Synthesis and characterization of light-driven dithienylcyclopentene switches with axial chirality.

Three new photochemically reversible but thermally stable dithienylcyclopentene switches with axial chirality were synthesized and characterized. All the compounds exhibited photochemically reversible isomerization with thermal stability between its open form and closed form in both organic solvent and liquid crystal host. Their photoresponsive behaviors in organic solvents were characterized by (1)H NMR, UV-vis, and CD spectra. These chiral molecular switches were found not only to be able to act as a chiral dopant and induce a helical superstructure in an achiral liquid crystal host but also to be able to reversibly and dynamically tune the transmittance and reflection of the resulting chiral phase upon light irradiation. The helical twisting powers, transmittance, and reflection spectra of photoswitchable cholesteric LCs were measured. Dopant 1 exhibited an unusually high helical twisting power, which is significantly larger than those of the known chiral diarylethenes reported as chiral dopants so far.