Photochemistry of Cyclopolysilanes and their Reaction Intermediates

采用激光在甲基环己烷（MCH）中293K的光解和在甲基环己烷-异戊烷（MP; 3:1, v/v）玻璃中77K的稳态光解对环聚硅烷进行了光解。光解模式明显依赖于环四硅烷的分子结构。在293K和77K的吸收峰分别为410 nm和415 nm。对于具有弯曲结构的过烷基环四硅烷，在293K下发生光解反应，得到相应的硅烯和环三硅烷，而在77K的MP玻璃中不发生光解反应。对于环己硅烷，即使在77K的MP玻璃中，也会发生光解反应生成二甲基硅烯。从脉冲后瞬态吸收的快速积累判断，这些光解作用源于激发单重态（S_1）。二异丙基硅烯、丁基甲基硅烯和二甲基硅烯分别在530、515和470 nm处观察到瞬态峰，在293K的MCH中寿命分别为38、50和380 ns。在77K的刚性玻璃中观察到环四硅烷的荧光具有极大的斯托克斯位移（高达13700 cm^<-1>）。从分子结构的角度讨论了环聚硅烷的光化学和光物理性质。

Photolysis of cyclopolysilanes has been carried out by laser flash photolysis in methylcyclohexane (MCH) at 293K and steady-state photolysis in methylcyclohexane-isopentane (MP; 3:1, v/v) glass at 77K. The photolysis patterns are remarkably dependent on the molecular structures of cyclotetrasilanes. The planar persilylcyclotetrasilanes give rise to the corresponding disilanes with absorption peaks at 410 nm at 293K and at 415 nm at 77K. For the peralkylcyclotetrasilanes having bent structures, photolysis occurs to give the corresponding silylene and cyclotrisilane at 293K, but not in MP glass at 77K. For cyclohexasilane, photolysis occurs to give dimethylsilylene even in MP glass at 77K. These photolyses originate from the excited singlet state (S_1), judging from a rapid build-up of the transient absorption after pulsing. Transient peaks for diisopropylsilylene, t-butylmethylsilylene and dimethylsilylene are observed at 530, 515, and 470 nm with lifetimes of 38, 50, and 380 ns in MCH at 293K, respectively. The fluorescence of cyclotetrasilanes with an extremely large Stokes shift (up to 13700 cm^<-1>) has been observed in rigid glass at 77K. The photochemical and photophysical properties of cyclopolysilanes have been discussed from the viewpoints of their molecular structures.