Axially Chiral TADF Imidazolium Salts for Circularly Polarized Light-Emitting Electrochemical Cells

A pair of axially chiral thermally activated delayed fluorescent (TADF) enantiomers, R-TCBN-ImEtPF(6) and S-TCBN-ImEtPF(6), with intrinsic ionic characteristics were efficiently synthesized by introducing imidazolium hexafluorophosphate to chiral TADF unit. The TADF imidazolium salts exhibited a high photoluminescence quantum yield (PLQY) of up to 92%, a small singlet-triplet energy gap (triangle E-ST) of 0.04eV, as well as reversible redox properties. Furthermore, the enantiomers showed distinct mirror-image CD and CPL activities with g(lum) values of -3.7x10(-3) and +3.4x10(-3). Notably, by doping the axial TADF imidazolium salts into achiral TADF sensitizer, sandwich-structured light-emitting electrochemical cells (LECs) without the addition of ionic liquids (ILs) or ionic transition-metal compounds (iTMCs) were fabricated. When driven at 50A m(-2), the LECs displayed an EQE of up to 5.2% and strong circularly polarized electroluminescence (CPEL) with g(EL) values of +3.3x10(-3) and -3.0x10(-3). This represents the first CP-LEC based on TADF materials and offers a promising strategy for the development of high-performance CPEL devices.