Competitive Spatial Donor/Acceptor Interaction toward Efficient Blue Thermally Activated Delayed Fluorescence

Abstract

Through-space charge-transfer (TSCT) thermally activated delayed fluorescence (TADF) emitters show great promise for blue organic light-emitting diodes (OLEDs) but face challenges such as low efficiency and limited color purity. In this study, we designed and synthesized three asymmetric TSCT-TADF materials─CzTPT-PA, CzTPT-CIA, and CzTPT-IA─based on a dual donor/acceptor (D₁/A/D₂) architecture. The molecular design strategically leverages dominant donor–acceptor interactions and auxiliary coupling effects within a unique sandwich-like π-stacked structure, enabling precise control over excited-state properties. This design achieves blue-shifted emission while maintaining high photoluminescence quantum yields, addressing efficiency loss and concentration quenching through spatially confined interactions and locked molecular conformations. The resulting OLEDs exhibited blue electroluminescence with color coordinates of (0.16, 0.27), (0.15, 0.18), and (0.15, 0.09) for CzTPT-PA, CzTPT-CIA, and CzTPT-IA, respectively, alongside maximum external quantum efficiencies of 25.0%, 15.5%, and 9.9%. Notably, the CzTPT-IA-based device achieved deep-blue emission with high color purity, representing a significant advancement in the field. This work introduces an effective design strategy for TSCT-TADF emitters, paving the way for high-performance, blue OLEDs with enhanced efficiency and color precision.