Ultrapure Blue Thermally Activated Delayed Fluorescence (TADF) Emitters Based on Rigid Sulfur/Oxygen-Bridged Triarylboron Acceptor: MR TADF and D-A TADF.

Organic light-emitting diodes (OLEDs) still face a significant challenge in finding blue thermally activated delayed fluorescence (TADF) emitters that can achieve narrowband emission and high efficiency. In this work, we successfully design and synthesize a novel kind of TADF emitters based on rigid sulfur/oxygen-bridged triarylboron acceptor for ultrapure blue with narrowband electroluminescence. Time-dependent density functional theory (TD-DFT) calculations and photophysical results indicate the different intramolecular charge-transfer (ICT) character of two emitters. Benefiting from the rigid aromatic framework, both emitters exhibited deep-blue emission at 444 and 447 nm with a small full-width at half-maximum (fwhm) of about 33 nm, and a small singlet (S)-triplet (T) energy gap (Δ) of 0.23 and 0.36 eV. Consequently, OLEDs based on and exhibit deep blue electroluminescence at 456 nm with fwhm of about 55 nm, affording high external quantum efficiencies (EQEs) of 16.69% with CIE coordinates of (0.14, 0.15) and 16.65% with CIE coordinates of (0.14, 0.12), respectively. These findings show that and are superior emitters in ultrapure blue TADF devices.