1
|
Isukapalli SVK, Vennapusa SR. Ultrafast T 1 generation in pyrene-4,5-dione and pyrene-4,5,9,10-tetrone. J Photochem Photobiol A Chem 2023. [DOI: 10.1016/j.jphotochem.2023.114695] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/28/2023]
|
2
|
Sarghein MG, Ghiasi R, Baniyaghoob S. CHEMISORPTION OF C2H2 ON C20 BOWL: A COMPUTATIONAL INVESTIGATION. J STRUCT CHEM+ 2022. [DOI: 10.1134/s0022476622100067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
|
3
|
Vasilchenko V, Levchenko S, Perebeinos V, Zhugayevych A. Small Polarons in Two-Dimensional Pnictogens: A First-Principles Study. J Phys Chem Lett 2021; 12:4674-4680. [PMID: 33979171 DOI: 10.1021/acs.jpclett.1c00929] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
We report the first-principles study of small polarons in the most stable two-dimensional pnictogen allotropes: blue and black phosphorene and arsenene. While both cations and anions of small hydrogen-passivated clusters show charge localization and local lattice distortions, only the hole polaron in the blue allotrope is stable in the infinite size cluster limit. The adiabatic polaron relaxation energy is found to be 0.1 eV for phosphorene and 0.15 eV for arsenene. The polaron is localized on lone-pair orbitals with half of the extra charge distributed among 13 atoms. In the blue phosphorene, these orbitals form the valence band's top with a relatively flat band dispersion. However, in the black phosphorene, lone-pair orbitals hybridize with bonding orbitals, which explains the difference in hole localization strength between the two topologically equivalent allotropes. The polaron's adiabatic barriers for motion are small compared to the most strongly coupled phonon frequency, implying the polaron barrierless motion.
Collapse
Affiliation(s)
| | - Sergey Levchenko
- Skolkovo Institute of Science and Technology, Moscow 143026, Russia
| | - Vasili Perebeinos
- Department of Electrical Engineering, University at Buffalo, Buffalo, New York 14260, United States
| | | |
Collapse
|
4
|
Sreelaja P, Ravikumar C. Structural and vibrational spectral contributions to the nonlinear optical properties of 2-Amino-3-nitropyridinium 4-hydroxybenzenesulfonate: A DFT study. J Mol Struct 2021. [DOI: 10.1016/j.molstruc.2020.129184] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
|
5
|
Nelson TR, White AJ, Bjorgaard JA, Sifain AE, Zhang Y, Nebgen B, Fernandez-Alberti S, Mozyrsky D, Roitberg AE, Tretiak S. Non-adiabatic Excited-State Molecular Dynamics: Theory and Applications for Modeling Photophysics in Extended Molecular Materials. Chem Rev 2020; 120:2215-2287. [PMID: 32040312 DOI: 10.1021/acs.chemrev.9b00447] [Citation(s) in RCA: 198] [Impact Index Per Article: 49.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Optically active molecular materials, such as organic conjugated polymers and biological systems, are characterized by strong coupling between electronic and vibrational degrees of freedom. Typically, simulations must go beyond the Born-Oppenheimer approximation to account for non-adiabatic coupling between excited states. Indeed, non-adiabatic dynamics is commonly associated with exciton dynamics and photophysics involving charge and energy transfer, as well as exciton dissociation and charge recombination. Understanding the photoinduced dynamics in such materials is vital to providing an accurate description of exciton formation, evolution, and decay. This interdisciplinary field has matured significantly over the past decades. Formulation of new theoretical frameworks, development of more efficient and accurate computational algorithms, and evolution of high-performance computer hardware has extended these simulations to very large molecular systems with hundreds of atoms, including numerous studies of organic semiconductors and biomolecules. In this Review, we will describe recent theoretical advances including treatment of electronic decoherence in surface-hopping methods, the role of solvent effects, trivial unavoided crossings, analysis of data based on transition densities, and efficient computational implementations of these numerical methods. We also emphasize newly developed semiclassical approaches, based on the Gaussian approximation, which retain phase and width information to account for significant decoherence and interference effects while maintaining the high efficiency of surface-hopping approaches. The above developments have been employed to successfully describe photophysics in a variety of molecular materials.
Collapse
Affiliation(s)
- Tammie R Nelson
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - Alexander J White
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - Josiah A Bjorgaard
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - Andrew E Sifain
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States.,U.S. Army Research Laboratory , Aberdeen Proving Ground , Maryland 21005 , United States
| | - Yu Zhang
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - Benjamin Nebgen
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | | | - Dmitry Mozyrsky
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - Adrian E Roitberg
- Department of Chemistry , University of Florida , Gainesville , Florida 32611 , United States
| | - Sergei Tretiak
- Theoretical Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| |
Collapse
|
6
|
Ondarse-Alvarez D, Nelson T, Lupton JM, Tretiak S, Fernandez-Alberti S. Let Digons be Bygones: The Fate of Excitons in Curved π-Systems. J Phys Chem Lett 2018; 9:7123-7129. [PMID: 30508376 DOI: 10.1021/acs.jpclett.8b03160] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We explore the diverse origins of unpolarized absorption and emission of molecular polygons consisting of π-conjugated oligomer chains held in a bent geometry by strain controlled at the vertex units. For this purpose, we make use of atomistic nonadiabatic excited-state molecular dynamics simulations of a bichromophore molecular polygon (digon) with bent chromophore chains. Both structural and photoexcited dynamics were found to affect polarization features. Bending strain induces exciton localization on individual chromophore units of the conjugated chains. The latter display different transition dipole moment orientations, a feature not present in the linear oligomer counterparts. In addition, bending makes exciton localization very sensitive to molecular distortions induced by thermal fluctuations. The excited-state dynamics reveals an ultrafast intramolecular energy redistribution that spreads the exciton equally among spatially separated chromophore fragments within the molecular system. As a result, digons become virtually unpolarized absorbers and emitters, in agreement with recent experimental studies on the single-molecule level.
Collapse
Affiliation(s)
| | - Tammie Nelson
- Theoretical Division, Physics and Chemistry of Materials (T-1) , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - John M Lupton
- Institut für Angewandte und Experimentelle Physik , Universität Regensburg , Universitätsstrasse 31 , 93053 Regensburg , Germany
| | - Sergei Tretiak
- Theoretical Division, Physics and Chemistry of Materials (T-1) , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | | |
Collapse
|
7
|
Stojanović L, Aziz SG, Hilal RH, Plasser F, Niehaus TA, Barbatti M. Nonadiabatic Dynamics of Cycloparaphenylenes with TD-DFTB Surface Hopping. J Chem Theory Comput 2017; 13:5846-5860. [DOI: 10.1021/acs.jctc.7b01000] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | - Saadullah G. Aziz
- Chemistry
Department, Faculty of Science, King Abdulaziz University, Jeddah B.O.
208203, Saudi Arabia
| | - Rifaat H. Hilal
- Chemistry
Department, Faculty of Science, King Abdulaziz University, Jeddah B.O.
208203, Saudi Arabia
- Chemistry
Department, Faculty of Science, Cairo University, Giza, Egypt
| | - Felix Plasser
- Institute
of Theoretical Chemistry, Faculty of Chemistry, University of Vienna, Währinger Straße 17, 1090 Vienna, Austria
| | - Thomas A. Niehaus
- Univ Lyon, Université
Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, F-69622 Lyon, France
| | | |
Collapse
|
8
|
Fieser ME, Ferrier MG, Su J, Batista E, Cary SK, Engle JW, Evans WJ, Lezama Pacheco JS, Kozimor SA, Olson AC, Ryan AJ, Stein BW, Wagner GL, Woen DH, Vitova T, Yang P. Evaluating the electronic structure of formal Ln II ions in Ln II(C 5H 4SiMe 3) 31- using XANES spectroscopy and DFT calculations. Chem Sci 2017; 8:6076-6091. [PMID: 28989638 PMCID: PMC5625586 DOI: 10.1039/c7sc00825b] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Accepted: 06/05/2017] [Indexed: 12/15/2022] Open
Abstract
The isolation of [K(2.2.2-cryptand)][Ln(C5H4SiMe3)3], formally containing LnII, for all lanthanides (excluding Pm) was surprising given that +2 oxidation states are typically regarded as inaccessible for most 4f-elements. Herein, X-ray absorption near-edge spectroscopy (XANES), ground-state density functional theory (DFT), and transition dipole moment calculations are used to investigate the possibility that Ln(C5H4SiMe3)31- (Ln = Pr, Nd, Sm, Gd, Tb, Dy, Y, Ho, Er, Tm, Yb and Lu) compounds represented molecular LnII complexes. Results from the ground-state DFT calculations were supported by additional calculations that utilized complete-active-space multi-configuration approach with second-order perturbation theoretical correction (CASPT2). Through comparisons with standards, Ln(C5H4SiMe3)31- (Ln = Sm, Tm, Yb, Lu, Y) are determined to contain 4f6 5d0 (SmII), 4f13 5d0 (TmII), 4f14 5d0 (YbII), 4f14 5d1 (LuII), and 4d1 (YII) electronic configurations. Additionally, our results suggest that Ln(C5H4SiMe3)31- (Ln = Pr, Nd, Gd, Tb, Dy, Ho, and Er) also contain LnII ions, but with 4f n 5d1 configurations (not 4f n+1 5d0). In these 4f n 5d1 complexes, the C3h-symmetric ligand environment provides a highly shielded 5d-orbital of a' symmetry that made the 4f n 5d1 electronic configurations lower in energy than the more typical 4f n+1 5d0 configuration.
Collapse
Affiliation(s)
| | | | - Jing Su
- Los Alamos National Laboratory , Los Alamos , NM 87545 , USA . ; ;
| | - Enrique Batista
- Los Alamos National Laboratory , Los Alamos , NM 87545 , USA . ; ;
| | - Samantha K Cary
- Los Alamos National Laboratory , Los Alamos , NM 87545 , USA . ; ;
| | - Jonathan W Engle
- Los Alamos National Laboratory , Los Alamos , NM 87545 , USA . ; ;
- University of Wisconsin , Madison , Wisconsin 53711 , USA
| | | | | | - Stosh A Kozimor
- Los Alamos National Laboratory , Los Alamos , NM 87545 , USA . ; ;
| | - Angela C Olson
- Los Alamos National Laboratory , Los Alamos , NM 87545 , USA . ; ;
| | - Austin J Ryan
- University of California , Irvine , CA 92697 , USA .
| | - Benjamin W Stein
- Los Alamos National Laboratory , Los Alamos , NM 87545 , USA . ; ;
| | - Gregory L Wagner
- Los Alamos National Laboratory , Los Alamos , NM 87545 , USA . ; ;
| | - David H Woen
- University of California , Irvine , CA 92697 , USA .
| | - Tonya Vitova
- Karlsruhe Institute of Technology , Institute for Nuclear Waste Disposal , P.O. Box 3640 , 76021 Karlsruhe , Germany
| | - Ping Yang
- Los Alamos National Laboratory , Los Alamos , NM 87545 , USA . ; ;
| |
Collapse
|
9
|
Wang CI, Hsu CH, Hua CC. The correspondence between the conformational and chromophoric properties of amorphous conjugated polymers in mesoscale condensed systems. Phys Chem Chem Phys 2017; 19:20818-20828. [PMID: 28744545 DOI: 10.1039/c7cp03415f] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
For π-conjugated polymers, the notion of spectroscopic units or "chromophores" provides illuminating insights into the experimentally observed absorption/emission spectra and the mechanisms of energy/charge transfer. To date, however, no statistical analysis has revealed a direct correspondence between chromophoric and conformational properties-with the latter being fundamental to polymer semiconductors. Herein, we propose a "persistence length" calculation to re-evaluate chain conformation over a full conjugation length. The mesoscale condensed systems of MEH-PPV and MEH-PPV/C60 hybrid (system size ∼10 × 10 × 10 nm3) are utilized as two prototypical model systems, along with a full range of segmental lengths (2-20-mer) and five lowest singlet excited states to hint at the generality of the features presented. We demonstrate, for the first time, that two properly re-defined conformational factors that characterize chain folding and planarity, respectively, capture excellently the population distribution of chromophores in both systems investigated. In contrast, the conventional strategy of utilizing two adjacent monomer units to characterize (local) chain conformation results in only an inconspicuous correlation between the two, as previously reported. It is further shown that chain folding-and not chain planarity-is more relevant in capturing the associated oscillator strength for the first excited state, where the transient dipole moments are known to align with the chain conformation, although the corresponding excitation energy and exciton size seem relatively unaffected. The observed effects of C60 on the MEH-PPV adsorption spectra also agree with recent experimental trends. Overall, the present findings are expected to aid future multiscale computer simulations and spectroscopy-data interpretations for polymer semiconductors and their hybrid systems.
Collapse
Affiliation(s)
- Chun I Wang
- Department of Chemical Engineering, National Chung Cheng University, Chia-Yi 62102, Taiwan, Republic of China.
| | | | | |
Collapse
|
10
|
Nelson T, Fernandez-Alberti S, Roitberg AE, Tretiak S. Electronic Delocalization, Vibrational Dynamics, and Energy Transfer in Organic Chromophores. J Phys Chem Lett 2017; 8:3020-3031. [PMID: 28603994 DOI: 10.1021/acs.jpclett.7b00790] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The efficiency of materials developed for solar energy and technological applications depends on the interplay between molecular architecture and light-induced electronic energy redistribution. The spatial localization of electronic excitations is very sensitive to molecular distortions. Vibrational nuclear motions can couple to electronic dynamics driving changes in localization. The electronic energy transfer among multiple chromophores arises from several distinct mechanisms that can give rise to experimentally measured signals. Atomistic simulations of coupled electron-vibrational dynamics can help uncover the nuclear motions directing energy flow. Through careful analysis of excited state wave function evolution and a useful fragmenting of multichromophore systems, through-bond transport and exciton hopping (through-space) mechanisms can be distinguished. Such insights are crucial in the interpretation of fluorescence anisotropy measurements and can aid materials design. This Perspective highlights the interconnected vibrational and electronic motions at the foundation of nonadiabatic dynamics where nuclear motions, including torsional rotations and bond vibrations, drive electronic transitions.
Collapse
Affiliation(s)
- Tammie Nelson
- Theoretical Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | | | - Adrian E Roitberg
- Department of Chemistry, University of Florida , Gainesville, Florida 32611, United States
| | - Sergei Tretiak
- Theoretical Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| |
Collapse
|
11
|
Wen J, Ma H. A fragmentation-based approach for evaluating the intra-chain excitonic couplings in conjugated polymers. Chem Phys Lett 2017. [DOI: 10.1016/j.cplett.2017.04.099] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
|
12
|
Simine L, Rossky PJ. Relating Chromophoric and Structural Disorder in Conjugated Polymers. J Phys Chem Lett 2017; 8:1752-1756. [PMID: 28350467 DOI: 10.1021/acs.jpclett.7b00290] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The optoelectronic properties of amorphous conjugated polymers are sensitive to the details of the conformational disorder, and spectroscopy provides the means for structural characterization of the fragments of the chain that interact with light-"chromophores". A faithful interpretation of spectroscopic conformational signatures, however, presents a theoretical challenge. Here we investigate the relationship between the ground-state optical gaps, the properties of the excited states, and the structural features of chromophores of a single molecule poly(3-hexyl)-thiophene (P3HT) using quantum-classical atomistic simulations. Our results demonstrate that chromophoric disorder arises through the interplay between excited-state delocalization and electron-hole polarization, controlled by the torsional disorder introduced by side chains. Within this conceptual framework, we predict and explain the counterintuitive spectral behavior of P3HT, a red-shifted absorption, despite shortening of chromophores, with increasing temperature. This discussion introduces the concept of disorder-induced separation of charges in amorphous conjugated polymers.
Collapse
Affiliation(s)
- Lena Simine
- Department of Chemistry, Rice University , Houston, Texas 77005, United States
| | - Peter J Rossky
- Department of Chemistry, Rice University , Houston, Texas 77005, United States
| |
Collapse
|
13
|
Pelzer KM, Vázquez-Mayagoitia Á, Ratcliff LE, Tretiak S, Bair RA, Gray SK, Van Voorhis T, Larsen RE, Darling SB. Molecular dynamics and charge transport in organic semiconductors: a classical approach to modeling electron transfer. Chem Sci 2017; 8:2597-2609. [PMID: 28553494 PMCID: PMC5431633 DOI: 10.1039/c6sc04547b] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Accepted: 01/03/2017] [Indexed: 11/21/2022] Open
Abstract
Organic photovoltaics (OPVs) are a promising carbon-neutral energy conversion technology, with recent improvements pushing power conversion efficiencies over 10%. A major factor limiting OPV performance is inefficiency of charge transport in organic semiconducting materials (OSCs). Due to strong coupling with lattice degrees of freedom, the charges form polarons, localized quasi-particles comprised of charges dressed with phonons. These polarons can be conceptualized as pseudo-atoms with a greater effective mass than a bare charge. We propose that due to this increased mass, polarons can be modeled with Langevin molecular dynamics (LMD), a classical approach with a computational cost much lower than most quantum mechanical methods. Here we present LMD simulations of charge transfer between a pair of fullerene molecules, which commonly serve as electron acceptors in OSCs. We find transfer rates consistent with experimental measurements of charge mobility, suggesting that this method may provide quantitative predictions of efficiency when used to simulate materials on the device scale. Our approach also offers information that is not captured in the overall transfer rate or mobility: in the simulation data, we observe exactly when and why intermolecular transfer events occur. In addition, we demonstrate that these simulations can shed light on the properties of polarons in OSCs. Much remains to be learned about these quasi-particles, and there are no widely accepted methods for calculating properties such as effective mass and friction. Our model offers a promising approach to exploring mass and friction as well as providing insight into the details of polaron transport in OSCs.
Collapse
Affiliation(s)
- Kenley M Pelzer
- Center for Nanoscale Materials , Argonne National Laboratory , 9700 Cass Ave., Lemont , IL 60439 , USA . ; Tel: +1-630-252-7020
- Materials Science Division , Argonne National Laboratory , 9700 Cass Ave, Lemont , IL 60439 , USA
| | - Álvaro Vázquez-Mayagoitia
- Argonne Leadership Computing Facility , Argonne National Laboratory , 9700 Cass Ave. , Lemont , IL 60439 , USA
| | - Laura E Ratcliff
- Argonne Leadership Computing Facility , Argonne National Laboratory , 9700 Cass Ave. , Lemont , IL 60439 , USA
| | - Sergei Tretiak
- Theoretical Division , Center for Nonlinear Studies , Center for Integrated Nanotechnologies , Los Alamos National Laboratory , Los Alamos , NM 87545 , USA
| | - Raymond A Bair
- Mathematics and Computer Science Division , Argonne National Laboratory , 9700 Cass Ave. , Argonne , IL 60439 , USA
- Computation Institute , University of Chicago , 5735 S. Ellis Ave. , Chicago , IL 60637 , USA
- Computer, Environment, and Life Sciences , Argonne National Laboratory , 9700 Cass Ave. , Lemont , IL 60439 , USA
| | - Stephen K Gray
- Center for Nanoscale Materials , Argonne National Laboratory , 9700 Cass Ave., Lemont , IL 60439 , USA . ; Tel: +1-630-252-7020
- Computation Institute , University of Chicago , 5735 S. Ellis Ave. , Chicago , IL 60637 , USA
| | - Troy Van Voorhis
- Department of Chemistry , Massachusetts Institute of Technology , 77 Massachusetts Ave , Cambridge , MA 02139 , USA
| | - Ross E Larsen
- Computational Science Center , National Renewable Energy Laboratory , 15301 Denver W. Parkway, Golden , CO 80401 , USA
| | - Seth B Darling
- Center for Nanoscale Materials , Argonne National Laboratory , 9700 Cass Ave., Lemont , IL 60439 , USA . ; Tel: +1-630-252-7020
- Institute for Molecular Engineering , University of Chicago , 5747 S. Ellis Ave. , Chicago , IL 60637 , USA
| |
Collapse
|
14
|
Coughlin JE, Zhugayevych A, Wang M, Bazan GC, Tretiak S. Charge delocalization characteristics of regioregular high mobility polymers. Chem Sci 2017; 8:1146-1151. [PMID: 28451255 PMCID: PMC5369528 DOI: 10.1039/c6sc01599a] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Accepted: 09/19/2016] [Indexed: 11/21/2022] Open
Abstract
Controlling the regioregularity among the structural units of narrow bandgap conjugated polymer backbones has led to improvements in optoelectronic properties, for example in the mobilities observed in field effect transistor devices. To investigate how the regioregularity affects quantities relevant to hole transport, regioregular and regiorandom oligomers representative of polymeric structures were studied using density functional theory. Several structural and electronic characteristics of the oligomers were compared, including chain planarity, cation spin density, excess charges on molecular units and internal reorganizational energy. The main difference between the regioregular and regiorandom oligomers is found to be the conjugated backbone planarity, while the reorganizational energies calculated are quite similar across the molecular family. This work constitutes the first step on understanding the complex interplay of atomistic changes and an oligomer backbone structure toward modeling the charge transport properties.
Collapse
Affiliation(s)
- J E Coughlin
- Center for Polymers and Organic Solids , Department of Chemistry and Biochemistry , University of California Santa Barbara , Santa Barbara , California 93106 , USA
| | - A Zhugayevych
- Skolkovo Institute of Science and Technology , Moscow , 143025 , Russia
| | - M Wang
- Center for Polymers and Organic Solids , Department of Chemistry and Biochemistry , University of California Santa Barbara , Santa Barbara , California 93106 , USA
| | - G C Bazan
- Center for Polymers and Organic Solids , Department of Chemistry and Biochemistry , University of California Santa Barbara , Santa Barbara , California 93106 , USA
| | - S Tretiak
- Center for Polymers and Organic Solids , Department of Chemistry and Biochemistry , University of California Santa Barbara , Santa Barbara , California 93106 , USA
- Skolkovo Institute of Science and Technology , Moscow , 143025 , Russia
- Theoretical Division , Center for Nonlinear Studies (CNLS) , Center for Integrated Nanotechnologies (CINT) , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , USA .
| |
Collapse
|
15
|
Neukirch AJ, Nie W, Blancon JC, Appavoo K, Tsai H, Sfeir MY, Katan C, Pedesseau L, Even J, Crochet JJ, Gupta G, Mohite AD, Tretiak S. Polaron Stabilization by Cooperative Lattice Distortion and Cation Rotations in Hybrid Perovskite Materials. NANO LETTERS 2016; 16:3809-16. [PMID: 27224519 DOI: 10.1021/acs.nanolett.6b01218] [Citation(s) in RCA: 112] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Solution-processed organometallic perovskites have rapidly developed into a top candidate for the active layer of photovoltaic devices. Despite the remarkable progress associated with perovskite materials, many questions about the fundamental photophysical processes taking place in these devices, remain open. High on the list of unexplained phenomena are very modest mobilities despite low charge carrier effective masses. Moreover, experiments elucidate unique degradation of photocurrent affecting stable operation of perovskite solar cells. These puzzles suggest that, while ionic hybrid perovskite devices may have efficiencies on par with conventional Si and GaAs devices, they exhibit more complicated charge transport phenomena. Here we report the results from an in-depth computational study of small polaron formation, electronic structure, charge density, and reorganization energies using both periodic boundary conditions and isolated structures. Using the hybrid density functional theory, we found that volumetric strain in a CsPbI3 cluster creates a polaron with binding energy of around 300 and 900 meV for holes and electrons, respectively. In the MAPbI3 (MA = CH3NH3) cluster, both volumetric strain and MA reorientation effects lead to larger binding energies at around 600 and 1300 meV for holes and electrons, respectively. Such large reorganization energies suggest appearance of small polarons in organometallic perovskite materials. The fact that both volumetric lattice strain and MA molecular rotational degrees of freedom can cooperate to create and stabilize polarons indicates that in order to mitigate this problem, formamidinium (FA = HC(NH2)2) and cesium (Cs) based crystals and alloys, are potentially better materials for solar cell and other optoelectronic applications.
Collapse
Affiliation(s)
- Amanda J Neukirch
- Theoretical Physics and Chemistry of Materials, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Wanyi Nie
- Materials Physics and Application, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Jean-Christophe Blancon
- Physical Chemistry and Applied Spectroscopy Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Kannatassen Appavoo
- Center for Functional Nanomaterials, Brookhaven National Laboratory , Upton, New York 11973, United States
| | - Hsinhan Tsai
- Materials Physics and Application, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Matthew Y Sfeir
- Center for Functional Nanomaterials, Brookhaven National Laboratory , Upton, New York 11973, United States
| | - Claudine Katan
- Institut des Sciences Chimiques de Rennes, ISCR, CNRS , Université de Rennes 1, 35042 Rennes, France
| | - Laurent Pedesseau
- Fonctions Optiques pour les Technologies de l'Information, FOTON UMR 6082, CNRS, INSA de Rennes , 35708 Rennes, France
| | - Jacky Even
- Fonctions Optiques pour les Technologies de l'Information, FOTON UMR 6082, CNRS, INSA de Rennes , 35708 Rennes, France
| | - Jared J Crochet
- Physical Chemistry and Applied Spectroscopy Division, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Gautam Gupta
- Materials Physics and Application, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Aditya D Mohite
- Materials Physics and Application, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Sergei Tretiak
- Theoretical Physics and Chemistry of Materials, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| |
Collapse
|
16
|
Heimel G. The Optical Signature of Charges in Conjugated Polymers. ACS CENTRAL SCIENCE 2016; 2:309-15. [PMID: 27280165 PMCID: PMC4882742 DOI: 10.1021/acscentsci.6b00073] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Indexed: 05/22/2023]
Abstract
Electrical charge flowing through organic semiconductors drives many of today's mobile phone displays and television screens, suggesting an internally consistent model of charge-carrier properties in these materials to have manifested. In conjugated polymers, charges give rise to additional absorption of light at wavelengths longer than those absorbed by the electrically neutral species. These characteristic absorption bands are universally being related to the emergence of localized energy levels shifted into the forbidden gap of organic semiconductors due to local relaxation of the molecular geometry. However, the traditional view on these energy levels and their occupation is incompatible with expected changes in electron removal and addition energies upon charging molecules. Here, I demonstrate that local Coulomb repulsion, as captured by nonempirically optimized electronic-structure calculations, restores compatibility and suggests a different origin of the charge-induced optical transitions. These results challenge a widely accepted and long-established picture, but an improved understanding of charge carriers in molecular materials promises a more targeted development of organic and hybrid organic/inorganic (opto-)electronic devices.
Collapse
|
17
|
Moral M, García G, Garzón A, Granadino-Roldán JM, Fernández-Gómez M. DFT study of the effect of fluorine atoms on the crystal structure and semiconducting properties of poly(arylene-ethynylene) derivatives. J Chem Phys 2016; 144:154902. [DOI: 10.1063/1.4945447] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Mónica Moral
- Renewable Energy Research Institute, University of Castilla-La Mancha, Paseo de la Investigación 1, 02071 Albacete, Spain
| | - Gregorio García
- Department of Chemistry, University of Burgos, Plaza Misael Bañuelos, s/n, 09001 Burgos, Spain
| | - Andrés Garzón
- Department of Physical Chemistry, Faculty of Pharmacy, University of Castilla-La Mancha, Paseo de los Estudiantes, 02071 Albacete, Spain
| | - José M. Granadino-Roldán
- Department of Physical and Analytical Chemistry, Faculty of Experimental Sciences, University of Jaén, Campus Las Lagunillas, s/n, 23071 Jaén, Spain
| | - Manuel Fernández-Gómez
- Department of Physical and Analytical Chemistry, Faculty of Experimental Sciences, University of Jaén, Campus Las Lagunillas, s/n, 23071 Jaén, Spain
| |
Collapse
|
18
|
Adamska L, Nazin GV, Doorn SK, Tretiak S. Self-Trapping of Charge Carriers in Semiconducting Carbon Nanotubes: Structural Analysis. J Phys Chem Lett 2015; 6:3873-3879. [PMID: 26722885 DOI: 10.1021/acs.jpclett.5b01729] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The spatial extent of charged electronic states in semiconducting carbon nanotubes with indices (6,5) and (7,6) was evaluated using density functional theory. It was observed that electrons and holes self-trap along the nanotube axis on length scales of about 4 and 8 nm, respectively, which localize cations and anions on comparable length scales. Self-trapping is accompanied by local structural distortions showing periodic bond-length alternation. The average lengthening (shortening) of the bonds for anions (cations) is expected to shift the G-mode frequency to lower (higher) values. The smaller-diameter nanotube has reduced structural relaxation due to higher carbon-carbon bond strain. The reorganization energy due to charge-induced deformations in both nanotubes is found to be in the 30-60 meV range. Our results represent the first theoretical simulation of self-trapping of charge carriers in semiconducting nanotubes, and agree with available experimental data.
Collapse
Affiliation(s)
- Lyudmyla Adamska
- Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - George V Nazin
- Department of Chemistry and Biochemistry, University of Oregon , 1253 University of Oregon, Eugene, Oregon 97403, United States
| | - Stephen K Doorn
- Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | - Sergei Tretiak
- Theoretical Division and Center for Nonlinear Studies, Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
- Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| |
Collapse
|
19
|
Kilina S, Kilin D, Tretiak S. Light-Driven and Phonon-Assisted Dynamics in Organic and Semiconductor Nanostructures. Chem Rev 2015; 115:5929-78. [DOI: 10.1021/acs.chemrev.5b00012] [Citation(s) in RCA: 140] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Svetlana Kilina
- Chemistry
and Biochemistry Department, North Dakota State University, Fargo, North Dakota 5810, United States
| | - Dmitri Kilin
- Department
of Chemistry, University of South Dakota, Vermillion, South Dakota 57069, United States
| | - Sergei Tretiak
- Theoretical
Division, Center for Nonlinear Studies (CNLS) and Center for Integrated
Nanotechnologies (CINT), Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States
| |
Collapse
|
20
|
Laquai F, Andrienko D, Mauer R, Blom PWM. Charge Carrier Transport and Photogeneration in P3HT:PCBM Photovoltaic Blends. Macromol Rapid Commun 2015; 36:1001-25. [DOI: 10.1002/marc.201500047] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2015] [Revised: 03/30/2015] [Indexed: 11/06/2022]
Affiliation(s)
- Frédéric Laquai
- Max Planck Institute for Polymer Research; Ackermannweg 10 D-55122 Mainz Germany
| | - Denis Andrienko
- Max Planck Institute for Polymer Research; Ackermannweg 10 D-55122 Mainz Germany
| | - Ralf Mauer
- Max Planck Institute for Polymer Research; Ackermannweg 10 D-55122 Mainz Germany
| | - Paul W. M. Blom
- Max Planck Institute for Polymer Research; Ackermannweg 10 D-55122 Mainz Germany
| |
Collapse
|
21
|
Liu J, Adamska L, Doorn SK, Tretiak S. Singlet and triplet excitons and charge polarons in cycloparaphenylenes: a density functional theory study. Phys Chem Chem Phys 2015; 17:14613-22. [DOI: 10.1039/c5cp01782c] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Upon excitation, electron–phonon coupling leads to spatial localization of the electronic wavefunction and distortion of molecular geometry.
Collapse
Affiliation(s)
- Jin Liu
- Department of Chemical Engineering
- University of Rochester
- Rochester
- USA
| | - Lyudmyla Adamska
- Theoretical Division (T-1) and Center for Nonlinear Studies (CNLS)
- Los Alamos National Laboratory
- Los Alamos
- USA
| | - Stephen K. Doorn
- Center for Integrated Nanotechnologies (CINT)
- Los Alamos National Laboratory
- Los Alamos
- USA
| | - Sergei Tretiak
- Theoretical Division (T-1) and Center for Nonlinear Studies (CNLS)
- Los Alamos National Laboratory
- Los Alamos
- USA
- Center for Integrated Nanotechnologies (CINT)
| |
Collapse
|
22
|
Adamska L, Nayyar I, Chen H, Swan AK, Oldani N, Fernandez-Alberti S, Golder MR, Jasti R, Doorn SK, Tretiak S. Self-trapping of excitons, violation of Condon approximation, and efficient fluorescence in conjugated cycloparaphenylenes. NANO LETTERS 2014; 14:6539-6546. [PMID: 25310514 DOI: 10.1021/nl503133e] [Citation(s) in RCA: 119] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Cycloparaphenylenes, the simplest structural unit of armchair carbon nanotubes, have unique optoelectronic properties counterintuitive in the class of conjugated organic materials. Our time-dependent density functional theory study and excited state dynamics simulations of cycloparaphenylene chromophores provide a simple and conceptually appealing physical picture explaining experimentally observed trends in optical properties in this family of molecules. Fully delocalized degenerate second and third excitonic states define linear absorption spectra. Self-trapping of the lowest excitonic state due to electron-phonon coupling leads to the formation of spatially localized excitation in large cycloparaphenylenes within 100 fs. This invalidates the commonly used Condon approximation and breaks optical selection rules, making these materials superior fluorophores. This process does not occur in the small molecules, which remain inefficient emitters. A complex interplay of symmetry, π-conjugation, conformational distortion and bending strain controls all photophysics of cycloparaphenylenes.
Collapse
Affiliation(s)
- Lyudmyla Adamska
- Theoretical Division, Center for Nonlinear Studies and Center for Integrated Nanotechnologies (CINT), Los Alamos National Laboratory , Los Alamos, New Mexico 87545, United States
| | | | | | | | | | | | | | | | | | | |
Collapse
|
23
|
Martino N, Fazzi D, Sciascia C, Luzio A, Antognazza MR, Caironi M. Mapping orientational order of charge-probed domains in a semiconducting polymer. ACS NANO 2014; 8:5968-78. [PMID: 24815931 DOI: 10.1021/nn5011182] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Structure-property relationships are of fundamental importance to develop quantitative models describing charge transport in organic semiconductor based electronic devices, which are among the best candidates for future portable and lightweight electronic applications. While microstructural investigations, such as those based on X-rays, electron microscopy, or polarized optical probes, provide necessary information for the rationalization of transport in macromolecular solids, a general model predicting how charge accommodates within structural maps is not yet available. Therefore, techniques capable of directly monitoring how charge is distributed when injected into a polymer film and how it correlates to structural domains can help fill this gap. Supported by density functional theory calculations, here we show that polarized charge modulation microscopy (p-CMM) can unambiguously and selectively map the orientational order of the only conjugated segments that are probed by mobile charge in the few nanometer thick accumulation layer of a high-mobility polymer-based field-effect transistor . Depending on the specific solvent-induced microstructure within the accumulation layer, we show that p-CMM can image charge-probed domains that extend from submicrometer to tens of micrometers size, with markedly different degrees of alignment. Wider and more ordered p-CMM domains are associated with improved carrier mobility, as extracted from device characteristics. This observation evidences the unprecedented opportunity to correlate, directly in a working device, electronic properties with structural information on those conjugated segments involved in charge transport at the buried semiconductor-dielectric interface of a field-effect device.
Collapse
Affiliation(s)
- Nicola Martino
- Center for Nano Science and Technology @PoliMi, Istituto Italiano di Tecnologia , Via G. Pascoli 70/3, 20133 Milano, Italy
| | | | | | | | | | | |
Collapse
|
24
|
Ma H, Qin T, Troisi A. Electronic Excited States in Amorphous MEH-PPV Polymers from Large-Scale First Principles Calculations. J Chem Theory Comput 2014; 10:1272-82. [DOI: 10.1021/ct4010799] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Affiliation(s)
- Haibo Ma
- Key Laboratory of Mesoscopic
Chemistry of MOE, School of Chemistry and Chemical Engineering, Institute
of Theoretical and Computational Chemistry, Nanjing University, Nanjing 210093, China
| | - Ting Qin
- Department of Chemistry and
Centre of Scientific Computing, University of Warwick, Coventry CV4 7AL, United Kingdom
| | - Alessandro Troisi
- Department of Chemistry and
Centre of Scientific Computing, University of Warwick, Coventry CV4 7AL, United Kingdom
| |
Collapse
|
25
|
Wang J, Li M, Qi D, Shen W, He R, Lin SH. Exploring photophysical properties of metal-free coumarin sensitizers: an efficient strategy to improve the performance of dye-sensitized solar cells. RSC Adv 2014. [DOI: 10.1039/c4ra07904c] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The five important parameters (φLHE,φinject,φreg,φcc,Voc) for DSSCs are improved by modifying the dyes with electron-deficient units.
Collapse
Affiliation(s)
- Jinghui Wang
- School of Chemistry and Chemical Engineering
- Southwest University
- Chongqing 400715, China
| | - Ming Li
- School of Chemistry and Chemical Engineering
- Southwest University
- Chongqing 400715, China
- Education Ministry Key Laboratory on Luminescence and Real-Time Analysis
- Southwest University
| | - Dan Qi
- School of Chemistry and Chemical Engineering
- Southwest University
- Chongqing 400715, China
| | - Wei Shen
- School of Chemistry and Chemical Engineering
- Southwest University
- Chongqing 400715, China
| | - Rongxing He
- School of Chemistry and Chemical Engineering
- Southwest University
- Chongqing 400715, China
- Education Ministry Key Laboratory on Luminescence and Real-Time Analysis
- Southwest University
| | - Sheng Hsien Lin
- Department of Applied Chemistry
- Institute of Molecular Science and Center for Interdisciplinary Molecular Science
- National Chiao-Tung University
- Hsinchu 300, Taiwan
| |
Collapse
|
26
|
Morphology and Charge Transport in P3HT: A Theorist’s Perspective. P3HT REVISITED – FROM MOLECULAR SCALE TO SOLAR CELL DEVICES 2014. [DOI: 10.1007/12_2014_277] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
|
27
|
Angelella M, Wang C, Tauber MJ. Resonance Raman Spectra of a Perylene Bis(dicarboximide) Chromophore in Ground and Lowest Triplet States. J Phys Chem A 2013; 117:9196-204. [DOI: 10.1021/jp407879k] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Maria Angelella
- Department of Chemistry and
Biochemistry, University of California at San Diego, La Jolla, California 92093, United States
| | - Chen Wang
- Department of Chemistry and
Biochemistry, University of California at San Diego, La Jolla, California 92093, United States
| | - Michael J. Tauber
- Department of Chemistry and
Biochemistry, University of California at San Diego, La Jolla, California 92093, United States
| |
Collapse
|
28
|
Kilina S, Dandu N, Batista ER, Saxena A, Martin RL, Smith DL, Tretiak S. Effect of Packing on Formation of Deep Carrier Traps in Amorphous Conjugated Polymers. J Phys Chem Lett 2013; 4:1453-1459. [PMID: 26282298 DOI: 10.1021/jz4003197] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We theoretically investigate the role of conformational disorder and intermolecular interactions on the localization properties of electronic states, leading to the formation of carrier traps in amorphous aggregates of conjugated polymers. Samples of amorphous conformations of poly(p-phenylene vinylene) (PPV), poly2-methoxy-5-(2-ethyl-hexyloxy)PPV (MEH-PPV), and [poly-(9,9'-dioctyluorene)] (PFO) oligomers are simulated by classical molecular dynamics, while their electronic structure is calculated using first-principles density functional theory. Localization and delocalization properties of molecular orbitals are studied based on the participation ratio analysis, an approach commonly used in inorganic semiconductors. Our simulations confirm that the alkyl side chains insignificantly affect the conformational disorder in amorphous polymers while having a dramatic effect on the intermolecular disorder and packing. The nature of the disorder and its impact on charge-carrier localization in amorphous polymers with alkyl side chains differ drastically from those of disordered polymers without side chains, such as PPVs. Thus, long-range intermolecular interactions and sparse packing are responsible for the formation of multiple, deep, highly localized trap states in amorphous MEH-PPVs and PFOs, while close packing in combination with conformational disorder leads to the trap states distributed mostly near the bandgap edges in PPV aggregates.
Collapse
Affiliation(s)
- Svetlana Kilina
- †Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58108, United States
| | - Naveen Dandu
- †Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58108, United States
| | | | | | | | | | | |
Collapse
|
29
|
Panda AN, Plasser F, Aquino AJA, Burghardt I, Lischka H. Electronically excited states in poly(p-phenylenevinylene): vertical excitations and torsional potentials from high-level ab initio calculations. J Phys Chem A 2013; 117:2181-9. [PMID: 23427902 PMCID: PMC3598239 DOI: 10.1021/jp400372t] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Ab
initio second-order algebraic diagrammatic construction (ADC(2)) calculations
using the resolution of the identity (RI) method have been performed
on poly-(p-phenylenevinylene) (PPV) oligomers with
chain lengths up to eight phenyl rings. Vertical excitation energies
for the four lowest π–π* excitations and geometry
relaxation effects for the lowest excited state (S1) are
reported. Extrapolation to infinite chain length shows good agreement
with analogous data derived from experiment. Analysis of the bond
length alternation (BLA) based on the optimized S1 geometry
provides conclusive evidence for the localization of the defect in
the center of the oligomer chain. Torsional potentials have been computed
for the four excited states investigated and the transition densities
divided into fragment contributions have been used to identify excitonic
interactions. The present investigation provides benchmark results,
which can be used (i) as reference for lower level methods and (ii)
give the possibility to parametrize an effective Frenkel exciton Hamiltonian
for quantum dynamical simulations of ultrafast exciton transfer dynamics
in PPV type systems.
Collapse
Affiliation(s)
- Aditya N Panda
- Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India
| | | | | | | | | |
Collapse
|