Novel diphenylacetylene-based room-temperature liquid crystalline molecules with alkylthio groups, and investigation of the role for terminal alkyl chains in mesogenic incidence and tendency

ABSTRACT

In this study, we offer a new family of alkylthio-containing diphenylacetylene-based liquid crystalline molecules (the so-called tolanes) showing nematic phases stable down to room temperature and high birefringence, with insights into the role for terminal alkyl chains in mesogenic incidence and tendency. A number of asymmetric tolane homologues having various alkyl chain lengths in the alkylthio and alkyl groups at each p-, p’-position were synthesised, and their phase transition behaviour was investigated by polarising optical microscope observation, differential scanning calorimetry and wide-angle X-ray diffraction measurement. Consequently, several homologues exhibited monotropic nematic or highly ordered smectic (soft crystal) phases stable down to room temperature. It is found that a long alkyl group on the side opposite to an alkylthio group is prerequisite for mesogenic incidence. In addition, a nematogenic homologue exhibited a higher birefringence value of 0.20 compared to that of 0.19 for an alkoxy counterpart.

Graphical Abstract

KEYWORDS:

• Diphenylacetylene
• tolane
• room-temperature liquid crystal
• birefringence
• sulphur atom

Acknowledgement

The authors thank Prof. Masatoshi Tokita for WAXD and birefringence measurements.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Additional information

Funding

This work was partly supported by JSPS KAKENHI Grant numbers 15H06285 and 17K14493, Toyota Physical and Chemical Research Institute scholars and research grants from the Nitto Foundation, the Toukai Foundation for Technology and Research Foundation for the Electrotechnology of Chubu.