A helix inversion from the temperature-dependent intramolecular chiral conflict

Abstract

A new liquid crystal, cholesteryl (S)-4′-(2-methylbutyl)biphenyl-4-carboxylate (CB15-COOChol*), has been designed, synthesised and characterised. CB15-COOChol* exhibits multiple liquid crystalline phases: smectic A (SmA), nematic (N) and chiral nematic (N*). When CB15-COOChol* is heated, two N* phases exhibiting opposite handedness (N_R* and N_L*) and opposite temperature dependence of the helical pitch separated by an N phase are observed above the SmA phase. The entire rare phase transition sequence can be described as crystalline Cr→SmA→N_R*→N→N_L*→I isotropic. The helix inversion behaviour occurs mainly due to the temperature-dependent intramolecular chiral conflict between the (S)-4′-2-methylbutyl and cholesteryl ester moieties with opposite handedness and opposite temperature dependence of the helical twisting power value.

Keywords:

• (S)-4′-2-methylbutyl
• cholesteryl ester
• chiral nematic liquid crystal
• helix inversion
• chiral conflict

Acknowledgements

This work was supported by the National Natural Science Fund for Distinguished Young Scholars (Grant No. 51025313), the National Natural Science Foundation (Grant No. 50973010), the Science and Technology Project of Beijing, China (Grant No. D090803044209001), the Research Fund of the State Key Laboratory for Advanced Metals and Materials and the Open Research Fund of the State Key Laboratory of Bioelectronics (Southeast University).