Abstract
Electronic absorption spectra are reported for four ethynylsilylenes (A,,,, nm), MesSiC=CH (524), MesSiC=CSiMe3 (545), MesSiC=CPh (500), and CH3SiC=CSiMe3 (473), generated in 3-methylpentane matrices by photolysis of the corresponding trisilanes, RR'Si(SiMe3)2. Calculations of the 'A' - lA (n - 3p) transition energies for these and for some vinyl- and phenylsilylenes, by ab initio methods including the use of spin-projection methods, provided results in good agreement with experiment. Vinyl, ethynyl, and aryl groups all decrease the transition energy of silylenes, compared with MezSi: (Le., they cause a red shift). Also when H in HSiMe is replaced by vinyl or phenyl groups, a bathochromic (red) shift results, but ethynyl induces a small blue shift. The calculated stabilization energies of the two electronic states suggests that the bathochromic shift is due to an excited-state stabilization (resulting from interaction of the singly-occupied 3p(Si) orbital with the ?r* orbital on the substituent) which is larger than the stabilization of the corresponding ground state.
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