Solvatochromic and emissive properties of pt(II) complexes with 1,1- and 1,2-ditholates

Abstract

A series ofPt(L-L)(S-S) complexes is studied where (N-N) is an α,α'-diimine, a diamine or a chelating phosphine ligand and (S-S) is either a dithiolate chelate or bis(thiolate) ligands. All of the diimine complexes show an intense solvatochromic band in the 400–500 nm region of the spectrum which shifts to higher energy with increasing solvent polarity whereas the absorption of the diamine and phosphine complexes is insensitive to solvent. The emission behavior of these complexes at low temperature depends on the (S-S) ligand. When (S-S) is maleonitriledithiolate (mnt), the emission in rigid glass is structured and shows single exponential behavior with both emission lifetime and intensity increasing with decreasing temperature. For the other Pt(diimine)(S-S) studied, the temperature dependence of the emission lifetime and quantum yield provide evidence of multiple emitting states. Complexes which contain a saturated diamine, diphosphine or bis(phosphine) ligands and show no solvatochromism, exhibit emission consistent with a single emitting state. Based on the spectroscopic data, the lowest energy absorption in the diimine complexes is assigned as a metal-dithiolate to diimine charge transfer transition. In diamine and phosphine complexes the absorption is assigned as a metal-to-dithiolate MLCT transition. For all the diimine complexes except those of mnt, the emission is assigned as 3(Pt(d)/S(p) - π diimine *) while for the mnt complexes, the emission corresponds to 3(Pt(d)/S(p) - π mnt *). Comparison of the spectroscopic results with extended Hückel molecular orbital calculations support these assignments.