Reactions of copper(I) halides with 1,1,1‐tris(diphenylphosphanylmethyl)ethane (triphos) in 1:1 molar ratio afforded mononuclear complexes of the type [CuX(triphos)] which on further treatment with one equivalent of the potassium thiolate salt of a heterocyclic thione gave rise to the formation of mixed‐ligand complexes of the formula [Cu(κ3‐triphos)(κ1‐thiolate)]. The molecular structures of [Cu(κ3‐triphos)(κ1‐py2S)]·C2H5OH (1) and [Cu(κ3‐triphos)(κ1‐pymt)] (2) have been established by single‐crystal X‐ray diffraction. The complexes adopt a rigid distorted tetrahedral geometry with the phosphane ligand acting in a tridentate chelating mode. The complexes are strongly luminescent in solution and in the solid state. The spectroscopic and electronic properties of the new copper(I) complexes have been computed by electronic structure computational techniques (TD‐DFT calculations), that contribute to the assignments of electronic spectra. The high‐energy absorptions in the absorption spectra of complexes 1 and 2, ranging from 210 to 270 nm, are assigned to MLCT/LLCT transitions and the same also holds true for the low‐energy absorptions found in the range 280 to 300 nm. In the lowest triplet excited state, T1, involved in the emission in the 456–502 nm range, the spin density is delocalized over the entire nuclear framework.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)