Evidence for the Specific Species of Benzyltriethoxysilane Derivatives with a High-Coordination Silicon Atom

Evidence for the specific species of benzyltriethoxysilane derivatives with a high-coordination silicon atom is presented. Nanosecond laser flash photolyses of benzyltriethoxysilane and triethoxysilyldiphenylmethane have been studied in polar and nonpolar solvents. For the transient absorption spectra of benzyltriethoxysilane and triethoxysilyldiphenylmethane in methanol, a characteristic band attributed to the benzyl radical or diphenylmethyl radical was observed at around 317 and 330 nm, with a second-order decay rate constant of 5.7 × 109 and 4.2 × 109 M–1 s–1, respectively. While in cyclohexane, an absorption band attributable to the specific species with a high-coordination silicon atom was observed at around 330 nm with a first-order decay rate constant of 5.7 × 104 and 1.2 × 104 s–1 for benzyltriethoxysilane and triethoxysilyldiphenylmethane, respectively. A two-step laser-induced fluorescence study of triethoxysilyldiphenylmethane supports the assignment that the transient absorption bands observed at around 330 nm in methanol and in cyclohexane are ascribed to the diphenylmethyl radical and the specific species of triethoxysilyldiphenylmethane with a high-coordination silicon atom, respectively. The candidates for this specific species with a high-coordination silicon atom have been calculated by means of the TD-DFT method and SAC-CI method, and their molecular structures were discussed.