Modification of thermally activated delayed fluorescence emitters comprising acridan–pyrimidine moieties for efficient sky-blue to greenish-blue OLEDs

Abstract

Thermally activated delayed fluorescence (TADF) is a promising approach to harvest triplet excitons and achieve high-performance organic light-emitting diodes (OLEDs) for displays. In this study, we synthesized two new TADF emitters, 4Ac25CzPy and 4Ac35CzPy, featuring acridan–pyrimidine–carbazole moieties. Remarkably, a slight modification in the carbazole group position enables precise control of luminous color, resulting in emissions at 483 nm and 494 nm for 4Ac25CzPy and 4Ac35CzPy, respectively, in the electroluminescent device. Both compounds exhibit small energy difference between their singlet and triplet states (ΔE_ST) of 0.14 eV and 0.15 eV, confirming their TADF characteristics. Notably, OLEDs utilizing 4Ac35CzPy achieve outstanding performance with the maximum external quantum efficiency (η_EQE) of 21.2% and a photoluminescence quantum yield of 65.1%. This high efficiency is attributed to efficient energy transfer from the host to the emitter. Moreover, the 4Ac35CzPy device exhibits a high light outcoupling efficiency of 0.3, further enhancing its remarkable performance.