Chemical Changes and Photoluminescence Properties of UV Modified Polypyrrole

Abstract

Effects of ultraviolet light (325 nm) irradiation on polypyrrole (PPy) properties were studied by time- resolved, standard photoluminescence (PL), optical absorption, and X-ray photoelectron (XPS) spectroscopies. PPy samples were prepared in thin films on gold, quartz, and H-terminated monocrystalline diamond (MCD) substrates by electrochemical and chemical oxidation. After the UV irradiation, all PPy samples converged to the same PL spectrum independent of initial preparation methods or substrates. We observed formation of a new, highly intensive PL band at 540 nm accompanied with few per cent increase in transmittance and structural and chemical changes of the PPy chains. The changes occurred only when the light intensity was from 0.1 to 10 W/cm2. The effect was reduced in vacuum. Thermal annealing had no influence. We explain the effect by chemical and structural modifications of PPy that lead to a permanent increase in quantum yield of intrachain exciton recombination.