Emissive Biphenyl Cyclometalated Gold(III) Diethyl Dithiocarbamate Complexes

We report here a series of emissive biphenyl cyclometalated gold(III) diethyl dithiocarbamate complexes having H, CF3, OMe, and Bu-t substitutions on the biphenyl moiety. Synthesis of these complexes was accomplished by a single-step reaction of the appropriate dilithio-biphenyl reagent with Au(dtc)Cl-2 (dtc = diethyl dithiocarbamate). All four complexes exhibit weak room-temperature phosphorescence in solution and much more intense phosphorescence in the solid state and in low temperature glasses with lifetimes in the microseconds. From experimental data and computational modeling, the emission originates mainly from a metal-perturbed (3)(pi-pi*) state of the biphenyl moiety with a minor contribution from ligand-to-ligand charge transfer. Weak solution emission is attributed to deactivation via a distorted charge-transfer state that is less accessible in the solid state or in a low-temperature glass.