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, ASi 2 , ASi 2 A, and ASi 3 A 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 PSi 2 is about 12.8 KJ more energetic than that of ASi 2 (Figure ). More interestingly, the X-ray structural studies reveal that ASi 3 A exists in a butterfly-like structure in agree-ment with other spectroscopic analyses that the two anthryl groups do not interact in their excited states, while those in ASi 2 A 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 ASi 3 A has imparted rigidity to the tri-silyl linkage. Potential applications of anthrylsilanes in material sciences will be explored. 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 La transition, which has a much higher oscillator strength than the S1Lb-transition of pyrenes (Figure ). We define the interaction in anthracene as a σ,π*(S1,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.