Estudo sistemático sobre a inserção de acilhidrazonas em cristais líquidos policatenares

Abstract

Liquid Crystals (LC) are materials which combine characteristics from solid state (organization and anisotropy) and liquid state (fluidity). Such materials have a great technological interest due to their unique properties, such as their self-organization and responses to thermal variation, being well known for their applications in displays, smart Windows and thermometers. The acylhydrazone is a rigid and linear functional group, easily synthetized and that shows the interesting characteristic of reversible photoisomerization, in which the molecular structure can be changed by the use of UV-Vis electromagnetic radiation. In order to merge both properties, in this work ten unpublished molecules containing the acylhydrazone unit and a structure that could generate mesomorphism were synthesized. Furthermore, aiming at a study of the structure-property relationship for this system, the molecules showed variation in the number of long alkoxy chains and in the size of the rigid unit. The molecules were synthesized through a partially convergent route in good yields for most of the compounds, all of which had their structure and purity proven by 1H NMR and HRMS. All target products showed the photoisomerization process in chloroform solution. The compounds with the expanded rigid core converted to the Z-isomer faster than their non-esterified counterparts. Three of the final molecules showed liquid-crystalline behavior, as verified by DSC, MOLP, XRD and SAXS. Molecules with three alkyl chains on each side showed stable Colh mesophase below 0 °C, these phases being commonly observed in discotic LC. In addition, the expansion of the rigid core favored a liquid-crystalline behavior for the molecules with a smaller number of alkyl chains, with the appearance of a SmC mesophase, typical for calamitic LC. On other hand, for the molecules with the largest number of side chains, this expansion generated a decrease in the mesomorphism range. Overall, this demonstrates that the acylhydrazone group is indeed promising for application in various LC.