Highly Efficient Circularly Polarized Electroluminescence Based on a Thermally Activated Delayed Fluorescence Mechanism

ConspectusCircularly polarized electroluminescence (CPEL) is pivotal for next-generation photonic technologies, including 3D displays, optical data storage, and quantum communication. However, its practical application has long been hindered by two fundamental challenges: low device efficiency (external quantum efficiency, EQE) and a small luminescence dissymmetry factor (g_EL), which quantifies the intensity of circular polarization. Traditional chiral fluorescent emitters suffer from limited exciton utilization of only 25%, while chiral phosphorescent emitters often rely on scarce metals. The emergence of thermally activated delayed fluorescence (TADF) offers a revolutionary pathway to overcome the device efficiency bottleneck by enabling full exciton harvesting through reverse intersystem crossing (RISC), yet integrating strong chirality into an efficient TADF molecular skeleton remains a significant hurdle.Our pioneering work established a comprehensive strategy to simultaneously boost EQE and g_EL. We introduced TADF as a core mechanism to achieve high EQE by harnessing triplet excitons via RISC. Concurrently, we devised diverse chiral structures, which range from small molecules and polymers to assembled ionic systems, to effectively amplify the dissymmetry factor. For instance, chiral supramolecular assemblies with TADF emitters enhance chirality transfer through assembled structural ordering, leading to significantly amplified g_EL values without compromising the radiative efficiency. This approach, which optimizes TADF photophysics for device efficiency and leverages advanced chiral structures for circular polarization, provides a holistic solution to the core challenges in CPEL.This Account chronicles our foundational journey in developing a highly efficient CPEL based on the TADF mechanism. We present a first-hand narrative of key breakthroughs, starting from the first demonstration of intrinsic TADF-driven circularly polarized organic light-emitting diodes (CP-OLEDs) and extending to the first chiral TADF polymers, TADF-sensitized fluorescent enantiomers, chiral TADF assemblies, and chiral TADF ionic salts for circularly polarized light-emitting electrochemical cells (CP-LECs). We elucidate the underlying design principles and mechanistic insights that unify these diverse material classes, bridging molecular design with device performance in both CP-OLEDs and emerging CP-LECs. By offering a consolidated perspective from the originators of this field, this Account aims to guide the future development of efficient circularly polarized light sources for advanced photonic applications.