High efficiency green TADF emitters of acridine donor and triazine acceptor D–A–D structures

Abstract

Two thermally activated delayed fluorescence (TADF) emitters with high synthetic yields were designed and synthesized. Both emitters, 10,10′-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(9,9-dimethyl-9,10-dihydroacridine) (TRZ-DDMAc) and 10,10′-(5-(4,6-diphenyl-1,3,5-triazin-2-yl)-1,3-phenylene)bis(9,9-diphenyl-9,10-dihydroacridine) (TRZ-DDPAc), showed excellent photophysical properties. Interestingly, both of the materials had a small energy difference between singlet and triplet levels, which confirmed that donor–acceptor based molecular design brought effective reverse intersystem crossing (RISC) to enable the TADF mechanism. The TADF characteristic was confirmed by a delay time of 10.32 and 10.37 μs for TRZ-DDMAc and TRZ-DDPAc, respectively. TRZ-DDPAc revealed a photoluminescence quantum yield of 79.7% in a doped film state. Moreover, several green OLED devices were fabricated by using different host materials along with various doping concentrations to ensure the optimal performance of each TADF material. The device with TRZ-DDPAc as an emitter (30%: DBFPO) exhibited excellent current and maximum external quantum efficiencies of 62.8 cd A⁻¹ and 27.3%, respectively. Green colour emission was observed from all devices, which originated through the TADF mechanism.