Precision design for high-performance TADF emitters with novel interlock D–A frameworks†

Achieving high-performance organic light-emitting diodes (OLEDs) remains a significant challenge, driven by the complex interdependence of charge transport, exciton dynamics, and light-emission processes. We present a novel approach utilizing positional isomerism of boron acceptors at para (p-CZN-B) and ortho (o-CZN-B) positions within a rigid donor–acceptor (D–A) framework, precisely combining carbazole as the electron donor and mesityl borane as the acceptor. This positional engineering profoundly influences the photophysical, thermal, and electroluminescent properties of the emitters. The ortho-configured o-CZN-B demonstrates exceptional separation of HOMO and LUMO levels and a minimized singlet–triplet energy gap (ΔE_ST = 0.17 eV), enabling sky-blue thermally activated delayed fluorescence (TADF) with an external quantum efficiency (EQE) of 23.3% and a full width at half maximum (FWHM) of 54 nm. Conversely, the para-configured p-CZN-B exhibits deep-blue fluorescence with an EQE of 2.6%, and CIE coordinates of (0.16, 0.03), surpassing the standard color Rec. 2020 specification of (0.131, 0.046), along with efficient amplified spontaneous emission (ASE) at a low threshold of 5.79 μJ cm⁻² and an ultranarrow FWHM of 4.7 nm, making it an excellent candidate for organic lasers. This study highlights the role of isomeric acceptor positioning in modulating the electronic and photophysical properties of TADF emitters, achieving notable advancements in OLED efficiency and emission color purity. The findings also provide a strong framework for designing next-generation optoelectronic devices with enhanced performance and tunable functionalities.