Multiplying the electroluminescence efficiencies of red TADF emitters via a regioisomeric approach of the donor unit

Abstract

A regioisomeric strategy is of great significance to the design of molecules with red thermally activated delayed fluorescence (TADF); however, previous studies have mainly focused on the regioisomerism of acceptor frameworks. Herein, we propose a donor-induced regioisomeric strategy for developing red TADF emitters for the first time. Intriguingly, DPDPZ-PXZPh, with 3-position connected 10-phenyl-10H-phenoxazine (PhPXZ) as the donor exhibits a faster radiative rate, lower reorganization energies, and a superior photoluminescence quantum yield compared with the control compound DPDPZ-PhPXZ containing a 14-position connected PhPXZ. The corresponding organic light-emitting diode (OLED) based on DPDPZ-PXZPh not only achieves an evidently redshifted emission peaking at 600 nm but also delivers a much-improved external quantum efficiency of 28.0%, which is a nearly 1.6-fold efficiency enhancement relative to the DPDPZ-PhPXZ-based device (17.8%). This result demonstrates the important role of donor linking engineering in constructing high-performance red TADF emitters, offering a new isomeric pattern for developing high-efficiency red OLEDs.