Photochemical and Photophysical Processes of Organosilicon Compounds

Abstract

Photochemical and photophysical processes of organosilicon compounds have been studied. Dual (local and CT) emission has been found in aromatic disilanes. The intramolecular CT fluorescence has a broad and structureless band with a large Stokes shift. The CT emission originates from the 1(2 pπ, 3 dπ) state having an in-plane long-axis polarization, which is produced by the 2 pπ* (aromatic ring) → vacant 3 deπ (Si-Si bond) intramolecular charge transfer. The CT state plays an important role in the photochemical and photophysical properties of phenyldisilanes. The intramolecular CT occurs very rapidly (< 10 ps) both in nonpolar media at 293 K and in a polar rigid matrix at 77 K. At room temperature a longlived 425 nm transient (silene) is produced with a time constant of 30 ps from the CT state. The photolysis of cyclotetrasilanes is remarkably dependent on their molecular structures: two molecules of the corresponding disilene are produced from the Si state of planar cyclotetrasilanes, while silylene is generated by ring contraction in the S, state of bent cyclotetrasilanes. Remarkably large Stokes shifts are observed in these cyclotetrasilanes. Dimethylsilylene with a transient peak at 470 nm is observed by laser photolysis of cyclohexasilane. The dynamic behaviors of the intermediates have been studied by nanosecond laser photolysis. The phenylsilyl radical is generated by photolysis of phenylsilanes in rigid glass at 77 K, which gives a structured emission similar to that of benzyl radical.