Dynamics of the Excited State of Polysilane Dendrimers: Origin of the Broad Visible Emission of Branched Silicon Chains

The excited-state dynamics of polysilane dendrimers are studied using time-resolved emission spectroscopy. The time-resolved emission spectra of polysilane dendrimers showed two bands, one in the UV and one in the visible region. The former was assigned to the emission from the excited state at the linear Si-Si chain, and the latter was assigned to that at the branching points. The intramolecular energy transfer between both excited states was demonstrated by the emission time profile, which showed a growth in intensity with increase in the delay time after laser excitation. The spectral shape of the visible emission can be expressed by a fitted curve using a Gaussian distribution function, which suggests that the configuration coordinates model is applicable to the photophysical processes of a Si-Si chain with a branching point. An MO calculation showed the distorted geometry around the branching point in the excited state, which corresponds to the localized excited state in the configuration coordinates model.