Photo-induced oxidation of polythiophene derivatives: Dependence on side chain structure

The photooxidation of poly(3-hexylthiophene) (P3HT) has previously been investigated and it is known that the sulfur atom of the thiophene ring is oxidized into sulfur oxides by a hydroxyl radical that arises through hydrogen abstraction at the hexyl side chain at the α-position. In this study, in order to further investigate the photooxidation mechanism of the polymer, the side chain at α-position was varied and three different polythiophene derivatives with phenyl (P3PhT), tert-pentyl (P3DMPT), and alkoxy (P3OOT) groups were synthesized with no α-hydrogens. We observed the differences in the photochemical behavior of the polythiophene derivatives by UV-vis-NIR and FT-IR (ATR) spectroscopy during simulated solar light irradiation. It was found that the photooxidation of P3PhT and P3DMPT progressed in the same way as P3HT, whereas the analogous decomposition of P3OOT was not observed.