Toward highly efficient TADF-active Cu(), Ag() and Au() carbene complexes using symmetry-based design strategy

Coinage metal( i ) complexes exhibiting thermally activated delayed fluorescence (TADF) have attracted worldwide attention as emitters for OLEDs. Reducing the emission lifetime and improving the quantum efficiency of such emitters is a current challenge in this hot field. To address this issue (challenge), a symmetry-based design strategy has been applied herein to obtain pseudo-symmetric complexes [M 2 (tdpb)(NHC) 2 ] 2+ (M = Cu, Ag, Au) scaffolded by 1,2,4,5-tetrakis(diphenylphosphino)benzene (tdpb) and N-heterocyclic carbene (NHC) ligands. In the solid state at ambient temperature, the synthesized compounds exhibit cyan to yellow TADF of the metal-to-ligand charge transfer type with excellent quantum yields (58-89%) and short decay times (2.5-15 μs). It is shown that the symmetry-based design strategy leads to a significant increase in the radiative rate constants for the "dimers" [M 2 (tdpb)(NHC) 2 ] 2+ compared to the "monomers" [M(dppb)(NHC)] + based on 1,2-bis(diphenylphosphino)benzene (dppb). The practical potential of the developed TADF emitters was also demonstrated through their application as innovative thermo- and vapor-chromic emission inks for advanced anti-counterfeiting labels. Tetraphosphine-carbene Cu( i ), Ag( i ) and Au( i ) complexes, synthesized via a symmetry-based design strategy, exhibit cyan to yellow TADF with excellent quantum yields (58-89%) and reduced lifetimes.