Dynamically Switchable Room Temperature Phosphorescence in Two-Coordinate Carbene-Metal-Amide Complexes via Mediation by Charge-Transfer States

Due to a weak spin–orbit coupling (SOC) seen in the majority of organic room temperature phosphorescence (RTP) emitters, their light emission profile embodies a substantial contribution from fluorescence, thus obstructing the visual perception of the phosphorescence signal. Here, we present an approach that allows tuning characteristics of organometallic RTP materials from fluorescence-dominated to fully phosphorescent. The investigation of a series of two-coordinate Cu(I), Ag(I), or Au(I)-based complexes bearing an amide-type acridone ligand and several carbene-type ligands with varied electrophilic properties reveals that the intersystem crossing (ISC) rate to the phosphorescent locally excited acridone triplet state (3LE) can be significantly increased if intermediate carbene-to-amide interligand charge-transfer (CT) states are populated during the photoexcitation process. At the same time, the compounds retain long phosphorescence lifetimes in the range of 1.5–73 ms. A purely phosphorescent complex 2-Au-Acr with a high photoluminescence quantum yield of 0.75 was obtained. By exploiting its susceptibility to O2-induced phosphorescence quenching, a dynamically on-and-off switchable phosphorescent polymer-emitter composite system is demonstrated, where the light emission can be controlled solely by the change in the excitation light intensity. The unique properties of the demonstrated complex open unexplored application directions of RTP materials, such as their use in luminescent light intensity sensors.