Electronic absorption spectra are reported for four ethynylsilylenes (X(max), nm), MesSiC drop CH (524), MesSiC drop CSiMe(3) (545), MesSiC drop CPh (500), and CH3SiC drop CSiMe(3) (473), generated in 3-methylpentane matrices by photolysis of the corresponding trisilanes, RR’Si(SiMe(3))(2). Calculations of the (1)A’ --> (1)A" (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 Me(2)Si : (i.e., 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 pi* orbital on the substituent) which is larger than the stabilization of the corresponding ground state.