Picosecond electron transfer dynamics in polymer systems in solutions: cellulose tris (9-ethylcarbazolyl-3-carbamate) and amylose tris (9-ethylcarbazolyl-3-carbamate)

摘要

Photoinduced electron transfer (ET) dynamics, such as charge separation (CS), charge recombination (CR), and hole transfer (HT) processes in cellulose tris (9-ethylcarbazolyl-3-carbamate) (CTCz) and amylose tris (9-ethylcarbazolyl-3-carbamate) (ATCz) with a guest electron acceptor in solutions were investigated by means of picosecond transient absorption spectroscopy. Each glucoside unit of these polymer chains has three carbazolyl (Cz) units in such a configuration that two of them are in a close proximity and the other stays apart. Hole transfer dynamics in these systems in the early stage following the excitation were analyzed on the basis of one-dimensional random walk model where cationic state migrates along the polymer chain. On the other hand, the deviation of the experimental results from the calculated curve based on the above model was observed in nanosecond time region. By integrating the kinetic profiles with the temporal evolution of the absorption spectra of the charge-separated state, the trapping process of the cation at the dimer site was found to be responsible for this deviation. By comparing the present results with those in the monomer and dimer model systems as well as in other Cz containing polymer systems, the role of dimer cation in the HT process was discussed.