Picosecond time-resolved infrared absorption studies on the photoexcited states of poly(p-phenylenevinylene)

Picosecond time-resolved infrared absorption spectra of the photoexcited states of poly(p-phenylenevinylene) [(-C6H4CH=CH-)(n), PPV] have been observed with tunable picosecond light pulses obtained by difference-frequency generation between signal and idler waves from an optical parametric generator and amplifier. The time-resolved photoinduced infrared absorption bands due to a vibrational transition observed at 1550 cm(-1) and an electronic transition at 3000 cm(-1) of the photoexcited PPV have fast (approximate to 1.7 ps) and slow (approximate to 50 ps) decay components. By comparison of the picosecond time-resolved infrared absorption spectra of short-lived (fast decay component) and long-lived (slow decay component) transient species with the photoinduced and doping-induced infrared difference spectra of PPV, the short-lived transient species is assigned to bound polaron pairs, and the long-lived transient species is assigned to positive and negative polarons.