Synthesis and Chiroptical Properties of Binaphthyl-Hinged [5]Helicenes

The synthesis, structure, and circularly polarized luminescence (CPL) of two types of shape-persistent [5]helicenes, hinged by a tethered (-OCH2CH2O-) or untethered (-OCH3) binaphthyl, are reported. The binaphthyl tethering system facilitated an effective Wittig ring-closure reaction in the synthesis of a macrocyclic precursor, which could be easily converted to the title compound via successive photocyclization. The tethered groups were replaced with untethered -OCH3 groups by treatment with BBr3 followed by methylation. Both compounds exhibited similar spectra, and their longest wavelength absorption band with a low intensity was attributed to the transition from HOMO to LUMO+1. These compounds exhibited CPL with higher dissymmetry factors g(lum) values than unlocked helicenes.

Automated summary

This study reports the synthesis, structure, and circularly polarized luminescence (CPL) of two types of shape-persistent [5]helicenes. The effective Wittig ring-closure reaction was facilitated by the binaphthyl tethering system, which resulted in the synthesis of a macrocyclic precursor that could be easily converted to the title compound via successive photocyclization. The tethered groups were replaced with untethered -OCH3 groups, and both compounds exhibited similar spectra and exhibited CPL with higher dissymmetry factors g(lum) values than unlocked helicenes.