Ultrafast Colour Changes in Organic Thin Films Based on Photoinduced Electron Transfer Reactions

Abstract

Colour changes due to photoinduced electron transfer reaction were studied by picosecond pulsed laser in thin polymer films containing 4,4′-bipyridinium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate salts as part of the main chain at 98–300 °K. The transient absorption at about 600 nm appeared in less than 20 ps upon excitation of ion-pair charge-transfer absorption, which was controlled by the laser pulse width. The decay curve was analyzed by a fast component with a fraction of about 0.2–0.3 and lifetime of a few hundreds ps together with an extremely slow one corresponding to steady and reversible colour changes. The lifetime of the former slightly increased with decreasing temperatures. A reaction mechanism is proposed based on these results.