widely used for analytical applications, time-resolved fluorescence measurements provide more detailed information about excited-state properties and the environment in the vicinity of the fluorophore. Many photophysical processes, such as photoinduced electron transfer (PET), rotational reorientation, solvent relaxation, and energy transfer, occur on a nanosecond (10 -9 s) timescale, thus affecting the lifetime of the fluorophores. Moreover, time-resolved microscopy methods, such asmore » lifetimeimaging, combine the benefits of the microscopic measurement and information-rich, timeresolved data. Thus, time-resolved fluorescence spectroscopy combined with microscopy can be used to quantify these processes and to obtain a deeper understanding of the chemical surroundings of the fluorophore in a small area under investigation. This thesis discusses various photophysical and super-resolution microscopic studies of organic and inorganic materials, which have been outlined below.« less

Structural and Functional Hierarchy in Photosynthetic Energy Conversion—from Molecules to Nanostructures

NASA Astrophysics Data System (ADS)

Szabó, Tibor; Magyar, Melinda; Hajdu, Kata; Dorogi, Márta; Nyerki, Emil; Tóth, Tünde; Lingvay, Mónika; Garab, Győző; Hernádi, Klára; Nagy, László

2015-12-01

Basic principles of structural and functional requirements of photosynthetic energy conversion in hierarchically organized machineries are reviewed. Blueprints of photosynthesis, the energetic basis of virtually all life on Earth, can serve the basis for constructing artificial light energy-converting molecular devices. In photosynthetic organisms, the conversion of light energy into chemical energy takes places in highly organized fine-tunable systems with structural and functional hierarchy. The incident photons are absorbed by light-harvesting complexes, which funnel the excitation energy into reaction centre (RC) protein complexes containing redox-active chlorophyll molecules; the primary charge separations in the RCs are followed by vectorial transport of charges (electrons and protons) in the photosynthetic membrane. RCs possess properties that make their use in solar energy-converting and integrated optoelectronic systems feasible. Therefore, there is a large interest in many laboratories and in the industry toward their use in molecular devices. RCs have been bound to different carrier matrices, with their photophysical and photochemical activities largely retained in the nano-systems and with electronic connection to conducting surfaces. We show examples of RCs bound to carbon-based materials (functionalized and non-functionalized single- and multiwalled carbon nanotubes), transitional metal oxides (ITO) and conducting polymers and porous silicon and characterize their photochemical activities. Recently, we adapted several physical and chemical methods for binding RCs to different nanomaterials. It is generally found that the P+(QAQB)- charge pair, which is formed after single saturating light excitation is stabilized after the attachment of the RCs to the nanostructures, which is followed by slow reorganization of the protein structure. Measuring the electric conductivity in a direct contact mode or in electrochemical cell indicates that there is an electronic interaction between the protein and the inorganic carrier matrices. This can be a basis of sensing element of bio-hybrid device for biosensor and/or optoelectronic applications.

Studies in organic and physical photochemistry - an interdisciplinary approach.

PubMed

Oelgemöller, Michael; Hoffmann, Norbert

2016-08-21

Traditionally, organic photochemistry when applied to synthesis strongly interacts with physical chemistry. The aim of this review is to illustrate this very fruitful interdisciplinary approach and cooperation. A profound understanding of the photochemical reactivity and reaction mechanisms is particularly helpful for optimization and application of these reactions. Some typical reactions and particular aspects are reported such as the Norrish-Type II reaction and the Yang cyclization and related transformations, the [2 + 2] photocycloadditions, particularly the Paternò-Büchi reaction, photochemical electron transfer induced transformations, different kinds of catalytic reactions such as photoredox catalysis for organic synthesis and photooxygenation are discussed. Particular aspects such as the structure and reactivity of aryl cations, photochemical reactions in the crystalline state, chiral memory, different mechanisms of hydrogen transfer in photochemical reactions or fundamental aspects of stereoselectivity are discussed. Photochemical reactions are also investigated in the context of chemical engineering. Particularly, continuous flow reactors are of interest. Novel reactor systems are developed and modeling of photochemical transformations and different reactors play a key role in such studies. This research domain builds a bridge between fundamental studies of organic photochemical reactions and their industrial application.

Rationalizing substituent effects in 1-azathioxanthone photophysics

NASA Astrophysics Data System (ADS)

Junker, Anne Kathrine R.; Just Sørensen, Thomas

2018-01-01

The influence of an electron donating substituent on the photophysical properties of 1-azathioxanthone dyes has been investigated using optical spectroscopy and theoretical models. The motivation behind the study is based on the fact that thioxanthones are efficient triplet sensitizers, and thus promising sensitizers for lanthanide centered emission. By adding an aza group to one of the phenyl ring systems, direct coordination to a lanthanide center becomes possible, which makes azathoixanthones great candidates as antenna chromophores in lanthanide(III) based dyes. Here, three 1-azathioxanthone derivatives have been synthesized targeting efficient triplet formation following absorption in the visible range of the spectrum. This is achieved by adding methoxy groups to the 1-azathioxanthone core. The derivatives were characterized using absorption, emission, and time-gated emission spectroscopy, where fluorescent quantum yields, singlet and triplet excited states lifetimes were determined. The experimentally determined photophysical properties of the three 1-azathioxanthone compounds are contrasted to those of the parent thioxanthone and is rationalized using the Strickler-Berg equation, Hückel MO theory, and Dewar’s rules in combination with computational chemistry. We find that the transition energies follow predictions, but that the overall photophysical properties are determined by the relative energies as well as the nature of the involved states in both the singlet and the triplet excited state manifolds.

Investigation of interaction of an alkaloid harmaline with cucurbit[7]uril: A spectroscopic and calorimetric study

NASA Astrophysics Data System (ADS)

Ahmed, Sayeed Ashique; Seth, Debabrata

2018-01-01

The photophysics of an alkaloid harmaline in aqueous buffer solution and in the presence of cucurbit[7]uril have been studied. The photophysical properties of harmaline were modulated several folds due to addition of cucurbit[7]uril in the aqueous buffer solution. We have observed quenching of fluorescence intensity of harmaline with gradual addition of CB7. Isothermal titration calorimetry technique (ITC) was performed to get an idea about the thermodynamic parameters involved in the complexation process. From ITC, we observed that the complexation process was exothermic in nature and enthalpy driven process.

Zn(II)-coordination modulated ligand photophysical processes – the development of fluorescent indicators for imaging biological Zn(II) ions

PubMed Central

Yuan, Zhao; Simmons, J. Tyler; Sreenath, Kesavapillai

2014-01-01

Molecular photophysics and metal coordination chemistry are the two fundamental pillars that support the development of fluorescent cation indicators. In this article, we describe how Zn(II)-coordination alters various ligand-centered photophysical processes that are pertinent to developing Zn(II) indicators. The main aim is to show how small organic Zn(II) indicators work under the constraints of specific requirements, including Zn(II) detection range, photophysical requirements such as excitation energy and emission color, temporal and spatial resolutions in a heterogeneous intracellular environment, and fluorescence response selectivity between similar cations such as Zn(II) and Cd(II). In the last section, the biological questions that fluorescent Zn(II) indicators help to answer are described, which have been motivating and challenging this field of research. PMID:25071933

Introducing asymmetry in tetradentate azadipyrromethene chromophores: a systematic study of the impact on electronic and photophysical properties.

PubMed

Bessette, André; Cibian, Mihaela; Bélanger, Francis; Désilets, Denis; Hanan, Garry S

2014-10-28

As analogues of the porphyrinoid and dipyrromethene families of dye, azadipyrromethene (ADPM) derivatives exhibit exciting photophysical properties. Their high absorbance (ε up to 100,000 M(-1) cm(-1)) in the yellow-to-red region and the strong NIR luminescence encountered in boron-chelated aza-BODIPY analogues are especially interesting in the context of light-harvesting and life science applications. In the present study, we endeavoured to compare symmetric and asymmetric tetradentate ADPM derivatives 1-6 versus two related bidentate ADPM references in order to gain insights into their structure-property relationship. This is of interest since the tetradentate motif opens the way for extended π-conjugation through metal-mediated planarization, in a bio-mimicry fashion of metalloporphyrinoids, and is known to induce a bathochromic shift toward the NIR. A new straightforward synthetic approach is used to access asymmetric derivatives 4-6 that avoids the tedious heterocycle formation of nitroso-pyrrole intermediates. In addition, photophysics, electrochemistry, computational modelization (DFT and TD-DFT) and X-ray structural characterization of ADPMs are used to better understand the potential of these new chromophores.

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.

Sol-Gel Electrolytes Incorporated by Lanthanide Luminescent Materials and Their Photophysical Properties

NASA Astrophysics Data System (ADS)

Yu, Chufang; Zhang, Zhengyang; Fu, Meizhen; Gao, Jinwei; Zheng, Yuhui

2017-10-01

A group of silica gel electrolytes with lanthanide luminescent hybrid materials were assembled and investigated. Photophysical studies showed that terbium and europium hybrids displayed characteristic green and red emissions within the electrolytes. The influence of different concentration of the lanthanide hybrids on the electrochemical behavior of a gelled electrolyte valve-regulated lead-acid battery were studied through cyclic voltammograms, electrochemical impedance spectroscopy, water holding experiments and mobility tests. The morphology and particle size were analyzed by scanning electron microscopy. The results proved that lanthanide (Tb3+/Eu3+) luminescent materials are effective additives which will significantly improve the electrochemical properties of lead-acid batteries.

Low-level lasers affect uncoupling protein gene expression in skin and skeletal muscle tissues

NASA Astrophysics Data System (ADS)

Canuto, K. S.; Sergio, L. P. S.; Paoli, F.; Mencalha, A. L.; Fonseca, A. S.

2016-03-01

Wavelength, frequency, power, fluence, and emission mode determine the photophysical, photochemical, and photobiological responses of biological tissues to low-level lasers. Free radicals are involved in these responses acting as second messengers in intracellular signaling processes. Irradiated cells present defenses against these chemical species to avoid unwanted effects, such as uncoupling proteins (UCPs), which are part of protective mechanisms and minimize the effects of free radical generation in mitochondria. In this work UCP2 and UCP3 mRNA gene relative expression in the skin and skeletal muscle tissues of Wistar rats exposed to low-level red and infrared lasers was evaluated. Samples of the skin and skeletal muscle tissue of Wistar rats exposed to low-level red and infrared lasers were withdrawn for total RNA extraction, cDNA synthesis, and the evaluation of gene expression by quantitative polymerase chain reaction. UCP2 and UCP3 mRNA expression was differently altered in skin and skeletal muscle tissues exposed to lasers in a wavelength-dependent effect, with the UCP3 mRNA expression dose-dependent. Alteration on UCP gene expression could be part of the biostimulation effect and is necessary to make cells exposed to red and infrared low-level lasers more resistant or capable of adapting in damaged tissues or diseases.

Photochemistry of transition-metal phthalocyanines. Analysis of the photochemical and photophysical properties of the acido(phthalocyaninato)rhodium(III) complexes

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

Ferraudi, G.; Muralidharan, S.

1983-04-01

The ultraviolet photochemistry of the rhodium(II) phthalocyanines Rh(ph)(CH/sub 3/OH)X with X = Cl/sup -/, Br/sup -/, and I/sup -/ was investigated at different wavelengths. The same action spectrum for the photoinduced hydrogen abstraction was obtained for the three compounds. The photonic energy of the excitation is degraded in part by emission at short wavelengths, e.g. lambda/sub max/ approx. = 420 nm. Such a violet emission, observed with phthalocyanines of Al(III), Rh(III), Co(III), and Ru(II), has been attributed to the relaxation of an upper /sup 3/par. deltapar. delta* excited state. The emissions spectra at 77 K exhibited vibronic components with amore » separation between successive peaks ..delta nu.. approx. = 1.3 x 10/sup 3/ cm/sup -1/. A comparison between the excitation and action spectra shows the difference in the paths that populate the reactive npar. delta* and upper emissive par. deltapar. delta* states. An investigation of the time dependence of the upper /sup 3/par. deltapar. delta* emission and lowest /sup 3/par. deltapar. delta* absorptions reveals the participation of triplet sublevels in the degradation of the excitation energy. The relationship between photoemissive and photoreactive states is discussed.« less

Photochemistry of transition-metal phthalocyanines. Analysis of the photochemical and photophysical properties of the acido(phthalocyaninato)rhodium(III) complexes

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

Ferraudi, G.; Muralidharan, S.

1983-01-01

The ultraviolet photochemistry of the rhodium(III) phthalocyanines Rh(ph)(CH/sub 3/OH)X with X = Cl/sup -/, Br/sup -/, and I/sup -/ was investigated at different wavelengths. The same action spectrum for the photoinduced hydrogen abstraction was obtained for the three compounds. The photonic energy of the excitation is degraded in part by emission at short wavelengths, e.g. lambda/sub max/ approx. = 420 nm. Such a violet emission, observed with phthalocyanines of Al(III), Rh(III), Co(III), and Ru(II), has been attributed to the relaxation of an upper /sup 3/pipi* excited state. The emission spectra at 77 K exhibited vibronic components with a separation betweenmore » successive peaks ..delta..v approx. = 1.3 x 10/sup 3/ cm/sup -1/. A comparison between the excitation and action spectra shows the difference in the paths that populate the reactive npi* and upper emissive pipi* states. An investigation of the time dependence of the upper /sup 3/pipi* emission and lowest /sup 3/pipi* absorptions reveals the participation of triplet sublevels in the degradation of the excitation energy. The relationship between photoemissive and photoreactive states is discussed. 40 references, 6 figures, 2 tables.« less

All you need is light

PubMed Central

St. Denis, Tyler G; Dai, Tianhong; Izikson, Leonid; Astrakas, Christos; Anderson, Richard Rox; Hamblin, Michael R

2011-01-01

The story of prevention and control of infectious diseases remains open and a series of highly virulent pathogens are emerging both in and beyond the hospital setting. Antibiotics were an absolute success story for a previous era. The academic and industrial biomedical communities have now come together to formulate consensus beliefs regarding the pursuit of novel and effective alternative anti-infective countermeasures. Photodynamic therapy was established and remains a successful modality for malignancies but photodynamic inactivation has been transformed recently to an antimicrobial discovery and development platform. The concept of photodynamic inactivation is quite straightforward and requires microbial exposure to light energy, typically wavelengths in the visible region, that causes the excitation of photosensitizer molecules (either exogenous or endogenous), which results in the production of singlet oxygen and other reactive oxygen species that react with intracellular components, and consequently produce cell inactivation. It is an area of increasing interest, as research is advancing (1) to identify the photochemical and photophysical mechanisms involved in inactivation, (2) to develop potent and clinically compatible photosensitizer, (3) to understand how photoinactivation is affected by key microbial phenotypic elements (multidrug resistance and efflux, virulence and pathogenesis determinants, biofilms), (4) to explore novel delivery platforms inspired by current trends in pharmacology and nanotechnology and (5) to identify photoinactivation applications beyond the clinical setting such as environmental disinfectants. PMID:21971183

Development of a tunable femtosecond stimulated raman apparatus and its application to beta-carotene.

PubMed

Shim, Sangdeok; Mathies, Richard A

2008-04-17

We have developed a tunable femtosecond stimulated Raman spectroscopy (FSRS) apparatus and used it to perform time-resolved resonance Raman experiments with <100 fs temporal and <35 cm(-1) spectral resolution. The key technical change that facilitates this advance is the use of a tunable narrow-bandwidth optical parametric amplifier (NB-OPA) presented recently by Shim et al. (Shim, S.; Mathies, R. A. Appl. Phys. Lett. 2006, 89, 121124). The practicality of tunable FSRS is demonstrated by examining the photophysical dynamics of beta-carotene. Using 560 nm Raman excitation, the resonant S1 state modes are enhanced by a factor of approximately 200 compared with 800 nm FSRS experiments. The improved signal-to-noise ratios facilitate the measurement of definitive time constants for beta-carotene dynamics including the 180 fs appearance of the S1 vibrational features due to direct internal conversion from S2 and their characteristic 9 ps decay to S0. By tuning the FSRS system to 590 nm Raman excitation, we are able to selectively enhance vibrational features of the hot ground state S hot 0 and monitor its approximately 5 ps cooling dynamics. This tunable FSRS system is valuable because it facilitates the direct observation of structural changes of selected resonantly enhanced states and intermediates during photochemical and photobiological reactions.

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.

Relaxation Mechanisms of 5-Azacytosine.

PubMed

Giussani, Angelo; Merchán, Manuela; Gobbo, João Paulo; Borin, Antonio Carlos

2014-09-09

The photophysics and deactivation pathways of the noncanonical 5-azacytosine nucleobase were studied using the CASPT2//CASSCF protocol. One of the most significant differences with respect to the parent molecule cytosine is the presence of a dark (1)(nNπ*) excited state placed energetically below the bright excited state (1)(ππ*) at the Franck-Condon region. The main photoresponse of the system is a presumably efficient radiationless decay back to the original ground state, mediated by two accessible conical intersections involving a population transfer from the (1)(ππ*) and the (1)(nNπ*) states to the ground state. Therefore, a minor contribution of the triplet states in the photophysics of the system is expected, despite the presence of a deactivation path leading to the lowest (3)(ππ*) triplet state. The global scenario on the photophysics and photochemistry of the 5-azacytosine system gathered on theoretical grounds is consistent with the available experimental data, taking especially into account the low values of the singlet-triplet intersystem crossing and fluorescence quantum yields observed.

Substituent effect on photophysical properties of bi-1,3,4-oxadiazole derivatives in solution

NASA Astrophysics Data System (ADS)

Chen, Fangyi; Tian, Taiji; Zhao, Chengxiao; Bai, Binglian; Li, Min; Wang, Haitao

2016-04-01

A series of phenyl substituted bi-1,3,4-oxadiazole derivatives were designed and synthesized; the effect of substituent on the photophysical properties and molecular electronic structures was fully studied by the combination of experimental techniques and theoretical calculations. Compared to parent compound without any substituent (BOXD), fluoro-substituent shows little effect on the absorption and emission spectra, whilst a little larger spectral red-shift could be observed for methoxy-, nitro-substituted derivatives and thienyl-substituted bi-1,3,4-oxadiazole (TBOXD). These spectral changes can be well explained by theoretically calculated HOMO and LUMO energy level changes. All these molecules show high fluorescence quantum yield except for nitro-substituted derivative in dilute solutions. The quantum yield of BOXD changes with the concentration and exhibits a high value at the concentrated solution. This work revealed the influence of substituent on the photophysical properties of bi-1,3,4-oxadizaole derivatives in dilute solutions and provided guidance for designing molecules with potential application.

The effect of annulation of benzene rings on the photophysics and electronic structure of tetraazachlorin molecules

NASA Astrophysics Data System (ADS)

Pershukevich, P. P.; Volkovich, D. I.; Gladkov, L. L.; Dudkin, S. V.; Kuzmitsky, V. A.; Makarova, E. A.; Solovyev, K. N.

2017-10-01

The photophysics and electronic structure of tribenzotetraazachlorins (H2, Zn, and Mg), which are novel analogues of phtalocyanines, have been studied experimentally and theoretically. At 293 K, the electronic absorption, fluorescence, and fluorescence excitation spectra are recorded and the fluorescence quantum yield and lifetime, as well as the quantum yield of singlet oxygen generation, are measured; at 77 K, the fluorescence, fluorescence excitation, and fluorescence polarization spectra are recorded and the fluorescence lifetime values are measured. The dependences of the absorption spectra and photophysical parameters on the structure variation are analyzed in detail. Quantum-chemical calculations of the electronic structure and absorption spectra of tribenzotetraazachlorins (H2, Mg) are performed using the INDO/Sm method (modified INDO/S method) based on molecular-geometry optimization by the DFT PBE/TZVP method. The results of quantum-chemical calculations of the electronic absorption spectra are in very good agreement with the experimental data for the transitions to two lower electronic states.

STUDY USING A THREE-DIMENSIONAL PHOTOCHEMICAL SMOG FORMATION MODEL UNDER CONDITIONS OF COMPLEX FLOW: APPLICATION OF THE URBAN AIRSHED MODEL TO THE TOKYO METROPOLITAN AREA

EPA Science Inventory

The purpose of this study is to evaluate the Urban Airshed Model (UAM), a three-dimensional photochemical urban air quality simulation model, using field observations from the Tokyo Metropolitan Area. mphasis was placed on the photochemical smog formation mechanism under stagnant...

Ultrafast studies of organometallic photochemistry: The mechanism of carbon-hydrogen bond activation in solution

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

Bromberg, S.E.

1998-05-01

When certain organometallic compounds are photoexcited in room temperature alkane solution, they are able to break or activate the C-H bonds of the solvent. Understanding this potentially practical reaction requires a detailed knowledge of the entire reaction mechanism. Because of the dynamic nature of chemical reactions, time-resolved spectroscopy is commonly employed to follow the important events that take place as reactants are converted to products. For the organometallic reactions examined here, the electronic/structural characteristics of the chemical systems along with the time scales for the key steps in the reaction make ultrafast UV/Vis and IR spectroscopy along with nanosecond Step-Scanmore » FTIR spectroscopy the ideal techniques to use for this study. An initial study of the photophysics of (non-activating) model metal carbonyls centering on the photodissociation of M(CO){sub 6} (M = Cr, W, Mo) was carried out in alkane solutions using ultrafast IR spectroscopy. Next, picosecond UV/vis studies of the C-H bond activation reaction of Cp{sup *}M(CO){sub 2} (M = Rh, Ir), conducted in room temperature alkane solution, are described in an effort to investigate the origin of the low quantum yield for bond cleavage ({approximately}1%). To monitor the chemistry that takes place in the reaction after CO is lost, a system with higher quantum yield is required. The reaction of Tp{sup *}Rh(CO){sub 2} (Tp{sup *} = HB-Pz{sub 3}{sup *}, Pz{sup *} = 3,5-dimethylpyrazolyl) in alkanes has a quantum yield of {approximately}30%, making time resolved spectroscopic measurements possible. From ultrafast IR experiments, two subsequently formed intermediates were observed. The nature of these intermediates are discussed and the first comprehensive reaction mechanism for a photochemical C-H activating organometallic complex is presented.« less

Photophysical studies on curcumin-sophorolipid nanostructures: applications in quorum quenching and imaging

PubMed Central

2018-01-01

Sophorolipid biosurfactants are biodegradable, less toxic and FDA approved. The purified acidic form of sophorolipid is stimuli-responsive with self-assembling properties and used for solubilizing hydrophobic drugs. This study encapsulated curcumin (CU) with acidic sophorolipid (ASL) micelles and analysed using photophysical studies like UV-visible spectroscopy, photoluminescence (PL) spectroscopy and time-correlated single photon counting (TCSPC). TEM images have revealed ellipsoid micelles of approximately 100 nm size and were confirmed by dynamic light scattering. The bacterial fluorescence uptake studies showed the uptake of formed CUASL nanostructures into both Gram-positive and Gram-negative bacteria. They also showed quorum quenching activity against Pseudomonas aeruginosa. The results have demonstrated this system has potential theranostic applications. PMID:29515826

The application of the micronucleus test in Chinese hamster V79 cells to detect drug-induced photogenotoxicity.

PubMed

Kersten, B; Zhang, J; Brendler-Schwaab, S Y; Kasper, P; Müller, L

1999-09-15

Recent reports on the photochemical carcinogenicity and photochemical genotoxicity of fluoroquinolone antibacterials led to an increasing awareness for the need of a standard approach to test for photochemical genotoxicity. In this study the micronucleus test using V79 cells was adapted to photogenotoxicity testing. Results of using different UVA/UVB relationships enabled us to identify a suitable irradiation regimen for the activation of different kinds of photosensitizers. Using this regimen, 8-methoxypsoralen and the fluoroquinolones lomefloxacin, grepafloxacin and Bay Y 3118 were identified to cause micronuclei and toxicity upon photochemical activation. Among the phenothiazines tested, chlorpromazine and 2-chlorophenothiazine, were positive for both endpoints, whereas triflupromazine was only slightly photoclastogenic in the presence of strong phototoxicity. Among the other potential human photosensitizers tested (oxytetracycline, doxycycline, metronidazole, emodin, hypericin, griseofulvin), only hypericin was slightly photogenotoxic. Photochemical toxicity in the absence of photochemical genotoxicity was noted for doxycycline and emodin. With the assay system described, it is possible to determine photochemical toxicity and photochemical genotoxicity concomitantly with sufficient reliability.

Analysis of the photophysical properties of zearalenone using density functional theory

USDA-ARS?s Scientific Manuscript database

The intrinsic photophysical properties of the resorcylic acid moiety of zearalenone offer a convenient label free method to determine zearalenone levels in contaminated agricultural products. Density functional theory and steady-state fluorescence methods were applied to investigate the role of stru...

Mitochondria-targeting for improved photodynamic therapy

NASA Astrophysics Data System (ADS)

Ngen, Ethel J.

Photodynamic therapy (PDT) is an emerging cancer therapeutic modality, with great potential to selectively treat surface cancers, thus minimizing systemic side effects. In this dissertation, two approaches to deliver photosensitizers to mitochondria were investigated: 1) Reducing photosensitizer sizes to improve endocytosis and lysosomal localization. Upon irradiation the photosensitizers would then produce singlet oxygen which could rupture the lysosomal membrane releasing the lysosomally trapped photosensitizers to the cytosol, from where they could relocalize to mitochondria by passive diffusion (photochemical internalization). 2) Using delocalized lipophilic cationic dyes (DLCs) to exploit membrane potential differences between the cytoplasm and mitochondria in delivering photosensitizers to mitochondria. To investigate the effects of steric hindrance on mitochondrial localization and photodynamic response, a series of eight thiaporphyrins were studied. Two new thiaporphyrin analogues 6 and 8 with reduced steric hindrance at the 10- and 15- meso positions were studied in comparison to 5,20-diphenyl-10,15-bis[4 (carboxymethyleneoxy)-phenyl]-21,23-dithiaporphyrin 1, previously validated as a potential second generation photosensitizer. Although 6 showed an extraordinarily high uptake (7.6 times higher than 1), it was less potent than 1 (IC 50 = 0.18 muM versus 0.13 muM) even though they both showed similar sub-cellular localization patterns. This low potency was attributed to its high aggregation tendency in aqueous media (4 times higher than 1), which might have affected its ability to generate singlet oxygen in vitro . 8 on the other hand showed an even lower potency than 6 (2.28 vs 0.18 muM). However this was attributed to its low cellular uptake (20 times less than 6) and inefficient generation of singlet oxygen. Overall, although the structural modifications did improve the cellular uptake of 6, 6 was still less potent than the lead photosensitizers 1. Thus, other strategies to target mitochondria for improved photodynamic activity were investigated. In a continuing project, we evaluated the ability of delocalized lipophilic cationic dyes to deliver photosensitizers to mitochondria by exploiting the membrane potential difference between the cytoplasm and mitochondria. Two conjugates: a porphyrin--rhodamine B conjugate (TPP--Rh) and a porphyrin-acridine orange conjugate (TPP--AO), each possessing a single delocalized lipophilic cation, were designed and synthesized. The conjugates were synthesized by conjugating a monohydroxy porphyrin (TPP-OH) to rhodamine B (Rh B) and acridine orange base (AO), respectively, via saturated hydrocarbon linkers. To evaluate the efficiency of the conjugates as photosensitizers, their photophysical properties and in vitro photodynamic activities were studied in comparison to those of TPP-OH, the parent porphyrin photosensitizer. Although fluorescence energy transfer (FRET) was observed in the conjugates, they were capable of generating singlet oxygen at rates comparable to TPP-OH. In a final project, we evaluated the photophysical potential of TPP-Rh to act as a two-photon photosensitizer for PDT. Two-photon PDT is a rational approach used to improve light penetration through the skin. Rhodamine B is an effective two-photon chromophore and could significantly improve the two-photon absorption of the porphyrin photosensitizer in the TPP-Rh dyad system following energy transfer. Thus the porphyrin--rhodamine B dyad (TPP--Rh), previously demonstrated to preferentially accumulate in the mitochondria, was photophysically evaluated as a potential two-photon photosensitizer. To evaluate the efficiency of TPP-Rh as a two-photon photosensitizer, its two-photon photophysical properties were compared with those of its individual components (Rh B and TPP-OH). This included: the two-photon cross sections (sigma 2), RET kinetics and dynamics and rates of singlet oxygen generation. A FRET efficiency of ~99 % was observed from the Rh moiety (donor) to the TPP moiety (acceptor) of the system. This significantly enhanced the sigma 2 of TPP-Rh by ˜ 100 % (20 GM) compared to the parent TPP-OH. Furthermore, TPP-Rh produced singlet oxygen at a significantly faster rate than TPP-OH upon two-photon excitation. Thus, this indicates that conjugating photosensitizers to Rh B via short saturated hydrocarbon linkers could provide deeper tissue penetration, in addition to preferential mitochondrial accumulation for improved photodynamic response. (Abstract shortened by UMI.)

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.

Solvent organization around the perfluoro group of coumarin 153 governs its photophysical properties: An experimental and simulation study of coumarin dyes in ethanol as well as fluorinated ethanol solvents.

PubMed

Mondal, Saptarsi; Halder, Ritaban; Biswas, Biswajit; Jana, Biman; Singh, Prashant Chandra

2016-05-14

The self-aggregation property of the perfluoro group containing molecules makes it important in the research fields of biology and polymer and organic synthesis. In the quest of understanding the role of the perfluoro group on the photophysical properties of perfluoro-containing molecules in biologically important fluoroethanol solvents, we have applied photophysical as well as molecular dynamics simulation techniques to explore the properties of perfluoro groups containing molecule coumarin-153 (C153) in ethanol (ETH), monofluoroethanol (MFE), difluoroethanol (DFE), and trifluoroethanol (TFE) and compared them with the molecules without perfluoro moiety, namely coumarin-6H (C6H) and coumarin-480 (C480). In contrast to C6H and C480, the excited state lifetime of C153 in fluorinated ETHs is not monotonic. The excited state lifetime of C153 decreases in MFE and DFE as compared to ETH, whereas in TFE, it increases as compared to MFE and DFE. Molecular dynamics simulation reveals that the carbon terminal away from the OH group of fluorinated ETHs has a preferential orientation near the perfluoro (CF3) group of C153. In MFE and DFE, the CF3 group of C153 prefers to have a CF2-F⋯H -(CHF) type of electrostatic interaction over CF2-F⋯F -(CH2) kind of dispersion interaction which increases the rate of nonradiative decay, probably due to the electrostatic nature of the CF2-F⋯H -(CHF) hydrogen bond. On the other hand, in TFE, C-F⋯ F-C type of dispersion interaction, also known as fluorous interaction, takes place between the CF3 groups of C153 and TFE which decreases the rate of nonradiative rate as compared to MFE and DFE, leading to the increased lifetime of C153 in TFE. Photophysical and MD simulation studies clearly depict that the structural organization of solvents and their interaction with the fluorocarbon group are crucial factors for the photophysical behavior of the fluorocarbon containing molecules.

Solvent organization around the perfluoro group of coumarin 153 governs its photophysical properties: An experimental and simulation study of coumarin dyes in ethanol as well as fluorinated ethanol solvents

NASA Astrophysics Data System (ADS)

Mondal, Saptarsi; Halder, Ritaban; Biswas, Biswajit; Jana, Biman; Singh, Prashant Chandra

2016-05-01

The self-aggregation property of the perfluoro group containing molecules makes it important in the research fields of biology and polymer and organic synthesis. In the quest of understanding the role of the perfluoro group on the photophysical properties of perfluoro-containing molecules in biologically important fluoroethanol solvents, we have applied photophysical as well as molecular dynamics simulation techniques to explore the properties of perfluoro groups containing molecule coumarin-153 (C153) in ethanol (ETH), monofluoroethanol (MFE), difluoroethanol (DFE), and trifluoroethanol (TFE) and compared them with the molecules without perfluoro moiety, namely coumarin-6H (C6H) and coumarin-480 (C480). In contrast to C6H and C480, the excited state lifetime of C153 in fluorinated ETHs is not monotonic. The excited state lifetime of C153 decreases in MFE and DFE as compared to ETH, whereas in TFE, it increases as compared to MFE and DFE. Molecular dynamics simulation reveals that the carbon terminal away from the OH group of fluorinated ETHs has a preferential orientation near the perfluoro (CF3) group of C153. In MFE and DFE, the CF3 group of C153 prefers to have a CF2—F⋯H —(CHF) type of electrostatic interaction over CF2—F⋯F —(CH2) kind of dispersion interaction which increases the rate of nonradiative decay, probably due to the electrostatic nature of the CF2—F⋯H —(CHF) hydrogen bond. On the other hand, in TFE, C—F⋯ F—C type of dispersion interaction, also known as fluorous interaction, takes place between the CF3 groups of C153 and TFE which decreases the rate of nonradiative rate as compared to MFE and DFE, leading to the increased lifetime of C153 in TFE. Photophysical and MD simulation studies clearly depict that the structural organization of solvents and their interaction with the fluorocarbon group are crucial factors for the photophysical behavior of the fluorocarbon containing molecules.

Ultrafast photophysics of transition metal complexes.

PubMed

Chergui, Majed

2015-03-17

The properties of transition metal complexes are interesting not only for their potential applications in solar energy conversion, OLEDs, molecular electronics, biology, photochemistry, etc. but also for their fascinating photophysical properties that call for a rethinking of fundamental concepts. With the advent of ultrafast spectroscopy over 25 years ago and, more particularly, with improvements in the past 10-15 years, a new area of study was opened that has led to insightful observations of the intramolecular relaxation processes such as internal conversion (IC), intersystem crossing (ISC), and intramolecular vibrational redistribution (IVR). Indeed, ultrafast optical spectroscopic tools, such as fluorescence up-conversion, show that in many cases, intramolecular relaxation processes can be extremely fast and even shorter than time scales of vibrations. In addition, more and more examples are appearing showing that ultrafast ISC rates do not scale with the magnitude of the metal spin-orbit coupling constant, that is, that there is no heavy-atom effect on ultrafast time scales. It appears that the structural dynamics of the system and the density of states play a crucial role therein. While optical spectroscopy delivers an insightful picture of electronic relaxation processes involving valence orbitals, the photophysics of metal complexes involves excitations that may be centered on the metal (called metal-centered or MC) or the ligand (called ligand-centered or LC) or involve a transition from one to the other or vice versa (called MLCT or LMCT). These excitations call for an element-specific probe of the photophysics, which is achieved by X-ray absorption spectroscopy. In this case, transitions from core orbitals to valence orbitals or higher allow probing the electronic structure changes induced by the optical excitation of the valence orbitals, while also delivering information about the geometrical rearrangement of the neighbor atoms around the atom of interest. With the emergence of new instruments such as X-ray free electron lasers (XFELs), it is now possible to perform ultrafast laser pump/X-ray emission probe experiments. In this case, one probes the density of occupied states. These core-level spectroscopies and other emerging ones, such as photoelectron spectroscopy of solutions, are delivering a hitherto unseen degree of detail into the photophysics of metal-based molecular complexes. In this Account, we will give examples of applications of the various methods listed above to address specific photophysical processes.

Air Quality Criteria for Ozone and Other Photochemical Oxidants. External Review Draft No 1. Volume III

EPA Science Inventory

This review of the effects of photochemical oxidants on vegetation and the responses of vegetation to photochemical oxidants first discusses the general methodologies used in studies of air pollution effects to provide a basis for understanding the methods, approaches, and experi...

A photophysical study of two fluorogen-activating proteins bound to their cognate fluorogens

NASA Astrophysics Data System (ADS)

Gaiotto, Tiziano; Nguyen, Hau B.; Jung, Jaemyeong; Gnanakaran, Gnana S.; Schmidt, Jurgen G.; Waldo, Geoffrey S.; Bradbury, Andrew M.; Goodwin, Peter M.

2011-03-01

We are exploring the use of fluorogen-activating proteins (FAPs) as reporters for single-molecule imaging. FAPs are single-chain antibodies selected to specifically bind small chromophoric molecules termed fluorogens. Upon binding to its cognate FAP the fluorescence quantum yield of the fluorogen increases giving rise to a fluorescent complex. Based on the seminal work of Szent-Gyorgyi et al. (Nature Biotechnology, Volume 26, Number 2, pp 235-240, 2008) we have chosen to study two fluorogen-activating single-chain antibodies, HL1.0.1-TO1 and H6-MG, bound to their cognate fluorogens, thiazole orange and malachite green derivatives, respectively. Here we use fluorescence correlation spectroscopy to study the photophysics of these fluorescent complexes.

Photophysical and electrical properties of polyphenylquinolines containing carbazole or indolo[3,2-b]carbazole fragments as new optoelectronic materials

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

Svetlichnyi, V. M., E-mail: valsvet@hq.macro.ru; Aleksandrova, E. L.; Myagkova, L. A.

2011-10-15

Photophysical and electrical properties of new synthesized 2,6-polyphenylquinolines (PPQs) containing an oxygen or phenylamine bridging group between quinoline cycles and, as an arylene radical, alkylated derivatives of carbazole or indolo[3,2-b]carbazole are studied. It is shown that the photosensitivity for new PPQs is 10{sup 4}-10{sup 5} cm{sup 2}/J and the photogeneration quantum yield of free carriers is as high as 0.15. Photophysical parameters increase with the phenylamine bridging group in place of the oxygen one and when using indolocarbazole instead of carbazole. It is found that a film of polyphenylquinoline containing an oxygen bridging group and an alkylcarbazole fragment in themore » polymer repeat unit exhibits 'white' luminescence. Both electron and hole transport with a mobility of {approx}10{sup -6} cm{sup 2}/(V s) are detected in films of all studied polymers. The conductivity value and type can be controlled by varying the chemical structure of the (oxygen or phenylamine) bridging group between PPQ cycles and by choosing carbazole or indolo[3,2-b]carbazole derivatives as an arylene radical.« less

Diiodobodipy-styrylbodipy Dyads: Preparation and Study of the Intersystem Crossing and Fluorescence Resonance Energy Transfer.

PubMed

Wang, Zhijia; Xie, Yun; Xu, Kejing; Zhao, Jianzhang; Glusac, Ksenija D

2015-07-02

2,6-Diiodobodipy-styrylbodipy dyads were prepared to study the competing intersystem crossing (ISC) and the fluorescence-resonance-energy-transfer (FRET), and its effect on the photophysical property of the dyads. In the dyads, 2,6-diiodobodipy moiety was used as singlet energy donor and the spin converter for triplet state formation, whereas the styrylbodipy was used as singlet and triplet energy acceptors, thus the competition between the ISC and FRET processes is established. The photophysical properties were studied with steady-state UV-vis absorption and fluorescence spectroscopy, electrochemical characterization, and femto/nanosecond time-resolved transient absorption spectroscopies. FRET was confirmed with steady state fluorescence quenching and fluorescence excitation spectra and ultrafast transient absorption spectroscopy (kFRET = 5.0 × 10(10) s(-1)). The singlet oxygen quantum yield (ΦΔ = 0.19) of the dyad was reduced as compared with that of the reference spin converter (2,6-diiodobodipy, ΦΔ = 0.85), thus the ISC was substantially inhibited by FRET. Photoinduced intramolecular electron transfer (ET) was studied by electrochemical data and fluorescence quenching. Intermolecular triplet energy transfer was studied with nanosecond transient absorption spectroscopy as an efficient (ΦTTET = 92%) and fast process (kTTET = 5.2 × 10(4) s(-1)). These results are useful for designing organic triplet photosensitizers and for the study of the photophysical properties.

UV laser photoactivation of hexachloroplatinate bound to individual nucleobases in vacuo as molecular level probes of a model photopharmaceutical.

PubMed

Matthews, Edward; Sen, Ananya; Yoshikawa, Naruo; Bergström, Ed; Dessent, Caroline E H

2016-06-01

Isolated molecular clusters of adenine, cytosine, thymine and uracil bound to hexachloroplatinate, PtCl6(2-), have been studied using laser electronic photodissociation spectroscopy to investigate photoactivation of a platinum complex in the vicinity of a nucleobase. These metal complex-nucleobase clusters represent model systems for identifying the fundamental photochemical processes occurring in photodynamic platinum drug therapies that target DNA. This is the first study to explore the specific role of a strongly photoactive platinum compound in the aggregate complex. Each of the clusters studied displays a broadly similar absorption spectra, with a strong λmax ∼ 4.6 eV absorption band and a subsequent increase in the absorption intensity towards higher spectral-energy. The absorption bands are traced to ligand-to-metal-charge-transfer excitations on the PtCl6(2-) moiety within the cluster, and result in Cl(-)·nucleobase and PtCl5(-) as primary photofragments. These results demonstrate how selective photoexcitation can drive distinctive photodecay channels for a model photo-pharmaceutical. In addition, cluster absorption due to excitation of nucleobase-centred chromophores is observed in the region around 5 eV. For the uracil cluster, photofragments consistent with ultrafast decay of the excited state and vibrational predissociation on the ground-state surface are observed. However, this decay channel becomes successively weaker on going from thymine to cytosine to adenine, due to differential coupling of the excited states to the electron detachment continuum. These effects demonstrate the distinctive photophysical characteristics of the different nucleobases, and are discussed in the context of the recently recorded photoelectron spectra of theses clusters.

Photochemical properties of squarylium cyanine dyes.

PubMed

Ferreira, D P; Conceição, D S; Ferreira, V R A; Graça, V C; Santos, P F; Vieira Ferreira, L F

2013-11-01

This study presents several new squarylium dyes derived from benzothiazole and benzoselenazole with several structural variations, namely the nature of the heteroaromatic ring and the length of the N,N'-dialkyl groups. Before being investigated in connection with their effect on living cells and/or tissues, these novel compounds were characterized, namely with respect to the determination of their main photophysical parameters. Therefore, a study of the ground state absorption, fluorescence emission (quantum yields and lifetimes) and singlet oxygen generation quantum yields was performed for all the compounds synthesized in order to evaluate their efficiency as photosensitizers. An increase of the alkyl chain length from ethyl to hexyl did not produce a clear change in the fluorescence quantum yields, showing no influence on the photoisomerization process. Heavy atom inclusion (Se instead of S) enhanced the singlet oxygen generation efficiency and decreased the intensity of the fluorescence emission. The external heavy atom effect (I(-) as a counterion instead of CF3SO3(-)) produced a significant increase in the singlet oxygen formation quantum yield (about 20%). Transient absorption studies in aerated and oxygen free samples revealed that the photoisomerization process, which could compete with the triplet state formation for all dyes in solution, is a negligible pathway for the excited state deactivation, in accordance with the rigidity introduced by the squaric ring into the polymethine chain of the dye, both in chloroform and ethanol. However, in the case of the chloroform solution a new transient was detected in air equilibrated solutions, resulting from a reaction of the excited squarylium dye in the singlet state with CHCl3˙, and assigned to the radical cation (SQ(+)˙) of the dye.

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.

Photochemical reactions of aromatic compounds and the concept of the photon as a traceless reagent.

PubMed

Hoffmann, Norbert

2012-11-01

Electronic excitation significantly changes the reactivity of chemical compounds. Compared to ground state reactions, photochemical reactions considerably enlarge the application spectrum of a particular functional group in organic synthesis. Multistep syntheses may be simplified and perspectives for target oriented synthesis (TOS) and diversity oriented synthesis (DOS) are developed. New compound families become available or may be obtained more easily. In contrast to common chemical reagents, photons don't generate side products resulting from the transformation of a chemical reagent. Therefore, they are considered as a traceless reagent. Consequently, photochemical reactions play a central role in the methodology of sustainable chemistry. This aspect has been recognized since the beginning of the 20th century. As with many other photochemical transformations, photochemical reactions of aromatic, benzene-like compounds illustrate well the advantages in this context. Photochemical cycloadditions of aromatic compounds have been investigated for a long time. Currently, they are applied in various fields of organic synthesis. They are also studied in supramolecular structures. The phenomena of reactivity and stereoselectivity are investigated. During recent years, photochemical electron transfer mediated reactions are particularly focused. Such transformations have likewise been performed with aromatic compounds. Reactivity and selectivity as well as application to organic synthesis are studied.

Photophysical characterization of fluorescent metal nanoclusters synthesized using oligonucleotides, proteins and small molecule ligands

NASA Astrophysics Data System (ADS)

Yeh, Hsin-Chih; Sharma, Jaswinder; Yoo, Hyojong; Martinez, Jennifer S.; Werner, James H.

2010-02-01

The size transition from bulk conducting metals to insulating nanoparticles and eventually to single atoms passes through the relatively unexplored few-atom nanocluster region. With dimensions close to the Fermi wavelength, these nanoclusters demonstrate molecule-like properties distinct from bulk metals or atoms, such as discrete and size-tunable electronic transitions which lead to photoluminescence. Current research aims to elucidate the fundamental photophysical properties of metal nanoclusters made by different means and based on different encapsulation agents. Here, we report the study of the photophysical properties, including quantum yields, lifetimes, extinction coefficients, blinking dynamics and sizes, of silver and gold nanoclusters synthesized using oligonucleotides, a protein (bovine serum albumin) and a Good's buffer molecule (MES, 2-(N-morpholino) ethanesulfonic acid) as encapsulation agents. We also investigate the change of photoluminescence as a function of temperature. Furthermore, we show that the fluorescent metal clusters can be used as a donor in forming a resonance energy transfer pair with a commercial organic quencher. These new fluorophores have great potential as versatile tools for a broad range of applications in biological and chemical detection.

Superradiance of J-Aggregated 2,2'-Cyanine Absorbed onto a Vesicle Surface

NASA Technical Reports Server (NTRS)

Akins, Daniel L.; Ozcelik, Serdar

1995-01-01

Phospholipid vesicles are used as substrates to form adsorbed aggregates of 2,2'-cyanine, also referred to as pseudoisocyanine (PIC). In this paper, we report photophysical parameters of two putative adsorbed aggregates species (cis- and trans-aggregates, relating to their makeup from mono-cis and all-transstereoisomers, respectively). Phase modulation picosecond fluorescence decay measurements reveal that superradiance and energy transfer are dominant features controlling photophysical processes. Superradiance, coherence size, energy transfer and exciton-phonon coupling are discussed for the two types of aggregates; as regards photophysical parameters, the fluorescence lifetimes, fluorescence quantum yields, and nonradiative rate constants are determined. It is suggested that structure plays the crucial role in excited state dynamics.

Photophysics of aggregated 9-methylthiacarbocyanine bound to polyanions

NASA Astrophysics Data System (ADS)

Chibisov, Alexander K.; Görner, Helmut

2002-05-01

The photophysical properties of 3,3 '-diethyl-9-methylthiacarbocyanine (DTC) were studied in the presence of polystyrene sulfonate (PSS), polyacrylic acid (PAA) and polymethacrylic acid (PMA). The absorption spectra reflect a monomer/dimer equilibrium in neat aqueous solution and a shift towards bound H-aggregates, bound dimers and bound monomers on increasing the ratio of polyanion residue to dye concentrations ( r). These equilibria also determine the photodeactivation modes of DTC. The fluorescence intensity is reduced, when dimers and aggregates are present and strongly enhanced for low dye loading ( r=10 4). In contrast, the quantum yield of intersystem crossing is enhanced for bound dimers ( r=10 3).

Asymmetric rhenium tricarbonyl complexes show superior luminescence properties in live cell imaging.

PubMed

Raszeja, Lukasz J; Siegmund, Daniel; Cordes, Anna L; Güldenhaupt, Jörn; Gerwert, Klaus; Hahn, Stephan; Metzler-Nolte, Nils

2017-01-16

The synthesis and photophysical properties of a novel series of rhenium tricarbonyl complexes based on tridentate phenanthridinyl-containing ligands are described. Photophysical data reveal beneficial luminescence behaviour especially for compounds with an asymmetric ligand set. These advantageous properties are not limited to organic solvents, but indeed also improved in aqueous solutions. The suitability of our new rhenium complexes as potent imaging agents has been confirmed by fluorescence microscopy on living cancer cells, which also confirms superior long-time stability under fluorescence microscopy conditions. Colocalisation studies with commercial organelle stains reveal an accumulation of the complexes in the endoplasmic reticulum for all tested cell lines.

A photophysical study of two fluorogen-activating proteins bound to their cognate fluorogens

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

Gaiotto, Tiziano; Nguyen, Hau B; Jung, Jaemyeong

We are exploring the feasibility of using recently developed flu orogen-activating proteins (FAPs) as reporters for single-molecule imaging. FAPs are single-chain antibodies choosen to specifically bind small chromophoric molecules termed f1uorogens. Upon binding to its cognate FAP the fluorescence quantum yield of the fluorogen can increase substantially giving rise to a fluorescent complex. Based on the seminal work of Szent-Gyorgyi et al. (Nature Biotechnology, Volume 26, Number 2, pp 235-240, 2008) we have chosen to study two fluorogen-activating single-chain antibodies, HL 1.0.1-TOI and H6-MG bound to their cognate fluorogens, thiazole orange and malachite green derivatives, respectively. Here we use fluorescencemore » correlation spectroscopy study the photophysics of these fluorescent complexes.« less

Reduction of CO2 using a Rhenium Bipyridine Complex Containing Ancillary BODIPY Redox Reservoirs

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

Teesdale, Justin; Pistner, Allen; Yapp, Glenn P. A.

2014-01-01

The reduction of carbon dioxide to chemical fuels such as carbon monoxide is an important challenge in the field of renewable energy conversion. Given the thermodynamic stability of carbon dioxide, it is difficult to efficiently activate this substrate in a selective fashion and the development of new electrocatalysts for CO2 reduction is of prime importance. To this end, we have prepared and studied a new fac-ReI(CO)3 complex supported by a bipyridine ligand containing ancillary BODIPY moieties ([Re(BB2)(CO)3Cl]). Voltammetry experiments revealed that this system displays a rich redox chemistry under N2, as [Re(BB2)(CO)3Cl] can be reduced by up to four electronsmore » at modest potentials. These redox events have been characterized as the ReI/0 couple, and three ligand based reductions two of which are localized on the BODIPY units. The ability of the BB2 ligand to serve as a noninnocent redox reservoir is manifest in an enhanced electrocatalysis with CO2 as compared to an unsubstituted Re-bipyridine complex lacking BODIPY units ([Re(bpy)(CO)3Cl]). The second order rate constant for reduction of CO2 by [Re(BB2)(CO)3Cl] was measured to be k = 3400 M 1s 1 at an applied potential of 2.0 V versus SCE, which is roughly three times greater than the corresponding unsubstituted Re-bipyridine homologue. Photophysical and photochemical studies were also carried out to determine if [Re(BB2)(CO)3Cl] was a competent platform for CO2 reduction using visible light. These experiments showed that this complex supports unusual excited state dynamics that are not typically observed for fac- ReI(CO)3 complexes.« less

Photochemically assisted fast abiotic oxidation of manganese and formation of δ-MnO 2 nanosheets in nitrate solution

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

Jung, Haesung; Chadha, Tandeep S.; Kim, Doyoon

This study introduces a new and previously unconsidered fast abiotic formation of Mn(IV) oxides. We report photochemically assisted fast abiotic oxidation of Mn 2+ (aq) to Mn(IV) (s) by superoxide radicals generated from nitrate photolysis. This photochemical pathway generates randomly stacked layered birnessite (δ-MnO 2) nanosheets.

Structural and photophysical properties of (2E)-3-[4-(dimethylamino) phenyl]-1-(naphthalen-1-yl) prop-2-en-1-one (DPNP) in different media.

PubMed

Pannipara, Mehboobali; Asiri, Abdullah M; Alamry, Khalid A; Salem, Ibrahim A; El-Daly, Samy A

2015-01-01

The spectral and photophysical properties of a new chalcone derivative (2E)-3-[4-(dimethylamino) phenyl]-1-(naphthalen-1-yl) prop-2-en-1-one (DPNP) containing donor-acceptor group has been synthesized and characterized on the basis of the spectral (IR, (1)HNMR & (13)C NMR) and X- ray crystallographic data. The effect of solvents on photophysical parameters such as singlet absorption, molar absorptivity, oscillator strength, dipole moment, fluorescence spectra, and fluorescence quantum yield of DPNP have been investigated comprehensively. Significant red shift was observed in the emission spectrum of DPNP compared to the absorption spectrum upon increasing the solvent polarity, indicating a higher dipole moment in the excited state than in the ground state. The difference between the excited and ground state dipole moments (Δμ) were obtained from Lippert-Mataga and Reichardts correlations by means of solvatochromic shift method. The effects of medium acidity on the electronic absorption and emission spectra of DPNP were studied. The interaction of DPNP with colloidal silver nanoparticles (AgNPs) was also studied in ethanol and ethylene glycol using steady state fluorescence quenching measurements. The fluorescence quenching data reveal that dynamic quenching and energy transfer play a major role in the fluorescence quenching of DPNP by Ag NPs.

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.

A study on the redox, spectroscopic, and photophysical characteristics of a series of octahedral hexamolybdenum(ii) clusters: [{Mo6X8}Y6]2- (X, Y = Cl, Br, or I).

PubMed

Akagi, Soichiro; Fujii, Sho; Kitamura, Noboru

2018-01-23

We report a systematic study on the redox, spectroscopic, and photophysical properties of a series of [{Mo 6 X 8 }Y 6 ] 2- (X, Y = Cl, Br, or I. 1-9). All of the [{Mo 6 X 8 }Y 6 ] 2- clusters show intense and long-lived phosphorescence in both CH 3 CN and crystalline phases at 298 K. We found that the emission quantum yields (Φ em ) of 1-9 increase in the sequences X = Cl < Br < I and Y = I < Br < Cl for given Y and X, respectively. The emission lifetimes (τ em ) of the clusters also increase in the sequence Y = I < Br < Cl for given {Mo 6 X 8 } 4+ -core clusters. The present data demonstrate that arbitrary combinations of X and Y in [{Mo 6 X 8 }Y 6 ] 2- could tune τ em and Φ em in the ranges of 85-300 μs and 0.09-0.47, respectively. Both capping (X) and terminal ligand (Y) effects on the photophysical properties of the clusters are discussed on the basis of the energy gap (i.e., emission energy) dependence of the nonradiative decay rate constant.

Semiclassical Monte Carlo: A first principles approach to non-adiabatic molecular dynamics

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

White, Alexander J.; Center for Nonlinear Studies; Gorshkov, Vyacheslav N.

2014-11-14

Modeling the dynamics of photophysical and (photo)chemical reactions in extended molecular systems is a new frontier for quantum chemistry. Many dynamical phenomena, such as intersystem crossing, non-radiative relaxation, and charge and energy transfer, require a non-adiabatic description which incorporate transitions between electronic states. Additionally, these dynamics are often highly sensitive to quantum coherences and interference effects. Several methods exist to simulate non-adiabatic dynamics; however, they are typically either too expensive to be applied to large molecular systems (10's-100's of atoms), or they are based on ad hoc schemes which may include severe approximations due to inconsistencies in classical and quantummore » mechanics. We present, in detail, an algorithm based on Monte Carlo sampling of the semiclassical time-dependent wavefunction that involves running simple surface hopping dynamics, followed by a post-processing step which adds little cost. The method requires only a few quantities from quantum chemistry calculations, can systematically be improved, and provides excellent agreement with exact quantum mechanical results. Here we show excellent agreement with exact solutions for scattering results of standard test problems. Additionally, we find that convergence of the wavefunction is controlled by complex valued phase factors, the size of the non-adiabatic coupling region, and the choice of sampling function. These results help in determining the range of applicability of the method, and provide a starting point for further improvement.« less

Photosymbiotic giant clams are transformers of solar flux.

PubMed

Holt, Amanda L; Vahidinia, Sanaz; Gagnon, Yakir Luc; Morse, Daniel E; Sweeney, Alison M

2014-12-06

'Giant' tridacnid clams have evolved a three-dimensional, spatially efficient, photodamage-preventing system for photosymbiosis. We discovered that the mantle tissue of giant clams, which harbours symbiotic nutrition-providing microalgae, contains a layer of iridescent cells called iridocytes that serve to distribute photosynthetically productive wavelengths by lateral and forward-scattering of light into the tissue while back-reflecting non-productive wavelengths with a Bragg mirror. The wavelength- and angle-dependent scattering from the iridocytes is geometrically coupled to the vertically pillared microalgae, resulting in an even re-distribution of the incoming light along the sides of the pillars, thus enabling photosynthesis deep in the tissue. There is a physical analogy between the evolved function of the clam system and an electric transformer, which changes energy flux per area in a system while conserving total energy. At incident light levels found on shallow coral reefs, this arrangement may allow algae within the clam system to both efficiently use all incident solar energy and avoid the photodamage and efficiency losses due to non-photochemical quenching that occur in the reef-building coral photosymbiosis. Both intra-tissue radiometry and multiscale optical modelling support our interpretation of the system's photophysics. This highly evolved 'three-dimensional' biophotonic system suggests a strategy for more efficient, damage-resistant photovoltaic materials and more spatially efficient solar production of algal biofuels, foods and chemicals.

Tetraphenylporphyrin derivatives possessing piperidine group as potential agents for photodynamic therapy.

PubMed

Liao, Ping-Yong; Gao, Ying-Hua; Wang, Xin-Rong; Bao, Lei-Lei; Bian, Jun; Hu, Tai-Shan; Zheng, Mei-Zhen; Yan, Yi-Jia; Chen, Zhi-Long

2016-12-01

Photodynamic therapy (PDT) is a noninvasive therapeutic and promising procedure in cancer treatment and has attracted considerable attention in recent years. In the present paper, 2-piperidinetetraphenylporphyrin derivatives (P1-P3) conjugated with different substituents (Cl, Me, MeO group) at phenyl position were synthesized via nucleophilic substitution of 2-nitroporphyrin copper derivatives with piperidine by refluxing under a nitrogen atmosphere and then demetalization. The combination of 1 H NMR, 13 C NMR and HR-MS was used to elucidate the identities of them. Their photophysical and photochemical properties, intracellular localization, cytotoxicity in vitro and in vivo against QBC-939 cells were investigated. They have absorption at wavelength about 650nm. All synthesized photosensitizers showed low dark cytotoxicity and comparable with that of hematoporphyrin monomethyl ether (HMME). And they were more phototoxic than HMME to QBC-939 cells in vitro. In bearing QBC-939 tumor BALB/c nude mice, when it treated with 5mg/kg dose of PS and laser light (650nm, 100J/cm 2 , 180mW/cm 2 ), the growth of tumor was inhibited compared to the control group. Among them, P3 exhibited better photodynamic antitumor efficacy on BALB/c nude mice at lower concentration. These results indicate that P3 is a new potential antitumor photosensitizer in photodynamic therapy and deserves further investigation. Copyright © 2016 Elsevier B.V. All rights reserved.

All you need is light: antimicrobial photoinactivation as an evolving and emerging discovery strategy against infectious disease.

PubMed

St Denis, Tyler G; Dai, Tianhong; Izikson, Leonid; Astrakas, Christos; Anderson, Richard Rox; Hamblin, Michael R; Tegos, George P

2011-01-01

The story of prevention and control of infectious diseases remains open and a series of highly virulent pathogens are emerging both in and beyond the hospital setting. Antibiotics were an absolute success story for a previous era. The academic and industrial biomedical communities have now come together to formulate consensus beliefs regarding the pursuit of novel and effective alternative anti-infective countermeasures. Photodynamic therapy was established and remains a successful modality for malignancies but photodynamic inactivation has been transformed recently to an antimicrobial discovery and development platform. The concept of photodynamic inactivation is quite straightforward and requires microbial exposure to visible light energy, typically wavelengths in the visible region, that causes the excitation of photosensitizer molecules (either exogenous or endogenous), which results in the production of singlet oxygen and other reactive oxygen species that react with intracellular components, and consequently produce cell inactivation. It is an area of increasing interest, as research is advancing i) to identify the photochemical and photophysical mechanisms involved in inactivation; ii) to develop potent and clinically compatible photosensitizer; iii) to understand how photoinactivation is affected by key microbial phenotypic elements (multidrug resistance and efflux, virulence and pathogenesis determinants, biofilms); iv) to explore novel delivery platforms inspired by current trends in pharmacology and nanotechnology; and v) to identify photoinactivation applications beyond the clinical setting such as environmental disinfectants.

Confocal ultrafast pump-probe spectroscopy: a new technique to explore nanoscale composites.

PubMed

Virgili, Tersilla; Grancini, Giulia; Molotokaite, Egle; Suarez-Lopez, Inma; Rajendran, Sai Kiran; Liscio, Andrea; Palermo, Vincenzo; Lanzani, Guglielmo; Polli, Dario; Cerullo, Giulio

2012-04-07

This article is devoted to the exploration of the benefits of a new ultrafast confocal pump-probe technique, able to study the photophysics of different structured materials with nanoscale resolution. This tool offers many advantages over standard stationary microscopy techniques because it directly interrogates excited state dynamics in molecules, providing access to both radiative and non-radiative deactivation processes at a local scale. In this paper we present a few different examples of its application to organic semiconductor systems. The first two are focussed on the study of the photophysics of phase-separated polymer blends: (i) a blue-emitting polyfluorene (PFO) in an inert matrix of PMMA and (ii) an electron donor polythiophene (P3HT) mixed with an electron acceptor fullerene derivative (PCBM). The experimental results on these samples demonstrate the capability of the technique to unveil peculiar interfacial dynamics at the border region between phase-segregated domains, which would be otherwise averaged out using conventional pump-probe spectroscopy. The third example is the study of the photophysics of isolated mesoscopic crystals of the PCBM molecule. Our ultrafast microscope could evidence the presence of two distinctive regions within the crystals. In particular, we could pinpoint for the first time areas within the crystals showing photobleaching/stimulated emission signals from a charge-transfer state. This journal is © The Royal Society of Chemistry 2012

A DFT-D study on the electronic and photophysical properties of ruthenium (II) complex with a chelating sulfoxide group

NASA Astrophysics Data System (ADS)

Li, Huifang; Zhang, Lisheng; Lin, Hui; Fan, Xiaolin

2014-06-01

Electronic and photophysical properties of [Ru(bpy)2(OSO)]+ (bpy = 2,2‧-bipyridine; OSO = methylsulfinylbenzoate) were examined theoretically to better understand the differences between S- and O-linked ruthenium sulfoxide complexes. It is found that the strength of Ru-O1 linkage is significantly larger than that of Ru-S linkage, which makes the charge transfer amount from surrounding ligands to central Ru decreased. The energy gap is closed due to the highest occupied molecular orbital energy increases to a larger extent than the lowest unoccupied molecular orbital energy. Thereby, red shifted absorption and emission maxima in such photochromic ruthenium sulfoxide complexes can be explained.

Spectral and photophysical properties of intramolecular charge transfer fluorescence probe: 4'-Dimethylamino-2,5-dihydroxychalcone

NASA Astrophysics Data System (ADS)

Xu, Zhicheng; Bai, Guan; Dong, Chuan

2005-12-01

The spectral and photophysical properties of a new intramolecular charge transfer (ICT) probe, namely 4'-dimethylamino-2,5-dihydroxychalcone (DMADHC) were studied in different solvents by using steady-state absorption and emission spectroscopy. Whereas the absorption spectrum undergoes minor change with increasing polarity of the solvents, the fluorescence spectrum experiences a distinct bathochromic shift in the band position and the fluorescence quantum yield increases reaching a maximum before decrease with increasing the solvent polarity. The magnitude of change in the dipole moment was calculated based on the Lippert-Mataga equation. These results give the evidence about the intramolecular charge transfer character in the emitting singlet state of this compound.

Spectral and photophysical properties of intramolecular charge transfer fluorescence probe: 4'-dimethylamino-2,5-dihydroxychalcone.

PubMed

Xu, Zhicheng; Bai, Guan; Dong, Chuan

2005-12-01

The spectral and photophysical properties of a new intramolecular charge transfer (ICT) probe, namely 4'-dimethylamino-2,5-dihydroxychalcone (DMADHC) were studied in different solvents by using steady-state absorption and emission spectroscopy. Whereas the absorption spectrum undergoes minor change with increasing polarity of the solvents, the fluorescence spectrum experiences a distinct bathochromic shift in the band position and the fluorescence quantum yield increases reaching a maximum before decrease with increasing the solvent polarity. The magnitude of change in the dipole moment was calculated based on the Lippert-Mataga equation. These results give the evidence about the intramolecular charge transfer character in the emitting singlet state of this compound.

Joey Luther | NREL

Science.gov Websites

Laboratory to study synthesis and chemical transformation of uniquely shaped colloidal nanocrystals for Advanced Solar Photophysics as well as in NREL's perovskite team. Education B.S. Electrical and Computer

Evaluation of different photosensitizers for use in photochemical gene transfection.

PubMed

Prasmickaite, L; Høgset, A; Berg, K

2001-04-01

Many potentially therapeutic macromolecules, e.g. transgenes used in gene therapy, are taken into the cells by endocytosis, and have to be liberated from endocytic vesicles in order to express a therapeutic function. To achieve this we have developed a new technology, named photochemical internalization (PCI), based on photochemical reactions inducing rupture of endocytic vesicles. The aim of this study was to clarify which properties of photosensitizers are important for obtaining the PCI effect improving gene transfection. The photochemical effect on transfection of human melanoma THX cells has been studied employing photosensitizers with different physicochemical properties and using two gene delivery vectors: the cationic polypeptide polylysine and the cationic lipid 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP). Photochemical treatment by photosensitizers that do not localize in endocytic vesicles (tetra[3-hydroxyphenyl]porphyrin and 5-aminolevulinic acid-induced protoporphyrin IX) do not stimulate transfection, irrespective of the gene delivery vector. In contrast, photosensitizers localized in endocytic vesicles stimulate polylysine-mediated transfection, and amphiphilic photosensitizers (disulfonated aluminium phthalocyanine [AlPcS2a] and meso-tetraphenylporphynes) show the strongest positive effect, inducing approximately 10-fold increase in transfection efficiency. In contrast, DOTAP-mediated transfection is inhibited by all photochemical treatments irrespective of the photosensitizer used. Neither AlPcS2a nor Photofrin affects the uptake of the transfecting DNA over the plasma membrane, therefore photochemical permeabilization of endocytic vesicles seems to be the most likely mechanism responsible for the positive PCI effect on gene transfection.

Degradation of artificial sweeteners via direct and indirect photochemical reactions.

PubMed

Perkola, Noora; Vaalgamaa, Sanna; Jernberg, Joonas; Vähätalo, Anssi V

2016-07-01

We studied the direct and indirect photochemical reactivity of artificial sweeteners acesulfame, saccharin, cyclamic acid and sucralose in environm entally relevant dilute aqueous solutions. Aqueous solutions of sweeteners were irradiated with simulated solar radiation (>290 nm; 96 and 168 h) or ultraviolet radiation (UVR; up to 24 h) for assessing photochemical reactions in surface waters or in water treatment, respectively. The sweeteners were dissolved in deionised water for examination of direct photochemical reactions. Direct photochemical reactions degraded all sweeteners under UVR but only acesulfame under simulated solar radiation. Acesulfame was degraded over three orders of magnitude faster than the other sweeteners. For examining indirect photochemical reactions, the sweeteners were dissolved in surface waters with indigenous dissolved organic matter or irradiated with aqueous solutions of nitrate (1 mg N/L) and ferric iron (2.8 mg Fe/L) introduced as sensitizers. Iron enhanced the photodegradation rates but nitrate and dissolved organic matter did not. UVR transformed acesulfame into at least three products: iso-acesulfame, hydroxylated acesulfame and hydroxypropanyl sulfate. Photolytic half-life was one year for acesulfame and more than several years for the other sweeteners in surface waters under solar radiation. Our study shows that the photochemical reactivity of commonly used artificial sweeteners is variable: acesulfame may be sensitive to photodegradation in surface waters, while saccharin, cyclamic acid and sucralose degrade very slowly even under the energetic UVR commonly used in water treatment.

Photophysical dynamics of the efficient emission and photosensitization of [Ir(pqi)2(NN)]+ complexes.

PubMed

Zanoni, Kassio P S; Ito, Akitaka; Grüner, Malte; Murakami Iha, Neyde Y; de Camargo, Andrea S S

2018-01-23

The photophysical dynamics of three complexes in the highly-emissive [Ir(pqi) 2 (NN)] + series were investigated aiming at unique photophysical features and applications in light-emitting and singlet oxygen sensitizing research fields. Rational elucidation and Franck-Condon analyses of the observed emission spectra in nitrile solutions at 298 and 77 K reveal the true emissive nature of the lowest-lying triplet excited state (T 1 ), consisting of a hybrid 3 MLCT/LC Ir(pqi)→pqi state. Emissive deactivations from T 1 occur mainly by very intense, yellow-orange phosphorescence with high quantum yields and radiative rates. The emission nature experimentally verified is corroborated by theoretical calculations (TD-DFT), with T 1 arising from a mixing of several transitions induced by the spin-orbit coupling, majorly ascribed to 3 MLCT/LC Ir(pqi)→pqi and increasing contributions of 3 MLCT/LLCT Ir(pqi)→NN . The microsecond-lived emission of T 1 is rapidly quenched by molecular oxygen, with an efficient generation of singlet oxygen. Our findings show that the photophysics of [Ir(pqi) 2 (NN)][PF 6 ] complexes is suitable for many applications, from the active layer of electroluminescent devices to photosensitizers for photodynamic therapy and theranostics.

Effects of ICG concentration and particle diameter on photophysical properties of ICG-doped nanoparticles

NASA Astrophysics Data System (ADS)

Crovisier, Jason; Bahmani, Baharak; Saleh, Reema; Vullev, Valentine; Anvari, Bahman

2014-03-01

The variety of nanoparticles developed by numerous investigators has presented a diverse platform for various optical imaging applications in biomedicine. We have previously reported that the FDA-approved chromophore Indocyanine Green (ICG) can be successfully encapsulated by cross-linked poly-allylamine hydrochloride (PAH)-Disodium Monophosphate (Na2HPO4) to form a nanoparticle for near-infrared imaging applications. The diameter of the constructs is dependent on the charge ratio between the polymer and salt used to encapsulate the chromophore. Modifications of the synthesis methods can alter the photophysical properties of the capsules, either through the adjustment of the charge ratio between PAH and Na2HPO4 or concentration of ICG successfully impregnated into the capsule. Through understanding the effects of tuning the nanoparticle properties, the photophysical characteristics of the constructs can be optimized. Here we present the results of adjusting the diameter of the nanoparticle and amount of ICG on the hydrodynamic diameters, absorption and fluorescence characteristics, and the relative fluorescence quantum yield. Optimizing the photophysical properties of the constructs can lead to increased imaging sensitivity and contrast for potential translational applications, including tumor imaging, which may utilize these nanoconstructs.

Furan Decorated Nucleoside Analogues as Fluorescent Probes: synthesis, photophysical evaluation and site-specific incorporation

PubMed Central

Greco, Nicholas J.; Tor, Yitzhak

2007-01-01

The synthesis and photophysical evaluation of modified nucleoside analogues in which a five-membered heterocycle (furan, thiophene, oxazole and thiazole) is attached to the 5 position of 2′-deoxyuridine are reported. The furan containing derivative is identified as the most promising responsive nucleoside of this family due to its emission quantum efficiency and degree of sensitivity to its microenvironment. The furan moiety was then attached to the 5 position of 2′-deoxycytidine as well as the 8 position of adenosine and guanosine. Photophysical evaluation of these four furan containing nucleoside analogues reveal distinct differences in the absorption, emission and quantum efficiency depending upon the class of nucleoside (pyrimidine or purine). Comparing the photophysical properties of all furan containing nucleosides, identifies the furan thymidine analogue, 5-(fur-2-yl)-2′-deoxyuridine, as the best candidate for use as a responsive fluorescent probe in nucleic acids. 5-(fur-2-yl)-2′-deoxyuridine was then converted to the corresponding phosphoramidite and site specifically incorporated into DNA oligonucleotides with greater than 88% coupling efficiency. Such furan-modified oligonucleotides form stable duplexes upon hybridization to their complementary DNA strands and display favorable fluorescent features. PMID:18431439

Photochemical Reaction Altered Cardiac Toxicity of Diesel Exhaust Inhalation

EPA Science Inventory

Rationale: Epidemiological studies have indicated an association between urban air pollution exposure and cardiovascular morbidity and mortality. The present study was designed to evaluate the cardiac effects of inhaled diesel exhaust and compared with photochemically altered d...

Photophysics of covalently functionalized single wall carbon nanotubes with verteporfin

NASA Astrophysics Data System (ADS)

Staicu, Angela; Smarandache, Adriana; Pascu, Alexandru; Pascu, Mihail Lucian

2017-09-01

Covalently functionalized single wall carbon nanotubes (SWCNT) with the photosensitizer verteporfin (VP) were synthesized and studied. Photophysical properties of the obtained compounds like optical absorption, laser-induced fluorescence and generated singlet oxygen were investigated. In order to highlight the features of the conjugated compound, its photophysical characteristics were compared with those of the mixtures of the initial components. The optical absorption data evidenced a compound that combines features of the primary SWCNTs and VP. This is the also the case of the laser induced fluorescence of the synthesized product. Moreover, fluorescence quantum yield (Φf) of the compound (Φf = 2.4%) is smaller than for the mixture of SWCNT and VP in (Φf = 3.2%). The behavior is expected, because linked VP (carrying the fluorescent moiety) transfers easier a part of its excitation energy to the SWCNT in the covalent structure. Relative to the quantum yield of singlet oxygen generation (ΦΔ) by Methylene Blue, it was found that the ΦΔ for the conjugated VP-SWCNT is 51% while for the mixture ΦΔ is 23%. The results indicate covalently functionalized single walled carbon nanotubes with verteporfin as potential compounds of interest in targeted drug delivery and photodynamic therapy.

Photophysical properties and photoisomerization processes of Methyl Red embedded in rigid polymer

NASA Astrophysics Data System (ADS)

Lee, Geon Joon; Kim, Dongho; Lee, Minyung

1995-01-01

The photophysical properties of Methyl Red molecules embedded in a poly(methyl methacrylate) (PMMA) matrix were investigated with photoinduced absorption, absorption kinetics, steady-state, and time-resolved luminescence spectroscopy. The excited singlet (S1) state lifetimes for trans and cis isomers of Methyl Red in PMMA at room temperature have been measured as 35 and 420 ps, respectively. The excited triplet (T1) state energy level and its lifetime at 77 K were also obtained. A slow trans-cis isomerization process having a time constant of a few hundred seconds was observed for the illuminated Methyl Red in rigid polymer. Based on measured photophysical properties and dynamic processes, an energy-level diagram for Methyl Red molecules in rigid polymer is introduced to explain these observations.

Inhalation of Photochemically Altered Urban Mixtures Depresses Cardiac Function in Mice

EPA Science Inventory

Rationale: Epidemiological studies have indicated an association between urban air pollution exposure and cardiovascular morbidity and mortality. The present study was designed to evaluate the cardiac effects of inhaled photochemical products in urban mixtures in a murine model. ...

Protein-induced Photophysical Changes to the Amyloid Indicator Dye Thioflavin T

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

L Wolfe; M Calabrese; A Nath

2011-12-31

The small molecule thioflavin T (ThT) is a defining probe for the identification and mechanistic study of amyloid fiber formation. As such, ThT is fundamental to investigations of serious diseases such as Alzheimer's disease, Parkinson disease, and type II diabetes. For each disease, a different protein undergoes conformational conversion to a {beta}-sheet rich fiber. The fluorescence of ThT exhibits an increase in quantum yield upon binding these fibers. Despite its widespread use, the structural basis for binding specificity and for the changes to the photophysical properties of ThT remain poorly understood. Here, we report the co-crystal structures of ThT withmore » two alternative states of {beta}-2 microglobulin ({beta}2m); one monomeric, the other an amyloid-like oligomer. In the latter, the dye intercalates between {beta}-sheets orthogonal to the {beta}-strands. Importantly, the fluorophore is bound in such a manner that a photophysically relevant torsion is limited to a range of angles generally associated with low, not high, quantum yield. Quantum mechanical assessment of the fluorophore shows the electronic distribution to be strongly stabilized by aromatic interactions with the protein. Monomeric {beta}2m gives little increase in ThT fluorescence despite showing three fluorophores, at two binding sites, in configurations generally associated with high quantum yield. Our efforts fundamentally extend existing understanding about the origins of amyloid-induced photophysical changes. Specifically, the {beta}-sheet interface that characterizes amyloid acts both sterically and electronically to stabilize the fluorophore's ground state electronic distribution. By preventing the fluorophore from adopting its preferred excited state configuration, nonradiative relaxation pathways are minimized and quantum yield is increased.« less

Protein-induced photophysical changes to the amyloid indicator dye thioflavin T

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

Wolfe, Leslie S.; Calabrese, Matthew F.; Nath, Abhinav

2010-10-04

The small molecule thioflavin T (ThT) is a defining probe for the identification and mechanistic study of amyloid fiber formation. As such, ThT is fundamental to investigations of serious diseases such as Alzheimer's disease, Parkinson disease, and type II diabetes. For each disease, a different protein undergoes conformational conversion to a {beta}-sheet rich fiber. The fluorescence of ThT exhibits an increase in quantum yield upon binding these fibers. Despite its widespread use, the structural basis for binding specificity and for the changes to the photophysical properties of ThT remain poorly understood. Here, we report the co-crystal structures of ThT withmore » two alternative states of {beta}-2 microglobulin ({beta}2m); one monomeric, the other an amyloid-like oligomer. In the latter, the dye intercalates between {beta}-sheets orthogonal to the {beta}-strands. Importantly, the fluorophore is bound in such a manner that a photophysically relevant torsion is limited to a range of angles generally associated with low, not high, quantum yield. Quantum mechanical assessment of the fluorophore shows the electronic distribution to be strongly stabilized by aromatic interactions with the protein. Monomeric {beta}2m gives little increase in ThT fluorescence despite showing three fluorophores, at two binding sites, in configurations generally associated with high quantum yield. Our efforts fundamentally extend existing understanding about the origins of amyloid-induced photophysical changes. Specifically, the {beta}-sheet interface that characterizes amyloid acts both sterically and electronically to stabilize the fluorophore's ground state electronic distribution. By preventing the fluorophore from adopting its preferred excited state configuration, nonradiative relaxation pathways are minimized and quantum yield is increased.« less

A mitochondria-selective near-infrared-emitting fluorescent dye for cellular imaging studies.

PubMed

Choi, Peter; Noguchi, Katsuya; Ishiyama, Munetaka; Denny, William A; Jose, Jiney

2018-05-03

This communication details the synthesis, evaluation of photophysical properties, and cellular imaging studies of cyanine chromophore based fluorescent dye 1 as a selective imaging agent for mitochondria. Copyright © 2018 Elsevier Ltd. All rights reserved.

Spectroscopic and kinetic studies of photochemical reaction of magnesium tetraphenylporphyrin with oxygen.

PubMed

Zhang, Jianbin; Zhang, Pengyan; Zhang, Zhengfu; Wei, Xionghui

2009-05-07

Magnesium tetraphenylporphyrin (MgTPP) was synthesized from meso-tetraphenylporphyrin (H(2)TPP) in N,N-dimethylformamide (DMF). The photochemical properties of MgTPP in the presence of oxygen were investigated in dichloromethane (CH(2)Cl(2)) by conventional fluorescence, UV-vis, (1)H NMR, MALDI-TOF-MS, FTIR, and XPS spectroscopic techniques. Spectral analyses showed that under irradiation, MgTPP molecules reacted with O(2) molecules, and a stable 1:1 adduct was produced. During the photochemical reaction process, one oxygen molecule was bound to the pyrrolenine nitrogens in the MgTPP molecule, and the characteristic N-O bonds were identified using the FTIR and XPS techniques. The kinetics of the photochemical reaction of MgTPP with O(2) has been studied in an oxygen-saturated solution. Under irradiation conditions, the experimental rate follows a pseudo-first-order reaction for MgTPP, having a half-life from 40 to 130 min under various irradiation intensities. The kinetic rate constant of photochemical reaction of MgTPP with O(2) showed a linear dependence.

Composition and Photochemical Reactivity of Turbine Engine Exhaust

DTIC Science & Technology

1984-09-01

ESL-TR-84-28 Composition and Photochemical Reactivity of Turbine Engine Exhaust In IL) C.W. SPICER. M.W. HOLDREN, T.F. LYON. and R.M. RIGGIN...NUMBER 2. GOVT ACCIESION NO RECIPIENT’S CATALOG NUMmE" 4. TITLE (aid Sub•ttlC) S. TYPE OF REPORT & PERIOD COvERE0 Composition and Photochemical...involved detailed exhaust organic composition studies with two -. full-scale turbine engines utilizing three fuels. Tiask 4 investigated the

A Photochemical Reactor for the Study of Kinetics and Adsorption Phenomena

ERIC Educational Resources Information Center

Poce-Fatou, J. A.; Gil, M. L. A.; Alcantara, R.; Botella, C.; Martin, J.

2004-01-01

The interaction between light and matter is examined with the help of a photochemical experiment. This experiment is useful for the investigation of heterogeneous catalysis, semiconductor properties and adsorption phenomena.

Photophysical properties of hexyl diethylaminohydroxybenzoylbenzoate (Uvinul A Plus), a UV-A absorber.

PubMed

Shamoto, Yuta; Yagi, Mikio; Oguchi-Fujiyama, Nozomi; Miyazawa, Kazuyuki; Kikuchi, Azusa

2017-09-13

Hexyl diethylaminohydroxybenzoylbenzoate (DHHB, Uvinul A Plus) is a photostable UV-A absorber. The photophysical properties of DHHB have been studied by obtaining the transient absorption, total emission, phosphorescence and electron paramagnetic resonance spectra. DHHB exhibits an intense phosphorescence in a hydrogen-bonding solvent (e.g., ethanol) at 77 K, whereas it is weakly phosphorescent in a non-hydrogen-bonding solvent (e.g., 3-methylpentane). The triplet-triplet absorption and EPR spectra for the lowest excited triplet state of DHHB were observed in ethanol, while they were not observed in 3-methylpentane. These results are explained by the proposal that in the benzophenone derivatives possessing an intramolecular hydrogen bond, intramolecular proton transfer is an efficient mechanism of the very fast radiationless decay from the excited singlet state. The energy level of the lowest excited triplet state of DHHB is higher than those of the most widely used UV-B absorbers, octyl methoxycinnamate (OMC) and octocrylene (OCR). DHHB may act as a triplet energy donor for OMC and OCR in the mixtures of UV-A and UV-B absorbers. The bimolecular rate constant for the quenching of singlet oxygen by DHHB was determined by measuring the near-IR phosphorescence of singlet oxygen. The photophysical properties of diethylaminohydroxybenzoylbenzoic acid (DHBA) have been studied for comparison. It is a closely related building block to assist in interpreting the observed data.

Photophysical and morphological implications of single-strand conjugated polymer folding in solution

DOE PAGES

Fauvell, Thomas J.; Zheng, Tianyue; Jackson, Nicholas E.; ...

2016-04-08

Organic semiconductors have garnered substantial interest in optoelectronics, but their device performances exhibit strong dependencies on material crystallinity and packing. In an effort to understand the interactions dictating the morphological and photophysical properties of a high-performing photovoltaic polymer, PTB7, a series of short oligomers and low molecular weight polymers of PTB7 were synthesized. Chain-length dependent optical studies of these oligomers demonstrate that PTB7’s low-energy visible absorption is largely due to self-aggregation-induced ordering, rather than in-chain charge transfer, as previously thought. By examining molecular weight and concentration dependent optical properties, supplemented by molecular dynamics simulations, we attribute polymeric PTB7’s unique midgapmore » fluorescence and concentration independent absorption spectrum to an interplay between low molecular weight unaggregated strands and high-molecular weight self-aggregated (folded) strands. Specifically, we propose that the onset of PTB7 self-folding occurs between 7 and 13 repeat units, but the aggregates characteristic of polymeric PTB7 only develop at lengths of ~30 repeat units. Atomistic molecular dynamics simulations of PTB7 corroborate these conclusions, and a simple relation is proposed which quantifies the free-energy of conjugated polymer folding. Lastly, this study provides detailed guidance in the design of intra- and interchain contributions to the photophysical and morphological properties of polymeric semiconductors.« less

Sky-blue emitting bridged diiridium complexes: beneficial effects of intramolecular π-π stacking.

PubMed

Congrave, Daniel G; Hsu, Yu-Ting; Batsanov, Andrei S; Beeby, Andrew; Bryce, Martin R

2018-02-06

The potential of intramolecular π-π interactions to influence the photophysical properties of diiridium complexes is an unexplored topic, and provides the motivation for the present study. A series of diarylhydrazide-bridged diiridium complexes functionalised with phenylpyridine (ppy)-based cyclometalating ligands is reported. It is shown by NMR studies in solution and single crystal X-ray analysis that intramolecular π-π interactions between the bridging and cyclometalating ligands rigidify the complexes leading to high luminescence quantum efficiencies in solution and in doped films. Fluorine substituents on the phenyl rings of the bridge promote the intramolecular π-π interactions. Notably, these non-covalent interactions are harnessed in the rational design and synthesis of the first examples of highly emissive sky-blue diiridium complexes featuring conjugated bridging ligands, for which they play a vital role in the structural and photophysical properties. Experimental results are supported by computational studies.

Photo-physical and interactional behavior of two members of group B vitamins in different solvent media

NASA Astrophysics Data System (ADS)

Zakerhamidi, M. S.; Zare Haghighi, L.; Seyed Ahmadian, S. M.

2017-09-01

In this paper, absorption and fluorescence spectra of vitamin B12 (cyanocobalamin) and vitamin B6 (pyridoxine) were recorded in solvents with different polarity, at room temperature. These vitamins' photo-physical behavior depends strongly on the solvent's nature along with different attached groups in their structures. In order to investigate the solvent-solute interactions and environmental effect on spectral variations, linear solvation energy relationships concept, suggested by Kamlet and Taft was used. Solvatochromic method was also used for measuring the ground and excited state dipole moments of these vitamins. According to our experimental results, dipole moment of these groups of vitamins in excited state is larger than ground state. Furthermore, obtained photo-physical and interactional properties of used vitamins can give important information on how this group of vitamins behaves in biological systems.

Facile synthesis, microstructure and photophysical properties of core-shell nanostructured (SiCN)/BN nanocomposites

PubMed Central

Zhang, Qian; Jia, Dechang; Yang, Zhihua; Cai, Delong; Laine, Richard M.; Li, Qian; Zhou, Yu

2017-01-01

Increasing structural complexity at nanoscale can permit superior control over photophysical properties in the precursor-derived semiconductors. We demonstrate here the synthesis of silicon carbonitride (SiCN)/boron nitride (BN) nanocomposites via a polymer precursor route wherein the cobalt polyamine complexes used as the catalyst, exhibiting novel composite structures and photophysical properties. High Resolution Transmission Electron Microscopy (HRTEM) analysis shows that the diameters of SiCN−BN core−shell nanocomposites and BN shells are 50‒400 nm and 5‒25 nm, respectively. BN nanosheets (BNNSs) are also observed with an average sheet size of 5‒15 nm. The photophysical properties of these nanocomposites are characterized using the UV-Vis and photoluminescence (PL) analyses. The as-produced composites have emission behavior including an emission lifetime of 2.5 ns (±20 ps) longer observed in BN doped SiCN than that seen for SiC nanoparticles. Our results suggest that the SiCN/BN nanocomposites act as semiconductor displaying superior width photoluminescence at wavelengths spanning the visible to near-infrared (NIR) spectral range (400‒700 nm), owing to the heterojunction of the interface between the SiC(N) nanowire core and the BN nanosheet shell. PMID:28084300

Sulfur Chemistry in the Early and Present Atmosphere of Mars

NASA Technical Reports Server (NTRS)

Levine, Joel S.; Summers, M. E.

2011-01-01

Atmospheric sulfur species resulting from volcanic emissions impact the composition and chemistry of the atmosphere, impact the climate, and hence, the habitability of Mars and impact the mineralogy and composition of the surface of Mars. The geochemical/ photochemical cycling of sulfur species between the interior (via volcanism), the atmosphere (atmospheric photochemical and chemical processes) and the deposition of sulfuric acid on the surface of Mars is an important, but as yet poorly understood geochemical/ photochemical cycle on Mars. There is no observational evidence to indicate that Mars is volcanically active at the present time, however, there is strong evidence that volcanism was an important and widespread process on early Mars. The chemistry and photochemistry of sulfur species in the early and present atmosphere of Mars will be assessed using a one-dimensional photochemical model. Since it is generally assumed that the atmosphere of early Mars was significantly denser than the present 6-millibar atmosphere, photochemical calculations were performed for the present atmosphere and for the atmosphere of early Mars with assumed surface pressures of 60 and 350-millibars, where higher surface pressure resulted from enhanced atmospheric concentrations of carbon dioxide (CO2). The following sections include the results of earlier modeling studies, a summary of the one-dimensional photochemical model used in this study, a summary of the photochemistry and chemistry of sulfur species in the atmosphere of Mars and some of the results of the calculations.

Photochemical Conversion of Surrogate Emissions for Use in Toxicological Studies: Role of Particulate- and Gas-Phase Products

EPA Science Inventory

The production of photochemical atmospheres under controlled conditions in an irradiated chamber permits the manipulation of a variety of parameters that influences resulting air pollutant chemistry and potential biological effects. To date no studies have examined how contrastin...

Photophysical analysis of 1,10-phenanthroline-embedded porphyrin analogues and their magnesium(II) complexes.

PubMed

Ishida, Masatoshi; Lim, Jong Min; Lee, Byung Sun; Tani, Fumito; Sessler, Jonathan L; Kim, Dongho; Naruta, Yoshinori

2012-11-05

The synthesis, characterization, photophysical properties, and theoretical analysis of a series of tetraaza porphyrin analogues (H-Pn: n=1-4) containing a dipyrrin subunit and an embedded 1,10-phenanthroline subunit are described. The meso-phenyl-substituted derivative (H-P1) interacts with a Mg(2+) salt (e.g., MgCl(2), MgBr(2), MgI(2), Mg(ClO(4))(2), and Mg(OAc)(2)) in MeCN solution, thereby giving rise to a cation-dependent red-shift in both the absorbance- and emission maxima. In this system, as well as in the other H-Pn porphyrin analogues used in this study, the four nitrogen atoms of the ligand interact with the bound magnesium cation to form Mg(2+)-dipyrrin-phenanthroline complexes of the general structure MgX-Pn (X=counteranion). Both single-crystal X-ray diffraction analysis of the corresponding zinc-chloride derivative (ZnCl-P1) and fluorescence spectroscopy of the Mg-adducts that are formed from various metal salts provide support for the conclusion that, in complexes such as MgCl-P1, a distorted square-pyramidal geometry persists about the metal cation wherein a chloride anion acts as an axial counteranion. Several analogues (HPn) that contain electron-donating and/or electron-withdrawing dipyrrin moieties were prepared in an effort to understand the structure-property relationships and the photophysical attributes of these Mg-dipyrrin complexes. Analysis of various MgX-Pn (X=anion) systems revealed significant substitution effects on their chemical, electrochemical, and photophysical properties, as well as on the Mg(2+)-cation affinities. The fluorescence properties of MgCl-Pn reflected the effect of donor-excited photoinduced electron transfer (d-PET) processes from the dipyrrin subunit (as a donor site) to the 1,10-phenanthroline acceptor subunit. The proposed d-PET process was analyzed by electron paramagnetic resonance (EPR) spectroscopy and by femtosecond transient absorption (TA) spectroscopy, as well as by theoretical DFT calculations. Taken together, these studies provide support for the suggestion that a radical species is produced as the result of an intramolecular charge-transfer process, following photoexcitation. These photophysical effects, combined with a mixed dipyrrin-phenanthroline structure that is capable of effective Mg(2+)-cation complexation, lead us to suggest that porphyrin-inspired systems, such as HPn, have a role to play as magnesium-cation sensors. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Analysis of photochemical pollution in summer and winter using a photochemical box model in the center of Tokyo, Japan.

PubMed

Huang, H; Akustu, Y; Arai, M; Tamura, M

2001-07-01

In order to give an effective and rapid analysis of the photochemical pollution and information for emission control strategies, a photochemical box model (PBM) was applied to one moderate summer episode, 11 July 1996, and one typical winter episode, 3 December 1996, in the center of Tokyo, Japan. The box model gave a good prediction of the photochemical pollution with minimal investment. As expected, the peak ozone in summer is higher than in winter. The NOx concentrations in winter are higher than those in summer. In summer, NO and NO2 have one peak in the morning. In winter, NO and NO2 show two peaks during the day. Three model runs including no reactions, a zero ozone boundary condition and dark reactions were conducted to understand the photochemical processes. The effects of emission reduction on the formation of the photochemical pollution in the center of Tokyo have been studied. The results show that the reduction of NMHC emission can decrease the ozone, however, the reduction of NOx emission can increase the ozone. It can be concluded that if the NOx emission are reduced, the reduction of NMHC should be more emphasized in order to decrease the ozone concentration in the center of Tokyo, Japan, especially the reduction of the NMHC from stationary source emission.

Anle138b and related compounds are aggregation specific fluorescence markers and reveal high affinity binding to α-synuclein aggregates.

PubMed

Deeg, Andreas A; Reiner, Anne M; Schmidt, Felix; Schueder, Florian; Ryazanov, Sergey; Ruf, Viktoria C; Giller, Karin; Becker, Stefan; Leonov, Andrei; Griesinger, Christian; Giese, Armin; Zinth, Wolfgang

2015-09-01

Special diphenyl-pyrazole compounds and in particular anle138b were found to reduce the progression of prion and Parkinson's disease in animal models. The therapeutic impact of these compounds was attributed to the modulation of α-synuclein and prion-protein aggregation related to these diseases. Photophysical and photochemical properties of the diphenyl-pyrazole compounds anle138b, anle186b and sery313b and their interaction with monomeric and aggregated α-synuclein were studied by fluorescence techniques. The fluorescence emission of diphenyl-pyrazole is strongly increased upon incubation with α-synuclein fibrils, while no change in fluorescence emission is found when brought in contact with monomeric α-synuclein. This points to a distinct interaction between diphenyl-pyrazole and the fibrillar structure with a high binding affinity (Kd=190±120nM) for anle138b. Several α-synuclein proteins form a hydrophobic binding pocket for the diphenyl-pyrazole compound. A UV-induced dehalogenation reaction was observed for anle138b which is modulated by the hydrophobic environment of the fibrils. Fluorescence of the investigated diphenyl-pyrazole compounds strongly increases upon binding to fibrillar α-synuclein structures. Binding at high affinity occurs to hydrophobic pockets in the fibrils. The observed particular fluorescence properties of the diphenyl-pyrazole molecules open new possibilities for the investigation of the mode of action of these compounds in neurodegenerative diseases. The high binding affinity to aggregates and the strong increase in fluorescence upon binding make the compounds promising fluorescence markers for the analysis of aggregation-dependent epitopes. Copyright © 2015 Elsevier B.V. All rights reserved.

Protein-encapsulated bilirubin: paving the way to a useful probe for singlet oxygen.

PubMed

Pimenta, Frederico M; Jensen, Jan K; Etzerodt, Michael; Ogilby, Peter R

2015-04-01

When dissolved in a bulk solvent, bilirubin efficiently removes singlet molecular oxygen, O2(a(1)Δg), through a combination of chemical reactions and by promoting the O2(a(1)Δg)→O2(X(3)Σg(-)) nonradiative transition to populate the ground state of oxygen. To elucidate how such processes can be exploited in the development of a biologically useful fluorescent probe for O2(a(1)Δg), pertinent photophysical and photochemical parameters of bilirubin encapsulated in a protein were determined. The motivation for studying a protein-encapsulated system reflects the ultimate desire to (a) use genetic engineering to localize the probe at a specific location in a living cell, and (b) provide a controlled environment around the chromophore/fluorophore. Surprisingly, explicit values of oxygen- and O2(a(1)Δg)-dependent parameters that characterize the behavior of a given chromophore/fluorophore encased in a protein are not generally available. To the end of quantifying the effects of such an encasing protein, a recently discovered bilirubin-binding protein isolated from a Japanese eel was used. The data show that this system indeed preferentially responds to O2(a(1)Δg) and not to the superoxide ion. However, this protein not only shields bilirubin such that the rate constants for interaction with O2(a(1)Δg) decrease relative to what is observed in a bulk solvent, but the fraction of the total O2(a(1)Δg)-bilirubin interaction that results in a chemical reaction between O2(a(1)Δg) and bilirubin also decreases appreciably. The rate constants thus obtained provide a useful starting point for the general design and development of reactive protein-encased fluorescent probes for O2(a(1)Δg).

Optimization of physiological parameter for macroscopic modeling of reacted singlet oxygen concentration in an in-vivo model

NASA Astrophysics Data System (ADS)

Wang, Ken Kang-Hsin; Busch, Theresa M.; Finlay, Jarod C.; Zhu, Timothy C.

2009-02-01

Singlet oxygen (1O2) is generally believed to be the major cytotoxic agent during photodynamic therapy (PDT), and the reaction between 1O2 and tumor cells define the treatment efficacy. From a complete set of the macroscopic kinetic equations which describe the photochemical processes of PDT, we can express the reacted 1O2 concentration, [1O2]rx, in a form related to time integration of the product of 1O2 quantum yield and the PDT dose rate. The production of [1O2]rx involves physiological and photophysical parameters which need to be determined explicitly for the photosensitizer of interest. Once these parameters are determined, we expect the computed [1O2]rx to be an explicit dosimetric indicator for clinical PDT. Incorporating the diffusion equation governing the light transport in turbid medium, the spatially and temporally-resolved [1O2]rx described by the macroscopic kinetic equations can be numerically calculated. A sudden drop of the calculated [1O2]rx along with the distance following the decrease of light fluence rate is observed. This suggests that a possible correlation between [1O2]rx and necrosis boundary may occur in the tumor subject to PDT irradiation. In this study, we have theoretically examined the sensitivity of the physiological parameter from two clinical related conditions: (1) collimated light source on semi-infinite turbid medium and (2) linear light source in turbid medium. In order to accurately determine the parameter in a clinical relevant environment, the results of the computed [1O2]rx are expected to be used to fit the experimentally-measured necrosis data obtained from an in vivo animal model.

Photoprotection vs. Photoinhibition of Photosystem II in Transplastomic Lettuce (Lactuca sativa) Dominantly Accumulating Astaxanthin.

PubMed

Fujii, Ritsuko; Yamano, Nami; Hashimoto, Hideki; Misawa, Norihiko; Ifuku, Kentaro

2016-07-01

Transplastomic (chloroplast genome-modified; CGM) lettuce that dominantly accumulates astaxanthin grows similarly to a non-transgenic control with almost no accumulation of naturally occurring photosynthetic carotenoids. In this study, we evaluated the activity and assembly of PSII in CGM lettuce. The maximum quantum yield of PSII in CGM lettuce was <0.6; however, the quantum yield of PSII was comparable with that in control leaves under higher light intensity. CGM lettuce showed a lower ability to induce non-photochemical quenching (NPQ) than the control under various light intensities. The fraction of slowly recovering NPQ in CGM lettuce, which is considered to be photoinhibitory quenching (qI), was less than half that of the control. In fact, 1 O 2 generation was lower in CGM than in control leaves under high light intensity. CGM lettuce contained less PSII, accumulated mostly as a monomer in thylakoid membranes. The PSII monomers purified from the CGM thylakoids bound echinenone and canthaxanthin in addition to β-carotene, suggesting that a shortage of β-carotene and/or the binding of carbonyl carotenoids would interfere with the photophysical function as well as normal assembly of PSII. In contrast, high accumulation of astaxanthin and other carbonyl carotenoids was found within the thylakoid membranes. This finding would be associated with the suppression of photo-oxidative stress in the thylakoid membranes. Our observation suggests the importance of a specific balance between photoprotection and photoinhibition that can support normal photosynthesis in CGM lettuce producing astaxanthin. © The Author 2015. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Has the Performance of Regional-Scale Photochemical Modelling Systems Changed over the Past Decade?

EPA Science Inventory

This study analyzed summertime ozone concentrations that have been simulated by various regional-scale photochemical modelling systems over the Eastern U.S. as part of more than ten independent studies. Results indicate that there has been a reduction of root mean square errors ...

Changes of Photochemical Properties of Dissolved Organic Matter During a Hydrological Year

NASA Astrophysics Data System (ADS)

Porcal, P.; Dillon, P. J.

2009-05-01

The fate of dissolved organic matter (DOM) in lakes and streams is significantly affected by photochemical transformation of DOM. A series of laboratory photochemical experiments has been conducted to describe long term changes in photochemical properties of DOM. The stream samples used in this study originated from three different watersheds in Dorset area (Ontario, Canada), the first watershed has predominantly coniferous cove, the second one is dominated by maple and birch, and a large wetland dominates to the third one. The first order kinetic constant rate was used as a suitable characteristic of photochemical properties of DOM. The higher rates were observed in samples from watershed dominated by coniferous forest while the lower rates were determined in deciduous forest. Kinetic rates from all three watersheds showed sinusoidal pattern during the hydrological year. The rates increased steadily during autumn and winter and decreased during spring and summer. The highest values were observed during the spring melt events when the fresh DOM was flushed out from terrestrial sources. The minimum rate constants were in summer when the discharge was lower. The photochemical properties of DOM changes during the hydrological year and correspond to the seasonal cycles of terrestrial organic matter.

A photochemical crosslinking technology for tissue engineering: enhancement of the physico-chemical properties of collagen-based scaffolds

NASA Astrophysics Data System (ADS)

Chan, Barbara P.

2005-04-01

Collagen gel is a natural biomaterial commonly used in tissue engineering because of its close resemblance to nature, negligible immunogenecity and excellent biocompatibility. However, unprocessed collagen gel is mechanically weak, highly water binding and vulnerable to chemical and enzymatic attacks that limits its use in tissue engineering in particular tissues for weight-bearing purposes. The current project aimed to strengthen and stabilize collagen scaffolds using a photochemical crosslinking technique. Photochemical crosslinking is rapid, efficient, non-thermal and does not involve toxic chemicals, comparing with other crosslinking methods such as glutaraldehyde and gamma irradiation. Collagen scaffolds were fabricated using rat-tail tendon collagen. An argon laser was used to process the collagen gel after equilibrating with a photosensitizing reagent. Scanning electronic microscope was used to characterize the surface and cross-sectional morphology of the membranes. Physico-chemical properties of the collagen scaffolds such as water-binding capacity, mechanical properties and thermostability were studied. Photochemical crosslinking significantly reduced the water-binding capacity, a parameter inversely proportional to the extent of crosslinking, of collagen scaffolds. Photochemical crosslinking also significantly increased the ultimate stress and tangent modulus at 90% of the rupture strain of the collagen scaffolds. Differential scanning calorimetry analysis showed a significantly higher shrinkage temperature and absence of the denaturation peak during the thermoscan comparing with the controls. This means greater thermostability in the photochemically crosslinked collagen scaffolds. This study demonstrates that the photochemical crosslinking technology is able to enhance the physicochemical propterties of collagen scaffolds by strengthening, stabilizing and controlling the swelling ratio of the collagen scaffolds so as to enable their use for tissue engineering.

Nonsymmetrical 3,4-dithienylmaleimides by cross-coupling reactions with indium organometallics: synthesis and photochemical studies.

PubMed

Mosquera, Angeles; Férnandez, M Isabel; Canle Lopez, Moisés; Pérez Sestelo, José; Sarandeses, Luis A

2014-10-27

The synthesis and photochemical study of novel nonsymmetrical 1,2-dithienylethenes (DTEs) with a maleimide bridge have been carried out. The synthetic approach to the DTEs was based on successive selective palladium-catalyzed cross-coupling reactions of 5-susbtituted-2-methyl-3-thiophenyl indium reagents with 3,4-dichloromaleimides. The required organoindium reagents were prepared from 2-methyl-3,5-dibromothiophene by a selective (C-5) coupling reaction with triorganoindium compounds (R3 In) and subsequent metal-halogen exchange. The coupling reactions usually gave good yields and have a high atom economy with substoichiometric amounts of R3 In. The results of photochemical studies show that these novel dithienylmaleimides undergo a photocyclization reaction upon irradiation in the UV region and a photocycloreversion after excitation in the visible region, thus they can be used as photochemical switches. ON-OFF operations can be repeated in successive cycles without appreciable loss of effectiveness in the process. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Design of organic ternary blends and small-molecule bulk heterojunctions: photophysical considerations

NASA Astrophysics Data System (ADS)

Rajesh, Kallarakkal Ramakrishnan; Paudel, Keshab; Johnson, Brian; Hallani, Rawad; Anthony, John; Ostroverkhova, Oksana

2015-01-01

We explored relationships between photophysical processes and solar cell characteristics in solution-processable bulk heterojunctions (BHJs), in particular: (1) polymer donor:fullerene acceptor:small-molecule (SM) nonfullerene acceptor, (2) polymer donor:SM donor:SM nonfullerene acceptor, and (3) SM donor:SM nonfullerene or fullerene acceptor. Addition of a nonfullerene SM acceptor to "efficient" polymer:fullerene BHJs led to a reduction in power conversion efficiency (PCE), mostly due to decreased charge photogeneration efficiency and increased disorder. By contrast, addition of an SM donor to "inefficient" polymer:SM nonfullerene acceptor BHJs led to a factor of two to three improvement in the PCE, due to improved charge photogeneration efficiency and transport. In most blends, exciplex formation was observed and correlated with a reduced short-circuit current (Jsc) without negatively impacting the open-circuit voltage (Voc). A factor of ˜5 higher PCE was observed in SM donor:fullerene acceptor BHJs as compared to SMBHJs with the same SM donor but nonfullerene acceptor, due to enhanced charge carrier photogeneration in the blend with fullerene. Our study revealed that the HOMO and LUMO energies of molecules comprising a blend are not reliable parameters for predicting Voc of the blend, and an understanding of the photophysics is necessary for interpreting solar cell characteristics and improving the molecular design of BHJs.

Effect of diblock copolymer properties on the photophysical properties of dendrimer silicon phthalocyanine nanoconjugates

NASA Astrophysics Data System (ADS)

Chen, Kuizhi; Pan, Sujuan; Zhuang, Xuemei; Lv, Hafei; Que, Shoulin; Xie, Shusen; Yang, Hongqin; Peng, Yiru

2016-07-01

1-2 generation poly(benzyl aryl ether) dendrimer silicon phthalocyanines with axially disubstituted cyano terminal functionalities (G n -DSiPc(CN)4 n , (G n = n-generation dendrimer, n = 1-2)) were synthesized. Their structures were characterized by elemental analysis, IR, 1H NMR, and ESI-MS. Polymeric nanoparticles (G n -DSiPc(CN)4 n /m) were formed through encapsulating G n -DSiPc(CN)4 n into three monomethoxyl poly(ethylene glycol)-poly(ɛ-caprolactone) diblock copolymers (MPEG-PCL) with different hydrophilic/hydrophobic proportion, respectively. The effect of dendritic generation and the hydrophilic/hydrophobic proportion of diblock copolymers on the UV/Vis and fluorescence spectra of G n -DSiPc(CN)4 n and G n -DSiPc(CN)4 n /m were studied. The photophysical properties of polymeric nanoparticles exhibited dendritic generation and hydrophilic/hydrophobic proportion dependence. The fluorescence intensities and lifetimes of G n -DSiPc(CN)4 n /m were lower than the corresponding free dendrimer phthalocyanines. G n -DSiPc(CN)4 n encapsulated into MPEG-PCL with hydrophilic/hydrophobic molecular weight ratio 2000:4000 exhibited excellent photophysical property. The mean diameter of MPEG2000-PCL2000 micelles was about 70 nm, which decreased when loaded with G n -DSiPc(CN)4 n .

Synthesis, photophysical properties, and computational studies of four-coordinate copper(I) complexes based on benzimidazolylidene N-heterocyclic carbene (NHC) ligands bearing aryl substituents

NASA Astrophysics Data System (ADS)

Xu, Shengxian; Wang, Jinglan; Liu, Shaobo; Zhao, Feng; Xia, Hongying; Wang, Yibo

2018-02-01

Three four-coordinate N-heterocyclic carbene (NHC) copper(I) complexes, [Cu(Ph-BenIm-Py)(POP)]PF6 (1), [Cu(Naph-BenIm-Py)(POP)]PF6 (2), and [Cu(Anthr-BenIm-Py)(POP)]PF6 (3) (Ph-BenIm-Py = 3-benzyl-1-(pyridin-2-yl)-1H-benzimidazolylidene, Naph-BenIm-Py = 3-(naphthalen-2-yl-1-(pyridin-2-yl)-1H- benzimidazolylidene, Anthr-BenIm-Py = 3-(anthracen-9-yl)-1-(pyridin-2-yl)-1H-benzimidazolylidene, and POP = bis[2-diphenylphosphino]-phenyl)ether) have been synthesized and characterized. The different aryl substituents (phenyl, naphthyl, and anthracyl groups) were introduced into NHC ligands and the corresponding photophysical properties of the complexes were systematically investigated. The absorption spectra of all NHCsbnd Cu(I) complexes show a characteristic feature of metal-to-ligand charge transfer (MLCT) in the lower-energy region. Complex 1 exhibited good photoluminescence (PL) properties companying with the high quantum yields and long excited-state lifetimes, whereas 2 and 3 with naphthyl and anthracyl groups show the low PL efficiency caused by the strong π-π stacking interactions. Density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations were employed to rationalize the photophysical properties of the NHCsbnd Cu(I) complexes.

Imaging, photophysical properties and DFT calculations of manganese blue (barium manganate(VI) sulphate)--a modern pigment.

PubMed

Accorsi, Gianluca; Verri, Giovanni; Acocella, Angela; Zerbetto, Francesco; Lerario, Giovanni; Gigli, Giuseppe; Saunders, David; Billinge, Rachel

2014-12-18

Manganese blue is a synthetic barium manganate(VI) sulphate compound that was produced from 1935 to the 1990s and was used both as a blue pigment in works of art and by conservators in the restoration of paintings. The photophysical properties of the compound are described as well as the setup needed to record the spatial distribution of the pigment in works of art.

Synthesis, photophysical, and electrochemical properties of wide band gap tetraphenylsilane-carbazole derivatives: Effect of the substitution position and naphthalene side chain

NASA Astrophysics Data System (ADS)

Ho, Kar Wei; Ariffin, A.

2016-12-01

Four tetraphenylsilane-carbazole derivatives with wide bandgaps (3.38-3.55 eV) were synthesized. The effects of the substitution position and of the presence of naphthalene groups on the photophysical, electrochemical and thermal properties were investigated. The derivatives exhibited maximum absorption peaks ranging from 293 to 304 nm and maximum emission peaks ranging from 347 to 386 nm. Changing the carbazole substitution position on the tetraphenylsilane did not significantly change the photophysical and electrochemical properties. However, p-substituted compounds exhibited higher glass transition temperatures than m-substituted compounds. Naphthalene groups with bulky structures had extended the conjugation lengths that red-shifted both the absorption and emission spectra. The LUMO level was decreased, which reduced the optical bandgap and triplet energy level. However, the naphthalene groups significantly improved the thermal stability by increasing the glass transition temperature of the compounds.

Protonated serotonin: Geometry, electronic structures and photophysical properties

NASA Astrophysics Data System (ADS)

Omidyan, Reza; Amanollahi, Zohreh; Azimi, Gholamhassan

2017-07-01

The geometry and electronic structures of protonated serotonin have been investigated by the aim of MP2 and CC2 methods. The relative stabilities, transition energies and geometry of sixteen different protonated isomers of serotonin have been presented. It has been predicted that protonation does not exhibit essential alteration on the S1 ← S0 electronic transition energy of serotonin. Instead, more complicated photophysical nature in respect to its neutral analogue is suggested for protonated system owing to radiative and non-radiative deactivation pathways. In addition to hydrogen detachment (HD), hydrogen/proton transfer (H/PT) processes from ammonium to indole ring along the NH+⋯ π hydrogen bond have been predicted as the most important photophysical consequences of SERH+ at S1 excited state. The PT processes is suggested to be responsible for fluorescence of SERH+ while the HD driving coordinate is proposed for elucidation of its nonradiative deactivation mechanism.

Photophysical Properties and Singlet Oxygen Generation Efficiencies of Water-Soluble Fullerene Nanoparticles

PubMed Central

Stasheuski, Alexander S; Galievsky, Victor A; Stupak, Alexander P; Dzhagarov, Boris M; Choi, Mi Jin; Chung, Bong Hyun; Jeong, Jin Young

2014-01-01

As various fullerene derivatives have been developed, it is necessary to explore their photophysical properties for potential use in photoelectronics and medicine. Here, we address the photophysical properties of newly synthesized water-soluble fullerene-based nanoparticles and polyhydroxylated fullerene as a representative water-soluble fullerene derivative. They show broad emission band arising from a wide-range of excitation energies. It is attributed to the optical transitions from disorder-induced states, which decay in the nanosecond time range. We determine the kinetic properties of the singlet oxygen (1O2) luminescence generated by the fullerene nanoparticles and polyhydroxylated fullerene to consider the potential as photodynamic agents. Triplet state decay of the nanoparticles was longer than 1O2 lifetime in water. Singlet oxygen quantum yield of a series of the fullerene nanoparticles is comparably higher ranging from 0.15 to 0.2 than that of polyhydroxylated fullerene, which is about 0.06. PMID:24893622

Using the Antenna Effect as a Spectroscopic Tool; Photophysics and Solution Thermodynamics of the Model Luminescent Hydroxypyridonate Complex [EuIII(3,4,3-LI(1,2-HOPO))]-

PubMed Central

Abergel, Rebecca J.; D'Aléo, Anthony; Leung, Clara Ng Pak; Shuh, David K.; Raymond, Kenneth N.

2009-01-01

While widely used in bioassays, the spectrofluorimetric method described here uses the antenna effect as a tool to probe the thermodynamic parameters of ligands that sensitize lanthanide luminescence. The Eu3+ coordination chemistry, solution thermodynamic stability and photophysical properties of the spermine-based hydroxypyridonate octadentate chelator 3,4,3-LI(1,2-HOPO) are reported. The complex [EuIII(3,4,3-LI(1,2-HOPO))]- luminesces with a long lifetime (805 μs) and a quantum yield of 7.0% in aqueous solution, at pH 7.4. These remarkable optical properties were exploited to determine the high (and proton-independent) stability of the complex (log β110 = 20.2(2)) and to define the influence of the ligand scaffold on the stability and photophysical properties. PMID:19902920

Enhanced photophysics of conjugated polymers

DOEpatents

Chen, Liaohai [Argonne, IL; Xu, Su [Santa Clara, CA; McBranch, Duncan [Santa Fe, NM; Whitten, David [Santa Fe, NM

2003-05-27

The addition of oppositely charged surfactant to fluorescent ionic conjugated polymer forms a polymer-surfactant complex that exhibits at least one improved photophysical property. The conjugated polymer is a fluorescent ionic polymer that typically has at least one ionic side chain or moiety that interacts with the specific surfactant selected. The photophysical property improvements may include increased fluorescence quantum efficiency, wavelength-independent emission and absorption spectra, and more stable fluorescence decay kinetics. The complexation typically occurs in a solution of a polar solvent in which the polymer and surfactant are soluble, but it may also occur in a mixture of solvents. The solution is commonly prepared with a surfactant molecule:monomer repeat unit of polymer ratio ranging from about 1:100 to about 1:1. A polymer-surfactant complex precipitate is formed as the ratio approaches 1:1. This precipitate is recoverable and usable in many forms.

Photophysical and lasing properties of new analogs of the boron-dipyrromethene laser dye pyrromethene 567 incorporated into or covalently bounded to solid matrices of poly(methyl methacrylate).

PubMed

López Arbeloa, F; Bañuelos Prieto, J; López Arbeloa, I; Costela, A; García-Moreno, I; Gómez, C; Amat-Guerri, F; Liras, M; Sastre, R

2003-07-01

The photophysical, lasing and thermostability properties of newly synthesized analogs of the commercial dye pyrromethene 567 (PM567) have been measured in polymeric matrices of poly(methyl methacrylate) both when used as a dopant and when covalently bounded to the polymeric chain. These analogs have an acetoxy or a polymerizable methacryloyloxy group at the end of a polymethylene chain at Position 8 of the PM567 chromophore core. Clear correlations between photophysical and lasing characteristics are observed. Linking chain lengths with three or more methylene units give the highest fluorescence quantum yields (as high as 0.89) and lasing efficiencies (as high as 41%). The covalent linkage of the chromophore to the polymeric chain via the methacryloyloxy group improves the photostability of the PM567 chromophore.

Changes in the photochemical environment of the temperate North Pacific troposphere in response to increased Asian emissions

NASA Astrophysics Data System (ADS)

Parrish, D. D.; Dunlea, E. J.; Atlas, E. L.; Schauffler, S.; Donnelly, S.; Stroud, V.; Goldstein, A. H.; Millet, D. B.; McKay, M.; Jaffe, D. A.; Price, H. U.; Hess, P. G.; Flocke, F.; Roberts, J. M.

2004-12-01

Measurements during the Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) field study characterized the springtime, eastern Pacific ozone distribution at two ground sites, from the National Oceanic and Atmospheric Administration WP-3D aircraft, and from a light aircraft operated by the University of Washington. D. Jaffe and colleagues compared the 2002 ozone distribution with measurements made in the region over the two previous decades and show that average ozone levels over the eastern midlatitude Pacific have systematically increased by ˜10 ppbv in the last two decades. Here we provide substantial evidence that a marked change in the photochemical environment in the springtime troposphere of the North Pacific is responsible for this increased O3. This change is evidenced in the eastern North Pacific ITCT 2K2 study region by (1) larger increases in the minimum observed ozone levels compared to more modest increases in the maximum levels, (2) increased peroxyacetyl nitrate (PAN) levels that parallel trends in NOx emissions, and (3) decreased efficiency of photochemical O3 destruction, i.e., less negative O3 photochemical tendency (or net rate of O3 photochemical production; P(O3)). This changed photochemical environment is hypothesized to be due to anthropogenic emissions from Asia, which are believed to have substantially increased over the two decades preceding the study. We propose that their influence has changed the springtime Pacific tropospheric photochemistry from predominately ozone destroying to more nearly ozone producing. However, chemical transport model calculations indicate the possible influence of a confounding factor; unusual transport of tropical air to the western North Pacific during one early field study may have played a role in this apparent change in the photochemistry.

The photophysics of monomeric bacteriochlorophylls c and d and their derivatives: properties of the triplet state and singlet oxygen photogeneration and quenching

NASA Technical Reports Server (NTRS)

Krasnovsky, A. A. Jr; Cheng, P.; Blankenship, R. E.; Moore, T. A.; Gust, D.

1993-01-01

Measurements of pigment triplet-triplet absorption, pigment phosphorescence and photosensitized singlet oxygen luminescence were carried out on solutions containing monomeric bacteriochlorophylls (Bchl) c and d, isolated from green photosynthetic bacteria, and their magnesium-free and farnesyl-free analogs. The energies of the pigment triplet states fell in the range 1.29-1.34 eV. The triplet lifetimes in aerobic solutions were 200-250 ns; they increased to 280 +/- 70 microseconds after nitrogen purging in liquid solutions and to 0.7-2.1 ms in a solid matrix at ambient or liquid nitrogen temperatures. Rate constants for quenching of the pigment triplet state by oxygen were (2.0-2.5) x 10(9) M-1 s-1, which is close to 1/9 of the rate constant for diffusion-controlled reactions. This quenching was accompanied by singlet oxygen formation. The quantum yields for the triplet state formation and singlet oxygen production were 55-75% in air-saturated solutions. Singlet oxygen quenching by ground-state pigment molecules was observed. Quenching was the most efficient for magnesium-containing pigments, kq = (0.31-1.2) x 10(9) M-1 s-1. It is caused mainly by a physical process of singlet oxygen (1O2) deactivation. Thus, Bchl c and d and their derivatives, as well as chlorophyll and Bchl a, combine a high efficiency of singlet oxygen production with the ability to protect photochemical and photobiological systems against damage by singlet oxygen.

Concepts and Principles of Photodynamic Therapy as an Alternative Antifungal Discovery Platform

PubMed Central

Dai, Tianhong; Fuchs, Beth B.; Coleman, Jeffrey J.; Prates, Renato A.; Astrakas, Christos; St. Denis, Tyler G.; Ribeiro, Martha S.; Mylonakis, Eleftherios; Hamblin, Michael R.; Tegos, George P.

2012-01-01

Opportunistic fungal pathogens may cause superficial or serious invasive infections, especially in immunocompromised and debilitated patients. Invasive mycoses represent an exponentially growing threat for human health due to a combination of slow diagnosis and the existence of relatively few classes of available and effective antifungal drugs. Therefore systemic fungal infections result in high attributable mortality. There is an urgent need to pursue and deploy novel and effective alternative antifungal countermeasures. Photodynamic therapy (PDT) was established as a successful modality for malignancies and age-related macular degeneration but photodynamic inactivation has only recently been intensively investigated as an alternative antimicrobial discovery and development platform. The concept of photodynamic inactivation requires microbial exposure to either exogenous or endogenous photosensitizer molecules, followed by visible light energy, typically wavelengths in the red/near infrared region that cause the excitation of the photosensitizers resulting in the production of singlet oxygen and other reactive oxygen species that react with intracellular components, and consequently produce cell inactivation and death. Antifungal PDT is an area of increasing interest, as research is advancing (i) to identify the photochemical and photophysical mechanisms involved in photoinactivation; (ii) to develop potent and clinically compatible photosensitizers; (iii) to understand how photoinactivation is affected by key microbial phenotypic elements multidrug resistance and efflux, virulence and pathogenesis determinants, and formation of biofilms; (iv) to explore novel photosensitizer delivery platforms; and (v) to identify photoinactivation applications beyond the clinical setting such as environmental disinfectants. PMID:22514547

Crosslinked polymer nanoparticles containing single conjugated polymer chains

NASA Astrophysics Data System (ADS)

Ponzio, Rodrigo A.; Marcato, Yésica L.; Gómez, María L.; Waiman, Carolina V.; Chesta, Carlos A.; Palacios, Rodrigo E.

2017-06-01

Conjugated polymer nanoparticles are widely used in fluorescent labeling and sensing, as they have mean radii between 5 and 100 nm, narrow size dispersion, high brightness, and are photochemically stable, allowing single particle detection with high spatial and temporal resolution. Highly crosslinked polymers formed by linking individual chains through covalent bonds yield high-strength rigid materials capable of withstanding dissolution by organic solvents. Hence, the combination of crosslinked polymers and conjugated polymers in a nanoparticulated material presents the possibility of interesting applications that require the combined properties of constituent polymers and nanosized dimension. In the present work, F8BT@pEGDMA nanoparticles composed of poly(ethylene glycol dimethacrylate) (pEGDMA; a crosslinked polymer) and containing the commercial conjugated polymer poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT) were synthesized and characterized. Microemulsion polymerization was applied to produce F8BT@pEDGMA particles with nanosized dimensions in a ∼25% yield. Photophysical and size distribution properties of F8BT@pEDGMA nanoparticles were evaluated by various methods, in particular single particle fluorescence microscopy techniques. The results demonstrate that the crosslinking/polymerization process imparts structural rigidity to the F8BT@pEDGMA particles by providing resistance against dissolution/disintegration in organic solvents. The synthesized fluorescent crosslinked nanoparticles contain (for the most part) single F8BT chains and can be detected at the single particle level, using fluorescence microscopy, which bodes well for their potential application as molecularly imprinted polymer fluorescent nanosensors with high spatial and temporal resolution.

Development and Application of Chemical Probes for Vibrational Imaging by Stimulated Raman Scattering

NASA Astrophysics Data System (ADS)

Hu, Fanghao

During the last decade, Raman microscopy is experiencing rapid development and increasingly applied in biological and medical systems. Especially, stimulated Raman scattering (SRS) microscopy, which significantly improves the sensitivity of Raman scattering through stimulated emission, has allowed direct visualization of many species that are previously challenging with conventional fluorescence imaging. Compared to fluorescence, SRS imaging requires no label or small label on the target molecule, thus with minimal perturbation to the molecule of interest. Moreover, Raman scattering is free from complicated photophysical and photochemical processes such as photobleaching, and has intrinsically narrower linewidth than fluorescence emission. This allows multiplexed Raman imaging with minimal spectral crosstalk and excellent photo-stability. To achieve the full potential of Raman microscopy, vibrational probes have been developed for Raman imaging. Multiple Raman probes with a few atoms in size are applied in Raman imaging with high sensitivity and specificity. An overview of both fluorescence and Raman microscopy and their imaging probes is given in Chapter 1 with a brief discussion on the SRS theory. Built on the current progress of Raman microscopy and vibrational probes, I write on my research in the development of carbon-deuterium, alkyne and nitrile probes for visualizing choline metabolism (Chapter 2), glucose uptake activity (Chapter 3), complex brain metabolism (Chapter 4) and polymeric nanoparticles (Chapter 5) in live cells and tissues, as well as the development of polyyne-based vibrational probes for super-multiplexed imaging, barcoding and analysis (Chapter 6).

Polymer-based chromophore-catalyst assemblies for solar energy conversion

NASA Astrophysics Data System (ADS)

Leem, Gyu; Sherman, Benjamin D.; Schanze, Kirk S.

2017-12-01

The synthesis of polymer-based assemblies for light harvesting has been motivated by the multi-chromophore antennas that play a role in natural photosynthesis for the potential use in solar conversion technologies. This review describes a general strategy for using polymer-based chromophore-catalyst assemblies for solar-driven water oxidation at a photoanode in a dye-sensitized photoelectrochemical cell (DSPEC). This report begins with a summary of the synthetic methods and fundamental photophysical studies of light harvesting polychormophores in solution which show these materials can transport excited state energy to an acceptor where charge-separation can occur. In addition, studies describing light harvesting polychromophores containing an anchoring moiety (ionic carboxylate) for covalent bounding to wide band gap mesoporous semiconductor surfaces are summarized to understand the photophysical mechanisms of directional energy flow at the interface. Finally, the performance of polychromophore/catalyst assembly-based photoanodes capable of light-driven water splitting to oxygen and hydrogen in a DSPEC are summarized.

Polymer-based chromophore-catalyst assemblies for solar energy conversion.

PubMed

Leem, Gyu; Sherman, Benjamin D; Schanze, Kirk S

2017-01-01

The synthesis of polymer-based assemblies for light harvesting has been motivated by the multi-chromophore antennas that play a role in natural photosynthesis for the potential use in solar conversion technologies. This review describes a general strategy for using polymer-based chromophore-catalyst assemblies for solar-driven water oxidation at a photoanode in a dye-sensitized photoelectrochemical cell (DSPEC). This report begins with a summary of the synthetic methods and fundamental photophysical studies of light harvesting polychormophores in solution which show these materials can transport excited state energy to an acceptor where charge-separation can occur. In addition, studies describing light harvesting polychromophores containing an anchoring moiety (ionic carboxylate) for covalent bounding to wide band gap mesoporous semiconductor surfaces are summarized to understand the photophysical mechanisms of directional energy flow at the interface. Finally, the performance of polychromophore/catalyst assembly-based photoanodes capable of light-driven water splitting to oxygen and hydrogen in a DSPEC are summarized.

An assessment of western North Pacific ozone photochemistry based on springtime observations from NASA's PEM-West B (1994) and TRACE-P (2001) field studies

NASA Astrophysics Data System (ADS)

Davis, D. D.; Chen, G.; Crawford, J. H.; Liu, S.; Tan, D.; Sandholm, S. T.; Jing, P.; Cunnold, D. M.; Dinunno, B.; Browell, E. V.; Grant, W. B.; Fenn, M. A.; Anderson, B. E.; Barrick, J. D.; Sachse, G. W.; Vay, S. A.; Hudgins, C. H.; Avery, M. A.; Lefer, B.; Shetter, R. E.; Heikes, B. G.; Blake, D. R.; Blake, N.; Kondo, Y.; Oltmans, S.

2003-11-01

The current study provides a comparison of the photochemical environments for two NASA field studies focused on the western North Pacific (PEM-West-B (PWB) and TRACE-P (TP)). These two studies were separated in calendar time by approximately 7 years. Both studies were carried out under springtime conditions, with PWB being launched in 1994 and TP being deployed in 2001 (i.e., 23 February-15 March 1994 and 10 March-15 April 2001, respectively). Because of the 7-year time separation, these two studies presented a unique scientific opportunity to assess whether evidence could be found to support the Department of Energy's projections in 1997 that increases in anthropogenic emissions from East Asia could reach 5%/yr. Such projections would lead one to the conclusion that a significant shift in the atmospheric photochemical properties of the western North Pacific would occur. To the contrary, the findings from this study support the most recent emission inventory data [, 2003] in that they show no significant systematic trend involving increases in any O3 precursor species and no evidence for a significant shift in the level of photochemical activity over the western North Pacific. This conclusion was reached in spite of there being real differences in the concentration levels of some species as well as differences in photochemical activity between PWB and TP. However, nearly all of these differences were shown to be a result of a near 3-week shift in TP's sampling window relative to PWB, thus placing it later in the spring season. The photochemical enhancements seen during TP were most noticeable for latitudes in the range of 25-45°N. Most important among these were increases in J(O1D), OH, and HO2 and values for photochemical ozone formation and destruction, all of which were typically two times larger than those calculated for PWB. A comparison of these airborne results with ozonesonde data from four Japanese stations provided further evidence showing that the 3-week shift in the respective sampling windows of PWB and TP was a likely cause for the differences seen in O3 levels and in photochemical activity between the two airborne studies.

Photophysical properties of fullerene-dendron-pyropheophorbide supramolecules

NASA Astrophysics Data System (ADS)

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

2004-05-01

Two novel monofullerene-bis(pyropheophorbide a) complexes were synthesized and their photophysical properties were studied by using both steady-state and time-resolved techniques. It was revealed that in the pyropheophorbide a (pyroPheo)-C 60 molecular system (FP1) strong quenching of the first excited singlet state of the pyroPheo and, as result, dramatically decreasing of photosensitized singlet oxygen generation occurs by efficient photoinduced electron transfer to the fullerene molecule with a rate constant of 2.5 × 10 9 s -1. In contrast, the fullerene hexaadduct-bis(pyroPheo) system (FHP1), which possesses five diethyl malonate addends in the remaining octahedral positions, shows a high singlet oxygen quantum yield which is due to the reduced fullerene chromophore which is not a good electron acceptor anymore.

PHOTOCHEMICAL REACTIONS AMONG FORMALDEHYDE, CHLORINE, AND NITROGEN DIOXIDE IN AIR

EPA Science Inventory

Photochemical reactions among chlorine, nitrogen dioxide, and formaldehyde were studied, using parts-per-million concentrations in 1 atm of air. The reactant mixtures were irradiated by ultraviolet fluorescent lamps and simultaneously analyzed by the Fourier transform infrared te...

Photochemical insertion of alkynes into Cp sub 2 Fe sub 2 (CO) sub 2 (. mu. -CO) sub 2 : A mechanistic study by laser flash photolysis

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

Bursten, B.E.; McKee, S.D.; Platz, M.S.

1989-04-26

Cp{sub 2}Fe{sub 2}(CO){sub 2}({mu}-CO){sub 2} (1: Cp = {eta}{sup 5}-C{sub 5}H{sub 5}) has a rich and diverse photochemistry, as evidenced by the plethora of synthetic and mechanistic studies of it in the literature. Early photochemical studies of 1 have demonstrated homolysis to the radical Cp(CO){sub 2}Fe{sup {sm bullet}} (2). Recent work on metal dimers indicates that a dinuclear species is formed concomitantly. Tyler, Schmidt, and Gray (TSG) first proposed that irradiation of 1 leads to the dinuclear species 3, which they suggested was the intermediate responsible for phosphine substitution. Research by other individuals has indicated that the substitutionally active speciesmore » is the CO-loss photoproduct CpFe({mu}-CO){sub 3}FeCp (4). The authors interest in the photochemistry of 1 stemmed from their theoretical studies on piano-stool dimers. One reaction of particular concern is the photochemical insertion of alkynes into 1 to yield dimetallacyclopentenone 5. On the basis of MO calculations, the authors proposed a possible LUMO-controlled mechanism for this reaction that involved alkyne addition to the TSG transition state 3, followed by CO loss. In this contribution, they report initial experimental studies which demonstrate that 4 is the photochemical intermediate responsible for this reaction. They consider this reaction to be a paradigm for photochemical substitution and insertion reaction in such systems.« less

Investigation on the photophysical properties of ESPT inspired salicylaldehyde-based sensor for fluoride sensing.

PubMed

Liu, Kai; Zhao, Xiaojun; Liu, Qingxiang; Huo, Jianzhong; Wang, Xing; Wu, Yanping

2015-04-05

A simple, highly selective and sensitive chemosensor (E)-2-((quinolin-8-ylimino) methyl) phenol (QP) has been developed for the fluoride, as demonstrated by the photophysical properties obtained by UV-vis and fluorescent methods. Excited-state inter/intramolecular proton transfer (ESPT) was suggested to be responsible for the fluoride-induced 'turn on' fluorescence and the blue shift of 25 nm in the emission spectrum. Copyright © 2014 Elsevier B.V. All rights reserved.

EFFECTS OF PHOTOCHEMICAL OXIDANTS ON PLANTS

EPA Science Inventory

Photochemical oxidants are found in 'photochemical smog' which is a complex mixture of primary and secondary air pollutants. The photochemical oxidants are secondary air pollutants formed by the action of sunlight on nitrogen oxides and reactive hydrocarbons, their precursors. Th...

Photochemical Transformation of Graphene Oxide in Sunlight

EPA Science Inventory

Graphene oxide (GO) is a graphene derivative that is more easily manufactured in large scale and used to synthesize reduced graphene oxide (rGO) with properties analogous to graphene. In this study, we investigate the photochemical fate of GO under sunlight conditions. The resu...

Oxidation of Fe(II) in rainwater.

PubMed

Willey, J D; Whitehead, R F; Kieber, R J; Hardison, D R

2005-04-15

Photochemically produced Fe(II) is oxidized within hours under environmentally realistic conditions in rainwater. The diurnal variation between photochemical production and reoxidation of Fe(II) observed in our laboratory accurately mimics the behavior of ferrous iron observed in field studies where the highest concentrations of dissolved Fe(ll) occur in afternoon rain during the period of maximum sunlight intensity followed by gradually decreasing concentrations eventually returning to early morning pre-light values. The experimental work presented here, along with the results of kinetics studies done by others, suggests thatthe primary process responsible for the decline in photochemically produced Fe(II) concentrations is oxidation by hydrogen peroxide. This reaction is first order with respect to both the concentrations of Fe(II) and H2O2. The second-order rate constant determined for six different authentic rain samples varied over an order of magnitude and was always less than or equal to the rate constant determined for this reaction in simple acidic solutions. Oxidation of photochemically produced ferrous iron by other oxidants including molecular oxygen, ozone, hydroxyl radical, hydroperoxyl/superoxide radical, and hexavalent chromium were found to be insignificant under the conditions present in rainwater. This study shows that Fe(II) occurs as at least two different chemical species in rain; photochemically produced Fe(II) that is oxidized over time periods of hours, and a background Fe(II) that is protected against oxidation, perhaps by organic complexation, and is stable against oxidation for days. Because the rate of oxidation of photochemically produced Fe(II) does not increase with increasing rainwater pH, the speciation of this more labile form of Fe(II) is also not controlled by simple hydrolysis reactions.

Photochemical transformation of graphene oxide in sunlight (journal)

EPA Science Inventory

Graphene oxide (GO) is a graphene derivative that is more easily manufactured in large scale and used to synthesize reduced graphene oxide (rGO) with properties analogous to graphene. In this study, we investigate the photochemical fate of GO under sunlight conditions. The resu...

High-temperature photochemical destruction of toxic organic wastes using concentrated solar radiation

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

Dellinger, B.; Graham, J.L.; Berman, J.M.

1994-05-01

Application of concentrated solar energy has been proposed to be a viable waste disposal option. Specifically, this concept of solar induced high-temperature photochemistry is based on the synergistic contribution of concentrated infrared (IR) radiation, which acts as an intense heating source, and near ultraviolet and visible (UV-VIS) radiation, which can induce destructive photochemical processes. Some significant advances have been made in the theoretical framework of high-temperature photochemical processes (Section 2) and development of experimental techniques for their study (Section 3). Basic thermal/photolytic studies have addressed the effect of temperature on the photochemical destruction of pure compounds (Section 4). Detailed studiesmore » of the destruction of reaction by-products have been conducted on selected waste molecules (Section 5). Some very limited results are available on the destruction of mixtures (Section 6). Fundamental spectroscopic studies have been recently initiated (Section 7). The results to date have been used to conduct some relatively simple scale-up studies of the solar detoxification process. More recent work has focused on destruction of compounds that do not directly absorb solar radiation. Research efforts have focused on homogeneous as well as heterogeneous methods of initiating destructive reaction pathways (Section 9). Although many conclusions at this point must be considered tentative due to lack of basic research, a clearer picture of the overall process is emerging (Section 10). However, much research remains to be performed and most follow several veins, including photochemical, spectroscopic, combustion kinetic, and engineering scale-up (Section 11).« less

Deepening Insights of Charge Transfer and Photophysics in a Novel Donor-Acceptor Cocrystal for Waveguide Couplers and Photonic Logic Computation.

PubMed

Zhu, Weigang; Zhu, Lingyun; Zou, Ye; Wu, Yishi; Zhen, Yonggang; Dong, Huanli; Fu, Hongbing; Wei, Zhixiang; Shi, Qiang; Hu, Wenping

2016-07-01

The charge transfer and photophysics in a new light-emitting cocrystal with ribbon-like morphology are revealed in-depth. These cocrystals can serve as an efficient 1D optical waveguide, and the cocrystal waveguide couplers fabricated by a probe-assisted crystal-moving technique exhibit interfacial white emission and can function as basic photonic logic gates, showing potential for future integrated photonics. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lanthanide complexes with aromatic o-phosphorylated ligands: synthesis, structure elucidation and photophysical properties.

PubMed

Shuvaev, Sergey; Utochnikova, Valentina; Marciniak, Łukasz; Freidzon, Alexandra; Sinev, Ilya; Van Deun, Rik; Freire, Ricardo O; Zubavichus, Yan; Grünert, Wolfgang; Kuzmina, Natalia

2014-02-28

Lanthanide complexes LnL3 (Ln = Sm, Eu, Tb, Dy, Tm, Yb, Lu) with aromatic o-phosphorylated ligands (HL(1) and HL(2)) have been synthesized and identified. Their molecular structure was proposed on the basis of a new complex approach, including DFT calculations, Sparkle/PM3 modelling, EXAFS spectroscopy and luminescent probing. The photophysical properties of all of the complexes were investigated in detail to obtain a deeper insight into the energy transfer processes.

Recent Developments in the Photophysics of Single-Walled Carbon Nanotubes for Their Use as Active and Passive Material Elements in Thin Film Photovoltaics

DTIC Science & Technology

2013-01-01

photons of energy hn > 1.1 eV, which is the same spectral range captured by a silicon solar cell . The thermodynamic limit for the efficiency of a solar ...Park, NC 27709-2211 15. SUBJECT TERMS Carbon nanotube photovoltaic photophysics solar cell perspective Michael S. Arnold, Jeffrey L. Blackburn...increasing the efficiency and functionality of next-generation solar cells . Widely tunable properties open up possibilities for using nanotubes in many

Anilinomethylrhodamines: pH sensitive probes with tunable photophysical properties by substituent effect.

PubMed

Best, Quinn A; Liu, Chuangjun; van Hoveln, Paul D; McCarroll, Matthew E; Scott, Colleen N

2013-10-18

A series of pH dependent rhodamine analogues possessing an anilino-methyl moiety was developed and shown to exhibit a unique photophysical response to pH. These anilinomethylrhodamines (AnMR) maintain a colorless, nonfluorescent spirocyclic structure at high pH. The spirocyclic structures open in mildly acidic conditions and are weakly fluorescent; however, at very low pH, the fluorescence is greatly enhanced. The equilibrium constants of these processes show a linear response to substituent effects, which was demonstrated by the Hammett equation.

The reactions of O(ID) and OH with CH3OH, oxidation of the HCO radial, and the photochemical oxidation of formaldehyde. [photochemical reactions in stratosphere

NASA Technical Reports Server (NTRS)

Osif, T. L.

1976-01-01

An experimental, laboratory study of the various photochemical reactions that can occur in the mesosphere and stratosphere is presented. N2O was photolyzed at 2139 A in the presence of CH3OH and CO. The O(id) produced in the photolysis reacted with CH3OH to produce OH radicals, and thus the reactions of both O(id) and OH were able to be studied. Also considered was the oxidation of the HCO radical. Mixtures of Cl2, O2, H2CO, and sometimes N2 or He were irradiated at 3660 A at several temperatures to photodecompose the Cl2. The photochemical oxidation of formaldehyde was studied as follows: formaldehyde in the presence of N2 and/or O2 (usually dry air) was photolyzed with a medium pressure Hg lamp used in conjunction with various filters which transmit different relative amounts of Hg lines from 2894 A to 3660 A. Results are presented and discussed, along with a description of experimental procedures and apparatus, and chemical reaction kinetics.

40 CFR 52.269 - Control strategy and regulations: Photochemical oxidants (hydrocarbons) and carbon monoxide.

Code of Federal Regulations, 2011 CFR

2011-07-01

...: Photochemical oxidants (hydrocarbons) and carbon monoxide. 52.269 Section 52.269 Protection of Environment... PLANS California § 52.269 Control strategy and regulations: Photochemical oxidants (hydrocarbons) and... provide for attainment and maintenance of the national standards for photochemical oxidants (hydrocarbons...

40 CFR 52.269 - Control strategy and regulations: Photochemical oxidants (hydrocarbons) and carbon monoxide.

Code of Federal Regulations, 2010 CFR

2010-07-01

...: Photochemical oxidants (hydrocarbons) and carbon monoxide. 52.269 Section 52.269 Protection of Environment... PLANS California § 52.269 Control strategy and regulations: Photochemical oxidants (hydrocarbons) and... provide for attainment and maintenance of the national standards for photochemical oxidants (hydrocarbons...

Diazobenzene-containing conjugated polymers as dark quenchers.

PubMed

Wu, Jiatao; Tan, Ying; Xie, Yonghua; Wu, Yi; Zhao, Rui; Jiang, Yuyang; Tan, Chunyan

2013-12-18

The synthesis and photophysical characterization of new conjugated polymers (CPs) with alternating phenylethynylene and diazobenzene (azo-PPE) units were reported, which showed broadened absorption and no measurable fluorescence. Quenching studies showed that azo-PPEs displayed high efficiency over a wide wavelength range.

Electrochemical, Spectroscopic and 1O2 Sensitization Characteristics of 10,10-Dimethylbiladiene Complexes of Zinc and Copper

DOE PAGES

Pistner, Allen; Pupillo, Rachel C.; Yapp, Glenn P. A.; ...

2014-09-04

The synthesis, electrochemistry and photophysical characterization of a 10,10- dimethylbiladiene tetrapyrrole bearing ancillary pentafluorophenyl groups at the 5 and 15-meso positions (DMBil1) is presented. This non-macrocyclic tetrapyrrole platform is robust and can serve as an excellent ligand scaffold for Zn 2+ and Cu 2+ centers. X-ray diffraction studies conducted for DMBil1 along with the corresponding Zn[DMBil1] and Cu[DMBil1] complexes show that this ligand scaffold binds a single metal ion within the tetrapyrrole core. Additionally, electrochemical experiments revealed that all three of the aforementioned compounds display an interesting redox chemistry, as the DMBil1 framework can be both oxidized and reduced bymore » two electrons. Spectroscopic and photophysical experiments carried out for DMBil1, Zn[DMBil1] and Cu[DMBil1] provide a basic picture of the electronic properties of these platforms. All three biladiene derivatives strongly absorb light in the visible region and are weakly emissive. The ability of these compounds to sensitize the formation of 1O 2 at wavelengths longer than 500 nm was probed. Both the freebase and Zn 2+ 10,10-dimethylbiladiene architectures show modest efficiencies for 1O 2 sensitization. The combination of structural, electrochemical and photophysical data detailed herein, provides a basis for the design of additional biladiene constructs for the activation of O 2 and other small molecules.« less

Trifluoromethyl-Substituted Iridium(III) Complexes: From Photophysics to Photooxidation of a Biological Target.

PubMed

Bevernaegie, Robin; Marcélis, Lionel; Laramée-Milette, Baptiste; De Winter, Julien; Robeyns, Koen; Gerbaux, Pascal; Hanan, Garry S; Elias, Benjamin

2018-02-05

Photodynamic therapeutic agents are of key interest in developing new strategies to develop more specific and efficient anticancer treatments. In comparison to classical chemotherapeutic agents, the activity of photodynamic therapeutic compounds can be finely controlled thanks to the light triggering of their photoreactivity. The development of type I photosensitizing agents, which do not rely on the production of ROS, is highly desirable. In this context, we developed new iridium(III) complexes which are able to photoreact with biomolecules; namely, our Ir(III) complexes can oxidize guanine residues under visible light irradiation. We report the synthesis and extensive photophysical characterization of four new Ir(III) complexes, [Ir(ppyCF 3 ) 2 (N^N)] + [ppyCF 3 = 2-(3,5-bis(trifluoromethyl)phenyl)pyridine) and N^N = 2,2'-dipyridyl (bpy); 2-(pyridin-2-yl)pyrazine (pzpy); 2,2'-bipyrazine (bpz); 1,4,5,8-tetraazaphenanthrene (TAP)]. In addition to an extensive experimental and theoretical study of the photophysics of these complexes, we characterize their photoreactivity toward model redox-active targets and the relevant biological target, the guanine base. We demonstrate that photoinduced electron transfer takes place between the excited Ir(III) complex and guanine which leads to the formation of stable photoproducts, indicating that the targeted guanine is irreversibly damaged. These results pave the way to the elaboration of new type I photosensitizers for targeting cancerous cells.

Determination of photophysical parameters of chlorophyll {alpha} in photosynthetic organisms using the method of nonlinear laser fluorimetry

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

Gostev, T S; Fadeev, V V

2011-05-31

We study the possibility of solving the multiparameter inverse problem of nonlinear laser fluorimetry of molecular systems with high local concentration of fluorophores (by the example of chlorophyll {alpha} molecules in photosynthetic organisms). The algorithms are proposed that allow determination of up to four photophysical parameters of chlorophyll {alpha} from the experimental fluorescence saturation curves. The uniqueness and stability of the inverse problem solution obtained using the proposed algorithms were assessed numerically. The laser spectrometer, designed in the course of carrying out the work and aimed at nonlinear laser fluorimetry in the quasi-stationary and nonstationary excitation regimes is described. Themore » algorithms, proposed in this paper, are tested on pure cultures of microalgae Chlorella pyrenoidosa and Chlamydomonas reinhardtii under different functional conditions. (optical technologies in biophysics and medicine)« less

Synthesis, Photophysical, and Biological Evaluation of Sulfated Polyglycerol Dendronized Perylenebisimides (PBIs)--A Promising Platform for Anti-Inflammatory Theranostic Agents?

PubMed

Heek, T; Kühne, C; Depner, H; Achazi, K; Dernedde, J; Haag, R

2016-03-16

A set of four water-soluble perylene bisimides (PBI) based on sulfated polyglycerol (PGS) dendrons were developed, their photophysical properties determined via UV/vis and fluorescence spectroscopy, and their performance as possible anti-inflammatory agents evaluated via biological in vitro studies. It could be shown that in contrast to charge neutral PG-PBIs the introduction of the additional electrostatic repulsion forces leads to a decrease in the dendron generation necessary for aggregation suppression, allowing the preparation of PBIs with fluorescence quantum yields of >95% with a considerable decreased synthetic effort. Furthermore, the values determined for L-selectin binding down to the nanomolar range, their limited impact on blood coagulation, and their minor activation of the complement system renders these systems ideal for anti-inflammatory purposes.

Photophysics of charge transfer in a polyfluorene/violanthrone blend

NASA Astrophysics Data System (ADS)

Cabanillas-Gonzalez, J.; Virgili, T.; Lanzani, G.; Yeates, S.; Ariu, M.; Nelson, J.; Bradley, D. D. C.

2005-01-01

We present a study of the photophysical and photovoltaic properties of blends of violanthrone in poly[9, 9-bis (2-ethylhexyl)-fluorene-2, 7-diyl ] (PF2/6) . Photoluminescence quenching and photocurrent measurements show moderate efficiencies for charge generation, characteristic of such polymer/dye blends. Pump-probe measurements on blend films suggest that while ˜47% of the total exciton population dissociates within 4ps of photoexcitation, only ˜32% subsequently results in the formation of dye anions. We attribute the discrepancy to the likely formation of complex species with long lifetimes, such as stabilized interface charge pairs or exciplexes. This conclusion is supported by the appearance of a long lifetime component of 2.4ns in the dynamics of the photoinduced absorption signal associated to polarons in photoinduced absorption bands centered at 560nm .

Photophysical properties of Schiff's bases from 3-(1,3-benzothiazol-2-yl)-2-hydroxy naphthalene-1-carbaldehyde.

PubMed

Satam, Manjaree A; Telore, Rahul D; Sekar, Nagaiyan

2014-11-11

A series of novel Schiff's bases have been synthesized from 3-(1,3-benzothiazol-2-yl)-2-hydroxynaphthalene-1-carbaldehyde. The presence of hydroxyl group ortho to the benzothiazolyl group as well as the imine linkage lead to the occurrence of excited state intramolecular proton transfer process. The computational strategy was used to study the ESIPT process of the synthesized Schiff's bases, which revealed surprisingly that the keto form predominantly exists in the ground state contradicting the ESIPT process. Density functional theory and time dependent density functional theory have been used to investigate the structural parameters and photophysical properties in different solvents of one of the Schiff's bases. The experimental results correlate well with the computed results. All Schiff's bases show good thermal stability. Copyright © 2014 Elsevier B.V. All rights reserved.

Photophysical Behaviors of Single Fluorophores Localized on Zinc Oxide Nanostructures

PubMed Central

Fu, Yi; Zhang, Jian; Lakowicz, Joseph R.

2012-01-01

Single-molecule fluorescence spectroscopy has now been widely used to investigate complex dynamic processes which would normally be obscured in an ensemble-averaged measurement. In this report we studied photophysical behaviors of single fluorophores in proximity to zinc oxide nanostructures by single-molecule fluorescence spectroscopy and time-correlated single-photon counting (TCSPC). Single fluorophores on ZnO surfaces showed enhanced fluorescence brightness to various extents compared with those on glass; the single-molecule time trajectories also illustrated pronounced fluctuations of emission intensities, with time periods distributed from milliseconds to seconds. We attribute fluorescence fluctuations to the interfacial electron transfer (ET) events. The fluorescence fluctuation dynamics were found to be inhomogeneous from molecule to molecule and from time to time, showing significant static and dynamic disorders in the interfacial electron transfer reaction processes. PMID:23109903

Regulatory effect of hydroquinone-tetraethylene glycol conjugates on zebrafish pigmentation.

PubMed

Le, Hoa Thi; Hong, Bin Na; Lee, Yeong Ro; Cheon, Ji Hyun; Kang, Tong Ho; Kim, Tae Woo

2016-01-15

We synthesized two hydroquinone-tetraethylene glycol conjugates (HQ-TGs) and investigated their logP, photophysical stability, and redox chemical stability. HQ-TGs are a little more hydrophilic than hydroquinone (HQ) and show an enhanced photophysical and redox chemical stability compared with HQ. In addition we studied the effect of HQ-TGs on cell viability and on zebrafish pigmentation. MTT assay in HF-16 cells showed HQ-TGs are less cytotoxic than HQ. The phenotype-based image analysis of zebrafish larvae suggests that HQ-TGs suppress the pigmentation of zebrafish in a dose-dependent manner. The comparative experiments on stability, cytotoxicity, and zebrafish pigmentation between HQ and HQ-TGs suggest that mono tetraethylene glycol-functionalization of HQ is an alternative solution to overcome the adverse effect of HQ. Copyright © 2015 Elsevier Ltd. All rights reserved.

Influence of functional groups on the photophysical properties of dimethylamino chalcones as laser dyes

NASA Astrophysics Data System (ADS)

Ibnaouf, K. H.; Elzupir, A. O.; AlSalhi, M. S.; Alaamer, Abdulaziz S.

2018-02-01

In this report, a series of 3-(4-(Dimethylamino) phenyl)-1-(4,3 di-substituted phenyl)-(2E) - propen -1-one chalcones was synthesised and examined as optical materials. The influence of functional groups (FG) and solvents on their photophysical properties was investigated. These include absorption, fluorescence, Stokes shift, and amplified spontaneous emission (ASE). The absorption spectra of all compounds showed a wavelength band in the range 404-429 nm, whereas the fluorescence spectra exhibited a band at 470-535 nm. We found that the fluorescence intensity was inversely proportional to the concentration of chalcones. The FGs and solvents had an amazing effect on the photophysical properties of the synthesised materials. Unexpectedly, the electron withdrawing group showed a highly red shift, whereas the electron donating group exhibited a blue shift. Further, these compounds showed large Stokes shifts (up to 5800 cm-1). ASE was observed under pump pulse laser excitation, and the wavelengths were tuned from 509 to 566 nm.

Photophysical properties of fluorescently-labeled peptoids.

PubMed

Rudat, Birgit; Birtalan, Esther; Vollrath, Sidonie B L; Fritz, Daniel; Kölmel, Dominik K; Nieger, Martin; Schepers, Ute; Müllen, Klaus; Eisler, Hans-Jürgen; Lemmer, Uli; Bräse, Stefan

2011-09-01

Fluorescently-labeled biomolecules are often utilized in biochemical or cellular experiments without further detailed spectroscopical characterization. This report is intended to narrow this gap and therefore presents the photophysical investigation of a library of 17 fluorescently-labeled molecules, namely peptoid transporters. First, one peptoid structure is labeled with seven different fluorophores and the spectroscopical properties are examined. Absorption and fluorescence maxima are almost identical for free dyes and conjugated dyes, suggesting free choice of a spectrally suitable fluorophore for different applications. Otherwise, extinction coefficients and quantum yields, and therefore the brightness of all seven dyes are strongly influenced. For the fluorophores, e.g. rhodamine B, the extent of this influence depends on the peptoid itself. This is shown by comparing different structures in the second part of this report. Especially the side chain functionalities influence the brightness. And finally, peptoids having two identical fluorescent labels are presented, which show decreased quantum yields. Possible reasons for the observed photophysical properties are discussed. Copyright © 2011 Elsevier Masson SAS. All rights reserved.

Emissive Synthetic Cofactors: An Isomorphic, Isofunctional, and Responsive NAD+ Analogue.

PubMed

Rovira, Alexander R; Fin, Andrea; Tor, Yitzhak

2017-11-08

The synthesis, photophysics, and biochemical utility of a fluorescent NAD + analogue based on an isothiazolo[4,3-d]pyrimidine core (N tz AD + ) are described. Enzymatic reactions, photophysically monitored in real time, show N tz AD + and N tz ADH to be substrates for yeast alcohol dehydrogenase and lactate dehydrogenase, respectively, with reaction rates comparable to that of the native cofactors. A drop in fluorescence is seen as N tz AD + is converted to N tz ADH, reflecting a complementary photophysical behavior to that of the native NAD + /NADH. N tz AD + and N tz ADH serve as substrates for NADase, which selectively cleaves the nicotinamide's glycosidic bond yielding tz ADP-ribose. N tz AD + also serves as a substrate for ribosyl transferases, including human adenosine ribosyl transferase 5 (ART5) and Cholera toxin subunit A (CTA), which hydrolyze the nicotinamide and transfer tz ADP-ribose to an arginine analogue, respectively. These reactions can be monitored by fluorescence spectroscopy, in stark contrast to the corresponding processes with the nonemissive NAD + .

The effect of copper on eumelanin photophysics and morphology

NASA Astrophysics Data System (ADS)

Birch, David J. S.; Sutter, Jens U.

2013-02-01

Despite being an important pigment in skin, hair, the eye and the brain, melanin remains one of the most enigmatic of pigments. Although the main constituents of melanin are known to be dihydroxyindoles, its photophysics is complex and its detailed structure remains unknown. In this work we have arrested prior to completion the usual synthesis of eumelanin formed via auto-oxidation of 3, 4-dihydroxy-L-phenylalanine (L-DOPA), by the addition of copper ions. Using fluorescence techniques we report how copper modifies the self assembly of eumelanin by reducing the time to the onset of aggregation at pH 10 and yet produces simplified photophysics in terms of a clearly-defined fluorescence spectrum and a fluorescence decay that is described well by a dominant single lifetime of ~ 6ns. This behavior is consistent with copper inducing an enhanced abundance of 5,5-dihydroxyindole-2-carboxylic acid (DHICA). Metal ion binding to melanin is of particular importance to neurology and has potential applications in optoelectronics.

Controlling photophysical properties of ultrasmall conjugated polymer nanoparticles through polymer chain packing

PubMed Central

Piwoński, Hubert; Michinobu, Tsuyoshi; Habuchi, Satoshi

2017-01-01

Applications of conjugated polymer nanoparticles (Pdots) for imaging and sensing depend on their size, fluorescence brightness and intraparticle energy transfer. The molecular design of conjugated polymers (CPs) has been the main focus of the development of Pdots. Here we demonstrate that proper control of the physical interactions between the chains is as critical as the molecular design. The unique design of twisted CPs and fine-tuning of the reprecipitation conditions allow us to fabricate ultrasmall (3.0–4.5 nm) Pdots with excellent photostability. Extensive photophysical and structural characterization reveals the essential role played by the packing of the polymer chains in the particles in the intraparticle spatial alignment of the emitting sites, which regulate the fluorescence brightness and the intraparticle energy migration efficiency. Our findings enhance understanding of the relationship between chain interactions and the photophysical properties of CP nanomaterials, providing a framework for designing and fabricating functional Pdots for imaging applications. PMID:28508857

The photochemical reflectance index from directional cornfield reflectances: Observations and simulations

USDA-ARS?s Scientific Manuscript database

The two-layer Markov chain Analytical Canopy Reflectance Model (ACRM) was linked with in situ hyperspectral leaf optical properties to simulate the Photochemical Reflectance Index (PRI) for a corn crop canopy at three different growth stages. This is an extended study after a successful demonstratio...

Methods for reducing biases and errors in regional photochemical model outputs for use in emission reduction and exposure assessments

EPA Science Inventory

In the United States, regional-scale photochemical models are being used to design emission control strategies needed to meet the relevant National Ambient Air Quality Standards (NAAQS) within the framework of the attainment demonstration process. Previous studies have shown that...

CARBON LOSS AND OPTICAL PROPERTY CHANGES DURING LONG-TERM PHOTOCHEMICAL AND BIOLOGICAL DEGRADATION OF ESTUARINE DISSOLVED ORGANIC MATTER

EPA Science Inventory

Terrestrially derived dissolved organic matter (DOM) impacts the optical properties of coastal seawater and affects carbon cycling on a global scale. We studied sequential long-term photochemical and biological degradation of estuarine dissolved organic matter from the
Satilla...

SMOG CHAMBERS: A TOOL TO EXAMINE EFFECTS OF PHOTOCHEMICALLY AGED AIR POLLUTANTS ON BIOLOGICAL SYSTEMS

EPA Science Inventory

Irradiative exposure chambers or 'Smog chambers' have been used at the University of North Carolina for over 30 years to study photochemically active mixtures of volatile organic compounds and their transformation products (a significant sub-set of Hazardous Air Pollutants, HAPs)...

Producing Hydrogen With Sunlight

NASA Technical Reports Server (NTRS)

Biddle, J. R.; Peterson, D. B.; Fujita, T.

1987-01-01

Costs high but reduced by further research. Producing hydrogen fuel on large scale from water by solar energy practical if plant costs reduced, according to study. Sunlight attractive energy source because it is free and because photon energy converts directly to chemical energy when it breaks water molecules into diatomic hydrogen and oxygen. Conversion process low in efficiency and photochemical reactor must be spread over large area, requiring large investment in plant. Economic analysis pertains to generic photochemical processes. Does not delve into details of photochemical reactor design because detailed reactor designs do not exist at this early stage of development.

Comparison of measured ozone in southeastern Virginia with computer predictions from a photochemical model

NASA Technical Reports Server (NTRS)

Wakelyn, N. T.; Gregory, G. L.

1980-01-01

Data for one day of the 1977 southeastern Virginia urban plume study are compared with computer predictions from a traveling air parcel model using a contemporary photochemical mechanism with a minimal description of nonmethane hydrocarbon (NMHC) constitution and chemistry. With measured initial NOx and O3 concentrations and a current separate estimate of urban source loading input to the model, and for a variation of initial NMHC over a reasonable range, an ozone increase over the day is predicted from the photochemical simulation which is consistent with the flight path averaged airborne data.

On the in vivo photochemical rate parameters for PDT reactive oxygen species modeling

NASA Astrophysics Data System (ADS)

Kim, Michele M.; Ghogare, Ashwini A.; Greer, Alexander; Zhu, Timothy C.

2017-03-01

Photosensitizer photochemical parameters are crucial data in accurate dosimetry for photodynamic therapy (PDT) based on photochemical modeling. Progress has been made in the last few decades in determining the photochemical properties of commonly used photosensitizers (PS), but mostly in solution or in vitro. Recent developments allow for the estimation of some of these photochemical parameters in vivo. This review will cover the currently available in vivo photochemical properties of photosensitizers as well as the techniques for measuring those parameters. Furthermore, photochemical parameters that are independent of environmental factors or are universal for different photosensitizers will be examined. Most photosensitizers discussed in this review are of the type II (singlet oxygen) photooxidation category, although type I photosensitizers that involve other reactive oxygen species (ROS) will be discussed as well. The compilation of these parameters will be essential for ROS modeling of PDT.

On the in-vivo photochemical rate parameters for PDT reactive oxygen species modeling

PubMed Central

Kim, Michele M.; Ghogare, Ashwini A.; Greer, Alexander; Zhu, Timothy C.

2017-01-01

Photosensitizer photochemical parameters are crucial data in accurate dosimetry for photodynamic therapy (PDT) based on photochemical modeling. Progress has been made in the last few decades in determining the photochemical properties of commonly used photosensitizers (PS), but mostly in solution or in-vitro. Recent developments allow for the estimation of some of these photochemical parameters in-vivo. This review will cover the currently available in-vivo photochemical properties of photosensitizers as well as the techniques for measuring those parameters. Furthermore, photochemical parameters that are independent of environmental factors or are universal for different photosensitizers will be examined. Most photosensitizers discussed in this review are of the type II (singlet oxygen) photooxidation category, although type I photosensitizers that involve other reactive oxygen species (ROS) will be discussed as well. The compilation of these parameters will be essential for ROS modeling of PDT. PMID:28166056

Enhanced Indirect Photochemical Transformation of Histidine and Histamine through Association with Chromophoric Dissolved Organic Matter.

PubMed

Chu, Chiheng; Lundeen, Rachel A; Remucal, Christina K; Sander, Michael; McNeill, Kristopher

2015-05-05

Photochemical transformations greatly affect the stability and fate of amino acids (AAs) in sunlit aquatic ecosystems. Whereas the direct phototransformation of dissolved AAs is well investigated, their indirect photolysis in the presence of chromophoric dissolved organic matter (CDOM) is poorly understood. In aquatic systems, CDOM may act both as sorbent for AAs and as photosensitizer, creating microenvironments with high concentrations of photochemically produced reactive intermediates, such as singlet oxygen (1O2). This study provides a systematic investigation of the indirect photochemical transformation of histidine (His) and histamine by 1O2 in solutions containing CDOM as a function of solution pH. Both His and histamine showed pH-dependent enhanced phototransformation in the CDOM systems as compared to systems in which model, low-molecular-weight 1O2 sensitizers were used. Enhanced reactivity resulted from sorption of His and histamine to CDOM and thus exposure to elevated 1O2 concentrations in the CDOM microenvironment. The extent of reactivity enhancement depended on solution pH via its effects on the protonation state of His, histamine, and CDOM. Sorption-enhanced reactivity was independently supported by depressed rate enhancements in the presence of a cosorbate that competitively displaced His and histamine from CDOM. Incorporating sorption and photochemical transformation processes into a reaction rate prediction model improved the description of the abiotic photochemical transformation rates of His in the presence of CDOM.

Temperature Sensitive Singlet Oxygen Photosensitization by LOV-Derived Fluorescent Flavoproteins.

PubMed

Westberg, Michael; Bregnhøj, Mikkel; Etzerodt, Michael; Ogilby, Peter R

2017-03-30

Optogenetic sensitizers that selectively produce a given reactive oxygen species (ROS) constitute a promising tool for studying cell signaling processes with high levels of spatiotemporal control. However, to harness the full potential of this tool for live cell studies, the photophysics of currently available systems need to be explored further and optimized. Of particular interest in this regard, are the flavoproteins miniSOG and SOPP, both of which (1) contain the chromophore flavin mononucleotide, FMN, in a LOV-derived protein enclosure, and (2) photosensitize the production of singlet oxygen, O 2 (a 1 Δ g ). Here we present an extensive experimental study of the singlet and triplet state photophysics of FMN in SOPP and miniSOG over a physiologically relevant temperature range. Although changes in temperature only affect the singlet excited state photophysics slightly, the processes that influence the deactivation of the triplet excited state are more sensitive to temperature. Most notably, for both proteins, the rate constant for quenching of 3 FMN by ground state oxygen, O 2 (X 3 Σ g - ), increases ∼10-fold upon increasing the temperature from 10 to 43 °C, while the oxygen-independent channels of triplet state deactivation are less affected. As a consequence, this increase in temperature results in higher yields of O 2 (a 1 Δ g ) formation for both SOPP and miniSOG. We also show that the quantum yields of O 2 (a 1 Δ g ) production by both miniSOG and SOPP are mainly limited by the fraction of FMN triplet states quenched by O 2 (X 3 Σ g - ). The results presented herein provide a much-needed quantitative framework that will facilitate the future development of optogenetic ROS sensitizers.

The elusive abnormal CO2 insertion enabled by metal-ligand cooperative photochemical selectivity inversion.

PubMed

Schneck, Felix; Ahrens, Jennifer; Finger, Markus; Stückl, A Claudia; Würtele, Christian; Schwarzer, Dirk; Schneider, Sven

2018-03-21

Direct hydrogenation of CO 2 to CO, the reverse water-gas shift reaction, is an attractive route to CO 2 utilization. However, the use of molecular catalysts is impeded by the general reactivity of metal hydrides with CO 2 . Insertion into M-H bonds results in formates (MO(O)CH), whereas the abnormal insertion to the hydroxycarbonyl isomer (MC(O)OH), which is the key intermediate for CO-selective catalysis, has never been directly observed. We here report that the selectivity of CO 2 insertion into a Ni-H bond can be inverted from normal to abnormal insertion upon switching from thermal to photochemical conditions. Mechanistic examination for abnormal insertion indicates photochemical N-H reductive elimination as the pivotal step that leads to an umpolung of the hydride ligand. This study conceptually introduces metal-ligand cooperation for selectivity control in photochemical transformations.

Diagnostic analysis of two-dimensional monthly average ozone balance with Chapman chemistry

NASA Technical Reports Server (NTRS)

Stolarski, Richard S.; Jackman, Charles H.; Kaye, Jack A.

1986-01-01

Chapman chemistry has been used in a two-dimensional model to simulate ozone balance phenomenology. The similarity between regions of ozone production and loss calculated using Chapman chemistry and those computed using LIMS and SAMS data with a photochemical equilibrium model indicate that such simplified chemistry is useful in studying gross features in stratospheric ozone balance. Net ozone production or loss rates are brought about by departures from the photochemical equilibrium (PCE) condition. If transport drives ozone above its PCE condition, then photochemical loss dominates production. If transport drives ozone below its PCE condition, then photochemical production dominates loss. Gross features of ozone loss/production (L/P) inferred for the real atmosphere from data are also simulated using only eddy diffusion. This indicates that one must be careful in assigning a transport scheme for a two-dimensional model that mimics only behavior of the observed ozone L/P.

Photothermal and photochemical effects of laser light absorption by indocyanine green (ICG)

NASA Astrophysics Data System (ADS)

Yaseen, Mohammad A.; Diagaradjane, Parmeswaran; Pikkula, Brian M.; Yu, Jie; Wong, Michael S.; Anvari, Bahman

2005-04-01

Indocyanine Green (ICG) is clinically used as a fluorescent dye for imaging purposes. Its rapid circulation kinetics and minimal toxicity has prompted investigation into ICG's utility as a photosentitizer for therapeutic applications. Traditionally, optically mediated tumor therapy has focused on photodynamic therapy, which employs a photochemical mechanism resulting from the absorption of low intensity CW laser light by localized photosensitizers such as Photofrin II, Benzoporphyrin Derivative (BPD), ICG. Treatment of cutaneous vascular malformations such as port-wine stains, on the other hand, is based on a photothermal mechanism resulting from the absorption of high intensity pulsed laser light by hemoglobin. In this study, we compared the effectiveness of combining photochemical and photothermal mechanisms during application of ICG in conjunction with laser irradiation with the intention that the combined approach may lead to a reduction in the threshold dose of pulsed laser light required to treat hypervascular malformations. The blood vessels in rabbit ears were used as an in vivo model for targeted vasculature. Irradiation of the ears with IR light (λ=785 nm, Δτ = 3 min, Io = 120 mW) was used to elicit photochemical damage, while photothermal damage was brought about using pulses from a ruby laser (λ=694 nm, τ = 3 ms) with different fluences. For the combined modality, photochemical damage was induced first and followed by photothermal irradiation. This modality was compared with photothermal irradiation alone. The effectiveness of each irradiation scheme was assessed using histopathological analysis. We present preliminary data that suggests that pretreatment with photodynamic therapy before photothermal coagulation results in more severe vascular damage with lower photothermal fluence levels. The results of this study provide the foundation work for further exploration of the therapeutic potentials of photochemical and photothermal effects during application of ICG in conjunction with laser irradiation.

Anaerobiosis Induced State Transition: A Non Photochemical Reduction of PQ Pool Mediated by NDH in Arabidopsis thaliana

PubMed Central

Tirupathi, Malavath; Subramanyam, Rajagopal

2012-01-01

Background Non photochemical reduction of PQ pool and mobilization of LHCII between PSII and PSI are found to be linked under abiotic stress conditions. The interaction of non photochemical reduction of PQ pool and state transitions associated physiological changes are critically important under anaerobic condition in higher plants. Methodology/Findings The present study focused on the effect of anaerobiosis on non-photochemical reduction of PQ pool which trigger state II transition in Arabidopsis thaliana. Upon exposure to dark-anaerobic condition the shape of the OJIP transient rise is completely altered where as in aerobic treated leaves the rise is unaltered. Rise in F o and F J was due to the loss of oxidized PQ pool as the PQ pool becomes more reduced. The increase in Fo′ was due to the non photochemical reduction of PQ pool which activated STN7 kinase and induced LHCII phosphorylation under anaerobic condition. Further, it was observed that the phosphorylated LHCII is migrated and associated with PSI supercomplex increasing its absorption cross-section. Furthermore, evidences from crr2-2 (NDH mutant) and pgr5 mutants (deficient in non NDH pathway of cyclic electron transport) have indicated that NDH is responsible for non photochemical reduction of the PQ pool. We propose that dark anaerobic condition accelerates production of reducing equivalents (such as NADPH by various metabolic pathways) which reduce PQ pool and is mediated by NDH leading to state II transition. Conclusions/Significance Anaerobic condition triggers non photochemical reduction of PQ pool mediated by NDH complex. The reduced PQ pool activates STN7 kinase leading to state II transition in A. thaliana. PMID:23185453

Laboratory photochemical processing of aqueous aerosols: formation and degradation of dicarboxylic acids, oxocarboxylic acids and α-dicarbonyls

NASA Astrophysics Data System (ADS)

Pavuluri, C. M.; Kawamura, K.; Mihalopoulos, N.; Swaminathan, T.

2015-01-01

To better understand the photochemical processing of dicarboxylic acids and related polar compounds, we conducted batch UV irradiation experiments on two types of aerosol samples collected from India, which represent anthropogenic (AA) and biogenic aerosols (BA), for time periods of 0.5 to 120 h. The irradiated samples were analyzed for molecular compositions of diacids, oxoacids and α-dicarbonyls. The results show that photochemical degradation of oxalic (C2) and malonic (C3) and other C8-C12 diacids overwhelmed their production in aqueous aerosols whereas succinic acid (C4) and C5-C7 diacids showed a significant increase (ca. 10 times) during the course of irradiation experiments. The photochemical formation of oxoacids and α-dicarbonyls overwhelmed their degradation during the early stages of experiment, except for ω-oxooctanoic acid (ωC8) that showed a similar pattern to that of C4. We also found a gradual decrease in the relative abundance of C2 to total diacids and an increase in the relative abundance of C4 during prolonged experiment. Based on the changes in concentrations and mass ratios of selected species with the irradiation time, we hypothesize that iron-catalyzed photolysis of C2 and C3 diacids dominates their concentrations in Fe-rich atmospheric waters, whereas photochemical formation of C4 diacid (via ωC8) is enhanced with photochemical processing of aqueous aerosols in the atmosphere. This study demonstrates that the ambient aerosols contain abundant precursors that produce diacids, oxoacids and α-dicarbonyls, although some species such as oxalic acid decompose extensively during an early stage of photochemical processing.

Laboratory photochemical processing of aqueous aerosols: formation and degradation of dicarboxylic acids, oxocarboxylic acids and α-dicarbonyls

NASA Astrophysics Data System (ADS)

Pavuluri, C. M.; Kawamura, K.; Mihalopoulos, N.; Swaminathan, T.

2015-07-01

To better understand the photochemical processing of dicarboxylic acids and related polar compounds, we conducted batch UV irradiation experiments on two types of aerosol samples collected from India, which represent anthropogenic (AA) and biogenic (BA) aerosols, for time periods of 0.5 to 120 h. The irradiated samples were analyzed for molecular compositions of diacids, oxoacids and α-dicarbonyls. The results show that photochemical degradation of oxalic (C2), malonic (C3) and other C8-C12 diacids overwhelmed their production in aqueous aerosols, whereas succinic acid (C4) and C5-C7 diacids showed a significant increase (ca. 10 times) during the course of irradiation experiments. The photochemical formation of oxoacids and α-dicarbonyls overwhelmed their degradation during the early stages of experiment except for ω-oxooctanoic acid (ωC8), which showed a similar pattern to that of C4. We also found a gradual decrease in the relative abundance of C2 to total diacids and an increase in the relative abundance of C4 during prolonged experiment. Based on the changes in concentrations and mass ratios of selected species with the irradiation time, we hypothesize that iron-catalyzed photolysis of C2 and C3 diacids controls their concentrations in Fe-rich atmospheric waters, whereas photochemical formation of C4 diacid (via ωC8) is enhanced with photochemical processing of aqueous aerosols in the atmosphere. This study demonstrates that the ambient aerosols contain abundant precursors that produce diacids, oxoacids and α-dicarbonyls, although some species such as oxalic acid decompose extensively during an early stage of photochemical processing.

Emission color tuning in AlQ3 complexes with extended conjugated chromophores.

PubMed

Pohl, Radek; Anzenbacher, Pavel

2003-08-07

[reaction: see text] A new method for the synthesis of 5-arylethynyl-8-hydroxyquinoline ligands using Sonogashira-Hagihara coupling was developed. The electronic nature of arylethynyl substituents affects the emission color and quantum yield of the resulting Al(III) complex. Photophysical properties of the metallocomplexes correspond to the electron-withdrawing/-donating character of the arylethynyl substituents. Optical properties of such Al(III) complexes correlate with the Hammett constant values of the respective substituents. This strategy offers a powerful tool for the preparation of electroluminophores with predictable photophysical properties.

Environmental Effects on the Photophysics of Organic-Inorganic Halide Perovskites.

PubMed

Galisteo-López, Juan F; Anaya, M; Calvo, M E; Míguez, H

2015-06-18

The photophysical properties of films of organic-inorganic lead halide perovskites under different ambient conditions are herein reported. We demonstrate that their luminescent properties are determined by the interplay between photoinduced activation and darkening processes, which strongly depend on the atmosphere surrounding the samples. We have isolated oxygen and moisture as the key elements in each process, activation and darkening, both of which involve the interaction with photogenerated carriers. These findings show that environmental factors play a key role in the performance of lead halide perovskites as efficient luminescent materials.

Environmental Effects on the Photophysics of Organic–Inorganic Halide Perovskites

PubMed Central

2015-01-01

The photophysical properties of films of organic–inorganic lead halide perovskites under different ambient conditions are herein reported. We demonstrate that their luminescent properties are determined by the interplay between photoinduced activation and darkening processes, which strongly depend on the atmosphere surrounding the samples. We have isolated oxygen and moisture as the key elements in each process, activation and darkening, both of which involve the interaction with photogenerated carriers. These findings show that environmental factors play a key role in the performance of lead halide perovskites as efficient luminescent materials. PMID:26266592

AnilinoMethylRhodamines: pH Sensitive Probes with Tunable Photophysical Properties by Substituent Effect

PubMed Central

Best, Quinn A.; Liu, Chuangjun; van Hoveln, Paul D.; McCarroll, Matthew E.

2013-01-01

A series of pH dependent rhodamine analogs possessing an anilino-methyl moiety was developed and shown to exhibit a unique photophysical response to pH. These Anilinomethylrhodamines (AnMR) maintain a colorless, non-fluorescent spiro-cyclic structure at high pH. The spiro-cyclic structures open in mildly acidic conditions and are weakly fluorescent; however at very low pH, the fluorescence is greatly enhanced. The equilibrium constants of these processes show a linear response to substituent effects, which was demonstrated by the Hammett equation. PMID:24050117

Studies on lasers and laser devices

NASA Technical Reports Server (NTRS)

Harris, S. E.; Siegman, A. E.; Young, J. F.

1983-01-01

The goal of this grant was to study lasers, laser devices, and uses of lasers for investigating physical phenomena are studied. The active projects included the development of a tunable, narrowband XUV light source and its application to the spectroscopy of core excited atomic states, and the development of a technique for picosecond time resolution spectroscopy of fast photophysical processes.

Shining light on the antenna chromophore in lanthanide based dyes.

PubMed

Junker, Anne Kathrine R; Hill, Leila R; Thompson, Amber L; Faulkner, Stephen; Sørensen, Thomas Just

2018-04-03

Lanthanide based dyes and assays exploit the antenna effect, where a sensitiser-chromophore is used as a light harvesting antenna and subsequent excited state energy transfer populates the emitting lanthanide centred excited state. A rudimentary understanding of the design criteria for designing efficient dyes and assays based on the antenna effect is in place. By preparing kinetically inert lanthanide complexes based on the DO3A scaffold, we are able to study the excited state energy transfer from a 7-methoxy-coumarin antenna chromophore to europium(iii) and terbium(iii) centred excited states. By contrasting the photophysical properties of complexes of metal centres with and without accessible excited states, we are able to separate the contributions from the heavy atom effect, photoinduced electron transfer quenching, excited state energy transfer and molecular conformations. Furthermore, by studying the photophysical properties of the antenna chromophore, we can directly monitor the solution structure and are able to conclude that excited state energy transfer from the chromophore singlet state to the lanthanide centre does occur.

The effect of substituted moiety on the optoelectronic and photophysical properties of tris (phenylbenzimidazolinato) Ir (III) carbene complexes and the OLED performance: a theoretical study

NASA Astrophysics Data System (ADS)

Srivastava, Ruby

2015-06-01

Density functional theory (DFT) and time-dependent density functional theory (TDDFT) are used to analyse theoretically the optoelectronic, photophysical properties and organic light-emitting diode performance of a series of fac-mer blue-emitting Iridium (III) carbene complexes. Swain-Lupton constant is used to discuss the substituents effect. 5d-orbital splitting and d-d* transitions are calculated to assess the efficiency of the studied complexes. The reorganisation energies (λ), transfer integrals, mobilities, radiative decay rate (kr), and triplet exciton generation fraction (χT) are also calculated. Due to the higher χT of these complexes, the formation of triplet exciton will be more and it will cause a faster intersystem crossing. Two host materials are proposed and host-guest match (Dexter-Förster energy) is also discussed. We hope that this unified work will surely help to design new blue-emitting phosphorescent materials in future.

Photophysical behavior of polyatomic molecules

NASA Astrophysics Data System (ADS)

Ware, W. R.

1980-10-01

Part one of this report deals with attempts over the past several years to devise a more sophisticated theory of diffusion controlled reactions than that presented by Collins and Kimball. In particular, the investigators were interested in a more realistic formulation of the problem of high concentration quenching where quenches in the vicinity of the molecular to be quenched must be considered. It was desired however, to obtain a formalism which was tractable mathematically and which contained parameters which would be related to experiment. Part two deals with the photophysics of systems exhibiting molecular association both in the ground and excited states has been studied. The emphasis has been on kinetic models, the measurement of rate constants associated with these models, and the determination of activation parameters and equilibrium thermodynamic parameters associated with the exciplex formation and disappearance. Studies of solvent effects and steric effects on the behavior of exciplex systems have been carried out. The case of rapid equilibrium where the monomer and exciplex decay with the same rate constant has also been examined.

Improving Joint Function Using Photochemical Hydrogels for Articular Surface Repair

DTIC Science & Technology

2012-10-01

with thrombin previously has been reported as a favorable scaffold for cartilage formation by encapsulated chondrocytes [10]. Studies over the past...during the photochemical crosslinking process. A full scale study is planned for the first quarter of year 3 to evaluate the fully formed cartilage ...Perform initial study of collagen and PEG gels with stem cells implanted in mice  Bone marrow MSCs were harvested from donor swine and grown in culture

Surface retention and photochemical reactivity of the diphenylether herbicide oxyfluorfen.

PubMed

Scrano, Laura; Bufo, Sabino A; Cataldi, Tommaso R I; Albanis, Triantafyllos A

2004-01-01

The photochemical behavior of oxyfluorfen [2-chloro-1-(3-etoxy-4-nitrophenoxy)-4-(trifluoromethyl) benzene] on two Greek soils was investigated. Soils were sampled from Nea Malgara and Preveza regions, characterized by a different organic matter content. Soils were spiked with the diphenyl-ether herbicide and irradiation experiments were performed either in the laboratory with a solar simulator (xenon lamp) or outside, under natural sunlight irradiation; other soil samples were kept in the dark to control the retention reaction. Kinetic parameters of both retention and photochemical reactions were calculated using zero-, first- and second- (Langmuir-Hinshelwood) order equations, and best fit was checked through statistical analysis. The soil behaviors were qualitatively similar but quantitatively different, with the soil sampled from the Nea Malgara region much more sorbent as compared with Preveza soil. All studied reactions followed second-order kinetics and photochemical reactions were influenced by retaining capability of the soils. The contributions of the photochemical processes to the global dissipation rates were also calculated. Two main metabolites were identified as 2-chloro-1-(3-ethoxy-4-hydroxyphenoxy)-4-(trifluoromethyl)benzene and 2-chloro-1- (3-hydroxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene.

Photochemical Copper Coating on 3D Printed Thermoplastics

NASA Astrophysics Data System (ADS)

Yung, Winco K. C.; Sun, Bo; Huang, Junfeng; Jin, Yingdi; Meng, Zhengong; Choy, Hang Shan; Cai, Zhixiang; Li, Guijun; Ho, Cheuk Lam; Yang, Jinlong; Wong, Wai Yeung

2016-08-01

3D printing using thermoplastics has become very popular in recent years, however, it is challenging to provide a metal coating on 3D objects without using specialized and expensive tools. Herein, a novel acrylic paint containing malachite for coating on 3D printed objects is introduced, which can be transformed to copper via one-step laser treatment. The malachite containing pigment can be used as a commercial acrylic paint, which can be brushed onto 3D printed objects. The material properties and photochemical transformation processes have been comprehensively studied. The underlying physics of the photochemical synthesis of copper was characterized using density functional theory calculations. After laser treatment, the surface coating of the 3D printed objects was transformed to copper, which was experimentally characterized by XRD. 3D printed prototypes, including model of the Statue of Liberty covered with a copper surface coating and a robotic hand with copper interconnections, are demonstrated using this painting method. This composite material can provide a novel solution for coating metals on 3D printed objects. The photochemical reduction analysis indicates that the copper rust in malachite form can be remotely and photo-chemically reduced to pure copper with sufficient photon energy.

Photochemical Copper Coating on 3D Printed Thermoplastics

PubMed Central

Yung, Winco K. C.; Sun, Bo; Huang, Junfeng; Jin, Yingdi; Meng, Zhengong; Choy, Hang Shan; Cai, Zhixiang; Li, Guijun; Ho, Cheuk Lam; Yang, Jinlong; Wong, Wai Yeung

2016-01-01

3D printing using thermoplastics has become very popular in recent years, however, it is challenging to provide a metal coating on 3D objects without using specialized and expensive tools. Herein, a novel acrylic paint containing malachite for coating on 3D printed objects is introduced, which can be transformed to copper via one-step laser treatment. The malachite containing pigment can be used as a commercial acrylic paint, which can be brushed onto 3D printed objects. The material properties and photochemical transformation processes have been comprehensively studied. The underlying physics of the photochemical synthesis of copper was characterized using density functional theory calculations. After laser treatment, the surface coating of the 3D printed objects was transformed to copper, which was experimentally characterized by XRD. 3D printed prototypes, including model of the Statue of Liberty covered with a copper surface coating and a robotic hand with copper interconnections, are demonstrated using this painting method. This composite material can provide a novel solution for coating metals on 3D printed objects. The photochemical reduction analysis indicates that the copper rust in malachite form can be remotely and photo-chemically reduced to pure copper with sufficient photon energy. PMID:27501761

Photochemical Copper Coating on 3D Printed Thermoplastics.

PubMed

Yung, Winco K C; Sun, Bo; Huang, Junfeng; Jin, Yingdi; Meng, Zhengong; Choy, Hang Shan; Cai, Zhixiang; Li, Guijun; Ho, Cheuk Lam; Yang, Jinlong; Wong, Wai Yeung

2016-08-09

3D printing using thermoplastics has become very popular in recent years, however, it is challenging to provide a metal coating on 3D objects without using specialized and expensive tools. Herein, a novel acrylic paint containing malachite for coating on 3D printed objects is introduced, which can be transformed to copper via one-step laser treatment. The malachite containing pigment can be used as a commercial acrylic paint, which can be brushed onto 3D printed objects. The material properties and photochemical transformation processes have been comprehensively studied. The underlying physics of the photochemical synthesis of copper was characterized using density functional theory calculations. After laser treatment, the surface coating of the 3D printed objects was transformed to copper, which was experimentally characterized by XRD. 3D printed prototypes, including model of the Statue of Liberty covered with a copper surface coating and a robotic hand with copper interconnections, are demonstrated using this painting method. This composite material can provide a novel solution for coating metals on 3D printed objects. The photochemical reduction analysis indicates that the copper rust in malachite form can be remotely and photo-chemically reduced to pure copper with sufficient photon energy.

Methods for the photochemical utilization of solar energy

NASA Technical Reports Server (NTRS)

Schwerzel, R. E.

1978-01-01

The paper considers the 'ground rules' which govern the efficiency of photochemical solar energy conversion and then summarizes the most promising approaches in each of three categories: photochemically assisted thermal systems for the heating and/or cooling of structures; photogalvanic systems for the production of electrical power in applications, such as photorechargeable batteries or inexpensive 'solar cells'; and photochemical formation of fuels for combustion and for use as chemical feedstocks or foods. Three concepts for the photochemical utilization of solar energy in space are found to be particularly promising: (1) photochemical trans-cis isomerization of indigold dyes for photoassisted heating or cooling, (2) the redox stabilized photoelectrolysis cell for the production of hydrogen (and/or oxygen or other useful chemicals), and (3) the liquid-junction photovoltaic cell for the production of electrical power.

Monolayer organic field effect phototransistors: photophysical characterization and modeling

NASA Astrophysics Data System (ADS)

Trukhanov, Vasily A.; Anisimov, Daniil S.; Bruevich, Vladimir V.; Agina, Elena V.; Borshchev, Oleg V.; Ponomarenko, Sergei; Zhang, Jiangbin; Bakulin, Artem A.; Paraschuk, Dmitri Yu.

2016-09-01

Organic field-effect transistors (OFET) can combine photodetection and light amplification and, for example, work as phototransistors. Such organic phototransistors can be used in light-controlled switches and amplifiers, detection circuits, and sensors of ultrasensitive images. In this work, we present photophysical characterization of well-defined ultrathin organic field-effect devices with a semiconductive channel based on Langmuir-Blodgett monolayer film. We observe clear generation of photocurrent under illumination with a modulated laser at 405 nm. The increase of photocurrent with the optical modulation frequency indicates the presence of defect states serving as traps for photogenerated carriers and/or the saturation of charge concentration in the thin active layer. We also propose a simple one-dimensional numerical model of a photosensitive OFET. The model is based on the Poisson, current continuity and drift-diffusion equations allows future evaluation of the photocurrent generation mechanism in the studied systems.

Rational Improvement of Molar Absorptivity Guided by Oscillator Strength: A Case Study with Furoindolizine-Based Core Skeleton.

PubMed

Lee, Youngjun; Jo, Ala; Park, Seung Bum

2015-12-21

The rational improvement of photophysical properties can be highly valuable for the discovery of novel organic fluorophores. Using our new design strategy guided by the oscillator strength, we developed a series of full-color-tunable furoindolizine analogs with improved molar absorptivity through the fusion of a furan ring into the indolizine-based Seoul fluorophore. The excellent correlation between the computable values (oscillator strength and theoretical S0 -S1 energy gap) and photophysical properties (molar absorptivity and emission wavelength) confirmed the effectualness of our design strategy. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution Non-Commercial NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

A UBI 31-38 Peptide-coumarin Conjugate: Photophysical Features, Imaging Tracking and Synergism with Amphotericin B Against Cryptococcus.

PubMed

Ferreira, Soraya M Z M D; Carneiro, Hellem C; Alves, Rosemeire B; Batista, Ana Carolina S; da Silva Junior, Eufranio N; Dias, Gleiston G; Resende, Jarbas M; Santos, Daniel A; Oliveira, Debora L; Rodrigues, Marcio L; Freitas, Rossimiriam P

2018-01-01

Cryptococcosis is a fungal disease of global significance for which new effective treatments are needed. The conjugation of the synthetic antimicrobial peptide fragment UBI 31-38 to a coumarin derivative showed to be an effective approach for the design of a novel anticryptococcal agent. In addition to antifungal activity, the conjugate exhibited intense fluorescence, which could be valuable for mechanistic investigations of this molecule. In this work, we studied the photophysical properties of the conjugate and confocal scanning laser microscopy was used to inspect the distribution of the peptide-coumarin conjugate in Cryptococcus cell. The synergism of this compound with amphotericin B or fluconazole against C. gattii and C. neoformans strains was also investigated. The results indicated that the fluorescent conjugate alone as well as its combination with amphotericin B are promising tools against cryptococcosis. Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.

Stable optical oxygen sensing materials based on click-coupling of fluorinated platinum(II) and palladium(II) porphyrins—A convenient way to eliminate dye migration and leaching

PubMed Central

Koren, Klaus; Borisov, Sergey M.; Klimant, Ingo

2012-01-01

Nucleophilic substitution of the labile para-fluorine atoms of 2,3,4,5,6-pentafluorophenyl groups enables a click-based covalent linkage of an oxygen indicator (platinum(II) or palladium(II) 5,10,15,20-meso-tetrakis-(2,3,4,5,6-pentafluorophenyl)-porphyrin) to the sensor matrix. Copolymers of styrene and pentafluorostyrene are chosen as polymeric materials. Depending on the reaction conditions either soluble sensor materials or cross-linked microparticles are obtained. Additionally, we prepared Ormosil-based sensors with linked indicator, which showed very high sensitivity toward oxygen. The effect of covalent coupling on sensor characteristics, stability and photophysical properties is studied. It is demonstrated that leaching and migration of the dye are eliminated in the new materials but excellent photophysical properties of the indicators are preserved. PMID:23576845

Physicochemical/photophysical characterization and angiogenic properties of Curcuma longa essential oil.

PubMed

Araújo, Lilhian A; Araújo, Rafael G M; Gomes, Flávia O; Lemes, Susy R; Almeida, Luciane M; Maia, Lauro J Q; Gonçalves, Pablo J; Mrué, Fátima; Silva-Junior, Nelson J; Melo-Reis, Paulo R DE

2016-01-01

This study analyzed the physicochemical and photophysical properties of essential oil of Curcuma longa and its angiogenic potential. The results showed that curcumin is the main fluorescent component present in the oil, although the amount is relatively small. The experimental chorioallantoic membrane model was used to evaluate angiogenic activity, showing a significant increase in the vascular network of Curcuma longa and positive control groups when compared to the neutral and inhibitor controls (P <0.05), but no significant difference was found between Curcuma longa essential oil and the positive control (P >0.05). Histological analysis showed extensive neovascularization, hyperemia and inflammation in the positive control group and Curcuma longa when compared to other controls (P <0.05), characteristic factors of the angiogenesis process. In conclusion, Curcuma longa oil showed considerable proangiogenic activity and could be a potential compound in medical applications.

The Effect of Pyrazolyl Substituents on the Photophysical and Photochemical Properties of Pyrazine Derivatives.

PubMed

Pizarro, Nancy; Prado, Gaspar; Saldías, Marianela; Sandoval-Altamirano, Catalina; Vega, Andrés

2018-02-15

The reaction of 2,5-dibromopyrazine with N-Lithium pyrazolate in a 1:2 ratio leads to a mixture of 2-bromo-5-(1H-pyrazol-1-yl)pyrazine (I) and 2,5-di(1H-pyrazol-1-yl)pyrazine (II). The structures of I and II are highly planar. Two absorption bands can be observed for the compounds in the UV-Vis region, having ε in the order of 10 4  m -1  cm -1 . TD-DFT computed results support the nature of the lower energy absorptions as π pyrazine →π* pyrazine transitions, including an additional intraligand charge transfer transition for I (π pyrazol →π* pyrazine ). Upon excitation at 280 or 320 nm, the emission of both compounds is almost not affected by solvent polarity or oxygen presence, showing two bands for I and one for II in the 350-450 nm region. Emission of II follows a mono-exponential decay, while I decays following a bi-exponential law, hypothesized from π pyrazine →π* pyrazine and π pyrazol →π* pyrazine transitions. Photodegradation of I and II follows a first-order kinetic with constants of 1.18 × 10 -2  min -1 and 0.13 × 10 -2  min -1 , respectively. Results suggest that photodegradation of I starts with the loose of bromide followed by intermolecular pyrazolyl subtraction and ring opening. This path is not available for II, which is reflected in its enhanced photostability. © 2018 The American Society of Photobiology.

Low-intensity red and infrared lasers affect mRNA expression of DNA nucleotide excision repair in skin and muscle tissue.

PubMed

Sergio, Luiz Philippe S; Campos, Vera Maria A; Vicentini, Solange C; Mencalha, Andre Luiz; de Paoli, Flavia; Fonseca, Adenilson S

2016-04-01

Lasers emit light beams with specific characteristics, in which wavelength, frequency, power, fluence, and emission mode properties determine the photophysical, photochemical, and photobiological responses. Low-intensity lasers could induce free radical generation in biological tissues and cause alterations in macromolecules, such as DNA. Thus, the aim of this work was to evaluate excision repair cross-complementing group 1 (ERCC1) and excision repair cross-complementing group 2 (ERCC2) messenger RNA (mRNA) expression in biological tissues exposed to low-intensity lasers. Wistar rat (n = 28, 4 for each group) skin and muscle were exposed to low-intensity red (660 nm) and near-infrared (880 nm) lasers at different fluences (25, 50, and 100 J/cm(2)), and samples of these tissues were withdrawn for RNA extraction, cDNA synthesis, and gene expression evaluation by quantitative polymerase chain reaction. Laser exposure was in continuous wave and power of 100 mW. Data show that ERCC1 and ERCC2 mRNA expressions decrease in skin (p < 0.001) exposed to near-infrared laser, but increase in muscle tissue (p < 0.001). ERCC1 mRNA expression does not alter (p > 0.05), but ERCC2 mRNA expression decreases in skin (p < 0.001) and increases in muscle tissue (p < 0.001) exposed to red laser. Our results show that ERCC1 and ERCC2 mRNA expression is differently altered in skin and muscle tissue exposed to low-intensity lasers depending on wavelengths and fluences used in therapeutic protocols.

Ruthenium porphyrin-induced photodamage in bladder cancer cells.

PubMed

Bogoeva, Vanya; Siksjø, Monica; Sæterbø, Kristin G; Melø, Thor Bernt; Bjørkøy, Astrid; Lindgren, Mikael; Gederaas, Odrun A

2016-06-01

Photodynamic therapy (PDT) is a noninvasive treatment for solid malignant and flat tumors. Light activated sensitizers catalyze photochemical reactions that produce reactive oxygen species which can cause cancer cell death. In this work we investigated the photophysical properties of the photosensitizer ruthenium(II) porphyrin (RuP), along with its PDT efficiency onto rat bladder cancer cells (AY27). Optical spectroscopy verified that RuP is capable to activate singlet oxygen via blue and red absorption bands and inter system crossing (ISC) to the triplet state. In vitro experiments on AY27 indicated increased photo-toxicity of RuP (20μM, 18h incubation) after cell illumination (at 435nm), as a function of blue light exposure. Cell survival fraction was significantly reduced to 14% after illumination of 20μM RuP with 15.6J/cm(2), whereas the "dark toxicity" of 20μM RuP was 17%. Structural and morphological changes of cells were observed, due to RuP accumulation, as well as light-dependent cell death was recorded by confocal microscopy. Flow cytometry verified that PDT-RuP (50μM) triggered significant photo-induced cellular destruction with a photoxicity of (93%±0.9%). Interestingly, the present investigation of RuP-PDT showed that the dominating mode of cell death is necrosis. RuP "dark toxicity" compared to the conventional chemotherapeutic drug cisplatin was higher, both evaluated by the MTT assay (24h). In conclusion, the present investigation shows that RuP with or without photoactivation induces cell death of bladder cancer cells. Copyright © 2016 Elsevier B.V. All rights reserved.

Photochemical Hydrogen Doping Induced Embedded Two-Dimensional Metallic Channel Formation in InGaZnO at Room Temperature.

PubMed

Kim, Myeong-Ho; Lee, Young-Ahn; Kim, Jinseo; Park, Jucheol; Ahn, Seungbae; Jeon, Ki-Joon; Kim, Jeong Won; Choi, Duck-Kyun; Seo, Hyungtak

2015-10-27

The photochemical tunability of the charge-transport mechanism in metal-oxide semiconductors is of great interest since it may offer a facile but effective semiconductor-to-metal transition, which results from photochemically modified electronic structures for various oxide-based device applications. This might provide a feasible hydrogen (H)-radical doping to realize the effectively H-doped metal oxides, which has not been achieved by thermal and ion-implantation technique in a reliable and controllable way. In this study, we report a photochemical conversion of InGaZnO (IGZO) semiconductor to a transparent conductor via hydrogen doping to the local nanocrystallites formed at the IGZO/glass interface at room temperature. In contrast to thermal or ionic hydrogen doping, ultraviolet exposure of the IGZO surface promotes a photochemical reaction with H radical incorporation to surface metal-OH layer formation and bulk H-doping which acts as a tunable and stable highly doped n-type doping channel and turns IGZO to a transparent conductor. This results in the total conversion of carrier conduction property to the level of metallic conduction with sheet resistance of ∼16 Ω/□, room temperature Hall mobility of 11.8 cm(2) V(-1) sec(-1), the carrier concentration at ∼10(20) cm(-3) without any loss of optical transparency. We demonstrated successful applications of photochemically highly n-doped metal oxide via optical dose control to transparent conductor with excellent chemical and optical doping stability.

Development of novel two-photon absorbing chromophores

NASA Astrophysics Data System (ADS)

Rogers, Joy E.; Slagle, Jonathan E.; McLean, Daniel G.; Sutherland, Richard L.; Krein, Douglas M.; Cooper, Thomas M.; Brant, Mark; Heinrichs, James; Kannan, Ramamurthi; Tan, Loon-Seng; Urbas, Augustine M.; Fleitz, Paul A.

2006-08-01

There has been much interest in the development of two-photon absorbing materials and many efforts to understand the nonlinear absorption properties of these dyes but this area is still not well understood. A computational model has been developed in our lab to understand the nanosecond nonlinear absorption properties that incorporate all of the measured one-photon photophysical parameters of a class of materials called AFX. We have investigated the nonlinear and photophysical properties of the AFX chromophores including the two-photon absorption cross-section, the excited state cross-section, the intersystem crossing quantum yield, and the singlet and triplet excited state lifetimes using a variety of experimental techniques that include UV-visible, fluorescence and phosphorescence spectroscopy, time correlated single photon counting, ultrafast transient absorption, and nanosecond laser flash photolysis. The model accurately predicts the nanosecond nonlinear transmittance data using experimentally measured parameters. Much of the strong nonlinear absorption has been shown to be due to excited state absorption from both the singlet and triplet excited states. Based on this understanding of the nonlinear absorption and the importance of singlet and triplet excited states we have begun to develop new two-photon absorbing molecules within the AFX class as well as linked to other classes of nonlinear absorbing molecules. This opens up the possibilities of new materials with unique and interesting properties. Specifically we have been working on a new class of two-photon absorbing molecules linked to platinum poly-ynes. In the platinum poly-yne chromophores the photophysics are more complicated and we have just started to understand what drives both the linear and non-linear photophysical properties.

Concentration-dependent photophysical switching in mixed self-assembled monolayers of pentacene and perylenediimide on gold nanoclusters.

PubMed

Kato, Daiki; Sakai, Hayato; Araki, Yasuyuki; Wada, Takehiko; Tkachenko, Nikolai V; Hasobe, Taku

2018-03-28

Photophysical control and switching on organic-inorganic hybrid interfaces are of great interest in diverse fundamental and applicative research areas. 6,13-Bis(triisopropylsilylethynyl)pentacene (TP) is well-known to exhibit efficient singlet fission (SF) for generation of high-yield triplet excited states in aggregated forms, whereas perylenediimide (PDI) ensembles show the characteristic excimer formation. Additionally, a combination of pentacene (electron donor: D) and PDI (electron acceptor: A) is expected to undergo an efficient photoinduced electron transfer (PET), and absorption of two chromophores combined covers the entire visible region. Therefore, the concentration-dependent mixed self-assembled monolayers (SAMs) composed of two chromophores enable us to control and switch the photophysical processes on a surface. In this work, a series of mixed SAMs composed of TP and PDI units on gold nanoclusters (GNCs) were newly synthesized by changing the relative molecular concentration ratios. Structural control of mixed SAMs on a gold surface based on the concentration ratios was successfully achieved. Time-resolved femtosecond and nanosecond transient absorption measurements clearly demonstrate photophysical control and switching of the above competitive reactions such as SF, electron transfer (ET) and excimer formation. The maximum quantum yields of triplet states (ΦT = ∼170%) and electron transfer (ΦET = ∼95%) were quantitatively evaluated by changing the concentration ratios. The rate constants of SF and excimer processes are largely dependent on the concentration ratios, whereas the rate constants of ET processes approximately remain constant. These findings are also discussed based on the statistical framework of the assembly of chromophores on the gold surface.

Catalysis of Photochemical Reactions.

ERIC Educational Resources Information Center

Albini, A.

1986-01-01

Offers a classification system of catalytic effects in photochemical reactions, contrasting characteristic properties of photochemical and thermal reactions. Discusses catalysis and sensitization, examples of catalyzed reactions of excepted states, complexing ground state substrates, and catalysis of primary photoproducts. (JM)

Photochemical mechanisms of ocular photic injury (Abstract Only)

NASA Astrophysics Data System (ADS)

Stuck, Bruce E.; Lund, David J.; Zuclich, Joseph A.

2000-03-01

Mechanisms of photic injury to the eye can be categorized as photochemical, photothermal or photodistruptive. Exposure wavelength, exposure duration, ocular tissue characteristics and response criteria are key factors in the delineation of the ocular injury mechanisms. Depending on the exposure condition, one or all of the laser-tissue interaction mechanisms can be involved. Although photic injury to the eye was initially assumed to involve thermal mechanisms, more recent research has demonstrated that ocular effects can be produced by light exposure without a significant retinal temperature rise. Photochemical mechanisms are also implicated in UV photic injury to the cornea and lens. Exposure of the retina to short visible wavelengths for prolonged durations results in photochemical retinal damage with negligible localized retinal temperature elevation. For exposure conditions where photochemical mechanisms are dominate, the reciprocity of irradiance and exposure duration is apparent. The latency until observation of a photochemical lesion is often 24-48 hours whereas a thermal lesion is observed immediately or within a few hours after the exposure. Action spectra for photochemical injury to the eye are discussed in the context of ocular injury thresholds and current permissible exposure limits.

The photophysics of fac-[Re(CO)3(NN)(bpa)](+) complexes: a theoretical/experimental study.

PubMed

Sousa, S F; Sampaio, R N; Barbosa Neto, N M; Machado, A E H; Patrocinio, A O T

2014-08-01

The influence of the polypyridyl ligand on the photophysics of fac-[Re(CO)3(NN)(bpa)](+), bpa = 1,2-bis-(4-pyridyl)ethane and NN = 1,10-phenanthroline (phen), pyrazino[2,3-f][1,10]-phenanthroline (dpq), and dipyrido[3,2-a:2'3'-c]phenazine (dppz) has been investigated by steady state and time-resolved emission spectroscopy combined with theoretical calculations using time-dependent density functional theory (TD-DFT). The fac-[Re(CO)3(phen)(bpa)](+) is a typical MLCT emitter in acetonitrile with ϕ = 0.11 and τ = 970 ns. The emission lifetime and quantum yield decrease significantly in fac-[Re(CO)3(dpq)(bpa)](+) (ϕ = 0.05; τ = 375 ns) due to the presence of a close lying dark charge transfer state located at the pyrazine ring of dpq, as indicated by TD-DFT data. The luminescence of these complexes is quenched by hydroquinone with kq = (2.9 ± 0.1) × 10(9) and (2.6 ± 0.1) × 10(9) L mol(-1) s(-1), respectively, for NN = phen or dpq. These values are increased respectively to (4.6 ± 0.1) × 10(9) and (4.2 ± 0.1) × 10(9) L mol(-1) s(-1) in the 1 : 1 H2O-CH3CN mixture. In this medium Stern-Volmer constants determined by steady-state and time-resolved measurements differ from each other, which is indicative of static quenching, i.e. the pre-association of hydroquinone and the complexes through hydrogen bonding between the remote N-atom in the bpa ligand (KA ≅ 1-2 × 10(1) L mol(-1)), followed by a concerted proton-electron transfer. In contrast to other investigated complexes, fac-[Re(CO)3(dppz)(bpa)](+) is weakly emissive in acetonitrile at room temperature (ϕ ≅ 10(-4)) and does not exhibit a rigidochromic effect. This photophysical behaviour as well as TD-DFT data indicate that the lowest lying triplet excited state can be described as (3)ILdppz. The results provide additional insight into the influence of the polypyridyl ligand on the photophysical properties of Re(I) complexes.

Excited-State Complexes of Conjugated Polymers: Novel Photophysical Processes and Optoelectronic Materials.

DTIC Science & Technology

1995-03-20

corresponding excited-state complexes were only recently discovered. The results of our extensive studies of intermolecular excimers and exciplexes of many...the luminescence of conjugated polymers. The luminescence and charge photogeneration in exciplexes of conjugated polymers with donor triarylamines will also be presented. jg

Synthesis, Photophysical Characterization, and Gelation Studies of a Stilbene-Cholesterol Derivative

ERIC Educational Resources Information Center

Geiger, H. Christina; Geiger, David K.; Baldwin, Christine

2006-01-01

Organogels are low molar mass organic compounds with the ability to immobilize an incredible quantity of solvent and fibrous aggregation of these compounds formed by noncovalent interaction usually involves hydrogen bonding. For stilbene-cholesterol based gelators, the driving force for molecular aggregation are weak van der Waal interactions…

Photophysics and catalysis of porphyrinoids

NASA Astrophysics Data System (ADS)

Aggarwal, Amit

Organic nanoparticles (ONP) of metalloporphyrins can be versatile catalysts for the selective oxidation of alkenes and other hydrocarbons. Herein, we report the catalytic activity of ONP of 5,10,15,20-tetrakis-[4-(1'H,1'H,2'H,2'H-heptadecafluorodecane-1-thiol)-2,3,5,6-tetrafluorophenyl] porphyrinato iron(III), Fe(III)TPPF84, and 5,10,15,20-tetakis-(2,3,4,5,6-pentafluorophenyl) porphyrinato manganese(III), Mn(III)TPPF20, for cyclohexene oxidation using molecular oxygen as an oxidant in water under ambient conditions. Sequential dipping of indium-tin-oxide electrodes into solutions of tetra cationic porphyrins and tetra anionic polyoxometalates results in the controlled formation of nm thick films. The potential applications of these robust films on electrodes range from catalysts to sensors. This chapter focuses on the electrochemistry of the multilayered films where it is found that the oxidation and reduction potentials of each species remain largely the same as found in solution. Photophysical properties of Porphyrinoids bearing four rigid hydrogen bonding motifs on the meso positions, self-assembled into a cofacial cage with four complementary bis(decyl)melamine units in dry solvents are presented here. Self-assembly was investigated by NMR spectroscopy, dynamic light scattering, and atomic force microscopy. The phototphysical properties of the cage formation involve the measurement of their absorption and emission spectra and the fluorescence life time in dry THF. The hydrocarbon chains on the bis(decyl)melamine mediate the formation of nanofilms on surfaces as the solvent slowly evaporates. A systematic study of the photophysical properties of a series of porphyrinoids is presented. The role of the location of a heavy atom in shunting the excited state from the singlet to the triplet manifolds is compared for three cases. It is well known that Pt(II) metalloporphyrins do not fluoresce. For meso pyridyl porphyrins, the fluorescence quantum yield decreases as the number of coordinatively attached Pt(II) complexes increase from 0-4, but the tetracoordinated species retains about 30% of the fluorescence. Covalently attaching a heavy metal complex e.g. Pt(II) complex to the macrocycle by an organometalic bond at the peripheral meso position causes greater than a 20-fold decrease in fluorescence quantum yield and may enhance some internal conversion to the ground state. For comparison, the fluorescence quantum yield decreases somewhat as the number of pyridyl groups on the meso positions increase 0-4. We also evaluate the photophysical properties of a series of porphyrins with nitro groups on the beta pyrrole position and on the meso phenyl group, which also quenches the fluorescence. These studies bear on the use of metal ions to enhance the photophysical properties of these dyes as photodynamic therapeutics and for supramolecular systems, while the nitrated macrocycles have potential application in non linear optics. The photophysical properties of non-hydrolysable tetra- thioglycosylated conjugates of chlorin (CGlc4), isobacteriochlorin (IGlc4) and bacteriochlorin (BGlc4) and core F20 platforms are reported here. These studies involve the measurement of absorption and emission spectra, fluorescence quantum yield, singlet oxygen quantum yield, and singlet state life time in three different solvents: phosphate buffer saline (PBS), ethanol, and ethylacetate. Compared to the porphyrin in PBS, CGlc4 has a markedly greater absorbance of red light near 650 nm and a 6-fold increase in fluorescence quantum yield; whereas IGlc4 has broad Q bands and a 12-fold increase in fluorescence quantum yield. Since IGlc4 CGlc4 very slowly bleach, these properties may enable their use as fluorescent tags to track biological processes. BGlc4 has a similar fluorescence quantum yield to PGlc4, (<10%), but the lowest energy absorption/emission peaks of BGlc4 are considerably red shifted to near 730 nm with a nearly 50-fold greater absorbance, which may allow this conjugate to be an effective PDT agent. (Abstract shortened by UMI.)

Preliminary Evaluation of Air Quality Model Performance Utilizing Measurements at the University of Houston Moody Tower and others during the TexAQS-II

NASA Astrophysics Data System (ADS)

Byun, D. W.; Rappenglueck, B.; Lefer, B.

2007-12-01

Accurate meteorological and photochemical modeling efforts are necessary to understand the measurements made during the Texas Air Quality Study (TexAQS-II). The main objective of the study is to understand the meteorological and chemical processes of high ozone and regional haze events in the Eastern Texas, including the Houston-Galveston metropolitan area. Real-time and retrospective meteorological and photochemical model simulations were performed to study key physical and chemical processes in the Houston Galveston Area. In particular, the Vertical Mixing Experiment (VME) at the University of Houston campus was performed on selected days during the TexAQS-II. Results of the MM5 meteorological model and CMAQ air quality model simulations were compared with the VME and other TexAQS-II measurements to understand the interaction of the boundary layer dynamics and photochemical evolution affecting Houston air quality.

Photophysical investigations of squaraine and cyanine dyes and their interaction with bovine serum albumin

NASA Astrophysics Data System (ADS)

Saikiran, M.; Sato, D.; Pandey, S. S.; Kato, T.

2016-04-01

A model far-red sensitive symmetrical squaraine dye (SQ-3) and unsymmetrical near infra-red sensitive cyanine dye (UCD-1) bearing direct-COOH functionalized indole ring were synthesized, characterized and subjected to photophysical investigations including their interaction with bovine serum albumin (BSA) as a model protein in phosphate buffer solution (PBS). Both of the dyes exhibit strong interaction with BSA in phosphate buffer with high apparent binding constant. A judicious tuning of hydrophobic main backbone with reactive functionality for associative interaction with active site of BSA has been found to be necessary for BSA detection in PBS.

Synthesis, characterization, and photophysical properties of a thiophene-functionalized bis(pyrazolyl) pyridine (BPP) tricarbonyl rhenium(I) complex.

PubMed

Lytwak, Lauren A; Stanley, Julie M; Mejía, Michelle L; Holliday, Bradley J

2010-09-07

A bromo tricarbonyl rhenium(I) complex with a thiophene-functionalized bis(pyrazolyl) pyridine ligand (L), ReBr(L)(CO)(3) (1), has been synthesized and characterized by variable temperature and COSY 2-D (1)H NMR spectroscopy, single-crystal X-ray diffraction, and photophysical methods. Complex 1 is highly luminescent in both solution and solid-state, consistent with phosphorescence from an emissive (3)MLCT excited state with an additional contribution from a LC (3)(pi-->pi*) transition. The single-crystal X-ray diffraction structure of the title ligand is also reported.

Heterodiazocines: Synthesis and Photochromic Properties, Trans to Cis Switching within the Bio-optical Window.

PubMed

Hammerich, Melanie; Schütt, Christian; Stähler, Cosima; Lentes, Pascal; Röhricht, Fynn; Höppner, Ronja; Herges, Rainer

2016-10-04

Diazocines, bridged azobenzenes, exhibit superior photophysical properties compared to parent azobenzenes such as high switching efficiencies, quantum yields, and particularly switching wavelengths in the visible range. Synthesis, however, proceeds with low yields, and derivatives are difficult to prepare. We now present two heterodiazocines which are easier to synthesize, and the general procedures should also provide facile access to derivatives. Moreover, both compounds can be switched with light in the far-red (650 nm). Accessibility and photophysical properties make them ideal candidates for applications such as photoswitchable drugs and functional materials.

Photophysical properties and fluorescence quenching of 2,3-diazabicyclo[2.2.2]oct-2-ene in zeolites

NASA Astrophysics Data System (ADS)

Pischel, Uwe; Galletero, Maria S.; García, Hermenegildo; Miranda, Miguel A.; Nau, Werner M.

2002-06-01

2,3-Diazabicyclo[2.2.2]oct-2-ene (DBO) was used as a long-lived fluorescent probe in zeolites (NaY, Na-mordenite, Na-ZSM-5, H-ZSM-5) and related oxide materials (all silica MCM-41, silica, silica-alumina, γ-alumina). The photophysical properties are dominated by a hydroxylic environment, caused by the inorganic framework and co-adsorbed water. The quenching of DBO by oxygen was strongly dependent on the type of zeolite. In ZSM-5 zeolites, the fluorescence decays were not monoexponential in the presence of oxygen (air).

Photophysical Properties of Organoplatinum(II) Compounds and Derived Self-Assembled Metallacycles and Metallacages: Fluorescence and its Applications.

PubMed

Saha, Manik Lal; Yan, Xuzhou; Stang, Peter J

2016-11-15

Over the past couple of decades, coordination-driven self-assembly has evolved as a broad multidisciplinary domain that not only covers the syntheses of aesthetically pleasing supramolecular architectures but also emerges as a method to form new optical materials, chemical sensors, theranostic agents, and compounds with light-harvesting and emissive properties. The majority of these applications depend upon investigations that reveal the photophysical nature and electronic structure of supramolecular coordination complexes (SCCs), including two-dimensional (2D) metallacycles and three-dimensional (3D) metallacages. As such, well-defined absorption and emission spectra are important for a given SCC to be used for sensing, bioimaging, and other applications with molecular fluorescence being an important component. In this Account, we summarize the photophysical properties of some bis(phosphine)organoplatinum(II) compounds and their discrete SCCs. The platinum(II) based organometallic precursors typically display spectral red-shifts and have low fluorescence quantum yields and short fluorescence lifetimes compared to their organic counterparts because the introduction of metal centers enhances both intersystem crossing (ISC) and intramolecular charge transfer (ICT) processes, which can compete with the fluorescence emissions. Likewise ligands with conjugation can also increase the ICT process; hence the corresponding organoplatinum(II) compounds undergo a further decrease in fluorescence lifetimes. The use of endohedral amine functionalized 120°-bispyridyl ligands can dramatically enhance the emission properties of the resultant organoplatinum(II) based SCCs. As such these SCCs display emissions in the visible region (ca. 400-500 nm) and are significantly red-shifted (ca. 80-100 nm) compared to the ligands. This key feature makes them suitable as supramolecular theranostic agents wherein these unique emission properties provide diagnostic spectroscopic handles and the organoplatinum(II) centers act as potential anticancer agents. Using steady state and time-resolved-spectroscopic techniques and quantum computations in concert, we have determined that the emissive properties stem from the ligand-centered transitions involving π-type molecular orbitals with modest contributions from the metal-based orbitals. The self-assembly and the photophysics of organoplatinum(II) ← 3-substituted pyridyl based SCCs are highly diverse. Subtle changes in the ligands' structures can form molecular congener systems with distinct conformational and photophysical properties. Furthermore, the heterometallic SCCs described herein possess rich photophysical properties and can be used for sensing based applications. Tetraphenylethylene (TPE) based SCCs display emissions in the aggregated state as well as in dilute solutions. This is a unique phenomenon that bridges the aggregation caused quenching (ACQ) and aggregation induced emission (AIE) effects. Moreover, a TPE based metallacage exhibits solvatoluminescence, including white light emission in THF solvent, and can act as a fluorescence-sensor for structurally similar ester compounds.

Heteroleptic Cu-Based Sensitizers in Photoredox Catalysis.

PubMed

Hernandez-Perez, Augusto C; Collins, Shawn K

2016-08-16

Photochemistry is an important tool in organic synthesis that has largely been underdeveloped in comparison to thermal activation. Recent advances in technology have ushered in a new era in synthetic photochemistry. The emergence of photocatalysis, which exploits sensitizers for the absorption of visible light, has provided organic chemists with a new route to the generation of radical intermediates for synthesis. Of particular interest is the development of Cu-based complexes for photocatalysis, which possess variable photophysical properties and can display complementary reactivity with common photocatalysts based on heavier transition metals such as Ru or Ir. Heteroleptic Cu-based sensitizers incorporating the presence of both a bisphosphine and diamine ligand bound to the copper center are a promising class of photocatalysts. Their synthesis is a single step, often involving only precipitation for purification. In addition, it was shown that the sensitizers could be formed in situ in the reaction mixture, simplifying the experimental setup. The heteroleptic nature of the Cu-complexes also affords opportunities to fine-tune properties. For example, structurally rigidified bisphosphines reinforce geometries about the metal center to extend the excited state lifetime. Variation of the diamine ligand can influence the excited state oxidation/reduction potentials and optical absorbances. The heteroleptic complex Cu(XantPhos)(neo)BF4 has demonstrated utility in the synthesis of helical polyaromatic carbocycles. The synthesis of [5]helicene, a relatively simple member of the helicene family, was improved from the existing UV-light mediated method by eliminating the formation of unwanted byproducts. In addition, the Cu-based sensitizers also promoted the formation of novel pyrene/helicene hybrids for materials science applications. The synthetic methods that were developed were augmented when combined with continuous flow technology. The irradiation of reaction mixtures as they are pumped through small diameter tubing provides a more homogeneous and increased photon flux compared with irradiation in round-bottom flasks or other batch reactors. The value of continuous flow methods is also evident when examining UV-light photochemistry, where the simple and safe experimental set-ups allow for further exploration of high energy light for synthetic purposes. The synthesis of functionalized complex carbazoles was also studied using both a visible light method exploiting a heteroleptic copper-based sensitizer and a UV-light mediated method. It was demonstrated that both the photocatalysis methods and UV light photochemistries were rendered more user-friendly, safe, and reproducible when using continuous flow methods. Interestingly, the two photochemical methods often afford contrasting selectivities as a result of their inherently different mechanisms. It can be expected that the complementarity of the various photochemical methods will be an asset to synthetic chemists as the field continues to evolve.

EMERGING TECHNOLOGY PROJECT BULLETIN: LASER INDUCED PHOTOCHEMICAL OXIDATIVE DESTRUCTION

EPA Science Inventory

The process developed by Energy and Environmental Engineering, Incorporated, is designed to photochemically oxidize organic compounds in wastewater by applying ultraviolet radiation using an Excimer laser. The photochemical reactor can destroy low to moderate concentrations...

Additive and Photochemical Manufacturing of Copper

PubMed Central

Yung, Winco K. C.; Sun, Bo; Meng, Zhengong; Huang, Junfeng; Jin, Yingdi; Choy, Hang Shan; Cai, Zhixiang; Li, Guijun; Ho, Cheuk Lam; Yang, Jinlong; Wong, Wai Yeung

2016-01-01

In recent years, 3D printing technologies have been extensively developed, enabling rapid prototyping from a conceptual design to an actual product. However, additive manufacturing of metals in the existing technologies is still cost-intensive and time-consuming. Herein a novel platform for low-cost additive manufacturing is introduced by simultaneously combining the laser-induced forward transfer (LIFT) method with photochemical reaction. Using acrylonitrile butadiene styrene (ABS) polymer as the sacrificial layer, sufficient ejection momentum can be generated in the LIFT method. A low-cost continuous wave (CW) laser diode at 405 nm was utilized and proved to be able to transfer the photochemically synthesized copper onto the target substrate. The wavelength-dependent photochemical behaviour in the LIFT method was verified and characterized by both theoretical and experimental studies compared to 1064 nm fiber laser. The conductivity of the synthesized copper patterns could be enhanced using post electroless plating while retaining the designed pattern shapes. Prototypes of electronic circuits were accordingly built and demonstrated for powering up LEDs. Apart from pristine PDMS materials with low surface energies, the proposed method can simultaneously perform laser-induced forward transfer and photochemical synthesis of metals, starting from their metal oxide forms, onto various target substrates such as polyimide, glass and thermoplastics. PMID:28000733

Additive and Photochemical Manufacturing of Copper

NASA Astrophysics Data System (ADS)

Yung, Winco K. C.; Sun, Bo; Meng, Zhengong; Huang, Junfeng; Jin, Yingdi; Choy, Hang Shan; Cai, Zhixiang; Li, Guijun; Ho, Cheuk Lam; Yang, Jinlong; Wong, Wai Yeung

2016-12-01

In recent years, 3D printing technologies have been extensively developed, enabling rapid prototyping from a conceptual design to an actual product. However, additive manufacturing of metals in the existing technologies is still cost-intensive and time-consuming. Herein a novel platform for low-cost additive manufacturing is introduced by simultaneously combining the laser-induced forward transfer (LIFT) method with photochemical reaction. Using acrylonitrile butadiene styrene (ABS) polymer as the sacrificial layer, sufficient ejection momentum can be generated in the LIFT method. A low-cost continuous wave (CW) laser diode at 405 nm was utilized and proved to be able to transfer the photochemically synthesized copper onto the target substrate. The wavelength-dependent photochemical behaviour in the LIFT method was verified and characterized by both theoretical and experimental studies compared to 1064 nm fiber laser. The conductivity of the synthesized copper patterns could be enhanced using post electroless plating while retaining the designed pattern shapes. Prototypes of electronic circuits were accordingly built and demonstrated for powering up LEDs. Apart from pristine PDMS materials with low surface energies, the proposed method can simultaneously perform laser-induced forward transfer and photochemical synthesis of metals, starting from their metal oxide forms, onto various target substrates such as polyimide, glass and thermoplastics.

Seasonal Photochemical Transformations of Nitrogen Species in a Forest Stream and Lake

PubMed Central

Porcal, Petr; Kopáček, Jiří; Tomková, Iva

2014-01-01

The photochemical release of inorganic nitrogen from dissolved organic matter is an important source of bio-available nitrogen (N) in N-limited aquatic ecosystems. We conducted photochemical experiments and used mathematical models based on pseudo-first-order reaction kinetics to quantify the photochemical transformations of individual N species and their seasonal effects on N cycling in a mountain forest stream and lake (Plešné Lake, Czech Republic). Results from laboratory experiments on photochemical changes in N speciation were compared to measured lake N budgets. Concentrations of organic nitrogen (Norg; 40–58 µmol L−1) decreased from 3 to 26% during 48-hour laboratory irradiation (an equivalent of 4–5 days of natural solar insolation) due to photochemical mineralization to ammonium (NH4 +) and other N forms (Nx; possibly N oxides and N2). In addition to Norg mineralization, Nx also originated from photochemical nitrate (NO3 −) reduction. Laboratory exposure of a first-order forest stream water samples showed a high amount of seasonality, with the maximum rates of Norg mineralization and NH4 + production in winter and spring, and the maximum NO3 − reduction occurring in summer. These photochemical changes could have an ecologically significant effect on NH4 + concentrations in streams (doubling their terrestrial fluxes from soils) and on concentrations of dissolved Norg in the lake. In contrast, photochemical reactions reduced NO3 − fluxes by a negligible (<1%) amount and had a negligible effect on the aquatic cycle of this N form. PMID:25551441

Singlet oxygen in the coupled photochemical and biochemical oxidation of dissolved organic matter.

PubMed

Cory, Rose M; McNeill, Kristopher; Cotner, James P; Amado, Andre; Purcell, Jeremiah M; Marshall, Alan G

2010-05-15

Dissolved organic matter (DOM) is a significant (>700 Pg) global C pool. Transport of terrestrial DOM to the inland waters and coastal zones represents the largest flux of reduced C from land to water (215 Tg yr(-1)) (Meybeck, M. Am. J. Sci. 1983, 282, 401-450). Oxidation of DOM by interdependent photochemical and biochemical processes largely controls the fate of DOM entering surface waters. Reactive oxygen species (ROS) have been hypothesized to play a significant role in the photooxidation of DOM, because they may oxidize the fraction of DOM that is inaccessible to direct photochemical degradation by sunlight. We followed the effects of photochemically produced singlet oxygen ((1)O(2)) on DOM by mass spectrometry with (18)O-labeled oxygen, to understand how (1)O(2)-mediated transformations of DOM may lead to altered DOM bioavailability. The photochemical oxygen uptake by DOM attributed to (1)O(2) increased with DOM concentration, yet it remained a minority contributor to photochemical oxygen uptake even at very high DOM concentrations. When DOM samples were exposed to (1)O(2)-generating conditions (Rose Bengal and visible light), increases were observed in DOM constituents with higher oxygen content and release of H(2)O(2) was detected. Differential effects of H(2)O(2) and (1)O(2)-treated DOM showed that (1)O(2)-treated DOM led to slower bacterial growth rates relative to unmodified DOM. Results of this study suggested that the net effect of the reactions between singlet oxygen and DOM may be production of partially oxidized substrates with correspondingly lower potential biological energy yield.

40 CFR 52.1877 - Control strategy: Photochemical oxidants (hydrocarbons).

Code of Federal Regulations, 2011 CFR

2011-07-01

... oxidants (hydrocarbons). 52.1877 Section 52.1877 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY....1877 Control strategy: Photochemical oxidants (hydrocarbons). (a) The requirements of Subpart G of this... national standard for photochemical oxidants (hydrocarbons) in the Metropolitan Cincinnati interstate...

40 CFR 52.1877 - Control strategy: Photochemical oxidants (hydrocarbons).

Code of Federal Regulations, 2010 CFR

2010-07-01

... oxidants (hydrocarbons). 52.1877 Section 52.1877 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY....1877 Control strategy: Photochemical oxidants (hydrocarbons). (a) The requirements of Subpart G of this... national standard for photochemical oxidants (hydrocarbons) in the Metropolitan Cincinnati interstate...

Modelling study of boundary-layer ozone over northern China - Part II: Responses to emission reductions during the Beijing Olympics

NASA Astrophysics Data System (ADS)

Tang, Guiqian; Zhu, Xiaowan; Xin, Jinyuan; Hu, Bo; Song, Tao; Sun, Yang; Wang, Lili; Wu, Fangkun; Sun, Jie; Cheng, Mengtian; Chao, Na; Li, Xin; Wang, Yuesi

2017-09-01

The implementation of emission reduction measures during the Olympics provided a valuable opportunity to study regional photochemical pollution over northern China. In this study, the fifth-generation Pennsylvania State University/National Centre for Atmospheric Research Mesoscale Model and Community Multiscale Air Quality model system was applied to conduct two sets of modelling analyses of the period from July 20 to September 20, 2008, to illustrate the influences of emission reduction measures on regional photochemical pollution over northern China during the Beijing Olympics. The results indicated that the implementation of emission control measures decreased the concentrations of ozone (O3) precursors, namely nitrogen oxide (NOx) and volatile organic compounds (VOCs), throughout the boundary layer. The concentrations of these compounds were reduced by 45% in the central urban area of Beijing at the ground level. Although the average O3 concentration in the central urban area increased by more than 8 ppbv, the total oxidant concentration decreased significantly by more than 5 ppbv. Greater O3 concentrations mainly occurred during periods with weak photochemical reactions. During periods of strong photochemical production, the O3 concentration decreased significantly due to a weakening vertical circulation between the lower and upper boundary layer. Consequently, the number of days when the O3 concentration exceeded 100 ppbv decreased by 25% in Beijing. The emission control measures altered the sensitivity of the regional O3 production. The coordinated control region of NOx and VOCs expanded, and the control region of VOCs decreased in size. The reduction of non-point-source emissions, such as fugitive VOCs and vehicles, was more useful for controlling regional photochemical pollution over northern China.

Photochemical Reactions of (n(5)-Pentamethylcyclpentadienyl)-Dicarbonyliron-Alkyl and -Silyl Complexes: Reversible Ethylene Insertion into an Iron-Silicon Bond and Implications for the Mechanism of Transition Metal-Catalyzed Hydrosilation of Alkenes.

DTIC Science & Technology

1985-12-11

RD-R162 462 PHOTOCHEMICAL REACTIONS OF(N(S)-P NTANETNYLCVCLPENTADIENYL)-DICARRONVLIR.. (U) MASSACHUSETTS INST OF TECH CAMBRIDGE DEPT OF CHEMISTRY...34 Photochemical Reactions of (n5-Pentamethylcyclpentadienyl)- Dicarbonyliron-Alkyl and -Silyl Complexes: Reversible Ethylene Insertion into an Iron-Silicon Bond...Chemical Society) PHOTOCHEMICAL REACTIONS OF (n5-PENTAMETHYLCYCLOPENTADIENYL)- DICARBONYLIRON-ALKYL AND -SILYL COMPLEXES: REVERSIBLE ETHYLENE INSERTION INTO

Photochemical water oxidation and origin of nonaqueous uranyl peroxide complexes.

PubMed

McGrail, Brendan T; Pianowski, Laura S; Burns, Peter C

2014-04-02

Sunlight photolysis of uranyl nitrate and uranyl acetate solutions in pyridine produces uranyl peroxide complexes. To answer longstanding questions about the origin of these complexes, we conducted a series of mechanistic studies and demonstrate that these complexes arise from photochemical oxidation of water. The peroxo ligands are easily removed by protonolysis, allowing regeneration of the initial uranyl complexes for potential use in catalysis.

Synthesis and optical properties of water-soluble biperylene-based dendrimers.

PubMed

Shao, Pin; Jia, Ningyang; Zhang, Shaojuan; Bai, Mingfeng

2014-05-30

We report the synthesis and photophysical properties of three biperylene-based dendrimers, which show red fluorescence in water. A fluorescence microscopy study demonstrated uptake of biperylene-based dendrimers in living cells. Our results indicate that these biperylene-based dendrimers are promising candidates in fluorescence imaging applications with the potential as therapeutic carriers.

Direct anisotropic growth of CdS nanocrystals in thermotropic liquid crystal templates for heterojunction optoelectronics.

PubMed

Yuan, Kai; Chen, Lie; Chen, Yiwang

2014-09-01

The direct growth of CdS nanocrystals in functional solid-state thermotropic liquid crystal (LC) small molecules and a conjugated LC polymer by in situ thermal decomposition of a single-source cadmium xanthate precursor to fabricate LC/CdS hybrid nanocomposites is described. The influence of thermal annealing temperature of the LC/CdS precursors upon the nanomorphology, photophysics, and optoelectronic properties of the LC/CdS nanocomposites is systematically studied. Steady-state PL and ultrafast emission dynamics studies show that the charge-transfer rates are strongly dependent on the thermal annealing temperature. Notably, annealing at liquid-crystal state temperature promotes a more organized nanomorphology of the LC/CdS nanocomposites with improved photophysics and optoelectronic properties. The results confirm that thermotropic LCs can be ideal candidates as organization templates for the control of organic/inorganic hybrid nanocomposites at the nanoscale level. The results also demonstrate that in situ growth of semiconducting nanocrystals in thermotropic LCs is a versatile route to hybrid organic/inorganic nanocomposites and optoelectronic devices. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Tuning the constrained photophysics of a pyrazoline dye 3-naphthyl-1-phenyl-5-(4-carboxyphenyl)-2-pyrazoline inside the cyclodextrin nanocavities: A detailed insight via experimental and theoretical approach

NASA Astrophysics Data System (ADS)

Varghese, Beena; Al-Busafi, Saleh N.; Suliman, FakhrEldin O.; Al-Kindy, Salma M. Z.

2017-02-01

The modulation in the photophysics of a pyrazoline dye 3-naphthyl-1-phenyl-5-(4-carboxyphenyl)-2-pyrazoline (NPCP), when it drifts from bulk water into the nanocages of aqueous cyclodextrin solutions was investigated. The intramolecular charge transfer (ICT) fluorescence band intensity was found to increase with a blue shift in the presence of cyclodextrins. The results from 1H NMR and 1Hsbnd H COSY NMR spectral analysis clearly points out the position of pyrazoline ring inside the cavity and its role in complexation process. A quantitative assessment of the emission intensity data on Benesi-Hildebrand (B-H) equation along with ESI-MS spectra reveals the probable stoichiometry of NPCP-CD complexes. Molecular docking and molecular dynamics studies were conducted for β/γ cyclodextrin associated inclusion complexes of NPCP. The results obtained by computational studies are in good relation with the data obtained through experimental methods and both ascertain the encapsulation of NPCP into cyclodextrins.

Rational design of tetraphenylethylene-based luminescent down-shifting molecules: photophysical studies and photovoltaic applications in a CdTe solar cell from small to large units.

PubMed

Li, Yilin; Li, Zhipeng; Ablekim, Tursunjan; Ren, Tianhui; Dong, Wen-Ji

2014-12-21

A rational design strategy of novel fluorophores for luminescent down-shifting (LDS) application was proposed and tested in this paper. Three new fluorophores (1a-c) with specific intramolecular charge transfer (ICT) and aggregation-induced emission (AIE) characteristics were synthesized as LDS molecules for increasing the output short circuit current density (Jsc) of a CdTe solar cell. Photophysical studies of their solution and solid states, and photovoltaic measurements of their PMMA solid films applied on a CdTe solar cell suggested that the specific spectroscopic properties and Jsc enhancement effects of these molecules were highly related to their chemical structures. The Jsc enhancement effects of these fluorophores were measured on both a CdTe small cell and a large panel. An increase in the output Jsc by as high as 5.69% for a small cell and 8.88% for a large panel was observed. Compared to a traditional LDS molecule, Y083, these fluorophores exhibited more superior capabilities of LDS.

Solution-based single molecule imaging of surface-immobilized conjugated polymers.

PubMed

Dalgarno, Paul A; Traina, Christopher A; Penedo, J Carlos; Bazan, Guillermo C; Samuel, Ifor D W

2013-05-15

The photophysical behavior of conjugated polymers used in modern optoelectronic devices is strongly influenced by their structural dynamics and conformational heterogeneity, both of which are dependent on solvent properties. Single molecule studies of these polymer systems embedded in a host matrix have proven to be very powerful to investigate the fundamental fluorescent properties. However, such studies lack the possibility of examining the relationship between conformational dynamics and photophysical response in solution, which is the phase from which films for devices are deposited. By developing a synthetic strategy to incorporate a biotin moiety as a surface attachment point at one end of a polyalkylthiophene, we immobilize it, enabling us to make the first single molecule fluorescence measurements of conjugated polymers for long periods of time in solution. We identify fluctuation patterns in the fluorescence signal that can be rationalized in terms of photobleaching and stochastic transitions to reversible dark states. Moreover, by using the advantages of solution-based imaging, we demonstrate that the addition of oxygen scavengers improves optical stability by significantly decreasing the photobleaching rates.

Luminol modified polycarbazole and poly(o-anisidine): Theoretical insights compared with experimental data.

PubMed

Jadoun, Sapana; Verma, Anurakshee; Riaz, Ufana

2018-06-07

With the aim to explore the effect of luminol as a multifunctional dopant for conjugated polymers, the present study reports the ultrasound-assisted doping of polycarbazole (PCz) and poly(o-anisidine) (PAnis) with luminol in basic, acidic and neutral media. The synthesized homopolymers and luminol doped polymers were characterized using FT-IR, UV-visible and XRD studies while the photo-physical properties were investigated via fluorescence spectroscopy. Density functional theory (DFT) calculations were performed to get insights into the structural, optical, and electronic properties of homopolymers of polycarbazole (PCz) and poly(o-anisidine) (PAnis). Vibrational bands B3LYP/6-311G (d,p) level, UV-vis spectral bands and electronic properties such as ionization potentials (IP), electron affinities (EA) and HOMO-LUMO band gap energies of the homopolymers and doped polymers were calculated and compared. Results revealed that luminol doped polymers showed different photo-physical characteristics in acidic, basic and neutral media which could be tuned to obtain near infrared (NIR) emitting polymers. Copyright © 2018 Elsevier B.V. All rights reserved.

Vibrational spectroscopic study, structural analysis, photophysical properties and theoretical calculations of cis-(±)-2,4,5-tris(pyridin-2-yl)imidazoline

NASA Astrophysics Data System (ADS)

Baldenebro-López, Jesús; Báez-Castro, Alberto; Glossman-Mitnik, Daniel; Höpfl, Herbert; Cruz-Enríquez, Adriana; Miranda-Soto, Valentín; Parra-Hake, Miguel; Campos-Gaxiola, José J.

2017-02-01

cis-(±)-2,4,5-tris(pyridin-2-yl)imidazoline has been fully characterized by FT-IR, FT-Raman, UV-Vis and fluorescence spectroscopy, one- and two-dimensional NMR spectroscopy (1H, 1H-1H gCOSY, 1H-1H gNOESY,13C{1H} ATP, 1H-13C and 1H-15N gHSQC and 1H-13C gHMBC), high-resolution mass spectrometry (HR-FAB+), TG-DSC analysis and low-temperature single-crystal X-ray diffraction analysis. Additionally, the molecular geometry and the vibrational infrared and Raman frequencies were calculated by density functional theory using the M06/6-31G(d) level of theory, showing good agreement with the experimental results. The title compound showed interesting photophysical properties, which were studied experimentally in solution and in the solid state by UV-Vis and fluorescence spectroscopy and compared to the theoretically obtained parameters using TD-DFT calculations. Natural and Mulliken atomic charges and the molecular electrostatic potential (MEP) have been mapped.

Sustainable metal alkynyl chemistry: 3d metals and polyaza macrocyclic ligands.

PubMed

Ren, Tong

2016-02-25

We describe the chemistry of 3d metal alkynyls based on polyaza macrocyclic ligands, an emerging area of alkynyl chemistry that has previously been dominated by 4d and 5d metals with soft ligands. The abundance of 3d metals and low cost of tetraazacyclotetradecane ligands make these compounds more affordable, sustainable alternatives to metal alkynyls based on precious metals. Taking advantage of the rich variety of starting materials available in the literature, trans-[M(cyclam)(C2R)2]X (cyclam = 1,4,8,11-tetraazacyclotetradecane) compounds have been prepared from the reactions between [M(cyclam)X2]X (M = Cr, Fe and Co; X = Cl or OTf) and LiC2R. With [Co(cyclam)Cl2](+), both the {trans-[Co(cyclam)Cl]2(μ-(C≡C)n)}(2+) and trans-[Co(cyclam)(C2R)Cl](+) compounds have been prepared by a dehydrohalogenation reaction. The latter compounds undergo the second alkynylation reaction to afford dissymmetric trans-[Co(cyclam)(C2R)(C2R')](+) compounds. Similar alkynylation chemistry with complexes of the cyclam derivatives TMC (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) and HMC (5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane) has been demonstrated in studies of [Ni(TMC)(C2R)](+) and trans-/cis-[Cr(HMC)(C2R)2](+). Me3TACN (1,4,7-N,N',N''-trimethyl-1,4,7-triazacyclononane) is also a supporting ligand that has been observed in transition metal alkynyls. The trans-[M(cyclam)(C2D)(C2A)](+) compounds (D = donor chromophore, A = acceptor chromophore) are excellent candidates for probing photoinduced electron transfer and related photophysical and photochemical processes. 3d Metal ions are often in high-spin ground states, which make these alkynyl compounds promising building blocks for magnetic materials.

PEM-West trajectory climatology and photochemical model sensitivity study prepared using retrospective meteorological data

NASA Technical Reports Server (NTRS)

Merrill, John T.; Rodriguez, Jose M.

1991-01-01

Trajectory and photochemical model calculations based on retrospective meteorological data for the operations areas of the NASA Pacific Exploratory Mission (PEM)-West mission are summarized. The trajectory climatology discussed here is intended to provide guidance for flight planning and initial data interpretation during the field phase of the expedition by indicating the most probable path air parcels are likely to take to reach various points in the area. The photochemical model calculations which are discussed indicate the sensitivity of the chemical environment to various initial chemical concentrations and to conditions along the trajectory. In the post-expedition analysis these calculations will be used to provide a climatological context for the meteorological conditions which are encountered in the field.

Time-resolved EPR study on the photochemical reactions of benzil

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

Mukai, Masahiro; Yamnauchi, Seigo; Hirota, Noboru

1992-04-16

TREPR and optical studies on the photochemical reactions of benzil in 2-propanol and benzene-TEA conclude that emissive signals are due to the reaction from T{sub n} produced via the S{sub n} pointing right T{sub n} intersystem crossing process. The free-pair radical-pair mechanism can account for the main features of the slow rise component of the chemically induced dynamic electron polarization signal of the ketyl radical in 2-propanol. 27 refs., 10 figs., 2 tabs.

Reverse saturable absorption (RSA) in fluorinated iridium derivatives

NASA Astrophysics Data System (ADS)

Ferry, Michael J.; O'Donnell, Ryan M.; Bambha, Neal; Ensley, Trenton R.; Shensky, William M.; Shi, Jianmin

2017-08-01

The photophysical properties of cyclometallated iridium compounds are beneficial for nonlinear optical (NLO) applications, such as the design of reverse saturable absorption (RSA) materials. We report on the NLO characterization of a family of compounds of the form [Ir(pbt)2(LX)], where pbt is 2-phenylbenzothiazole and LX is a beta-diketonate ligand. In particular, we investigate the effects of trifluoromethylation on compound solubility and photophysics compared to the parent acetylacetonate (acac) version. The NLO properties, such as the singlet and triplet excited-state cross sections, of these compounds were measured using the Z-scan technique. The excited-state lifetimes were determined from visible transient absorption spectroscopy.

The Chameleonic Nature of Platinum(II) Imidazopyridine Complexes.

PubMed

Pinter, Piermaria; Pittkowski, Rebecca; Soellner, Johannes; Strassner, Thomas

2017-10-12

The synthesis and characterization of cyclometalated C^C* platinum(II) complexes with unique photophysical properties, aggregation induced enhancement of the quantum yields with a simultaneous decrease of phosphorescence lifetimes, is reported. Additionally, a change of emission color is induced by variation of the excitation wavelength. The aggregation behavior of these complexes is controlled by the steric demand of the substituents. The photophysical properties of these complexes are investigated through emission-excitation matrix analysis (EEM). The monomeric complexes are excellent room temperature phosphorescent blue emitters with emission maxima below 470 nm and quantum yields of up to 93 %. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

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

Auto-FPFA: An Automated Microscope for Characterizing Genetically Encoded Biosensors.

PubMed

Nguyen, Tuan A; Puhl, Henry L; Pham, An K; Vogel, Steven S

2018-05-09

Genetically encoded biosensors function by linking structural change in a protein construct, typically tagged with one or more fluorescent proteins, to changes in a biological parameter of interest (such as calcium concentration, pH, phosphorylation-state, etc.). Typically, the structural change triggered by alterations in the bio-parameter is monitored as a change in either fluorescent intensity, or lifetime. Potentially, other photo-physical properties of fluorophores, such as fluorescence anisotropy, molecular brightness, concentration, and lateral and/or rotational diffusion could also be used. Furthermore, while it is likely that multiple photo-physical attributes of a biosensor might be altered as a function of the bio-parameter, standard measurements monitor only a single photo-physical trait. This limits how biosensors are designed, as well as the accuracy and interpretation of biosensor measurements. Here we describe the design and construction of an automated multimodal-microscope. This system can autonomously analyze 96 samples in a micro-titer dish and for each sample simultaneously measure intensity (photon count), fluorescence lifetime, time-resolved anisotropy, molecular brightness, lateral diffusion time, and concentration. We characterize the accuracy and precision of this instrument, and then demonstrate its utility by characterizing three types of genetically encoded calcium sensors as well as a negative control.

Photophysical properties of the series fac- and mer-(1-phenylisoquinolinato-N∧C2')(x)(2-phenylpyridinato-N∧C2')(3-x)iridium(III) (x = 1-3).

PubMed

Deaton, Joseph C; Young, Ralph H; Lenhard, Jerome R; Rajeswaran, Manju; Huo, Shouquan

2010-10-18

The photophysical properties of tris-cyclometalated iridium(III) complexes have been probed by chemical and geometric variation through the series fac- and mer-Ir(piq)(x)(ppy)(3-x) (x = 1-3; piq = 1-phenylisoquinolinato-N(∧)C(2'), ppy = 2-phenylpyridinato-N(∧)C(2')). The phosphorescent decays were recorded in solution at 295 K and in polymer films from 2 to 295 K. In the heteroleptic complexes, emission occurs based solely on the piq ligand(s), at least by the nanosecond time scale, as its excited states are the lowest energy. Because fac-Ir(piq)(3) and fac-Ir(ppy)(3) possess practically the same oxidation potential, comparison of photophysical properties through the series fac-Ir(piq)(x)(ppy)(3-x) (x = 1-3) revealed the effects of having one, two, or three emissive piq ligands with no confounding effects from differences in electron withdrawing or donating properties between the spectator ppy ligands and the piq ligands. Effects of placement of piq ligands in different coordination geometries were elucidated by comparisons to the mer series.

Solar Irradiation of Bilirubin: An Experiment in Photochemical Oxidation

ERIC Educational Resources Information Center

Pillay A. E.; Salih, F. M.

2006-01-01

An experiment in photochemical oxidation, which deals with bilirubin, a well-known light-sensitive biological compound that is pedagogically ideal for photochemical experiments at tertiary institutes, is presented. The experiment would benefit students in chemistry who eventually branch out into the health sciences or biochemistry.

Feedbacks between microphysics and photochemical aging in viscous aerosol

NASA Astrophysics Data System (ADS)

Dou, Jing; Corral Arroyo, Pablo; Alpert, Peter A.; Ammann, Markus; Peter, Thomas; Krieger, Ulrich K.

2017-04-01

Fe(III)-citrate complex photochemistry, which plays an important role in aerosol aging, especially in lower troposphere, has been widely recognized in both solution and solid states. It can get excited by light below about 500 nm, inducing the oxidation of carboxylate ligands and the production of peroxides (e.g., OH•, HO2•), which have a significant impact on the climate, air quality and health. Recently, there is literature reporting that aqueous aerosol particles may attain highly viscous, semi-solid or even glassy physical states under a wide range of atmospheric conditions. However, systematic studies on the effect of high viscosity on photochemical processes are scarce. In this research, mass and size changes of a single, aqueous Fe(III)-citrate/citric acid particle levitated in an electrodynamic balance (EDB) are tracked during photochemical processing. We observe an overall mass loss during photochemical processing due to evaporation of volatile (e.g., CO2) and semi-volatile (e.g., ketones) compounds. It is known that relative humidity and temperature strongly effects the viscosity of citric acid. Hence, under light intensities large enough not limiting photochemical processing (at a wavelength of either 375 nm or 473 nm), the quasi-steady state evaporation rate in our experiments depends on relative humidity and temperature. The same holds true for the characteristic time scale for reaching thermodynamic equilibrium after switching off the light source. We are focusing on the high viscosity case (i.e., reduced molecular mobility and low water content), which slows down the transport of products but can also affect chemical reaction rates (e.g., initial absorption process, charge and energy transfer). Data are compared to kinetic modeling and diffusivities for semi-volatile compounds are estimated aiming at a more detailed understanding of the feedbacks between microphysics and photochemical aging.

Formulation design and photochemical studies on nanocrystal solid dispersion of curcumin with improved oral bioavailability.

PubMed

Onoue, Satomi; Takahashi, Haruki; Kawabata, Yohei; Seto, Yoshiki; Hatanaka, Junya; Timmermann, Barbara; Yamada, Shizuo

2010-04-01

Considerable interest has been focused on curcumin due to its use to treat a wide variety of disorders, however, the therapeutic potential of curcumin could often be limited by its poor solubility, bioavailability, and photostability. To overcome these drawbacks, efficacious formulations of curcumin, including nanocrystal solid dispersion (CSD-Cur), amorphous solid dispersion (ASD-Cur), and nanoemulsion (NE-Cur), were designed with the aim of improving physicochemical and pharmacokinetic properties. Physicochemical properties of the prepared formulations were characterized by scanning/transmission electron microscope for morphological analysis, laser diffraction, and dynamic light scattering for particle size analysis, and polarized light microscope, powder X-ray diffraction and differential scanning calorimetry for crystallinity assessment. In dissolution tests, all curcumin formulations exhibited marked improvement in the dissolution behavior when compared with crystalline curcumin. Significant improvement in pharmacokinetic behavior was observed in the newly developed formulations, as evidenced by 12- (ASD-Cur), 16- (CSD-Cur), and 9-fold (NE-Cur) increase of oral bioavailability. Upon photochemical characterization, curcumin was found to be photoreactive and photodegradable in the solution state, possibly via type 2 photochemical reaction, whereas high photochemical stability was seen in the solid formulations, especially CSD-Cur. On the basis of these observations, taken together with dissolution and pharmacokinetic behaviors, CSD strategy would be efficacious to enhance bioavailability of curcumin with high photochemical stability. 2009 Wiley-Liss, Inc. and the American Pharmacists Association

An ab initio study of the potential energy surface in the S 1 state of 2-hydroxypyridine

NASA Astrophysics Data System (ADS)

Sobolewski, Andrzej L.; Adamowicz, Ludwik

1996-12-01

The potential energy (PE) surface of the lowest excited singlet state relevant to the photophysics of interconversion of the 2-hydroxypyridine/2 (1H)-pyridinone (2HP/2PY) system is characterized by ab initio calculations. The geometry optimizations in the S 1 state performed at the CIS/6-31G (d,p) level confirm the experimental findings that the 2HP form is planar in this state whereas the 2PY form is significantly out-of-plane distorted. The lowest-energy first-order saddle-points which are relevant to the photophysics of the "mobile" hydrogen atom on the S 1 PE surface lead toward its dissociation from the molecule. There is no saddle-point for a "direct" proton transfer reaction on the S 1 PE surface leading from the 2HP form to the 2PY form. The results confirm the hypothesis that the photo-induced dissociation-association (PIDA) mechanism is probably responsible for the excited-state tautomerization observed in this system.

A solution-based single-molecule study of surface-bound PBIs: solvent-mediated environmental effects on molecular flexibility.

PubMed

Lee, Ji-Eun; Han, Ye Ri; Ham, Sujin; Jun, Chul-Ho; Kim, Dongho

2017-11-08

We have investigated the fundamental photophysical properties of surface-bound perylene bisimide (PBI) molecules in a solution-phase at the single-molecule level. By efficient immobilization of single PBIs on glass, we were able to simultaneously monitor fluorescence intensity trajectories, fluorescence lifetimes, and emission spectra of individual PBIs in organic and aqueous media using confocal microscopy. We showed that the fluorescence dynamics of single PBIs in the solution phase is highly dependent on their local and chemical environments. Furthermore, we visualized different spatial-fluctuations of surface-bound PBIs using defocused wide-field imaging. While PBIs show more steric flexibility in organic media, the flexible motion of PBI molecules in aqueous solution is relatively prohibited due to a cage effect by a hydrogen bonding network, which is previously unobserved. Our method opens up a new possibility to investigate the photophysical properties of multi-chromophoric systems in various solvents at the single-molecule level for developing optimal molecular devices such as water-proof devices.

Non-radiative decay paths in rhodamines: new theoretical insights.

PubMed

Savarese, Marika; Raucci, Umberto; Adamo, Carlo; Netti, Paolo A; Ciofini, Ilaria; Rega, Nadia

2014-10-14

We individuate a photoinduced electron transfer (PeT) as a quenching mechanism affecting rhodamine B photophysics in solvent. The PeT involves an electron transfer from the carboxylate group to the xanthene ring of rhodamine B. This is finely modulated by the subtle balance of coulombic and non-classical interactions between the carboxyphenyl and xanthene rings, also mediated by the solvent. We propose the use of an electronic density based index, the so called DCT index, as a new tool to assess and quantify the nature of the excited states involved in non-radiative decays near the region of their intersection. In the present case, this analysis allows us to gain insight on the interconversion process from the bright state to the dark state responsible for the quenching of rhodamine B fluorescence. Our findings encourage the use of density based indices to study the processes affecting excited state reactions that are characterized by a drastic change in the excitation nature, in order to rationalize the photophysical behavior of complex molecular systems.

Synthesis, crystal structure, photophysical properties and theoretical studies of a novel bis(phenylisoxazolyl) benzene derivative

NASA Astrophysics Data System (ADS)

de Brito, A. C. F.; Correa, R. S.; Pinto, A. A.; Matos, M. J. S.; Tenorio, J. C.; Taylor, J. G.; Cazati, T.

2018-07-01

Isoxazoles have well established biological activities but, have been underexplored as synthetic intermediates for applications in materials science. The aims of this work are to synthesis a novel isoxazole and analyze its structural and photophysical properties for application in electronic organic materials. The novel bis (phenylisoxazolyl) benzene compound was synthesized in four steps and characterized by NMR, high resolution mass spectrometry, differential thermal analysis, infrared spectroscopy, cyclic voltammetry, ultraviolet-visible spectroscopy, fluorescence spectroscopy, DFT and TDDFT calculations. The molecule presented optical absorption in the ultraviolet region (from 290 nm to 330 nm), with maximum absorption length centered at 306 nm. The molar extinction coefficients (ε), fluorescence emission spectra and quantum efficiencies in chloroform and dimethylformamide solution were determined. Cyclic voltammetry analysis was carried out for estimating the HOMO energy level and these properties make it desirable material for photovoltaic device applications. Finally, the excited-state properties of present compound were calculated by time-dependent density functional theory (TDDFT).

Origin of Light Induced Photophysical Effects in Organic Metal Halide Perovskites in the Presence of Oxygen.

PubMed

Anaya, Miguel; Galisteo-López, Juan F; Calvo, Mauricio Ernesto; Espinos, Juan P; Miguez, Hernan

2018-06-21

Herein we present a combined study of the evolution of both the photoluminescence and the surface chemical structure of organic metal halide perovskites as environmental oxygen pressure rises from ultra-high vacuum up to a few thousandths of an atmosphere. Analyzing the changes occurring at the semiconductor surface upon photo-excitation under controlled oxygen atmosphere in an X-ray photoelectron spectroscopy (XPS) chamber, we can rationalize the rich variety of photophysical phenomena observed and provide a plausible explanation for light-induced ion migration, one of the most conspicuous and debated concomitant effects detected during photoexcitation. We find direct evidence of the formation of a superficial layer of negatively charged oxygen species capable of repelling the halide anions away from the surface and towards the bulk. The reported photoluminescence (PL) transient dynamics, the partial recovery of the initial state when photoexcitation stops and the eventual degradation after intense exposure times can thus be rationalized.

Effect of TiO2 nanoparticles on some photophysical characteristics of ketocyanine dyes.

PubMed

Thipperudrappa, Javuku; Raghavendra, U P; Basanagouda, Mahantesha

2017-11-01

The effect of titanium dioxide (TiO 2 ) nanoparticles (NPs) on photophysical characteristics of 2,5-di[(E)-1-(4-dimethylaminophenyl) methylidine]-1-cyclopentanone (2,5-DMAPMC) and 2,5-di[(E)-1-(4-diethylaminophenyl)methylidine]-1-cyclopentanone (2,5-DEAPMC) ketocyanine dyes has been studied using absorption, steady-state and time-resolved fluorescence spectroscopy. The magnitudes of association constants determined based on modified absorption spectrum of dyes due to the presence of TiO 2 NPs indicate the interaction of TiO 2 NPs with dye molecules. The quenching of fluorescence intensity of dyes by TiO 2 NPs is observed and it follows linear Stern-Volmer (S-V) equation. The magnitude of quenching rate parameter suggests the involvement of static quenching mechanism. The involvement of electron transfer process in reducing fluorescence intensity of dyes has been discussed. Also, varying influence of TiO 2 NPs on two dyes is explained based on the presence of different alkyl substituent in two dyes. Copyright © 2017 John Wiley & Sons, Ltd.

Prolonged spontaneous emission and dephasing of localized excitons in air-bridged carbon nanotubes

NASA Astrophysics Data System (ADS)

Sarpkaya, Ibrahim; Zhang, Zhengyi; Walden-Newman, William; Wang, Xuesi; Hone, James; Wong, Chee W.; Strauf, Stefan

2013-07-01

The bright exciton emission of carbon nanotubes is appealing for optoelectronic devices and fundamental studies of light-matter interaction in one-dimensional nanostructures. However, to date, the photophysics of excitons in carbon nanotubes is largely affected by extrinsic effects. Here we perform time-resolved photoluminescence measurements over 14 orders of magnitude for ultra-clean carbon nanotubes bridging an air gap over pillar posts. Our measurements demonstrate a new regime of intrinsic exciton photophysics with prolonged spontaneous emission times up to T1=18 ns, about two orders of magnitude better than prior measurements and in agreement with values hypothesized by theorists about a decade ago. Furthermore, we establish for the first time exciton decoherence times of individual nanotubes in the time domain and find fourfold prolonged values up to T2=2.1 ps compared with ensemble measurements. These first observations motivate new discussions about the magnitude of the intrinsic dephasing mechanism while the prolonged exciton dynamics is promising for applications.

Blue light induced free radicals from riboflavin on E. coli DNA damage.

PubMed

Liang, Ji-Yuan; Yuann, Jeu-Ming P; Cheng, Chien-Wei; Jian, Hong-Lin; Lin, Chin-Chang; Chen, Liang-Yu

2013-02-05

The micronutrients in many cellular processes, riboflavin (vitamin B(2)), FMN, and FAD are photo-sensitive to UV and visible light to generate reactive oxygen species (ROS). The riboflavin photochemical treatment with UV light has been applied for the inactivation of microorganisms to serve as an effective and safe technology. Ultra-violet or high-intensity radiation is, however, considered as a highly risky practice. This study was working on the application of visible LED lights to riboflavin photochemical reactions to development an effective antimicrobial treatment. The photosensitization of bacterial genome with riboflavin was investigated in vitro and in vivo by light quality and irradiation dosage. The riboflavin photochemical treatment with blue LED light was proved to be able to inactivate E. coli by damaging nucleic acids with ROS generated. Riboflavin is capable of intercalating between the bases of bacterial DNA or RNA and absorbs lights in the visible regions. LED light illumination could be a more accessible and safe practice for riboflavin photochemical treatments to achieve hygienic requirements in vitro. Copyright © 2013 Elsevier B.V. All rights reserved.

Photochemical and Thermal Stability of Green and Blue Proteorhodopsins: Implications for Protein-Based Bioelectronic Devices

PubMed Central

Ranaghan, Matthew J.; Shima, Sumie; Ramos, Lavosier; Poulin, Daniel S.; Whited, Gregg; Rajasekaran, Sanguthevar; Stuart, Jeffery A.; Albert, Arlene D.; Birge, Robert R.

2010-01-01

The photochemical and thermal stability of the detergent solubilized blue- and green-absorbing proteorhodpsins, BPR and GPR respectively, are investigated to determine viability of these proteins for photonic device applications. Photochemical stability is studied by using pulsed laser excitation and differential uv-vis spectroscopy to assign the photocyclicity. GPR, with a cyclicity of 7×104 photocycles protein−1, is 4–5 times more stable than BPR (9×103 photocycles protein−1), but is less stable than native bacteriorhodopsin (9×105 photocycles protein−1) or the 4-keto-bacteriorhodopsin analog (1×105 photocycles protein−1). The thermal stabilities are assigned by using differential scanning calorimetry and thermal bleaching experiments. Both proteorhodopsins display excellent thermal stability, with melting temperatures above 85°C, and remain photochemically stable up to 75°C. The biological relevance of our results is also discussed. The lower cyclicity of BPR is found to be adequate for the long-term biological function of the host organism at ocean depths of 50 m or more. PMID:20964279

The chitosan - Porphyrazine hybrid materials and their photochemical properties.

PubMed

Chełminiak-Dudkiewicz, Dorota; Ziegler-Borowska, Marta; Stolarska, Magdalena; Sobotta, Lukasz; Falkowski, Michal; Mielcarek, Jadwiga; Goslinski, Tomasz; Kowalonek, Jolanta; Węgrzynowska-Drzymalska, Katarzyna; Kaczmarek, Halina

2018-04-01

Three magnesium sulfanyl porphyrazines differing in the size of peripheral substituents (3,5-dimethoxybenzylsulfanyl, (3,5-dimethoxybenzyloxy)benzylsulfanyl, 3,5-bis[(3,5-bis[(3,5-dimethoxybenzyloxy)benzyloxy]benzylsulfanyl) were exposed to visible and ultraviolet radiation (UV A + B + C) in order to determine their photochemical properties. The course of photochemical reactions in dimethylformamide solutions and the ability of the systems to generate singlet oxygen were studied by UV-Vis spectroscopy, which additionally gave information on aggregation processes. The porphyrazines were found to be stable upon visible light irradiation conditions, but when exposed to high energy UV radiation, the efficient photodegradation of these macrocycles was observed. Therefore, these three magnesium sulfanyl porphyrazines were incorporated into chitosan matrix. The obtained thin films of chitosan doped with porphyrazines were subjected to polychromatic UV-radiation and studied by spectroscopic methods (UV-Vis, FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Application of chitosan as a polymer matrix for porphyrazines was found to be successful method that effectively stopped the unwelcome degradation of macrocycles, thus worth considering for their photoprotection. In addition, the surface properties of the hybrid material were determined by contact angle measurements and calculation of surface free energy. Intermolecular interactions between these novel porphyrazines and chitosan were detected. The mechanism of photochemical reactions occurring in studied systems has been discussed. Copyright © 2018 Elsevier B.V. All rights reserved.

76 FR 72919 - Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants

Federal Register 2010, 2011, 2012, 2013, 2014

2011-11-28

... Science Assessment for Ozone and Related Photochemical Oxidants AGENCY: Environmental Protection Agency... Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants'' (EPA/600/R-10/076B... national ambient air quality standards (NAAQS) for ozone. DATES: The public comment period began on...

76 FR 60820 - Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants

Federal Register 2010, 2011, 2012, 2013, 2014

2011-09-30

... Science Assessment for Ozone and Related Photochemical Oxidants AGENCY: Environmental Protection Agency... Review Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants'' (EPA/600/R-10... standards (NAAQS) for ozone. EPA is releasing this draft document to seek review by the Clean Air Scientific...

76 FR 17121 - Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants

Federal Register 2010, 2011, 2012, 2013, 2014

2011-03-28

... Science Assessment for Ozone and Related Photochemical Oxidants AGENCY: Environmental Protection Agency... Draft Integrated Science Assessment for Ozone and Related Photochemical Oxidants'' (EPA/600/R-10/076A... ambient air quality standards (NAAQS) for ozone. DATES: The public comment period began on February 28...

Photochemical Dimerization of Dibenzylideneacetone: A Convenient Exercise in [2+2] Cycloaddition Using Chemical Ionization Mass Spectrometry

ERIC Educational Resources Information Center

Rao, G. Nageswara; Janardhana, Chelli; Ramanathan, V.; Rajesh, T.; Kumar, P. Harish

2006-01-01

Chemical reactions induced by light have been utilized for synthesizing highly strained, thermodynamically unstable compounds, which are inaccessible through non-photochemical methods. Photochemical cycloaddition reactions, especially those leading to the formation of four-membered rings, constitute a convenient route to compounds that are…

INTERACTIONS BETWEEN PHOTOCHEMICAL AND MICROBIAL DECOMPOSITION IN MODIFYING THE BIOLOGICAL AVAILABILITY AND OPTICAL PROPERTIES OF ESTUARINE DISSOLVED ORGANIC MATTER

EPA Science Inventory

Direct photodecomposition and photochemically-mediated bacterial degradation (via photochemical modification of otherwise refractory DOM into biologically labile forms) provide
important pathways for the loss of dissolved organic matter in coastal waters. Here we report
lab...

Photochemical Effects of Sunlight

PubMed Central

Daniels, Farrington

1972-01-01

The importance of sunlight in bringing about not only photosynthesis in plants, but also other photochemical effects, is reviewed. More effort should be devoted to photochemical storage of the sun's energy without the living plant. There is no theoretical reason to believe that such reactions are impossible. Ground rules for searching for suitable solar photochemical reactions are given, and a few attempts are described, but nothing successful has yet been found. Future possibilities are suggested. Photogalvanic cells which convert sunlight into electricity deserve further research. Eugene Rabinowitch has been an active pioneer in these fields. PMID:5037333

Photochemical effects of sunlight.

PubMed

Daniels, F

1972-07-01

The importance of sunlight in bringing about not only photosynthesis in plants, but also other photochemical effects, is reviewed. More effort should be devoted to photochemical storage of the sun's energy without the living plant. There is no theoretical reason to believe that such reactions are impossible. Ground rules for searching for suitable solar photochemical reactions are given, and a few attempts are described, but nothing successful has yet been found. Future possibilities are suggested. Photogalvanic cells which convert sunlight into electricity deserve further research. Eugene Rabinowitch has been an active pioneer in these fields.

Axi-symmetrical flow reactor for .sup.196 Hg photochemical enrichment

DOEpatents

Grossman, Mark W.

1991-01-01

The present invention is directed to an improved photochemical reactor useful for the isotopic enrichment of a predetermined isotope of mercury, especially, .sup.196 Hg. Specifically, two axi-symmetrical flow reactors were constructed according to the teachings of the present invention. These reactors improve the mixing of the reactants during the photochemical enrichment process, affording higher yields of the desired .sup.196 Hg product. Measurements of the variation of yield (Y) and enrichment factor (E) along the flow axis of these reactors indicates very substantial improvement in process uniformity compared to previously used photochemical reactor systems. In one preferred embodiment of the present invention, the photoreactor system was built such that the reactor chamber was removable from the system without disturbing the location of either the photochemical lamp or the filter employed therewith.

Molecular-beam Studies of Primary Photochemical Processes

DOE R&D Accomplishments Database

Lee, Y. T.

1982-12-01

Application of the method of molecular-beam photofragmentation translational spectroscopy to the investigation of primary photochemical processes of polyatomic molecules is described. Examples will be given to illustrate how information concerning the energetics, dynamics, and mechanism of dissociation processes can be obtained from the precise measurements of angular and velocity distributions of products in an experiment in which a well-defined beam of molecules is crossed with a laser.

Increased Sensitivity of HIV-1 p24 ELISA Using a Photochemical Signal Amplification System.

PubMed

Bystryak, Simon; Santockyte, Rasa

2015-10-01

In this study we describe a photochemical signal amplification method (PSAM) for increasing of the sensitivity of enzyme-linked immunosorbent assay (ELISA) for determination of HIV-1 p24 antigen. The photochemical signal amplification method is based on an autocatalytic photochemical reaction of a horseradish peroxidase (HRP) substrate, orthophenylenediamine (OPD). To compare the performance of PSAM-boosted ELISA with a conventional colorimetric ELISA for determination of HIV-1 p24 antigen we employed a PerkinElmer HIV-1 p24 ELISA kit, using conventional ELISA alongside ELISA + PSAM. In the present study, we show that PSAM technology allows one to increase the analytical sensitivity and dynamic range of a commercial HIV-1 p24 ELISA kit, with and without immune-complex disruption, by a factor of approximately 40-fold. ELISA + PSAM is compatible with commercially available microtiter plate readers, requires only an inexpensive illumination device, and the PSAM amplification step takes no longer than 15 min. This method can be used for both commercially available and in-house ELISA tests, and has the advantage of being considerably simpler and less costly than alternative signal amplification methods. This method can be used for both commercially available and in-house ELISA tests, and has the advantage of being considerably simpler and less costly than alternative signal amplification methods.

Photochemical reduction of UO(2)(2+) in the presence of alcohol studied by density functional theory calculations.

PubMed

Tsushima, Satoru

2009-06-01

A well-known photochemical process of U(VI)O(2)(2+) reduction to U(V)O(2)(+) in the presence of alcohols was studied by density functional theory (DFT) calculations. It was found that the first process which takes place is a photoexcitation of the ground-state UO(2)(2+) to the triplet excited state (*UO(2)(2+)) followed by a significant shortening of the *UO(2)(2+)-to-alcohol O(ax)-H distance. A charge transfer from *UO(2)(2+) to alcohol and hydrogen abstraction takes place in the following step. Consequently, U(VI)O(2)(2+) gets reduced to U(V)O(OH)(2+). The photochemical byproduct RCHOH acts further as a reducing agent toward UO(2)(2+) to yield UO(2)(+) and RCHO (aldehyde). Only a combination of these two reactions can explain a high quantum yield of this reaction. In the absence of alcohol, the lowest-lying triplet state exhibits a different character, and photoreduction is unlikely to take place via the same mechanism. The present results agree well with recent experimental finding [J. Am. Chem. Soc. 2006, 128, 14024] and supports the idea that the O(ax)-H linkage between UO(2)(2+) and the solvent molecule is the key to the photochemical reduction process.

Synthesis, photophysical analysis, and in vitro cytotoxicity assessment of the multifunctional (magnetic and luminescent) core@shell nanomaterial based on lanthanide-doped orthovanadates

NASA Astrophysics Data System (ADS)

Szczeszak, Agata; Ekner-Grzyb, Anna; Runowski, Marcin; Mrówczyńska, Lucyna; Grzyb, Tomasz; Lis, Stefan

2015-03-01

Rare earths orthovanadates (REVO4) doped with luminescent lanthanide ions (Ln3+) play an important role as promising light-emitting materials. Gadolinium orthovanadate exhibits strong absorption of ultraviolet radiation and as a matrix doped with Eu3+ ions is well known for its efficient and intense red emission, induced by energy transfer from the VO4 3- groups to Eu3+ ions. In the presented study, Fe3O4@SiO2@GdVO4:Eu3+ 5 % nanomaterial was investigated. The core@shell structures demonstrate attractive properties, such as higher thermal stability, enhanced water solubility, increased optical response, higher luminescence, longer decay times, and magnetic properties. Silica coating may protect nanocrystals from the surrounding environment. Therefore, such silica-covered nanoparticles (NPs) are successfully utilized in biomedical research. Multifunctional magnetic nanophosphors are very interesting due to their potential biomedical applications such as magnetic resonance imaging, hyperthermic treatment, and drug delivery. Therefore, the aim of our study was to investigate photophysical, chemical, and biological properties of multifunctional REVO4 doped with Ln3+. Moreover, the studied NPs did not affect erythrocyte sedimentation rate, cell membrane permeability, and morphology of human red blood cells.

A new twist in the photophysics of the GFP chromophore: a volume-conserving molecular torsion couple† †Electronic supplementary information (ESI) available: Synthetic methods and characterization; fluorescence up-conversion data; additional computational details; Cartesian coordinates of key structures; photochemical isomerization data; data for the anion of I. See DOI: 10.1039/c7sc04091a

PubMed Central

Conyard, Jamie; Heisler, Ismael A.; Chan, Yohan; Bulman Page, Philip C.

2018-01-01

The simple structure of the chromophore of the green fluorescent protein (GFP), a phenol and an imidazolone ring linked by a methyne bridge, supports an exceptionally diverse range of excited state phenomena. Here we describe experimentally and theoretically the photochemistry of a novel sterically crowded nonplanar derivative of the GFP chromophore. It undergoes an excited state isomerization reaction accompanied by an exceptionally fast (sub 100 fs) excited state decay. The decay dynamics are essentially independent of solvent polarity and viscosity. Excited state structural dynamics are probed by high level quantum chemical calculations revealing that the fast decay is due to a conical intersection characterized by a twist of the rings and pyramidalization of the methyne bridge carbon. The intersection can be accessed without a barrier from the pre-twisted Franck–Condon structure, and the lack of viscosity dependence is due to the fact that the rings twist in the same direction, giving rise to a volume-conserving decay coordinate. Moreover, the rotation of the phenyl, methyl and imidazolone groups is coupled in the sterically crowded structure, with the methyl group translating the rotation of one ring to the next. As a consequence, the excited state dynamics can be viewed as a torsional couple, where the absorbed photon energy leads to conversion of the out-of-plane orientation from one ring to the other in a volume conserving fashion. A similar modification of the range of methyne dyes may provide a new family of devices for molecular machines, specifically torsional couples. PMID:29675225

In Search of the Perfect Photocage: Structure-Reactivity Relationships in meso-Methyl BODIPY Photoremovable Protecting Groups.

PubMed

Slanina, Tomáš; Shrestha, Pradeep; Palao, Eduardo; Kand, Dnyaneshwar; Peterson, Julie A; Dutton, Andrew S; Rubinstein, Naama; Weinstain, Roy; Winter, Arthur H; Klán, Petr

2017-10-25

A detailed investigation of the photophysical parameters and photochemical reactivity of meso-methyl BODIPY photoremovable protecting groups was accomplished through systematic variation of the leaving group (LG) and core substituents as well as substitutions at boron. Efficiencies of the LG release were evaluated using both steady-state and transient absorption spectroscopies as well as computational analyses to identify the optimal structural features. We find that the quantum yields for photorelease with this photocage are highly sensitive to substituent effects. In particular, we find that the quantum yields of photorelease are improved with derivatives with higher intersystem crossing quantum yields, which can be promoted by core heavy atoms. Moreover, release quantum yields are dramatically improved by boron alkylation, whereas alkylation in the meso-methyl position has no effect. Better LGs are released considerably more efficiently than poorer LGs. We find that these substituent effects are additive, for example, a 2,6-diiodo-B-dimethyl BODIPY photocage features quantum yields of 28% for the mediocre LG acetate and a 95% quantum yield of release for chloride. The high chemical and quantum yields combined with the outstanding absorption properties of BODIPY dyes lead to photocages with uncaging cross sections over 10 000 M -1 cm -1 , values that surpass cross sections of related photocages absorbing visible light. These new photocages, which absorb strongly near the second harmonic of an Nd:YAG laser (532 nm), hold promise for manipulating and interrogating biological and material systems with the high spatiotemporal control provided by pulsed laser irradiation, while avoiding the phototoxicity problems encountered with many UV-absorbing photocages. More generally, the insights gained from this structure-reactivity relationship may aid in the development of new highly efficient photoreactions.

Zinc(II) mediated imine-enamine tautomerization as a new chemosensory protocol

NASA Astrophysics Data System (ADS)

Basa, Premnath

Zinc (II) and copper (II) are prime transition cations that are not only abundant in free state in the human body but also in bound form. They play a key role in enzymes, electron transport, and oxygen transport systems. Recently, these cations have gained interest because of their implications in Alzheimer's disease, Parkinson's disease, and other neurodegenerative disorders. Although numerous fluorescent chemosensors are currently available, less is known about their homeostasis or their etiological role in serious neurological disorders. Therefore, the current research is dedicated to developing novel chemosensors with excellent photophysical and photochemical properties and investigating their potential application for real-life problems. The dynamic nature of imines has been well utilized for the selective detection of zinc by blocking the E/Z isomerization process. However, other mechanistic pathways are available for imines; analyte-induced imine hydrolysis and metal-triggered tautomerization approaches are proving to be attractive sensory protocols. The current project is focused on understanding the basic principles that dictate Zn(II)-triggered tautomerization as a new "OFF-ON" type chemosensor. Synthesis of target compounds was achieved and confirmed through elemental analysis, 1H NMR and 13C NMR, ESI-MS, FTIR, and single-crystal XRD techniques. Zinc sensitivity and selectivity in the presence of 16 other transition, alkali, and alkaline earth cations was monitored by means of various spectroscopic and spectrometric techniques (fluorescence, UV-Vis absorbance, NMR and ESI-MS). The environmental parameters (solvents, pH) of zinc-induced fluorescence were also investigated and details will be discussed. A second project that describes Cu(II)-catalyzed imine hydrolysis via colorimetric and fluorescence change was also investigated.

P2X7 receptor as a novel drug delivery system to increase the entrance of hydrophilic drugs into cells during photodynamic therapy.

PubMed

Pacheco, Paulo Anastácio Furtado; Ferreira, Leonardo Braga Gomes; Mendonça, Leonardo; Ferreira, Dinarte Neto M; Salles, Juliana Pimenta; Faria, Robson Xavier; Teixeira, Pedro Celso Nogueira; Alves, Luiz Anastacio

2016-08-01

The second-generation photosensitizer methylene blue (MB) exhibits photochemical and photophysical properties suitable for photodynamic therapy (PDT)-based cancer treatment. However, the clinical application of MB is limited because of its high hydrophilicity, which hinders its penetration into tumor tissues. Therefore, new methods to improve the entry of MB into the cytoplasm of target cells are necessary. Because MB has a mass of 319 Da, transient pores on the plasma membrane, such as the pore induced by the P2X7 receptor (P2X7R) that allows the passage of molecules up to 900 Da, could be used. Using MTT viability assays, flow cytometry experiments, and fluorescence microscopy, we evaluated the toxicity and phototoxicity of MB and potentiation effects of ATP and MB on cell death processes in the J774 cell line (via a P2X7-associated pore). We observed that treatment with 5 μM MB for 15 min promoted the rate of entry of MB into the cytoplasm to 4.7 %. However, treatment with 5 μM MB and 1 mM ATP for the same amount of time increased this rate to 90.2 %. However, this effect was inhibited by pretreatment with a P2X7 antagonist. We used peritoneal macrophages and a cell line that does not express P2X7R as controls. These cells were more resistant to PDT with MB under the same experimental conditions. Taken together, these results suggest the use of the pore associated with P2X7R as a drug delivery system to increase the passage of hydrophilic drugs into cells that express this receptor, thus facilitating PDT.

Infrared Spectroscopy of Ammonia - Hydrocarbon Ices Relevant to Jupiter's Clouds

NASA Astrophysics Data System (ADS)

Engel, P. A.; Kalogerakis, K. S.

2005-12-01

Observational evidence and thermochemical models indicate an abundance of ammonia ice clouds in Jupiter's atmosphere. However, spectrally identifiable ammonia ice clouds are found covering less than 1% of Jupiter's atmosphere, notably in turbulent areas.1,2 This discrepancy highlights an important gap in our understanding of ammonia and its spectral signatures in Jupiter's atmosphere. Current literature suggests two possible explanations: coating by a hydrocarbon haze and/or photochemical processing ("tanning").2,3 We are performing laboratory experiments that investigate the above hypotheses. Thin films of ammonia ices are deposited in a cryogenic apparatus, coated with hydrocarbons, and characterized by infrared spectroscopy. The ice films can be irradiated by ultraviolet light. These spectroscopic measurements aim to identify the photophysical and chemical processes that control the optical properties of the ice mixtures and quantify their dependence on the identity of the coating, the temperature, and the ice composition. Our current results indicate a consistent suppression of the ammonia absorption feature at 3 μm with coverage by thin layers of hexane, cyclohexane, and benzene. Furthermore, strongest suppression is observed in the case of benzene, followed in magnitude by hexane and cyclohexane. Funding from the NSF Planetary Astronomy Program under grant AST-0206270 is gratefully acknowledged. The participation of Patricia A. Engel was made possible by the NSF Research Experiences for Undergraduates Program under grant PHY-0353745. 1. S. K. Atreya, A.-S. Wong, K. H. Baines, M. H. Wong, T. C. Owen, Planet. Space Science 53, 498 (2005). 2. K. H. Baines, R. W. Carlson, and L. W. Kamp, Icarus 159, 74 (2002). 3. A.-S. Wong, Y. L. Yung, and A. J. Friedson, Geophys. Res. Lett. 30, 1447 (2003).

Generalized trajectory surface-hopping method for internal conversion and intersystem crossing

NASA Astrophysics Data System (ADS)

Cui, Ganglong; Thiel, Walter

2014-09-01

Trajectory-based fewest-switches surface-hopping (FSSH) dynamics simulations have become a popular and reliable theoretical tool to simulate nonadiabatic photophysical and photochemical processes. Most available FSSH methods model internal conversion. We present a generalized trajectory surface-hopping (GTSH) method for simulating both internal conversion and intersystem crossing processes on an equal footing. We consider hops between adiabatic eigenstates of the non-relativistic electronic Hamiltonian (pure spin states), which is appropriate for sufficiently small spin-orbit coupling. This choice allows us to make maximum use of existing electronic structure programs and to minimize the changes to available implementations of the traditional FSSH method. The GTSH method is formulated within the quantum mechanics (QM)/molecular mechanics framework, but can of course also be applied at the pure QM level. The algorithm implemented in the GTSH code is specified step by step. As an initial GTSH application, we report simulations of the nonadiabatic processes in the lowest four electronic states (S0, S1, T1, and T2) of acrolein both in vacuo and in acetonitrile solution, in which the acrolein molecule is treated at the ab initio complete-active-space self-consistent-field level. These dynamics simulations provide detailed mechanistic insight by identifying and characterizing two nonadiabatic routes to the lowest triplet state, namely, direct S1 → T1 hopping as major pathway and sequential S1 → T2 → T1 hopping as minor pathway, with the T2 state acting as a relay state. They illustrate the potential of the GTSH approach to explore photoinduced processes in complex systems, in which intersystem crossing plays an important role.

Picosecond dynamics of photoexcited DNO-bound myoglobin probed by femtosecond vibrational spectroscopy.

PubMed

Lee, Taegon; Hwang, Sungu; Lim, Manho

2015-02-05

Like nitric oxide (NO), nitroxyl (HNO), a reduced form of NO, plays many biologically important roles including neurological function and vascular regulation. Although HNO is unstable in aqueous solution, it is exceptionally stable on binding to ferrous myoglobin (Mb) to form MbHNO. Various experimental and theoretical investigations has been carried out to unveil the structure of the active site and binding characteristics of MbHNO that can explain its functioning mechanism and the origin of its unusual stability. However, the binding dynamics of HNO to Mb, as well as the photochemical and photophysical processes associated with binding, have not been fully established. Herein, femtosecond vibrational spectroscopy was used to probe the photoexcitation dynamics of excited MbDNO in D2O solution at 294 K with a 575 nm pulse. Time-resolved spectra were described by three vibrational bands near 1380 cm(-1), in the expected N-O stretching (νN-O) mode of MbDNO, and all three bands showed instantaneous bleach that decays on a picosecond time scale. The three bands were assigned based on isotope shifts upon (15)N substitution and ab initio calculation of the vibrational frequency on a DNO-bound model heme. These three bands likely arise from Fermi interactions between the strong νN-O mode and the weak overtone and combination modes of the N atom-related modes. The immediate appearance of the bleach in these bands and the picosecond decay of the bleach indicate that most of the photoexcited MbDNO undergoes picosecond geminate rebinding (GR) of DNO to Mb subsequent to its immediate deligation. Ultrafast and efficient GR of DNO likely arises from the bonding structure of the ligand and high reactivity between DNO and Mb.

Near-field photochemical and radiation-induced chemical fabrication of nanopatterns of a self-assembled silane monolayer

PubMed Central

Hentschel, Carsten; Fontein, Florian; Stegemann, Linda; Hoeppener, Christiane; Fuchs, Harald; Hoeppener, Stefanie

2014-01-01

Summary A general concept for parallel near-field photochemical and radiation-induced chemical processes for the fabrication of nanopatterns of a self-assembled monolayer (SAM) of (3-aminopropyl)triethoxysilane (APTES) is explored with three different processes: 1) a near-field photochemical process by photochemical bleaching of a monomolecular layer of dye molecules chemically bound to an APTES SAM, 2) a chemical process induced by oxygen plasma etching as well as 3) a combined near-field UV-photochemical and ozone-induced chemical process, which is applied directly to an APTES SAM. All approaches employ a sandwich configuration of the surface-supported SAM, and a lithographic mask in form of gold nanostructures fabricated through colloidal sphere lithography (CL), which is either exposed to visible light, oxygen plasma or an UV–ozone atmosphere. The gold mask has the function to inhibit the photochemical reactions by highly localized near-field interactions between metal mask and SAM and to inhibit the radiation-induced chemical reactions by casting a highly localized shadow. The removal of the gold mask reveals the SAM nanopattern. PMID:25247126

Electro Optical Properties of Copolymer Blends: Lasing, Electroluminescence and Photophysics

DTIC Science & Technology

2006-04-15

conjugated main chain structures with high photoluminescent and electroluminescent quantum yields. The structures incorporated fluorene containing moieties...The systems studied focused on novel conjugated main chain structures with high photoluminescent and electroluminescent quantum yields. The structures...the quantum efficient fluorine group. The properties of segmented copolymers that incorporate fluorenes were compared to the homo-PPV type systems

A saponification-triggered gelation of ester-based Zn(II) complex through conformational transformations.

PubMed

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

2014-09-11

Novel saponification-triggered gelation in an ester-based bis-salen Zn(II) complex (1) is described. Strategic structural modifications induced by NaOH in 1 tune the dipolar-/π-interactions leading to J-aggregation and the creation of an inorganic gel material (IGM), which has been established by photophysical, DFT and rheological studies.

Chloroplast Response to Low Leaf Water Potentials

PubMed Central

Boyer, J. S.; Potter, J. R.

1973-01-01

The effect of decreases in turgor on chloroplast activity was studied by measuring the photochemical activity of intact sunflower (Helianthus annuus L. cv. Russian Mammoth) leaves having low water potentials. Leaf turgor, calculated from leaf water potential and osmotic potential, was found to be affected by the dilution of cell contents by water in the cell walls, when osmotic potentials were measured with a thermocouple psychrometer. After the correction of measurements of leaf osmotic potential, both the thermocouple psychrometer and a pressure chamber indicated that turgor became zero in sunflower leaves at leaf water potentials of −10 bars. Since most of the loss in photochemical activity occurred at water potentials below −10 bars, it was concluded that turgor had little effect on the photochemical activity of the leaves. PMID:16658486

Chloroplast response to low leaf water potentials: I. Role of turgor.

PubMed

Boyer, J S; Potter, J R

1973-06-01

The effect of decreases in turgor on chloroplast activity was studied by measuring the photochemical activity of intact sunflower (Helianthus annuus L. cv. Russian Mammoth) leaves having low water potentials. Leaf turgor, calculated from leaf water potential and osmotic potential, was found to be affected by the dilution of cell contents by water in the cell walls, when osmotic potentials were measured with a thermocouple psychrometer. After the correction of measurements of leaf osmotic potential, both the thermocouple psychrometer and a pressure chamber indicated that turgor became zero in sunflower leaves at leaf water potentials of -10 bars. Since most of the loss in photochemical activity occurred at water potentials below -10 bars, it was concluded that turgor had little effect on the photochemical activity of the leaves.

The photochemical alkylation and reduction of heteroarenes.

PubMed

McCallum, T; Pitre, S P; Morin, M; Scaiano, J C; Barriault, L

2017-11-01

The functionalization of heteroarenes has been integral to the structural diversification of medicinally active molecules such as quinolines, pyridines, and phenanthridines. Electron-deficient heteroarenes are electronically compatible to react with relatively nucleophilic free radicals such as hydroxyalkyl. However, the radical functionalization of such heteroarenes has been marked by the use of transition-metal catalyzed processes that require initiators and stoichiometric oxidants. Herein, we describe the photochemical alkylation of quinolines, pyridines and phenanthridines, where through direct excitation of the protonated heterocycle, alcohols and ethers, such as methanol and THF, can serve as alkylating agents. We also report the discovery of a photochemical reduction of these heteroarenes using only iPrOH and HCl. Mechanistic studies to elucidate the underlying mechanism of these transformations, and preliminary results on catalytic methylations are also reported.

A renewable amine for photochemical reduction of CO(2).

PubMed

Richardson, Robert D; Holland, Edward J; Carpenter, Barry K

2011-04-01

Photochemical reduction of CO₂ (to produce formic acid) can be seen both as a method to produce a transportable hydrogen-based fuel and also to reduce levels of CO₂ in the atmosphere. However, an often overlooked necessity for photochemical CO₂ reduction is the need for a sacrificial electron donor, usually a tertiary amine. Here, we describe a new strategy for coupling the photochemical reduction of CO₂ to photochemical water splitting, and illustrate this with a prototype example. Instead of seeking to eliminate the use of an external reducing agent altogether, our alternative strategy makes the reducing agent recyclable. This has two potential advantages over the direct coupling of CO₂ reduction and water oxidation. First, it allows the two redox reactions to be carried out with existing chemistry, and second, it permits these reactions to be conducted under mutually incompatible conditions.

Axi-symmetrical flow reactor for [sup 196]Hg photochemical enrichment

DOEpatents

Grossman, M.W.

1991-04-30

The present invention is directed to an improved photochemical reactor useful for the isotopic enrichment of a predetermined isotope of mercury, especially, [sup 196]Hg. Specifically, two axi-symmetrical flow reactors were constructed according to the teachings of the present invention. These reactors improve the mixing of the reactants during the photochemical enrichment process, affording higher yields of the desired [sup 196]Hg product. Measurements of the variation of yield (Y) and enrichment factor (E) along the flow axis of these reactors indicates very substantial improvement in process uniformity compared to previously used photochemical reactor systems. In one preferred embodiment of the present invention, the photoreactor system was built such that the reactor chamber was removable from the system without disturbing the location of either the photochemical lamp or the filter employed therewith. 10 figures.

Structural and photophysical considerations of singlet fission organic thin films for solar photochemistry

NASA Astrophysics Data System (ADS)

Ryerson, Joseph L.

Singlet fission (SF) is a multichromophore charge multiplication process in organic systems in which a singlet exciton shares its energy with a neighboring chromophore, thus generating two triplet excitons from one photon. SF chromophores can boost photocurrent in solar cells, raising the maximum theoretical power conversion efficiency of a single-junction solar cell from ˜33% to ˜45. Thin film (TF) preparation techniques, steady-state and time-resolved spectroscopic methods, and numerous advanced calculations were used to study the three systems presented here, all of which exhibit polymorphism. TFs of 1,3-diphenylisobenzofuran (1), were prepared and two polymorphs, alpha1 and beta-1, were discovered and characterized. alpha-1films exhibit phiTnear 200% and low phiF, whereas the dominant photophysical processes in the beta-1 polymorph are prompt and excimer emissions, with phi T around 10%. Absorption fitting revealed that the S1 state of beta-1 is lower than alpha-1, and therefore SF and the correlated triplet 1(TT) is energetically inaccessible to beta-1. The SF mechanism in TFs of each polymorph is outlined in great detail. Polymorphism in tetracene (Tc), a near 200% phiT SF material, has been previously documented, although morphology considerations have been neglected. While crystallite size has been shown to affect dynamics, the two Tc polymorphs, I and II, have not been analyzed in a thorough comparison of dynamics and photophysics. Tc II films show SF rates that are independent of crystallite size and SF occurs more rapidly than in Tc I. The slower Tc I SF rates are highly dependent on grain size. Coupling calculations suggested that Tc I should be faster, but these calculations are limited, and more sophisticated, multimolecule calculations are needed to support experimental results. Two extremely stable indigo derivatives, Cibalackrot (2) and a tert-butylated derivative(3) were structurally and photophysically characterized in solution and in TFs. Two crystalline polymorphs ( 2alpha, 2beta) and an amorphous phase (2a), as well as a crystalline (3alpha) and amorphous (3a) phase of 3 were deposited by thermal evaporation. phiT values of less than 25% were observed for all morphologies, except in 2beta(phi T= 50%). Excimer formation dominates relaxation pathways in TFs of 2 and 3.

Solvent and substituent effects on the photochemistry of norbornadiene-diarylacetylene Pauson-Khand adducts.

PubMed

Ji, Yining; Verdaguer, Xavier; Riera, Antoni

2011-03-28

The photochemistry of Pauson-Khand cycloadducts of norbornadiene with a series of bis-aryl alkynes has been studied. Two types of photochemical transformation take place: photorearrangement to tricyclic ketones or photochemical 6π electrocyclization. High selectivity levels have been attained for each pathway, controlled by the polarity of the solvent, irradiation wavelength, and presence (or absence) of oxygen. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Simulation of photoreactive transients and of photochemical transformation of organic pollutants in sunlit boreal lakes across 14 degrees of latitude: A photochemical mapping of Sweden.

PubMed

Koehler, Birgit; Barsotti, Francesco; Minella, Marco; Landelius, Tomas; Minero, Claudio; Tranvik, Lars J; Vione, Davide

2018-02-01

Lake water constituents, such as chromophoric dissolved organic matter (CDOM) and nitrate, absorb sunlight which induces an array of photochemical reactions. Although these reactions are a substantial driver of pollutant degradation in lakes they are insufficiently understood, in particular on large scales. Here, we provide for the first time comprehensive photochemical maps covering a large geographic region. Using photochemical kinetics modeling for 1048 lakes across Sweden we simulated the steady-state concentrations of four photoreactive transient species, which are continuously produced and consumed in sunlit lake waters. We then simulated the transient-induced photochemical transformation of organic pollutants, to gain insight into the relevance of the different photoreaction pathways. We found that boreal lakes were often unfavorable environments for photoreactions mediated by hydroxyl radicals (OH) and carbonate radical anions (CO 3 - ), while photoreactions mediated by CDOM triplet states ( 3 CDOM*) and, to a lesser extent, singlet oxygen ( 1 O 2 ) were the most prevalent. These conditions promote the photodegradation of phenols, which are used as plastic, medical drug and herbicide precursors. When CDOM concentrations increase, as is currently commonly the case in boreal areas such as Sweden, 3 CDOM* will also increase, promoting its importance in photochemical pathways even more. Copyright © 2017 Elsevier Ltd. All rights reserved.

Self-assembled nanostructures of linear arylacetylenes and their aza-substituted analogues

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

Xu, Jia-Ju; Department of Physics and Materials Science and Centre of Super Diamond and Advanced Films; Yang, Xiong-Bo

2016-06-15

A series of linear phenylene ethynylene molecules have been synthesized, and aza-substitution has been used as a strategy to fine-tune the properties of the molecules. All the compounds exhibited pure blue emission both in solution and solid state, and fluorescence quantum yields as high as 0.66, 0.63 and 0.82 were found in chloroform solutions. The well-defined nanostructures such as quasi-cubes, cubes and rods were fabricated by self-assembly method from these compounds. The photophysical properties and aggregation behavior of self-assembled structures were analyzed in detail. The morphology as well as photophysical properties of these nanostructures have been tuned with selective requirements.

Ultrafast Extreme Ultraviolet Spectroscopy of Methylammonium Lead Iodide Perovskite for Carrier Specific Photophysics

NASA Astrophysics Data System (ADS)

Verkamp, Max A.; Lin, Ming-Fu; Ryland, Elizabeth S.; Benke, Kristin; Vura-Weis, Josh

2017-06-01

Methyl ammonium lead iodide (perovskite) is a leading candidate for next-generation solar cell devices. However, the fundamental photophysics responsible for its strong photovoltaic qualities are not fully understood. Ultrafast extreme ultraviolet (XUV) spectroscopy was used to investigate relaxation dynamics in perovskite with carrier specific signals arising from transitions from the common inner-shell level (I 4d) to the valence and conduction bands. Ultrashort (30 fs) pulses of XUV radiation in a broad spectrum (40-70 eV) were obtained using high-harmonic generation in a tabletop instrument. Transient absorption measurements with visible pump and XUV probe directly observed the dynamics of charge carriers after above-band and band-edge excitation.

UV-induced photochemical heterogeneity of dissolved and attached organic matter associated with cyanobacterial blooms in a eutrophic freshwater lake.

PubMed

Xu, Huacheng; Jiang, Helong

2013-11-01

Cyanobacterial blooms represent a significant ecological and human health problem worldwide. In aquatic environments, cyanobacterial blooms are actually surrounded by dissolved organic matter (DOM) and attached organic matter (AOM) that bind with algal cells. In this study, DOM and AOM fractionated from blooming cyanobacteria in a eutrophic freshwater lake (Lake Taihu, China) were irradiated with a polychromatic UV lamp, and the photochemical heterogeneity was investigated using fluorescence excitation-emission matrix (EEM)-parallel factor (PARAFAC) analysis and synchronous fluorescence (SF)-two dimensional correlation spectroscopy (2DCOS). It was shown that a 6-day UV irradiation caused more pronounced mineralization for DOM than AOM (59.7% vs. 41.9%). The EEM-PARAFAC analysis identified one tyrosine-, one humic-, and two tryptophan-like components in both DOM and AOM, and high component photodegradation rates were observed for DOM versus AOM (k > 0.554 vs. <0.519). Moreover, SF-2DCOS found that the photodegradation of organic matters followed the sequence of tyrosine-like > humic-like > tryptophan-like substances. Humic-like substances promoted the indirect photochemical reactions, and were responsible for the higher photochemical rate for DOM. The lower photodegradation of AOM benefited the integrality of cells in cyanobacterial blooms against the negative impact of UV irradiation. Therefore, the photochemical behavior of organic matter was related to the adaptation of enhanced-duration cyanobacterial blooms in aquatic environments. Copyright © 2013 Elsevier Ltd. All rights reserved.

Poly(ferulic acid-co-tyrosine): Effect of the Regiochemistry on the Photophysical and Physical Properties en Route to Biomedical Applications

PubMed Central

2015-01-01

The photophysical and mechanical properties of novel poly(carbonate-amide)s derived from two biorenewable resources, ferulic acid (FA) and l-tyrosine ethyl ester, were evaluated in detail. From these two bio-based precursors, a series of four monomers were generated (having amide and/or carbonate coupling units with remaining functionalities to allow for carbonate formation) and transformed to a series of four poly(carbonate-amide)s. The simplest monomer, which was biphenolic and was obtained in a single amidation synthetic step, displayed bright, visible fluorescence that was twice brighter than FA. Multidimensional fluorescence spectroscopy of the polymers in solution highlighted the strong influence that regioselectivity and the degree of polymerization have on their photophysical properties. The regiochemistry of the system had little effect on the wettability, surface free energy, and Young’s modulus (ca. 2.5 GPa) in the solid state. Confocal imaging of solvent-cast films of each polymer revealed microscopically flat surfaces with fluorescent emission deep into the visible region. Fortuitously, one of the two regiorandom polymers (obtainable from the biphenolic monomer in only an overall two synthetic steps from FA and l-tyrosine ethyl ester) displayed the most promising fluorescent properties both in the solid state and in solution, allowing for the possibility of translating this system as a self-reporting or imaging agent in future applications. To further evaluate the potential of this polymer as a biodegradable material, hydrolytic degradation studies at different pH values and temperatures were investigated. Additionally, the antioxidant properties of the degradation products of this polymer were compared with its biphenolic monomer and FA. PMID:25364040

Photochemically Switching Diamidocarbene Spin States Leads to Reversible Büchner Ring Expansions.

PubMed

Perera, Tharushi A; Reinheimer, Eric W; Hudnall, Todd W

2017-10-18

The discovery of thermal and photochemical control by Woodward and Hoffmann revolutionized how we understand chemical reactivity. Similarly, we now describe the first example of a carbene that exhibits differing thermal and photochemical reactivity. When a singlet ground-state N,N'-diamidocarbene 1 was photolyzed at 380 nm, excitation to a triplet state was observed. The triplet-state electronic structure was characteristic of the expected biradical σ 1 p π 1 spin configuration according to a combination of spectroscopic and computational methods. Surprisingly, the triplet state of 1 was found to engage a series of arenes in thermally reversible Büchner ring expansion reactions, marking the first examples where both cyclopropanation and ring expansion of arenes were rendered reversible. Not only are these photochemical reactions different from the known thermal chemistry of 1, but the reversibility enabled us to perform the first examples of photochemically induced arene exchange/expansion reactions at a single carbon center.

Method of making gold thiolate and photochemically functionalized microcantilevers

DOEpatents

Boiadjiev, Vassil I [Knoxville, TN; Brown, Gilbert M [Knoxville, TN; Pinnaduwage, Lal A [Knoxville, TN; Thundat, Thomas G [Knoxville, TN; Bonnesen, Peter V [Knoxville, TN; Goretzki, Gudrun [Nottingham, GB

2009-08-25

Highly sensitive sensor platforms for the detection of specific reagents, such as chromate, gasoline and biological species, using microcantilevers and other microelectromechanical systems (MEMS) whose surfaces have been modified with photochemically attached organic monolayers, such as self-assembled monolayers (SAM), or gold-thiol surface linkage are taught. The microcantilever sensors use photochemical hydrosilylation to modify silicon surfaces and gold-thiol chemistry to modify metallic surfaces thereby enabling individual microcantilevers in multicantilever array chips to be modified separately. Terminal vinyl substituted hydrocarbons with a variety of molecular recognition sites can be attached to the surface of silicon via the photochemical hydrosilylation process. By focusing the activating UV light sequentially on selected silicon or silicon nitride hydrogen terminated surfaces and soaking or spotting selected metallic surfaces with organic thiols, sulfides, or disulfides, the microcantilevers are functionalized. The device and photochemical method are intended to be integrated into systems for detecting specific agents including chromate groundwater contamination, gasoline, and biological species.

Investigation of the photochemical changes of chlorogenic acids induced by ultraviolet light in model systems and in agricultural practice with Stevia rebaudiana cultivation as an example.

PubMed

Karaköse, Hande; Jaiswal, Rakesh; Deshpande, Sagar; Kuhnert, Nikolai

2015-04-08

Mono- and diacyl chlorogenic acids undergo photochemical trans-cis isomerization under ultraviolet (UV) irradiation. The photochemical equilibrium composition was established for eight selected derivatives. In contrast to all other dicaffeoylquinic acid derivatives, cynarin (1,3-dicaffeoylquinic acid) undergoes a [2 + 2] photochemical cycloaddition reaction, constituting a first example of Schmidt's law in a natural product family. The relevance of photochemical isomerization in agricultural practice was investigated using 120 samples of Stevia rebaudiana leave samples grown under defined cultivation conditions. Ratios of cis to trans chlorogenic acids were determined in leaf samples and correlated with climatic and harvesting conditions. The data indicate a clear correlation between the formation of cis-caffeoyl derivatives and sunshine hours prior to harvesting and illustrate the relevance of UV exposure to plant material affecting its phytochemical composition.

Photochemical degradation of the carbapenem antibiotics imipenem and meropenem in aqueous solutions under solar radiation.

PubMed

Reina, Alejandro Cabrera; Martínez-Piernas, Ana B; Bertakis, Yannis; Brebou, Christina; Xekoukoulotakis, Nikolaos P; Agüera, Ana; Sánchez Pérez, José Antonio

2018-01-01

This paper deals with the photochemical fate of two representative carbapenem antibiotics, namely imipenem and meropenem, in aqueous solutions under solar radiation. The analytical method employed for the determination of the target compounds in various aqueous matrices, such as ultrapure water, municipal wastewater treatment plant effluents, and river water, at environmentally relevant concentrations, was liquid chromatography coupled with hybrid triple quadrupole-linear ion trap-mass spectrometry. The absorption spectra of both compounds were measured in aqueous solutions at pH values from 6 to 8, and both compounds showed a rather strong absorption band centered at about 300 nm, while their molar absorption coefficient was in the order from 9 × 10 3 -10 4  L mol -1  cm -1 . The kinetics of the photochemical degradation of the target compounds was studied in aqueous solutions under natural solar radiation in a solar reactor with compound parabolic collectors. It was found that the photochemical degradation of both compounds at environmentally relevant concentrations follows first order kinetics and the quantum yield was in the order of 10 -3  mol einsten -1 . Several parameters were studied, such as solution pH, the presence of nitrate ions and humic acids, and the effect of water matrix. In all cases, it was found that the presence of various organic and inorganic constituents in the aqueous matrices do not contribute significantly, either positively or negatively, to the photochemical degradation of both compounds under natural solar radiation. In a final set of photolysis experiments, the effect of the level of irradiance was studied under simulated solar radiation and it was found that the quantum yield for the direct photodegradation of both compounds remained practically constant by changing the incident solar irradiance from 28 to 50 W m -2 . Copyright © 2017 Elsevier Ltd. All rights reserved.

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.

Water-Soluble 2-Hydroxyisophthalamides for Sensitization of Lanthanide Luminescence

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

Samuel, Amanda P. S.; Moore, Evan G.; Melchior, Marco

2008-02-20

A series of octadentate ligands featuring the 2-hydroxyisophthalamide (IAM) antenna chromophore (to sensitize Tb(III) and Eu(III) luminescence) has been prepared and characterized. The length of the alkyl amine scaffold that links the four IAM moieties has been varied in order to investigate the effect of the ligand backbone on the stability and photophysical properties of the Ln(III) complexes. The amine backbones utilized in this study are N,N,N{prime},N{prime}-tetrakis-(2-aminoethyl)-ethane-1,2-diamine [H(2,2)-], N,N,N{prime},N{prime}-tetrakis-(2-aminoethyl)-propane-1,3-diamine [H(3,2)-] and N,N,N{prime},N{prime}-tetrakis-(2-aminoethyl)-butane-1,4-diamine [H(4,2)-]. These ligands also incorporate methoxyethylene [MOE] groups on each of the IAM chromophores to increase their water solubility. The aqueous ligand protonation constants and Tb(III) and Eu(III)more » formation constants were determined from solution thermodynamic studies. The resulting values indicate that at physiological pH, the Eu(III) and Tb(III) complexes of H(2,2)-IAM-MOE and H(4,2)-IAM-MOE are sufficiently stable to prevent dissociation at nanomolar concentrations. The photophysical measurements for the Tb(III) complexes gave overall quantum yield values of 0.56, 0.39, and 0.52 respectively for the complexes with H(2,2)-IAM-MOE, H(3,2)-IAM-MOE and H(4,2)-IAM-MOE, while the corresponding Eu(III) complexes displayed significantly weaker luminescence, with quantum yield values of 0.0014, 0.0015, and 0.0058, respectively. Analysis of the steady state Eu(III) emission spectra provides insight into the solution symmetries of the complexes. The combined solubility, stability and photophysical performance of the Tb(III) complexes in particular make them well suited to serve as the luminescent reporter group in high sensitivity time-resolved fluoroimmunoassays.« less

Does infrared or ultraviolet light damage the lens?

PubMed Central

Söderberg, P G; Talebizadeh, N; Yu, Z; Galichanin, K

2016-01-01

In daylight, the human eye is exposed to long wavelength ultraviolet radiation (UVR), visible radiation and short wavelength infrared radiation (IRR). Almost all the UVR and a fraction of the IRR waveband, respectively, left over after attenuation in the cornea, is absorbed in the lens. The time delay between exposure and onset of biological response in the lens varies from immediate-to-short-to-late. After exposure to sunlight or artificial sources, generating irradiances of the same order of magnitude or slightly higher, biological damage may occur photochemically or thermally. Epidemiological studies suggest a dose-dependent association between short wavelength UVR and cortical cataract. Experimental data infer that repeated daily in vivo exposures to short wavelength UVR generate photochemically induced damage in the lens, and that short delay onset cataract after UVR exposure is photochemically induced. Epidemiology suggests that daily high-intensity short wavelength IRR exposure of workers, is associated with a higher prevalence of age-related cataract. It cannot be excluded that this effect is owing to a thermally induced higher denaturation rate. Recent experimental data rule out a photochemical effect of 1090 nm in the lens but other wavelengths in the near IRR should be investigated. PMID:26768915

Photochemical studies on aromatic γ,δ-epoxy ketones: efficient synthesis of benzocyclobutanones and indanones.

PubMed

Shao, Yutian; Yang, Chao; Gui, Weijun; Liu, Yang; Xia, Wujiong

2012-04-11

Irradiation of terminal aromatic γ,δ-epoxy ketones with a 450 W UV lamp led to Norrish type II cyclization/semi-pinacol rearrangement cascade reaction which formed the benzocyclobutanones containing a full-carbon quaternary center, whereas irradiation of substituted aromatic γ,δ-epoxy ketones led to the indanones through a photochemical epoxy rearrangement and 1,5-biradicals cyclization tandem reaction. This journal is © The Royal Society of Chemistry 2012

Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies: Evaluation Number 18

NASA Technical Reports Server (NTRS)

Burkholder, J. B.; Sander, S. P.; Abbatt, J. P. D.; Barker, J. R.; Huie, R. E.; Kolb, C. E.; Kurylo, M. J.; Orkin, V. L.; Wilmouth, D. M.; Wine, P. H.

2015-01-01

This is the eighteenth in a series of evaluated sets of rate constants, photochemical cross sections, heterogeneous parameters, and thermochemical parameters compiled by the NASA Panel for Data Evaluation. The data are used primarily to model stratospheric and upper tropospheric processes, with particular emphasis on the ozone layer and its possible perturbation by anthropogenic and natural phenomena. The evaluation is available in electronic form from the following Internet URL: http://jpldataeval.jpl.nasa.gov/

Quantum Mechanics/Molecular Mechanics Free Energy Maps and Nonadiabatic Simulations for a Photochemical Reaction in DNA: Cyclobutane Thymine Dimer.

PubMed

Mendieta-Moreno, Jesús I; Trabada, Daniel G; Mendieta, Jesús; Lewis, James P; Gómez-Puertas, Paulino; Ortega, José

2016-11-03

The absorption of ultraviolet radiation by DNA may result in harmful genetic lesions that affect DNA replication and transcription, ultimately causing mutations, cancer, and/or cell death. We analyze the most abundant photochemical reaction in DNA, the cyclobutane thymine dimer, using hybrid quantum mechanics/molecular mechanics (QM/MM) techniques and QM/MM nonadiabatic molecular dynamics. We find that, due to its double helix structure, DNA presents a free energy barrier between nonreactive and reactive conformations leading to the photolesion. Moreover, our nonadiabatic simulations show that most of the photoexcited reactive conformations return to standard B-DNA conformations after an ultrafast nonradiative decay to the ground state. This work highlights the importance of dynamical effects (free energy, excited-state dynamics) for the study of photochemical reactions in biological systems.

Status and summary of laser energy conversion. [for space power transmission systems

NASA Technical Reports Server (NTRS)

Lee, G.

1978-01-01

This paper presents a survey of the status of laser energy converters. Since the inception of these devices in the early 1970's, significant advances have been made in understanding the basic conversion processes. Numerous theoretical and experimental studies have indicated that laser energy can be converted at wavelengths from the ultraviolet to the far-infrared. These converters can be classified into five general categories: photovoltaics, heat engines, thermoelectronic, optical diode, and photochemical. The conversion can be directly into electricity (such as the photovoltaic, thermoelectronic, and optical diode) or it can go through an intermediate stage of conversion to mechanical energy, as in the heat engines. The photochemical converters result in storable energy such as hydrogen. Projected conversion efficiencies range from about 30% for the photochemical to nearly 75% for the heat engines.

Atmospheric Production of Perchlorate on Earth and Mars

NASA Astrophysics Data System (ADS)

Claire, M.; Catling, D. C.; Zahnle, K. J.

2009-12-01

Natural production and preservation of perchlorate on Earth occurs only in arid environments. Isotopic evidence suggests a strong role for atmospheric oxidation of chlorine species via pathways including ozone or its photochemical derivatives. As the Martian atmosphere is both oxidizing and drier than the driest places on Earth, we propose an atmospheric origin for the Martian perchlorates measured by NASA's Phoenix Lander. A variety of hypothetical formation pathways can be proposed including atmospheric photochemical reactions, electrostatic discharge, and gas-solid reactions. Here, we investigate gas phase formation pathways using a 1-D photochemical model (Catling et al. 2009, accepted by JGR). Because perchlorate-rich deposits in the Atacama desert are closest in abundance to perchlorate measured at NASA's Phoenix Lander site, we start with a study of the means to produce Atacama perchlorate. We found that perchlorate can be produced in sufficient quantities to explain the abundance of perchlorate in the Atacama from a proposed gas phase oxidation of chlorine volatiles to perchloric acid. These results are sensitive to estimated reaction rates for ClO3 species. The feasibility of gas phase production for the Atacama provides justification for further investigations of gas phase photochemistry as a possible source for Martian perchlorate. In addition to the Atacama results, we will present a preliminary study incorporating chlorine chemistry into an existing Martian photochemical model (Zahnle et al. JGR 2008).

Photochemically induced focal cochlear lesions in the guinea pig: II. A transmission electron microscope study.

PubMed

Miyashita, H; Iwasaki, S; Hoshino, T

1998-05-15

Photochemically induced focal lesions in guinea pig cochleas were studied by light microscopy and transmission electron microscopy. The lesions were induced in the second cochlear turns of 35 adult guinea pigs by illumination for 10 minutes with a focused green light immediately after a rose bengal solution was injected into the jugular vein. The cochlear lateral wall and organ of Corti were examined 5, 10, 20, 30, and 90 minutes, 12 and 24 hours, and 3, 7, and 30 days after the procedure. Aggregations of platelets and red blood cells were found in strial capillaries at 5 minutes after illumination. After 30 minutes, marginal cell surfaces protruded into the endolymphatic space; surface membranes were ruptured and the cytoplasm was expelled into the space. In outer hair cells, disruption of the cellular membrane was found near the cuticular plate 12 hours after the procedure. All cellular elements of the lateral wall and organ of Corti were markedly degenerated in the 30-day specimens. Histological changes found in the stria vascularis were consistent with cell damage caused by active oxygen species. It is likely that the stria vascularis is more sensitive to the photochemical reaction than other parts of the cochlea. Cell damage in other parts of the cochlea seemed to have been caused by local microvascular ischemia in addition to the action of active oxygen species induced by the photochemical reaction.

A borane-bithiophene-BODIPY triad: intriguing tricolor emission and selective fluorescence response towards fluoride ions.

PubMed

Sarkar, Samir Kumar; Thilagar, Pakkirisamy

2013-10-04

The structure and photophysical properties of a new triad (borane–bithiophene–BODIPY) 1 have been investigated. Triad 1 exhibits unprecedented tricolour emission when excited at the borane centred high energy absorption band and also acts as a selective fluorescent and colorimetric sensor for fluoride ions with ratiometric response. The experimental results are supported by computational studies.

Photodynamic characterization of amino acid conjugated 15(1)-hydroxypurpurin-7-lactone for cancer treatment.

PubMed

Lim, Siang Hui; Yam, Mun Li; Lam, May Lynn; Kamarulzaman, Fadzly Azhar; Samat, Norazwana; Kiew, Lik Voon; Chung, Lip Yong; Lee, Hong Boon

2014-09-02

This study aims to improve the photodynamic properties and biological effectiveness of 15(1)-hydroxypurpurin-7-lactone dimethyl ester (G2), a semisynthetic photosensitizer, for the PDT treatment of cancer. The strategy we undertook was by conjugating G2 with aspartic acid and lysine amino acid moieties. The photophysical properties, singlet oxygen generation, distribution coefficiency (Log D in octanol/PBS pH 7.4), and photostability of these analogues and their in vitro bioactivities such as cellular uptake, intracellular localization, and photoinduced cytotoxicity were evaluated. In addition, selected analogues were also investigated for their PDT-induced vasculature occlusion in the chick chorioallantoic membrane model and for their antitumor efficacies in Balb/C mice bearing 4T1 mouse mammary tumor. From the study, conjugation with aspartic acid improved the aqueous solubility of G2 without affecting its photophysical characteristics. G2-Asp showed similar in vitro and in vivo antitumor efficacies compared to the parent compound. Given the hydrophilic nature of G2-Asp, the photosensitizer is a pharmaceutically advantageous candidate as it can be formulated easily for systemic administration and has reduced risk of aggregation in vascular system.

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.

Photophysics of Ru(II)— and Os(II)—polypyridine complexes in poly(ethyleneoxide) matrices

NASA Astrophysics Data System (ADS)

Campagna, Sebastiano; Bartolotta, Antonino; Marco, Gaetano Di

1993-04-01

Photophysical properties of Ru(bpy) 32+, Ru(bpy) 2(biq) 2+, and Os(bpy) 32+ (bpy=2,2'-bipyridine; biq=2,2'-biquinoline) in poly(ethyleneoxide) matrices (PEO) constituted by (CH 2CH 2O) repeating units, with average molecular weight 400 (PEO-400, a highly viscous fluid) and 600000 dalton (PEO-600000, a semicrystalline solid) have been studied at room temperature and 77 K. Comparison with similar systems is made. The absorption spectra, luminescence spectra and lifetimes at room temperature of the three complexes in both matrices are in agreement with the typical features reported for the same complexes in fluid solutions, and indicate that fast excited state relaxation via solvent reorganization occurs in both PEO matrices at room temperature. Such behaviour is not usual for solid matrices and is attributed to the microheterogeneous nature of PEO-600000 and to the ability of the solid PEO amorphous region to stabilize polar species within the timescale of radiative relaxation. The results suggest that PEO-600000 is a promising medium for studying electron and energy transfer processes having mild driving forces in the solid state at room temperature.

Photophysicochemical, calf thymus DNA binding and in vitro photocytotoxicity properties of tetra-morpholinoethoxy-substituted phthalocyanines and their water-soluble quaternized derivatives.

PubMed

Koçan, Halit; Kaya, Kerem; Özçeşmeci, İbrahim; Sesalan, B Şebnem; Göksel, Meltem; Durmuş, Mahmut; Burat, Ayfer Kalkan

2017-12-01

In this study, morpholinoethoxy-substituted metal-free (3), zinc(II) (4) and indium(III) (5) phthalocyanines were synthesized. These phthalocyanines were converted to their water-soluble quaternized derivatives (3Q-5Q) using excess methyl iodide as a quaternization agent. All these phthalocyanines (Pcs) were characterized by elemental analysis and different spectroscopic methods such as FT-IR, 1 H NMR, UV-Vis and mass spectrometry. The photophysical and photochemical properties such as fluorescence and generation of singlet oxygen were investigated for determination of these phthalocyanines as photosensitizers in photodynamic therapy (PDT) applications. The binding properties of quaternized phthalocyanines (3Q-5Q) to calf thymus DNA (CT-DNA) were investigated by UV-Vis and fluorescence spectrophotometric methods. The quenching effect of all quaternized phthalocyanines on the fluorescence intensity of SYBR Green-DNA complex was determined. The mixtures of 3Q, 4Q or 5Q and DNA solutions were used to determine the change in T m of double helix DNA with thermal denaturation profile. In addition, thermodynamic parameters considering their aggregation in buffer solution, which shows the spontaneity of the reactions between DNA and quaternized Pcs were investigated. On the other hand, in vitro phototoxicity and cytotoxicity behavior of the quaternized water-soluble phthalocyanine photosensitizers (3Q-5Q) were tested against the cervical cancer cell line named HeLa for evaluation of their suitability for treatment of cancer by PDT method. Peripherally tetra-substituted neutral and quaternized metal-free and metallophthalocyanines (MPcs) (Zn, In) bearing morpholinoethoxy groups were prepared. The binding of quaternized compounds (3Q-5Q) to CT-DNA were examined using UV-Vis, fluorescence spectra, thermal denaturation profiles and K SV values. Besides, thermodynamic studies indicated that binding of 3Q-5Q to DNA was spontaneous. On the other hand, in vitro phototoxicity and cytotoxicity behavior of the quaternized water-soluble phthalocyanine photosensitizers (3Q-5Q) were tested against the cervical cancer cell line named HeLa for evaluation of their suitability for treatment of cancer by PDT method.

JPRS Report, Science & Technology, USSR: Chemistry

DTIC Science & Technology

1990-11-08

desorption cycle. The photochemical activity of the oxides was determined by irradiating them with UV light at 353 K during the oxidation reactions of...No 1, Jan 90] 8 Acid-Base Properties Photochemically Active Titanium Oxide Surfaces [N D. Konovalova, V. I. Stepanenko, etal; UKRAINSKIY...Figures 4; references 13: 10 Russian, 3 Western. UDC 541.183 Acid-Base Properties Photochemically Active Titanium Oxide Surfaces 907M0149B Kiev

Spin-vibronic quantum dynamics for ultrafast excited-state processes.

PubMed

Eng, Julien; Gourlaouen, Christophe; Gindensperger, Etienne; Daniel, Chantal

2015-03-17

Ultrafast intersystem crossing (ISC) processes coupled to nuclear relaxation and solvation dynamics play a central role in the photophysics and photochemistry of a wide range of transition metal complexes. These phenomena occurring within a few hundred femtoseconds are investigated experimentally by ultrafast picosecond and femtosecond transient absorption or luminescence spectroscopies, and optical laser pump-X-ray probe techniques using picosecond and femtosecond X-ray pulses. The interpretation of ultrafast structural changes, time-resolved spectra, quantum yields, and time scales of elementary processes or transient lifetimes needs robust theoretical tools combining state-of-the-art quantum chemistry and developments in quantum dynamics for solving the electronic and nuclear problems. Multimode molecular dynamics beyond the Born-Oppenheimer approximation has been successfully applied to many small polyatomic systems. Its application to large molecules containing a transition metal atom is still a challenge because of the nuclear dimensionality of the problem, the high density of electronic excited states, and the spin-orbit coupling effects. Rhenium(I) α-diimine carbonyl complexes, [Re(L)(CO)3(N,N)](n+) are thermally and photochemically robust and highly flexible synthetically. Structural variations of the N,N and L ligands affect the spectroscopy, the photophysics, and the photochemistry of these chromophores easily incorporated into a complex environment. Visible light absorption opens the route to a wide range of applications such as sensors, probes, or emissive labels for imaging biomolecules. Halide complexes [Re(X)(CO)3(bpy)] (X = Cl, Br, or I; bpy = 2,2'-bipyridine) exhibit complex electronic structure and large spin-orbit effects that do not correlate with the heavy atom effects. Indeed, the (1)MLCT → (3)MLCT intersystem crossing (ISC) kinetics is slower than in [Ru(bpy)3](2+) or [Fe(bpy)3](2+) despite the presence of a third-row transition metal. Counterintuitively, singlet excited-state lifetime increases on going from Cl (85 fs) to Br (128 fs) and to I (152 fs). Moreover, correlation between the Re-X stretching mode and the rate of ISC is observed. In this Account, we emphasize on the role of spin-vibronic coupling on the mechanism of ultrafast ISC put in evidence in [Re(Br)(CO)3(bpy)]. For this purpose, we have developed a model Hamiltonian for solving an 11 electronic excited states multimode problem including vibronic and SO coupling within the linear vibronic coupling (LVC) approximation and the assumption of harmonic potentials. The presence of a central metal atom coupled to rigid ligands, such as α-diimine, ensures nuclear motion of small amplitudes and a priori justifies the use of the LVC model. The simulation of the ultrafast dynamics by wavepacket propagations using the multiconfiguration time-dependent Hartree (MCTDH) method is based on density functional theory (DFT), and its time-dependent extension to excited states (TD-DFT) electronic structure data. We believe that the interplay between time-resolved experiments and these pioneering simulations covering the first picoseconds and including spin-vibronic coupling will promote a number of quantum dynamical studies that will contribute to a better understanding of ultrafast processes in a wide range of organic and inorganic chromophores easily incorporated in biosystems or supramolecular devices for specific functions.

The road not taken: Applications of fluorescence spectroscopy and electronic structure theory to systems of materials and biological relevance

NASA Astrophysics Data System (ADS)

Carlson, Philip Joseph

Applications of Fluorescence Spectroscopy and Electronic Structure Theory to Systems of Materials and Biological Relevance. The photophysics of curcumin was studied in micelles and the solvation dynamics were probed. The high-energy ionic liquid HEATN was also studied using the fragment molecular orbital method. The solvation dynamics of the HEATN system were determined. This marks the first study of the solvation dynamics in a triazolium ionic liquid system.

LASER BIOLOGY AND MEDICINE: Application of laser fluorimetry for determining the influence of a single amino-acid substitution on the individual photophysical parameters of a fluorescent form of a fluorescent protein mRFP1

NASA Astrophysics Data System (ADS)

Banishev, A. A.; Vrzheshch, E. P.; Shirshin, E. A.

2009-03-01

Individual photophysical parameters of the chromophore of a fluorescent protein mRFP1 and its two mutants (amino-acid substitution at position 66 - mRFP1/ Q66C and mRFP1/Q66S proteins) are determined. For this purpose, apart from conventional methods of fluorimetry and spectrophotometry, nonlinear laser fluorimetry is used. It is shown that the individual extinction coefficients of the chromophore of proteins correlate (correlation coefficient above 0.9) with the volume of the substituted amino-acid residue at position 66 (similar to the positions of the absorption, fluorescence excitation and emission maxima).

Enhanced Efficiency and Stability of Perovskite Solar Cells via Anti-Solvent Treatment in Two-Step Deposition Method.

PubMed

Li, Minghua; Yan, Xiaoqin; Kang, Zhuo; Liao, Xinqin; Li, Yong; Zheng, Xin; Lin, Pei; Meng, Jingjing; Zhang, Yue

2017-03-01

The low-cost inorganic-organic lead halide perovskite materials become particularly promising for solar cells with high photovoltaic conversion efficiency. The uniform and pinhole-free perovskite films play an important role for high-performance solar cells. We demonstrate an antisolvent treatment by controlling the PbI 2 morphology to enhance the perovskite conversion and photophysical properties, including high absorption, crystallinity, and rapid carrier transfer. The fabricated perovskite solar cells show tremendous PCE improvement to about 16.1% from 12% with less hysteresis, and retain over 90% initial PCE after 30 days in ambient and dark atmosphere. In prospect, this antisolvent treatment will be a feasible route to prepare high-quality perovskite films including favorite photophysical properties.

Influence of Bridgehead Substitution and Ring Annelation on the Photophysical Properties of Polycyclic DBO-Type Azoalkanes.

PubMed

Adam, Waldemar; Nikolaus, Achim; Sauer, Jürgen

1999-05-14

The photophysical data for the polycyclic, bridgehead-substituted derivatives 1-10 of the photoreluctant diazabicyclo[2.2.2]oct-2-ene (DBO) are presented. Substitution on the bridgehead positions with radical-stabilizing substituents enhances the photoreactivity (Phi(r)) and decreases the fluorescence quantum yields (Phi(f)) and lifetimes (tau) compared to the parent DBO. The annelated rings have no influence on the photoreactivity, except when steric interactions with an alpha substituent hinder the optimal radical-stabilizing conformation. The fused rings and some of the bridgehead substituents reduce the solvent-induced quenching of the singlet-excited azo chromophore by steric shielding of the azo group and, thus, increase the fluorescence quantum yields and lifetimes.

1,2-diketones promoted degradation of poly(epsilon-caprolactone)

NASA Astrophysics Data System (ADS)

Danko, Martin; Borska, Katarina; Ragab, Sherif Shaban; Janigova, Ivica; Mosnacek, Jaroslav

2012-07-01

Photochemical reactions of Benzil and Camphorquinone were used for modification of poly(ɛ-caprolactone) polymer films. Photochemistry of dopants was followed by infrared spectroscopy, changes on polymer chains of matrix were followed by gel permeation chromatography. Benzoyl peroxide was efficiently photochemically generated from benzyl in solid polymer matrix in the presence of air. Following decomposition of benzoyl peroxide led to degradation of matrix. Photochemical transformation of benzil in vacuum led to hydrogen abstraction from the polymer chains in higher extent, which resulted to chains recombination and formation of gel. Photochemical transformation of camphorquinone to corresponding camphoric peroxide was not observed. Only decrease of molecular weight of polymer matrix doped with camphorquinone was observed during the irradiation.

Atmospheric Photochemical Modeling of Turbine Engine Fuels. Phase I. Experimental Studies. Volume 1. Results and Discussion.

DTIC Science & Technology

1984-09-01

ambient air was drawn through Purafil beds (to remove NOx), compressed by a liquid (water) ring compressor to 100 psig, and passed successively...AD-R48 716 ATMOSPHERIC PHOTOCHEMICAL MODELING OF TURBNNE ENGINE 1/2 FUELS PHASE I EXPERI..(U) CALIFORNIA UNIV RIVERSIDE STATEWIDE AIR POLLUTION...of II Results and Disussion : t W.P.L. CARTER, A.M. WINER, R. ATKINSON, M.C. DODD, W.D. LONG, and S.M. ASCHMANN STATEWIDE AIR POLLUTION RESEARCH

Formation of fatty acids in photochemical conversions of saturated hydrocarbons

NASA Technical Reports Server (NTRS)

Telegina, T. A.; Pavlovskaya, T. Y.; Ladyzhenskaya, A. I.

1977-01-01

Abiogenic synthesis of fatty acids was studied in photochemical conversions of saturated hydrocarbons. It was shown that, in a hydrocarbon water CaCO3 suspension, the action of 254 nm UV rays caused the formation of fatty acids with a maximum number of carbon atoms in the chain not exceeding that in the initial hydrocarbon. Synthesis of acetic, propionic, butyric, valeric, caproic, enanthic and caprylic (in the case of octane) acids occurs in heptane water CaCO3 and octane water CaCO3 systems.

Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies Evaluation Number 15

NASA Technical Reports Server (NTRS)

Sander, S. P.; Friedl, R. R.; Golden, D. M.; Kurylo, M. J.; Moortgat, G. K.; Wine, P. H.; Ravishankara, A. R.; Kolb, C. E.; Molina, M. J.; Finlayson-Pitts, B. J.;

Photochemical Ignition Studies. 3. Ignition by Efficient and Resonant Multiphoton Photochemical Formation of Microplasmas

DTIC Science & Technology

1987-06-01

Fragments," Chem. Phys., Vol. 33, p. 161, 1978. 5. R.C. Sausa, A.J. Alfano , and A.W. Miziolek, "ArF Laser Photoproduction and Sensitive Detection of Carbon...Unlversity/APL Chemical Propulsion I Purdue University Information Agency Department of Chomistry ATTN: TW. Christian ATTN: H. Grant Johns Hopkins...of Chemistry ATTN: T.W. Christian ATTN: E. Grant Johns Hopkins Road West Lafayette, IN 47906 Laurel, MD 20707 2 Purdue University University of

Photochemically Induced Intramolecular Radical Cyclization Reactions with Imines.

PubMed

Lefebvre, Corentin; Michelin, Clément; Martzel, Thomas; Djou'ou Mvondo, Vaneck; Bulach, Véronique; Abe, Manabu; Hoffmann, Norbert

2018-02-16

The photochemically induced intramolecular hydrogen abstraction or hydrogen atom transfer in cyclic imines 8a,b followed by a cyclization is investigated. Two types of products are observed, one resulting from the formation of a C-C bond, the other from the formation of a C-N bond. A computational study reveals that hydrogen is exclusively transferred to the imine nitrogen leading to a triplet diradical intermediate. After intersystem crossing, the resulting zwitterionic intermediate undergoes cyclization leading to the final product.

Production of hydrogen by electron transfer catalysis using conventional and photochemical means

NASA Technical Reports Server (NTRS)

Rillema, D. P.

1981-01-01

Alternate methods of generating hydrogen from the sulfuric acid thermal or electrochemical cycles are presented. A number of processes requiring chemical, electrochemical or photochemical methods are also presented. These include the design of potential photoelectrodes and photocatalytic membranes using Ru impregnated nafion tubing, and the design of experiments to study the catalyzed electrolytic formation of hydrogen and sulfuric acid from sulfur dioxide and water using quinones as catalysts. Experiments are carried out to determine the value of these approaches to energy conversion.

Effects of 1,3-Butadiene, Isoprene, and Their Photochemical Degradation Products on Human Lung Cells

PubMed Central

Doyle, Melanie; Sexton, Kenneth G.; Jeffries, Harvey; Bridge, Kevin; Jaspers, Ilona

2004-01-01

Because of potential exposure both in the workplace and from ambient air, the known carcinogen 1,3-butadiene (BD) is considered a priority hazardous air pollutant. BD and its 2-methyl analog, isoprene (ISO), are chemically similar but have very different toxicities, with ISO showing no significant carcinogenesis. Once released into the atmosphere, reactions with species induced by sunlight and nitrogen oxides convert BD and ISO into several photochemical reaction products. In this study, we determined the relative toxicity and inflammatory gene expression induced by exposure of A549 cells to BD, ISO, and their photochemical degradation products in the presence of nitric oxide. Gas chromatography and mass spectrometry analyses indicate the initial and major photochemical products produced during these experiments for BD are acrolein, acetaldehyde, and formaldehyde, and products for ISO are methacrolein, methyl vinyl ketone, and formaldehyde; both formed < 200 ppb of ozone. After exposure the cells were examined for cytotoxicity and interleukin-8 (IL-8) gene expression, as a marker for inflammation. These results indicate that although BD and ISO alone caused similar cytotoxicity and IL-8 responses compared with the air control, their photochemical products significantly enhanced cytotoxicity and IL-8 gene expression. This suggests that once ISO and BD are released into the environment, reactions occurring in the atmosphere transform these hydrocarbons into products that induce potentially greater adverse health effects than the emitted hydrocarbons by themselves. In addition, the data suggest that based on the carbon concentration or per carbon basis, biogenic ISO transforms into products with proinflammatory potential similar to that of BD products. PMID:15531432

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.

Steady-state and time-resolved studies on the photophysical properties of fullerene-pyropheophorbide a complexes in polar and nonpolar solvents

NASA Astrophysics Data System (ADS)

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

2004-04-01

A novel monofullerene-bis(pyropheophorbide a) dyad has been photophysically characterized by steady-state as well as time-resolved techniques. It was revealed that in this complex strong and fast quenching of the first excited singlet state of the pyropheophorbide a (pyroPheo) molecule occurs by efficient photoinduced electron transfer to the fullerene moiety in both polar (DMF) and nonpolar (toluene) solvents. In DMF the energy of the charge-separated state is 0.94 eV and it undergoes directly transition to the ground state resulting in a very low value of photosensitized singlet oxygen generation. In contrast to the situation in a polar solvent, in toluene the charge-separated state lies above the exited triplet state of pyroPheo as well as that of C 60. It has been shown that in a nonpolar solvent a sufficient amount of singlet oxygen was generated by energy transfer from the excited triplet state of pyroPheo which has been populated via relaxation of the charge-separated state.

Biosorption of arsenic from groundwater using Vallisneria gigantea plants. Kinetics, equilibrium and photophysical considerations.

PubMed

Iriel, Analia; Lagorio, M Gabriela; Fernández Cirelli, Alicia

2015-11-01

Arsenic (V) uptake from groundwater by using Vallisneria gigantea plants was studied using batch experiments. Reflectance and fluorescence of intact plants were investigated and changes in photophysical properties following arsenic absorption were reported. Good correlations have been found between arsenic concentration in groundwater and parameters derived from reflectance and fluorescence measurements. This system reached its equilibrium after seven days when the removal quantities were strongly dependent on the initial arsenic concentration. Interestingly, Vallisneria plants were able to accumulate from 100 to 600 mg As kg(-1) in roots and fronds although the translocation factors were low (0.6-1.6). Kinetic data for biosorption process followed a first-order law. At low arsenic concentrations the uptake in plants was governed by diffusion aspects. Langmuir, Freundlich and Dubinin-Radushkevich models were applied and results demonstrated that arsenic uptake was better described by the Langmuir model. As a final remark we concluded that a plant of this species should be able to remove 1mg As per week. Copyright © 2015 Elsevier Ltd. All rights reserved.

Determinants of the efficiency of photon upconversion by triplet-triplet annihilation in the solid state: zinc porphyrin derivatives in PVA.

PubMed

Rautela, Ranjana; Joshi, Neeraj K; Novakovic, Sacha; Wong, Wallace W H; White, Jonathan M; Ghiggino, Kenneth P; Paige, Matthew F; Steer, Ronald P

2017-08-30

Spectroscopic, photophysical and computational studies designed to expose and explain the differences in the efficiencies of non-coherent photon upconversion (NCPU) by triplet-triplet annihilation (TTA) have been carried out for a new series of alkyl-substituted diphenyl and tetraphenyl zinc porphyrins, both in fluid solution and in solid films. Systematic variations in the alkyl-substitution of the phenyl groups in both the di- and tetraphenyl porphyrins introduces small, but well-understood changes in their spectroscopic and photophysical properties and in their TTA efficiencies. In degassed toluene solution TTA occurs for all derivatives and produces the fluorescent S 2 product states in all cases. In PVA matrices, however, none of the di-phenylporphyrins exhibit measurable NCPU whereas all the tetraphenyl-substituted compounds remain upconversion-active. In PVA the NCPU efficiencies of the zinc tetraphenylporphyrins vary significantly with their steric characteristics; the most sterically crowded tetraphenyl derivative exhibits the greatest efficiency. DFT-D computations have been undertaken and help reveal the sources of these differences.

The spectroscopic characterization of newly developed emissive materials and the effects of environment on their photophysical properties

NASA Astrophysics Data System (ADS)

McNamara, Louis Edward, III

The development of new materials capable of efficient charge transfer and energy storage has become increasingly important in many areas of modern chemical research. This is especially true for the development of emissive optoelectronic devices and in the field of solar to electric energy conversion. The characterization of the photophysical properties of new molecular systems for these applications has become critical in the design and development of these materials. Many molecular building blocks have been developed and understanding the properties of these molecules at a fundamental level is essential for their successful implementation and future engineering. This dissertation focuses on the characterization of some of these newly-developed molecular systems. The spectroscopic studies focus on the characterization of newly-developed molecules based on perylene and indolizine derivatives for solar to electric energy conversion, thienopyrazine derivatives for near infrared (NIR) emissive applications, an SCS pincer complex for blue emissive materials and a fluorescent probe for medical applications. The effects of noncovalent interactions are also investigated on these systems and a benchmark biological molecule trimethylamine N-oxide (TMAO).

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

Manser, Joseph S.; Christians, Jeffrey A.; Kamat, Prashant V.

Here, a new chapter in the long and distinguished history of perovskites is being written with the breakthrough success of metal halide perovskites (MHPs) as solution-processed photovoltaic (PV) absorbers. The current surge in MHP research has largely arisen out of their rapid progress in PV devices; however, these materials are potentially suitable for a diverse array of optoelectronic applications. Like oxide perovskites, MHPs have ABX 3 stoichiometry, where A and B are cations and X is a halide anion. Here, the underlying physical and photophysical properties of inorganic (A = inorganic) and hybrid organic-inorganic (A = organic) MHPs are reviewedmore » with an eye toward their potential application in emerging optoelectronic technologies. Significant attention is given to the prototypical compound methylammonium lead iodide (CH 3NH 3PbI 3) due to the preponderance of experimental and theoretical studies surrounding this material. We also discuss other salient MHP systems, including 2- dimensional compounds, where relevant. More specifically, this review is a critical account of the interrelation between MHP electronic structure, absorption, emission, carrier dynamics and transport, and other relevant photophysical processes that have propelled these materials to the forefront of modern optoelectronics research.« less

DFT/TDDFT investigation on the photophysical properties of a series of phosphorescent cyclometalated complexes based on the benchmark complex FIrpic

NASA Astrophysics Data System (ADS)

Han, Deming; Gong, Ping; Lv, Shuhui; Zhao, Lihui; Zhao, Henan

2018-05-01

The photophysical properties of four Ir(III) complexes have been investigated by means of the density functional theory/time-dependent density functional theory (DFT/TDDFT). The effect of the electron-withdrawing and electron-donating substituents on charge injection, transport, absorption and phosphorescent properties has been studied. The theoretical calculation shows that the lowest-lying singlet absorptions for complexes 1-4 are located at 387, 385, 418 and 386 nm, respectively. For 1-4, the phosphorescence at 465, 485, 494 and 478 nm is mainly attributed to the LUMO → HOMO and LUMO → HOMO-1 transition configurations characteristics. In addition, ionisation potential (IP), electron affinities (EAs) and reorganisation energy have been investigated to evaluate the charge transfer and balance properties between hole and electron. The balance of the reorganisation energies for complex 3 is better than others. The difference between hole transport and electron transport for complex 3 is the smallest among these complexes, which is beneficial to achieve the hole and electron transfer balance in emitting layer.

Photo-physics study of an hydroxy-quinoline derivative as inhibitor of Pim-1 kinase: ultraviolet-visible linear dichroism spectroscopy and quantum chemical calculations.

PubMed

Lamhasni, T; Ait Lyazidi, S; Hnach, M; Haddad, M; Desmaële, D; Spanget-Larsen, J; Nguyen, D D; Ducasse, L

2013-09-01

The photophysical properties of the antiviral 7-nicotinoyl-styrylquinoline (MB96) were investigated by means of UV-Vis linear dichroism (LD) spectroscopy on molecular samples aligned in stretched polyvinylalcohol (PVA), supported by time dependent density functional theory (TD-DFT) calculations. Experimentally, the directions of the transitions moments with respect to the long axis of the molecule were deduced from the orientation K factors, determined by means of "trial-and-error" procedure. The absorption spectrum presents two parts. The main transition in the lowest energy part, observed around 365 nm and showing the highest K value 0.8, is longitudinally in-plane polarized. The highest energy part which is extended between 230 and 320 nm, large, diffuse, and of weak intensity, shows estimated K values between 0.2 and 0.5. This complex structure is transversally polarized with some contamination by the longitudinal character of the first strong band. The TD-DFT results agree fairly well with the LD measurements. Copyright © 2013 Elsevier B.V. All rights reserved.

Screening of biologically important Zn2 + by a chemosensor with fluorescent turn on-off mechanism

NASA Astrophysics Data System (ADS)

Khan, Tanveer A.; Sheoran, Monika; Nikhil Raj M., Venkata; Jain, Surbhi; Gupta, Diksha; Naik, Sunil G.

2018-01-01

Reported herein the synthesis, characterization and biologically important zinc ion binding propensity of a weakly fluorescent chemosensor, 4-methyl-2,6-bis((E)-(2-(4-phenylthiazol-2-yl)hydrazono)methyl)phenol (1). 1H NMR spectroscopic titration experiment reveals the binding knack of 1 to the essential Zn2 +. The photo-physical studies of 1 exhibit an enhancement in the fluorescence by several folds upon binding with the zinc ions attributed to PET-off process, with a binding constant value of 5.22 × 103 M- 1. 1 exhibits an excellent detection range for Zn2 + with lower detection limit value of 2.31 × 10- 8 M. The selectivity of 1 was studied with various mono and divalent metal cations and it was observed that most cations either quenches the fluorescence or remains unchanged except for Cd2 +, which shows a slight enhancement in fluorescence intensity of 1. The ratiometric displacement of Cd2 + ions by Zn2 + ions shows an excellent selectivity towards in-situ detection of Zn2 + ions. Photo-physical studies also support the reversible binding of 1 to Zn2 + ions having on and off mechanism in presence of EDTA. Such recognition of the biologically important zinc ions finds potential application in live cell imaging.

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.

Photochemical coatings for the prevention of bacterial colonization.

PubMed

Dunkirk, S G; Gregg, S L; Duran, L W; Monfils, J D; Haapala, J E; Marcy, J A; Clapper, D L; Amos, R A; Guire, P E

1991-10-01

Biomaterials are being used with increasing frequency for tissue substitution. Implantable, prosthetic devices are instrumental in the saving of patients' lives and enhancing the quality of life for many others. However, the greatest barrier to expanding the use of biomedical devices is the high probability of bacterial adherence and proliferation, causing very difficult and often untreatable medical-device centered infections. The difficulty in treating such infections results in great danger to the patient, and usually retrieval of the device with considerable pain and suffering. Clearly, development of processes that make biomedical devices resistant to bacterial adherence and colonization would have widespread application in the field of biomedical technology. A photochemical surface modification process is being investigated as a generic means of applying antimicrobial coatings to biomedical devices. The photochemical process results in covalent immobilization of coatings to all classes of medical device polymers. A discussion of the photochemical surface modification process and preliminary results demonstrating the success of photochemical coatings in formulating microbial-resistant surfaces are presented in this paper.

Photochemical oxidation: A solution for the mixed waste dilemma

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

Prellberg, J.W.; Thornton, L.M.; Cheuvront, D.A.

1995-12-31

Numerous technologies are available to remove organic contamination from water or wastewater. A variety of techniques also exist that are used to neutralize radioactive waste. However, few technologies can satisfactorily address the treatment of mixed organic/radioactive waste without creating unacceptable secondary waste products or resulting in extremely high treatment costs. An innovative solution to the mixed waste problem is on-site photochemical oxidation. Liquid-phase photochemical oxidation has a long- standing history of successful application to the destruction of organic compounds. By using photochemical oxidation, the organic contaminants are destroyed on-site leaving the water, with radionuclides, that can be reused or disposedmore » of as appropriate. This technology offers advantages that include zero air emissions, no solid or liquid waste formation, and relatively low treatment cost. Discussion of the photochemical process will be described, and several case histories from recent design testing, including cost analyses for the resulting full-scale installations, will be presented as examples.« less

Electronic-carrier-controlled photochemical etching process in semiconductor device fabrication

DOEpatents

Ashby, C.I.H.; Myers, D.R.; Vook, F.L.

1988-06-16

An electronic-carrier-controlled photochemical etching process for carrying out patterning and selective removing of material in semiconductor device fabrication includes the steps of selective ion implanting, photochemical dry etching, and thermal annealing, in that order. In the selective ion implanting step, regions of the semiconductor material in a desired pattern are damaged and the remainder of the regions of the material not implanted are left undamaged. The rate of recombination of electrons and holes is increased in the damaged regions of the pattern compared to undamaged regions. In the photochemical dry etching step which follows ion implanting step, the material in the undamaged regions of the semiconductor are removed substantially faster than in the damaged regions representing the pattern, leaving the ion-implanted, damaged regions as raised surface structures on the semiconductor material. After completion of photochemical dry etching step, the thermal annealing step is used to restore the electrical conductivity of the damaged regions of the semiconductor material.

Electronic-carrier-controlled photochemical etching process in semiconductor device fabrication

DOEpatents

Ashby, Carol I. H.; Myers, David R.; Vook, Frederick L.

1989-01-01

An electronic-carrier-controlled photochemical etching process for carrying out patterning and selective removing of material in semiconductor device fabrication includes the steps of selective ion implanting, photochemical dry etching, and thermal annealing, in that order. In the selective ion implanting step, regions of the semiconductor material in a desired pattern are damaged and the remainder of the regions of the material not implanted are left undamaged. The rate of recombination of electrons and holes is increased in the damaged regions of the pattern compared to undamaged regions. In the photochemical dry etching step which follows ion implanting step, the material in the undamaged regions of the semiconductor are removed substantially faster than in the damaged regions representing the pattern, leaving the ion-implanted, damaged regions as raised surface structures on the semiconductor material. After completion of photochemical dry etching step, the thermal annealing step is used to restore the electrical conductivity of the damaged regions of the semiconductor material.

Photochemical transformations accelerated in continuous-flow reactors: basic concepts and applications.

PubMed

Su, Yuanhai; Straathof, Natan J W; Hessel, Volker; Noël, Timothy

2014-08-18

Continuous-flow photochemistry is used increasingly by researchers in academia and industry to facilitate photochemical processes and their subsequent scale-up. However, without detailed knowledge concerning the engineering aspects of photochemistry, it can be quite challenging to develop a suitable photochemical microreactor for a given reaction. In this review, we provide an up-to-date overview of both technological and chemical aspects associated with photochemical processes in microreactors. Important design considerations, such as light sources, material selection, and solvent constraints are discussed. In addition, a detailed description of photon and mass-transfer phenomena in microreactors is made and fundamental principles are deduced for making a judicious choice for a suitable photomicroreactor. The advantages of microreactor technology for photochemistry are described for UV and visible-light driven photochemical processes and are compared with their batch counterparts. In addition, different scale-up strategies and limitations of continuous-flow microreactors are discussed. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Improving Joint Function Using Photochemical Hydrogels for Articular Surface Repair

DTIC Science & Technology

2013-10-01

riboflavin and blue light in hypoxic conditions. Control gels were not photochemically crosslinked . New cartilage matrix was formed in vivo in mice after 4...Sections were probed with AlexaFluor 568- conjugated secondary antibodies and counterstained with DAPI for cell nuclei. All samples were processed at...calcium deposits demonstrated with von Kossa stains; 2) A degradable form of photochemically crosslinked PEG norbomene gel was formulated and growth

Photochemical and thermal bergman cyclization of a pyrimidine enediynol and enediynone.

PubMed

Choy, N; Blanco, B; Wen, J; Krishan, A; Russell, K C

2000-11-30

[reaction: see text] Novel 10-membered pyrimidine enediynes (3 and 4) were synthesized in seven and eight steps, respectively. These compounds were compared for their abilities to undergo Bergman cyclization both thermally and photochemically. Alcohol 3 readily cyclized both thermally and photochemically in (i)PrOH, while ketone 4 only showed efficient thermal cyclization. Both compounds were also shown to cleave dsDNA under the appropriate conditions.

Photochemical processing of diesel fuel emissions as a large secondary source of isocyanic acid (HNCO)

NASA Astrophysics Data System (ADS)

Link, M. F.; Friedman, B.; Fulgham, R.; Brophy, P.; Galang, A.; Jathar, S. H.; Veres, P.; Roberts, J. M.; Farmer, D. K.

2016-04-01

Isocyanic acid (HNCO) is a well-known air pollutant that affects human health. Biomass burning, smoking, and combustion engines are known HNCO sources, but recent studies suggest that secondary production in the atmosphere may also occur. We directly observed photochemical production of HNCO from the oxidative aging of diesel exhaust during the Diesel Exhaust Fuel and Control experiments at Colorado State University using acetate ionization time-of-flight mass spectrometry. Emission ratios of HNCO were enhanced, after 1.5 days of simulated atmospheric aging, from 50 to 230 mg HNCO/kg fuel at idle engine operating conditions. Engines operated at higher loads resulted in less primary and secondary HNCO formation, with emission ratios increasing from 20 to 40 mg HNCO/kg fuel under 50% load engine operating conditions. These results suggest that photochemical sources of HNCO could be more significant than primary sources in urban areas.

Viscosity and medium effects on the fluorescence and photochemical behaviour of some aryl chalcones

NASA Astrophysics Data System (ADS)

Ebeid, El-Zeiny M.; Abdel-Kader, Mahmood H.; Issa, Raafat M.; El-Daly, Samy A.

1988-05-01

The emission, excitation and absorption spectra toghether with the fluorescence and photochemical quantum yields of some chalcone derivatives have been studied in organic solvents and micellar and microemulsion media. Both 4-[2-(2-pyridyl)ethenyl] ( I) and 4-[2-(4-pyridyl)ethenyl ( II) chalcones show large positive solvatochromic effects. The fluorescence quantum yields increase substantially as the medium viscosity increases with a subsequent decrease in the photochemical quatum yield. Compounds I and II undergo excited-state molecular aggregation in concentrated solutions giving excimer-like emission that coincides with emission from crystalline samples. The enthalpies of photoassociation have been estimated. The chalcone derivative I acts as an efficient quencher of the fluorescence of the laser dye 1,4-bis (β-pyridyl-2-vinyl)benzene via a long-range mechanism. The excited-state lifetimes of both I and II are short and at 20°C their τ values are less than 800 ps.

The photochemical alkylation and reduction of heteroarenes† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc03768f Click here for additional data file.

PubMed Central

McCallum, T.; Pitre, S. P.; Morin, M.

2017-01-01

The functionalization of heteroarenes has been integral to the structural diversification of medicinally active molecules such as quinolines, pyridines, and phenanthridines. Electron-deficient heteroarenes are electronically compatible to react with relatively nucleophilic free radicals such as hydroxyalkyl. However, the radical functionalization of such heteroarenes has been marked by the use of transition-metal catalyzed processes that require initiators and stoichiometric oxidants. Herein, we describe the photochemical alkylation of quinolines, pyridines and phenanthridines, where through direct excitation of the protonated heterocycle, alcohols and ethers, such as methanol and THF, can serve as alkylating agents. We also report the discovery of a photochemical reduction of these heteroarenes using only iPrOH and HCl. Mechanistic studies to elucidate the underlying mechanism of these transformations, and preliminary results on catalytic methylations are also reported. PMID:29163892

Photochemical and photocatalytic degradation of trans-resveratrol.

PubMed

Silva, Cláudia Gomes; Monteiro, Judith; Marques, Rita R N; Silva, Adrián M T; Martínez, Cristina; Canle, Moisés; Faria, Joaquim Luís

2013-04-01

Photochemical and photocatalytic degradation of the emerging pollutant trans-resveratrol has been studied under different irradiation wavelengths and using different TiO2 catalysts. trans-Resveratrol was more easily degraded when irradiated using the whole spectral range (UV-Vis) rather than with UV and near-UV to visible irradiation. The main intermediate of trans-resveratrol phototransformation was identified as its isomer cis-resveratrol. Different TiO2 catalysts were used to carry out the photocatalytic degradation of trans-resveratrol. Catalysts properties such as crystallite dimensions, surface area and presence of hydroxy surface groups are shown to be crucial to the photocatalytic efficiency of the materials tested. From the point of view of trans-resveratrol abatement, the photocatalytic process was more efficient than the pure photochemical one resulting in higher degradation rates and higher organic content removal. Six photoproducts of trans-resveratrol phototransformation were identified mainly resulting from the attack of the hydroxyl radical to the organic molecule.

A model approach to assess the long-term trends of indirect photochemistry in lake water. The case of Lake Maggiore (NW Italy).

PubMed

Minella, Marco; Rogora, Michela; Vione, Davide; Maurino, Valter; Minero, Claudio

2011-08-15

A model-based approach is here developed and applied to predict the long-term trends of indirect photochemical processes in the surface layer (5m water depth) of Lake Maggiore, NW Italy. For this lake, time series of the main parameters of photochemical importance that cover almost two decades are available. As a way to assess the relevant photochemical reactions, the modelled steady-state concentrations of important photogenerated transients ((•)OH, ³CDOM* and CO₃(-•)) were taken into account. A multivariate analysis approach was adopted to have an overview of the system, to emphasise relationships among chemical, photochemical and seasonal variables, and to highlight annual and long-term trends. Over the considered time period, because of the decrease of the dissolved organic carbon (DOC) content of water and of the increase of alkalinity, a significant increase is predicted for the steady-state concentrations of the radicals (•)OH and CO₃(-•). Therefore, the photochemical degradation processes that involve the two radical species would be enhanced. Another issue of potential photochemical importance is related to the winter maxima of nitrate (a photochemical (•)OH source) and the summer maxima of DOC ((•)OH sink and ³CDOM* source) in the lake water under consideration. From the combination of sunlight irradiance and chemical composition data, one predicts that the processes involving (•)OH and CO₃(-•) would be most important in spring, while the reactions involving ³CDOM* would be most important in summer. Copyright © 2011 Elsevier B.V. All rights reserved.

Towards the elaboration of new gold-based optical theranostics.

PubMed

Doulain, Pierre-Emmanuel; Decréau, Richard; Racoeur, Cindy; Goncalves, Victor; Dubrez, Laurence; Bettaieb, Ali; Le Gendre, Pierre; Denat, Franck; Paul, Catherine; Goze, Christine; Bodio, Ewen

2015-03-21

Four new red BODIPY-gold(I) theranostic compounds were synthesized. Some of them were vectorized by tethering a biovector (glucose or bombesin derivatives) to the metallic center. Their photophysical properties were studied. Additionally, their cytotoxicity was examined on different cancer cell lines and on a normal cell line, they were tracked in vitro by fluorescence detection, and their uptake was evaluated by ICP-MS measurements.

Eddy mixing coefficient upper limit derived from the photochemical balance of O2

NASA Technical Reports Server (NTRS)

Rosenqvist, J.; Chassefiere, E.

1993-01-01

This work is based on the study of the photochemical balance of molecular oxygen in the martian atmosphere by using a one-dimensional model of photochemical reactions involving species derived from CO2 and H2O. The model is basically similar to one used previously for the study of the regulation of CO on a global scale, but the chemical rates are taken from another source. In the present scheme, the regulation of molecular oxygen is studied over timescales of the order of its photochemical lifetime (approximately equals 30 yr), which is much shorter than typical escape timescales. Thus, the escape fluxes are fixed to the values given by 3 and 4. We examine the calculated equilibrium abundances of O2 for given thermal, eddy diffusion coefficients and H2O profiles. The thermal profile is taken from in the lower atmosphere. At higher levels, in order to include the diurnal and seasonal thermal profile variability, we have also used the IRTM data. In order to study the influence of both temperature and pressure profiles on the O2 mixing ratio, we have made several tests corresponding to different martian seasons. The results show that the influence of pressure and temperature is quantitatively weak compared to the one of K and of the water vapor density (H2O). Thus, in the following we have fixed the pressure at the surface to a value of 7 mbar and we have used unique standard thermal profile corresponding to a profile roughly averaged over the year, the season, and the day: T equal 205 K at 0 km altitude, 175 K at 25 km, and 145 K at 50 km.

The Dynamics of the Photofragmentation of Ketene 3-Cyclopentenone, 3,5-Cycloheptadienone, and Tropone.

DTIC Science & Technology

1985-01-01

suggested that the concerted reaction should be allowed photochemically and the conrotatory mode should be favored. The data were in accord with this...crossing), or (4) reaction to form products, e.g., isomers or fragments, directly from the excited state. Further radiative, non-radiative, and photochemical ...processes can occur from intermediate excited states. Typical photochemical reactions observed in simple ketones in the gas phase are: (1) Norrish

1,2-diketones promoted degradation of poly(epsilon-caprolactone)

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

Danko, Martin; Borska, Katarina; Ragab, Sherif Shaban

2012-07-11

Photochemical reactions of Benzil and Camphorquinone were used for modification of poly({epsilon}-caprolactone) polymer films. Photochemistry of dopants was followed by infrared spectroscopy, changes on polymer chains of matrix were followed by gel permeation chromatography. Benzoyl peroxide was efficiently photochemically generated from benzyl in solid polymer matrix in the presence of air. Following decomposition of benzoyl peroxide led to degradation of matrix. Photochemical transformation of benzil in vacuum led to hydrogen abstraction from the polymer chains in higher extent, which resulted to chains recombination and formation of gel. Photochemical transformation of camphorquinone to corresponding camphoric peroxide was not observed. Only decreasemore » of molecular weight of polymer matrix doped with camphorquinone was observed during the irradiation.« less

Net ozone photochemical production over the eastern and central North Pacific as inferred from GTE/CITE 1 observations during fall 1983

NASA Technical Reports Server (NTRS)

Chameides, W. L.; Davis, D. D.; Rodgers, M. O.; Bradshaw, J.; Sandholm, S.; Sachse, G.; Hill, G.; Gregory, G.

1987-01-01

The role of photochemistry in the budget of tropospheric ozone is studied. Measurements of O3, NO, CO, H2O vapor, and temperature obtained during the fall of 1983 during the GTE/CITE project over the eastern and central North Pacific Ocean are analyzed. The effect of altitude on the measurements is discussed. The analysis reveals a correlation between ozone and NO levels; both increase in concentration and variability with altitude. It is observed that an additional source of secondary importance associated wih CO-rich air parcels exists. A photochemical model is utilized to calculate the net rate of ozone production by photochemical reactions. A net photochemical source of ozone in the free troposphere and a net sink in the boundary layer are detected. The relation between the ozone source in the free troposphere and NO is examined. It is estimated that photochemistry provides a net ozone source to the free troposphere overlying the eastern and central North Pacific Ocean of about 5 x 10 to the 10th molecules/sq cm sec and a net sink of ozone to the boundary layer overlying this region of about 3 x 10 to the 10th molecules/sq cm sec.

Volatile Organic Compounds from Logwood Combustion: Emissions and Transformation under Dark and Photochemical Aging Conditions in a Smog Chamber.

PubMed

Hartikainen, Anni; Yli-Pirilä, Pasi; Tiitta, Petri; Leskinen, Ari; Kortelainen, Miika; Orasche, Jürgen; Schnelle-Kreis, Jürgen; Lehtinen, Kari E J; Zimmermann, Ralf; Jokiniemi, Jorma; Sippula, Olli

2018-04-17

Residential wood combustion (RWC) emits high amounts of volatile organic compounds (VOCs) into ambient air, leading to formation of secondary organic aerosol (SOA), and various health and climate effects. In this study, the emission factors of VOCs from a logwood-fired modern masonry heater were measured using a Proton-Transfer-Reactor Time-of-Flight Mass Spectrometer. Next, the VOCs were aged in a 29 m 3 Teflon chamber equipped with UV black lights, where dark and photochemical atmospheric conditions were simulated. The main constituents of the VOC emissions were carbonyls and aromatic compounds, which accounted for 50%-52% and 30%-46% of the detected VOC emission, respectively. Emissions were highly susceptible to different combustion conditions, which caused a 2.4-fold variation in emission factors. The overall VOC concentrations declined considerably during both dark and photochemical aging, with simultaneous increase in particulate organic aerosol mass. Especially furanoic and phenolic compounds decreased, and they are suggested to be the major precursors of RWC-originated SOA in all aging conditions. On the other hand, dark aging produced relatively high amounts of nitrogen-containing organic compounds in both gas and particulate phase, while photochemical aging increased especially the concentrations of certain gaseous carbonyls, particularly acid anhydrides.

Photophysical and redox properties of molecule-like CdSe nanoclusters.

PubMed

Dolai, Sukanta; Dass, Amala; Sardar, Rajesh

2013-05-21

Advancing our understanding of the photophysical and electrochemical properties of semiconductor nanoclusters with a molecule-like HOMO-LUMO energy level will help lead to their application in photovoltaic devices and photocatalysts. Here we describe an approach to the synthesis and isolation of molecule-like CdSe nanoclusters, which displayed sharp transitions at 347 nm (3.57 eV) and 362 nm (3.43 eV) in the optical spectrum with a lower energy band extinction coefficient of ~121,000 M(-1) cm(-1). Mass spectrometry showed a single nanocluster molecular weight of 8502. From this mass and various spectroscopic analyses, the nanoclusters are determined to be of the single molecular composition Cd34Se20(SPh)28, which is a new nonstiochiometric nanocluster. Their reversible electrochemical band gap determined in Bu4NPF6/CH3CN was found to be 4.0 V. There was a 0.57 eV Coulombic interaction energy of the electron-hole pair involved. The scan rate dependent electrochemistry suggested diffusion-limited transport of nanoclusters to the electrode. The nanocluster diffusion coefficient (D = 5.4 × 10 (-4) cm(2)/s) in acetonitrile solution was determined from cyclic voltammetry, which suggested Cd34Se20(SPh)28 acts as a multielectron donor or acceptor. We also present a working model of the energy level structure of the newly discovered nanocluster based on its photophysical and redox properties.

Spectroscopic Analysis of Red Fluorescent Proteins and Development of a Microfluidic Cell Sorter for the Generation of Improved Variants

NASA Astrophysics Data System (ADS)

Lubbeck, Jennifer L.

The discovery of the green fluorescent protein (GFP) launched the development of a wide variety of fluorescent protein (FP) mutants whose spectral and photophysical diversity revolutionized in vivo imaging. The excitation and emission spectra of red fluorescent proteins (RFPs), in particular, have been ideally tuned to a window optically favorable for in vivo work. However, their quantum yields, photostabilities and fluorescence intermittency properties require improvement if they are to be broadly employed for low-copy or single-molecule measurements. Attempts to engineer improved RFPs often result in optimization of one photophysical property at the expense of others. We developed a microfluidic-based cytometer for screening HeLa cell-based genetic RFP-libraries simultaneously on the basis of fluorescence lifetime (a proxy for quantum yield), photostability, and brightness. Ten 532 nm excitation beams interrogate each cell in flow. The first is electro-optically modulated (30 MHz) to enable lifetime measurement with phase fluorimetry. The remaining beams act as a pulse sequence for isolating the irreversible photobleaching time constant. Optical-force switching is employed to sort cells based on any combination of the photophysical parameters. Screening with this instrument enables identification of regions of the structure that synergistically affect quantum yield and photostability and the sorting capability provides a new tool for accelerating the development of next generation RFPs.

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.

Self-organization, interfacial interaction and photophysical properties of gold nanoparticle complexes derived from resilin-mimetic fluorescent protein rec1-resilin.

PubMed

Mayavan, Sundar; Dutta, Naba K; Choudhury, Namita R; Kim, Misook; Elvin, Christopher M; Hill, Anita J

2011-04-01

In this investigation we report the synthesis of optically coupled hybrid architectures based on a new biomimetic fluorescent protein rec1-resilin and nanometer-scale gold nanoparticles (AuNPs) in a one-step method using a non-covalent mode of binding protocol. The presence of uniformly distributed fluorophore sequences, -Ser(Thr)-Tyr-Gly- along the molecular structure of rec1-resilin provides significant opportunity to synthesize fluorophore-modified AuNPs bioconjugates with unique photophysical properties. The detailed analyses of the AuNP-bioconjugates, synthesized under different experimental conditions using spectroscopic, microscopic and scattering techniques demonstrate the organizational pathways and the electronic and photophysical properties of the developed AuNP-rec1-resilin bioconjugates. The calculation of the bimolecular quenching constant using the Stern-Volmer equation confirms that the dominant mechanism involved in quenching of fluorescence of rec1-resilin in the presence of AuNP is static. Photoacoustic infrared spectroscopy was employed to understand the nature of the interfacial interaction between the AuNP and rec1-resilin and its evolution with pH. In such bioconjugates the quenched emission of fluorescence by AuNP on the fluorophore moiety of rec1-resilin in the immediate vicinity of the AuNP has significant potential for fluorescence-based detection schemes, sensors and also can be incorporated into nanoparticle-based devices. Copyright © 2011 Elsevier Ltd. All rights reserved.

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.

Photophysics and Photochemistry

ERIC Educational Resources Information Center

Letokhov, V. S.

1977-01-01

Discusses recent progress in using tunable lasers to selectively separate substances at the atomic and molecular level. Emphasizes biological applications, such as selective excitation and breaking of hydrogen bonds in DNA. (MLH)

Degradation of two fluoroquinolone antibiotics photoinduced by Fe(III)-microalgae suspension in an aqueous solution.

PubMed

Ge, Liyun; Deng, Huanhuan

2015-04-01

The widespread presence of fluoroquinolone antibiotics (FQs) in natural ecosystems is a health hazard for humans and other living organisms. In this work, the photochemical degradation process of two antibiotics in the presence of Fe(III) and marine microalgae has been studied. Two fluoroquinolone (FQ) antibiotics, enrofloxacin (ENR) and ciprofloxacin hydrochloride (CIP), and two marine microalgae, Platymonas subcordiformis and Isochrysis galbana, were investigated under irradiation with a high-pressure mercury lamp (HPML) in a laboratory-scale experiment. The effects of the initial concentration of antibiotics on the degradation of these two FQs in Fe(III)-algae suspensions were also investigated. On the basis of the information in this study, compared to other systems, the efficiency of photo-degradation of the two FQs is better at lower FQ concentrations in the Fe(III)-algae system. Moreover, the low initial concentration of antibiotics benefits the photochemical process of antibiotics. This work demonstrated that the Fe(III)-algae system is an interesting and valuable research area and could be considered as a promising photochemical system for seawater remediation.

Atmospheric origins of perchlorate on Mars and in the Atacama

NASA Astrophysics Data System (ADS)

Catling, D. C.; Claire, M. W.; Zahnle, K. J.; Quinn, R. C.; Clark, B. C.; Hecht, M. H.; Kounaves, S.

2010-01-01

Isotopic studies indicate that natural perchlorate is produced on Earth in arid environments by the oxidation of chlorine species through pathways involving ozone or its photochemical products. With this analogy, we propose that the arid environment on Mars may have given rise to perchlorate through the action of atmospheric oxidants. A variety of hypothetical pathways can be proposed including photochemical reactions, electrostatic discharge, and gas-solid reactions. Because perchlorate-rich deposits in the Atacama desert are closest in abundance to perchlorate measured at NASA's Phoenix Lander site, we made a preliminary study of the means to produce Atacama perchlorate to help shed light on the origin of Martian perchlorate. We investigated gas phase pathways using a 1-D photochemical model. We found that perchlorate can be produced in sufficient quantities to explain the abundance of perchlorate in the Atacama from a proposed gas phase oxidation of chlorine volatiles to perchloric acid. The feasibility of gas phase production for the Atacama provides justification for future investigations of gas phase photochemistry as a possible source for Martian perchlorate.

Photophysical studies on the interaction of acridinedione dyes with universal protein denaturant: guanidine hydrochloride.

PubMed

Kumaran, R; Varalakshmi, T; Malar, E J Padma; Ramamurthy, P

2010-09-01

Photophysical studies of photoinduced electron transfer (PET) and non-PET based acridinedione dyes with guanidine hydrochloride (GuHCl) were carried out in water and methanol. Addition of GuHCl to photoinduced electron transfer (PET) based acridinedione dye (ADR 1) results in a fluorescence enhancement, whereas a non-PET based dye (ADR 2) shows no significant change in the fluorescence intensity and lifetime. Addition of GuHCl to ADR 1 dye in methanol results in single exponential decay behaviour, on the contrary a biexponential decay pattern was observed on the addition of GuHCl in water. Absorption and emission spectral studies of ADR 1 dye interaction with GuHCl reveals that the dye molecule is not in the protonated form in aqueous GuHCl solution, and the dye is confined to two distinguishable microenvironment in the aqueous phase. A large variation in the microenvironment around the dye molecule is created on the addition of GuHCl and this was ascertained by time-resolved area normalized emission spectroscopy (TRANES) and time-resolved emission spectroscopy (TRES). The dye molecule prefers to reside in the hydrophobic microenvironment, rather in the hydrophilic aqueous phase is well emphasized by time-resolved fluorescence lifetime studies. The mechanism of fluorescence enhancement of ADR 1 dye by GuHCl is attributed to the suppression of the PET process occurring through space.

Fluorescence Microscopy of Single Molecules

ERIC Educational Resources Information Center

Zimmermann, Jan; van Dorp, Arthur; Renn, Alois

2004-01-01

The investigation of photochemistry and photophysics of individual quantum systems is described with the help of a wide-field fluorescence microscopy approach. The fluorescence single molecules are observed in real time.

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.

Investigation of the Photochemical Method for Uranium Isotope Separation

DOE R&D Accomplishments Database

Urey, H. C.

1943-07-10

To find a process for successful photochemical separation of isotopes several conditions have to be fulfilled. First, the different isotopes have to show some differences in the spectrum. Secondly, and equally important, this difference must be capable of being exploited in a photochemical process. Parts A and B outline the physical and chemical conditions, and the extent to which one might expect to find them fulfilled. Part C deals with the applicability of the process.

IV INTERNATIONAL CONFERENCE ON ATOM AND MOLECULAR PULSED LASERS (AMPL'99): Radiative and photochemical properties of organic compounds excited by high-power XeCl laser radiation

NASA Astrophysics Data System (ADS)

Kopylova, T. N.; Kuznetsova, Rimma T.; Svetlichnyi, Valerii A.; Sergeev, A. K.; Tel'minov, E. N.; Filinov, D. N.

2000-06-01

Radiative and photochemical properties of a number of laser dyes excited by focused radiation of a XeCl laser with intensity up to 200 MW cm-2 were studied. A method for measuring the gain of organic molecules under high-power excitation is proposed. The dependence of the dye transmittance for the pump radiation on its intensity was studied. It is shown that changes in energy, spectral, and time characteristics of radiation and the photostability of compounds under high-power excitation are associated with the formation of superluminescence.

Problem of photochemical equilibrium of ozone in planetary atmospheres: Ozone distribution in the lower atmosphere of Mars

NASA Technical Reports Server (NTRS)

Grams, G. W.; SHARDANAND

1972-01-01

The inherent errors of applying terrestrial atmospheric ozone distribution studies to the atmosphere of other planets are discussed. Limitations associated with some of the earlier treatments of photochemical equilibrium distributions of ozone in planetary atmospheres are described. A technique having more universal application is presented. Ozone concentration profiles for the Martian atmosphere based on the results of the Mariner 4 radio occultation experiment and the more recent results with Mariner 6 and Mariner 7 have been calculated using this approach.

Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies Evaluation Number 16. Supplement to Evaluation 15: Update of Key Reactions

NASA Technical Reports Server (NTRS)

Sander, S. P.; Friedl, R. R.; Barker, J. R.; Golden, D. M.; Kurylo, M. J.; Wine, P. H.; Abbatt, J.; Burkholder, J. B.; Kolb, C. E.; Moortgat, G. K.;

Construction of a photochemical reactor combining a CCD spectrophotometer and a LED radiation source.

PubMed

Gombár, Melinda; Józsa, Éva; Braun, Mihály; Ősz, Katalin

2012-10-01

An inexpensive photoreactor using LED light sources and a fibre-optic CCD spectrophotometer as a detector was built by designing a special cell holder for standard 1.000 cm cuvettes. The use of this device was demonstrated by studying the aqueous photochemical reaction of 2,5-dichloro-1,4-benzoquinone. The developed method combines the highly quantitative data collection of CCD spectrophotometers with the possibility of illuminating the sample independently of the detecting light beam, which is a substantial improvement of the method using diode array spectrophotometers as photoreactors.

Photochemical Approaches to Complex Chemotypes: Applications in Natural Product Synthesis.

PubMed

Kärkäs, Markus D; Porco, John A; Stephenson, Corey R J

2016-09-14

The use of photochemical transformations is a powerful strategy that allows for the formation of a high degree of molecular complexity from relatively simple building blocks in a single step. A central feature of all light-promoted transformations is the involvement of electronically excited states, generated upon absorption of photons. This produces transient reactive intermediates and significantly alters the reactivity of a chemical compound. The input of energy provided by light thus offers a means to produce strained and unique target compounds that cannot be assembled using thermal protocols. This review aims at highlighting photochemical transformations as a tool for rapidly accessing structurally and stereochemically diverse scaffolds. Synthetic designs based on photochemical transformations have the potential to afford complex polycyclic carbon skeletons with impressive efficiency, which are of high value in total synthesis.

Effect of chemical kinetics uncertainties on calculated constituents in a tropospheric photochemical model

NASA Technical Reports Server (NTRS)

Thompson, Anne M.; Stewart, Richard W.

1991-01-01

Random photochemical reaction rates are employed in a 1D photochemical model to examine uncertainties in tropospheric concentrations and thereby determine critical kinetic processes and significant correlations. Monte Carlo computations are used to simulate different chemical environments and their related imprecisions. The most critical processes are the primary photodissociation of O3 (which initiates ozone destruction) and NO2 (which initiates ozone formation), and the OH/methane reaction is significant. Several correlations and anticorrelations between species are discussed, and the ozone/transient OH correlation is examined in detail. One important result of the modeling is that estimates of global OH are generally about 25 percent uncertain, limiting the precision of photochemical models. Techniques for reducing the imprecision are discussed which emphasize the use of species and radical species measurements.

Photovoltaic Effects and Charge Transport Studies in Phycobiliproteins

DTIC Science & Technology

1993-06-30

phycobilins are shown in Figure 1. Phycoerythrin (PE). phycocyanin (PC) and allophycocyanin (APC) are the individual biliproteins that self-assemble to form... phycocyanin and (b) phycocrythrin. thin films. The dark current-voltage (I-V) characteristics of ihc Au-proicin-Au samples were determined prior to optical...understanding of the potcnial or thc.sc proteins in device applications and may lead to a more fundamental appreciation of the biochemistry and photophysics of

2-(Alkylamino)-3-aryl-6,7-dihydrobenzofuran-4(5H)-ones: Improved Synthesis and their Photophysical Properties

PubMed Central

Kumar, Manoj; Kumawat, Lokesh Kumar; Gupta, Vinod Kumar; Sharma, Anuj

2015-01-01

Furans are an important class of compounds and exhibit a diverse range of activities and properties. As such, improved synthetic access to furans is an important research goal. In the present report, a solvent- and catalyst-free reaction between 5,5-dimethyl-1,3-cyclohexanedione (dimedone), an aryl aldehyde and an isocyanide under microwave irradiation is presented. This method is significantly improved from previously described protocols in terms of applicability of wide ranging aryl aldehydes, better yields, shorter reaction times, facile work up and essentially no need of column chromatography. The photophysical properties of this series of compounds were studied for their possible applicability in the field of metal ion sensors. In solution, two compounds, 2-(cyclohexylamino)-3-(1H-indol-3-yl)-6,6-dimethyl-6,7-dihydrobenzofuran-4(5H)-one (1 i) and 2-(tert-butylamino)-3-(1H-indol-3-yl)-6,6-dimethyl-6,7-dihydrobenzofuran-4(5H)-one (1 j), underwent an observable color change from yellow to colorless in the presence of aluminum(III) ions. Further studies to investigate the UV absorption and luminescence behavior of these compounds revealed their utility as “naked-eye sensors” for aluminum detection. PMID:26491643

Photophysics of sunscreen molecules in the gas phase: a stepwise approach towards understanding and developing next-generation sunscreens

PubMed Central

Rodrigues, Natércia D. N.; Staniforth, Michael

2016-01-01

The relationship between exposure to ultraviolet (UV) radiation and skin cancer urges the need for extra photoprotection, which is presently provided by widespread commercially available sunscreen lotions. Apart from having a large absorption cross section in the UVA and UVB regions of the electromagnetic spectrum, the chemical absorbers in these photoprotective products should also be able to dissipate the excess energy in a safe way, i.e. without releasing photoproducts or inducing any further, harmful, photochemistry. While sunscreens are tested for both their photoprotective capability and dermatological compatibility, phenomena occurring at the molecular level upon absorption of UV radiation are largely overlooked. To date, there is only a limited amount of information regarding the photochemistry and photophysics of these sunscreen molecules. However, a thorough understanding of the intrinsic mechanisms by which popular sunscreen molecular constituents dissipate excess energy has the potential to aid in the design of more efficient, safer sunscreens. In this review, we explore the potential of using gas-phase frequency- and time-resolved spectroscopies in an effort to better understand the photoinduced excited-state dynamics, or photodynamics, of sunscreen molecules. Complementary computational studies are also briefly discussed. Finally, the future outlook of expanding these gas-phase studies into the solution phase is considered. PMID:27956888

Photophysics of sunscreen molecules in the gas phase: a stepwise approach towards understanding and developing next-generation sunscreens

NASA Astrophysics Data System (ADS)

Rodrigues, Natércia D. N.; Staniforth, Michael; Stavros, Vasilios G.

2016-11-01

The relationship between exposure to ultraviolet (UV) radiation and skin cancer urges the need for extra photoprotection, which is presently provided by widespread commercially available sunscreen lotions. Apart from having a large absorption cross section in the UVA and UVB regions of the electromagnetic spectrum, the chemical absorbers in these photoprotective products should also be able to dissipate the excess energy in a safe way, i.e. without releasing photoproducts or inducing any further, harmful, photochemistry. While sunscreens are tested for both their photoprotective capability and dermatological compatibility, phenomena occurring at the molecular level upon absorption of UV radiation are largely overlooked. To date, there is only a limited amount of information regarding the photochemistry and photophysics of these sunscreen molecules. However, a thorough understanding of the intrinsic mechanisms by which popular sunscreen molecular constituents dissipate excess energy has the potential to aid in the design of more efficient, safer sunscreens. In this review, we explore the potential of using gas-phase frequency- and time-resolved spectroscopies in an effort to better understand the photoinduced excited-state dynamics, or photodynamics, of sunscreen molecules. Complementary computational studies are also briefly discussed. Finally, the future outlook of expanding these gas-phase studies into the solution phase is considered.

Triphenylamine Derived 3-Acetyl and 3-Benzothiazolyl Bis and Tris Coumarins: Synthesis, Photophysical and DFT Assisted Hyperpolarizability Study

NASA Astrophysics Data System (ADS)

Erande, Yogesh; Kothavale, Shantaram; Sreenath, Mavila C.; Chitrambalam, Subramaniyan; Joe, Isaac H.; Sekar, Nagaiyan

2018-02-01

Triphenylamine derived bis- and tris-branched donor-pi-acceptor coumarins with acetyl and benzothiazolyl acceptors are studied for their linear and nonlinear optical properties that originate from their photophysical and molecular structure. Plots of solvent polarities versus the Stokes shift, frontier molecular orbital analysis and Generalised Mulliken Hush analysis have established their strong charge transfer character supported by the strong emission solvatochromism of these chromophores. On the basis of excited state intramolecular charge transfer, the first-, second- and third-order polarizability of these dyes are determined by a solvatochromic method and supported by density functional theory calculations using CAM-B3LYP/6-31g(d). Compared to the acetyl group, the benzothiazolyl group is a strong acceptor, and its corresponding derivatives show enhanced absorption, emission maxima and non-linear optical response. Bond length alternation and bond order alternation analysis reveals that these chromophores approach the cyanine-like framework which is responsible for maximum perturbation to produce high nonlinear optical response. Third order nonlinear susceptibility for dyes 1 and 2 is determined by Z-scan measurement. All of these methods are used to determine the nonlinear optical properties, and thermogravimetric analysis suggests that these chromophores are thermally robust and efficient nonlinear optical materials.

Anion dependent self-assembly of 56-metal Cd-Ln nanoclusters with enhanced near-infrared luminescence properties

NASA Astrophysics Data System (ADS)

Yang, Xiaoping; Schipper, Desmond; Zhang, Lijie; Yang, Keqin; Huang, Shaoming; Jiang, Jijun; Su, Chengyong; Jones, Richard A.

2014-08-01

Two series of Cd-Ln clusters: nano-drum [Ln8Cd24L12(OAc)48] and nano-double-drum [Ln12Cd44L20Cl30(OAc)54] (Ln = Nd and Yb) were prepared using a flexible Schiff base ligand bearing two aryl-Br groups. Chloride (Cl-) ions, together with the interactions of Br with other electronegative atoms, play a key role in the formation of the nano-double-drums. The structures were studied by TEM and photophysical properties were determined.Two series of Cd-Ln clusters: nano-drum [Ln8Cd24L12(OAc)48] and nano-double-drum [Ln12Cd44L20Cl30(OAc)54] (Ln = Nd and Yb) were prepared using a flexible Schiff base ligand bearing two aryl-Br groups. Chloride (Cl-) ions, together with the interactions of Br with other electronegative atoms, play a key role in the formation of the nano-double-drums. The structures were studied by TEM and photophysical properties were determined. Electronic supplementary information (ESI) available: Full experimental and characterization details for 1-4. CCDC 972369-972372. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4nr03075c

Evaluation of Data Used for Modelling the Stratosphere of Saturn

NASA Astrophysics Data System (ADS)

Armstrong, Eleanor Sophie; Irwin, Patrick G. J.; Moses, Julianne I.

2015-11-01

Planetary atmospheres are modeled through the use of a photochemical and kinetic reaction scheme constructed from experimentally and theoretically determined rate coefficients, photoabsorption cross sections and branching ratios for the molecules described within them. The KINETICS architecture has previously been developed to model planetary atmospheres and is applied here to Saturn’s stratosphere. We consider the pathways that comprise the reaction scheme of a current model, and update the reaction scheme according the to findings in a literature investigation. We evaluate contemporary photochemical literature, studying recent data sets of cross-sections and branching ratios for a number of hydrocarbons used in the photochemical scheme of Model C of KINETICS. In particular evaluation of new photodissociation branching ratios for CH4, C2H2, C2H4, C3H3, C3H5 and C4H2, and new cross-sectional data for C2H2, C2H4, C2H6, C3H3, C4H2, C6H2 and C8H2 are considered. By evaluating the techniques used and data sets obtained, a new reaction scheme selection was drawn up. These data are then used within the preferred reaction scheme of the thesis and applied to the KINETICS atmospheric model to produce a model of the stratosphere of Saturn in a steady state. A total output of the preferred reaction scheme is presented, and the data is compared both with the previous reaction scheme and with data from the Cassini spacecraft in orbit around Saturn.One of the key findings of this work is that there is significant change in the model’s output as a result of temperature dependent data determination. Although only shown within the changes to the photochemical portion of the preferred reaction scheme, it is suggested that an equally important temperature dependence will be exhibited in the kinetic section of the reaction scheme. The photochemical model output is shown to be highly dependent on the preferred reaction scheme used within it by this thesis. The importance of correct and temperature-appropriate photochemical and kinetic data for the atmosphere under examination is emphasised as a consequence.

Utilization of UARS Data in Validation of Photochemical and Dynamical Mechanisms in Stratospheric Models

NASA Technical Reports Server (NTRS)

Ko, M. K. W.; Rodriquez, J. M.; Hu, W.; Danilin, M. Y.; Shia, R.-L.

1998-01-01

The proposed work utilized Upper Atmosphere Research Satellite (UARS) measurements of short-lived and long-lived species, in conjunction with existing photochemical "box" models, trajectory models, and two-dimensional global models, to elucidate outstanding questions in our understanding of photochemical and dynamical mechanisms in the stratosphere. Particular emphasis was given to arriving at the best possible understanding of the chemical and dynamical contributions to the stratospheric ozone budget. Such understanding will increase confidence in the simulations carried out by assessment models.

Utilization of UARS Data in Validation of Photochemical and Dynamical Mechanisms in Stratospheric Models

NASA Technical Reports Server (NTRS)

Ko, Malcolm K. W.; Rodriquez, Jose M.; Hu, Wenjie; Danilin, Michael Y.; Shia, Run-Li

1998-01-01

The proposed work utilized Upper Atmosphere Research Satellite (UARS) measurements of short-lived and long-lived species, in conjunction with existing photochemical "box" models, trajectory models, and two-dimensional global models, to elucidate outstanding questions in our understanding of photochemical and dynamical mechanisms in the stratosphere. Particular emphasis was given to arriving at the best possible understanding of the chemical and dynamical contribution to the stratospheric ozone budget. Such understanding will increase confidence in the simulations carried out by assessment models.

Upper atmosphere research: Reaction rate and optical measurements

NASA Technical Reports Server (NTRS)

Stief, L. J.; Allen, J. E., Jr.; Nava, D. F.; Payne, W. A., Jr.

1990-01-01

The objective is to provide photochemical, kinetic, and spectroscopic information necessary for photochemical models of the Earth's upper atmosphere and to examine reactions or reactants not presently in the models to either confirm the correctness of their exclusion or provide evidence to justify future inclusion in the models. New initiatives are being taken in technique development (many of them laser based) and in the application of established techniques to address gaps in the photochemical/kinetic data base, as well as to provide increasingly reliable information.

Engineering Designed Proteins for Light Capture, Energy Transfer, and Emissive Sensing In Vivo

NASA Astrophysics Data System (ADS)

Mancini, Joshua A.

Proteins that are used for photosynthetic light harvesting and biological signaling are critical to life. These types of proteins act as scaffolds that hold small, sometimes metal-containing organic molecules in precise locations for light absorption and successive use. For signaling proteins, this energy can be used to induce a photoisomerization of the small molecule that can turn on or off a signaling cascade that controls the physiology of an organism. Alternatively, photosynthetic light-harvesting proteins funnel this energy in a directional manner towards a charge separating catalytic component that can change this light energy into chemical energy. The protein environment also serves to tune the photophysical properties of the small molecules. This is seen extensively with the linear tetrapyrroles that are used in both photosynthetic and signaling proteins. Many efforts have been made to harness these natural proteins for societal use, including improving photophysical properties and interfacing capabilities with manmade catalytic components. Several methods of achieving improvement have entailed structurally guided mutation and directed evolution. However, these methods all have their limitations due to the inherent complexity and fragility of the natural proteins. This work presents an alternative more robust method to natural proteins. My thesis states: that man-made proteins, known as maquettes, employing basic rules of protein folding, can be designed to become light harvesting and signaling proteins that can be assembled fully in vivo providing an alternative, robust, and versatile platform for meeting the diverse array of societal "green chemistry" and biomedical needs. This in vivo assembly is carried out by interacting with cyanobacterial protein and pigment machinery, both as stand-alone units and as protein fusions with natural antenna complexes. Additionally, this work offers insight for fast and tight binding of circular and linear tetrapyrroles to the maquettes both in vitro and in vivo. Design principles are also established for increasing the amount of linear tetrapyrrole attachment to the maquette as well as modulating their photophysical properties. Fast and tight binding of cofactors, high cofactor attachment yields, and control of cofactor photophysical properties are all prerequisites for the maquettes to be successful in vivo photosynthetic light harvesting and signaling proteins.