Molecular design for high exciton utilization based donor-π-acceptor type fluorescent emitter for OLEDs application

The “hot exciton” mechanism becomes an effective strategy to enhance singlet exciton utilization through reverse intersystem crossing (RISC) process from high-lying triplet to low-lying singlet excited states, resulting in high electroluminescent (EL) performance of organic light emitting diodes (OLEDs). Herein, six compounds (1–6) based on D-π-A molecular architecture using 5-butyl-5,10-dihydroindolo[3,2-b]indole (IDL) or 10H-benzo [4,5]thieno[3,2-b]indole (BTI) as electron donating units, and 1,3,5-triphenyl- triazine (TAZ) derivative as a core of electron acceptor were demonstrated as an emissive material for OLEDs application. All compounds showed good thermal stability and photophysical properties. Utilizing them as an emitter, doped OLED devices of IDL-TAZ series (1–3) displayed green emission, while BIT-TAZ series (4–6) illuminated sky-blue. Interestingly, all devices showed EQEs higher than that of theoretical EQEs. Moreover, their doped OLED devices exposed the exciton utilization efficiency (ηs) over the spin statistic limitation of traditional fluorescent OLEDs at 25%. Among them, the doped OLEDs device of compound 3 exhibited the most superior EL performance of emission peak at 540 nm, with the maximum luminance of 17960 cd m−2 and the maximum external quantum efficiency (EQE) of 7.50%. It indicated that the efficient RISC process via “hot exciton” channel can be achieved through the combination between an electron donating IDL or BTI with an electron acceptor TAZ.