Electric field effect on the charge migration of methylene-linked carbazole and terephthalic acid methyl ester in PMMA polymer films

Photoinduced inter- and intramolecular electron transfer reactions of methylene-linked (n) carbazole and terephthalic acid methyl ester (abbreviated as D-(n)-A, n=4 and 12) have been examined by using external electromodulated fluorescence spectroscopy and photocurrent measurement, which allow one to obtain information about the Stark shift and the efficiency of fluorescence quenching as well as photocarrier generation induced by an electric field. The action spectra of the photocurrent could be successfully measured at various concentrations in the absorption region of carbazole (240-365 nm). The obtained action spectra agree well with the simultaneously measured fluorescence excitation spectra, indicating that photocarrier generation occurs following the relaxations including internal conversion to Si and excitation energy migration among carbazole chromophores. Furthermore, the efficiency of photocarrier generation of D-(12)-A is higher than that of D-(4)-A, indicating that an intramolecular recombination process plays an important role in charge recombination of a photogenerated ion-pair state.