Photosensitive bent-core liquid crystals based on methyl substituted 3-hydroxybenzoic acid

Abstract

Photosensitive liquid crystals are of contemporary interest not only from the scientific point of view but also for various applications. Herein we report the first photosensitive materials based on laterally substituted 3-hydroxybenzoic acid. The molecular self-assembly of these new materials was characterized using different physical techniques including differential scanning calorimetry (DSC), X-ray diffraction (XRD) measurements, electro-optical investigations and dielectric spectroscopy. We show that the number and position of azo units with respect to the lateral substitution on the molecular core significantly influence mesomorphic properties of the materials. Based on the position of the substituent, either non-polar or polar smectic C phases are formed. The optimum combination of both the structural elements results in an achiral material which shows a broad polymorphism and exhibits a stable dark-conglomerate crystalline phase with macroscopically chiral domains at room temperature. The structure of this phase differs from the previously described fluid sponge-like distorted smectic phases as well as from helical nano-filament phases, thus, adding new information on the possible variations in the nanostructures of this kind of phase. Moreover, the photosensitivity of these materials has been studied using ¹H NMR spectroscopy.