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Sample records for oligophenylenes

  1. Quinoxaline-Based Cyclo(oligophenylenes).

    PubMed

    Marin, Lidia; Kudrjasova, Julija; Verstappen, Pieter; Penxten, Huguette; Robeyns, Koen; Lutsen, Laurence; Vanderzande, Dirk J M; Maes, Wouter

    2015-02-20

    A series of fully conjugated quinoxaline-based oligophenylene macrocycles is synthesized by Ni(0)-mediated Yamamoto-type diaryl homocoupling of (fluorinated) 2,3-bis(4'-bromophenyl)quinoxaline precursors. Cyclotrimers and cyclotetramers are obtained as the dominant reaction products. The cyclooligomers are fully characterized, including single-crystal X-ray structures, and their optoelectronic properties are analyzed with respect to possible applications in host-guest chemistry and organic electronics.

  2. Repetitive synthetic method for o,o,p-oligophenylenes using C-H arylation.

    PubMed

    Manabe, Kei; Kimura, Takeshi

    2013-01-18

    A synthetic method for the preparation of o,o,p-oligophenylenes has been developed. It involves Miura's C-H arylation of 2-biphenols with aryl nonaflates as the key step. Oligophenylenes with defined lengths are successfully synthesized using this method. PMID:23289430

  3. Aggregates of a hetero-oligophenylene derivative as reactors for the generation of palladium nanoparticles: a potential catalyst in the Sonogashira coupling reaction under aerial conditions.

    PubMed

    Walia, Preet Kamal; Pramanik, Subhamay; Bhalla, Vandana; Kumar, Manoj

    2015-12-18

    The utilization of Pd nanoparticles stabilized by aggregates of hetero-oligophenylene derivative 3 as an excellent catalyst in a copper/amine free Sonogashira coupling reaction under aerial conditions at room temperature has been demonstrated. PMID:26460180

  4. Long-Range Ruthenium-Amine Electronic Communication through the para-Oligophenylene Wire

    PubMed Central

    Shen, Jun-Jian; Zhong, Yu-Wu

    2015-01-01

    The studies of long-range electronic communication are hampered by solubility and potential-splitting issues. A “hybridized redox-asymmetry” method using a combination of organic and inorganic redox species is proposed and exemplified to overcome these two issues. Complexes 1(PF6)–6(PF6) (from short to long in length) with the organic redox-active amine and inorganic cyclometalated ruthenium termini bridged by the para-oligophenylene wire have been prepared. Complex 6 has the longest Ru-amine geometrical distance of 27.85 Å. Complexes 3(PF6) and 4(PF6) show lamellar crystal packing on the basis of a head-to-tail anti-parallelly aligned dimeric structure. Two redox waves are observed for all complexes in the potential region between +0.2 and +0.9 V vs Ag/AgCl. The electrochemical potential splitting is 410, 220, 143, 112, 107, and 105 mV for 1(PF6) through 6(PF6), respectively. Ruthenium (+2) to aminium (N•+) charge transfer transitions have been identified for the odd-electron compounds 12+–62+ by spectroelectrochemical measurements. The electronic communication between amine and ruthenium decreases exponentially with a decay slope of −0.137 Å−1. DFT calculations have been performed to complement these experimental results. PMID:26344929

  5. Conformation-controlled electron transport in single-molecule junctions containing oligo(phenylene ethynylene) derivatives.

    PubMed

    Wang, Le-Jia; Yong, Ai; Zhou, Kai-Ge; Tan, Lin; Ye, Jian; Wu, Guo-Ping; Xu, Zhu-Guo; Zhang, Hao-Li

    2013-08-01

    Understanding the relationships between the molecular structure and electronic transport characteristics of single-molecule junctions is of fundamental and technological importance for future molecular electronics. Herein, we report a combined experimental and theoretical study on the single-molecule conductance of a series of oligo(phenylene ethynylene) (OPE) molecular wires, which consist of two phenyl-ethynyl-phenyl π units with different dihedral angles. The molecular conductance was studied by scanning tunneling microscopy (STM)-based break-junction techniques under different conditions, including variable temperature and bias potential, which suggested that a coherent tunneling mechanism takes place in the OPE molecular wires with a length of 2.5 nm. The conductance of OPE molecular junctions are strongly affected by the coupling strength between the two π systems, which can be tuned by controlling their intramolecular conformation. A cos(2)θ dependence was revealed between the molecular conductance and dihedral angles between the two conjugated units. Theoretical investigations on the basis of density functional theory and nonequilibrium Green's functions (NEGF) gave consistent results with the experimental observations and provided insights into the conformation-dominated molecular conductance.

  6. Long-Range Ruthenium-Amine Electronic Communication through the para-Oligophenylene Wire

    NASA Astrophysics Data System (ADS)

    Shen, Jun-Jian; Zhong, Yu-Wu

    2015-09-01

    The studies of long-range electronic communication are hampered by solubility and potential-splitting issues. A “hybridized redox-asymmetry” method using a combination of organic and inorganic redox species is proposed and exemplified to overcome these two issues. Complexes 1(PF6)-6(PF6) (from short to long in length) with the organic redox-active amine and inorganic cyclometalated ruthenium termini bridged by the para-oligophenylene wire have been prepared. Complex 6 has the longest Ru-amine geometrical distance of 27.85 Å. Complexes 3(PF6) and 4(PF6) show lamellar crystal packing on the basis of a head-to-tail anti-parallelly aligned dimeric structure. Two redox waves are observed for all complexes in the potential region between +0.2 and +0.9 V vs Ag/AgCl. The electrochemical potential splitting is 410, 220, 143, 112, 107, and 105 mV for 1(PF6) through 6(PF6), respectively. Ruthenium (+2) to aminium (N•+) charge transfer transitions have been identified for the odd-electron compounds 12+-62+ by spectroelectrochemical measurements. The electronic communication between amine and ruthenium decreases exponentially with a decay slope of -0.137 Å-1. DFT calculations have been performed to complement these experimental results.

  7. Cyclometalated Osmium-Amine Electronic Communication through the p-Oligophenylene Wire.

    PubMed

    Shen, Jun-Jian; Shao, Jiang-Yang; Gong, Zhong-Liang; Zhong, Yu-Wu

    2015-11-16

    A series of bis-tridentate cyclometalated osmium complexes with a redox-active triarylamine substituent have been prepared, where the amine substituent is separated from the osmium ion by a p-oligophenylene wire of various lengths. X-ray crystallographic data of complexes 3(PF6) and 4(PF6) with three or four repeating phenyl units between the osmium ion and the amine substituent are presented. These complexes show two consecutive anodic redox couples between +0.1 and +0.9 V vs Ag/AgCl, with the potential splitting in the range of 300-390 mV. A combined experimental and theoretical study suggests that, in the one-electron-oxidized state, the odd electron is delocalized for short congeners and localized on the osmium component for long congeners. The electronic coupling parameter (Vab) was estimated by the Marcus-Hush analysis. The distance dependence plot of ln(Vab) versus the osmium-amine geometrical distance (Rab) gives a negative linear relationship with a decay slope of -0.19 Å(-1), which is slightly steeper with respect to the previously reported ruthenium-amine series with the same molecular wire. DFT calculations with the long-range-corrected UCAM-B3LYP functional gave more reasonable results for the osmium complexes with respect to those with UB3LYP. PMID:26567859

  8. Folding-induced modulation of excited-state dynamics in an oligophenylene-ethynylene-tethered spiral perylene bisimide aggregate.

    PubMed

    Son, Minjung; Fimmel, Benjamin; Dehm, Volker; Würthner, Frank; Kim, Dongho

    2015-06-01

    The excited-state photophysical behavior of a spiral perylene bisimide (PBI) folda-octamer (F8) tethered to an oligophenylene-ethynylene scaffold is comprehensively investigated. Solvent-dependent UV/Vis and fluorescence studies reveal that the degree of folding in this foldamer is extremely sensitive to the solvent, thus giving rise to an extended conformation in CHCl(3) and a folded helical aggregate in methylcyclohexane (MCH). The exciton-deactivation dynamics are largely governed by the supramolecular structure of F8. Femtosecond transient absorption (TA) in the near-infrared region indicates a photoinduced electron-transfer process from the backbone to the PBI core in the extended conformation, whereas excitation power- and polarization-dependent TA measurements combined with computational modeling showed that excitation energy transfer between the unit PBI chromophores is the major deactivation pathway in the folded counterpart. PMID:25827823

  9. Facile Decoration of Multiwalled Carbon Nanotubes with Hetero-oligophenylene Stabilized-Gold Nanoparticles: Visible Light Photocatalytic Degradation of Rhodamine B Dye.

    PubMed

    Kaur, Sharanjeet; Bhalla, Vandana; Kumar, Manoj

    2015-08-01

    A hetero-oligophenylene derivative 3 has been designed and synthesized which forms fluorescent spherical aggregates in mixed aqueous media due to its aggregation-induced emission enhancement characteristics. These fluorescent aggregates act as a ratiometric probe for the detection of gold ions in aqueous media and serve as reactors and stabilizers for the preparation of gold nanoparticles. The in situ generated gold nanoparticles have been decorated on multiwalled carbon nanotubes to form AuNPs@MWCNTs nanohybrid materials, which serve as recyclable photocatalysts for carrying out degradation of rhodamine dye in aqueous media.

  10. Experimental and Theoretical Analysis of Nanotransport in Oligophenylene Dithiol Junctions as a Function of Molecular Length and Contact Work Function.

    PubMed

    Xie, Zuoti; Bâldea, Ioan; Smith, Christopher E; Wu, Yanfei; Frisbie, C Daniel

    2015-08-25

    We report the results of an extensive investigation of metal-molecule-metal tunnel junctions based on oligophenylene dithiols (OPDs) bound to several types of electrodes (M1-S-(C6H4)n-S-M2, with 1 ≤ n ≤ 4 and M1,2 = Ag, Au, Pt) to examine the impact of molecular length (n) and metal work function (Φ) on junction properties. Our investigation includes (1) measurements by scanning Kelvin probe microscopy of electrode work function changes (ΔΦ = ΦSAM - Φ) caused by chemisorption of OPD self-assembled monolayers (SAMs), (2) measurements of junction current-voltage (I-V) characteristics by conducting probe atomic force microscopy in the linear and nonlinear bias ranges, and (3) direct quantitative analysis of the full I-V curves. Further, we employ transition voltage spectroscopy (TVS) to estimate the energetic alignment εh = EF - EHOMO of the dominant molecular orbital (HOMO) relative to the Fermi energy EF of the junction. Where photoelectron spectroscopy data are available, the εh values agree very well with those determined by TVS. Using a single-level model, which we justify via ab initio quantum chemical calculations at post-density functional theory level and additional UV-visible absorption measurements, we are able to quantitatively reproduce the I-V measurements in the whole bias range investigated (∼1.0-1.5 V) and to understand the behavior of εh and Γ (contact coupling strength) extracted from experiment. We find that Fermi level pinning induced by the strong dipole of the metal-S bond causes a significant shift of the HOMO energy of an adsorbed molecule, resulting in εh exhibiting a weak dependence with the work function Φ. Both of these parameters play a key role in determining the tunneling attenuation factor (β) and junction resistance (R). Correlation among Φ, ΔΦ, R, transition voltage (Vt), and εh and accurate simulation provide a remarkably complete picture of tunneling transport in these prototypical molecular junctions.

  11. Curved Oligophenylenes as Donors in Shape-Persistent Donor-Acceptor Macrocycles with Solvatofluorochromic Properties.

    PubMed

    Kuwabara, Takuya; Orii, Jun; Segawa, Yasutomo; Itami, Kenichiro

    2015-08-10

    Many optoelectronic organic materials are based on donor-acceptor (D-A) systems with heteroatom-containing electron donors. Herein, we introduce a new molecular design for all-carbon curved oligoparaphenylenes as donors, which results in the generation of unique shape-persistent D-A macrocycles. Two types of acceptor-inserted cycloparaphenylenes were synthesized. These macrocycles display positive solvatofluorochromic properties owing to their D-A characteristics, which were confirmed by theoretical and electrochemical studies. PMID:26140706

  12. Two-level spatial modulation of vibronic conductance in conjugated oligophenylenes on boron nitride.

    PubMed

    Palma, Carlos-Andres; Joshi, Sushobhan; Hoh, Tobias; Ecija, David; Barth, Johannes V; Auwärter, Willi

    2015-04-01

    Intramolecular current-induced vibronic excitations are reported in highly ordered monolayers of quaterphenylene dicarbonitriles at an electronically patterned boron nitride on copper platform (BN/Cu(111)). A first level of spatially modulated conductance at the nanometer-scale is induced by the substrate. Moreover, a second level of conductance variations at the molecular level is found. Low temperature scanning tunneling microscopy studies in conjunction with molecular dynamics calculations reveal collective amplification of the molecule's interphenylene torsion angles in the monolayer. Librational modes influencing these torsion angles are identified as initial excitations during vibronic conductance. Density functional theory is used to map phenylene breathing modes and other vibrational excitations that are suggested to be at the origin of the submolecular features during vibronic conductance. PMID:25756645

  13. Topography and transport properties of oligo(phenylene ethynylene) molecular wires studied by scanning tunneling microscopy

    NASA Technical Reports Server (NTRS)

    Dholakia, Geetha R.; Fan, Wendy; Koehne, Jessica; Han, Jie; Meyyappan, M.

    2003-01-01

    Conjugated phenylene(ethynylene) molecular wires are of interest as potential candidates for molecular electronic devices. Scanning tunneling microscopic study of the topography and current-voltage (I-V) characteristics of self-assembled monolayers of two types of molecular wires are presented here. The study shows that the topography and I-Vs, for small scan voltages, of the two wires are quite similar and that the electronic and structural changes introduced by the substitution of an electronegative N atom in the central phenyl ring of these wires does not significantly alter the self-assembly or the transport properties.

  14. Comparison of DC and AC Transport in 1.5-7.5 nm Oligophenylene Imine Molecular Wires across Two Junction Platforms: Eutectic Ga-In versus Conducting Probe Atomic Force Microscope Junctions.

    PubMed

    Sangeeth, C S Suchand; Demissie, Abel T; Yuan, Li; Wang, Tao; Frisbie, C Daniel; Nijhuis, Christian A

    2016-06-15

    We have utilized DC and AC transport measurements to measure the resistance and capacitance of thin films of conjugated oligophenyleneimine (OPI) molecules ranging from 1.5 to 7.5 nm in length. These films were synthesized on Au surfaces utilizing the imine condensation chemistry between terephthalaldehyde and 1,4-benzenediamine. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy yielded molecular tilt angles of 33-43°. To probe DC and AC transport, we employed Au-S-OPI//GaOx/EGaIn junctions having contact areas of 9.6 × 10(2) μm(2) (10(9) nm(2)) and compared to previously reported DC results on the same OPI system obtained using Au-S-OPI//Au conducting probe atomic force microscopy (CP-AFM) junctions with 50 nm(2) areas. We found that intensive observables agreed very well across the two junction platforms. Specifically, the EGaIn-based junctions showed: (i) a crossover from tunneling to hopping transport at molecular lengths near 4 nm; (ii) activated transport for wires >4 nm in length with an activation energy of 0.245 ± 0.008 eV for OPI-7; (iii) exponential dependence of conductance with molecular length with a decay constant β = 2.84 ± 0.18 nm(-1) (DC) and 2.92 ± 0.13 nm(-1) (AC) in the tunneling regime, and an apparent β = 1.01 ± 0.08 nm(-1) (DC) and 0.99 ± 0.11 nm(-1) (AC) in the hopping regime; (iv) previously unreported dielectric constant of 4.3 ± 0.2 along the OPI wires. However, the absolute resistances of Au-S-OPI//GaOx/EGaIn junctions were approximately 100 times higher than the corresponding CP-AFM junctions due to differences in metal-molecule contact resistances between the two platforms.

  15. A strategy for antimicrobial regulation based on fluorescent conjugated oligomer-DNA hybrid hydrogels.

    PubMed

    Cao, Ali; Tang, Yanli; Liu, Yue; Yuan, Huanxiang; Liu, Libing

    2013-06-21

    New fluorescent oligo(phenylene ethynylene)-DNA hydrogels have been prepared and used for the controllable biocidal activity driven by DNase. This study opens a new way of controllable drug release and antimicrobial regulation.

  16. Nano-rings with a handle - Synthesis of substituted cycloparaphenylenes.

    PubMed

    Tran-Van, Anne-Florence; Wegner, Hermann A

    2014-01-01

    The research of cycloparaphenylenes (CPPs), the smallest armchair carbon nanotube, has been a quest for the past decades which experienced a revival in 2008 when the first synthesis was achieved. Since then CPPs with various ring sizes have been realized. The incorporation of substituents and the synthesis of CPPs with building blocks different from phenyl rings bear challenges of their own. Such structures, however, are highly interesting, as they allow for an incorporation of CPPs as defined nano-objects for other applications. Therefore, this review provides a status report about the current efforts in synthesizing CPPs beyond the parent unsubstituted oligo-phenylene structure. PMID:25247115

  17. Fabrication of carbon nanotube nanogap electrodes by helium ion sputtering for molecular contacts

    SciTech Connect

    Thiele, Cornelius; Vieker, Henning; Beyer, André; Gölzhäuser, Armin; Flavel, Benjamin S.; Hennrich, Frank; Muñoz Torres, David; Eaton, Thomas R.; Mayor, Marcel; Kappes, Manfred M.; Löhneysen, Hilbert v.; and others

    2014-03-10

    Carbon nanotube nanogaps have been used to contact individual organic molecules. However, the reliable fabrication of a truly nanometer-sized gap remains a challenge. We use helium ion beam lithography to sputter nanogaps of only (2.8 ± 0.6) nm size into single metallic carbon nanotubes embedded in a device geometry. The high reproducibility of the gap size formation provides a reliable nanogap electrode testbed for contacting small organic molecules. To demonstrate the functionality of these nanogap electrodes, we integrate oligo(phenylene ethynylene) molecular rods, and measure resistance before and after gap formation and with and without contacted molecules.

  18. Methods of Attaching or Grafting Carbon Nanotubes to Silicon Surfaces and Composite Structures Derived Therefrom

    NASA Technical Reports Server (NTRS)

    Tour, James M. (Inventor); Chen, Bo (Inventor); Flatt, Austen K. (Inventor); Stewart, Michael P. (Inventor); Dyke, Christopher A. (Inventor); Maya, Francisco (Inventor)

    2012-01-01

    The present invention is directed toward methods of attaching or grafting carbon nanotubes (CNTs) to silicon surfaces. In some embodiments, such attaching or grafting occurs via functional groups on either or both of the CNTs and silicon surface. In some embodiments, the methods of the present invention include: (1) reacting a silicon surface with a functionalizing agent (such as oligo(phenylene ethynylene)) to form a functionalized silicon surface; (2) dispersing a quantity of CNTs in a solvent to form dispersed CNTs; and (3) reacting the functionalized silicon surface with the dispersed CNTs. The present invention is also directed to the novel compositions produced by such methods.

  19. Nano-rings with a handle – Synthesis of substituted cycloparaphenylenes

    PubMed Central

    Tran-Van, Anne-Florence

    2014-01-01

    Summary The research of cycloparaphenylenes (CPPs), the smallest armchair carbon nanotube, has been a quest for the past decades which experienced a revival in 2008 when the first synthesis was achieved. Since then CPPs with various ring sizes have been realized. The incorporation of substituents and the synthesis of CPPs with building blocks different from phenyl rings bear challenges of their own. Such structures, however, are highly interesting, as they allow for an incorporation of CPPs as defined nano-objects for other applications. Therefore, this review provides a status report about the current efforts in synthesizing CPPs beyond the parent unsubstituted oligo-phenylene structure. PMID:25247115

  20. Raman scattering in molecular junctions: a pseudoparticle formulation.

    PubMed

    White, Alexander J; Tretiak, Sergei; Galperin, Michael

    2014-02-12

    We present a formulation of Raman spectroscopy in molecular junctions based on a many-body state representation of the molecule. The approach goes beyond the previous effective single orbital formalism and provides a convenient way to incorporate computational methods and tools proven for equilibrium molecular spectroscopy into the realm of current carrying junctions. The presented framework is illustrated by first principle simulations of Raman response in a three-ring oligophenylene vinylene terminating in amine functional groups (OPV3) junction. The calculated shift in Stokes lines and estimate of vibrational heating by electric current agree with available experimental data. In particular, our results suggest that participation of the OPV3 cation in Raman scattering under bias may be responsible for the observed shift, and that the direction of the shift depends on renormalization of normal modes. This work is a step toward atomistic quantum ab initio modeling of the optical response of nonequilibrium electronic dynamics in molecular junctions. PMID:24447295

  1. Insulator-protected mechanically controlled break junctions for measuring single-molecule conductance in aqueous environments

    NASA Astrophysics Data System (ADS)

    Muthusubramanian, N.; Galan, E.; Maity, C.; Eelkema, R.; Grozema, F. C.; van der Zant, H. S. J.

    2016-07-01

    We present a method to fabricate insulated gold mechanically controlled break junctions (MCBJ) by coating the metal with a thin layer of aluminum oxide using plasma enhanced atomic layer deposition. The Al2O3 thickness deposited on the MCBJ devices was varied from 2 to 15 nm to test the suppression of leakage currents in deionized water and phosphate buffered saline. Junctions coated with a 15 nm thick oxide layer yielded atomically sharp electrodes and negligible conductance counts in the range of 1 to 10-4 G0 (1 G0 = 77 μS), where single-molecule conductances are commonly observed. The insulated devices were used to measure the conductance of an amphiphilic oligophenylene ethynylene derivative in deionized water.

  2. Probing the local environment of a single OPE3 molecule using inelastic tunneling electron spectroscopy

    PubMed Central

    2015-01-01

    Summary We study single-molecule oligo(phenylene ethynylene)dithiol junctions by means of inelastic electron tunneling spectroscopy (IETS). The molecule is contacted with gold nano-electrodes formed with the mechanically controllable break junction technique. We record the IETS spectrum of the molecule from direct current measurements, both as a function of time and electrode separation. We find that for fixed electrode separation the molecule switches between various configurations, which are characterized by different IETS spectra. Similar variations in the IETS signal are observed during atomic rearrangements upon stretching of the molecular junction. Using quantum chemistry calculations, we identity some of the vibrational modes which constitute a chemical fingerprint of the molecule. In addition, changes can be attributed to rearrangements of the local molecular environment, in particular at the molecule–electrode interface. This study shows the importance of taking into account the interaction with the electrodes when describing inelastic contributions to transport through single-molecule junctions. PMID:26885460

  3. Coverage-mediated suppression of blinking in solid state quantum dot conjugated organic composite nanostructures.

    PubMed

    Hammer, Nathan I; Early, Kevin T; Sill, Kevin; Odoi, Michael Y; Emrick, Todd; Barnes, Michael D

    2006-07-27

    Size-correlated single-molecule fluorescence measurements on CdSe quantum dots functionalized with oligo(phenylene vinylene) (OPV) ligands exhibit modified fluorescence intermittency (blinking) statistics that are highly sensitive to the degree of ligand coverage on the quantum dot surface. As evidenced by a distinct surface height signature, fully covered CdSe-OPV nanostructures (approximately 25 ligands) show complete suppression of blinking in the solid state on an integration time scale of 1 s. Some access to dark states is observed on finer time scales (100 ms) with average persistence times significantly shorter than those from ZnS-capped CdSe quantum dots. This effect is interpreted as resulting from charge transport from photoexcited OPV into vacant trap sites on the quantum dot surface. These results suggest exciting new applications of composite quantum dot/organic systems in optoelectronic systems.

  4. Efficient electronic coupling and improved stability with dithiocarbamate-based molecular junctions

    NASA Astrophysics Data System (ADS)

    von Wrochem, Florian; Gao, Deqing; Scholz, Frank; Nothofer, Heinz-Georg; Nelles, Gabriele; Wessels, Jurina M.

    2010-08-01

    Molecular electronic devices require stable and highly conductive contacts between the metal electrodes and molecules. Thiols and amines are widely used to attach molecules to metals, but they form poor electrical contacts and lack the robustness required for device applications. Here, we demonstrate that dithiocarbamates provide superior electrical contact and thermal stability when compared to thiols on metals. Ultraviolet photoelectron spectroscopy and density functional theory show the presence of electronic states at 0.6 eV below the Fermi level of Au, which effectively reduce the charge injection barrier across the metal-molecule interface. Charge transport measurements across oligophenylene monolayers reveal that the conductance of terphenyl-dithiocarbamate junctions is two orders of magnitude higher than that of terphenyl-thiolate junctions. The stability and low contact resistance of dithiocarbamate-based molecular junctions represent a significant step towards the development of robust, organic-based electronic circuits.

  5. Efficient electronic coupling and improved stability with dithiocarbamate-based molecular junctions.

    PubMed

    von Wrochem, Florian; Gao, Deqing; Scholz, Frank; Nothofer, Heinz-Georg; Nelles, Gabriele; Wessels, Jurina M

    2010-08-01

    Molecular electronic devices require stable and highly conductive contacts between the metal electrodes and molecules. Thiols and amines are widely used to attach molecules to metals, but they form poor electrical contacts and lack the robustness required for device applications. Here, we demonstrate that dithiocarbamates provide superior electrical contact and thermal stability when compared to thiols on metals. Ultraviolet photoelectron spectroscopy and density functional theory show the presence of electronic states at 0.6 eV below the Fermi level of Au, which effectively reduce the charge injection barrier across the metal-molecule interface. Charge transport measurements across oligophenylene monolayers reveal that the conductance of terphenyl-dithiocarbamate junctions is two orders of magnitude higher than that of terphenyl-thiolate junctions. The stability and low contact resistance of dithiocarbamate-based molecular junctions represent a significant step towards the development of robust, organic-based electronic circuits. PMID:20562871

  6. Supramolecular self-assembly of conjugated diblock copolymers.

    SciTech Connect

    Wang, H.; You, W.; Jiang, P.; Yu, L.; Wang, H. H.; Univ. of Chicago

    2004-02-20

    This paper describes the synthesis and characterization of a novel series of copolymers with different lengths of oligo(phenylene vinylene) (OPV) as the rod block, and poly(propylene oxide) as the coil block. Detailed characterization by means of transmission electron microscopy (TEM), atomic force microscopy (AFM), and small-angle neutron scattering (SANS) revealed the strong tendency of these copolymers to self-assemble into cylindrical micelles in solution and as-casted films on a nanometer scale. These micelles have a cylindrical OPV core surrounded by a poly(propylene glycol) (PPG) corona and readily align with each other to form parallel packed structures when mica is used as the substrate. A packing model has been proposed for these cylindrical micelles.

  7. Suppression of single-molecule conductance fluctuations using extended anchor groups on graphene and carbon-nanotube electrodes

    NASA Astrophysics Data System (ADS)

    Péterfalvi, Csaba G.; Lambert, Colin J.

    2012-08-01

    Devices formed from single molecules attached to noble-metal electrodes exhibit large conductance fluctuations, which inhibit their development as reproducible functional units. We demonstrate that single molecules with planar anchor groups attached to carbon-based electrodes are more resilient to atomic-scale variation in the contacts and exhibit significantly lower conductance fluctuations. We examine the conductance of a 2,6-dibenzylamino core-substituted naphthalenediimide chromophore attached to carbon electrodes by either phenanthrene anchors or more extended anchor groups, which include oligophenylene ethynylene spacers. We demonstrate that for the more spatially extended anchor groups conductance fluctuations are significantly reduced. The current-voltage characteristic arising from long-range tunneling is found to be strongly nonlinear with pronounced conductance suppression below a threshold voltage of approximately 2.5 V.

  8. Nonsymmetric bent-core liquid crystals based on a 1,3,4-thiadiazole core unit and their nematic mesomorphism

    SciTech Connect

    Seltmann, Jens; Marini, Alberto; Mennucci, Benedetta; Dey, Sonal; Kumar, Satyendra; Lehmann, Matthias

    2012-09-06

    The synthesis and thermotropic properties of novel V-shaped molecules having a central 1,3,4-thiadiazole core with a bend-angle of 160 degrees are reported. The compounds consist of a shape-persistent oligo(phenylene ethynylene) scaffold with lateral alkyloxy substituents. One of the terminal aromatic units possesses an alkoxy chain capped by an ethyl ester group while the second terminus is a pyridyl group. They exhibit enantiotropic nematic phases and are characterized by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. Results from conoscopy indicate a biaxial nature of the nematic phase near room temperature. DFT calculations of dipole moments and molecular polarizabilities are used to substantiate the experimental findings.

  9. Cycloparaphenylenes and related nanohoops.

    PubMed

    Lewis, Simon E

    2015-04-21

    The first synthesis of a cyclic oligophenylene possessing a radial π system was reported in 2008. In the short period that has elapsed since, there has been an ever-increasing level of interest in molecules of this type, as evidenced by the volume of publications in this area. This interest has been driven by the highly unusual properties of these molecules in comparison to their linear oligoarene analogues, as well as the diverse array of potential applications for them. Notably, CPPs and related structures were proposed as viable templates for the bottom-up synthesis of single-walled carbon nanotubes (SWCNTs), a proposition which has recently been realised. This review gives a comprehensive and strictly chronological (by date of first online publication) treatment of literature reports from the inception of the field, with emphasis on both synthesis and properties of CPPs and related nanohoops. (The scope of this review is restricted to molecules possessing a radial π system consisting entirely of subunits which are aromatic in isolation, e.g. CPPs, but not cycloparaphenyleneacetylenes or cyclopolyacetylenes). PMID:25735813

  10. Gold nanoparticles assembled with dithiocarbamate-anchored molecular wires.

    PubMed

    Reeler, Nini E A; Lerstrup, Knud A; Somerville, Walter; Speder, Jozsef; Petersen, Søren V; Laursen, Bo W; Arenz, Matthias; Qiu, Xiaohui; Vosch, Tom; Nørgaard, Kasper

    2015-01-01

    A protocol for the bottom-up self-assembly of nanogaps is developed through molecular linking of gold nanoparticles (AuNPs). Two π-conjugated oligo(phenylene ethynylene) molecules (OPE) with dithiocarbamate anchoring groups are used as ligands for the AuNPs. OPE-4S with a dithiocarbamate in each end of the molecule and a reference molecule OPE-2S with only a single dithiocarbamate end group. The linking mechanism of OPE-4S is investigated by using a combination of TEM, UV-Vis absorption and surface enhanced Raman spectroscopy (SERS) as well as studying the effect of varying the OPE-4S to AuNP concentration ratio. UV-Vis absorption confirms the formation of AuNP aggregates by the appearance of an extended plasmon band (EPB) for which the red shift and intensity depend on the OPE-4S:AuNP ratio. SERS confirms the presence of OPE-4S and shows a gradual increase of the signal intensity with increasing OPE-4S:AuNP ratios up to a ratio of about 4000, after which the SERS intensity does not increase significantly. For OPE-2S, no linking is observed below full coverage of the AuNPs indicating that the observed aggregate formation at high OPE-2S:AuNP ratios, above full AuNP coverage, is most likely of a physical nature (van der Waals forces or π-π interactions). PMID:26471461

  11. Self-Assembled Monolayers of Oligophenylenecarboxylic Acids on Silver Formed at the Liquid-Solid Interface.

    PubMed

    Aitchison, Hannah; Lu, Hao; Hogan, Simon W L; Früchtl, Herbert; Cebula, Izabela; Zharnikov, Michael; Buck, Manfred

    2016-09-20

    A series of para-oligophenylene mono- and dicarboxylic acids (R-(C6H4)nCOOH, n = 1-3, R = H,COOH) was studied. Adsorbed on Au(111)/mica modified by an underpotential deposited bilayer of Ag, the self-assembled monolayers (SAMs) were analyzed by near-edge X-ray absorption fine structure spectroscopy, X-ray photoelectron spectroscopy, and scanning tunneling microscopy. In all cases SAMs are formed with molecules adopting an upright orientation and anchored to the substrate by a carboxylate. Except benzoic acid, all SAMs could be imaged at molecular resolution, which revealed highly crystalline layers with a dense molecular packing. The structures of the SAMs are described by a rectangular (5 × √3) unit cell for the prevailing phase of the monocarboxylic acids and an oblique ([Formula: see text]) unit cell for the dicarboxylic acids, thus evidencing a pronounced influence of the second COOH moiety on the SAM structure. Density functional theory calculations suggest that hydrogen bonding between the SAM-terminating COOH moieties accounts for the difference. Contrasting other classes of SAMs, the systems studied here are determined by intermolecular interactions whereas molecule-substrate interactions play a secondary role. Thus, eliminating problems arising from the mismatch between the molecular and the substrate lattices, coordinatively bonded carboxylic acids on silver should provide considerable flexibility in the design of SAM structures. PMID:27588836

  12. On the nucleation and initial film growth of rod-like organic molecules

    NASA Astrophysics Data System (ADS)

    Winkler, Adolf

    2016-10-01

    In this article, some fundamental topics related to the initial steps of organic film growth are reviewed. General conclusions will be drawn based on experimental results obtained for the film formation of oligophenylene and pentacene molecules on gold and mica substrates. Thin films were prepared via physical vapor deposition under ultrahigh-vacuum conditions and characterized in-situ mainly by thermal desorption spectroscopy, and ex-situ by X-ray diffraction and atomic force microscopy. In this short review article the following topics will be discussed: What are the necessary conditions to form island-like films which are either composed of flat-lying or of standing molecules? Does a wetting layer exist below and in between the islands? What is the reason behind the occasionally observed bimodal island size distribution? Can one describe the nucleation process with the diffusion-limited aggregation model? Do the impinging molecules directly adsorb on the surface or rather via a hot-precursor state? Finally, it will be described how the critical island size can be determined by an independent measurement of the deposition rate dependence of the island density and the capture-zone distribution via a universal relationship.

  13. Gold nanoparticles assembled with dithiocarbamate-anchored molecular wires

    PubMed Central

    Reeler, Nini E. A.; Lerstrup, Knud A.; Somerville, Walter; Speder, Jozsef; Petersen, Søren V.; Laursen, Bo W.; Arenz, Matthias; Qiu, Xiaohui; Vosch, Tom; Nørgaard, Kasper

    2015-01-01

    A protocol for the bottom-up self-assembly of nanogaps is developed through molecular linking of gold nanoparticles (AuNPs). Two π-conjugated oligo(phenylene ethynylene) molecules (OPE) with dithiocarbamate anchoring groups are used as ligands for the AuNPs. OPE-4S with a dithiocarbamate in each end of the molecule and a reference molecule OPE-2S with only a single dithiocarbamate end group. The linking mechanism of OPE-4S is investigated by using a combination of TEM, UV-Vis absorption and surface enhanced Raman spectroscopy (SERS) as well as studying the effect of varying the OPE-4S to AuNP concentration ratio. UV-Vis absorption confirms the formation of AuNP aggregates by the appearance of an extended plasmon band (EPB) for which the red shift and intensity depend on the OPE-4S:AuNP ratio. SERS confirms the presence of OPE-4S and shows a gradual increase of the signal intensity with increasing OPE-4S:AuNP ratios up to a ratio of about 4000, after which the SERS intensity does not increase significantly. For OPE-2S, no linking is observed below full coverage of the AuNPs indicating that the observed aggregate formation at high OPE-2S:AuNP ratios, above full AuNP coverage, is most likely of a physical nature (van der Waals forces or π-π interactions). PMID:26471461

  14. Linear dipole behavior in single CdSe-oligo(phenylene vinylene) nanostructures.

    PubMed

    Early, K T; McCarthy, K D; Odoi, M Y; Sudeep, P K; Emrick, T; Barnes, M D

    2009-02-24

    We report on linearly polarized absorption and emission from individual (4.3 nm) CdSe quantum dots whose surfaces are coordinated with monodisperse oligo-phenylene vinylene ligands. Shown previously to suppress quantum dot blinking, we demonstrate here that the electronic interaction of photoexcited ligands with the quantum dot core is manifested as a strong polarization anisotropy in absorption (M = 0.5), as well as distinct linear dipole emission patterns from the quantum dot core. Further, there is a correlation between the quantum dot emission moment and polarization orientation corresponding to the absorption maxima that is manifested as fluctuations in emission moment orientation in the X-Y plane. The observed polarization effects can be switched off by tuning the excitation away from the ligand absorption band. We propose a mechanism based on exciton dissociation from the photoexcited ligand, followed by the pinning of electrons at the quantum dot surface. The resulting Stark interaction is sufficiently strong to break the 2D degeneracy of the emission moment within the dot, and may therefore account for the linear dipole emission character.

  15. Electrical properties and mechanical stability of anchoring groups for single-molecule electronics.

    PubMed

    Frisenda, Riccardo; Tarkuç, Simge; Galán, Elena; Perrin, Mickael L; Eelkema, Rienk; Grozema, Ferdinand C; van der Zant, Herre S J

    2015-01-01

    We report on an experimental investigation of transport through single molecules, trapped between two gold nano-electrodes fabricated with the mechanically controlled break junction (MCBJ) technique. The four molecules studied share the same core structure, namely oligo(phenylene ethynylene) (OPE3), while having different aurophilic anchoring groups: thiol (SAc), methyl sulfide (SMe), pyridyl (Py) and amine (NH2). The focus of this paper is on the combined characterization of the electrical and mechanical properties determined by the anchoring groups. From conductance histograms we find that thiol anchored molecules provide the highest conductance; a single-level model fit to current-voltage characteristics suggests that SAc groups exhibit a higher electronic coupling to the electrodes, together with better level alignment than the other three groups. An analysis of the mechanical stability, recording the lifetime in a self-breaking method, shows that Py and SAc yield the most stable junctions while SMe form short-lived junctions. Density functional theory combined with non-equlibrium Green's function calculations help in elucidating the experimental findings.

  16. Role of solvent environments in single molecule conductance used insulator-modified mechanically controlled break junctions

    NASA Astrophysics Data System (ADS)

    Muthusubramanian, Nandini; Maity, Chandan; Galan Garcia, Elena; Eelkema, Rienk; Grozema, Ferdinand; van der Zant, Herre; Kavli Institute of Nanoscience Collaboration; Department of Chemical Engineering Collaboration

    We present a method for studying the effects of polar solvents on charge transport through organic/biological single molecules by developing solvent-compatible mechanically controlled break junctions of gold coated with a thin layer of aluminium oxide using plasma enhanced atomic layer deposition (ALD). The optimal oxide thickness was experimentally determined to be 15 nm deposited at ALD operating temperature of 300°C which yielded atomically sharp electrodes and reproducible single-barrier tunnelling behaviour across a wide conductance range between 1 G0 and 10-7 G0. The insulator protected MCBJ devices were found to be effective in various solvents such as deionized water, phosphate buffered saline, methanol, acetonitrile and dichlorobenzene. The yield of molecular junctions using such insulated electrodes was tested by developing a chemical protocol for synthesizing an amphipathic form of oligo-phenylene ethynylene (OPE3-PEO) with thioacetate anchoring groups. This work has further applications in studying effects of solvation, dipole orientation and other thermodynamic interactions on charge transport. Eu Marie Curie Initial Training Network (ITN). MOLECULAR-SCALE ELECTRONICS: ``MOLESCO'' Project Number 606728.

  17. Hexaarylbenzene: Evolution of Properties and Applications of Multitalented Scaffold.

    PubMed

    Vij, Varun; Bhalla, Vandana; Kumar, Manoj

    2016-08-24

    The easily rotatable peripheral aromatic rings around central benzene in hexaarylbenzene (HAB) derivatives create a very intriguing nonplanar, propeller-shaped geometry. Because of the very low susceptibility toward self-aggregation, HAB derivatives are much stronger candidates among various polyphenylenes/hetero-oligophenylenes when poor molecular cohesion and inefficient packing is required. However, the native properties of hexaphenylbenzene (HPB) can be varied by proper tailoring and substitution of the HAB core. The cohesion and packing in the structures of HAB aggregates induce effective structural variations so as to modify the fundamental features. Recently, HAB derivatives attracted a lot of research interest because of their significant role as liquid crystalline materials, organic light-emitting diodes, photochemical switches, redox materials, and molecular receptors. Herein, detailed attention is given to the pioneering work based on synthetic optimization of different HAB cores, elaborated study of their crystal engineering, various interesting applications of HAB derivatives, and future possibilities and capabilities of this still underexplored scaffold. PMID:27498592

  18. Efficient light emission from inorganic and organic semiconductor hybrid structures by energy-level tuning

    PubMed Central

    Schlesinger, R.; Bianchi, F.; Blumstengel, S.; Christodoulou, C.; Ovsyannikov, R.; Kobin, B.; Moudgil, K.; Barlow, S.; Hecht, S.; Marder, S.R.; Henneberger, F.; Koch, N.

    2015-01-01

    The fundamental limits of inorganic semiconductors for light emitting applications, such as holographic displays, biomedical imaging and ultrafast data processing and communication, might be overcome by hybridization with their organic counterparts, which feature enhanced frequency response and colour range. Innovative hybrid inorganic/organic structures exploit efficient electrical injection and high excitation density of inorganic semiconductors and subsequent energy transfer to the organic semiconductor, provided that the radiative emission yield is high. An inherent obstacle to that end is the unfavourable energy level offset at hybrid inorganic/organic structures, which rather facilitates charge transfer that quenches light emission. Here, we introduce a technologically relevant method to optimize the hybrid structure's energy levels, here comprising ZnO and a tailored ladder-type oligophenylene. The ZnO work function is substantially lowered with an organometallic donor monolayer, aligning the frontier levels of the inorganic and organic semiconductors. This increases the hybrid structure's radiative emission yield sevenfold, validating the relevance of our approach. PMID:25872919

  19. Ambipolar Phosphine Derivatives to Attain True Blue OLEDs with 6.5% EQE.

    PubMed

    Kondrasenko, Ilya; Tsai, Zheng-Hua; Chung, Kun-You; Chen, Yi-Ting; Ershova, Yana Yu; Doménech-Carbó, Antonio; Hung, Wen-Yi; Chou, Pi-Tai; Karttunen, Antti J; Koshevoy, Igor O

    2016-05-01

    A family of new branched phosphine derivatives {Ph2N-(C6H4)n-}3P → E (E = O 1-3, n = 1-3; E = S 4-6, n = 1-3; E = Se 7-9, n = 1-3; E = AuC6F5 4-6, n = 1-3), which are the donor-acceptor type molecules, exhibit efficient deep blue room temperature fluorescence (λem = 403-483 nm in CH2Cl2 solution, λem = 400-469 nm in the solid state). Fine tuning the emission characteristics can be achieved varying the length of aromatic oligophenylene bridge -(C6H4)n-. The pyramidal geometry of central R3P → E fragment on the one hand disrupts π-conjugation between the branches to preserve blue luminescence and high triplet energy, while on the other hand provides amorphous materials to prevent excimer formation and fluorescence self-quenching. Hence, compounds 2, 3, 5, and 12 were used as emitters to fabricate nondoped and doped electroluminescent devices. The luminophore 2 (E = O, n = 2) demonstrates excellently balanced bipolar charge transport and good nondoped device performance with a maximum external quantum efficiency (EQEmax) of 3.3% at 250 cd/m(2) and Commission International de L'Eclairage (CIE) coordinates of (0.15, 0.08). The doped device of 3 (E = O, n = 3) shows higher efficiency (EQEmax of 6.5, 6.0 at 100 cd/m(2)) and high color purity with CIE (0.15, 0.06) that matches the HDTV standard blue. The time-resolved electroluminescence measurement indicates that high efficiency of the device can be attributed to the triplet-triplet annihilation to enhance generation of singlet excitons. PMID:27100797

  20. Role of Geometric Distortion and Polarization in Localizing Electronic Excitations in Conjugated Polymers.

    PubMed

    Nayyar, Iffat H; Batista, Enrique R; Tretiak, Sergei; Saxena, Avadh; Smith, Darryl L; Martin, Richard L

    2013-02-12

    Five different Density Functional Theory (DFT) models (ranging from pure GGA to long-range-corrected hybrid functionals) were used to study computationally the nature of the self-trapped electronic states in oligophenylene vinylenes. The electronic excitations in question include the lowest singlet (S1) and triplet (T1(†)) excitons (calculated using Time Dependent DFT (TD-DFT) method), positive (P(+)) and negative (P(-)) polarons, and the lowest triplet (T1) states (computed with the Self-Consistent Field (SCF) scheme). The polaron formation (spatial localization of excitations) is observed only with the use of range-corrected hybrid DFT models including long-range electronic exchange interactions. The extent of localization for all studied excitations is found to be invariant with respect to the size of the oligomer chain in their corresponding optimal geometries. We have analyzed the interdependence between the extent of the geometrical distortion and the localization of the orbital and spin density, and have observed that the localization of the P(+) and P(-) charged species is quite sensitive to solvent polarization effects and the character of the DFT functional used, rather than the structural deformations. In contrast, the localization of neutral states, S1 and T1(†), is found to follow the structural distortions. Notably, T1 excitation obtained with the mean field SCF approach is always strongly localized in range-corrected hybrid DFT models. The molecular orbital energetics of these excitations was further investigated to identify the relationship between state localization and the corresponding orbital structure. A characteristic stabilization (destabilization) of occupied (virtual) orbitals is observed in hybrid DFT models, compared to tight-binding model-like orbital filling in semilocal GGA functionals. The molecular and natural orbital representation allows visualization of the spatial extent of the underlying electronic states. In terms of

  1. Homoleptic "star" Ru(II) polypyridyl complexes: shielded chromophores to study charge-transfer at the sensitizer-TiO2 interface.

    PubMed

    Johansson, Patrik G; Zhang, Yongyi; Meyer, Gerald J; Galoppini, Elena

    2013-07-15

    Three homoleptic star-shaped ruthenium polypyridyl complexes, termed Star YZ1, Star YZ2, and Star YZ3, where the Ru(II) center is coordinated to three bipyridine ligands each carrying two oligo(phenylene ethynylene) (OPE) rigid linker units terminating with isophthalic ester (Ipa) groups for binding to metal-oxide surfaces were synthesized. In Star YZ3, each OPE linker was substituted with two n-butoxy (n-BuO) solubilizing groups. Star complex YZ4, which is homoleptic but lacks the octahedral symmetry, was synthesized as a reference compound. The Star complexes were synthesized using two approaches: in the first, Ru(4,4'-(Br)2-2,2'-bpy)3 was reacted in a Sonogashira cross coupling reaction with the ethynyl-OPE-Ipa linkers; in the second, the 2,2'-bpy-OPE-Ipa ligands were reacted with Ru(DMSO)4(PF6)2. The photophysical behavior of the Star complexes were studied in fluid solution and anchored to the surface of mesoporous nanocrystalline TiO2 thin films (Star/TiO2). To a first approximation the excited state behavior in CH3CN was unchanged when the compounds were anchored to a TiO2 thin film, indicating that the highly symmetrical (octahedral) and rigid molecular structure of the ligands shielded the chromophoric core from the TiO2 semiconductor. Inefficient excited state injection, φ(inj) < 0.05, was observed to occur on a nanosecond time scale with slow recombination. In addition, the presence of n-BuO groups on the linker unit gave a large increase in the extinction coefficient of YZ3, which allows for enhanced harvesting of sunlight. The results indicate that molecular design on the nanometer length scale can be utilized to control excited state relaxation pathways at semiconductor surfaces.

  2. Non-Interpenetrated Metal-Organic Frameworks Based on Copper(II) Paddlewheel and Oligoparaxylene-Isophthalate Linkers: Synthesis, Structure, and Gas Adsorption.

    PubMed

    Yan, Yong; Juríček, Michal; Coudert, François-Xavier; Vermeulen, Nicolaas A; Grunder, Sergio; Dailly, Anne; Lewis, William; Blake, Alexander J; Stoddart, J Fraser; Schröder, Martin

    2016-03-16

    Two metal-organic framework materials, MFM-130 and MFM-131 (MFM = Manchester Framework Material), have been synthesized using two oligoparaxylene (OPX) tetracarboxylate linkers containing four and five aromatic rings, respectively. Both fof-type non-interpenetrated networks contain Kagomé lattice layers comprising [Cu2(COO)4] paddlewheel units and isophthalates, which are pillared by the OPX linkers. Desolvated MFM-130, MFM-130a, shows permanent porosity (BET surface area of 2173 m(2)/g, pore volume of 1.0 cm(3)/g), high H2 storage capacity at 77 K (5.3 wt% at 20 bar and 2.2 wt% at 1 bar), and a higher CH4 adsorption uptake (163 cm(3)(STP)/cm(3) (35 bar and 298 K)) compared with its structural analogue, NOTT-103. MFM-130a also shows impressive selective adsorption of C2H2, C2H4, and C2H6 over CH4 at room temperature, indicating its potential for separation of C2 hydrocarbons from CH4. The single-crystal structure of MFM-131 confirms that the methyl substituents of the paraxylene units block the windows in the Kagomé lattice layer of the framework, effectively inhibiting network interpenetration in MFM-131. This situation is to be contrasted with that of the doubly interpenetrated oligophenylene analogue, NOTT-104. Calculation of the mechanical properties of these two MOFs confirms and explains the instability of MFM-131 upon desolvation in contrast to the behavior of MFM-130. The incorporation of paraxylene units, therefore, provides an efficient method for preventing network interpenetration as well as accessing new functional materials with modified and selective sorption properties for gas substrates.

  3. Ambipolar Phosphine Derivatives to Attain True Blue OLEDs with 6.5% EQE.

    PubMed

    Kondrasenko, Ilya; Tsai, Zheng-Hua; Chung, Kun-You; Chen, Yi-Ting; Ershova, Yana Yu; Doménech-Carbó, Antonio; Hung, Wen-Yi; Chou, Pi-Tai; Karttunen, Antti J; Koshevoy, Igor O

    2016-05-01

    A family of new branched phosphine derivatives {Ph2N-(C6H4)n-}3P → E (E = O 1-3, n = 1-3; E = S 4-6, n = 1-3; E = Se 7-9, n = 1-3; E = AuC6F5 4-6, n = 1-3), which are the donor-acceptor type molecules, exhibit efficient deep blue room temperature fluorescence (λem = 403-483 nm in CH2Cl2 solution, λem = 400-469 nm in the solid state). Fine tuning the emission characteristics can be achieved varying the length of aromatic oligophenylene bridge -(C6H4)n-. The pyramidal geometry of central R3P → E fragment on the one hand disrupts π-conjugation between the branches to preserve blue luminescence and high triplet energy, while on the other hand provides amorphous materials to prevent excimer formation and fluorescence self-quenching. Hence, compounds 2, 3, 5, and 12 were used as emitters to fabricate nondoped and doped electroluminescent devices. The luminophore 2 (E = O, n = 2) demonstrates excellently balanced bipolar charge transport and good nondoped device performance with a maximum external quantum efficiency (EQEmax) of 3.3% at 250 cd/m(2) and Commission International de L'Eclairage (CIE) coordinates of (0.15, 0.08). The doped device of 3 (E = O, n = 3) shows higher efficiency (EQEmax of 6.5, 6.0 at 100 cd/m(2)) and high color purity with CIE (0.15, 0.06) that matches the HDTV standard blue. The time-resolved electroluminescence measurement indicates that high efficiency of the device can be attributed to the triplet-triplet annihilation to enhance generation of singlet excitons.

  4. Important issues facing model-based approaches to tunneling transport in molecular junctions

    NASA Astrophysics Data System (ADS)

    Bâldea, Ioan

    Extensive studies on thin films indicated a generic cubic current-voltage $I-V$ dependence as a salient feature of charge transport by tunneling. A quick glance at $I-V$ data for molecular junctions suggests a qualitatively similar behavior. This would render model-based studies almost irrelevant, since, whatever the model, its parameters can always be adjusted to fit symmetric (asymmetric) $I-V$ curves characterized by two (three) expansion coefficients. Here, we systematically examine popular models based on tunneling barrier or tight-binding pictures and demonstrate that, for a quantitative description at biases of interest ($V$ slightly higher than the transition voltage $V_t$), cubic expansions do not suffice. A detailed collection of analytical formulae as well as their conditions of applicability are presented to facilitate experimentalists colleagues to process and interpret their experimental data by obtained by measuring currents in molecular junctions. We discuss in detail the limits of applicability of the various models and emphasize that uncritically adjusting model parameters to experiment may be unjustified because the values deduced in this way may fall in ranges rendering a specific model invalid or incompatible to ab initio estimates. We exemplify with the benchmark case of oligophenylene-based junctions, for which results of ab initio quantum chemical calculations are also reported. As a specific issue, we address the impact of the spatial potential profile and show that it is not notable up to biases V somewhat larger than V_t, unlike at higher biases, where it may be responsible for negative differential resistance effects.

  5. Molecular Self-Assembly into One-Dimensional Nanostructures

    PubMed Central

    PALMER, LIAM C.; STUPP, SAMUEL I.

    2008-01-01

    appear as nanofiber bundles. Surprisingly, TEM of a PA substituted by a nitrobenzyl group revealed assembly into quadruple helical fibers with a braided morphology. Upon photocleavage of this the nitrobenzyl group, the helices transform into single cylindrical nanofibers. Finally, inspired by the tobacco mosaic virus, we used a dumbbell-shaped, oligo(phenylene ethynylene) template to control the length of a PA nanofiber self-assembly (<10 nm). AFM showed complete disappearance of long nanofibers in the presence of this rigid-rod template. Results from quick-freeze/deep-etch TEM and dynamic light scattering demonstrated the templating behavior in aqueous solution. This strategy could provide a general method to control size the length of non-spherical supramolecular nanostructures. PMID:18754628

  6. Axially assembled photosynthetic reaction center mimics composed of tetrathiafulvalene, aluminum(III) porphyrin and fullerene entities.

    PubMed

    Poddutoori, Prashanth K; Lim, Gary N; Sandanayaka, Atula S D; Karr, Paul A; Ito, Osamu; D'Souza, Francis; Pilkington, Melanie; van der Est, Art

    2015-07-28

    The distance dependence of sequential electron transfer has been studied in six, vertical, linear supramolecular triads, (TTF-Ph(n)-py → AlPor-Ph(m)-C60, n = 0, 1 and m = 1, 2, 3), constructed using tetrathiafulvalene (TTF), aluminum(III) porphyrin (AlPor) and fullerene (C60) entities. The C60 and TTF units are bound to the Al center on opposite faces of the porphyrin; the C60 through a covalent axial bond using a benzoate spacer, and the TTF through a coordination bond via an appended pyridine. Time-resolved optical and EPR spectroscopic methods and computational studies are used to demonstrate that excitation of the porphyrin leads to step-wise, sequential electron transfer (ET) between TTF and C60, and to study the electron transfer rates and exchange coupling between the components of the triads as a function of the bridge lengths. Femtosecond transient absorption studies show that the rates of charge separation, k(CS) are in the range of 10(9)-10(11) s(-1), depending on the length of the bridges. The lifetimes of the charge-separated state TTF˙(+)-C₆₀˙⁻ obtained from transient absorbance experiments and the singlet lifetimes of the radical pairs obtained by time-resolved EPR are in good agreement with each other and range from 60-130 ns in the triads. The time-resolved EPR data also show that population of the triplet sublevels of the charge-separated state in the presence of a magnetic field leads to much longer lifetimes of >1 μs. The data show that a modest stabilization of the charge separation lifetime occurs in the triads. The attenuation factor β = 0.36 Å(-1) obtained from the exchange coupling values between TTF˙(+) and C₆₀˙⁻ is consistent with values reported in the literature for oligophenylene bridged TTF-C60 conjugates. The singlet charge recombination lifetime shows a much weaker dependence on the distance between the donor and acceptor, suggesting that a simple superexchange model is not sufficient to describe the back

  7. Electron Transport, Energy Transfer, and Optical Response in Single Molecule Junctions

    NASA Astrophysics Data System (ADS)

    White, Alexander James

    interactions quantum mechanically within nonequilibrium molecular junctions. Finally we perform preliminary calculations of the Raman spectrum of a three-ring oligophenylene vinylene terminating in amine functional groups molecule in a molecular junction and compare our results to experimental measurements. This work is the rst steps towards full calculations of the optical response of current-carrying molecular junction, which should combine classical calculations of the plasmon enhanced electric field with quantum calculations for the plasmon-molecular exciton interaction and nonequilibrium Raman scattering.

  8. Supported Intrinsically Porous Oligomers as Hybrid Materials for Separations, Storage, and Sensing

    NASA Astrophysics Data System (ADS)

    Thompson, Anthony Boone

    Adsorption-desorption phenomena are often difficult to study at the molecular level because the surfaces on which they occur can be heterogeneous, giving a wide distribution of adsorption sites and associated energies. Considering that these phenomena underlie an incredibly wide variety of industrially important processes, a better understanding could aid in the development of more efficient methods. In this work, we describe an approach to designing materials with well-defined adsorption sites by covalently attaching intrinsically porous molecules to solid surfaces by a rigid multidentate linker. These cup-shaped molecules are intended to act as adsorption sites on the material, whereas the rigid attachment to the solid support serves to prevent movement and conformational changes of the sites, leading to better understanding of adsorption phenomena. As a proof-of-concept application, materials were used for adsorption of n-butanol biofuel and related compounds from dilute aqueous solution. The materials were thermally and hydrolytically stable, and adsorption phenomena were reversible. Adsorption sites containing more hydrophobic molecular area led to stronger adsorption, suggesting that it is driven by weak van der Waals forces. Likewise, adsorption sites that were strongly polarized performed poorly, possibly reflecting a greater energy penalty of removing water molecules from the cavity. Upon placing a Lewis acidic metal at the bottom of the cavity, an enhancement was seen only with the most acidic metal, which may indicate weak guest coordination. Observing that hydrophobic interactions dominate adsorption on these materials, efforts were made to develop hybrid materials with large hydrophobic area for adsorption. Glaser coupling of diethynylbenzene was used to grow oligo(phenylene butadiynylene)s from the surface of silica, resulting in materials that were more than 25% organic by weight. In addition to their potential use as adsorbents, these materials may

  9. Axially assembled photosynthetic reaction center mimics composed of tetrathiafulvalene, aluminum(iii) porphyrin and fullerene entities

    NASA Astrophysics Data System (ADS)

    Poddutoori, Prashanth K.; Lim, Gary N.; Sandanayaka, Atula S. D.; Karr, Paul A.; Ito, Osamu; D'Souza, Francis; Pilkington, Melanie; van der Est, Art

    2015-07-01

    The distance dependence of sequential electron transfer has been studied in six, vertical, linear supramolecular triads, (TTF-Phn-py --> AlPor-Phm-C60, n = 0, 1 and m = 1, 2, 3), constructed using tetrathiafulvalene (TTF), aluminum(iii) porphyrin (AlPor) and fullerene (C60) entities. The C60 and TTF units are bound to the Al center on opposite faces of the porphyrin; the C60 through a covalent axial bond using a benzoate spacer, and the TTF through a coordination bond via an appended pyridine. Time-resolved optical and EPR spectroscopic methods and computational studies are used to demonstrate that excitation of the porphyrin leads to step-wise, sequential electron transfer (ET) between TTF and C60, and to study the electron transfer rates and exchange coupling between the components of the triads as a function of the bridge lengths. Femtosecond transient absorption studies show that the rates of charge separation, kCS are in the range of 109-1011 s-1, depending on the length of the bridges. The lifetimes of the charge-separated state TTF&z.rad;+-C&z.rad;-60 obtained from transient absorbance experiments and the singlet lifetimes of the radical pairs obtained by time-resolved EPR are in good agreement with each other and range from 60-130 ns in the triads. The time-resolved EPR data also show that population of the triplet sublevels of the charge-separated state in the presence of a magnetic field leads to much longer lifetimes of >1 μs. The data show that a modest stabilization of the charge separation lifetime occurs in the triads. The attenuation factor β = 0.36 Å-1 obtained from the exchange coupling values between TTF&z.rad;+ and C&z.rad;-60 is consistent with values reported in the literature for oligophenylene bridged TTF-C60 conjugates. The singlet charge recombination lifetime shows a much weaker dependence on the distance between the donor and acceptor, suggesting that a simple superexchange model is not sufficient to describe the back reaction

  10. Design and synthesis of polyphosphazenes: Hard tissue scaffolding biomaterials and physically crosslinked elastomers

    NASA Astrophysics Data System (ADS)

    Modzelewski, Tomasz

    oar's on adjacent polymer chains, and lock the chains in place, similar to the way in which the oars on one ship will interdigitate with the oars of another ship if they get too close. Chapter 6 expands the chemistry of the non-traditional elastomers described in Chapter 5. Specifically, the substituent groups on the cyclotriphosphazene groups are changed from 2,2,2- trifluoroethoxy to phenoxy, while the remaining chlorine atoms along the polymer backbone are still replaced with 2,2,2-trifluoroethoxide. The new polymers are shown to have better mechanical properties then the polymers described in Chapter 5. Chapter 7 describes a further extension of the ideas in Chapters 5 and 6. Specifically it involves the synthesis and mechanical testing of polyphosphazenes bearing oligo-p-phenylene groups co-substituted with 2,2,2-trifluoroethoxide. The oligo-phenylene groups are incorporated to act as variable length cross-linking moieties to further expand the new family of non-traditional polyphosphazene elastomers. The mechanical and physical properties of these polymers reveal a strong dependence on both the length and concentration of the oligo-phenylene minor co-substituent groups. (Abstract shortened by UMI.).

  11. Syntheses of the smallest carbon nanohoops and the emergence of unique physical phenomena.

    PubMed

    Golder, Matthew R; Jasti, Ramesh

    2015-03-17

    The design and construction of non-natural products have fascinated and perplexed organic chemists for years. Their assembly, akin to what has been accomplished for the total synthesis of natural products, has stretched the limits of what can be prepared in the laboratory. Unlike many natural products, however, carbon-rich structures often lack heteroatoms, further complicating their construction. Consider some of the classical molecules in this genre: cubane and dodecahedrane. While highly symmetric, their assembly is far from trivial. These fascinating hydrocarbon targets have fueled the development of carbon-carbon bond-forming reactions, as new methods are needed to access these types of compounds. Among these carbon-rich structures, polycyclic aromatics such as helicenes, fullerenes, and some fullerenes share common ground due to the distortion of one or more aromatic rings out of planarity. Recently added to this group are the [n]cycloparaphenylenes ([n]CPPs), "carbon nanohoops". Here, a linear string of benzene rings connected at the para positions is wrapped back upon itself to form a cyclic structure. Clearly a simple linear p-oligophenylene cannot be cyclized in this manner without extremely harsh reaction conditions. In order to access these structures using solution-phase organic chemistry, clever synthetic strategies that can compensate for this severe distortion are required. Although cycloparaphenylenes can be considered the smallest possible fragment of an armchair carbon nanotube (CNT), they were envisioned as synthetic targets long before CNTs were discovered in 1991. CPP synthesis was first attempted in 1934, almost 70 years before Iijima's first report on CNTs. The long-forgotten targets reemerged in 1993 with a report from Vögtle, though he ultimately was unsuccessful in achieving their synthesis. More than a decade later, in 2008, CPPs succumbed to total synthesis by Jasti and Bertozzi, allowing access to three different-sized carbon

  12. Syntheses of the smallest carbon nanohoops and the emergence of unique physical phenomena.

    PubMed

    Golder, Matthew R; Jasti, Ramesh

    2015-03-17

    The design and construction of non-natural products have fascinated and perplexed organic chemists for years. Their assembly, akin to what has been accomplished for the total synthesis of natural products, has stretched the limits of what can be prepared in the laboratory. Unlike many natural products, however, carbon-rich structures often lack heteroatoms, further complicating their construction. Consider some of the classical molecules in this genre: cubane and dodecahedrane. While highly symmetric, their assembly is far from trivial. These fascinating hydrocarbon targets have fueled the development of carbon-carbon bond-forming reactions, as new methods are needed to access these types of compounds. Among these carbon-rich structures, polycyclic aromatics such as helicenes, fullerenes, and some fullerenes share common ground due to the distortion of one or more aromatic rings out of planarity. Recently added to this group are the [n]cycloparaphenylenes ([n]CPPs), "carbon nanohoops". Here, a linear string of benzene rings connected at the para positions is wrapped back upon itself to form a cyclic structure. Clearly a simple linear p-oligophenylene cannot be cyclized in this manner without extremely harsh reaction conditions. In order to access these structures using solution-phase organic chemistry, clever synthetic strategies that can compensate for this severe distortion are required. Although cycloparaphenylenes can be considered the smallest possible fragment of an armchair carbon nanotube (CNT), they were envisioned as synthetic targets long before CNTs were discovered in 1991. CPP synthesis was first attempted in 1934, almost 70 years before Iijima's first report on CNTs. The long-forgotten targets reemerged in 1993 with a report from Vögtle, though he ultimately was unsuccessful in achieving their synthesis. More than a decade later, in 2008, CPPs succumbed to total synthesis by Jasti and Bertozzi, allowing access to three different-sized carbon