π-Extended D–A Type [5]Helicenes: Cyano-Based Construction and Enhanced CPL Performance

Two cyano-based D–A type [5]helicenes, N[5]Hs and P[5]Hs, were synthesized through key steps, including the Rosenmund–von Braun reaction, the Horner–Wadsworth–Emmons reaction, and elimination. Enhanced fluorescence emission is achieved with ΦFL reaching 39%; this enhancement is attributed to a strengthened intramolecular charge transfer (ICT) effect, which reduces the nonradiative rate (knr) in turn. The emission wavelength can be tuned by introducing different functional groups. Among them, P[5]HE3CN exhibited exceptional circularly polarized luminescence (CPL) properties, achieving a luminescence dissymmetry factor (|glum|) of up to 8.7 × 10–3. These results demonstrate that rational molecular design with a donor–acceptor framework can effectively modulate CPL performance parameters of materials such as glum and ΦFL.