Sample records for tetracene

  1. Geometry optimization and vibrational frequencies of tetracene ...

    African Journals Online (AJOL)

    Tetracene is an organic semiconductor with chemical formula C18H12 used in organic field effecttransistor (OFET) and organic light emitting diode (OLED). In this work, the molecular geometry (optimized bond lengths and bond angles), vibrational frequencies and intensities, HOMO-LUMO Energy gap and Atomic charge ...

  2. Coverage dependence of the structure of tetracene on Ag(110)

    Energy Technology Data Exchange (ETDEWEB)

    Huang Han; Song Fei; Lu Bin; Zhang Hanjie; Dou Weidong; Li Haiyang; He Pimo; Bao Shining [Physics Department, Zhejiang University, Hangzhou 310027 (China); Chen Qiao [Department of Chemistry, School of Life Sciences, University of Sussex, Falmer, Brighton BN1 9QJ (United Kingdom); Zhou Wuzong [School of Chemistry, University of St Andrews, St Andrews KY16 9ST (United Kingdom)], E-mail:, E-mail:


    The ordered adsorption structures of tetracene on Ag(110) have been studied by low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. At a low coverage, as calibrated with LEED, both p(4 x 4) and c(8 x 4) ordered structures are simultaneously formed on an Ag(110) surface at room temperature. STM images suggest the molecular plane is parallel to the Ag surface with its long molecular axis aligned along the [001] azimuth. DFT optimization reveals a separation of 0.3 nm between the molecular plane and substrate surface while the center of the tetracene molecule is on the long bridge site. Increasing coverage slightly, a ({sub 2}{sup 6} {sub 5}{sup 2}) structure is formed while the adsorbed molecules maintain the flat-lying geometry with adjacent molecules alternating their height relative to the surface.

  3. Correlation Between Morphology and Field-Effect-Transistor Mobility in Tetracene Thin Films

    NARCIS (Netherlands)

    Cicoira, Fabio; Santato, Clara; Dinelli, Franco; Murgia, Mauro; Loi, Maria Antonietta; Biscarini, Fabio; Zamboni, Roberto; Heremans, Paul; Muccini, Michele


    The growth of vacuum-sublimed tetracene thin films on silicon dioxide has been investigated from the early stages of the process. The effects of deposition flux and substrate silanization on film morphology and electrical properties have been explored. Tetracene shows an island growth, resulting in

  4. Straightforward Synthesis of 2- and 2,8-Substituted Tetracenes. (United States)

    Woodward, Simon; Ackermann, Miriam; Ahirwar, Saurabh K; Burroughs, Laurence; Garrett, Mary Robert; Ritchie, John; Shine, Jonathan; Tyril, Björk; Simpson, Kevin; Woodward, Peter


    A simple regiospecific route to otherwise problematic substituted tetracenes is described. The diverse cores (E)-1,2-Ar(1) CH2 (HOCH2 )C=C(CH2 OH)I (Ar(1) =Ph, 4-MePh, 4-MeOPh, 4-FPh) and (E)-1,2-I(HOCH2 )C=C(CH2 OH)I, accessed from ultra-low cost HOCH2 C≡CCH2 OH at multi-gram scales, allow the synthesis of diol libraries (E)-1,2-Ar(1) CH2 (HOCH2 )C=C(CH2 OH)CH2 Ar(2) (Ar(2) =Ph, 4-MePh, 4-iPrPh, 4-MeOPh, 4-FPh, 4-BrPh, 4-biphenyl, 4-styryl; 14 examples) by efficient Negishi coupling. Copper-catalysed aerobic oxidation cleanly provides dialdehydes (E)-1,2-Ar(1) CH2 (CHO)C=C(CHO)CH2 Ar(2) , which in many cases undergo titanium(IV) chloride-induced double Bradsher closure, providing a convenient method for the synthesis of regiochemically and analytically pure tetracenes (12 examples). The sequence is typically chromatography-free, scalable, efficient and technically simple to carry out. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  5. One-pot synthesis of stable NIR tetracene diimides via double cross-coupling. (United States)

    Yue, Wan; Gao, Jing; Li, Yan; Jiang, Wei; Di Motta, Simone; Negri, Fabrizia; Wang, Zhaohui


    Tetracene tetracarboxylic diimides have been synthesized based on direct double ring extension of electron-deficient naphthalene diimides involving metallacyclopentadienes. Atomic structure and electronic transitions responsible for their NIR absorption spectra are investigated with quantum-chemical calculations. In light of their unique structure and admirable photophysical and electronic properties, this new molecular skeleton is promising candidate for n-type semiconductors.

  6. Spontaneous site reorientation in a mixed molecular crystal : Tetracene in benzoic acid

    NARCIS (Netherlands)



    Absorption and fluorescence spectra of tetracene in a benzoic acid host crystal at 1.5 K are presented. The fluorescence zero-phonon line is shifted by more than 800 cm–1 to the red of the maximum of the 120 cm–1 broad absorption origin. This shift is attributed to a lateral site reorientation of

  7. Tetraceno[2,1,12,11-opqra]tetracene-extended tetrathiafulvalene - redox-controlled generation of a large PAH core

    DEFF Research Database (Denmark)

    Broman, Søren Lindbæk; Andersen, Cecilie Lindholm; Jousselin-Oba, Tanguy


    Two tetraceno[2,1,12,11-opqra]tetracene-extended tetrathia-fulvalenes were prepared and found to undergo reversible conversion into their planar polycyclic aromatic hydrocarbons (PAHs) upon electrochemical oxidation – at potentials probing the best valence bond representations......Two tetraceno[2,1,12,11-opqra]tetracene-extended tetrathia-fulvalenes were prepared and found to undergo reversible conversion into their planar polycyclic aromatic hydrocarbons (PAHs) upon electrochemical oxidation – at potentials probing the best valence bond representations...

  8. Thiophene-fused tetracene diimide with low band gap and ambipolar behavior

    KAUST Repository

    Ye, Qun


    The first tetracene diimide derivative fused with four thiophene rings, TT-TDI, was synthesized by an FeCl3 mediated oxidative cyclodehydrogenation reaction. TT-TDI exhibited a low band gap of 1.52 eV and amphoteric redox behavior. TT-TDI also showed a liquid crystalline property and ambipolar charge transport in thin film field-effect transistors. © 2011 American Chemical Society.

  9. Rubrene: The interplay between intramolecular and intermolecular interactions determines the planarization of its tetracene core in the solid state

    KAUST Repository

    Sutton, Christopher


    Rubrene is one of the most studied molecular semiconductors; its chemical structure consists of a tetracene backbone with four phenyl rings appended to the two central fused rings. Derivatization of these phenyl rings can lead to two very different solid-state molecular conformations and packings: One in which the tetracene core is planar and there exists substantive overlap among neighboring π-conjugated backbones; and another where the tetracene core is twisted and the overlap of neighboring π-conjugated backbones is completely disrupted. State-of-the-art electronic-structure calculations show for all isolated rubrene derivatives that the twisted conformation is more favorable (by -1.7 to -4.1 kcal mol-1), which is a consequence of energetically unfavorable exchange-repulsion interactions among the phenyl side groups. Calculations based on available crystallographic structures reveal that planar conformations of the tetracene core in the solid state result from intermolecular interactions that can be tuned through well-chosen functionalization of the phenyl side groups, and lead to improved intermolecular electronic couplings. Understanding the interplay of these intramolecular and intermolecular interactions provides insight into how to chemically modify rubrene and similar molecular semiconductors to improve the intrinsic materials electronic properties.

  10. Anionic sigmatropic-electrocyclic-Chugaev cascades: accessing 12-aryl-5-(methylthiocarbonylthio)tetracenes and a related anthra[2,3-b]thiophene. (United States)

    Burroughs, Laurence; Ritchie, John; Ngwenya, Mkhethwa; Khan, Dilfaraz; Lewis, William; Woodward, Simon


    1,4-Diols resulting from the double addition of ArCCLi (Ar = Ph, substituted phenyl, 2-thienyl) to ortho-C6H4(CHO)2 undergo cascades to tetracenes on simple admixture of LiHDMS, CS2 and MeI. Acene formation proceeds by [3,3]-sigmatropic rearrangement of xanthate anions followed by 6π electrocyclisations. The reactions are terminated by E2 or anionic Chugaev-type eliminations. Structural packing motifs and electronic properties are reported for the tetracenes.

  11. The Second-Order Stark Effect on the 1B2u Electronic Origin of Tetracene and Pentacene in p-Terphenyl

    NARCIS (Netherlands)

    Meyling, Jan H.; Wiersma, Douwe A.


    The electric field induced shift of the electronic origin of the lowest B2u singlet state of tetracene and pentacene in p-terphenyl at 1.8°K has been measured. From this shift we calculate the difference in polarizability of this state and the ground state along the long molecular axis to be 4.5 ±

  12. Who's on first? Tracking in real time the growth of multiple crystalline phases of an organic semiconductor: Tetracene on SiO2 (United States)

    Nahm, R. K.; Engstrom, J. R.


    We have examined the effect of growth rate on the evolution of two polymorphs of thin films of tetracene on SiO2 using synchrotron X-ray radiation and molecular beam techniques. Ex situ X-ray reflectivity shows that tetracene forms two phases on SiO2: a thin-film phase and a bulk phase. We have used in situ, real-time grazing incidence diffraction during growth to reveal the nature of growth concerning these two phases. We observe that there is initially growth of only the thin-film phase, up to a thickness of several monolayers. This is followed by the nucleation of the bulk phase, growth of both phases, and finally growth of only the bulk phase. We find that the deposited thickness when the bulk phase nucleates increases with increasing growth rate. Similarly, we find that the deposited thickness at which the thin-film phase saturates also increases with increasing growth rate. These apparent dependencies on growth rate are actually a consequence of the local coverage, which depends on growth rate, particularly for the former effect. At low growth rates, there is 3D growth resulting from the upward transport of tetracene at island edges, resulting in tall features where molecules escape the influence of the substrate and form into the bulk phase. Increasing the growth rate leads to growth that is more 2D and uniform in coverage, delaying the formation of the bulk phase.

  13. Control of Energy Flow Dynamics between Tetracene Ligands and PbS Quantum Dots by Size Tuning and Ligand Coverage

    Energy Technology Data Exchange (ETDEWEB)

    Kroupa, Daniel M. [National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States; Arias, Dylan H. [National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States; Blackburn, Jeffrey L. [National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States; Carroll, Gerard M. [National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States; Granger, Devin B. [Department; Anthony, John E. [Department; Beard, Matthew C. [National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States; Johnson, Justin C. [National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States


    We have prepared a series of samples with the ligand 6,13-bistri(iso-propyl)silylethynyl tetracene 2-carboxylic acid (TIPS-Tc-COOH) attached to PbS quantum dot (QD) samples of three different sizes in order to monitor and control the extent and time scales of energy flow after photoexcitation. Fast energy transfer (~1 ps) to the PbS QD occurs upon direct excitation of the ligand for all samples. The largest size QD maintains the microsecond exciton lifetime characteristic of the as-prepared oleate terminated PbS QDs. However, two smaller QD sizes with lowest exciton energies similar to or larger than the TIPS-Tc-COO- triplet energy undergo energy transfer between QD core and ligand triplet on nanosecond to microsecond timescales. For the intermediate size QDs in particular, energy can be recycled many times between ligand and core, but the triplet remains the dominant excited species at long times, living for ~3 us for fully exchanged QDs and up to 30 us for partial ligand exchange, which is revealed as a method for controlling the triplet lifetime. A unique upconverted luminescence spectrum is observed that results from annihilation of triplets after exclusive excitation of the QD core.

  14. Detailed Wave Function Analysis for Multireference Methods: Implementation in the Molcas Program Package and Applications to Tetracene. (United States)

    Plasser, Felix; Mewes, Stefanie A; Dreuw, Andreas; González, Leticia


    High-level multireference computations on electronically excited and charged states of tetracene are performed, and the results are analyzed using an extensive wave function analysis toolbox that has been newly implemented in the Molcas program package. Aside from verifying the strong effect of dynamic correlation, this study reveals an unexpected critical influence of the atomic orbital basis set. It is shown that different polarized double-ζ basis sets produce significantly different results for energies, densities, and overall wave functions, with the best performance obtained for the atomic natural orbital (ANO) basis set by Pierloot et al. Strikingly, the ANO basis set not only reproduces the energies but also performs exceptionally well in terms of describing the diffuseness of the different states and of their attachment/detachment densities. This study, thus, not only underlines the fact that diffuse basis functions are needed for an accurate description of the electronic wave functions but also shows that, at least for the present example, it is enough to include them implicitly in the contraction scheme.

  15. Electronic energy transfer in tetracene-doped p-terphenyl nanoparticles: Extraordinarily high fluorescence enhancement and quenching efficiency

    Energy Technology Data Exchange (ETDEWEB)

    Mitsui, Masaaki, E-mail:; Kawano, Yuya


    Highlights: ► Tc/pTP-NPs at various doping ratios are produced by reprecipitation in water. ► The energy transfer in Tc/pTP-NPs is investigated. ► More than 10{sup 4}pTP donors were quenched by a single Tc acceptor. ► Efficient energy transfer is attributed to the rapid exciton diffusion in the NPs. - Abstract: A series of tetracene (Tc)-doped p-terphenyl (pTP) nanoparticles (Tc/pTP-NPs) were produced at various doping ratios by reprecipitation in water. The Tc/pTP-NPs are disk-like with a mean diameter of 75 nm and height of 7 nm, which were determined by scanning electron microscopy and atomic force microscopy, and exhibited electronic delocalization through H-type aggregation of the pTP molecules. Electronic energy transfer in the Tc/pTP-NPs was examined using steady-state and time-resolved fluorescence spectroscopy and fluorescence anisotropy experiments: pTP-NPs serve as an excellent light-harvesting nano-matrix with a large absorption coefficient that exceeds 10{sup 9} M{sup −1} cm{sup −1}. Furthermore, Stern–Volmer analysis of the donor emission was performed by changing the dopant concentration; this showed that a single Tc acceptor quenched more than 10{sup 4}pTP donors. Comparison of the experimental and theoretical energy transfer efficiencies indicated that the efficient energy transfer can be attributed to two-dimensional exciton diffusion in the host nanoparticles.

  16. Synthesis and crystallochromy of 1,4,7,10-tetraalkyltetracenes: tuning of solid-state optical properties of tetracenes by alkyl side-chain length. (United States)

    Kitamura, Chitoshi; Abe, Yasushi; Ohara, Takuya; Yoneda, Akio; Kawase, Takeshi; Kobayashi, Takashi; Naito, Hiroyoshi; Komatsu, Toshiki


    We synthesized a series of 1,4,7,10-tetraalkyltetracenes using a new 2,6-naphthodiyne precursor and 2,5-dialkylfurans as starting materials (alkyl=methyl to hexyl). Surprisingly, the solid-state color of the tetracenes ranges through yellow, orange, and red. Both yellow and red solids are obtained for the butyl derivative. Optical properties in solution show no marked differences; however, those in the solid state show characteristics that vary with alkyl side-chain length: methyl, propyl, and pentyl derivatives are orange; ethyl and butyl derivatives are yellow; and another butyl and hexyl derivative are red. X-ray analyses reveal that the molecular structures are planar, semi-chair, or chair forms; the chair form takes a herringbone-like arrangement and the other forms take slipped parallel arrangements. The mechanism of crystallochromy is discussed in terms of molecular structure, crystal packing, and calculations that take account of exciton coupling.

  17. Solvent-Controlled Branching of Localized versus Delocalized Singlet Exciton States and Equilibration with Charge Transfer in a Structurally Well-Defined Tetracene Dimer

    Energy Technology Data Exchange (ETDEWEB)

    Cook, Jasper D. [Department; Carey, Thomas J. [Department; Arias, Dylan H. [National Renewable Energy Laboratory, Golden, Colorado 80401, United States; Johnson, Justin C. [National Renewable Energy Laboratory, Golden, Colorado 80401, United States; Damrauer, Niels H. [Department


    A detailed photophysical picture is elaborated for a structurally well-defined and symmetrical bis-tetracene dimer in solution. The molecule was designed for interrogation of the initial photophysical steps (S1 - 1TT) in intramolecular singlet fission (SF). (Triisopropylsilyl)acetylene substituents on the dimer TIPS-BT1 as well as a monomer model TIPS-Tc enable a comparison of photophysical properties, including transient absorption dynamics, as solvent polarity is varied. In nonpolar toluene solutions, TIPS-BT1 decays via radiative and nonradiative pathways to the ground state with no evidence for dynamics related to the initial stages of SF. This contrasts with the behavior of the previously reported unsubstituted dimer BT1 and is likely a consequence of energetic perturbations to the singlet excited-state manifold of TIPS-BT1 by the (trialkylsilyl)acetylene substituents. In polar benzonitrile, two key findings emerge. First, photoexcited TIPS-BT1 shows a bifurcation into both arm-localized (S1-loc) and dimer-delocalized (S1-dim) singlet exciton states. The S1-loc decays to the ground state, and weak temperature dependence of its emissive signatures suggests that once it is formed, it is isolated from S1-dim. Emissive signatures of the S1-dim state, on the other hand, are strongly temperature-dependent, and transient absorption dynamics show that S1-dim equilibrates with an intramolecular charge-transfer state in 50 ps at room temperature. This equilibrium decays to the ground state with little evidence for formation of long-lived triplets nor 1TT. These detailed studies spectrally characterize many of the key states in intramolecular SF in this class of dimers but highlight the need to tune electronic coupling and energetics for the S1 - 1TT photoreaction.

  18. Analytic derivative couplings and first-principles exciton/phonon coupling constants for an ab initio Frenkel-Davydov exciton model: Theory, implementation, and application to compute triplet exciton mobility parameters for crystalline tetracene (United States)

    Morrison, Adrian F.; Herbert, John M.


    Recently, we introduced an ab initio version of the Frenkel-Davydov exciton model for computing excited-state properties of molecular crystals and aggregates. Within this model, supersystem excited states are approximated as linear combinations of excitations localized on molecular sites, and the electronic Hamiltonian is constructed and diagonalized in a direct-product basis of non-orthogonal configuration state functions computed for isolated fragments. Here, we derive and implement analytic derivative couplings for this model, including nuclear derivatives of the natural transition orbital and symmetric orthogonalization transformations that are part of the approximation. Nuclear derivatives of the exciton Hamiltonian's matrix elements, required in order to compute the nonadiabatic couplings, are equivalent to the "Holstein" and "Peierls" exciton/phonon couplings that are widely discussed in the context of model Hamiltonians for energy and charge transport in organic photovoltaics. As an example, we compute the couplings that modulate triplet exciton transport in crystalline tetracene, which is relevant in the context of carrier diffusion following singlet exciton fission.

  19. Analytic derivative couplings and first-principles exciton/phonon coupling constants for an ab initio Frenkel-Davydov exciton model: Theory, implementation, and application to compute triplet exciton mobility parameters for crystalline tetracene. (United States)

    Morrison, Adrian F; Herbert, John M


    Recently, we introduced an ab initio version of the Frenkel-Davydov exciton model for computing excited-state properties of molecular crystals and aggregates. Within this model, supersystem excited states are approximated as linear combinations of excitations localized on molecular sites, and the electronic Hamiltonian is constructed and diagonalized in a direct-product basis of non-orthogonal configuration state functions computed for isolated fragments. Here, we derive and implement analytic derivative couplings for this model, including nuclear derivatives of the natural transition orbital and symmetric orthogonalization transformations that are part of the approximation. Nuclear derivatives of the exciton Hamiltonian's matrix elements, required in order to compute the nonadiabatic couplings, are equivalent to the "Holstein" and "Peierls" exciton/phonon couplings that are widely discussed in the context of model Hamiltonians for energy and charge transport in organic photovoltaics. As an example, we compute the couplings that modulate triplet exciton transport in crystalline tetracene, which is relevant in the context of carrier diffusion following singlet exciton fission.

  20. Bowl shaped deformation in a planar aromatic polycycle upon reduction. Li and Na separated dianions of the aromatic polycycle 5,6:11,12-di-o-phenylene-tetracene. (United States)

    Wombacher, T; Goddard, R; Lehmann, C W; Schneider, J J


    Herein we report the synthesis and crystal structures of three light alkali metal salts of the dianion of the polycyclic aromatic hydrocarbon 5,6:11,12-di-o-phenylenetetracene (L DOPT ). The compounds are obtained by reaction of L DOPT with an excess of lithium or sodium metal in different O-donor solvents (DME, diglyme) and crystallize as naked, solvated-cation separated dianions exhibiting no interaction between the alkali metal ion and the aromatic π-system of L DOPT . Depending on the aprotic etheral solvent and the hardness of the alkaline metal agent a significant structural perturbation of the conjugated carbon framework of L DOPT is observed resulting in a bowl shaped curvature of the anionic π-perimeter, in contrast to its fully planar neutral state. Reduction of L DOPT with lithium in DME results in the formation of the solvent-separated molecular structure of {[(DME-κ 2 O) 3 Li + ] 2 (L DOPT 2- )} 2 1 containing naked isolated units of dianionic L DOPT . A similar structural arrangement is observed for the corresponding sodium compound {[(DME-κ 2 O) 3 Na + ] 2 (L DOPT 2- )} 2 2 in which, however, a lesser curvature of the isolated dianionic ligand skeleton compared to 1 is observed. In contrast to 1 and 2 reduction with sodium in diglyme results in the formation of {[(diglyme-κ 3 O) 2 Na + ] 2 (L DOPT 2- )} 0.5 3. The deformation of the peripheric phenylene rings of [L DOPT 2- ] in 3 is not as pronounced as compared to 1 and 2. Nevertheless, molecular structures of 1-3 deviate from full-planarity as observed in the parent neutral L DOPT . No preferential endo- or exo-site coordination of the alkaline metal cations Li + and Na + on the curved dianionic π-perimeter is observed.

  1. CCDC 980734: Experimental Crystal Structure Determination : 9,18-bis(4-t-butylphenyl)-5,14-bis((4-t-butylphenyl)ethynyl)dinaphtho[3,2,1-de:3',2',1'-mn]tetracene chloroform solvate

    KAUST Repository

    Sun, Zhe


    An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

  2. DoD Contractors’ Safety Manual for Ammunition and Explosives (United States)


    use as initiating elements in an explosive train. Examples are wet lead azide, wet lead styphnate, wet mercury fulminate , wet tetracene, and dry PETN...original shipping conLdiner or equivalent) L 1.3 Mercury Fulminate , wet A 1.I Nitrates (inorganic), except ammonium nitrate (in original shipping container...dry HMX, dry Lead azide, wet Lead styphnate, wet Mercury fulminate , wet PETN, dry Tetracene, wet GROUP B Cartridge cases, primed (w/o propellant

  3. Cascade Organic Solar Cells

    KAUST Repository

    Schlenker, Cody W.


    We demonstrate planar organic solar cells consisting of a series of complementary donor materials with cascading exciton energies, incorporated in the following structure: glass/indium-tin-oxide/donor cascade/C 60/bathocuproine/Al. Using a tetracene layer grown in a descending energy cascade on 5,6-diphenyl-tetracene and capped with 5,6,11,12-tetraphenyl- tetracene, where the accessibility of the π-system in each material is expected to influence the rate of parasitic carrier leakage and charge recombination at the donor/acceptor interface, we observe an increase in open circuit voltage (Voc) of approximately 40% (corresponding to a change of +200 mV) compared to that of a single tetracene donor. Little change is observed in other parameters such as fill factor and short circuit current density (FF = 0.50 ± 0.02 and Jsc = 2.55 ± 0.23 mA/cm2) compared to those of the control tetracene-C60 solar cells (FF = 0.54 ± 0.02 and Jsc = 2.86 ± 0.23 mA/cm2). We demonstrate that this cascade architecture is effective in reducing losses due to polaron pair recombination at donor-acceptor interfaces, while enhancing spectral coverage, resulting in a substantial increase in the power conversion efficiency for cascade organic photovoltaic cells compared to tetracene and pentacene based devices with a single donor layer. © 2011 American Chemical Society.

  4. Charged Frenkel biexcitons in organic molecular crystals

    CERN Document Server

    Agranovich, V M; Kamchatnov, A M


    It is known that the energy of the lowest electronic transition in neutral molecules of anthracene, tetracene and other polyacenes is blue shifted in comparison with the corresponding transition energy in mono-valent molecular ions. This effect in molecular crystal may be responsible for the attraction between molecular (Frenkel) exciton and charge carrier. Due to this attraction the bound state of Frenkel exciton and free charge (charged Frenkel exciton) may be formed. The same mechanism can be responsible for formation of charged biexcitons (bound state of two Frenkel excitons and a charge carrier). Calculations are performed for molecular crystals like tetracene by means of one-dimensional lattice model

  5. Anionic sigmatropic-electrocyclic-Chugaev cascades: accessing 12-aryl-5-(methylthiocarbonylthiotetracenes and a related anthra[2,3-b]thiophene

    Directory of Open Access Journals (Sweden)

    Laurence Burroughs


    Full Text Available 1,4-Diols resulting from the double addition of ArCCLi (Ar = Ph, substituted phenyl, 2-thienyl to ortho-C6H4(CHO2 undergo cascades to tetracenes on simple admixture of LiHDMS, CS2 and MeI. Acene formation proceeds by [3,3]-sigmatropic rearrangement of xanthate anions followed by 6π electrocyclisations. The reactions are terminated by E2 or anionic Chugaev-type eliminations. Structural packing motifs and electronic properties are reported for the tetracenes.

  6. DOD Ammunition and Explosives Safety Standards (United States)


    following: bulk lead azide, lead styphnate, mercury fulminate , tetracene, dry cyclotrimethylenetrinitramine (RDX) (also known as cyclonite, hexogen, or...primary explosives are lead azide and mercury fulminate . AP1.191. Primary fragment. A fragment from material in intimate contact with reacting AE

  7. Browse Title Index

    African Journals Online (AJOL)

    Items 301 - 350 of 650 ... Vol 2, No 2 (2009), Future prospects for ethanol fuel use - a review, Abstract PDF. G Ahmed, S ... Vol 10, No 1 (2017), Geometry optimization and vibrational frequencies of tetracene molecule in gas phase and in methanol based on Density Funtional Theory and Restricted Hartree-Fock, Abstract PDF.

  8. Two Birds with One Stone: Tailoring Singlet Fission for Both Triplet Yield and Exciton Diffusion Length

    Energy Technology Data Exchange (ETDEWEB)

    Zhu, Tong [Department of Chemistry, Purdue University, West Lafayette IN 47907 USA; Wan, Yan [Department of Chemistry, Purdue University, West Lafayette IN 47907 USA; Guo, Zhi [Department of Chemistry, Purdue University, West Lafayette IN 47907 USA; Johnson, Justin [National Renewable Energy Laboratory, 15013 Denver West Pkwy Golden CO 80401 USA; Huang, Libai [Department of Chemistry, Purdue University, West Lafayette IN 47907 USA


    By direct imaging of singlet and triplet populations with ultrafast microscopy, it is shown that the triplet diffusion length and singlet fission yield can be simultaneously optimized for tetracene and its derivatives, making them ideal structures for application in bilayer solar cells.

  9. Author Details

    African Journals Online (AJOL)

    The effect of water solubles on Kelvin effects of the Maritime Polluted aerosols. Abstract PDF · Vol 10, No 1 (2017) - Articles Geometry optimization and vibrational frequencies of tetracene molecule in gas phase and in methanol based on Density Funtional Theory and Restricted Hartree-Fock Abstract PDF. ISSN: 2006-6996.

  10. Exploring conditions for the enhancement of acene semiconductors through the use of the Diels-alder reaction (United States)

    Qualizza, Brittni A.

    This dissertation demonstrates the application of SAMs to the surface of acene crystals, specifically of tetracene and rubrene, using the Diels-Alder reaction. The second chapter details preliminary reaction results and two analytical methods which were employed to confirm adsorption of the dienophile on the surface of single crystals, tetracene and rubrene. These were mass spectrometry and X-ray photoelectron spectroscopy (XPS). Mass spectrometry experiments distinguish the chemical identity of adduct on the crystals and also it discerned chemi- and physisorbed molecules from one another. XPS was used to prove face selectivity of the reaction by the detection of dichloromaleic anhydride. From a mechanistic standpoint, this system demonstrated unusual steric effects: the reaction of one face of the tetracene crystal was virtually inert, while another face was facile. The dienophiles' steric bulk was also expected to play critical role for these confined systems, however analysis of surface data was hindered by the relative lack of corresponding solution kinetic data. While the rate of anthracene's reaction has been studied extensively with a range of dienophiles and tetracene/pentacene has been studied theoretically (with limited experimental reports), an expansive report was generated to aid in future interpretations of acene systems. These kinetic results constitute chapter three.

  11. New concepts for light-emitting transistors (United States)

    Hepp, Aline; Ahles, Marcus; Heil, Holger; Schmechel, Roland; von Seggern, Heinz; Weiler, Ulrich; Mayer, Thomas; Jaegermann, Wolfram


    In this study we report on new concepts to generate light emission in organic thin film transistors. The initial physical understanding of light emission from tetracene based field-effect transistors was proposed to be originated from a strong underetching of the drain and source electrodes. This underetched electrodes in combination with the evaporated tetracene is thereby believed to generate a virtual OLED at the drain electrode. Accumulated holes have to leave the gate oxide interface to reach the drain electrode by crossing the bulk of the organic semiconductor. Light then occurs by injection of electrons in a large electric field in the bulk. Today's transistors do not show the underetching anymore but are still emitting light only at the drain electrode, again supporting the initial interpretation of a defect state at the edge of the drain electrode. In this context the question how electrons can overcome a potential barrier of 2.7 eV is still open. Therefore an investigation of the gold tetracene interface by UPS and XPS techniques has been started and preliminary data indicate the unexpected result that the barrier for electrons is comparable to that for holes. In a further step the generation of an ambipolar transistor by interface doping with calcium was tried and an n-type pentacene transistor could be fabricated but the strategy failed for tetracene. Finally an electrochemical interface doping was performed by the application of Lithium triflate in PEO to a thin interface layer between gate oxide and tetracene. This leads to light emission but unfortunately also to the loss of the gate voltage influence. Based on these results a possible strategy will be presented.

  12. TEM characterization of organic nanocrystals grown in sol-gel thin films

    Energy Technology Data Exchange (ETDEWEB)

    Monnier, Virginie; Bacia, Maria [CNRS and Universite Joseph Fourier, Institut Neel (France); Putaux, Jean-Luc [ICMG-CNRS, Centre de Recherches sur les Macromolecules Vegetales (France); Ibanez, Alain [CNRS and Universite Joseph Fourier, Institut Neel (France)], E-mail:


    The tetracene molecule (2,3-benzanthracene, C{sub 8}H{sub 12}) was used to synthesize nanocrystals grown in sol-gel thin films, ranging from 10 to 100 nm of diameter. This confined nucleation and growth was compared to microcrystallizations of the same molecule in free solution. Transmission electron microscopy (TEM) was used to characterize these two kinds of tetracene crystals. The observation was performed under low-dose illumination to avoid amorphization of the samples during electron irradiation. Spatial confinement and size distribution of micro- and nanocrystals were compared. Using electron microdiffraction and diffraction patterns simulations, we showed that free microcrystals and nanocrystals confined in gel glasses exhibit the same triclinic P-bar 1 structure. In addition, time-resolved spectroscopy was used to record fluorescence decays, showing a monoexponential fluorescence decay for nanocrystals while microcrystals exhibit a multiexponential decay. The simple signature of nanocrystals luminescence is promising for the future development of chemical or biological sensors.

  13. Towards atomic-level mechanics: Adhesive forces between aromatic molecules and carbon nanotubes (United States)

    Lechner, Christoph; Sax, Alexander F.


    The adhesive forces for desorption of the four aromatic compounds benzene, anthracene, pyrene, and tetracene from a (8,0) carbon nanotube (CNT) are investigated and compared to the desorption from graphene. The desorption energies are found to be proportional to the size of the contact zone in the adsorbent/adsorbate complex while maximum adhesive forces are proportional to the part of the contact zone where attractive interactions are reduced when external forces pull on the adsorbate. To assess the influence of the curvature, type of CNT, and the adsorbate's orientation, the desorption processes from six zigzag CNT and four armchair CNT are studied for pyrene and tetracene. For some properties, the results are independent of the curvature of the adsorbent, whereas for others we find marked differences. Aspects of elasticity are considered as well as the influence of the Pauli exclusion principle on the equilibrium geometries in adsorbent/adsorbate complexes.

  14. A Rapid Chemical Analysis of the Ingredients of NOL-130 Primer Mix (United States)


    potassium chlorate, copper (I) thiocyanate, antimony sulfide, lead azide, and mercury fulminate . Wild (refs. 2,3) developed a method for tetracene based...on its dissolution in hydrochloric acid to give a well-defined reduction wave at the dropping mercury electrode. He also developed a method for the...374 Polarographic Analyzer (Princeton Applied Research Corporation, Princeton, NJ) and a model 303 Static Mercury Drop Electrode. For this work, the

  15. Impact of Molecular Orientation and Packing Density on Electronic Polarization in the Bulk and at Surfaces of Organic Semiconductors

    KAUST Repository

    Ryno, Sean M.


    The polarizable environment surrounding charge carriers in organic semiconductors impacts the efficiency of the charge transport process. Here, we consider two representative organic semiconductors, tetracene and rubrene, and evaluate their polarization energies in the bulk and at the organic-vacuum interface using a polarizable force field that accounts for induced-dipole and quadrupole interactions. Though both oligoacenes pack in a herringbone motif, the tetraphenyl substituents on the tetracene backbone of rubrene alter greatly the nature of the packing. The resulting change in relative orientations of neighboring molecules is found to reduce the bulk polarization energy of holes in rubrene by some 0.3 eV when compared to tetracene. The consideration of model organic-vacuum interfaces highlights the significant variation in the electrostatic environment for a charge carrier at a surface although the net change in polarization energy is small; interestingly, the environment of a charge even just one layer removed from the surface can be viewed already as representative of the bulk. Overall, it is found that in these herringbone-type layered crystals the polarization energy has a much stronger dependence on the intralayer packing density than interlayer packing density.

  16. Singlet Fission in Rubrene Derivatives: Impact of Molecular Packing

    KAUST Repository

    Sutton, Christopher


    We examine the properties of six recently synthesized rubrene derivatives (with substitutions on the side phenyl rings) that show vastly different crystal structures. In order to understand how packing in the solid state affects the excited states and couplings relevant for singlet fission, the lowest excited singlet (S), triplet (T), multiexciton (TT), and charge-transfer (CT) states of the rubrene derivatives are compared to known singlet fission materials [tetracene, pentacene, 5,12-diphenyltetracene (DPT), and rubrene itself]. While a small difference of less than 0.2 eV is calculated for the S and TT energies, a range of 0.50 to 1.2 eV in the CT energies and nearly 3 orders of magnitude in the electronic couplings are computed for the rubrene derivatives in their crystalline packings, which strongly affects the role of the CT state in facilitating SF. To rationalize experimental observations of singlet fission occurring in amorphous phases of rubrene, DPT, and tetracene, we use molecular dynamics (MD) simulations to assess the impact of molecular packing and orientations and to gain a better understanding of the parameters that control singlet fission in amorphous films compared to crystalline packings. The MD simulations point to a crystalline-like packing for thin films of tetracene; on the other hand, DPT, rubrene, and the rubrene derivatives all show various degrees of disorder with a number of sites that have larger electronic couplings than in the crystal, which can facilitate singlet fission in such thin films. Our analysis underlines the potential of these materials as promising candidates for singlet fission and helps understand how various structural motifs affect the critical parameters that control the ability of a system to undergo singlet fission.

  17. Fast identification of rubrene polymorphs by lattice phonon Raman microscopy (United States)

    Socci, Joseph; Salzillo, Tommaso; Della Valle, Raffaele Guido; Venuti, Elisabetta; Brillante, Aldo


    Confocal Raman microscopy in the lattice phonon region has been used to study the polymorphism of the organic semiconductor 5,6,11,12-tetraphenyl-tetracene (rubrene). Following literature guidelines, crystals of rubrene have been prepared using a number of solution growth and vapour deposition methods, obtaining samples of different morphologies which could be related to the various polymorphs of this compound. The technique has enabled us an easy and non invasive identification of the three known polymorphs and of their phase homogeneity with a lateral spatial resolution below 1 μm.

  18. The quantum coherent mechanism for singlet fission: experiment and theory. (United States)

    Chan, Wai-Lun; Berkelbach, Timothy C; Provorse, Makenzie R; Monahan, Nicholas R; Tritsch, John R; Hybertsen, Mark S; Reichman, David R; Gao, Jiali; Zhu, X-Y


    The absorption of one photon by a semiconductor material usually creates one electron-hole pair. However, this general rule breaks down in a few organic semiconductors, such as pentacene and tetracene, where one photon absorption may result in two electron-hole pairs. This process, where a singlet exciton transforms to two triplet excitons, can have quantum yields as high as 200%. Singlet fission may be useful to solar cell technologies to increase the power conversion efficiency beyond the so-called Shockley-Queisser limit. Through time-resolved two-photon photoemission (TR-2PPE) spectroscopy in crystalline pentacene and tetracene, our lab has recently provided the first spectroscopic signatures in singlet fission of a critical intermediate known as the multiexciton state (also called a correlated triplet pair). More importantly, we found that population of the multiexciton state rises at the same time as the singlet state on the ultrafast time scale upon photoexcitation. This observation does not fit with the traditional view of singlet fission involving the incoherent conversion of a singlet to a triplet pair. However, it provides an experimental foundation for a quantum coherent mechanism in which the electronic coupling creates a quantum superposition of the singlet and the multiexciton state immediately after optical excitation. In this Account, we review key experimental findings from TR-2PPE experiments and present a theoretical analysis of the quantum coherent mechanism based on electronic structural and density matrix calculations for crystalline tetracene lattices. Using multistate density functional theory, we find that the direct electronic coupling between singlet and multiexciton states is too weak to explain the experimental observation. Instead, indirect coupling via charge transfer intermediate states is two orders of magnitude stronger, and dominates the dynamics for ultrafast multiexciton formation. Density matrix calculation for the crystalline

  19. A simple model of burst nucleation. (United States)

    Baronov, Alexandr; Bufkin, Kevin; Shaw, Dan W; Johnson, Brad L; Patrick, David L


    We introduce a comprehensive quantitative treatment for burst nucleation (BN)-a kinetic pathway toward self-assembly or crystallization defined by an extended post-supersaturation induction period, followed by a burst of nucleation, and finally the growth of existing stable assemblages absent the formation of new ones-based on a hybrid mean field rate equation model incorporating thermodynamic treatment of the saturated solvent from classical nucleation theory. A key element is the inclusion of a concentration-dependent critical nucleus size, determined self-consistently along with the subcritical cluster population density. The model is applied to an example experimental study of crystallization in tetracene films prepared by organic vapor-liquid-solid deposition, where good agreement is observed with several aspects of the experiment using a single, physically well-defined adjustable parameter. The model predicts many important features of the experiment, and can be generalized to describe other self-organizing systems exhibiting BN kinetics.

  20. A Simple Hubbard Model for the Excited States of $\\pi$ Conjugated -acene Molecules

    CERN Document Server

    Sadeq, Z S


    In this paper we present a model that elucidates in a simple way the electronic excited states of $\\pi$ conjugated -acene molecules such as tetracene, pentacene, and hexacene. We use a tight-binding and truncated Hubbard model written in the electron-hole basis to describe the low lying excitations with reasonable quantitative accuracy. We are able to produce semi-analytic wavefunctions for the electronic states of the system, which allows us to compute the density correlation functions for various states such as the ground state, the first two singly excited states, and the lowest lying doubly excited state. We show that in this lowest lying doubly excited state, a state which has been speculated as to being involved in the singlet fission process, the electrons and holes behave in a triplet like manner.

  1. Description of ground and excited electronic states by ensemble density functional method with extended active space (United States)

    Filatov, Michael; Martínez, Todd J.; Kim, Kwang S.


    An extended variant of the spin-restricted ensemble-referenced Kohn-Sham (REKS) method, the REKS(4,4) method, designed to describe the ground electronic states of strongly multireference systems is modified to enable calculation of excited states within the time-independent variational formalism. The new method, the state-interaction state-averaged REKS(4,4), i.e., SI-SA-REKS(4,4), is capable of describing several excited states of a molecule involving double bond cleavage, polyradical character, or multiple chromophoric units. We demonstrate that the new method correctly describes the ground and the lowest singlet excited states of a molecule (ethylene) undergoing double bond cleavage. The applicability of the new method for excitonic states is illustrated with π stacked ethylene and tetracene dimers. We conclude that the new method can describe a wide range of multireference phenomena.

  2. Quantifying local exciton, charge resonance, and multiexciton character in correlated wave functions of multichromophoric systems (United States)

    Casanova, David; Krylov, Anna I.


    A new method for quantifying the contributions of local excitation, charge resonance, and multiexciton configurations in correlated wave functions of multichromophoric systems is presented. The approach relies on fragment-localized orbitals and employs spin correlators. Its utility is illustrated by calculations on model clusters of hydrogen, ethylene, and tetracene molecules using adiabatic restricted-active-space configuration interaction wave functions. In addition to the wave function analysis, this approach provides a basis for a simple state-specific energy correction accounting for insufficient description of electron correlation. The decomposition scheme also allows one to compute energies of the diabatic states of the local excitonic, charge-resonance, and multi-excitonic character. The new method provides insight into electronic structure of multichromophoric systems and delivers valuable reference data for validating excitonic models.


    Chen, Edward S; Chen, Edward C M


    The anion mass spectral lifetimes for several aromatic hydrocarbons reported in the subject article were related to significantly different electron affinities. The different values are rationalized using negative ion mass spectral data. Electron affinities for polycyclic aromatic hydrocarbons are reported from the temperature dependence of unpublished electron capture detector data. These are compared with published values and the largest values are assigned to the ground state. The ground state adiabatic electron affinities: (eV) pentacene, 1.41(3); tetracene, 1.058(5); benz(a)pyrene, 0.82(4); benz(a) anthracene, 0.69(2) anthracene, 0.68(2); and pyrene, 0.59(1) are used to assign excited state adiabatic electron affinities: (eV) tetracene: 0.88(4); anthracene 0.53(1) ; pyrene, 0.41(1); benz(a)anthracene, 0.39(10); chrysene, 0.32(1); and phenanthrene, 0.12(2) and ground state adiabatic electron affinities: (eV) dibenz(a,j)anthracene, 0.69(2); dibenz(a,h)anthracene, 0.68(2); benz(e)pyrene, 0.60(2); and picene, 0.59(2) from experimental data. The lifetime of benz(a)pyrene is predicted to be larger than 150 μsec and for picene about 40 μsec, from ground state adiabatic electron affinities. The assignments of adiabatic electron affinities of aromatic hydrocarbons determined from electron capture detector and mass spectrometric data to ground and excited states are supported by constant electronegativities. A set of consistent ground state adiabatic electron affinities for fifteen polycyclic aromatic hydrocarbons is related to lifetimes from the subject article. This article is protected by copyright. All rights reserved.

  4. Computational study of the effect of dispersion interactions on the thermochemistry of aggregation of fused polycyclic aromatic hydrocarbons as model asphaltene compounds in solution. (United States)

    Moreira da Costa, Leonardo; Stoyanov, Stanislav R; Gusarov, Sergey; Seidl, Peter R; Walkimar de M Carneiro, José; Kovalenko, Andriy


    Density functional theory (DFT), Møller-Plesset second-order perturbation theory (MP2), and semiempirical methods are employed for the geometry optimization and thermochemistry analysis of π-π stacked di-, tri-, tetra-, and pentamer aggregates of the fused polycyclic aromatic hydrocarbons (PAHs) naphthalene, anthracene, phenanthrene, tetracene, pyrene, and coronene as well as benzene. These aggregates (stabilized by dispersion interactions) are highly relevant to the intermolecular aggregation of asphaltenes, major components of heavy petroleum. The strength of π-π stacking interaction is evaluated with respect to the π-stacking distance and thermochemistry results, such as aggregation enthalpies, entropies, and Gibbs free energies (ΔG(298)). For both π-stacking interplanar distances and thermochemistry, the ωB97X-D functional with an augmented damped R(-6) dispersion correction term and MP2 are in the closest agreement with the highly accurate spin-component scaled MP2 (SCS-MP2) method that we selected as a reference. The ΔG(298) values indicate that the aggregation of coronene is spontaneous at 298 K and the formation of pyrene dimers occurs spontaneously at temperature lower than 250 K. Aggregates of smaller PAHs would be stable at even lower temperature. These findings are supported by X-ray crystallographic determination results showing that among the PAHs studied only coronene forms continuous stacked aggregates in single crystals, pyrene forms dimers, and smaller PAHs do not form π-π stacked aggregates. Thermochemistry analysis results show that PAHs containing more than four fused benzene rings would spontaneously form aggregates at 298 K. Also, round-shaped PAHs, such as phenanthrene and pyrene, form more stable aggregates than linear PAHs, such as anthracene and tetracene, due to decreased entropic penalty. These results are intended to help guide the synthesis of model asphaltene compounds for spectroscopic studies so as to help understand

  5. Application and evaluation of solvent-free matrix-assisted laser desorption/ionization mass spectrometry for the analysis of derivatized fullerenes. (United States)

    Kotsiris, Sotirios G; Vasil'ev, Yury V; Streletskii, Alexey V; Han, Ming; Mark, Lewis P; Boltalina, Olga V; Chronakis, Nikos; Orfanopoulos, Michael; Hungerbühler, Hartmut; Drewello, Thomas


    A variety of derivatized fullerenes have been studied by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. Of particular emphasis has been the evaluation of a recently introduced solvent-free sample/target preparation method. Solvent-free MALDI is particularly valuable in overcoming adverse solvent-related effects, such as insolubility and/or degradation of the sample. The method was applied to fullerene derivatives susceptible to decomposition under insufficiently "soft" MALDI conditions. Analytes included the hydrofullerene: C(60)H(36), fluorofullerenes: C(60)F(x) where x = 18, 36, 46, 48 and C(70)F(x) where x = 54, 56, methano-bridged amphiphilic ligand adducts to C(60) and the [4 + 2] cycloadduct of tetracene to C(60). The new solvent-free sample preparation is established as an exceedingly valuable addition to the repertoire of preparation protocols within MALDI. The MALDI mass spectra were of very high quality throughout, providing a testimony that "soft" MALDI conditions could be achieved. Using the [4 + 2] cycloadduct of tetracene to C(60) as the model analyte for direct comparison with solvent-based MALDI, the solvent-free approach led to less fragmentation and more abundant analyte ions. Applying solvent-free sample preparation, different matrix compounds have been examined for use in the MALDI of derivatized fullerenes, including sulfur, tetracyanoquinodimethane (TCNQ), 9-nitroanthracene (9-NA) and trans-2-[3-(4-tert-butylphenyl)-2-methyl-2- propenylidene]malononitrile (DCTB). DCTB was confirmed as the best performing matrix, reducing unwanted decomposition and suppression effects.

  6. First-Principles DFT Studies of the Vibrational Properties of Germanene Nanoflakes (United States)

    Richardson, Steven; Peroparde, Borja; Andrade, Xavier; Aspuru-Guzik, AláN.

    The germanium analogue of graphene, germanene, is a potentially new atomically thin quantum material which theory predicts will possess unique transport and optoelectronic properties. Recently, there have been a number of experimental efforts to successfully grow two-dimensional films of germanene on noble metal substrates using molecular beam epitaxy. In addition to this top-down approach of synthesizing large scale films of germanene, we would like to focus on a bottom-up approach where nanoflakes of germanene could be used as molecular seeds or precursors to grow large films of two-dimensional germanene. A knowledge of their infrared and Raman spectra will be critical for characterizing these germanene nanoflakes in future experiments. In this work we used density-functional theory (DFT) to compute the vibrational spectra of a selected number of lower order germanene nanoflakes (e.g. hexagermabenzene, germa-naphthalene, germa-anthracene, germa-phenanthrene, germa-pyrene, germa-tetracene, and germa-pentacene). Our DFT studies also reveal that these germanene nanoflakes are vibrationally stable with buckling of these molecules from their normal two-dimensional planar forms which exist in graphene nanoflakes. This research is supported by NSF Grant No. DMR-1231319.

  7. The nature of singlet excitons in oligoacene molecular crystals

    KAUST Repository

    Yamagata, H.


    A theory for polarized absorption in crystalline oligoacenes is presented, which includes Frenkel exciton coupling, the coupling between Frenkel and charge-transfer (CT) excitons, and the coupling of all neutral and ionic excited states to the dominant ring-breathing vibrational mode. For tetracene, spectra calculated using all Frenkel couplings among the five lowest energy molecular singlet states predict a Davydov splitting (DS) of the lowest energy (0-0) vibronic band of only -32cm-1, far smaller than the measured value of 631cm-1 and of the wrong sign-a negative sign indicating that the polarizations of the lower and upper Davydov components are reversed from experiment. Inclusion of Frenkel-CT coupling dramatically improves the agreement with experiment, yielding a 0-0 DS of 601cm-1 and a nearly quantitative reproduction of the relative spectral intensities of the 0-n vibronic components. Our analysis also shows that CT mixing increases with the size of the oligoacenes. We discuss the implications of these results on exciton dissociation and transport. © 2011 American Institute of Physics.

  8. Two different ground states in K-doped polyacenes (United States)

    Heguri, Satoshi; Phan Thi Nhu, Quynh; Tamura, Hiroyuki; Nakano, Takehito; Nozue, Yasuo; Tanigaki, Katsumi; AIMR Team; Department of Physics Team; Osaka University Team

    The electronic states of potassium (K) doped zigzag-type polycyclic aromatic hydrocarbon (polyacenes (PLAs)) Kx(PLAs), are studied for a series of the four smallest molecules: naphthalene (NN), anthrance (AN), tetracene (TN), and pentacene (PN), focusing on their 1:1 stoichiometric phases. Clear experimental differences are identified between the first group (K1(NN) and K1(AN)) and the second group (K1(TN) and K1(PN)) by magnetic, vibrational, and optical measurements. The first group is categorized as a Mott insulator with an antiferromagnetic ground state with energy of c.a. 10 meV, while the second group is classified as a band insulator via dimer formation due to the spin Peierls instability. In the latter system, the first thermally accessible triplet states are located far apart from the singlet ground states at room temperature, and are not detected by electron spin resonance spectroscopy until 300 K, being very different from what is observed for hole doped PN reported earlier. The results give a new systematic understanding on the electronic states of electron doped PLAs sensitive to the energetic balance among on-site Coulomb repulsion, band width and the Peierls instability.

  9. Controlled Growth of Organic Semiconductor Films Using Liquid Crystal Solvents (United States)

    Bufkin, Kevin; Ohlson, Brooks; Hillman, Ben; Johnson, Brad; Patrick, David


    Interest in using organic semiconductors in applications such as large area displays, photovoltaic devices, and RFID tags stems in part from their prospects for enabling significantly reduced manufacturing costs compared to traditional inorganic semiconductors. However many of the best performing prototype devices produced so far have involved expensive or time-consuming fabrication methods, such as the use of single crystals or thin films deposited under high vacuum conditions. We present a new approach for growing low molecular weight organic crystalline films at ambient conditions based on a vapor-liquid-solid growth mechanism using thermotropic nematic liquid crystal (LC) solvents. Tetracene is deposited via atmospheric-pressure sublimation onto substrates coated by a LC layer oriented using rubbed polyimide, producing films that are highly crystalline, with large grain sizes, and possessing macroscopic uniaxial orientation. This poster will describe the growth mechanism, discuss the effects of processing conditions such as LC layer thickness, substrate temperature and flux rate, and compare the results to a model of deposition-diffusion aggregation accounting for the finite thickness of the solvent layer.

  10. Rubrene endoperoxide acetone monosolvate

    Directory of Open Access Journals (Sweden)

    Kiyoaki Shinashi


    Full Text Available The title acetone solvate, C42H28O2·C3H6O [systematic name: 1,3,10,12-tetraphenyl-19,20-dioxapentacyclo[,11.04,9.013,18]icosa-2(11,3,5,7,9,13,15,17-octaene acetone monosolvate], is a photooxygenation product of rubrene (systematic name: 5,6,11,12-tetraphenyltetracene. The molecule bends at the bridgehead atoms, which are linked by the O—O transannular bond, with a dihedral angle of 49.21 (6° between the benzene ring and the naphthalene ring system of the tetracene unit. In the crystal, the rubrene molecules are linked by C—H...O hydrogen bonds into a column along the c axis. The acetone solvent molecules form a dimer around a crystallographic inversion centre through a carbonyl–carbonyl dipolar interaction. A C—H...O hydrogen bond between the rubrene and acetone molecules is also observed.

  11. Investigating the effect of acene-fusion and trifluoroacetyl substitution on the electronic and charge transport properties by density functional theory

    Directory of Open Access Journals (Sweden)

    Ahmad Irfan


    Full Text Available We designed novel derivatives of 4,6-di(thiophen-2-ylpyrimidine (DTP. Two benchmark strategies including mesomerically deactivating group, as well as the extension of π-conjugation bridge (acene-fusion have been employed to enhance the electrical and charge transport properties. The density functional theory (DFT and time dependent DFT methods have been used to get optimized geometries in ground and first excited state, respectively. The structural properties (geometric parameters, electronic properties (frontier molecular orbitals; highest occupied and lowest unoccupied molecular orbitals, photophysical properties (absorption, fluorescence and phosphorescence, and important charge transport properties are discussed to establish a molecular level structure–property relationship among these derivatives. Our calculated electronic spectra i.e., absorption, fluorescence and phosphorescence have been found in good semi-quantitative agreement with available experimental data. All the newly designed derivatives displayed significantly improved electron injection ability than those of the parent molecule. The values of reorganization energy and transfer integral elucidate that DTP is a potential hole transport material. Based on our present investigation, it is expected that the naphtho and anthra derivatives of DTP are better hole transporters than those of some well-known charge transporter materials like naphthalene, anthracene, tetracene and pentacene.

  12. White-Emissive Self-Assembled Organic Microcrystals. (United States)

    Li, Zhi Zhou; Liang, Feng; Zhuo, Ming Peng; Shi, Ying Li; Wang, Xue Dong; Liao, Liang Sheng


    Organic semiconductor micro-/nanocrystals with regular shapes have been demonstrated for many applications, such as organic field-effect transistors, organic waveguide devices, organic solid-state lasers, and therefore are inherently ideal building blocks for the key circuits in the next generation of miniaturized optoelectronics. In the study, blue-emissive organic molecules of 1,4-bis(2-methylstyryl)benzene (o-MSB) can assemble into rectangular microcrystals at a large scale via the room-temperature solution-exchange method. Because of the Förster resonance energy transfer, the energy of the absorbed photons by the host matrix organic molecules of o-MSB can directly transfer to the dopant organic molecules of tetracene or 1,2:8,9-dibenzopentacene (DBP), which then emit visible photons in different colors from blue to green, and to yellow. More impressively, by modulating the doping molar ratios of DBP to o-MSB, bright white-emissive organic microcrystals with well-preserved rectangular morphology can be successfully achieved with a low doping ratio of 1.5%. These self-assembled organic semiconductor microcrystals with multicolor emissions can be the white-light sources for the integrated optical circuits at micro-/nanoscale. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. High-Resolution IR Absorption Spectroscopy of Polycyclic Aromatic Hydrocarbons: The Realm of Anharmonicity (United States)

    Maltseva, Elena; Petrignani, Annemieke; Candian, Alessandra; Mackie, Cameron J.; Huang, Xinchuan; Lee, Timothy J.; Tielens, Alexander G. G. M.; Oomens, Jos; Buma, Wybren Jan


    We report on an experimental and theoretical investigation of the importance of anharmonicity in the 3 micrometers CH stretching region of Polycyclic Aromatic Hydrocarbon (PAH) molecules. We present mass-resolved, high-resolution spectra of the gas-phase cold ((is) approximately 4K) linear PAH molecules naphthalene, anthracene, and tetracene. The measured IR spectra show a surprisingly high number of strong vibrational bands. For naphthalene, the observed bands are well separated and limited by the rotational contour, revealing the band symmetries. Comparisons are made to the harmonic and anharmonic approaches of the widely used Gaussian software. We also present calculated spectra of these acenes using the computational program SPECTRO, providing anharmonic predictions enhanced with a Fermi-resonance treatment that utilizes intensity redistribution. We demonstrate that the anharmonicity of the investigated acenes is strong, dominated by Fermi resonances between the fundamental and double combination modes, with triple combination bands as possible candidates to resolve remaining discrepancies. The anharmonic spectra as calculated with SPECTRO lead to predictions of the main modes that fall within 0.5% of the experimental frequencies. The implications for the Aromatic Infrared Bands, specifically the 3-m band are discussed.

  14. New Soluble Pentacene Precursors for the Application of Organic Thin-Film Transistors

    Energy Technology Data Exchange (ETDEWEB)

    Joung, Meyoung Ju; Kang, Seung Youl; Baek, Kyu Ha [Electronics and Telecommunications Research Institute, Daejeon (Korea, Republic of); and others


    Research into organic semiconductors often focuses either on solution processable semiconducting polymer or on small molecules. Solution processed semiconducting materials are of particular interest for large area coverage, structural flexibility, low-temperature processing, and, especially, ultralow-cost application since they allow the use of spin-coating, spraycoating, screen printing, or ink-jet printing. As semiconducting polymer for OTFTs, poly(3-hexylthiophene) (P3HT) was fabricated by solution process, the devices showed field effect mobilities ranging from 0.05 to 0.1 cm{sup 2}/Vs and on-off current ratios of >10{sup 6}. Another active layer polymer is poly(9,9-dioctylfluorene-co-bithiophene) (F8T2), which was spin-coated from xylene solution and high mobility of 0.02 cm{sup 2}/Vs and on-off current ratios of 10{sup 5} were obtained. The high mobility 0.22 cm{sup 2}/Vs has been reported for OTFTs using precursor-route poly(2,5-thienylene) (PTV) as semiconducting polymer. Small molecule semiconductors, such as oligothiophenes and the hydrocarbons (pentacene and tetracene), may be suitable for applications requiring electrical performance similar to that of amorphous silicon TFTs.

  15. Synthesis of extended polycyclic aromatic hydrocarbons by oxidative tandem spirocyclization and 1,2-aryl migration (United States)

    Zhang, Xuan; Xu, Zhanqiang; Si, Weili; Oniwa, Kazuaki; Bao, Ming; Yamamoto, Yoshinori; Jin, Tienan


    The extended polycyclic aromatic hydrocarbons (PAHs) have received significant interdisciplinary attention due to their semiconducting applications in diverse organic electronics as well as intriguing structural interests of well-defined graphene segments. Herein, a highly efficient oxidative spirocyclization and 1,2-aryl migration tandem synthetic method for the construction of extended polyaromatic hydrocarbons (PAHs) has been developed. The CuCl-catalyst/PhCO3 tBu or DDQ oxidation system in the presence of trifluoroacetic acid enables the selective single-electron oxidation to take place preferentially at the more electron-rich alkene moiety of o-biphenylyl-substituted methylenefluorenes, giving rise to the subsequent tandem process. A variety of structurally diverse extended PAHs including functionalized dibenzo[g,p]chrysenes, benzo[f]naphtho[1,2-s]picene, hexabenzo[a,c,fg,j,l,op]tetracene, tetrabenzo[a,c,f,m]phenanthro[9,10-k]tetraphene, tetrabenzo[a,c,f,k]phenanthro[9,10-m]tetraphene, tetrabenzo[a,c,f,o]phenanthro[9,10-m]picene and S-type helicene have been readily synthesized.

  16. Surface chemistry of rare-earth oxide surfaces at ambient conditions: reactions with water and hydrocarbons (United States)

    Külah, Elçin; Marot, Laurent; Steiner, Roland; Romanyuk, Andriy; Jung, Thomas A.; Wäckerlin, Aneliia; Meyer, Ernst


    Rare-earth (RE) oxide surfaces are of significant importance for catalysis and were recently reported to possess intrinsic hydrophobicity. The surface chemistry of these oxides in the low temperature regime, however, remains to a large extent unexplored. The reactions occurring at RE surfaces at room temperature (RT) in real air environment, in particular, in presence of polycyclic aromatic hydrocarbons (PAHs), were not addressed until now. Discovering these reactions would shed light onto intermediate steps occurring in automotive exhaust catalysts before reaching the final high operational temperature and full conversion of organics. Here we first address physical properties of the RE oxide, nitride and fluoride surfaces modified by exposure to ambient air and then we report a room temperature reaction between PAH and RE oxide surfaces, exemplified by tetracene (C18H12) on a Gd2O3. Our study evidences a novel effect - oxidation of higher hydrocarbons at significantly lower temperatures (~300 K) than previously reported (>500 K). The evolution of the surface chemical composition of RE compounds in ambient air is investigated and correlated with the surface wetting. Our surprising results reveal the complex behavior of RE surfaces and motivate follow-up studies of reactions between PAH and catalytic surfaces at the single molecule level.

  17. Green primary explosives: 5-nitrotetrazolato-N2-ferrate hierarchies. (United States)

    Huynh, My Hang V; Coburn, Michael D; Meyer, Thomas J; Wetzler, Modi


    The sensitive explosives used in initiating devices like primers and detonators are called primary explosives. Successful detonations of secondary explosives are accomplished by suitable sources of initiation energy that is transmitted directly from the primaries or through secondary explosive boosters. Reliable initiating mechanisms are available in numerous forms of primers and detonators depending upon the nature of the secondary explosives. The technology of initiation devices used for military and civilian purposes continues to expand owing to variations in initiating method, chemical composition, quantity, sensitivity, explosive performance, and other necessary built-in mechanisms. Although the most widely used primaries contain toxic lead azide and lead styphnate, mixtures of thermally unstable primaries, like diazodinitrophenol and tetracene, or poisonous agents, like antimony sulfide and barium nitrate, are also used. Novel environmentally friendly primary explosives are expanded here to include cat[Fe(II)(NT)(3)(H(2)O)(3)], cat(2)[Fe(II)(NT)(4)(H(2)O)(2)], cat(3)[Fe(II)(NT)(5)(H(2)O)], and cat(4)[Fe(II)(NT)(6)] with cat = cation and NT(-) = 5-nitrotetrazolato-N(2). With available alkaline, alkaline earth, and organic cations as partners, four series of 5-nitrotetrazolato-N(2)-ferrate hierarchies have been prepared that provide a plethora of green primaries with diverse initiating sensitivity and explosive performance. They hold great promise for replacing not only toxic lead primaries but also thermally unstable primaries and poisonous agents. Strategies are also described for the systematic preparation of coordination complex green primaries based on appropriate selection of ligands, metals, and synthetic procedures. These strategies allow for maximum versatility in initiating sensitivity and explosive performance while retaining properties required for green primaries.

  18. Photophysical characterization and time-resolved spectroscopy of a anthradithiophene dimer: exploring the role of conformation in singlet fission

    KAUST Repository

    Dean, Jacob C.


    Quantitative singlet fission has been observed for a variety of acene derivatives such as tetracene and pentacene, and efforts to extend the library of singlet fission compounds is of current interest. Preliminary calculations suggest anthradithiophenes exhibit significant exothermicity between the first optically-allowed singlet state, S1, and 2 × T1 with an energy difference of >5000 cm−1. Given the fulfillment of this ingredient for singlet fission, here we investigate the singlet fission capability of a difluorinated anthradithiophene dimer (2ADT) covalently linked by a (dimethylsilyl)ethane bridge and derivatized by triisobutylsilylethynyl (TIBS) groups. Photophysical characterization of 2ADT and the single functionalized ADT monomer were carried out in toluene and acetone solution via absorption and fluorescence spectroscopy, and their photo-initiated dynamics were investigated with time-resolved fluorescence (TRF) and transient absorption (TA) spectroscopy. In accordance with computational predictions, two conformers of 2ADT were observed via fluorescence spectroscopy and were assigned to structures with the ADT cores trans or cis to one another about the covalent bridge. The two conformers exhibited markedly different excited state deactivation mechanisms, with the minor trans population being representative of the ADT monomer showing primarily radiative decay, while the dominant cis population underwent relaxation into an excimer geometry before internally converting to the ground state. The excimer formation kinetics were found to be solvent dependent, yielding time constants of ∼1.75 ns in toluene, and ∼600 ps in acetone. While the difference in rates elicits a role for the solvent in stabilizing the excimer structure, the rate is still decidedly long compared to most singlet fission rates of analogous dimers, suggesting that the excimer is neither a kinetic nor a thermodynamic trap, yet singlet fission was still not observed. The result

  19. Interaction of radiation with matter

    Energy Technology Data Exchange (ETDEWEB)


    During 1978, these conclusions were reached and are reported: Innershell Coulomb ionization cross sections show significant relativistic effects even for the lighter atoms, because ionization occurs near the nucleus in our range of low particle energies. Atomic excitation and ionization in deep atom--atom collisions can be described in terms of a model with random walk in energy space to the continuum. This model may be best suited for the analysis of heavy ion--atom encounters. Energy straggling of charged particles in matter are affected by inhomogeneities in and surface conditions of the medium. Using molecular ions as incident projectiles it is concluded that moving protons do not have bound states in solids. Projectiles in close proximity to each other exhibit larger energy losses than isolated projectiles indicating interactions of the electron density fluctuations established behind moving projectiles in solids. Heterogeneous oxidation of SO/sub 2/ by holes has been found at an organic (PAH) aqueous interface. The process has a reasonably high quantum efficiency (approx. >0.1) for anthracene. Various experiments are being carried out to determine whether SO/sub 3//sup =/ or HSO/sub 3/- is involved. Photoemission from PAH organic aerosols has been investigated. The rate of emission from tetracene is found to go as the maximum electron kinetic energy cubed. It is found that the particle may be used as an electron spectrometer for determining the electron kinetic energy distribution. A new way of characterizing small aerosols by mass has been found. The method utilizes the detection of a single electron imbalance in a Millikan chamber. Aerosol masses as small as 1 pgm can be measured to better than 1%. The potent carcinogen benzo (a) pyrene (BP) when metabolized in vivo is found to have a physical structure in which the BP7,8-dihydrodial 9,10-oxide adduct (BPDE) is bound on the outside of the helix.

  20. The Larger Linear N-Heteroacenes

    KAUST Repository

    Bunz, Uwe H. F.


    tetraazaacenes, azapentacenes, azahexacenes, and azaheptacenes are accessible. Pd-catalysis-based coupling methods for both activated and nonactivated o-dihalides have been developed. The larger azaacene representatives were unknown before but are of conceptual and theoretical interest. Azaacenes, particularly the symmetrical bis(triisopropylsilylethynyl)-substituted tetraazapentacene, are primarily used in organic field-effect transistors, but smaller azaacenes shine in the field as organic light-emitting diode (OLED) emitters. Diazatetracenes and substituted benzoquinoxalines are successful, improving electron injection and increasing OLED brightness, as compared to that of pure tetracenes. On the basis of the acene framework, nitrogen atoms in the acene perimeter and aggregation-precluding molecular appendages create solid-state fluorescent species. Azaacenes are expanding the range and complementing the purview of acenes in organic electronic applications. They enlarge the profiles of acenes with respect to synthetic strategies, structures, properties, and applications.

  1. An In Silico Study on the Isomers of Pentacene: The Case for Air-Stable and Alternative C22H14 Acenes for Organic Electronics. (United States)

    Jones, Leighton; Lin, Long


    Pentacene is one of the most investigated candidates for organic thin film transistor (OTFT) applications over the last few decades even though it unstable in air (Eg = 1.80 eV), owing in part to its planar nature and high charge-transfer mobilities as both a single crystal (35 cm2 V-1 s-1) and as a thin-film (3.0 cm2 V-1 s-1). Until now, picene is the only isomer of pentacene to be investigated for organic electronic applications, due to its greater stability (Eg = 4.21 eV) and high-charge transfer mobility (3.0 cm2 V-1 s-1); even benefiting from oxygen doping. In the present study, a total of 12 fused-ring isomers (including pentacene, picene and ten other structures) of the formula C22H14 were analyzed and investigated for their electronic and optical properties for worth in OTFT applications. We screened several pure and hybrid DFT functionals against the experimental frontier molecular orbitals (FMOs) of pentacene, then deployed Marcus Theory, Koopmans' Theorem and Green's function with the P3 electron propagator variant, for the internal hole reorganization energy, the hole transfer integral (via the "splitting-in-dimer method" at d = 3.0, 3.5, and 4.0 Å), the charge transfer rate constant, and vertical ionization energies. Using these as a basis, we studied pentacene's isomers and found that the four nonplanar structures, namely, benzo[g]chrysene (3), naphtho[c]phenanthrene (7), benzo[c]chrysene (11) and dibenzo[c,c']phenthrene (12), are (I) more stable than pentacene, by up to 2 eV, and (II) have relatively similar ionization energies (7.5-7.6 eV) to those of picene's experimental value (7.51 eV). The largest charge transfer rates at 3.5 Å dimer separations were given by the isomers benzo[b]chrysene 4, naphtha[c]phenanthrene 7, dibenzo[a,c]anthracene 8 and benzo[a]tetracene 10 and found to be 2.92, 1.72, 1.30, and 3.09 × 1014 s-1 respectively. In comparison to that of pentacene (KCT = 3.97 × 1014 s-1), these unusual isomers are thus promising air

  2. Explicitly correlated Wn theory: W1-F12 and W2-F12. (United States)

    Karton, Amir; Martin, Jan M L


    In an attempt to extend the applicability of the W1 and W2 ab initio computational thermochemistry methods, we propose explicitly correlated versions thereof, denoted W1-F12 and W2-F12. In W2-F12, we can "save" one cardinal number (viz., angular momentum) in the basis set sequences without loss in accuracy; in W1-F12, we can do so for first-row compounds but not for second-row compounds. At a root mean square deviation (RMSD) = 0.19 kcal/mol for the first-row molecules in the W4-11 benchmark dataset, W1-F12 is in fact superior to ordinary W1 theory. For the entire W4-11 set, W2-F12 yields a RMSD = 0.20 kcal/mol, comparable to 0.19 kcal/mol from ordinary W2 theory. The extended applicability ranges of W1-F12 and W2-F12 are not just due to the lower computational cost but also to greatly reduced memory and especially storage requirements. They are illustrated through applications to nucleic acids and to polyacenes (with up to four rings), for which the following revised gas-phase heats of formation are found: Δ(f)H(298)(∘) = 19.6 (benzene), 34.94 (naphthalene), 53.9, (anthracene), 73.9 (naphthacene/tetracene), 54.9 (adenine), -16.3 (cytosine), 5.1 (guanine), -80.6 (thymine), and -71.6 (uracil) kcal/mol. Our theoretical values for the DNA/RNA bases largely confirm recent predictions based on much lower-level calculations. The W1-F12 theoretical values for benzene, naphthalene, and anthracene are in very good to reasonable agreement with experiment. However, both W1-F12 and other computational estimates show that the accepted experimental value for naphthacene cannot be reconciled with those for the lower acenes: we suggest that Δ(f)H(298)(∘)[naphthacene(g)] = 74.25 ± 1 kcal/mol is a more realistic estimate.

  3. Probing the accuracy and precision of Hirshfeld atom refinement withHARtinterfaced withOlex2. (United States)

    Fugel, Malte; Jayatilaka, Dylan; Hupf, Emanuel; Overgaard, Jacob; Hathwar, Venkatesha R; Macchi, Piero; Turner, Michael J; Howard, Judith A K; Dolomanov, Oleg V; Puschmann, Horst; Iversen, Bo B; Bürgi, Hans-Beat; Grabowsky, Simon


    Hirshfeld atom refinement (HAR) is a novel X-ray structure refinement technique that employs aspherical atomic scattering factors obtained from stockholder partitioning of a theoretically determined tailor-made static electron density. HAR overcomes many of the known limitations of independent atom modelling (IAM), such as too short element-hydrogen distances, r ( X -H), or too large atomic displacement parameters (ADPs). This study probes the accuracy and precision of anisotropic hydrogen and non-hydrogen ADPs and of r ( X -H) values obtained from HAR. These quantities are compared and found to agree with those obtained from (i) accurate neutron diffraction data measured at the same temperatures as the X-ray data and (ii) multipole modelling (MM), an established alternative method for interpreting X-ray diffraction data with the help of aspherical atomic scattering factors. Results are presented for three chemically different systems: the aromatic hydro-carbon rubrene (orthorhombic 5,6,11,12-tetra-phenyl-tetracene), a co-crystal of zwitterionic betaine, imidazolium cations and picrate anions (BIPa), and the salt potassium hydrogen oxalate (KHOx). The non-hydrogen HAR-ADPs are as accurate and precise as the MM-ADPs. Both show excellent agreement with the neutron-based values and are superior to IAM-ADPs. The anisotropic hydrogen HAR-ADPs show a somewhat larger deviation from neutron-based values than the hydrogen SHADE-ADPs used in MM. Element-hydrogen bond lengths from HAR are in excellent agreement with those obtained from neutron diffraction experiments, although they are somewhat less precise. The residual density contour maps after HAR show fewer features than those after MM. Calculating the static electron density with the def2-TZVP basis set instead of the simpler def2-SVP one does not improve the refinement results significantly. All HARs were performed within the recently introduced HARt option implemented in the Olex2 program. They are easily launched

  4. Structural and photophysical considerations of singlet fission organic thin films for solar photochemistry (United States)

    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

  5. Ferrocene-fused derivatives of acenes, tropones and thiepins (United States)

    Maharjan, Bidhya Laxmi

    This research project is concentrated on tuning the properties of small organic molecules, namely polyacenes, tropones and thiepins, by incorporating redox-active transition metal centers pi-bonded to terminal cyclopentadienyl ligands. Organometallicfused acenequinones, tropones, thiepins and cyclopentadiene-capped polyacenes were synthesized and characterized. This work was divided into three parts: first, the synthesis of ferrocene-fused acenequinones, cyclopentadiene-capped acenequinones and their subsequent aromatization to polyacenes; second, the synthesis of ferrocene-fused tropones, thiotropones and tropone oxime; and third, the synthesis of ferrocene-fused thiepins. Ferrocene-fused quinones are the precursors to our target complexes. Our synthetic route to ferrocenequinones involved two-fold aldol condensation between 1,2- diformylferrocene and naphthalene-1,4-diol or anthracene-1,4-diol, and four-fold condensation between 1,2-diformylferrocene and 1,4-cyclohexanedione. Reduction of ferrocene-fused quinones with borane in THF resulted in ferrocene-fused dihydroacenes. Attempts to reduce ferrocene-fused acenequinones with sodium dithionite led to metalfree cyclopentadiene- (Cp-) capped acenequinones. Cp-capped acenequinones were aromatized to bis(triisopropylsilyl)ethynyl polyacenes by using lithium (triisopropylsilyl)acetylide (TIPSC≡CLi) with subsequent dehydroxylation by stannous chloride. The compounds were characterized by using spectroscopic methods and X-ray crystallography. Further, the electronic properties of these compounds were studied by using cyclic voltammetry and UV-visible spectroscopy. Cyclic voltammetry showed oxidation potentials of Cp-capped TIPS-tetracene and bis-Cp-capped TIPS-anthracene as 0.49 V and 0.61 V, respectively (vs. ferrocene/ferrocenium). The electrochemical band gaps were 2.15 eV and 2.58 eV, respectively. Organic thin-film transistor device performance of Cp-capped polyacenes was studied using solution deposition

  6. Unconventional, Chemically Stable, and Soluble Two-Dimensional Angular Polycyclic Aromatic Hydrocarbons: From Molecular Design to Device Applications

    KAUST Repository

    Zhang, Lei


    Polycyclic aromatic hydrocarbons (PAHs), consisting of laterally fused benzene rings, are among the most widely studied small-molecule organic semiconductors, with potential applications in organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). Linear acenes, including tetracene, pentacene, and their derivatives, have received particular attention due to the synthetic flexibility in tuning their chemical structure and properties and to their high device performance. Unfortunately, longer acenes, which could exhibit even better performance, are susceptible to oxidation, photodegradation, and, in solar cells which contain fullerenes, Diels-Alder reactions. This Account highlights recent advances in the molecular design of two-dimensional (2-D) PAHs that combine device performance with environmental stability. New synthetic techniques have been developed to create stable PAHs that extend conjugation in two dimensions. The stability of these novel compounds is consistent with Clar\\'s sextet rule as the 2-D PAHs have greater numbers of sextets in their ground-state configuration than their linear analogues. The ionization potentials (IPs) of nonlinear acenes decrease more slowly with annellation in comparison to their linear counterparts. As a result, 2-D bistetracene derivatives that are composed of eight fused benzene rings are measured to be about 200 times more stable in chlorinated organic solvents than pentacene derivatives with only five fused rings.Single crystals of the bistetracene derivatives have hole mobilities, measured in OFET configuration, up to 6.1 cm2 V-1 s-1, with remarkable Ion/Ioff ratios of 107. The density functional theory (DFT) calculations can provide insight into the electronic structures at both molecular and material levels and to evaluate the main charge-transport parameters. The 2-D acenes with large aspect ratios and appropriate substituents have the potential to provide favorable interstack electronic interactions

  7. Part I: Synthesis and study of nonacene derivatives; Part II: Optoelectronic properties of metal-semiconductor nanocomposites in strongly coupled regime (United States)

    Khon, Dmitriy

    Acenes are polycyclic aromatic hydrocarbons (PAHs) consisting of linearly fused benzene rings. In the recent past, acenes have been of interest from fundamental and applied perspectives. Smaller acenes such as benzene, naphthalene, and anthracene are among the most studied organic compounds and their properties are well explored. Pentacene has received considerable attention as the most promising active semiconductor for use in organic thin film transistors (TFT) because of its high charge-carrier mobility; however, poor environmental stability is one of the problems limiting its practical application. As the number of rings increases, the members of the acene family become increasingly reactive. The successful synthesis of heptacene developed by Mondal et al. used the Strating-Zwanenberg photodecarbonylation reaction. The lesser stability of the tetracene moieties in the nonacene photoprecursor compared to the anthracene moieties of the heptacene process make its synthesis more challenging. The latter scheme requires 2,3-dibromoanthracene as one of the starting materials. Besides the poor solubility of 2,3-dibromoanthracene, failure was also due to insufficient formation of anthracyne upon treatment of 2,3-dibromoanthracene with n-BuLi. Although the initial idea didn't work we used the same scheme replacing 2,3-dibromoanthracene with 7,8-dibromo-1,4-dihydroanthracene. The reaction of the latter with 5,6,7,8-tetramethylenebicyclo[2.2.2]oct-2-ene gave 1,4,7,8,9,12,15,18,19,20-octadecahydro-8,19-diethenononacene albeit in low yield. Multiple attempts to dehydrogenate the non-aromatic rings using DDQ and other reagents under various conditions failed to produce the desired compound. Recently Miller reported the synthesis of relatively stable heptacene derivatives having a combination of arylthio and o-dialkylphenyl substituents. Miller's scheme used 1,2,4,5-tetrakis(bromomethyl)-3,6-bis(4'- t-butylthiophenyl)benzene as the core precursor. Another synthetic approach

  8. EDITORIAL: Focus on Molecular Electronics FOCUS ON MOLECULAR ELECTRONICS (United States)

    Scheer, Elke; Reineker, Peter


    experimental and theoretical investigations allows for a comparison of the spectra of two molecules with the same backbone (tetracene and rubrene). The transport of charge through a molecule occurs possibly in a stationary, but at any rate in a non-equilibrium situation. The study of dissipation in such situations requires special approaches, both in theory and in experiments. One key issue is the understanding of the role of the microscopic phenomena such as the excitation of vibrational modes and their macroscopic outcome, i.e. the dissipation. This topic is addressed in several contributions both theoretically and experimentally. From the theoretical side, for the investigation of the heat production during the electron transfer, non-equilibrium Green's functions have been utilized. In another contribution a combination of the non-equilibrium Green's function technique together with the density functional method has been developed for the calculation of the elastic and inelastic electronic transport. To calculate the transport of indistinguishable particles a path integral Monte Carlo approach has been put forward. In single-molecule transistors the gate-voltage dependence on the Kondo temperature and an accompanying strong Coulomb blockade can be explained by taking into account a strong electron-vibron interaction including anharmonicities of the molecular potential surface. The transport of charges is heavily influenced by disorder. The case of static disorder is investigated for linear chains, carbon nanotubes and graphene ribbons. Finally it is shown that the charge transport through a single energy level coupled to a localized vibrational mode and two leads shows hysteretic effects which could possibly be used in a memory device. For applications the control of the current through a molecular junction is considered theoretically. Two possible mechanisms are discussed: the control via coherent destruction using predefined ultrafast laser pulses and the formation of