Ultraviolet and visible spectroscopy of poly(paraphenylene vinylene)

Abstract

The UV–visible spectrum of 200 nm thick films of poly(p-phenylene vinylene) (PPV) shows three absorption bands, with maxima at 6.12, 5.06, and 3.09 eV. The first two absorption bands are related to localized molecular states while the band at 3.08 eV has a more complicated character with a 1.5 eV bandwidth, a 2.49 eV band edge and a maximum absorption coefficient of 1.5×105 cm−1. Semiempirical MO calculations at the INDO and PPP levels and VEH techniques have been applied in an interpretation of the electronic structure and excitations in this electrically conducting polymer. A description of the lower energy excited states of PPV has been achieved using an exciton model in which the polymer chain is treated as an ordered array of identical molecules. The 3.08 eV polymer absorption band is then attributed to an electron excitation spread over several monomer units strongly perturbed by electronic–vibrational coupling.