Triarylboron-cored multi-donors TADF emitter with high horizontal dipole orientation ratio achieving high performance OLEDs with near 39% external quantum efficiency and small efficiency Roll-off

Abstract

The combination of acridine/phenoxazine donors and triarylboron acceptor has afforded two thermally activated delayed fluorescence (TADF) emitters with D3-A typed architectures, namely 3DMAC-TB and 3PXZ-TB. Attributing to the highly steric hindrance between D/A groups as well as intense intramolecular charge transfer state, both emitters exhibit well-separated frontier molecular orbitals (FMOs) distributions and distinct TADF characteristics. The high rigidity molecular structures of 3DMAC-TB and 3PXZ-TB contribute to high photoluminescence quantum yields (PLQYs) up to 0.94 and 0.89, respectively. The “star-shaped” configuration endows both emitters with high ratios of horizontal dipole orientation of 86% and 80%, respectively. The organic light emitting diodes (OLEDs) involving 3DMAC-TB and 3PXZ-TB as emitting dopants achieve maximum external quantum efficiencies of 38.8% and 29.4%, respectively. The efficiency of 3DMAC-TB based device is among the state-of-the-art efficiency for green TADF OLEDs. This work unveils great potential with triarylboron-cored multi-donors molecular design strategy in the development of excellent TADF molecules simultaneously possessing high quantum yields and preferentially horizontal emitting dipole orientations.