Abstract
The method of UV absorption spectroscopy is used to study the influence of the cholesteric pitch on the efficiency of previtamin D (photoisomer of provitamin D3) cis-trans isomerization in a cholesteric liquid crystal (nematic + optically active dopant + provitamin D3). It is found that a change in pitch from 14 to 0.364 μm due to an increase in the concentration of an optically active dopant in a wide range (1.6–61 wt %) only slightly reduces the efficiency of the cis-trans isomerization. However, small changes in pitch (0.364–0.368 μm) due to an increase in the provitamin D3 concentration within the range of 0.07–2.2 wt % significantly increase the efficiency. Reducing in the influence of provitamin D3 concentration on the cis-trans isomerization efficiency with an increase in mesophase temperature was found in both nematic and cholesteric liquid crystals up to the disappearing of the concentration dependence in the isotropic phase. Altogether, the obtained results indicate the collective character of cis-trans isomerization in liquid crystals due to the ordering of the medium.
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