Solvent effect of the hole migration along a poly(N-vinylcarbazole) chain as revealed by picosecond transient absorption and dichroism measurements

Photoinduced electron-transfer dynamics (charge separation, charge recombination, and hole transfer reactions) in poly (N-vinylcarbazole) (PVCz) and solvent effects on the reaction profiles were studied by means of picosecond transient absorption spectroscopy and transient dichroism measurements, Electron-transfer dynamics in PVCz in rather polar solutions was well-described by the simple scheme that the cation state of the carbazolyl (Cz(+)) moiety continuously migrates along pendant Cz moieties in the polymer chain with the charge recombination at the initial position of the charge separation. The rate constant of the hole transfer (HT) from the Cz(+) to neighboring ones was (230 ps)(-1) in pyridine. With a decrease in the solvent polarity, the HT rate constant drastically decreased, and it was less than or equal to10(7) s(-1) in chloroform solution. This solvent polarity effect was accounted for not only by the increase in the attractive Coulombic interaction with decreasing solvent polarity but also by the delocalization of the cationic state over Cz units. By integrating the present results with those in other aromatic vinyl polymers, the factors regulating the hole-transfer process in aromatic vinyl polymers were discussed.