Document Detail


Exciton Dynamics in Disordered Poly(para-phenylene vinylene) II: Exciton Diffusion.
MedLine Citation:
PMID:  23030335     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
We present a first principles theory of exciton diffusion in conformationally disordered conjugated polymers. Central to our theory is that exciton transfer occurs from vibrationally relaxed states (VRS) to local exciton ground states (LEGS). LEGSs are determined by the diagonal and off-diagonal disorder induced by density and torsional fluctuations, while VRSs are further localized by exciton-phonon coupling. The theory is implemented using the Frenkel-Holstein model to calculate the wavefunctions and energies of the LEGSs and VRSs. The coupling of VRSs and LEGSs via long range dipole-dipole interactions leads to the familiar line-dipole approximation for the exciton transfer integral. The exciton transfer rates are derived from the Fermi Golden rule. The theory is applied to an ensemble of conformationally disordered poly-(para-phenylene-vinylene) chains using a kinetic Monte Carlo algorithm. It is shown that: (i) Torsional disorder and trans-cis defects reduce the exciton diffusion length. (ii) Radiative recombination occurs from VRSs in the tail of their density of states. (iii) Torsional disorder increases the band gap, the line width of the density of states, and the Stokes shift. As a consequence, it causes a blue-shift in the vertical absorption, but a red-shift in the emission. (iv) The energy of the radiated photon decreases as -log t, with a gradient that increases with torsional disorder. The predicted exciton diffusion lengths of ~ 8-11 nm are in good agreement with experimental values.
Authors:
William Barford; Eric R Bittner; Alec Ward
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-10-3
Journal Detail:
Title:  The journal of physical chemistry. A     Volume:  -     ISSN:  1520-5215     ISO Abbreviation:  J Phys Chem A     Publication Date:  2012 Oct 
Date Detail:
Created Date:  2012-10-3     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9890903     Medline TA:  J Phys Chem A     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
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