Spectroscopic Study of Anisotropic Excitons in Single Crystal Hexacene † † ‡ ‡ ‡ † Alexey Chernikov,*, Omer Yaffe, Bharat Kumar, Yu Zhong, Colin Nuckolls, and Tony F

Total Page:16

File Type:pdf, Size:1020Kb

Spectroscopic Study of Anisotropic Excitons in Single Crystal Hexacene † † ‡ ‡ ‡ † Alexey Chernikov,*, Omer Yaffe, Bharat Kumar, Yu Zhong, Colin Nuckolls, and Tony F Letter pubs.acs.org/JPCL Spectroscopic Study of Anisotropic Excitons in Single Crystal Hexacene † † ‡ ‡ ‡ † Alexey Chernikov,*, Omer Yaffe, Bharat Kumar, Yu Zhong, Colin Nuckolls, and Tony F. Heinz*, † Departments of Physics and Electrical Engineering, Columbia University, New York, New York 10027, United States ‡ Department of Chemistry, Columbia University, New York, New York 10027, United States *S Supporting Information ABSTRACT: The linear optical response of hexacene single crystals over a spectral range of 1.3−1.9 eV was studied using polarization-resolved reflectance spectroscopy at cryogenic temperatures. We observe strong polarization anisotropy for all optical transitions. Pronounced deviations from the single-molecule, solution-phase spectra are present, with a measured Davydov splitting of 180 meV, indicating strong intermolecular coupling. The energies and oscillator strengths of the relevant optical transitions and polarization-dependent absorption coefficients are extracted from quantitative analysis of the data. SECTION: Spectroscopy, Photochemistry, and Excited States inear acenes, that is, naphthalene, anthracene, tetracene, established between the degree of CT character and the so- L and pentacene, form a unique family of organic semi- called Davydov splitting (DS)19 of the low-lying excitons conductors. These materials readily form large (>100 μm2) observed in polarization-resolved optical absorption spectra.6 single crystals that exhibit a “herring-bone” packing motif in Thus, experimental characterization of the intrinsic optical 1 which aromatic edge-to-face interactions dominate. During the properties of organic crystals also facilitates rational design of last few decades, this family has been the subject of many advanced optoelectronic devices. Naturally, the steady increase 2 experimental and theoretical studies, especially motivated by of the intermolecular coupling from naphthalene to pentacene fl potential applications in exible, low-cost optoelectronic crystals provides a strong impetus for a systematic study of even 3−5 devices. The strength of the intermolecular interactions in larger linear acenes. Such studies have been inhibited by the linear acene crystals is now understood to increase steadily with ff 6 lack of suitable synthetic methods. Recently, however, e ective the length of the acene molecule. This increased interaction is synthesis and crystallization methods for hexacene have been correlated with two major trends: an increase in charge carrier 7 7 reported. In a previous work, we made use of this method to mobility and an increase in the extent to which the molecular investigate the rate of singlet fission in polycrystalline hexacene electronic structure is perturbed by intermolecular coupling films and the room-temperature optical response of hexacene effects.6,8,9 The latter manifests itself directly in the optical single crystals.20 spectra of the materials. Single crystals of smaller acenes Here, we study the linear optical response of hexacene single preserve the characteristic absorption features of the individual crystals by polarization-resolved reflectance spectroscopy at molecules in solution, with transitions of Frenkel excitons cryogenic temperatures. From quantitative analysis of the data, featuring well-resolved vibronic sidebands. The optical response of the pentacene crystals, however, already shows marked we extract the energies and oscillator strengths of the relevant, bright optical transitions and polarization-dependent absorp- deviations from the molecular picture, indicating the ffi pronounced influence of intermolecular interactions.6,8,10 tion coe cients. The optical response of the crystalline fi In addition, increased intermolecular coupling is accom- hexacene is found to deviate signi cantly from the correspond- panied by a delocalization of the excitonic wave function, which ing single-molecule solution-phase spectrum (measured in Si oil 21 is distributed among several neighboring molecules and can to avoid oxidation), indicating the presence of strong also lead to an increased charge-transfer (CT) character of the intermolecular interactions. low-energy excitons.8,9,11,12 Such CT states are considered to be crucial for multiexciton effects such as singlet fission, an energy Received: August 11, 2014 conversion process where an excited singlet state converts into Accepted: October 6, 2014 − two long-lived triplet states.9,12 18 Correlation has been Published: October 6, 2014 © 2014 American Chemical Society 3632 dx.doi.org/10.1021/jz501693g | J. Phys. Chem. Lett. 2014, 5, 3632−3635 The Journal of Physical Chemistry Letters Letter Hexacene single crystals with an average thickness of several presented in Figure 1). The sin2 curves shown in the same plot microns and lateral areas of 20−50 μm2 were grown on a fused illustrate the pronounced polarization anisotropy of the silica substrate using a recently reported synthesis and growth respective transitions with about 90° between the a and b procedure.7 Micrographs of typical crystals are presented in the resonances. The amplitudes of the a- and b-related peaks nearly Supporting Information. Previous single crystal X-ray diffrac- vanish in the spectra with the opposite polarization, with tion measurements have established that such crystals adopt a residual intensities attributed to a small angular tilt of the out- triclinic structure with a nearly rectangular in-plane unit-cell of-plane crystal axis or inhomogeneities. lying parallel to the substrate.7 Optical reflection measurements To extract the energy and the oscillator strengths of the were performed at normal incidence, with samples held in a spectrally overlapping resonances in the reflectance spectra, we cryostat at a temperature of 77 K. We used a tungsten quartz apply a quantitative analysis scheme based on a standard multi- halogen lamp as a broadband radiation source, with the incident Lorentzian parametrization22 of the complex dielectric function light linearly polarized by a rotatable absorptive polarization ϵ(E) with photon energy E and for the two polarizations along filter. The reflected radiation was spectrally dispersed in a the principal optical axis grating spectrometer and detected by a liquid-nitrogen-cooled f CCD. Measurements were performed only on the thickest k ϵ=ϵ+()E b ∑ 22 crystals (see micrographs in Supporting Information). These k EEiE0,k −−γk (1) crystals were opaque and could be treated as semi-infinite in E2 γ f extent in the analysis below. To obtain absolute reflectance with 0,k, k and k denoting the peak energy, spectral k spectra for each polarization angle, we normalized the reflection broadening and the oscillator strength of the th transition, ϵ from the sample by that from the fused silica substrate. respectively. The background constant is represented by b. ϵ ϵ The measured reflectance spectra of the hexacene crystal are The real and imaginary parts 1 and 2 of the dielectric function ϵ E n iκ presented in Figure 1a for polarization angles between 0° and ( ) are related to the complex refractive index ( + ) via ⎡ 1 ⎤1/2 n()E =ϵ+ϵ+ϵ⎢ ()2 2 ⎥ ⎣ 2 112 ⎦ (2) ⎡ 1 ⎤1/2 κ()E =−ϵ+ϵ+ϵ⎢ ()2 2 ⎥ ⎣ 2 112 ⎦ (3) The reflectance spectrum for a semi-infinite bulk crystal at the normal incidence is then obtained from n and κ using [1]n −+22κ R()E = [1]n ++22κ (4) ϵ E a a b b The peak parameters in ( ) for the 1, ..., 4 and 1, ..., 4 transitions are adjusted to ensure a fit of the multi-Lorentzian model to the measured reflectance spectra. Two different dielectric functions are obtained for the a- and fl b-polarized cases, illustrating the anisotropy of the dielectric Figure 1. (a) Linearly polarized re ectance spectra of a hexacene 23,24 T ° ° tensor in the acene crystals. In general, this analysis single crystal at = 77 K for polarization angles between 0 and 90 . fi The resonances excited with light polarized along the a axis (0°) and b procedure is justi ed when the chosen polarization angles are ° a a b b axis (90 ) of the crystal are denoted by 1, ..., 4 and 1, ..., 4, close to or equivalent to the principal optical axis of the b ° respectively. The spectral region around the 4 resonance in the 90 dielectric tensor. In the present case the substrate plane spectrum is presented in the inset. (b) Schematic representation of the corresponds to the ab plane of the hexacene crystals and the hexacene crystal structure perpendicular to the growth direction with latter is almost rectangular (γ ≈ 90°),7,20 that is, the crystal the symmetry axes denoted by “a” and “b”. (c) Polar plot of the structure is nearly orthorhombic. For pentacene, the principal a b normalized peak intensities of the lowest-lying exciton states ( 1, 1)as axes a and b indeed closely correspond to the orthogonal in- a function of polarization angle. For comparison, the solid lines show plane directions x and y,10 justifying the assignment of the 0° sin2 functions. and 90° polarization angles as being close to both principal optical and crystallographic axes. 90°. The two angles are typically assigned to be roughly aligned The results of the above procedure are presented in Figure along the a and b symmetry axes of the crystal, schematically 2a, b, and c for the a-polarized (0°), unpolarized, and b- shown in Figure 1b. A manifold of resonances is observed with polarized (90°) spectra along with the measured data. The a strong dependence on the polarization angle. The optical unpolarized spectrum is obtained by averaging the a- and b- a a b b fl transitions are labeled by 1, ..., 4 and 1, ..., 4 according to the polarized re ectance. The agreement of the results from the a b respective polarization conditions. The resonances 1 and 1 are multi-Lorentzian analysis with the experimental data allows for identified as the bright low-energy excitons measured at room- a meaningful extraction of the peak parameters and related temperature in the previous study,20 exhibiting a DS of their observables, such as the absorption coefficients α(E)= respective peak energies.19 The similarity of the optical spectra κ(E)(2E/ℏc).22 The latter are presented in Figure 2d, e, and at room- and low-temperature indicates that there is no f for the three polarization conditions.
Recommended publications
  • Refining Crude Oil
    REFINING CRUDE OIL New Zealand buys crude oil from overseas, as well as drilling for some oil locally. This oil is a mixture of many hydrocarbons that has to be refined before it can be used for fuel. All crude oil in New Zealand is refined by The New Zealand Refining Company at their Marsden Point refinery where it is converted to petrol, diesel, kerosene, aviation fuel, bitumen, refinery gas (which fuels the refinery) and sulfur. The refining process depends on the chemical processes of distillation (separating liquids by their different boiling points) and catalysis (which speeds up reaction rates), and uses the principles of chemical equilibria. Chemical equilibrium exists when the reactants in a reaction are producing products, but those products are being recombined again into reactants. By altering the reaction conditions the amount of either products or reactants can be increased. Refining is carried out in three main steps. Step 1 - Separation The oil is separated into its constituents by distillation, and some of these components (such as the refinery gas) are further separated with chemical reactions and by using solvents which dissolve one component of a mixture significantly better than another. Step 2 - Conversion The various hydrocarbons produced are then chemically altered to make them more suitable for their intended purpose. For example, naphthas are "reformed" from paraffins and naphthenes into aromatics. These reactions often use catalysis, and so sulfur is removed from the hydrocarbons before they are reacted, as it would 'poison' the catalysts used. The chemical equilibria are also manipulated to ensure a maximum yield of the desired product.
    [Show full text]
  • General Disclaimer One Or More of the Following Statements May Affect
    General Disclaimer One or more of the Following Statements may affect this Document This document has been reproduced from the best copy furnished by the organizational source. It is being released in the interest of making available as much information as possible. This document may contain data, which exceeds the sheet parameters. It was furnished in this condition by the organizational source and is the best copy available. This document may contain tone-on-tone or color graphs, charts and/or pictures, which have been reproduced in black and white. This document is paginated as submitted by the original source. Portions of this document are not fully legible due to the historical nature of some of the material. However, it is the best reproduction available from the original submission. Produced by the NASA Center for Aerospace Information (CASI) NASA CR - 159480 EXXON/GRUS. 1KWD. 78 NIGH PERFORMANCE, HIGH DENSITY HYDROCARBON FUELS J. W. Frankenfeld, T. W. Hastings, M. Lieberman and W. F. Taylor EXXON RESEARCH AND ENGINEERING COMPANY prepared for NATIONAL AERONAUTICS AND SPACE ADMINISTRATION (NASA-CR-159''PO) HIGH PEPPOFMANCF, HIGH V79-20267 DENSTTv HYDR I-CARBON FTIELS (Exxon P.esearch and Engineering Co.) 239 rp HC A11/MF A01 CSCL 21D 'Inclas G3/28 19456 NASA Lewis Research Center Contract NAS 3-20394 Qnr{l,,Y^ ^'Pr I€ ^i NASA CR - 159480 EXXON/GRUS . 1KWD . 78 L: HIGH PERFORMANCE, HIGH DENSITY HYDROCARBON FUELS J. W. Frankenfeld, T. W. Hastings, M. Lieberman and W. F. Taylor EXXON RESEARCH AND ENGINEERING COMPANY prepared for NATIONAL AERONAUTICS AND SPACE ADMINISTRATION NASA Lewis Research Center Contract NAS 3-20394 FOREWARD The research described in this report was performed at Exxon Research and Engineering Company, Linden, New Jersey and Contract NAS 320394 with Mr.
    [Show full text]
  • Polycyclic Aromatic Hydrocarbon Structure Index
    NIST Special Publication 922 Polycyclic Aromatic Hydrocarbon Structure Index Lane C. Sander and Stephen A. Wise Chemical Science and Technology Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899-0001 December 1997 revised August 2020 U.S. Department of Commerce William M. Daley, Secretary Technology Administration Gary R. Bachula, Acting Under Secretary for Technology National Institute of Standards and Technology Raymond G. Kammer, Director Polycyclic Aromatic Hydrocarbon Structure Index Lane C. Sander and Stephen A. Wise Chemical Science and Technology Laboratory National Institute of Standards and Technology Gaithersburg, MD 20899 This tabulation is presented as an aid in the identification of the chemical structures of polycyclic aromatic hydrocarbons (PAHs). The Structure Index consists of two parts: (1) a cross index of named PAHs listed in alphabetical order, and (2) chemical structures including ring numbering, name(s), Chemical Abstract Service (CAS) Registry numbers, chemical formulas, molecular weights, and length-to-breadth ratios (L/B) and shape descriptors of PAHs listed in order of increasing molecular weight. Where possible, synonyms (including those employing alternate and/or obsolete naming conventions) have been included. Synonyms used in the Structure Index were compiled from a variety of sources including “Polynuclear Aromatic Hydrocarbons Nomenclature Guide,” by Loening, et al. [1], “Analytical Chemistry of Polycyclic Aromatic Compounds,” by Lee et al. [2], “Calculated Molecular Properties of Polycyclic Aromatic Hydrocarbons,” by Hites and Simonsick [3], “Handbook of Polycyclic Hydrocarbons,” by J. R. Dias [4], “The Ring Index,” by Patterson and Capell [5], “CAS 12th Collective Index,” [6] and “Aldrich Structure Index” [7]. In this publication the IUPAC preferred name is shown in large or bold type.
    [Show full text]
  • Chemistry of Acenes, [60]Fullerenes, Cyclacenes and Carbon Nanotubes
    University of New Hampshire University of New Hampshire Scholars' Repository Doctoral Dissertations Student Scholarship Spring 2011 Chemistry of acenes, [60]fullerenes, cyclacenes and carbon nanotubes Chandrani Pramanik University of New Hampshire, Durham Follow this and additional works at: https://scholars.unh.edu/dissertation Recommended Citation Pramanik, Chandrani, "Chemistry of acenes, [60]fullerenes, cyclacenes and carbon nanotubes" (2011). Doctoral Dissertations. 574. https://scholars.unh.edu/dissertation/574 This Dissertation is brought to you for free and open access by the Student Scholarship at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact [email protected]. CHEMISTRY OF ACENES, [60]FULLERENES, CYCLACENES AND CARBON NANOTUBES BY CHANDRANI PRAMANIK B.Sc., Jadavpur University, Kolkata, India, 2002 M.Sc, Indian Institute of Technology Kanpur, India, 2004 DISSERTATION Submitted to the University of New Hampshire in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Materials Science May 2011 UMI Number: 3467368 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. UMI Dissertation Publishing UMI 3467368 Copyright 2011 by ProQuest LLC. All rights reserved. This edition of the work is protected against unauthorized copying under Title 17, United States Code. ProQuest LLC 789 East Eisenhower Parkway P.O.
    [Show full text]
  • Excited States of Molecules with Density Functional Theory and Many Body Perturbation Theory
    Excited States of Molecules with Density Functional Theory and Many Body Perturbation Theory by Samia M. Hamed A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemistry in the Graduate Division of the University of California, Berkeley Committee in charge: Professor Jeffrey B. Neaton, Chair Professor Martin Head-Gordon, Co-chair Professor Naomi Ginsberg Professor Michael F. Crommie Summer 2020 Excited States of Molecules with Density Functional Theory and Many Body Perturbation Theory Copyright 2020 by Samia M. Hamed 1 Abstract Excited States of Molecules with Density Functional Theory and Many Body Perturbation Theory by Samia M. Hamed Doctor of Philosophy in Chemistry University of California, Berkeley Professor Jeffrey B. Neaton, Chair Professor Martin Head-Gordon, Co-chair The accurate prediction of electronic excitation energies in molecules is an area of intense research of significant fundamental interest and is critical for many applications. Today, most excited state calculations use time-dependent density functional theory (TDDFT) in conjunction with an approximate exchange-correlation functional. In this dissertation, I have examined and critically assessed an alternative method for predicting charged and low-lying neutral excitations with similar computational cost: the ab initio Bethe-Salpeter equation (BSE) approach. Rigorously based on many-body Green's function theory but incorporating information from density functional theory, the predictive power of the BSE approach remained at the beginning of this work unexplored for the neutral and charged electronic excitations of organic molecules. Here, the results and implications of several systematic benchmarks are laid out in detail. i Contents Contents i List of Figures iii List of Tables vii 1 Electronic excited state calculations in molecules: challenges and oppor- tunities 1 1.1 Case Study 1: Biomimetic light harvesting complexes .
    [Show full text]
  • WO 2016/074683 Al 19 May 2016 (19.05.2016) W P O P C T
    (12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (19) World Intellectual Property Organization International Bureau (10) International Publication Number (43) International Publication Date WO 2016/074683 Al 19 May 2016 (19.05.2016) W P O P C T (51) International Patent Classification: (81) Designated States (unless otherwise indicated, for every C12N 15/10 (2006.01) kind of national protection available): AE, AG, AL, AM, AO, AT, AU, AZ, BA, BB, BG, BH, BN, BR, BW, BY, (21) International Application Number: BZ, CA, CH, CL, CN, CO, CR, CU, CZ, DE, DK, DM, PCT/DK20 15/050343 DO, DZ, EC, EE, EG, ES, FI, GB, GD, GE, GH, GM, GT, (22) International Filing Date: HN, HR, HU, ID, IL, IN, IR, IS, JP, KE, KG, KN, KP, KR, 11 November 2015 ( 11. 1 1.2015) KZ, LA, LC, LK, LR, LS, LU, LY, MA, MD, ME, MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO, NZ, OM, (25) Filing Language: English PA, PE, PG, PH, PL, PT, QA, RO, RS, RU, RW, SA, SC, (26) Publication Language: English SD, SE, SG, SK, SL, SM, ST, SV, SY, TH, TJ, TM, TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW. (30) Priority Data: PA 2014 00655 11 November 2014 ( 11. 1 1.2014) DK (84) Designated States (unless otherwise indicated, for every 62/077,933 11 November 2014 ( 11. 11.2014) US kind of regional protection available): ARIPO (BW, GH, 62/202,3 18 7 August 2015 (07.08.2015) US GM, KE, LR, LS, MW, MZ, NA, RW, SD, SL, ST, SZ, TZ, UG, ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, RU, (71) Applicant: LUNDORF PEDERSEN MATERIALS APS TJ, TM), European (AL, AT, BE, BG, CH, CY, CZ, DE, [DK/DK]; Nordvej 16 B, Himmelev, DK-4000 Roskilde DK, EE, ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, (DK).
    [Show full text]
  • Arxiv:1604.00041V1 [Cond-Mat.Mtrl-Sci] 31 Mar 2016
    , Structural and excited-state properties of oligoacene crystals from first principles 1, 2, 3 4, 1 1, 5 Tonatiuh Rangel, ∗ Kristian Berland, Sahar Sharifzadeh, Florian Brown-Altvater, Kyuho Lee,1 Per Hyldgaard,6, 7 Leeor Kronik,8 and Jeffrey B. Neaton1, 2, 9 1Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720,USA 2Department of Physics, University of California, Berkeley, California 94720-7300, USA 3Centre for Material Science and Nanotechnology, University of Oslo, NO-0316 Oslo, Norway 4Department of Electrical and Computer Engineering and Division of Materials Science and Engineering, Boston University, Boston, MA 02215, USA 5Department of Chemistry, University of California, Berkeley, California 94720-7300, USA 6Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology,SE-41296 G¨oteborg, Sweden 7Materials Science and Applied Mathematics, Malm¨oUniversity, Malm¨oSE-205 06, Sweden 8Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel 9Kavli Energy NanoSciences Institute at Berkeley, Berkeley, California 94720-7300, USA (Dated: March 27, 2018) Molecular crystals are a prototypical class of van der Waals (vdW)-bound organic materials with excited state properties relevant for optoelectronics applications. Predicting the structure and excited state properties of molecular crystals presents a challenge for electronic structure theory, as standard approximations to density functional theory (DFT) do not capture long-range vdW dispersion interactions and do not yield excited-state properties. In this work, we use a combination of DFT including vdW forces{ using both non-local correlation functionals and pair-wise correction methods { together with many-body perturbation theory (MBPT) to study the geometry and excited states, respectively, of the entire series of oligoacene crystals, from benzene to hexacene.
    [Show full text]
  • The Pennsylvania State University the Eberly College of Science
    The Pennsylvania State University The Eberly College of Science Department of Chemistry SYNTHESIS OF CARBON MATERIALS VIA THE COLD COMPRESSION OF AROMATIC MOLECULES AND CARBON NANOSTRUCTURES A Dissertation in Chemistry by Thomas C. Fitzgibbons 2014 Thomas C. Fitzgibbons Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy August 2014 ii The dissertation of Thomas C. Fitzgibbons was reviewed and approved* by the following: John V. Badding Professor of Chemistry Dissertation Advisor Chair of Committee Ayusman Sen Distinguished Professor of Chemistry A. Welford Castleman, Jr Evan Pugh Professor of Chemistry and Physics William B. White Professor Emeritus of Geosciences Barbara J. Garrison Shapiro Professor of Chemistry Head of the Department of Chemistry *Signatures are on file in the Graduate School iii ABSTRACT Carbon’s ability for catenation makes it a remarkable element and allows for many interesting and surprising properties and structures. Carbon can exist in one of its two thermodynamically stable bulk crystals, graphite or diamond, one of its several nanostructures: fullerene, nanotube, or graphene, or as an amorphous material with a mixed bonding pattern. Carbon also has an ability to bond heteroatoms such as hydrogen which can increase its properties and structures even further. Pressure has been shown to be able to drastically change the bonding in and structure of carbon based materials. In this dissertation I will present how pressure can be used to synthesize new amorphous hydrogenated carbons and how a battery of analytical techniques can be used to elicit the microstructure of the carbon networks. This microstructure can then be related back to the reaction conditions and more importantly the starting small molecule.
    [Show full text]
  • A Systematic (Time-Dependent) Density Functional Theory Study
    Electronic and optical properties of families of polycyclic aromatic hydrocarbons: a systematic (time-dependent) density functional theory study G. Malloci a,∗, G. Cappellini a,b, G. Mulas b, A. Mattoni a aCNR–IOM and Dipartimento di Fisica, Universit`adegli Studi di Cagliari, Cittadella Universitaria, Strada Prov. le Monserrato–Sestu Km 0.700, I–09042 Monserrato (CA), Italy bINAF – Osservatorio Astronomico di Cagliari–Astrochemistry Group, Strada 54, Localit`aPoggio dei Pini, I–09012 Capoterra (CA), Italy Abstract Homologous classes of Polycyclic Aromatic Hydrocarbons (PAHs) in their crys- talline state are among the most promising materials for organic opto-electronics. Following previous works on oligoacenes we present a systematic comparative study of the electronic, optical, and transport properties of oligoacenes, phenacenes, cir- cumacenes, and oligorylenes. Using density functional theory (DFT) and time- dependent DFT we computed: (i) electron affinities and first ionization energies; (ii) quasiparticle correction to the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap; (iii) molecular reorganization energies; (iv) electronic absorption spectra of neutral and ±1 charged systems. The excitonic effects are estimated by comparing the optical gap and the quasiparticle corrected HOMO-LUMO energy gap. For each molecular property computed, general trends as a function of molecular size and charge state are discussed. Overall, we find that circumacenes have the best transport properties, displaying a steeper decrease of the molecular reorganization energy at increasing sizes, while oligorylenes are much arXiv:1104.2978v1 [cond-mat.mtrl-sci] 15 Apr 2011 more efficient in absorbing low–energy photons in comparison to the other classes. Key words: PAHs, Electronic absorption, Charge–transport, Density functional theory, Time–dependent density functional theory ∗ Corresponding author.
    [Show full text]
  • Chemical Stability and Performance Influence of Choice Substituents and Core Conjugation of Organic Semiconductors
    University of Massachusetts Amherst ScholarWorks@UMass Amherst Doctoral Dissertations Dissertations and Theses March 2019 CHEMICAL STABILITY AND PERFORMANCE INFLUENCE OF CHOICE SUBSTITUENTS AND CORE CONJUGATION OF ORGANIC SEMICONDUCTORS Jack Ly University of Massachusetts Amherst Follow this and additional works at: https://scholarworks.umass.edu/dissertations_2 Part of the Polymer and Organic Materials Commons, Polymer Science Commons, and the Semiconductor and Optical Materials Commons Recommended Citation Ly, Jack, "CHEMICAL STABILITY AND PERFORMANCE INFLUENCE OF CHOICE SUBSTITUENTS AND CORE CONJUGATION OF ORGANIC SEMICONDUCTORS" (2019). Doctoral Dissertations. 1516. https://doi.org/10.7275/13323135 https://scholarworks.umass.edu/dissertations_2/1516 This Open Access Dissertation is brought to you for free and open access by the Dissertations and Theses at ScholarWorks@UMass Amherst. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. CHEMICAL STABILITY AND PERFORMANCE INFLUENCE OF CHOICE SUBSTITUENTS AND CORE CONJUGATION OF ORGANIC SEMICONDUCTORS A Dissertation Presented By JACK THANH LY Submitted to the Graduate School of the University of Massachusetts Amherst in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY February 2019 Polymer Science and Engineering © Copyright by Jack Thanh Ly 2019 All Rights Reserved CHEMICAL STABILITY AND PERFORMANCE INFLUENCE OF CHOICE
    [Show full text]
  • Polycyclic Aromatic Hydrocarbons As Model Cases for Structural and Optical Studies R
    Special Issue: Review Commentary Received: 24 August 2009, Revised: 2 October 2009, Accepted: 13 October 2009, Published online in Wiley InterScience: 3 February 2010 (www.interscience.wiley.com) DOI 10.1002/poc.1644 Forever young: polycyclic aromatic hydrocarbons as model cases for structural and optical studies R. Riegera and K. Mu¨ llena* Polycyclic aromatic hydrocarbons (PAHs) are popular research subjects due to their high stability, their rigid planar structure, and their characteristic optical spectra. The recent discovery of graphene, which can be regarded as giant PAH, has further stimulated the interest in this area. For this reason, the relationship between the geometric and electronic structure and the optical spectra of PAHs are reviewed, pointing out the versatile properties of this class of molecules. Extremely stable fully-benzenoid PAHs with high optical gaps are encountered on the one side and the very reactive acenes with low optical gaps on the other side. A huge range of molecular sizes is covered from the simplest case benzene with its six carbon atoms up to disks containing as much as 96 carbon atoms. Furthermore, the impact of non-planarity is discussed as model cases for the highly important fullerenes and carbon nanotubes. The detailed analysis of the electronic structure of PAHs is very important with regard to their application as fluorescent dyes or organic semiconductors. The presented research results shall encourage developments of new PAH structures to exploit novel materials properties. Copyright ß 2010 John Wiley & Sons, Ltd. Keywords: aromaticity; dyes; photophysics; polycyclic aromatic hydrocarbons; UV/vis INTRODUCTION dramatically different optical and chemical properties are observed.
    [Show full text]
  • How Much Aromatic Naphthalene and Graphene Are?
    How much aromatic naphthalene and graphene are? Yashita Y. Singh,a and Vaibhav A. Dixit*b aDepartment of Pharmaceutical Chemistry, School of Pharmacy & Technology Management, Shri Vile Parle Kelavani Mandal’s (SVKM's), Narsee Monjee Institute of Management Studies (NMIMS), Mukesh Patel Technology Park, Babulde, Bank of Tapi River, Mumbai-Agra Road, Shirpur, Dist. Dhule 425405 India. bDepartment of Pharmacy, Birla Institute of Technology and Sciences Pilani (BITS-Pilani), VidyaVihar Campus, street number 41, Pilani, 333031, Rajasthan. India. Phone No. +91 1596 255652, Mob. No. +91-7709129400, Corresponding author: Vaibhav A. Dixit Corresponding author email: [email protected], [email protected] Abstract Naphthalene, (Aromatic stabilization Energy; ASE, 50-60 kcal/mol) polyacenes and graphene are considered aromatic. Existing models for polyacenes predict a linearly increasing ASE and give little insights into their high reactivity and decreasing stability. Graphene’s aromaticity has been studied earlier qualitatively suggesting alternate Clar’s sextet and two-electrons per ring, but ASE estimates have not been reported yet. In this paper, various Heat of Hydrogenation (HoH) and isodesmic schemes have been proposed and compared for the estimation of naphthalene ASE. Results show that HoH schemes are simple to design, are equivalent to isodesmic schemes, and unconjugated unsaturated reference systems predict ASE values in agreement with literature reports. Partially aromatic reference systems underestimate ASE. HoH schemes require calculations for a smaller number of structures, and offer scope for experimental validation, and involve enthalpy differences. Polyacene (X-axis extensions of benzene) ASE estimates (using HoH scheme) correlate well with experimental instability data and offer new physical insights explaining the absence of arbitrarily larger polyacenes.
    [Show full text]