Engineering Intramolecular π‐Stacking Interactions of Through‐Space Charge‐Transfer TADF Emitters for Highly Efficient OLEDs with Improved Color Purity

Abstract Purely organic compounds with thermally activated delayed fluorescence (TADF) are promising sustainable emitters for organic light‐emitting diodes. But the simultaneous realization of a high efficiency, short lifetime, and good color purity in single TADF molecule remains challenging. Herein it is reported that the confinement of rigid and planar N‐ and B‐centered donor and acceptor in sandwich‐type structures, named BNB‐m and BNB‐p, can lead to green TADF emissions with up to unity efficiency and improved color purity from through‐space charge‐transfer excited states. The full width at half maximum of 58 nm (0.28 eV) for BNB‐m is significantly smaller than those for most of the TADF emitters having a twisted donor‐acceptor structure. Single‐crystal structures, NMR spectroscopy, and theoretical simulations manifest the presence of strong noncovalent π‐stacking interactions in BNB‐m which account for the reduced intramolecular motions and enhanced through‐space electronic coupling. With a relatively short delayed fluorescence lifetime of 11 µs, the emitter BNB‐m demonstrates attractive green electroluminescence with a maximum external quantum efficiency (EQE) of 34.9% and an EQE of 27.4% at 1000 cd m⁻². This work validates a promising molecular design to TADF emitters which can realize a balanced emission property in terms of color purity and emission lifetime.