Synthesis of polycatenar photoisomerizable liquid crystals based on an expanded acylhydrazone core

Liquid Crystals (LC) are known as the fourth state of matter, showing simultaneously properties from the solid (organization and anisotropy) and the liquid state (fluidity), besides unique characteristic not found in both.1 This makes these materials attractive to a wide variety of applications, like in displays, smart windows, thermometers, photovoltaic cells, semiconductors, among many others.1,2 Acylhydrazone is a functional group that shows reversible E-Z photoisomerization under the incidence of UV light3 and has not been much explored in the synthesis of LC. Therefore, the properties of these new liquid cristalline materials may be reversible modulated from a macroscopic level. In order to continue our investigations on how changes in molecular structure affects the properties of these materials, five new compounds derived from an expanded acylhydrazone core were synthesized (Figure 1). The molecules differ on the number and position of long alkoxy chains. All compounds were synthesize in good yield and had their structure and purity confirmed by NMR. TGA measurements show that they are stable up to 250 °C, while POM (Figure 2), DSC, XRD and SAXS (using Synchrotron radiation) confirm their liquid crystalline behavior. Compound 1-HDZES-1 shows a SmC mesophase between 198 °C and 212 °C while 3-HDZES-3 shows a Colh mesophase, ranging from below the room temperature until 118 °C. This strong difference in the molecular arrangement with the change on the number of alkoxy chains indicates an interesting polycatenar behavior. Preliminary studies confirm photoisomerization in chloroform solution.