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To investigate the intramolecular charge-transfer (ICT) process of (p-cyanophenyl)pentamethyldisilane (CPDS), laser-induced fluorescence, dispersed fluorescence, and two-color resonance enhanced two-photon ionization spectra were measured in a jet-cooled isolated condition. Dual fluorescence of CPDS was observed from a ground vibrational level in the locally excited pipi state. Similar to an emission from the charge-transfer (CT) state in solution, one of the dual emissions of the isolated molecule in the jet was assigned as the CT emission. A significant vibrational dependence on the ICT process was found as exciting vibronic levels of the molecule. It was identified that the promoting mode of the ICT process is a torsional motion of the disilanyl group with respect to the phenyl ring. It was also revealed that an effective appearance energy of the CPDS cation via the CT state is much lower than that via the locally excited pipi state suggesting that the electronic configuration of the CT state is similar to that of the cation. On the basis of an electronic configuration of the cationic state, that of the CT state was suggested to be of the (sigma(Si)(-)(Si), 2ppi) type.

To investigate the microscopic solvation effect on the intramolecular charge-transfer (ICT) reaction of (pcyanophenyl)pentamethyldisilane (CPDS), laser-induced fluorescence and dispersed fluorescence (DF) spectra of clusters of CPDS solvated by H 2 O or acetonitrile (AN) were observed in supersonic jets. In both clusters, a dual emission originating from a locally excited (LE) ππ* and a charge-transfer (CT) state was observed. Two significant microscopic solvation effects were observed: an increase in the Stokes shift and an acceleration of the ICT process. The increases in the Stokes shift were found to be 1100 and 1700 cm -1 for CPDS-(H 2 O) 1 and -(AN) 1 , respectively. A trend of these clusters was related to the stabilization of the CT state by the dipole-dipole interaction with the solvent molecule. Concerning the rate of the ICT process, an unexpected result was found by lifetime measurements. The rate of the ICT process is found to be slower in the case of the CPDS-(AN) 1 cluster than that of the CPDS-(H 2 O) 1 cluster, while the stabilization of the CT state is larger in the former. It was considered that this behavior reflects a reduction of a Franck-Condon overlap between the LE and the CT states, which comes from changes in the relative orientations between the LE and the CT states in the cases of these clusters.

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