Photoemission study of the thermal and photochemical decomposition of a urethane-substituted polythiophene

Abstract

X-ray and ultraviolet photoelectron spectroscopies have been used to study the thermal and photochemical decomposition of films of poly[2-(3-thienyl)ethanol n-butoxycarbonylmethylurethane], a polythiophene with a hydrogen-bond forming urethane side-chain. The films were heated in vacuum and in a partial pressure of oxygen. In both cases, decomposition of the side-chain, as evidenced by a loss of N 1s intensity, is observed to occur in the range 200–300 °C, consistent with thermogravimetric analyses. A modest irreversible thermochromism is also observed for spin-coated films, with the maximum optical absorption shifting from 444 to 412 nm upon heating from room temperature to 460 °C. Films heated to 480 °C show core level signals consistent with complete side-chain decomposition to volatile species, leaving the thiophene backbone on the surface. He I and X-ray valence spectroscopic measurements indicate that the presence of the urethane side-chains broadens the π-conjugation features to such an extent that they cannot be resolved until the side-chains decompose. Photochemical stability studies of the polymer films exposed in air to 585, 532 and 397 nm light demonstrate that only the latter induces decomposition, as detected by the emergence of an additional S 2p peak.