A Chiral Propeller-Shaped Triple Helicene Shows Multi-Resonant Thermally Activated Delayed Fluorescence

Abstract

Multi-resonant thermally activated delayed fluorescence (MR-TADF) helicenes show great potential as chiral emitters due to their typically high photoluminescence quantum yield and that they emit circularly polarized luminescence. Here, a new propeller-shaped chiral MR-TADF helicene DiKTa3, integrating three DiKTa moieties, was designed and synthesized aiming to achieve co-parallel electronic and magnitude transition dipole moments that would lead to a high dissymmetry factor, g. It emits at λ_PL of 491 nm, with a full width at half maximum of 52 nm and has a moderate ΔE_ST value of 0.24 eV in toluene. The separated (P,P,P) enantiomer shows an absorption dissymmetry factor |g_abs| of 6.8×10⁻⁴ at 450 nm, which results from a lower symmetry conformation adopted by the compound in solution than the C₃-symmetric optimized structure. This work highlights the strong influence that geometry can have on the chiroptical properties of the emitter.