D–A–D Thermally Activated Delayed Fluorescence Emitters with Isomerized Bithiophene/Bithiazole Imide Acceptors for Efficient Organic Light-Emitting Diodes

Aromatic imides have garnered considerable attention as electron-accepting units for designing thermally activated delayed fluorescence (TADF) emitters due to their strong electron-withdrawing capacity and high photoluminescence quantum yields. However, heptagonal aromatic imides remain largely unexplored as acceptors in constructing donor–acceptor (D–A)-type TADF emitters. Herein, we report a series of D–A–D-type molecules (iBTI-TPA, iBTI-TPE, iBTI-POZ, iBTzI-TPA, iBTzI-TPE, and iBTzI-POZ) based on isomerized bithiophene/bithiazole imide (iBTI/iBTzI) acceptors coupled with triphenylamine (TPA), tetraphenylethylene (TPE), or phenoxazine (POZ) donors. Among them, the POZ-substituted derivatives iBTI-POZ and iBTzI-POZ exhibit pronounced TADF characteristics, with photoluminescence quantum yields (ΦPLs) of 72 and 61%, respectively, at 10 wt % doping in a 3,5DCzPPy host. Corresponding vacuum-deposited doped organic light-emitting diodes display greenish-yellow emission with maximum external quantum efficiency (EQEmax) values of 13.6 and 10.1%.