Thermally Activated Delayed Fluorescent and Fluorescent Emitters Based on Pyrazino[2,3-f] [1], [10]Phenanthroline for Efficient Organic Light-Emitting Diodes

Achieving optimal thermally activated delayed fluorescence (TADF) performance in organic light-emitting diodes (OLEDs) necessitates specific molecular characteristics, including a low singlet-triplet energy gap $(\Delta E_{\text{ST}})$ and high photoluminescence quantum yield. In this study, three $\mathrm{D}-\pi-\mathrm{A}-\pi-\mathrm{D}$ type fluorescent/TADF compounds, including DTCz-DPPN, DAC-DPPN, and DPXZ-DPPN. These compounds were synthesized using a pyrazino[2,3-f][1], [10]phenanthroline acceptor connecting with different donors. Thorough photophysical studies revealed versatile color tuning from sky blue to yellow and aggregation-induced emission (AIE) properties due to the decoration of different donors. Among the three emitters, the DPXZ-DPPN-based OLEDs exhibited yellow emission with a maximum EQE of 20.1% and Commission Internationale de l'eclairage (CIE) coordinates of (0.49, 0.50). In contrast, DAC-DPPN and DTCz-DPPN emitted green and sky-blue light with EQE values of 5.8% and 1.7%, respectively, and CIE coordinates of (0.28, 0.52) and (0.15,0.23), respectively. These results underscore the promising suitability of these DPPN-based compounds as TADF emitters for OLED applications.