Hockey-stick indoles: turning a calamitic neutral mesogen into an ionic liquid crystal

ABSTRACT

Novel hockey-stick-shaped mesogens were synthesised via tricyclic bromoindoles as key intermediates. Mesomorphic properties were investigated by differential scanning calorimetry, polarising optical microscopy and X-ray diffractometry (WAXS and SAXS). While the attachment of 4-alkoxyphenyl, 3,4-dialkoxyphenyl or 3,4,5-trialkoxyphenyl to the tricyclic bromoindole did not lead to mesomorphic hockey sticks, elongation of the ‘stick’ by a 4-dodecycloxybiphenyl unit provided liquid crystalline hockey sticks with monotropic nematic phases. By attaching an N-methyl-imidazolium head group via a flexible hexyl spacer to the indole N-atom instead of the ethylcarbamate protecting group, hockey stick ionic liquid crystals were obtained, which showed SmA phases but suffered from thermal decomposition due to the high clearing points.

Graphical abstract

KEYWORDS:

• Indole
• calamitic
• hockey-stick mesogen
• ionic liquid crystal

Acknowledgements

Generous financial support by the Deutsche Forschungsgemeinschaft (grant # LA907/17-1, LA907/17-2), the Ministerium für Wissenschaft, Forschung und Kunst des Landes Baden-Württemberg and the Carl-Schneider-Stiftung Aalen (shared instrumentation grant) is gratefully acknowledged.

Disclosure statement

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

Additional information

Funding

This work was supported by the Deutsche Forschungsgemeinschaft [LA907/17-1, LA907/17-2]; Ministerium für Wissenschaft, Forschung und Kunst Baden-Württemberg; Carl-Schneider-Stiftung Aalen.