<title>Photochemical switching between a compensated nematic phase and a twisted nematic phase by photoisomerization of chiral azobenzene molecules</title>

Abstract

Three azobenzene compounds with chiral moieties were prepared. A cholesteric phase was induced by mixing each chiral azobenzene in a host nematic liquid crystal. The twisting power of the chiral azobenzene compounds was decreased by ultraviolet irradiation to cause trans - cis photoisomerization of the azobenzene compounds. In addition, a compensated nematic phase was induced by mixing of a chiral azobenzene and a non-photochromic chiral compound having opposite chiral ability to the chiral azobenzene in the host nematic liquid crystal when the twisting powers of both chiral compounds were balanced. The photoisomerization of the chiral azobenzene broke the balanced state in the twisting power, resulting in the transformation of the compensated nematic phase into a cholesteric phase. Effect of the trans-cis photoisomerization on the phase structure of liquid crystals containing the chiral compounds will be discussed.