Direct detection of electron transfer processes in photoconductive poly(N-vinylcarbazole) solid film doped with electron acceptors: Temperature dependence of femtosecond to microsecond dynamics

Primary processes of photoinduced electron transfer dynamics in a poly(N-vinylcarbazole) solid film doped with electron acceptors were investigated by means of transient absorption spectroscopy in femtosecond to microsecond time region as well as dichroism measurements. Picosecond transient dichroism measurement revealed that the rate constant of the hole shift reaction was independent of the temperature in the range between 10 and 295 K. The femtosecond transient absorption spectroscopy in the NIR wavelength region showed that the delocalization of the cationic states in sub-ps to several ps time region occurred immediately after the charge separation even at 10 K. These results indicated that the rapid delocalization of the cationic states, probably due to the small fluctuation, took an important role in the large rate constant of the hole shift reaction in PVCz solid film. In μs time region, weak temperature dependence was observed for the dynamic behaviors. This temperature dependence was attributed to the trapping/detrapping and the charge recombination processes, which were temperature dependent. The analysis including these rate constants and the temperature independent hole shift reaction rate constant could reproduce the experimental results in the temperature range of 10–295 K, of which results also supported the temperature independence of the hole shift reaction in PVCz solid film.