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‐ImEtPF6 and S‐TCBN‐ImEtPF6, 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 (∆EST) of 0.04 eV, as well as reversible redox properties. Furthermore, the enantiomers showed distinct mirror‐image CD and CPL activities with glum values of ‐3.7×10‐3 and +3.4×10‐3. 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 50 A m‐2, the LECs displayed an EQE of up to 5.2% and strong circularly polarized electroluminescence (CPEL) with gEL values of +3.3×10‐3 and ‐3.0×10‐3. This represents the first CP‐LEC based on TADF materials and offers a promising strategy for the development of high‐performance CPEL devices.