Judicious Heteroatom Doping Produces High‐Performance Deep‐Blue/Near‐UV Multiresonant Thermally Activated Delayed Fluorescence OLEDs

Abstract

Two multiresonant thermally activated delayed fluorescence (MR-TADF) emitters are presented and it is shown how further borylation of a deep-blue MR-TADF emitter, DIDOBNA-N, both blueshifts and narrows the emission producing a new near-UV MR-TADF emitter, MesB-DIDOBNA-N, are shown. DIDOBNA-N emits bright blue light (Φ_PL = 444 nm, FWHM = 64 nm, Φ_PL = 81%, τ_d = 23 ms, 1.5 wt% in TSPO1). The deep-blue organic light-emitting diode (OLED) based on this twisted MR-TADF compound shows a very high maximum external quantum efficiency (EQE_max ) of 15.3% for a device with CIE_y of 0.073. The fused planar MR-TADF emitter, MesB-DIDOBNA-N shows efficient and narrowband near-UV emission (λ_PL = 402 nm, FWHM = 19 nm, Φ_PL = 74.7%, τ_d = 133 ms, 1.5 wt% in TSPO1). The best OLED with MesB-DIDOBNA-N, doped in a co-host, shows the highest efficiency reported for a near-UV OLED at 16.2%. With a CIE_y coordinate of 0.049, this device also shows the bluest EL reported for a MR-TADF OLED to date.