Structural, spectroscopic and DFT theoretical studies of phosphorescent CuIP₂S-containing cuprous complexes

Luminescent cuprous complexes are important coordination compounds due to their relative abundance, low cost and ability to display excellent luminescence. The structures of two CuIP₂S-type cuprous complexes, namely, iodido(thiourea-κS)bis(triphenylphosphane-κP)copper(I), [CuI(CH₄N₂S)(C₁₈H₁₅P)₂] or [CuI(TU)(TPP)₂] (I), and (2,3-dihydrobenzimidazole-2-thione-κS)iodidobis(triphenylphosphane-κP)copper(I), [CuI(C₇H₆N₂S)(C₁₈H₁₅P)₂] or [CuI(DHBIT)(TPP)₂] (II), are described. In these two structures, the complex molecules of both are constructed by one copper(I) centre, one iodide ion, two TPP ligands and one thione ligand (TU for I and DHBIT for II). The copper(I) centres of I and II are both located in a distorted CuIP₂S tetrahedron and are coordinated by two P atoms from two TPP ligands, one S atom from the thione ligand and the I atom. The UV-Vis absorption and photoluminescence properties of these CuIP₂S-type cuprous complexes have been studied using crystalline powder samples. Detailed time-dependent density functional theory (TD-DFT) calculations and wavefunction analysis reveal that the pale-blue-green phosphorescence emission should originate from intra-ligand (TPP for I and DHBIT for II) charge transfer, with a small component of the metal-to-ligand charge transfer ³(IL+ML)CT excited state.