Pyrazino[2,3-f][1,10]phenanthroline-based color-tunable thermally activated delayed fluorescence emitters with AIE characteristics for high-efficiency organic light-emitting diodes

Abstract

The widespread use of organic light emitting diodes (OLEDs) is driven by their self-emission, vivid colours, and efficiency, while achieving optimal thermally activated delayed fluorescence (TADF) performance requires specific molecular characteristics such as low singlet–triplet energy gap (ΔE_ST) and high photoluminescence quantum yield (PLQY). In this work, three color tunable D–π–A–π–D type skeleton TADF compounds, namely, 2,3-bis(4-(3,6-di-tert-butyl-9H-carbazol-9-yl)phenyl)pyrazino[2,3-f][1,10]phenanthroline (tCz-DPPN), 2,3-bis(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)pyrazino[2,3-f][1,10]phenanthroline (Ac-DPPN), and 2,3-bis(4-(10H-phenoxazin-10-yl)phenyl)pyrazino[2,3-f][1,10]phenanthroline (PXZ-DPPN), based on the pyrazino[2,3-f][1,10]phenanthroline acceptor were synthesized. Comprehensive photophysical studies of these compounds not only showed wonderful colour tuning from sky blue to yellow due to different donors, but also aggregation induced emission (AIE) properties. Among the three TADF emitters, PXZ-DPPN emitter doped OLED fabricated with the vacuum-deposition method exhibited emission in the yellow-orange region with a maximum EQE of 20.1% and Commission Internationale de I’Eclairage (CIE) coordinates of (0.49, 0.50), while Ac-DPPN and tCz-DPPN were found to exhibit green and sky-blue emissions with EQE values of 5.8% and 1.7% and CIE coordinates of (0.28, 0.52) and (0.15, 0.23) respectively.