Orlova T. Optical and spectral properties of liquid crystals with photosensitive chiral steroid dopant

In this work the influence of UV-induced transformations of dopant chiral molecules 7-dehydrocholesterol (7-DHC, provitamin D3) on the optical properties and structure of nematic and cholesteric LCs is investigated. On the other hand, features of previtamin D (photoisomer of 7-DHC) cis-trans photoisomerization in ordered nematic and cholesteric LC media are studied. It is shown that trans-isomer with flexible molecular structure which formed under UV irradiation affects anisotropic interaction of the LC molecules more distinctly than 7-DHC with rigid molecular structure. It is obtained, that efficiency of previtamin D cis-trans isomerization in nematic and cholesteric LCs strongly depends on the 7-DHC concentration contrary to isotropic solvents. The concentration dependence of cis-trans isomerization indicates the collective character in LC matrices with 7-DHC concentration rising. It is found that trans-isomer is the left-handed chiral dopant. Dynamics of induced cholesteric phase structure (nematic+ 7-DHC) under UV irradiation is investigated. The optimum LC composition (nematic + chiral dopant + 7-DHC) for UV biosensor with a visual estimation of vitamin-D synthetic capacity solar and artificial UV light is found.