Synthesis and optical behaviour of hydrogen-bonded liquid crystals based on a chiral pyridine derivative

Abstract

Three series of cholesteryl-containing supramolecular hydrogen-bonded (H-bonded) liquid crystal (LC) complexes with different number of fluoro-substituent were synthesised and characterised. Cholesteryl isonicotinate as proton acceptor and 4-n-alkoxybenzoic acids with or without fluoro-substituent as proton donor had been mixed in tetrahydrofuran to obtain H-bonded LC complexes. The effect of lateral substitution and the length of terminal chain in the H-bonded precursors on the formation of the supramolecular complexes had been examined. It was found that the introduction of fluoro substituent on the induced mesogens could widen the molecular width and thus reduce the molecular aspect ratio of the complexes, therefore it could lead to compress the formation of the LCs. However, the fluoro substituent played a positive role in enhancing the intermolecular interactions and stabilising the H-bond structure of the complexes. The influence of terminal length on the mesogenic behaviours is also discussed. On increasing the spacer length, the clear point and the thermal range of induced mesophase-like cholesteric phase decreased, and an induced chiral smectic phase began to appear in some complexes with long terminal tails.

Keywords:

• liquid crystal
• hydrogen bond
• self-assembly
• fluoro-substitution
• cholesteryl

Acknowledgements

This research was supported by the China Postdoctoral Science Foundation (Grant No. 20100470205), the National Natural Science Foundation Youth Fund of China (Grant No. 61007016), the National Natural Science Fund for Distinguished Young Scholars (Grant No. 51025313), the National Natural Science Foundation (Grant No. 50973010), the Flat-Panel Display Special Project of China 863 Plan (Grant No. 2008AA03A318) and the Science and Technology Project of Beijing, China (Grant No. D090803044209001).