Photochemistry of dianthrylsilanes: A study of σ,π*-interaction

In this article, we demonstrated by the application of time-resolved spectroscopy, X-ray structural analysis and other spectroscopic techniques that 9-Anthrylsilanes exhibits σ,π*-interaction between 9-anthryl group and the Si-Si linkage in anthryl-disilanes, ASi₂, ASi₂A, and ASi₃A which does not occur in the analogous alkyl derivatives as well as the pyrenylsilane derivatives, in spite of the fact that the 0,0-band of PSi₂ is about 12.8 KJ more energetic than that of ASi₂ (Figure 1). More interestingly, the X-ray structural studies reveal that ASi₃A exists in a butterfly-like structure in agreement with other spectroscopic analyses that the two anthryl groups do not interact in their excited states, while those in ASi₂A do. This is in contrast to the analogous pyrenylsilanes; the trisilanes exhibits a stronger excimer interaction than that of disilane.^10b Our results show that the σ,π*-interactions in ASi₃A has imparted rigidity to the tri-silyl linkage. Potential applications of anthrylsilanes in material sciences will be explored.⁵ This work provides evidence that σ,π*-interaction between the 9-anthryl group and disilyl linkage does play an important role in the properties of disilanes. We attribute this enhanced σ,π*-interaction to the nature of the lowest excited state (S₁ state) of anthracenes, the L_a transition, which has a much higher oscillator strength than the S₁L_b-transition of pyrenes (Figure 1). We define the interaction in anthracene as a σ,π*(S_1.La) interaction. This interaction lends a substantial barrier to the Si-Si bond with the excited anthryl nucleus in anthrylsilanes. The scope and potential applications of this phenomenon are discussed.