PHOTOOXIDATION OF FREELY SUSPENDED SUBMICRON FILMS OF POLY(3-NONYLTHIOPHENE)

A new technique for preparing freely suspended submicron films of poly (3-nonylthiophene) (PNT) has been developed. These films were characte rized by both i.r. and u.v. spectroscopy, allowing us to qualitatively analyse the effects of photo-oxidation and how these effects change w ith the period of time after the end of the irradiation treatment. Bef ore these spectroscopic measurements were made, PNT was compensated wi th hydrazine in order to remove any chemical impurities resulting from the polymerization catalyst. The i.r. experiments indicate that when PNT was irradiated by light of wavelength longer than 466 nm, electron s were transferred from the PNT to oxygen. Thus, the photo-oxidation p rocess resulted in the formation of positive polarons on the polymer c hains, plus superoxide anions. In the dark, electrons were transferred back to the polymer chains, which therefore returned to their neutral state. This mechanism was supported by e.s.r. experiments. Irradiatio n by light of wavelength shorter than 466 nm induced i.r. absorptions due to both polarons and sulfonyl groups, as well as conjugation-break ing reactions. When impurities were not removed, the formation of pola rons and sulfonyl groups was observed even if wavelengths shorter than 466 nm were excluded. These impurities also accelerated the conjugati on-breaking reactions.