Construction of high-performance circularly polarized multiple-resonance thermally activated delayed fluorescence materials via the structural optimization of peripheral groups

Abstract

Circularly polarized multiple-resonance thermally activated delayed fluorescence (CP-MR-TADF) materials have attracted increasing attention recently, but it is still a formidable challenge to design materials with a large asymmetry factor (g), narrowband emission and high photoluminescence quantum yield (PLQY) simultaneously. Here, we perform a systematic theoretical study on the design of high-performance CP-MR-TADF materials via the structural optimization of peripheral groups. It was found that the introduction of relatively weak electron-donating/withdrawing groups is in favor of optimizing the θ_μ,m values and increasing the g values, and the molecular modification with sterically hindered groups (–CF₃ and –C(CN)₃) could further optimize the molecular helical arrangement with a φ₁ (a dihedral angle between QAO and an intermediate benzene ring) of 60–70° and enhance the chirality with g values on the order of 10⁻³–10⁻². The molecules possessing electron-withdrawing units exhibit excellent circularly polarized luminescence (CPL) properties evaluated with a figure of merit (FM) by comprehensively considering the balance between the g value and the PLQY. So the electron-donating/withdrawing abilities of the peripheral groups and the steric hindrance effects should be two key optimization parameters in constructing high-performance materials. These findings and insights are of great importance for revealing the structure–property relationship and providing in-depth understanding of the design of such helical CP-MR-TADF materials.