Cholesterol-based nonsymmetric dimers comprising phenyl 4-(benzoyloxy)benzoate core: the occurrence of frustrated phases

ABSTRACT

The synthesis and mesomorphism of sixteen new nonsymmetric liquid crystal dimers formed by covalently attaching cholesterol with a three-ring mesogenic core, namely, phenyl 4-(benzoyloxy)benzoate, via an ω-oxyalkanoyl spacer are described. The lengths of the terminal chain attached to the three-ring core, as well as those of the ω-oxyalkanoyl spacer, have been varied; accordingly, they have been grouped into four sets. They display an enantiotropic chiral nematic (N*) behaviour with the isotropization temperature crossing over 200 ^oC. Four dimers having an odd-parity spacer were found to additionally show blue phase-I/II (BP-I/II), and the smectic A (SmA) phase. Twelve dimers with an even-membered spacer also stabilise either chiral smectic C (SmC*) or twist grain boundary (TGB) phase having SmC* slabs (TGBC* phase). The dimers with longer spacer and terminal tail favour the formation of the TGBC* phase. Thus, the lengths of both the terminal tail and the central spacer are seen to direct the type of mesophase and liquid crystal phase sequences to be formed. X-ray diffraction measurements have been carried out on representative samples to corroborate the structure of the mesophases. The N* phase has been probed with the aid of CD technique to figure out the handedness of the helicoidal structure.

Graphical Abstract

KEYWORDS:

• Liquid crystals
• dimers
• frustrated phases
• chiral nematic phase
• chiral smectic c phase
• twist grain boundary phase

Acknowledgments

C.V.Y. gratefully acknowledges and expresses his profound gratitude to the Science and Engineering Research Board Established (SERB), Department of Science & Technology (DST), Government of India, for granting a research project, bearing SERB number CRG/2020/001779, for carrying out the work presented herein.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the DST, SERB, Government of India [CRG/2020/001779].