Mechanistic Studies of Photochemical Silylene Extrusion from 2,2-Diphenylhexamethyltrisilane

Photophysics and photochemistry of 2,2-diphenylhexamethyltrisilane ( 1 ) was investigated in detail. Diphenyltrisilane 1 showed an intense fluorescence band assignable to the intramolecular charge-transfer (ICT) band in a polar solvent. Whereas silylene extrusion and 1,3-silyl migration were the major photoreactions of 1 in a nonpolar solvent, solvolytic cleavage of the Si−Si bond occurred significantly in an ethanol−hexane mixture; the ICT state is responsible for the latter reaction. Solvent and temperature dependence of the product distribution has indicated that both the silylene extrusion and the 1,3-silyl migration take place from the nonpolar but electronically different excited states of 1 . On the basis of the photoreactions of 1 using a nonresonant two-photon (NRTP) excitation method, it is suggested that the silylene extrusion occurs via the 1 L a state of 1 as a silyl-substituted benzene.