Photochemistry of Cyclopolysilanes and their Reaction Intermediates

通过293 K下甲基环己烷（MCH）中的激光闪光光解和77 K下甲基环己烷-异戊烷（MP; 3：1，v/v）玻璃中的稳态光解，进行了环聚硅烷的光解。光解模式是显着依赖于环四硅烷的分子结构。平面全硅基环四硅烷生成相应的二硅烷，其吸收峰分别位于293 K的410 nm和77 K的415 nm处。对于具有弯曲结构的全烷基环四硅烷，在293 K下发生光解，得到相应的硅烯和环三硅烷，而在MP玻璃中在77 K下不发生光解。对于环己基硅烷，即使在MP玻璃中，在77 K下也发生光解产生二甲基硅烯。这些光解起源于激发单重态（S_1），从脉冲后的瞬态吸收的快速建立判断。二异丙基甲硅烷基，叔丁基甲基甲硅烷基和二甲基甲硅烷基的瞬态峰在530，515，和470 nm处观察到的MCH在293 K的寿命分别为38，50，和380 ns。在77 K下，在刚性玻璃中观察到具有极大斯托克斯位移（高达13700 cm-3）的环四硅烷的荧光<-1>。从分子结构的角度讨论了环聚硅烷的光化学和物理性质。

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.