Smectic behaviour of methyl 4-alkoxybenzoates with a partially fluorinated alkyl chain

ABSTRACT

A series of 4-alkoxybenzoic acids 1[m,n] and their methyl esters 2[m,n] containing a partially fluorinated alkyl chain was prepared and their physical properties were investigated by optical, thermal and powder X-ray diffraction (XRD) methods. The former exhibits an SmC phase, while the latter form an SmA phase. XRD analysis indicated liquid-like character of the linking alkyl chains, and showed a decreasing layer thermal expansion coefficient from positive to negative upon increasing the degree of fluorination. The new esters 2[m,n] expanded the series and permitted analysis of trends in thermal stability of the SmA phase. The results demonstrate that the SmA–I transition temperature increases by about +20 K per CF₂CF₂ unit, and is destabilised by –5.6 K upon extending the hydrocarbon part by each CH₂CH₂ group. Data for the expanded series 2[m,n] were used for comparative analysis of mesogenic behaviour in two other series of derivatives of 1[m,n]. Synthetic methods for 1[m,n] and 2[m,n] are reviewed.

Graphical Abstract

KEYWORDS:

• Synthesis
• fluorination
• smectic phases
• powder XRD
• structure–property relationship

Acknowledgement

This work was supported by the National Science Centre grants (2013/09/B/ST5/01230 and 2014/13/B/ST5/04525).

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by the National Science Centre grants (2013/09/B/ST5/01230 and 2014/13/B/ST5/04525).