Deep blue thermally activated delayed fluorescence emitters with 9,9′-spirobifluorene-fused xanthone acceptor for efficient OLEDs

Abstract

Efficient and stable blue luminescent materials are highly required for organic light-emitting diodes (OLEDs) but still challenging. Herein, we report two deep blue thermally activated delayed fluorescence (TADF) small molecules, mSBFXT-TC and mSBFXT-PC, consisting of 9,9′-spirobifluorene-fused xanthone acceptor and carbazole-based donors. mSBFXT-TC and mSBFXT-PC exhibit deep blue emissions peaking at 434 and 436 nm in toluene solutions, and at 456−471 nm in doped films with photoluminescence quantum yields of 87−98% and good horizontal dipole ratios of 77.5% for mSBFXT-TC and 84.0% for mSBFXT-PC. Consequently, their doped OLEDs show excellent electroluminescence (EL) performances, with EL peaks at around 452−481 nm and maximum external quantum efficiencies (EQEmaxs) of 21.8% and 26.0%. Based on their good EL properties, high-efficiency blue and green sensitized OLEDs are fabricated by using mSBFXT-TC and mSBFXT-PC as sensitizers and the narrow spectral multi-resonance materials as emitters, achieving high EQEmaxs of 26.0% and 32.4% with small full width at half maximum of 18 and 29 nm. These findings demonstrate that both deep blue TADF small molecules are promising emitters and sensitizers for fabricating efficient OLEDs.