A Deep‐Red Emissive Sulfur‐Doped Double [7]Helicene Photosensitizer: Synthesis, Structure and Chiral Optical Properties

Abstract

Doping of polycyclic conjugated hydrocarbons (PCHs) with sulfur atoms is becoming more and more important as a means of creating unique functional materials. Recently, thiophene‐containing multiple helicenes have garnered enormous attention due to their intriguing electronic and (chir)optical properties compared with carbohelicenes. However, the efficient synthesis of thiopyran‐containing multiple helicenes and the underlying sulfur doping mechanisms are rather unexplored. Herein, the synthesis and structural analysis of a thiopyran‐containing double [7]helicene 3 are reported. X‐ray crystallographic analysis reveals 3 and its dication with C2‐symmetric propeller‐shape structure and compact p‐p interaction in the solid state. 3 exhibits deep‐red to near‐infrared (NIR) fluorescence emission. Tunable aromaticity of the central benzene ring and thiopyran rings is found by chemical oxidation, which is further confirmed by nucleus‐independent chemical shift (NICS), anisotropy of the induced current density (AICD) and harmonic oscillator model of aromaticity (HOMA) analysis. Furthermore, the chiral and photosensitizing characters of 3 are investigated. The excellent deep‐red to NIR fluorescence, circularly polarized luminescence (CPL) and photosensitizing activities suggest that 3 can be used as an outstanding photosensitizer in photodynamic therapy (PDT) and bioimaging, especially paving the way for future CPL‐PDT and CPL‐bio‐probe applications.