Circularly polarized multiple-resonance thermally activated delayed fluorescence (CP-MR-TADF) emitters have gained immense interest in advanced optoelectronics due to their unique combination of narrow emission, efficient TADF, and chirality. However, their rational design requires a deeper understanding of the intricate structure-property relationships that govern their photophysical and chiroptical behavior. In this work, we systematically explore a series of helicene-based CP-MR-TADF emitters through four strategic modifications: the core framework (B-N-B vs. N-B-N), MR-TADF skeleton architecture, chiral unit variation, and the heavy-atom effect (O, S, Se). Employing high-level STEOM-DLPNO-CCSD calculations benchmarked against experimental data, we theoretically design 28 novel molecules to target highly efficient CPL properties and accurately predict excited-state energies. Our analysis reveals that the B-N-B framework consistently yields superior color purity, with FWHM values as narrow as ∼14 nm, resulting from minimized structural relaxation. The incorporation of heavy atoms (O, S, Se) systematically enhances reverse intersystem crossing (RISC) rates up to ∼107 s−1 by strengthening SOC and reducing the ΔEST gap, making it ideally suited for the TADF process. All designed molecules exhibit high luminescence dissymmetry factors on the order of ∼10−3, with the N-B-N framework yielding the maximum values, up to 4.17×10−3, attributed to its characteristic enhanced transition electric-magnetic dipole moment angles. Notably, the N-B-N framework significantly increases the racemization barrier by ∼20 kcal mol−1 relative to the B-N-B framework, thereby ensuring configurational stability under ambient conditions. This study establishes clear structure-property relationships and outlines a design framework for developing high-performance CP-MR-TADF emitters with balanced narrow-width emission, efficient triplet harvesting, and strong chiroptical activity.
Mahaan et al. (Fri,) studied this question.