Structure and optical characteristics of poly(p-phenylenevinylene) prepared by vapor deposition polymerization

Abstract

Films based on poly(p-phenylenevinylene) are prepared by pyrolitic polymerization of α,α′-dichloro-p-xylene. During monomer precipitation, the temperature on a substrate is 25, 50, or −196°C. Subsequent annealing of the precursor at 250°C yields the final product: the copolymer of p-phenylenevinylene and p-xylylene with an approximate composition of 4: 1. The surface morphology, structure, and optical characteristics of the polymer are studied. The mean-square surface roughness of the precursor is 5 nm. Thermal treatment increase the samples’ roughness up to 10 nm. When the precursor is transformed into poly(p-phenylenevinylene), the roughness coefficient decreases from 0.85 ± 0.05 to 0.74 ± 0.05 owing to the formation of a rougher surface. Characterization of the optical characteristics of the synthesized poly(p-phenylenevinylene) shows that the maximum effective conjugation chain length achieves 12 units in the copolymer prepared when the temperature on the substrate is −196°C. As the temperature on the substrate increases, the conjugation length decreases to 8 units upon precipitation. Luminescence analysis reveals the effective excitation-energy transfer from short chain fragments of poly(p-phenylenevinylene) to long chain fragments. Electron parameters of the material are estimated: i.e., the band gap, the Huang-Rhys factor, the Stokes shift, and the oscillation energy of molecules.