In this article we present a time-dependent quantum/classical model for the dynamics of excitons in photoexcited conjugated polymer systems. Within this model, the excitation is treated quantum mechanically as a fully correlated electron/hole pair that interacts self-consistently with the vibrational motions of the polymer lattice. Spin and spatial symmetry considerations allow us to segregate singlet and triplet components into odd and even parity 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 for the exciton wave function and the lattice. Ths approach includes the electronic correlations necessary to reproduce excitonic behavior and allows the 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 exciton at T = 0 K starting from an initially free state. Within our model, the net stabilization of the singlet exciton upon localization is 238 cm(-1) indicating 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].