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 tBu 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)­Cl2 (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(π–π*) 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.