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Fluorescence of ethylcarbazole doped in PMMA polymer films is quenched by an external electric field in the presence of dimethyl terephthalate, indicating that the rate of the intermolecular electron transfer from a photoexcited molecule of ethyl carbazole to dimethyl terephthalate is enhanced by an applied electric field. The field effect on the electron transfer as well as the transfer rate at zero field increases with a decrease of the electron donor-acceptor distance. The free energy change of the electron transfer reaction from photoexcited ethylcarbazole to dimethyl terephthalate is estimated to be about -0.7 eV in PMMA polymer films, based on the external electric field effect on fluorescence intensity of ethylcarbazole combined with the fluorescence lifetime. The molecular polarizability of fluorescent exciplex formed in a mixture of ethylcarbazole and dimethyl terephthalate is also estimated, based on the Stark shift of the exciplex fluorescence.

Exciplex fluorescence in a mixture of N-ethylcarbazole (ECZ) and dimethyl terephthalate (DMTP) doped in a PMMA polymer film, which appears as a result of photoinduced electron transfer from ECZ to DMTP, is quenched by an electric field as the concentration of the electron donor, i.e., ECZ, is increased. Even when the DMTP concentration is increased, the exciplex fluorescence is not quenched by an external electric field as long as the ECZ concentration is low. These concentration dependences indicate that a hole transport occurs very efficiently and that an electron transport does not occur in this photoinduced electron-transfer system. In fact, a photocurrent could be detected in a mixture of ECZ and DMTP in PMMA films only when the concentration of ECZ was high.

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