Comparative analysis of fluorine-containing mesogenic derivatives of carborane, bicyclo[2.2.2]octane, cyclohexane, and benzene using the Maier-Meier theory

Two series of related three-ring nematoges with Δε > 0 and containing 12-vetex carborane (A), 10-vertex carborane (B), bicyclo[2.2.2]octane (C), cyclohexane (D) and benzene (E) were prepared and investigated as additives to 6-CHBT nematic host and in the pure form (series 2). Dielectric results were analyzed with the Maier-Meier relationship to gain an understanding of behavior of additives in nematic solutions. Molecular parameters for each nematogen were obtained at the B3LYP/6-31G(d,p) level of theory in the host's dielectric medium, and dielectric data was used as the only experimental parameter to calculate apparent order parameter Sapp and the Kirkwood factor g. The results demonstrated that compounds in series 1 stabilize the nematic phase (high Sapp) of the host more than additives in series 2 (low Sapp), and carbocycles C and D are more effective (higher Sapp) than carborane analogues A and B (lower Sapp). The method provides insight into behavior of additives in nematic solutions and is useful for comparative analysis of a series of compounds or a series of hosts.

Study of azo dye surface command photoalignment material for photonics applications

We provide detailed quantitative characterization of sulfonic bisazodye SD1 as a photoalignment material for photonics applications. The reversibility of photoalignment was tested for transformations between planar and 90 degrees twist orientation states in a liquid crystal (LC) cell using polarized UV light. No degradation was observed for 100 cycles of transformations. A given twist angle of the LC orientation was obtained in a single step, as well as in a sequence of gradually increasing angles. A hysteresis is revealed in the latter case for planar-twist-planar cycles. The material was used for obtaining patterned orientation of a LC polymer providing similarly good quality photoalignment for UV as well as visible light. High efficiency large area and high spatial frequency optical axis gratings (or, polarization gratings) were demonstrated on a polycarbonate substrate. We show the opportunity of obtaining photoalignment in a multilayer system with single exposure to a polarized light. Finally, we provide evidence of a positive feedback in the dynamics of photoalignment due to the orientational effect of an increasing number of aligned molecules.