Comparative study of chiro- and photo-optical properties of three novel chiral photochromic liquid crystalline azobenzene-containing comb-shaped polyacrylates was performed. The synthesized polymers contain the same polyacrylate backbones and uniform spacer size (10 methylene units), but have different structure of azobenzene-containing mesogenic groups with different chiral tail. The polymers are characterized by crystalline, SmA*, SmC*, and N* phases formation depending on chemical structure of the variable fragments. Presence of the lateral chlorine substituent in the mesogen fragment leads to an extreme decrease of isotropization temperature and causes a disappearance of cholesteric mesophase. Circular dichroism (CD) spectra demonstrate formation of helical order elements even in the amorphousized spin-coated polymer films. Possibility of manipulation of CD values and degree of the helical order by light and annealing was established and studied. UV-irradiation of all polymers induces E – Z isomerization of azobenzene groups and thus disrupting the LC-order. Besides, irradiation of films by polarized light leads to photoorientation process due to cycles of E – Z – E isomerization. As a result, appearance of significant linear dichroism dependent on the relative position of azobenzene moiety in aromatic core was evidenced.
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Bobrovsky et al. (2013) studied this question.
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