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Abstract
Ten new non-symmetric liquid crystal dimers belonging to the family of compounds α-(4-benzylidene-substituted-aniline-4′-oxy)-ω-(2-methylbutyl-4′-(4″-phenyl)benzoateoxy)-alkanes have been synthesised and their transitional properties characterised. The dimers contain either a hexamethylene or octamethylene spacer, while the terminal substituents on the 4-benzylideneaniline fragment are H, CH3, F, Cl and Br. The unsubstituted dimers are not liquid crystalline, while the remaining compounds exhibit enantiotropic nematic behaviour. The trends in the clearing temperatures, according to the chemical nature of the terminal substituent, are largely consistent with those established for conventional low molar mass liquid crystals. Three of the dimers also exhibit an intercalated smectic A phase, specifically the two bromo-substituted dimers and the chloro-substituted dimer containing a hexamethylene spacer. The driving force for the formation of this phase is considered to be, at least in part, the specific anisotropic interaction between the unlike mesogenic units. The absence of smectic behaviour for the isosteric methyl-substituted dimers reveals that steric factors alone cannot stabilise the intercalated smectic A phase.
Acknowledgements
The corresponding author (G.-Y. Yeap) wishes to thank the Malaysian government, and in particular the Higher Education Ministry and the Ministry of Science, Technology and Innovation (MOSTI), for financial support through the provision of the Fundamental Research Grant Scheme (FRGS Grant No. 203/PKIMIA/671025), as well as eScience (Grant No. 305/PKIMIA/613328). The indirect contribution from staff in the Research and Creativity Management Office (RCMO) of the Universiti Sains Malaysia has also been essential to ensure the success of this project.