Smectic nanoclusters in the nematic mesophases of dimeric compounds composed of rod-like azo moieties with lateral substituents

Monika M., Arun Roy and Veena Prasad
New J. Chem., 41, 11576-11583 (2017)

The first photochromic liquid crystalline dimers forming smectic nano clusters in the nematic mesophases and capable of forming organogels have been reported. Here, two rod-like non-mesogenic laterally substituted azo moieties are connected to each other by an alkylene spacer through ester linkages. In all these dimers, the end alkoxy chain length is kept constant and the length of the spacer chain is varied. An odd–even effect of methylene groups in the spacer chain is observed in addition to a clear effect of lateral substituents at different positions and the direction of ester linkages on the mesomorphic properties. These dimers exhibit nematic and smectic mesophases. The X-ray diffraction studies revealed that the nematic phases are composed of skewed smectic nanoclusters (NcybC) irrespective of whether a smectic phase exists below the nematic phase or not. We did not observe any bent-core phases in these dimers. They are photo-switching both in solution and in their nematic mesophases. We observed that the photo-induced effect is more pronounced in the case of dimers with an odd-spacer when compared to those with an even-spacer. Some of the dimers formed organogels with different solvents. These organogels were undergoing thermo-reversible as well as photo-reversible sol – gel transitions, a property that can be exploited for practical applications.