Deep-red thermally activated delayed fluorescence emitters based on a phenanthroline-containing planar acceptor

Abstract Organic luminescent materials possessing thermally activated delayed fluorescence (TADF) feature have aroused the tremendous attention. In this work, two novel TADF emitters, 10-(acenaphtho [1′,2':5,6]pyrazino [2,3-f] [1,10]phenanthrolin-12-yl)-10H-phenoxazine (APPT-PXZ) and 7-(acenaphtho [1′,2':5,6]pyrazino [2,3-f] [1,10]phenanthrolin-12-yl)-7H-benzo [c]phenoxazine (APPT-BPXZ), are developed via combining the strong electron-donating and electron-withdrawing units. Both target compounds exhibit orthogonal configurations to decrease singlet-triplet splitting energy (ΔEST) for the remarkable TADF property. Furthermore, APPT-PXZ and APPT-BPXZ-based devices realize the maximum external quantum efficiencies of 7.2% and 2.0% with the electroluminescence peaks at 640 nm and 665 nm, respectively. This work facilitates the development of the deep-red organic light-emitting diodes.