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Title: Exciton Absorption Spectra by Linear Response Methods: Application to Conjugated Polymers

Authors:
ORCiD logo [1]; ORCiD logo [2];  [1];  [1];  [2]; ORCiD logo [1];  [1]
  1. Department of Chemistry and the Materials Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
  2. Department of Chemistry and the Materials Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States; Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Lemont, Illinois 60439, United States
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Argonne-Northwestern Solar Energy Research Center (ANSER)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1388123
DOE Contract Number:
SC0001059
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of the American Chemical Society; Journal Volume: 139; Journal Issue: 10; Related Information: ANSER partners with Northwestern University (lead); Argonne National Laboratory; University of Chicago; University of Illinois, Urbana-Champaign; Yale University
Country of Publication:
United States
Language:
English
Subject:
catalysis (homogeneous), catalysis (heterogeneous), solar (photovoltaic), solar (fuels), photosynthesis (natural and artificial), bio-inspired, hydrogen and fuel cells, electrodes - solar, defects, charge transport, spin dynamics, membrane, materials and chemistry by design, optics, synthesis (novel materials), synthesis (self-assembly)

Citation Formats

Mosquera, Martín A., Jackson, Nicholas E., Fauvell, Thomas J., Kelley, Matthew S., Chen, Lin X., Schatz, George C., and Ratner, Mark A.. Exciton Absorption Spectra by Linear Response Methods: Application to Conjugated Polymers. United States: N. p., 2017. Web. doi:10.1021/jacs.6b12405.
Mosquera, Martín A., Jackson, Nicholas E., Fauvell, Thomas J., Kelley, Matthew S., Chen, Lin X., Schatz, George C., & Ratner, Mark A.. Exciton Absorption Spectra by Linear Response Methods: Application to Conjugated Polymers. United States. doi:10.1021/jacs.6b12405.
Mosquera, Martín A., Jackson, Nicholas E., Fauvell, Thomas J., Kelley, Matthew S., Chen, Lin X., Schatz, George C., and Ratner, Mark A.. Thu . "Exciton Absorption Spectra by Linear Response Methods: Application to Conjugated Polymers". United States. doi:10.1021/jacs.6b12405.
@article{osti_1388123,
title = {Exciton Absorption Spectra by Linear Response Methods: Application to Conjugated Polymers},
author = {Mosquera, Martín A. and Jackson, Nicholas E. and Fauvell, Thomas J. and Kelley, Matthew S. and Chen, Lin X. and Schatz, George C. and Ratner, Mark A.},
abstractNote = {},
doi = {10.1021/jacs.6b12405},
journal = {Journal of the American Chemical Society},
number = 10,
volume = 139,
place = {United States},
year = {Thu Mar 02 00:00:00 EST 2017},
month = {Thu Mar 02 00:00:00 EST 2017}
}
  • The theoretical description of the timeevolution of excitons requires, as an initial step, the calculation of their spectra, which has been inaccessible to most users due to the high computational scaling of conventional algorithms and accuracy issues caused by common density functionals. Previously (J. Chem. Phys. 2016, 144, 204105), we developed a simple method that resolves these issues. Our scheme is based on a two-step calculation in which a linear-response TDDFT calculation is used to generate orbitals perturbed by the excitonic state, and then a second linear-response TDDFT calculation is used to determine the spectrum of excitations relative to themore » excitonic state. Herein, we apply this theory to study near-infrared absorption spectra of excitons in oligomers of the ubiquitous conjugated polymers poly(3-hexylthiophene) (P3HT), poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV), and poly(benzodithiophene-thieno[3,4-b]thiophene) (PTB7). For P3HT and MEH-PPV oligomers, the calculated intense absorption bands converge at the longest wavelengths for 10 monomer units, and show strong consistency with experimental measurements. The calculations confirm that the exciton spectral features in MEH-PPV overlap with those of the bipolaron formation. In addition, our calculations identify the exciton absorption bands in transient absorption spectra measured by our group for oligomers (1, 2, and 3 units) of PTB7. For all of the cases studied, we report the dominant orbital excitations contributing to the optically active excited state-excited state transitions, and suggest a simple rule to identify absorption peaks at the longest wavelengths. We suggest our methodology could be considered for further evelopments in theoretical transient spectroscopy to include nonadiabatic effects, coherences, and to describe the formation of species such as charge-transfer states and polaron pairs.« less
  • Integrated three-pulse stimulated echo peak shift data are compared for N,N-bis-dimethylphenyl-2,4,6,8-perylenetetracarbonyl diamide and poly[2-(2{sup '}-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV) in toluene solvent. These two molecules represent a model probe of solvation dynamics and a prototypical soluble, electroluminescent conjugated polymer, respectively. The results indicate that it is inappropriate to describe the linear absorption spectrum of MEH-PPV as being primarily inhomogeneously broadened. Conformational disorder along the polymer backbone gives rise to an ensemble of polyene electronic oscillators that are strongly coupled to each other. As a consequence, fluctuations in the electronic energy gap on a time-scale of 50-fs derive primarily from bath-mediated exciton scattering. Themore » data reported here provide an explanation for the broad, structureless electronic absorption of MEH-PPV. This interpretation provides a valuable insight into the nature of the initial photoexcited state, and the efficient population of the emissive state. (c) 2000 The American Physical Society.« less
  • Computational investigation of the longest wavelength excitations in a series of cyanines and linear n-acenes is undertaken with the use of standard spin-conserving linear response time-dependent density functional theory (TD-DFT) as well as its spin-flip variant and a ΔSCF method based on the ensemble DFT. The spin-conserving linear response TD-DFT fails to accurately reproduce the lowest excitation energy in these π-conjugated systems by strongly overestimating the excitation energies of cyanines and underestimating the excitation energies of n-acenes. The spin-flip TD-DFT is capable of correcting the underestimation of excitation energies of n-acenes by bringing in the non-dynamic electron correlation into themore » ground state; however, it does not fully correct for the overestimation of the excitation energies of cyanines, for which the non-dynamic correlation does not seem to play a role. The ensemble DFT method employed in this work is capable of correcting for the effect of missing non-dynamic correlation in the ground state of n-acenes and for the deficient description of differential correlation effects between the ground and excited states of cyanines and yields the excitation energies of both types of extended π-conjugated systems with the accuracy matching high-level ab initio multireference calculations.« less
  • Conjugated polymers are modeled as a system of one-dimensional {pi} electrons interacting via a short-range Coulomb interaction and coupled to an underlying harmonic lattice, i.e., as an extended Peierls-Hubbard model. A perturbative bosonization procedure is employed to map the original Hamiltonian onto an effective one describing a coupled, one-dimensional exciton-phonon gas (EPG), which should be especially useful in discussing nonlinear optics. This approach treats excitons as ideal Bose (quasi)particles subject to effective interactions, which in turn are the microscopic origin of the nonlinear optics response of the material. In particular, we derive effective interaction vertices for (i) exciton-exciton scattering, (ii)more » exciton-phonon coupling, and (iii) (nonlinear) exciton-light coupling within a semiclassical approximation. As an application of the EPG model to nonlinear optics of conjugated polymers, we study, in the collisionless regime, the steady-state response of a coherently pumped EPG with respect to a spectrally broad test laser. The EPG approach discusses this particular four-wave-mixing experiment in terms of an externally driven, interacting two-component Bose gas. It explains optical Stark effects and inverse Raman scattering as due to composite excitations whose electronic and phononic degrees of freedom depend upon pump frequency and pump intensity. {copyright} {ital 1996 The American Physical Society.}« less
  • No abstract prepared.