Sulfonyl-locking and steric hindrance engineering achieve efficient blue multi-resonance TADF emitters

Abstract

Creating multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters that satisfy the National Television System Committee (NTSC) blue emission standard remains a critical challenge in organic light-emitting diodes (OLEDs). Herein, we propose a molecular design strategy combining sulfonyl-locking and steric hindrance engineering, and develop two efficient blue carbonyl/nitrogen (C=O/N) MR-TADF emitters, TP-SDO and 2TP-SDO, by incorporating a sulfonyl unit into a planar C=O/N fused core and introducing bulky tert-butylphenyl groups at the periphery. In doped films, these emitters show efficient blue emission with peaks at 463–468 nm, full width at half maxima (FWHMs) of 30–34 nm, and photoluminescence quantum yields of 61% and 80%. The corresponding OLEDs exhibit narrow electroluminescence with peaks at 463–468 nm and maximum external quantum efficiencies of 9.2–15.8% in a simple unsensitized device. Notably, the device based on 1 wt% doped 2TP-SDO achieves CIE coordinates of (0.145, 0.083), closely approaching the NTSC standard blue (0.14, 0.08), with a narrow FWHM of 25 nm. This work provides a rational design paradigm for high-performance C=O/N based blue MR-TADF emitters.