Emission spectra of σ-π-conjugated organosilicon copolymers consisting of alternating dimethylsilylene and aromatic units

Emission measurements were performed on a series of σ-π-conjugated organosilicon copolymers, -[(SiMe₂)_mA]_n - (m = 1, 2, 3, 4, and 6), with alternating dimethylsilylene and π-conjugated units (A = phenylene, diphenylene, and anthranylene) in various solvents. The copolymers with m ≥ 2 exhibit a broad emission ascribable to an intramolecular charge transfer (CT) excited state resulting from the charge transfer between the dimethylsilylene and aromatic units. The solvatochromism of the emission spectra was observed for the organosilicon copolymers, where the emission maximum shifted to longer wavelength in polar solvents. The influence of the dimethylsilylene chain-length and the π-conjugated unit on the CT emission was investigated. The molecular orbital calculations on a model compound suggest that the vibronically structured emission is attributed to the π-character of the aromatic unit, and the structureless broad emission is ascribed to the σ-character of the Si-Si bond in the excited states. The emission lifetime and the quantum yield also show the dimethylsilylene chain-length dependence.