A study on excited-state properties of conjugated polymers using the Pariser-Parr-Pople-Peierls model combined with configuration-interaction-singles

Abstract

Singlet and triplet excited-state properties of a single poly-p-phenylenevinylene (PPV) chain are studied using the Pariser-Parr-Pople-Peierls (P-P-P-P) model combined with the configuration interaction singles (CIS) formalism. The analytic CIS energy gradient is derived using the coupled perturbed Hartree-Fock (CPHF) equations in order to perform excited-state geometry optimizations. According to whether the diagonal elements of transition density matrices being zero or not, all excited states can be classified into two types: type I with nonzero diagonal elements, and type II with zero diagonal elements. In general, type I excited states can be directly generated upon photoexcitation, and there is high probability to find the electron and the hole very close to each other. While type II excited states cannot be directly generated upon photoexcitation, and there is high probability to find the electron and the hole far to each other. Using the parameters developed for this model, we examine the energy levels, oscillator strengths, optical absorption spectrum, and optimized excited-state geometries of the excited states at low energies, and they are consistent with other theoretical work very well. This work provides a new perspective on the excited-state properties of conjugated polymers.