Electric field- and light-responsive oxadiazole bent-core polycatenar liquid crystals

Abstract

Alkyl chain engineering of polycatenar liquid crystals (LCs), which consist of a rigid aromatic core with flexible chains at both ends, serves as an effective method for controlling their self-assembled nanostructures. Incorporating stimuli-responsive molecular units into the design of polycatenars represents a promising strategy for developing novel functional LC materials. In this study, we present the design and synthesis of new oxadiazole-based bent-core tetracatenar LCs with alkoxy azobenzene terminals. These compounds form 3D bicontinuous cubic (Cub_bi) or columnar phases depending on the length of the terminal chains. The shortest homologue displays a Cub_bi phase of the double gyroid type (Cub_bi/Iad) and a triple-network phase with the I23 space group (Cub_bi/I23). Longer homologues form a hexagonal columnar LC phase. This columnar phase could be aligned by cooling a molten sample under an applied electric field, and the alignment was attributed to dielectric polarization induced by the oxadiazole ring. Furthermore, the incorporation of fluorinated azobenzene facilitated orientation switching from a random to an aligned state within the columnar LC phases. Using UV irradiation, we successfully modified the LC phase structure via the reversible trans-to-cis photoisomerization of the azobenzene units. These findings underscore the potential applications of the reported materials in information-storage devices.