The electron inductive effect of dual non-conjugated trifluoromethyl acceptors for highly efficient thermally activated delayed fluorescence OLEDs

Recently, pure organic twisted donor-acceptor (D-A) structured thermally activated delayed fluorescence (TADF) materials have been extensively demonstrated as a new generation emitter in organic light-emitting diodes (OLEDs) due to their low-cost and high-efficiency. Herein, we designed and synthesized a highly twisted TADF emitter 2,3,5,6-tetra(3,6-di-tert-butyl-9H-carbazol-9-yl)bis(trifluoromethyl)benzene (4tCzDCF(3)Ph) by a facile catalyst-free C-N coupling reaction. The two electron-withdrawing non-conjugated trifluoromethyl (CF3) moieties bearing strong electron inductive effects instead of other widely reported conjugation effects contributes for the necessary D-A interactions for TADF emission. 4tCzDCF(3)Ph exhibited an extremely small singlet-triplet energy gap (Delta E-ST) of 0.02 eV, fast k(RISC) rate of 7.02 x 10(5) s(-1) and modest photoluminescence quantum yield (PLOY) of similar to 70%. A low turn-on voltage of 2.6 V, along with maximum current efficiency of 50.6 cd A(-1), power efficiency of 40.7 lm W-1 and external quantum efficiency (EQE) of 16.2% could be facilely achieved for 4tCzDCF(3)Ph based green TADF OLEDs, which is significantly higher than <1% of 4CzCF(3)Ph and 9.5% of 5CzCF(3)Ph TADF emitters based on single trifluoromethyl acceptor.