Synthesis, characterization and photoreactivity of liquid crystalline cinnamates

A series of liquid crystalline cinnamate derivatives has been synthesized and characterized. The reactivity of photoreactive samples containing these compounds and a low percentage of a triplet sensitizer has been investigated at different temperatures and phases. No topochemical reaction occurs by irradiation on the solid phase. However, by irradiation at mesophase the presence of photoproducts have been detected by FTIR and UV-Vis. However, when temperature increases above 200 °C, thermal reactivity predominates. The photoproducts were studied by NMR. A relatively low percentage of E–Z isomerization was measured together with [2+2] photocycloaddition. The resulting isomeric cyclobutane rings depend on the molecular ordering of the fluid phase. Thus smectic mesomorphic ordering mainly favors a β-truxinic acid derivative but isotropic phase mainly favors a δ-truxinic acid derivative.