Spirofluorene‐Based Multi‐Resonance Thermally Activated Delayed Fluorescence Materials for Quenching‐Resistant Organic Light‐Emitting Diodes

Abstract

Multiple‐resonance thermally activated delayed fluorescence (MR‐TADF) materials offer advantages for organic light‐emitting diodes (OLEDs) but face notable aggregation‐caused quenching (ACQ) at high doping concentrations, subsequently causing spectral broadening and efficiency declining. In this study, two emitters, CzSO‐DtCzB and CzSO‐BNO, are developed by incorporating a bulky spirofluorene‐based moiety, spiro[indolo[3,2,1‐ de ]acridine‐8,9′‐thioxanthene]10′,10′‐dioxide (CzSO), at the periphery of the classic MR‐TADF cores. Pronounced steric hindrance generated through the specific connection between the MR‐TADF core and the spirofluorene unit effectively suppresses the ACQ effect. Furthermore, the sulfone group on the spirofluorene moiety influences the emission color, inducing a distinct bathochromic shift in both emitters compared to their parent MR‐TADF cores. OLEDs employing CzSO‐DtCzB and CzSO‐BNO at a 5 wt% doping concentration exhibit emission peaks at 504 and 473 nm, with maximum external quantum efficiencies (EQE max ) of 28.2% and 23.5%, respectively. Notably, stable EL spectra are maintained across a doping range from 5 to 30 wt%, with no significant spectral redshift or broadening observed. Besides, OLED based on CzSO‐BNO maintains an EQE max of 17.8% at the doped concentration of 30 wt%. These results demonstrate that the proposed molecular design strategy effectively enables MR‐TADF materials to suppress the ACQ effect and achieve quenching‐resistant device performance.