The photochemical and photophysical properties of phenyl- and naphthyl-silanes have been studied quantitatively. It was found that the photochemical reaction of naphthyldisilanes originates from the intramolecular charge-transfer state ¹(2pπ, 3dπ) produced by 2pπ^*→ 3dπ charge transfer. The rearrangement (ϕ_r) and decrease (ϕ_R) quantum yields at 254 nm and the quantum yield (ϕ_ct) for the charge-transfer emission for disilanylnaphthalenes decreased markedly with solvent polarity because of fast intersystem crossing (through the charge-transfer state) in competition with the radiative and reaction rates. Activation parameters for the photochemical reaction have been obtained. It is demonstrated that the substitution of a disilanyl group into a phenyl or naphthyl species strongly affects not only the photochemical reaction but also the photophysical processes containing fast intersystem crossing.