Design synthesis and characterisation of photoswitchable azo-benzene-based four-ring bent core mesogen and their Cu complexes

In this study, we present the design and synthesis of a series of unsymmetrical four-ring bent-core compounds, featuring terminal tetradecylxoy, (-OC14H29), hexadecyloxy, (-OC16H33) and octadecyloxy (-OC18H37) alkyl chains, along with their corresponding copper complexes. The synthesised compounds, designated as 1a, 1b and 1c, exhibit enantiotropic nematic mesophases. Upon coordination with copper acetate, the resulting complexes (1a-Cu, 1b-Cu and 1c-Cu) undergo a phase transition, exhibiting monotropic nematic and smectic A mesophases. Both the original compounds and their copper complexes exhibit photoisomerisation behaviour due to the incorporation of azo (-N=N-) moieties, which function as photoswitchable units within the molecular structure.