Controlling ambidextrous mirror symmetry breaking in photosensitive supramolecular polycatenars by alkyl-chain engineering

Abstract

Liquid crystalline (LC) photo sensitive materials capable of forming mirror-symmetry broken mesophases are of great interest to produce nano-structured materials for optical and photonic applications. Herein we report how mirror-symmetry breaking could be controlled in photo sensitive supramolecular polycatenars by alkyl chain engineering. For this purpose, three new series of supramolecular photo-switchable multi-chain complexes (polycatenars) formed by intermolecular hydrogen bonding interaction between azopyridines with one variable terminal chain as the proton-acceptors and Y-shaped or taper shaped benzoic acids having either two or three terminal chains as the hydrogen bond-donors were synthesized. The LC self-assembly of these supramolecules was characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and X-ray diffraction (XRD). Depending on the number and length of terminal chains spontaneously chiral isotropic liquid (Iso1[*]) as well as two different types of three dimensional (3D) bicontinous cubic phases are observed, which are either chiral (Cubbi[*]/I23) or achiral (Cubbi/Iad). Moreover, UV light irradiation leads to the first fast and reversible photoinduced transformation between chiral and achiral 3D cubic phases as well as between a chiral crystalline and a chiral cubic liquid crystalline phase.