The Role of Chalcogen Substitution and Helical Frameworks in Designing Efficient Chiral Multi-Resonant TADF Emitters

Multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters that display efficient reverse intersystem crossing (RISC) rates and circularly polarized luminescence (CPL) are of great interest for next-generation organic light-emitting diode (OLED) applications, owing to their narrowband emission, high efficiency, and remarkable color purity. Here, the photophysical and chiroptical properties of three series of molecules derived from boron/nitrogen-embedded MR cores by systematically introducing chalcogen atoms (O, S, Se) and/or incorporating ortho-fused benzo or naphtho groups are investigated. Highly correlated quantum-chemical calculations reveal that steric repulsions resulting from the ortho-fused positions induce molecular distortions and twist the molecular backbone into helical structures, which enhances the chiral properties; the incorporation of heavier chalcogens increases spin–orbit coupling (SOC), leading to enhanced RISC rates. These findings demonstrate that several of the molecules that are considered exhibit high radiative decay rates (≈10⁸ s⁻¹), substantial RISC rates (≈10⁴–10⁸ s⁻¹), and values of the dissymmetry factor g of the order of 10⁻³, which makes them potential candidates for CPL applications. Overall, this study highlights the complex interplay among chalcogen substitution, structural modifications, and electronic structure in governing the photophysical and chiroptical properties of MR-TADF emitters, and offers valuable insight for the rational design of next-generation CPL-enabled OLEDs.