Vibrational spectra and DFT calculations of PPV-oligomers

Abstract

Abstract The first two members of the p -phenylenevinylene-oligomer family (i.e. 1,4-distyrylbenzene and 4,4′-distyrylstilbene) were synthesized and their infrared and Raman spectra recorded and empirically assigned. Molecular geometries were optimized for the planar point group ( C 2 h ) by the density functional theory (DFT) method using the B3LYP functional and 6-31G* basis set. Calculations of vibrational spectra, including intensities, were carried out subsequently using the DFT method with the same basis set and linear scaling was applied. Calculated vibrational wavenumbers are in a fair agreement with our own experimental spectra. In order to explore changes in vibrational dynamics that are obtained with the extension of the chain, differences in potential energy distribution of normal modes are investigated and discussed. It was shown that B3LYP functional well describes the mentioned differences in infrared and Raman spectra and presents a sound basis for a more thorough research. The results are compared with those of trans -stilbene, a molecule structurally most closely related to the members of the p -phenylenevinylenes family.