Two chiral dimethacrylate and one chiral diacrylate monomer containing an azobenzene group were synthesized and dissolved in a commercial ferroelectric liquid crystal (FLC) host. With two of the monomers, thermally induced radical polymerization with the mixture exposed to linearly polarized irradiation results in a bulk alignment of FLC in the direction perpendicular to the polarization of irradiation light as a result of the photoinduced orientation of azobenzene groups related to the transcis isomerization. The monomer that is most effective for photoalignment of FLC displays a polymer network formed by strings of colloidal particles (∼250 nm in diameter), which exerts a commanding effect on the alignment of FLC as being able to reorient the FLC by changing the polarization direction of subsequent irradiation. The study suggests that the network of colloidal particles is isotropic and that the photoalignment of azobenzene moieties on the large surface of the network dictates the alignment of FLC.

The Arrhenius equation for the ring-opening isomerization of cyclopropylmethyl radicals (R*) to 3-buten-l-yl radicals (R") for the 303-362 K temperature range was determined by thermolysis of (cyclopropylmethyl)(1 -hydroxy-1 -methylethyl)diazene in the presence of excess 1,1,3,3-tetramethylisoindolin-2-yloxy (V). Rate constants for coupling of R* with Y* were assumed to be proportional to diffusion-controlled rate constants (kd) and rate constants (k,) for the isomerization were calculated from kd (corrected) and product ratios (RY/R'Y). The temperature dependence of k" given by log {k-Js~') = (13.9 ± 0.4) -(7.6 ± 0.2)/9, is significantly different from that determined by kinetic EPR spectroscopy in the temperature range 128-153 K; log (kj/s-') = (11.34 ± 0.85) -(5.94 ± 0.57)/9, where = 2.3/?7kcal mol-1.

No abstract

No abstract