Helically chiral multiresonant thermally activated delayed fluorescent emitters and their use in hyperfluorescent organic light-emitting diodes

Abstract

Chiral multiresonant thermally activated delayed fluorescence (MR-TADF) materials show great potential as emitters in circularly polarized (CP) organic light-emitting diodes (CP-OLEDs) owing to their bright and narrowband CP emission. Here, two new chiral MR-TADF emitters tBuPh-BN and DPA-tBuPh-BN possessing intrinsically helical chirality have been synthesized and studied. The large steric interactions between the tert-butylphenyl groups not only induce the helical chirality but also provide a notable configurational stability to the enantiomers. Racemic mixtures of tBuPh-BN and DPA-tBuPh-BN show narrowband emission at 490 and 477 nm with full-width at half maximum (FWHM) of 25 and 28 nm and photoluminescence quantum yields, Φ_PL, of 85 and 54% in toluene. The separated enantiomers of tBuPh-BN and DPA-tBuPh-BN show symmetric circularly polarized luminescence (CPL) with respective dissymmetry factors |g_PL| values of 1.5 × 10⁻³ and 0.9 × 10⁻³. The hyperfluorescence organic light-emitting diodes (HF-OLEDs) with tBuPh-BN and DPA-tBuPh-BN acting as terminal emitters and 2,3,4,5,6-penta-(9H-carbazol-9-yl)benzonitrile (5CzBN) as their assistant dopant exhibited, respectively, maximum external quantum efficiencies (EQE_max) of 20.9 and 15.9% at 492 and 480 nm with FWHM of 34 and 38 nm. This work demonstrates a strategy for developing intrinsically helically chiral MR-TADF emitters possessing significant configurational stability, which can be used in HF-OLEDs.