The geometrical structures of binuclear Au(I) complexes, trans-[Au-2(PH2CH2SR)(2)](2+) (R = H (1), Me (2), Cy (3) and Ph (4)), and their solvated species (1-4) (.) (MeCN)(2) in the ground and excited states were optimized by the MP2 and CIS methods, respectively. It is shown that the effect of thio substituents in the Au(I) complexes raises the emission energy (< 0.29 eV) in going from 1 to 2-4, but does not change the intrinsic sigma(s,p(z)) -> sigma* (d(y)(2)-(2)(z), d(x)(2)) transition. For structural and spectroscopic properties of binuclear Au(I) complexes, the SH provides a satisfactory model for the SR (R = Me, Cy and Ph). (c) 2006 Elsevier B.V. All rights reserved.