Hemithioindigo-based molecular motors controlling helicity in liquid crystals by visible light

Molecular motors are promising tools for the amplification of the motion from nanoscale to macroscopic scale. In this account, hemithioindigo-based molecular motors are presented since they can rotate under irradiation with visible light, making them interesting for biological applications in which the use of the UV light must be reduced. Since these molecules have a tetrasubstituted double bond, their synthesis require several reactions and, in this work, a new synthetic approach with fewer steps and an opportunity of a post-functionalization is presented. The strategy involves a convergent synthesis in which the lower and upper halves are synthesized separately, and joined through a coupling reaction. Chiral purification and full characterization of the thus synthesized functionalized motors were carried out. The integration of an enantiomerically pure hemithioindigo-based molecular motor in nematic liquid crystals can promote the formation of a cholesteric mesophase, which is characterized by a helical conformation leading to a chiral system. Each isomer can lead to a cholesteric helix with different pitch and handedness. The power of a chiral dopant to induce the formation of a cholesteric mesophase was determined by the helical twisting power (HTP).