Concerted Intramolecular and Intermolecular Charge Transfer for High‐Efficiency Near‐Infrared Thermally Activated Delayed Fluorescent Materials Approaching 900 nm

Abstract

AbstractHindered by the energy gap law, the development of high‐efficiency near‐infrared (NIR) thermally activated delayed fluorescence (TADF) emitters with emission peaks over 800 nm remains challenging. The conventional strategy of enhancing intramolecular charge transfer for bathochromic shift commonly results in low radiative decay rates (kr) and emission efficiency. Herein, a superior strategy of concerted intramolecular CT (intra‐CT) and intermolecular CT (inter‐CT) for high‐efficiency NIR‐TADF materials is demonstrated. As a proof‐of‐concept, two novel emitters DTPZ and DtBuTPZ are developed based on a new acceptor phenazine‐2,3‐dicarbonitrile (PZ). High kr is achieved by large oscillator strength from appropriate intra‐CT property in monomers and effective electronic couplings between inter‐CT and intra‐CT states in aggregates. Suppressed nonradiative decay processes are realized through strong inter‐CT properties, abundant intermolecular attractive interactions, and negligible π∙∙∙π stacking. Consequently, organic light‐emitting diodes based on those emitters showed record‐high maximum external quantum efficiencies and radiances of 2.28%, 24.18 W Sr−1 m−2 at 817 nm, 0.57%, 14.38 W Sr−1 m−2 at 877 nm for DTPZ, and 2.34%, 23.55 W Sr−1 m−2 at 807 nm for DtBuTPZ, respectively.