Dual Enhancement of Emission and Luminescence Dissymmetry Factor by Si-Heteroannulation of Double π-Helix

Organic emitters of circularly polarized luminescence (CPL), especially chiral π-conjugated molecules, are attracting research interest, but they remain challenges to maintain both high luminescence dissymmetry factor (glum) and photoluminescence quantum yield (ΦPL). Herein, we present a novel kind of CPL emitter by integrating a double π-helix and Si-heteroannulation. The targeted cyclooctatetraene-embedded perylene diimide dimers, namely, sila- and disila-annulated double π-helices (3 and 4), are synthesized via one-pot palladium-catalyzed Si–C bond formation. Single-crystal analyses reveal their unique double π-helical frameworks featuring a cyclobis[3]helicene substructure with enhanced structural rigidity and coplanarity by Si-heteroannulation. Enhanced fluorescence emission is thus achieved with ΦPL reaching 70%, which is attributed to the mitigation of nonradiative energy loss revealed by the theoretical results of reorganization energy and Huang–Rhys factors. Notably, the symmetrically bilateral disila-annulated double π-helix 4 exhibit excellent chiral activities both in the ground and excited states, with dissymmetry factors |gabs| of up to 0.015, |glum| of up to 0.013, and CPL brightness (BCPL) of 207.3 M–1 cm–1, outperforming pristine double π-helix 2. These results indicated that a comprehensive CPL performance could be achieved by rational molecular design.