Dynamic Stokes Shift of 9,9 '-Bianthryl in Ionic Liquids: A Temperature Dependence Study

作者：Nagasawa Yutaka^*; Oishi Akito; Itoh Tsuyoshi; Yasuda Masakazu; Muramatsu Masayasu; Ishibashi Yukihide; Ito Syoji; Miyasaka Hiroshi

来源：Journal of Physical Chemistry C, 2009, 113(27): 11868-11876.

DOI：10.1021/jp9020454

The temperature dependence of the fluorescence behaviors of 9,9'-bianthryl (BA) in the charge-transferred (CT) state in imidazolium ionic liquids (IL) was investigated by means of steady-state as well as time-resolved detections. At ambient and higher temperatures, the emission peak of BA in ILs shifted to longer wavelengths with decreasing temperature, which is a phenomenon commonly observed in normal polar solvents. On the other hand, the emission peak shifted toward shorter wavelengths with decreasing temperature below ca. 290 K. Time-resolved fluorescence (TRF) spectroscopy was carried out to investigate the dynamic Stokes shift, i.e., the time-dependent red-shift of the fluorescence peak. In highly viscous ILs, the time constant of the dynamic Stokes shift becomes comparable or longer than the lifetime of the CT state. In such a case, the ground state of BA is recovered before the completion of the solvation process. It is concluded that the origin of the blue-shifted emission at lower temperatures is due to the fluorescence from the unrelaxed CT state. It is confirmed that the charge separation process of BA in ILs occurs prior to the nanosecond fluorescence red-shift due to the slow solvation process in the CT state in the temperature range we have studied.

• 出版日期2009-7-9