Novel photochromic liquid crystals

The combination of photochromic units and liquid crystal mesogens has over the years been investigated intensively. However the focus of this work has been on very few photochromic groups. The overall aim of this work is to combine photochromic groups, that have not been used in combination with liquid crystal phase behaviour inducing groups, with the aim to generate new liquid crystalline photochromes. The imidazole based lophine group was functionalised symmetrically to induce liquid crystalline properties. The modification of the lophine core involved the introduction of a spacer using hydrocarbon and siloxane groups, a mesogenic group and the variation of the spacing between the mesogenic groups and the imidazole. The first room temperature liquid crystalline triphenyl imidazoles were thus generated and the photochromic and liquid crystal properties were explored using UV-Vis spectroscopy, optical polarising microscopy, differential scanning calorimetry and X-ray diffraction methods. Additionally the synthesis and the functionalisation of a diazocine unit, which is a derivative of the commonaly known transazobenzene compound was explored.The results of the work carried out was the synthesis of a set of novel photochromic liquid crystalline materials, with the alteration of the structure and the method of linking the liquid crystalline mesogen and the photochromic unit. This reduced the transition temperatures to the isotropic phase by 2°C and causing a shift in the absorption spectra if the irradiated species from 450nm to 550nm. It was also observed that the irradiation and subsequent radicalisation of the hexaarybiimidazole group did not alter the liquid crystalline properies but did induce a bulk colour change in the material in the smectic A phase