π‐Bridge mediated coupling between inter‐ and intra‐molecular charge transfer in aggregates for highly efficient near‐infrared emission

Abstract

AbstractIntermolecular charge transfer (inter‐CT) is commonly considered to quench luminescence in molecular aggregates, especially for near‐infrared (NIR) emission. Herein, by elaborate comparison of π‐bridge effects in donor/acceptor (D/A) molecules, it is disclosed that a π‐bridge is essential in D/A molecule to involve inter‐CT in aggregates for inducing desired thermally activated delayed fluorescence (TADF) and largely suppressing non‐radiative decays, and importantly, electron‐donating π‐bridge is critical to maximize radiative decay for inter‐CT dominated emission by effective electronic coupling with bright intramolecular charge transfer (intra‐CT) for high‐efficiency NIR emission. As a proof‐of‐concept, TPATAP with thienyl as π‐bridge realized prominent photoluminescence quantum yields of 18.9% at 788 nm in solid films, and achieved record‐high maximum external quantum efficiencies of 4.53% at 785 nm in devices. These findings provide fresh insight into interplay between inter‐CT and intra‐CT in molecular aggregates and open a new avenue to attenuate the limitation of energy gap law for developing highly efficient NIR emitters and improving the luminescent efficiency of various inter‐CT systems, such as organic photovoltaic, organic long persistent luminescence, etc.