The structures of ground state and lowest energy triplet excited state for [Au-2(PH2CH2PH2)(2)](2+) (1), [Au-2(PH2CH2PH2)(SHCH2SH)](2+) (2) and [Au-2(SHCH2SH)(2)](2+) (3) as well as their solvated 1-3.(MeCN)(2) species are fully optimized by the MP2 and CIS methods, respectively. The (3)[sigma* (d)sigma(s)] excited states give the 300-390 emissions in the gas phase, red shifting to 500-730 nm in acetonitrile. The coordination of solvent molecule to the gold atom in the excited states is responsible for such a red shift. For 2, all the possible geometries, the substituent effect of rnethyl groups on P and/or S atoms and the comparison with thiolate complex [Au-2(PH2CH2PH2)(SCH2S)] (6) are discussed. The unrestricted MP2 calculations on 1- 3, head-to-tail [Au-2(PH2CH2SH)(2)](2+) (7) and head-to-head [Au-2(PH2CH2SH)(2)](2+) (8) confirm the CIS results in both optimized geometry and emissive energy related to the (3)[sigma*(d)sigma(s)] state. The frequency calculations at the MP2 level indicate that the Au(I)-Au(I) interaction is weak in the ground state (v(Au-2) = 89-101 cm(-1)) but is strongly strengthened in the excited state (v(Au-2) = 144-189 cm(-1)).