Title

Role of Geometric Distortion and Polarization in Localizing Electronic Excitations in Conjugated Polymers

Authors

Authors

I. H. Nayyar; E. R. Batista; S. Tretiak; A. Saxena; D. L. Smith;R. L. Martin

Comments

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Abbreviated Journal Title

J. Chem. Theory Comput.

Keywords

FIELD-EFFECT TRANSISTORS; ENERGY-TRANSFER; MEH-PPV; PHENYLENEVINYLENE; OLIGOMERS; PHOTOEXCITED POLYFLUORENES; EXCITON DISSOCIATION; SYMMETRY-BREAKING; POLARON FORMATION; RADICAL CATIONS; HARTREE-FOCK; Chemistry, Physical; Physics, Atomic, Molecular & Chemical

Abstract

Five different Density Functional Theory (DFT) models (ranging from pure GGA to long-range-corrected hybrid functionals) were used to study computationally the nature of the self-trapped electronic states in oligophenylene vinylenes. The electronic excitations in question include the lowest singlet (S-1) and triplet (T-1(dagger)) excitons (calculated using Time Dependent DFT (TD-DFT) method), positive (P+) and negative (P-) polarons, and the lowest triplet (T-1) states (computed with the Self-Consistent Field (SCF) scheme). The polaron formation (spatial localization of excitations) is observed only with the use of range-corrected hybrid DFT models including long-range electronic exchange interactions. The extent of localization for all studied excitations is found to be invariant with respect to the size of the oligomer chain in their corresponding optimal geometries. We have analyzed the interdependence between the extent of the geometrical distortion and the localization of the orbital and spin density, and have observed that the localization of the P+ and P- charged species is quite sensitive to solvent polarization effects and the character of the DFT functional used, rather than the structural deformations. In contrast, the localization of neutral states, S-1 and T-1(dagger), is found to follow the structural distortions. Notably, T-1 excitation obtained with the mean field SCF approach is always strongly localized in range-corrected hybrid DFT models. The molecular orbital energetics of these excitations was further investigated to identify the relationship between state localization and the corresponding orbital structure. A characteristic stabilization (destabilization) of occupied (virtual) orbitals is observed in hybrid DFT models, compared to tight-binding model-like orbital filling in semilocal GGA functionals. The molecular and natural orbital representation allows visualization of the spatial extent of the underlying electronic states. In terms of stabilization energies, neutral excitons have higher binding energies compared to charged excitations. In contrast, the polaronic species exhibit the highest solvation energies among all electronic states studied.

Journal Title

Journal of Chemical Theory and Computation

Volume

9

Issue/Number

2

Publication Date

1-1-2013

Document Type

Article

Language

English

First Page

1144

Last Page

1154

WOS Identifier

WOS:000315018300032

ISSN

1549-9618

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