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.