A photoswitchable and thermally stable axially chiral dithienylperfluorocyclopentene dopant with high helical twisting power

Abstract

A chiral dithienylperfluorocyclopentene molecule bearing two bridged binaphthyl units was designed and synthesized by a Suzuki–Miyaura cross-coupling reaction between chiral binaphthyl iodide and dithienylperfluorocyclopentene-derived bis(boronic ester). Its photoresponsive properties were investigated in both organic solvent and liquid crystal media. The UV-vis spectra exhibited typical photochromic changes of diarylethenes upon UV irradiation. The CD spectral changes upon light irradiation indicated that the conformation of binaphthyl units and the chiroptical properties of this molecule could be modulated by light. More importantly, when using as a chiral dopant in nematic liquid crystals, this molecule could induce cholesteric liquid crystals with very high helical twisting powers. At very low doping concentrations, this dopant was able to induce a reversible isothermal phase transition between nematic and cholesteric phases upon light irradiation. The photochemical control of the pitch length of cholesteric phases at higher doping concentrations enabled the reversible reflection wavelength control in the visible region. Superior thermal stability and excellent fatigue resistance were also observed during the photoswitching process, which are important properties for applications.