An Air- and Moisture-stable Zinc(II) Carbene Dithiolate Dimer Showing Fast TADF and Dexter Energy Transfer Catalysis

A dimeric ZnII carbene complex featuring bridging and chelating benzene-1,2-dithiolate ligands is highly stable towards air and water. The donor-Zn-acceptor structure leads to visible light emission in the solid state, solution and polymer matrices with max between 577-657 nm and, for zinc(II) complexes, unusually high radiative rate constants for triplet exciton decay of up to kr = 1.5105 s-1 at room temperature. Variable temperature and DFT/MRCI studies show that a small energy gap between the 1/3LL/LMCT states of only 79 meV is responsible for efficient TADF. Time-resolved luminescence and transient absorption studies confirm the occurrence of long-lived, dominantly ligand-to-ligand charge transfer excited states in solution, allowing for application in Dexter energy transfer photocatalysis.