Synthesis and optical characterization of novel imidazole-based Azo materials

We synthesized novel imidazole-based azo compounds and their optical properties were investigated. In the course of recrystallization, pink-orange and violet products were obtained. The violet one shows poor solubility for most organic solvents except polar aprotic solvents such as dimethylsulfoxide (DMSO) and dimethylfolmamide (DMF). The spectra of NMR in DMSO-d₆ and UV-vis absorption spectra in DMSO for both products were found to be identical. However, there were differences in FT-IR absorption spectra. The violet solid compound exhibited broad bands that could be attributed to N-H⋯N hydrogen bonding. These results show that the violet product consists of an aggregation of molecules formed via intermolecular hydrogen bonding. Additionally, imidazole-based azo copolymers containing liquid crystalline side chain groups were also synthesized. The photoinduced birefringence of these copolymers was observed by irradiation of a linearly polarized 532 nm laser beam as a pumping light. It was confirmed that the material exhibited photoisomerization properties and the observed birefringence was attributed to photoinduced molecular reorientation. Moreover, the dipolar effect in photoinduced birefringence was briefly discussed.