In order to determine an equilibrium structure of phenylpentamethyldisilane in the S₀ and S₁ states, high-resolution laser-induced fluorescence spectra were measured. An analysis of rotational envelopes of the 0⁰₀ and 6b¹₀ bands were carried out. As a result, the most stable form was found to be a configuration in which the disilanyl group lies in a plane perpendicular to the phenyl ring, and it was found that a conjugative interaction between the σ_Si-Si and π orbitals becomes strong in the S₁ state. A strong vibronic interaction, which gives a substantial transition intensity to the “forbidden” 6b¹₀ band, is discussed. The structure of the 6b¹ level in the S₁ state indicates that a σ_Si-Siπ^* type charge-transfer state exhibits an appreciable contribution to the vibronic interaction. In (p-cyanophenyl)ethynylpentamethyldisilane, it was also found that the similar strong vibronic interactions involved in their spectral feature.