1
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Gonzalvez Perez I, Barford W. Ultrafast Fluorescence Depolarization in Conjugated Polymers. J Phys Chem Lett 2021; 12:5344-5348. [PMID: 34076446 DOI: 10.1021/acs.jpclett.1c01354] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
We report on large-scale simulations of intrachain exciton dynamics in poly(para-phenylenevinylene). Our theoretical model describes Frenkel exciton coupling to both fast, quantized C-C bond vibrations and slow, classical torsional modes. We also incorporate system-bath interactions. The dynamics is simulated using the time evolution block decimation method, which avoids the failures of the Ehrenfest approximation to describe decoherence processes and nonadiabatic interstate conversion. System-bath interactions are modeled using quantum trajectories and Lindblad quantum jump operators. We find that following photoexcitation, the quantum mechanical entanglement of the exciton and C-C bond phonons causes exciton-site decoherence. Next, system-bath interactions cause the stochastic collapse of high-energy delocalized excitons into chromophores. Finally, torsional relaxation causes additional exciton-density localization. We relate these dynamical processes to the predicted fluorescence depolarization, extract the time scales corresponding to them, and thus interpret the observed sub-ps fluorescence depolarization.
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Affiliation(s)
- Isabel Gonzalvez Perez
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, United Kingdom
| | - William Barford
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, United Kingdom
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2
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Nieman R, Aquino AJA, Lischka H. Benchmark ab initio calculations on intermolecular structures and the exciton character of poly(p-phenylenevinylene) dimers. J Chem Phys 2020; 152:044306. [DOI: 10.1063/1.5139411] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Affiliation(s)
- Reed Nieman
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, USA
| | - Adelia J. A. Aquino
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, USA
- School of Pharmaceutical Sciences and Technology, Tianjin University, Tianjin 300072, People’s Republic of China
| | - Hans Lischka
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, Texas 79409-1061, USA
- School of Pharmaceutical Sciences and Technology, Tianjin University, Tianjin 300072, People’s Republic of China
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3
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Mroczek DP, Lankevich V, Bittner ER. How charges separate: correlating disorder, free energy, and open-circuit voltage in organic photovoltaics. Faraday Discuss 2019; 216:236-251. [PMID: 31012876 DOI: 10.1039/c8fd00182k] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In order for a photovoltaic cell to function, charge carriers produced by photoexcitation must fully dissociate and overcome their mutual Coulomb attraction to form free polarons. This becomes problematic in organic systems in which the low dielectric constant of the material portends a long separation distance between independent polaron pairs. In this paper, we discuss our recent efforts to correlate the role of density of states, entropy, and configurational and energetic disorder to the open-circuit voltage, VOC, of model type-II organic polymer photovoltaics. By comparing the results of a fully interacting lattice model to those predicted by a Wigner-Weisskopf type model we find that energetic disorder does play a significant role in determining the VOC; however, mobility perpendicular to the interface plays the deciding role in the eventual fate of a charge-separated pair.
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Affiliation(s)
| | - Vladimir Lankevich
- University of Houston, Department of Chemistry, Department of Physics, Houston, TX, USA.
| | - Eric R Bittner
- University of Houston, Department of Chemistry, Department of Physics, Houston, TX, USA.
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4
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Dimitrov SD, Azzouzi M, Wu J, Yao J, Dong Y, Tuladhar PS, Schroeder BC, Bittner ER, McCulloch I, Nelson J, Durrant JR. Spectroscopic Investigation of the Effect of Microstructure and Energetic Offset on the Nature of Interfacial Charge Transfer States in Polymer: Fullerene Blends. J Am Chem Soc 2019; 141:4634-4643. [PMID: 30807130 PMCID: PMC6429453 DOI: 10.1021/jacs.8b11484] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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Despite
performance improvements of organic photovoltaics, the
mechanism of photoinduced electron–hole separation at organic
donor–acceptor interfaces remains poorly understood. Inconclusive
experimental and theoretical results have produced contradictory models
for electron–hole separation in which the role of interfacial
charge-transfer (CT) states is unclear, with one model identifying
them as limiting separation and another as readily dissociating. Here,
polymer–fullerene blends with contrasting photocurrent properties
and enthalpic offsets driving separation were studied. By modifying
composition, film structures were varied from consisting of molecularly
mixed polymer–fullerene domains to consisting of both molecularly
mixed and fullerene domains. Transient absorption spectroscopy revealed
that CT state dissociation generating separated electron–hole
pairs is only efficient in the high energy offset blend with fullerene
domains. In all other blends (with low offset or predominantly molecularly
mixed domains), nanosecond geminate electron–hole recombination
is observed revealing the importance of spatially localized electron–hole
pairs (bound CT states) in the electron–hole dynamics. A two-dimensional
lattice exciton model was used to simulate the excited state spectrum
of a model system as a function of microstructure and energy offset.
The results could reproduce the main features of experimental electroluminescence
spectra indicating that electron–hole pairs become less bound
and more spatially separated upon increasing energy offset and fullerene
domain density. Differences between electroluminescence and photoluminescence
spectra could be explained by CT photoluminescence being dominated
by more-bound states, reflecting geminate recombination processes,
while CT electroluminescence preferentially probes less-bound CT states
that escape geminate recombination. These results suggest that apparently
contradictory studies on electron–hole separation can be explained
by the presence of both bound and unbound CT states in the same film,
as a result of a range of interface structures.
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Affiliation(s)
- S D Dimitrov
- SPECIFIC, College of Engineering , Swansea University , Bay Campus , Swansea SA1 8EN , United Kingdom
| | | | | | | | | | | | - B C Schroeder
- Department of Chemistry , University College , London WC1H 0AJ , United Kingdom
| | - E R Bittner
- Department of Chemistry , University of Houston , Houston , Texas 77204 , United States
| | - I McCulloch
- Physical Sciences and Engineering Division, KAUST Solar Center (KSC) , King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900 , Kingdom of Saudi Arabia
| | | | - J R Durrant
- SPECIFIC, College of Engineering , Swansea University , Bay Campus , Swansea SA1 8EN , United Kingdom
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5
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Lankevich V, Bittner ER. Relating free energy and open-circuit voltage to disorder in organic photovoltaic systems. J Chem Phys 2018; 149:244123. [DOI: 10.1063/1.5050506] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Affiliation(s)
- V. Lankevich
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
| | - E. R. Bittner
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
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6
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Chen XK, Coropceanu V, Brédas JL. Assessing the nature of the charge-transfer electronic states in organic solar cells. Nat Commun 2018; 9:5295. [PMID: 30546009 PMCID: PMC6294259 DOI: 10.1038/s41467-018-07707-8] [Citation(s) in RCA: 69] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Accepted: 11/16/2018] [Indexed: 11/13/2022] Open
Abstract
The charge-transfer electronic states appearing at the donor-acceptor interfaces in organic solar cells mediate exciton dissociation, charge generation, and charge recombination. To date, the characterization of their nature has been carried out on the basis of models that only involve the charge-transfer state and the ground state. Here, we demonstrate that it is essential to go beyond such a two-state model and to consider explicitly as well the electronic and vibrational couplings with the local absorbing state on the donor and/or acceptor. We have thus developed a three-state vibronic model that allows us: to provide a reliable description of the optical absorption features related to the charge-transfer states; to underline the erroneous interpretations stemming from the application of the semi-classical two-state model; and to rationalize how the hybridization between the local-excitation state and charge-transfer state can lead to lower non-radiative voltage losses and higher power conversion efficiencies. Previous descriptions of the charge-transfer absorptions in organic solar cells only involve the charge transfer state and the ground state. Here Chen et al. underline that a third state, i.e., the local absorbing state on the donor and/or acceptor, needs to be considered.
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Affiliation(s)
- Xian-Kai Chen
- School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia, 30332-0400, USA
| | - Veaceslav Coropceanu
- School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia, 30332-0400, USA.
| | - Jean-Luc Brédas
- School of Chemistry and Biochemistry and Center for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia, 30332-0400, USA.
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7
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Donati G, Lingerfelt DB, Petrone A, Rega N, Li X. “Watching” Polaron Pair Formation from First-Principles Electron–Nuclear Dynamics. J Phys Chem A 2016; 120:7255-61. [DOI: 10.1021/acs.jpca.6b06419] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Greta Donati
- Dipartimento
di Scienze Chimiche, Università di Napoli ‘Federico
II’, Complesso Universitario di M. S. Angelo, via Cintia, I-80126 Napoli, Italy
| | - David B. Lingerfelt
- Department
of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Alessio Petrone
- Department
of Chemistry, University of Washington, Seattle, Washington 98195, United States
| | - Nadia Rega
- Dipartimento
di Scienze Chimiche, Università di Napoli ‘Federico
II’, Complesso Universitario di M. S. Angelo, via Cintia, I-80126 Napoli, Italy
- Italian Institute
of Technology, IIT@CRIB Center for Advanced Biomaterials for Healthcare,
Largo Barsanti e Matteucci, I-80125 Napoli, Italy
| | - Xiaosong Li
- Department
of Chemistry, University of Washington, Seattle, Washington 98195, United States
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8
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Vella E, Li H, Grégoire P, Tuladhar SM, Vezie MS, Few S, Bazán CM, Nelson J, Silva-Acuña C, Bittner ER. Ultrafast decoherence dynamics govern photocarrier generation efficiencies in polymer solar cells. Sci Rep 2016; 6:29437. [PMID: 27412119 PMCID: PMC4944175 DOI: 10.1038/srep29437] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Accepted: 06/17/2016] [Indexed: 11/23/2022] Open
Abstract
All-organic-based photovoltaic solar cells have attracted considerable attention because of their low-cost processing and short energy payback time. In such systems the primary dissociation of an optical excitation into a pair of photocarriers has been recently shown to be extremely rapid and efficient, but the physical reason for this remains unclear. Here, two-dimensional photocurrent excitation spectroscopy, a novel non-linear optical spectroscopy, is used to probe the ultrafast coherent decay of photoexcitations into charge-producing states in a polymer:fullerene based solar cell. The two-dimensional photocurrent spectra are interpreted by introducing a theoretical model for the description of the coupling of the electronic states of the system to an external environment and to the applied laser fields. The experimental data show no cross-peaks in the twodimensional photocurrent spectra, as predicted by the model for coherence times between the exciton and the photocurrent producing states of 20 fs or less.
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Affiliation(s)
- Eleonora Vella
- Department of Physics and Regroupement québécois sur les matériaux de pointe, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal H3C 3J7, Canada
| | - Hao Li
- Department of Chemistry, University of Houston, Houston, Texas 77204, USA
| | - Pascal Grégoire
- Department of Physics and Regroupement québécois sur les matériaux de pointe, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal H3C 3J7, Canada
| | - Sachetan M. Tuladhar
- Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom
| | - Michelle S. Vezie
- Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom
| | - Sheridan Few
- Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom
| | - Claudia M. Bazán
- Department of Physics and Regroupement québécois sur les matériaux de pointe, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal H3C 3J7, Canada
| | - Jenny Nelson
- Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom
| | - Carlos Silva-Acuña
- Department of Physics and Regroupement québécois sur les matériaux de pointe, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal H3C 3J7, Canada
- Department of Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom
| | - Eric R. Bittner
- Department of Physics and Regroupement québécois sur les matériaux de pointe, Université de Montréal, C.P. 6128, Succursale centre-ville, Montréal H3C 3J7, Canada
- Department of Chemistry, University of Houston, Houston, Texas 77204, USA
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9
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Polkehn M, Tamura H, Eisenbrandt P, Haacke S, Méry S, Burghardt I. Molecular Packing Determines Charge Separation in a Liquid Crystalline Bisthiophene-Perylene Diimide Donor-Acceptor Material. J Phys Chem Lett 2016; 7:1327-1334. [PMID: 26987362 DOI: 10.1021/acs.jpclett.6b00277] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Combined electronic structure and quantum dynamical calculations are employed to investigate charge separation in a novel class of covalently bound bisthiophene-perylene diimide type donor-acceptor (DA) co-oligomer aggregates. In an earlier spectroscopic study of this DA system in a smectic liquid crystalline (LC) film, efficient and ultrafast (subpicosecond) initial charge separation was found to be followed by rapid recombination. By comparison, the same DA system in solution exhibits ultrafast resonant energy transfer followed by slower (picosecond scale) charge separation. The present first-principles study explains these contrasting observations, highlighting the role of an efficient intermolecular charge-transfer pathway that results from the molecular packing in the LC phase. Despite the efficiency of this primary charge-transfer step, long-range charge separation is impeded by a comparatively high Coulomb barrier in conjunction with small electron- and hole-transfer integrals. Quantum dynamical calculations are carried out for a fragment-based model Hamiltonian, parametrized by ab initio second-order Algebraic Diagrammatic Construction (ADC(2)) and Time-Dependent Density Functional Theory (TDDFT) electronic structure calculations. Simulations of coherent vibronic quantum dynamics for up to 156 electronic states and 48 modes are performed using the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method. Excellent agreement with experimentally determined charge separation time scales is obtained, and the spatially coherent nature of the dynamics is analyzed.
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Affiliation(s)
- Matthias Polkehn
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt , Max-von-Laue-Str. 7, 60438 Frankfurt, Germany
| | - Hiroyuki Tamura
- WPI-Advanced Institute for Material Research, Tohoku University , 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Pierre Eisenbrandt
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt , Max-von-Laue-Str. 7, 60438 Frankfurt, Germany
| | - Stefan Haacke
- Institut de Physique et Chimie des Matériaux de Strasbourg, Université de Strasbourg - CNRS , 67034 Strasbourg Cedex 2, France
| | - Stéphane Méry
- Institut de Physique et Chimie des Matériaux de Strasbourg, Université de Strasbourg - CNRS , 67034 Strasbourg Cedex 2, France
| | - Irene Burghardt
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt , Max-von-Laue-Str. 7, 60438 Frankfurt, Germany
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10
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Galindo JF, Atas E, Altan A, Kuroda DG, Fernandez-Alberti S, Tretiak S, Roitberg AE, Kleiman VD. Dynamics of Energy Transfer in a Conjugated Dendrimer Driven by Ultrafast Localization of Excitations. J Am Chem Soc 2015; 137:11637-44. [DOI: 10.1021/jacs.5b04075] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Johan F. Galindo
- Department
of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Evrim Atas
- Department
of Chemistry, University of Florida, Gainesville, Florida 32611, 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
| | - Adrian E. Roitberg
- Department
of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Valeria D. Kleiman
- Department
of Chemistry, University of Florida, Gainesville, Florida 32611, United States
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11
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Huix-Rotllant M, Tamura H, Burghardt I. Concurrent Effects of Delocalization and Internal Conversion Tune Charge Separation at Regioregular Polythiophene-Fullerene Heterojunctions. J Phys Chem Lett 2015; 6:1702-1708. [PMID: 26263337 DOI: 10.1021/acs.jpclett.5b00336] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Quantum-dynamical simulations are used to investigate the interplay of exciton delocalization and vibronically induced internal conversion processes in the elementary charge separation steps at regioregular donor-acceptor heterojunctions. Ultrafast internal conversion leads to efficient deexcitation within the excitonic and charge transfer manifolds, thus modifying the charge separation dynamics. We address a model donor-acceptor junction representative of regioregular P3HT-PCBM, using high-dimensional quantum dynamics simulations by multiconfigurational methods. While partial trapping into an interfacial charge separated state occurs, long-range charge-separated states are accessed as previously demonstrated in the work of Tamura and Burghardt [J. Am. Chem. Soc. 2013, 135, 16364]. For an H-aggregate type, stacked donor species, the initial bright state undergoes ultrafast internal conversion within the excitonic manifold, creating multiple charge transfer pathways before reaching the lowest-energy dark exciton, which is uncoupled from the charge transfer manifold. This process profoundly affects the charge separation mechanism and efficiency. For small energetic offsets between the interfacial excitonic and charge transfer states, a delocalized initial bright state proves less prone to electron-hole capture by the interfacial trap than a localized, vibronic wavepacket close to the interface. For both delocalized and localized initial states, a comparable yield of free carriers is obtained, which is found to be optimal for energetic offsets of the order of the Coulomb barrier to charge separation. Interfacial trapping is significantly reduced as the barrier height decreases with fullerene aggregation. Despite the high-dimensional nature of the system, charge separation is an ultrafast coherent quantum process exhibiting oscillatory features as observed in recent experiments.
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Affiliation(s)
- Miquel Huix-Rotllant
- †Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt, Germany
| | - Hiroyuki Tamura
- ‡WPI-Advanced Institute for Material Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
| | - Irene Burghardt
- †Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt, Germany
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12
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Cardozo TM, Aquino AJA, Barbatti M, Borges I, Lischka H. Absorption and fluorescence spectra of poly(p-phenylenevinylene) (PPV) oligomers: an ab initio simulation. J Phys Chem A 2014; 119:1787-95. [PMID: 25415930 PMCID: PMC4353058 DOI: 10.1021/jp508512s] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
![]()
The
absorption and fluorescence spectra of poly(p-phenylenevinylene)
(PPV) oligomers with up to seven repeat units
were theoretically investigated using the algebraic diagrammatic construction
method to second order, ADC(2), combined with the resolution-of-the-identity
(RI) approach. The ground and first excited state geometries of the
oligomers were fully optimized. Vertical excitation energies and oscillator
strengths of the first four transitions were computed. The vibrational
broadening of the absorption and fluorescence spectra was studied
using a semiclassical nuclear ensemble method. After correcting for
basis set and solvent effects, we achieved a balanced description
of the absorption and fluorescence spectra by means of the ADC(2)
approach. This fact is documented by the computed Stokes shift along
the PPV series, which is in good agreement with the experimental values.
The experimentally observed band width of the UV absorption and fluorescence
spectra is well reproduced by the present simulations showing that
the nuclear ensemble generated should be well suitable for consecutive
surface hopping dynamics simulations.
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Affiliation(s)
- Thiago M Cardozo
- Instituto de Química, Universidade Federal do Rio de Janeiro , Avenida Athos da Silveira Ramos, 149, 21941-909 - Cidade Universitária - Rio de Janeiro, RJ, Brazil
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13
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14
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Noise-induced quantum coherence drives photo-carrier generation dynamics at polymeric semiconductor heterojunctions. Nat Commun 2014; 5:3119. [DOI: 10.1038/ncomms4119] [Citation(s) in RCA: 97] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2013] [Accepted: 12/16/2013] [Indexed: 01/05/2023] Open
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15
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Bittner ER, Lankevich V, Gélinas S, Rao A, Ginger DA, Friend RH. How disorder controls the kinetics of triplet charge recombination in semiconducting organic polymer photovoltaics. Phys Chem Chem Phys 2014; 16:20321-8. [DOI: 10.1039/c4cp01776e] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Theoretical models of polymer–fullerene interfaces indicate that inhomogeneous broadening of fullerene energy levels introduces strong coupling between the interfacial3CT and nearby fullerene triplet excitons that can enhance the decay of these states in systems with higher degrees of energetic disorder.
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Affiliation(s)
| | | | - Simon Gélinas
- Cavendish laboratory
- University of Cambridge
- Cambridge, UK
| | - Akshay Rao
- Cavendish laboratory
- University of Cambridge
- Cambridge, UK
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16
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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.
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Affiliation(s)
- Aditya N Panda
- Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, 781039, Assam, India
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17
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Affiliation(s)
- William Barford
- Department of Chemistry, Physical
and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, United Kingdom
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18
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Nayyar IH, Batista ER, Tretiak S, Saxena A, Smith DL, Martin RL. Role of Geometric Distortion and Polarization in Localizing Electronic Excitations in Conjugated Polymers. J Chem Theory Comput 2013; 9:1144-54. [DOI: 10.1021/ct300837d] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Iffat H. Nayyar
- Theoretical
Division and Center for Nonlinear Studies and ‡Center for Integrated Nanotechnologies, Los Alamos National Laboratory, New
Mexico 87545, United States
- NanoScience Technology Center and ∥Department of Physics, University of Central Florida, Orlando,
Florida 32826, United States
| | - Enrique R. Batista
- Theoretical
Division and Center for Nonlinear Studies and ‡Center for Integrated Nanotechnologies, Los Alamos National Laboratory, New
Mexico 87545, United States
- NanoScience Technology Center and ∥Department of Physics, University of Central Florida, Orlando,
Florida 32826, United States
| | - Sergei Tretiak
- Theoretical
Division and Center for Nonlinear Studies and ‡Center for Integrated Nanotechnologies, Los Alamos National Laboratory, New
Mexico 87545, United States
- NanoScience Technology Center and ∥Department of Physics, University of Central Florida, Orlando,
Florida 32826, United States
| | - Avadh Saxena
- Theoretical
Division and Center for Nonlinear Studies and ‡Center for Integrated Nanotechnologies, Los Alamos National Laboratory, New
Mexico 87545, United States
- NanoScience Technology Center and ∥Department of Physics, University of Central Florida, Orlando,
Florida 32826, United States
| | - Darryl L. Smith
- Theoretical
Division and Center for Nonlinear Studies and ‡Center for Integrated Nanotechnologies, Los Alamos National Laboratory, New
Mexico 87545, United States
- NanoScience Technology Center and ∥Department of Physics, University of Central Florida, Orlando,
Florida 32826, United States
| | - Richard L. Martin
- Theoretical
Division and Center for Nonlinear Studies and ‡Center for Integrated Nanotechnologies, Los Alamos National Laboratory, New
Mexico 87545, United States
- NanoScience Technology Center and ∥Department of Physics, University of Central Florida, Orlando,
Florida 32826, United States
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19
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Binder R, Wahl J, Römer S, Burghardt I. Coherent exciton transport driven by torsional dynamics: a quantum dynamical study of phenylene-vinylene type conjugated systems. Faraday Discuss 2013; 163:205-22; discussion 243-75. [DOI: 10.1039/c3fd20148a] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
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20
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Tozer OR, Barford W. Exciton Dynamics in Disordered Poly(p-phenylenevinylene). 1. Ultrafast Interconversion and Dynamical Localization. J Phys Chem A 2012; 116:10310-8. [DOI: 10.1021/jp307040d] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Oliver Robert Tozer
- Department of Chemistry, Physical and Theoretical
Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, United Kingdom
- University College, University of Oxford, Oxford OX1 4BH, United Kingdom
| | - William Barford
- Department of Chemistry, Physical and Theoretical
Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, United Kingdom
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21
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Bittner ER, Zaster S, Silva C. Thermodynamics of exciton/polaritons in one and two dimensional organic single-crystal microcavities. Phys Chem Chem Phys 2012; 14:3226-33. [PMID: 22416284 DOI: 10.1039/c2cp23204a] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We consider here the thermodynamics and phase-diagram of exciton/polaritons formed in low-dimensional organic single-crystal microcavities. Using the Dicke model for a lattice of Frenkel excitons coupled to a common cavity mode, we explore the transition between normal and condensate regimes as depending upon the exciton band-width and temperature of the polariton gas. We show that for one-dimensional conjugated polymers, the coexistence curve at low temperatures shifts towards lower critical coupling strengths as the exciton band-width is increased. We also consider the effect of orientational disorder in a two-dimensional polyacene slab on the formation of the polariton BEC. Our results indicate that while a small degree of orientational disorder will not have a profound effect on the critical exciton/photon coupling strength needed to produce the transition from normal to BEC regimes, BEC will likely be suppressed in glassy or strongly disordered molecular films.
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Affiliation(s)
- Eric R Bittner
- Department of Chemistry, University of Houston, Houston, TX 77204, USA.
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22
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Barford W, Boczarow I, Wharram T. Ultrafast Dynamical Localization of Photoexcited States in Conformationally Disordered Poly(p-phenylenevinylene). J Phys Chem A 2011; 115:9111-9. [DOI: 10.1021/jp204822h] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- William Barford
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, OX1 3QZ, United Kingdom
- Balliol College, University of Oxford, Oxford, OX1 3BJ, United Kingdom
| | - Igor Boczarow
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, OX1 3QZ, United Kingdom
- Balliol College, University of Oxford, Oxford, OX1 3BJ, United Kingdom
| | - Thomas Wharram
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, OX1 3QZ, United Kingdom
- University College, University of Oxford, Oxford, OX1 4BH, United Kingdom
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23
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Banerji N, Cowan S, Leclerc M, Vauthey E, Heeger AJ. Exciton formation, relaxation, and decay in PCDTBT. J Am Chem Soc 2010; 132:17459-70. [PMID: 21087001 DOI: 10.1021/ja105290e] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The nature and time evolution of the primary excitations in the pristine conjugated polymer, PCDTBT, are investigated by femtosecond-resolved fluorescence up-conversion spectroscopy. The extensive study includes data from PCDTBT thin film and from PCDTBT in chlorobenzene solution, compares the fluorescence dynamics for several excitation and emission wavelengths, and is complemented by polarization-sensitive measurements. The results are consistent with the photogeneration of mobile electrons and holes by interband π-π* transitions, which then self-localize within about 100 fs and evolve to a bound singlet exciton state in less than 1 ps. The excitons subsequently undergo successive migrations to lower energy localized states, which exist as a result of disorder. In parallel, there is also slow conformational relaxation of the polymer backbone. While the initial self-localization occurs faster than the time resolution of our experiment, the exciton formation, exciton migration, and conformational changes lead to a progressive relaxation of the inhomogeneously broadened emission spectrum with time constants ranging from about 500 fs to tens of picoseconds. The time scales found here for the relaxation processes in pristine PCDTBT are compared to the time scale (<0.2 ps) previously reported for photoinduced charge transfer in phase-separated PCDTBT:fullerene blends (Phys. Rev. B 2010, 81, 125210). We point out that exciton formation and migration in PCDTBT occur at times much longer than the ultrafast photoinduced electron transfer time in PCDTBT:fullerene blends. This disparity in time scales is not consistent with the commonly proposed idea that photoinduced charge separation occurs after diffusion of the polymer exciton to a fullerene interface. We therefore discuss alternative mechanisms that are consistent with ultrafast charge separation before localization of the primary excitation to form a bound exciton.
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Affiliation(s)
- Natalie Banerji
- Center for Polymers and Organic Solids, University of California at Santa Barbara, Santa Barbara, California 93106-5090, USA
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24
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Schumacher S, Ruseckas A, Montgomery NA, Skabara PJ, Kanibolotsky AL, Paterson MJ, Galbraith I, Turnbull GA, Samuel IDW. Effect of exciton self-trapping and molecular conformation on photophysical properties of oligofluorenes. J Chem Phys 2010; 131:154906. [PMID: 20568883 DOI: 10.1063/1.3244984] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Electronic absorption and fluorescence transitions in fluorene oligomers of differing lengths are studied experimentally and using density functional theory (DFT) and time-dependent DFT. Experimental values are determined in two ways: from the measured molar absorption coefficient and from the radiative rate deduced from a combination of fluorescence quantum yield and lifetime measurements. Good agreement between the calculated and measured transition dipoles is achieved. In both theory and experiment a gradual increase in transition dipoles with increasing oligomer length is found. In absorption the transition dipole follows an approximately n(0.5) dependence on the number of fluorene units n for the range of 2 < or = n < or = 12, whereas a clear saturation of the transition dipole with oligomer length is found in fluorescence. This behavior is attributed to structural relaxation of the molecules in the excited state leading to localization of the excitation (exciton self-trapping) in the middle of the oligomer for both twisted and planar backbone conformations. Twisted oligofluorene chains were found to adopt straight or bent geometries depending on alternation of the dihedral angle between adjacent fluorene units. These different molecular conformations show the same values for the transition energies and the magnitude of the transition dipole.
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Affiliation(s)
- Stefan Schumacher
- Department of Physics, School of Engineering and Physical Sciences, SUPA, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
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25
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Dykstra TE, Hennebicq E, Beljonne D, Gierschner J, Claudio G, Bittner ER, Knoester J, Scholes GD. Conformational disorder and ultrafast exciton relaxation in PPV-family conjugated polymers. J Phys Chem B 2009; 113:656-67. [PMID: 19105646 DOI: 10.1021/jp807249b] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
We report combined experimental and theoretical studies of excitation relaxation in poly[2-methoxy,5-(2'-ethyl-hexoxy)-1,4-phenylenevinylene] (MEH-PPV), oligophenylenevinylene (OPV) molecules of varying length, and model PPV chains. We build on the paradigm that the basic characteristics of conjugated polymers are decided by conformational subunits defined by conjugation breaks caused by torsional disorder along the chain. The calculations reported here indicate that for conjugated polymers like those in the PPV family, these conformational subunits electronically couple to neighboring subunits, forming subtly delocalized collective states of nanoscale excitons that determine the polymer optical properties. We find that relaxation among these exciton states can lead to a decay of anisotropy on ultrafast time scales. Unlike in Forster energy transfer, the exciton does not necessarily translate over a large distance. Nonetheless, the disorder in the polymer chain means that even small changes in the exciton size or location has a significant effect on the relaxation pathway and therefore the anisotropy decay.
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Affiliation(s)
- Tieneke E Dykstra
- Lash-Miller Chemical Laboratories, Institute for Optical Sciences and Centre for Quantum Information and Quantum Control, University of Toronto, 80 St. George Street, Toronto, Ontario, M5S 3H6 Canada
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26
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Ultrafast Photophysics of Organic Semiconductor Junctions. SPRINGER SERIES IN CHEMICAL PHYSICS 2009. [DOI: 10.1007/978-3-642-02306-4_8] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
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27
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Singh J, Bittner ER, Beljonne D, Scholes GD. Fluorescence depolarization in poly[2-methoxy-5-((2-ethylhexyl)oxy)-1,4-phenylenevinylene]: Sites versus eigenstates hopping. J Chem Phys 2009; 131:194905. [DOI: 10.1063/1.3259549] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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28
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Tamura H, Ramon JGS, Bittner ER, Burghardt I. Phonon-Driven Exciton Dissociation at Donor−Acceptor Polymer Heterojunctions: Direct versus Bridge-Mediated Vibronic Coupling Pathways. J Phys Chem B 2007; 112:495-506. [DOI: 10.1021/jp077270p] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- Hiroyuki Tamura
- Département de Chimie, Ecole Normale Supérieure, 24 rue Lhomond, F−75231 Paris cedex 05, France, and Department of Chemistry and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204
| | - John G. S. Ramon
- Département de Chimie, Ecole Normale Supérieure, 24 rue Lhomond, F−75231 Paris cedex 05, France, and Department of Chemistry and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204
| | - Eric R. Bittner
- Département de Chimie, Ecole Normale Supérieure, 24 rue Lhomond, F−75231 Paris cedex 05, France, and Department of Chemistry and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204
| | - Irene Burghardt
- Département de Chimie, Ecole Normale Supérieure, 24 rue Lhomond, F−75231 Paris cedex 05, France, and Department of Chemistry and Texas Center for Superconductivity, University of Houston, Houston, Texas 77204
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29
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Bittner ER. Lattice theory of ultrafast excitonic and charge-transfer dynamics in DNA. J Chem Phys 2007; 125:094909. [PMID: 16965121 DOI: 10.1063/1.2335452] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We propose a lattice fermion model suitable for studying the ultrafast photoexcitation dynamics of ordered chains of deoxyribonucleic acid (DNA) polymers. The model includes both parallel (intrachain) and perpendicular (cross-chain) terms as well as diagonal cross-chain terms coupling neighboring bases. The general form of our Hamiltonian is borrowed from lattice fermion models of quantum chromodynamics. The band structure for this model can be determined analytically, and we use this as a basis for computing the singly excited states of the poly(dA)poly(dT) DNA duplex using configuration interaction singles. Parameters for the model are taken from various literature sources and our own ab initio calculations. Results indicate that the excited states consist of a low energy band of dark charge-separated states followed by separate bands of delocalized excitonic states which have weak mixing between the thymidine and adenosine sides of the DNA chain. We then propose a lattice exciton model based upon the transition dipole-dipole couplings between bases and compare the analytical results for the survival probability of an initially localized exciton to exact numerical results. The results herein underscore the competing role of excitonic and charge-transfer dynamics in these systems.
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Affiliation(s)
- Eric R Bittner
- Department of Chemistry, University of Houston, Houston, Texas 77204, USA.
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30
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Bittner ER. Frenkel exciton model of ultrafast excited state dynamics in AT DNA double helices. J Photochem Photobiol A Chem 2007. [DOI: 10.1016/j.jphotochem.2006.12.007] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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31
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Tamura H, Bittner ER, Burghardt I. Exciton dissociation at donor-acceptor polymer heterojunctions: Quantum nonadiabatic dynamics and effective-mode analysis. J Chem Phys 2007; 126:021103. [PMID: 17228931 DOI: 10.1063/1.2431358] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The quantum-dynamical mechanism of photoinduced subpicosecond exciton dissociation and the concomitant formation of a charge-separated state at a semiconducting polymer heterojunction is elucidated. The analysis is based upon a two-state vibronic coupling Hamiltonian including an explicit 24-mode representation of a phonon bath comprising high-frequency (C==C stretch) and low-frequency (torsional) modes. The initial relaxation behavior is characterized by coherent oscillations, along with the decay through an extended nonadiabatic coupling region. This region is located in the vicinity of a conical intersection hypersurface. A central ingredient of the analysis is a novel effective mode representation, which highlights the role of the low-frequency modes in the nonadiabatic dynamics. Quantum dynamical simulations were carried out using the multiconfiguration time-dependent Hartree method.
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Affiliation(s)
- Hiroyuki Tamura
- Département de Chimie, Ecole Normale Supérieure, 24 rue Lhomond, F-75231 Paris cedex 05, France.
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32
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Bittner ER, Ramon JGS. Exciton and Charge-Transfer Dynamics in Polymer Semiconductors. QUANTUM DYNAMICS OF COMPLEX MOLECULAR SYSTEMS 2007. [DOI: 10.1007/978-3-540-34460-5_3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
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33
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Ramon JGS, Bittner ER. Exciton Regeneration Dynamics in Model Donor−Acceptor Polymer Heterojunctions. J Phys Chem B 2006; 110:21001-9. [PMID: 17048918 DOI: 10.1021/jp061751b] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We present a theoretical investigation on various semiconducting materials that exhibit photovoltaic and photoluminecent properties. Our focus is on the relaxation dynamics that occur upon photoexcitation of a couple of type II donor-acceptor heterojunction systems. In addition to the diabatic approach our two-band exciton model employs to study the phonon-assisted relaxations, we adopt the Marcus-Hush semiclassical method to incorporate lattice reorganization. This enables us to look at the state-to-state interconversions from the relaxed excited-state configurations in model polymer blends of poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB) with poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) and poly(9,9-dioctylfluorene-co-bis-N,N-(4-butylphenyl)-bis-N,N-phenyl-1,4-phenylenediamine) (PFB) with F8BT. Our results stress the significance of vibrational relaxation in the state-to-state relaxation. Furthermore, while a tightly bound charge-transfer state (exciplex) remains the lowest excited state, we show that the regeneration of the optically active lowest excitonic state in TFB:F8BT is possible via the existence of a steady state.
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Affiliation(s)
- John Glenn S Ramon
- Department of Chemistry and Center for Materials Chemistry, University of Houston, Texas 77204, USA
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34
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Pereverzev A, Bittner ER. Time-convolutionless master equation for mesoscopic electron-phonon systems. J Chem Phys 2006; 125:104906. [PMID: 16999549 DOI: 10.1063/1.2348869] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The time-convolutionless master equation for the electronic populations is derived for a generic electron-phonon Hamiltonian. The equation can be used in the regimes where the golden rule approach is not applicable. The equation is applied to study the electronic relaxation in several models with the finite number of normal modes. For such mesoscopic systems the relaxation behavior differs substantially from the simple exponential relaxation. In particular, the equation shows the appearance of the recurrence phenomena on a time scale determined by the slowest mode of the system. The formal results are quite general and can be used for a wide range of physical systems. Numerical results are presented for a two level system coupled to Ohmic and super-Ohmic baths, as well as for a model of charge-transfer dynamics between semiconducting organic polymers.
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Affiliation(s)
- Andrey Pereverzev
- Center for Materials Chemistry, Department of Chemistry, University of Houston, Houston, TX 77204, USA.
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35
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Grey JK, Kim DY, Donley CL, Miller WL, Kim JS, Silva C, Friend RH, Barbara PF. Effect of Temperature and Chain Length on the Bimodal Emission Properties of Single Polyfluorene Copolymer Molecules. J Phys Chem B 2006; 110:18898-903. [PMID: 16986881 DOI: 10.1021/jp057361r] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Fluorescence emission spectra were recorded for isolated polymer chains of the polyfluorene copolymer, F8BT [poly(9,9-di-n-octylfluorene-alt-benzothiadiazole)], at 298 and 20 K for two molecular weights (chain lengths). For long-chain F8BT at 298 K, the observed distribution of single-molecule emission maxima G(Emax) is bimodal, with peaks at approximately 2.35 eV ("blue") and approximately 2.25 eV ("red"). Previously, the red forms have been assigned to polymer chains that possess intrachain contacts, which lowers the local singlet exciton energy. At approximately 20 K, G(Emax) collapses into a single broad distribution centered at approximately 2.3 eV for long-chain F8BT. However, this distribution can be further divided into a high-energy edge that is dominated by the "blue" form, while the remainder of the distribution is composed of the "red" form. Low-molecular-weight F8BT samples emit exclusively from the blue form, and no shift in peak maxima with low temperature was observed. A Franck-Condon analysis reveals a decrease in emitting state displacements between spectra measured at 298 and 20 K, suggesting that temperature-induced structural displacements are responsible for the change in the bimodal emission.
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Affiliation(s)
- John K Grey
- Center for Nano and Molecular Science and Technology and Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA
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36
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Ruseckas A, Samuel IDW. Exciton self-trapping in MEH-PPV films studied by ultrafast emission depolarization. ACTA ACUST UNITED AC 2006. [DOI: 10.1002/pssc.200562715] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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37
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Excited state dynamics of a conformationally disordered conjugated polymer: A comparison of solutions and film. Chem Phys 2005. [DOI: 10.1016/j.chemphys.2005.04.001] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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38
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Beenken WJD, Lischka H. Spectral broadening and diffusion by torsional motion in biphenyl. J Chem Phys 2005; 123:144311. [PMID: 16238395 DOI: 10.1063/1.2049269] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have studied biphenyl by time-dependent density-functional theory. In particular, we have analyzed the dependence of singlet excitation energies and transition dipoles on the torsional angle between the phenyl groups. The torsional spectrum has been computed quantum mechanically as well as semiclassically in order to understand how this influences the broadening of absorption and luminescence spectra. Our results are in best agreement with supersonic jet spectroscopy data, but also fit astonishingly well to spectra of biphenyl in condensed phase. Furthermore, we compare the torsional and vibrational relaxation and discuss qualitatively the general consequences for poly-para-phenylenes and related conjugated polymers as poly-thiophenes, considering, in particular, how side chains and solvents may affect the optical spectra.
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Affiliation(s)
- Wichard J D Beenken
- Department of Theoretical Physics I, Technische Universität Ilmenau, Postfach 100565, 98684 Ilmenau, Germany.
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39
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Bittner ER, Ramon JGS, Karabunarliev S. Exciton dissociation dynamics in model donor-acceptor polymer heterojunctions. I. Energetics and spectra. J Chem Phys 2005; 122:214719. [PMID: 15974774 DOI: 10.1063/1.1924540] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In this paper we consider the essential electronic excited states in parallel chains of semiconducting polymers that are currently being explored for photovoltaic and light-emitting diode applications. In particular, we focus upon various type II donor-acceptor heterojunctions and explore the relation between the exciton binding energy to the band offset in determining the device characteristic of a particular type II heterojunction material. As a general rule, when the exciton binding energy is greater than the band offset at the heterojunction, the exciton will remain the lowest-energy excited state and the junction will make an efficient light-emitting diode. On the other hand, if the offset is greater than the exciton binding energy, either the electron or hole can be transferred from one chain to the other. Here we use a two-band exciton to predict the vibronic absorption and emission spectra of model polymer heterojunctions. Our results underscore the role of vibrational relaxation and suggest that intersystem crossings may play some part in the formation of charge-transfer states following photoexcitation in certain cases.
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Affiliation(s)
- Eric R Bittner
- Department of Chemistry and Center for Materials Chemistry, University of Houston, Houston, Texas 77204, USA.
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40
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Bittner ER, Karabunarliev S, Ye A. Photoconductivity and current producing states in molecular semiconductors. J Chem Phys 2005; 122:34707. [PMID: 15740217 DOI: 10.1063/1.1829032] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present a methodology for computing photocurrent production in molecular semiconducting molecules. Our model combines a single-configuration interaction picture with the nonequilibrium Green's function approach to compute the current response of a molecular semiconducting wire following excitation. We give detailed analysis of the essential excitonic, charge transfer, and dipole states for poly-(phenylenevinylene) chains of length 32 and 48 repeat units under an electric field bias and use this to develop a reduced dimensional tunneling model which accounts for chain-length and field-dependent behavior. In this paper, we consider the decay of an excited electron/hole state on a molecular wire under bias attached to semiconducting leads at either end. We find that the current produced by the decay of an excitation depends not only upon the lifetime of the state, as given by the imaginary part of its complex eigenvalue, but also upon the net charge on terminal ends of the molecule. We also find that weakly bound electron/hole charge-transfer pairs can decay into the continuum via field induced tunneling and produce a net current whereas excitonic states decay via tunneling but give no net current contribution.
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Affiliation(s)
- Eric R Bittner
- Department of Chemistry and Center for Materials Chemistry, University of Houston, Houston, Texas 77204, USA
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41
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42
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Beenken WJD, Pullerits T. Spectroscopic Units in Conjugated Polymers: A Quantum Chemically Founded Concept? J Phys Chem B 2004; 108:6164-9. [PMID: 18950096 DOI: 10.1021/jp037332l] [Citation(s) in RCA: 212] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
| | - Tõnu Pullerits
- Department of Chemical Physics, Lund University, 22100 Lund, Sweden
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43
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Karabunarliev S, Bittner ER. Electroluminescence Yield in Donor−Acceptor Copolymers and Diblock Polymers: A Comparative Theoretical Study. J Phys Chem B 2004. [DOI: 10.1021/jp036587w] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Stoyan Karabunarliev
- Department of Chemistry and Center for Materials Chemistry, University of Houston, Houston, Texas 77204-5003
| | - Eric R. Bittner
- Department of Chemistry and Center for Materials Chemistry, University of Houston, Houston, Texas 77204-5003
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44
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Karabunarliev S, Bittner ER. Dissipative dynamics of spin-dependent electron–hole capture in conjugated polymers. J Chem Phys 2003. [DOI: 10.1063/1.1591719] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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