TADF active carbene-metal-amide complexes exhibiting through-space charge transfer: an impact of metal atom

The impact of metal atom on the photophysical properties of luminescent organometallic carbene-metal-amide complexes exhibiting through-space charge transfer is investigated. The substitution of copper atom with gold alters the excited state energy level configuration of the emitter. While in the copper-based emitters the lowest triplet excited state (T-1) is related to a through-space charge transfer between the carbazolide donor and carbene-bound phenylsulphonyl acceptor, in the gold-bearing structural analogue T-1 level is accompanied by an additional closely situated triplet state T-2, which features a charge transfer between the carbazolide donor and imidazolidine carbene acceptor. Because of a significant spin-orbit coupling provided by Au atom T-2 state exhibits relatively fast phosphorescence rate of 8x10(4) s(-1). Consequently, the emissive process for the gold-functionalized compound can be characterized with a co-occurring thermally activated delayed fluorescence (TADF) and phosphorescence, in contrast to the copper-based structural analogues, where only TADF is observed.