Macrocyclised pheynyl cinnamate dimer utilisable as photoresponsive chiral dopant for nematic liquid crystals

A macrocyclised phenyl cinnamate dimer with a chiral spacer was prepared, and its photochemistry was compared with that of a precursor linear dimer and corresponding monomeric compounds. Although ultraviolet irradiation of the monomer resulted merely in cis–trans isomerisation of a cinnamate, irradiation of the cyclic and linear dimers induced intra-molecular [2 + 2] photodimerisation of cinnamate groups. Photodimerisation in the cyclic dimer proceeded 20 times faster than in the linear dimer. In a nematic liquid crystal, the cyclic dimer exhibited a high helical twisting power of 27.5 μm−1, which decreased to 6.7 μm−1 with dimerisation. A macrocyclised dimer such as this can be used as a photoresponsive chiral dopant for nematic liquid crystals.