Thermally activated delayed fluorescence emitters with a LUMO-extended boron-containing acceptor for high-efficiency and long-lifetime blue OLEDs

Abstract

Organic light-emitting diodes (OLEDs) exhibiting thermally activated delayed fluorescence (TADF) demonstrate high quantum efficiencies. However, their drawbacks include a short device lifetime and low efficiencies in the high-luminance region. This study synthesizes a blue TADF emitter by modifying robust, stable 5,9-dioxa-13b-boranaphtho[3,2,1-de]anthracene (DOBNA). By introducing a benzonitrile group into DOBNA as an acceptor with extended π-conjugation and using a carbazole donor, a donor–acceptor–donor structure (DOB-1) is formed. To increase the lifetime and efficiency, carbazole derivative donors substituted with tert-butyl (DOB-2) or phenyl (DOB-3) are introduced at both the 3 and 6 positions to enhance the electron-donating characteristics, achieving a high photoluminescence quantum yield (PLQY), a superior horizontal transition dipole orientation (HTDO) ratio, and fast reverse intersystem crossing (RISC). As-synthesized DOB-2 and DOB-3 exhibit higher PLQYs (0.92 and 0.95) than DOB-1 (0.83), along with fast RISC (∼10⁵ s⁻¹) and better HTDO ratios (0.86 and 0.90) than DOB-1 (0.74). The TADF OLEDs employing DOB-2 and DOB-3 demonstrate 1.69 and 2.05 times higher external quantum efficiencies, respectively. Notably, the DOB-2 and DOB-3-based OLEDs exhibit operational lifetimes (LT₅₀ at 2000 cd m⁻²) of 706 and 1377 h, which are 2.52 and 4.54 times longer than that of DOB-1 emitters. Our results will advance research on efficient, long-lifetime TADF materials for OLEDs.