The Effect of Pre-solvation in the Ground State on Photoinduced Electron Transfer in Ionic Liquids
Photoinduced intramolecular charge transfer (CT) dynamics of the asymmetric and symmetric molecules, 4-(9-anthryl)-N,N-dimethylaniline (ADMA) and 9,9′-bianthryl (BA), was investigated by means of time-resolved fluorescence (TRF) spectroscopy and compared with the solvation dynamics of coumarin 153 (C153) in several ionic liquids (ILs). The normalized dynamic Stokes shift (DSS) function for the CT state emission of ADMA in the sub-ns to ns time scale is almost the same as those of BA and C153 in most of the ILs studied, in spite of the much larger Stokes shift of ADMA compared to those of BA and C153. On the other hand, the contribution from ultrafast DSS within 30 ps, which was undetectable with the time resolution in the present study, was estimated to be smaller for BA than that for ADMA. Meanwhile, in phosphonium IL, the DSS in sub-ns to ns time range was solute dependent. This peculiarity in phosphonium IL is discussed from the viewpoint of the hierarchy of the solvation dynamics.
KeywordsIonic liquids Solvation dynamics Photoinduced charge transfer Time-resolved fluorescence spectra
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