Stable optical emission from annealed poly (p-phenylene vinylene) derivative films containing oxadiazole

The structure and optical properties of poly {[2-methoxy-5-(2- ethylhexyloxy)-p-phenylene vinylene]-alt-[2,5-diphenylene-1,3,4-oxadiazole vinylene]} (MEH-OPPV) are studied by examining and analyzing the photoluminescence, absorption, and Fourier transform infrared spectra of the MEH-OPPV films annealed at different temperatures. It is revealed that MEH-OPPV is of high thermal stability due to aryl-substituted oxadiazole groups introduced in the polymer backbone, which increases the conformational disorder to result in short conjugation lengths in MEH-OPPV. Because the interchain distance and the conjugation length are restricted by the large dihedral angle between the adjacent monomer units, the relaxation of the polymer chains cannot change the electron structures during thermal annealing. As a result, the optical properties of MEH-OPPV in the film are nearly unaffected by thermal annealing.