A dynamic model for exciton self-trapping in conjugated polymers. I. Theory

In this article we present a time-dependent quantum/classical model for the dynamics of excitons in photoexcited conjugated polymer systems. Within th is model, the excitation is treated quantum mechanically as a fully correla ted electron/hole pair that interacts self-consistently with the vibrationa l motions of the polymer lattice. Spin and spatial symmetry considerations allow us to segregate singlet and triplet components into odd and even pari ty manifolds upon exchange of coordinates. We adapt the parameters used in various semiempirical models to produce a Hamiltonian that is continuous in the two-dimensional space and integrate the coupled equations of motion fo r the exciton wave function and the lattice. Ths approach includes the elec tronic correlations necessary to reproduce excitonic behavior and allows th e study of both singlet and triplet exciton states. In this article, we use the approach to study the structure and formation of a self-trapped excito n at T = 0 K starting from an initially free state. Within our model, the n et stabilization of the singlet exciton upon localization is 238 cm(-1) ind icating that self-trapped exciton states in these systems are weakly bound relative to a free exciton. (C) 2000 American Institute of Physics. [S0021- 9606(00)70411-9].