Unsymmetric Dithienosilole Insertion into Helicene Enhances Circularly Polarized Luminescence

Three S,Si-heterohelicenes, STB[6]H, STB[7]H, and DSTB[7]H, with unsymmetric dithienosilole (DTS) were synthesized via a three-step strategy featuring Wittig and McMurry reactions, followed by photocyclization of diarylethene precursors. Their helically molecular structures were confirmed by X-ray crystal analysis. Their fluorescence quantum yields (ΦFL) were enhanced with the increase of the benzene unit or DTS moiety in the helicene skeletons. The enantiomers of DSTB[7]H containing two DTS moieties exhibit better performance of circularly polarized luminescence (CPL) than that of STB[7]H, with both luminescence dissymmetry factors (|glum|) reaching magnitudes on the order of 10⁻³.