Influence of substituents and chain length on the optical properties of poly(p-phenylenevinylene) oligomers

Electronic-structure calculations based upon the Pariser-Parr-Pople semiempirical Hamiltonian were applied to short-chain oligomers of the conducting polymer poly (p-phenylenevinylene) (PPV) to study the effects of appending methoxy groups along the backbone as well as push-pull nitro and amino groups at the ends of the oligomers. Optical absorption spectra were calculated utilizing configuration interaction methods at the single-excitation level, and the nonlinear optical properties of the push-pull oligomers were studied using the sum-over-states approach. In short-chain oligomers, the calculated electronic and optical properties are controlled by the nature of the pendant groups. However, in the longest oligomers studied, these molecular properties are relatively insensitive to any of the studied modifications.