Influence of peripheral alkyl chain length on the mesomorphic behaviours of hexasubstituted triphenylene 2,3-dicarboxylic esters

ABSTRACT

A comparative study of our established synthetic approaches to hexasubsituted triphenylenes 2,3-dicarboxylic esters containing four identical β-alkoxy and two adjacent β-alkoxycarbonyl side chains shows that the phase behaviours of small-sized discotic liquid crystals can be tailored over a wide range by simply varying the length of the peripheral alkyl chains. All the prepared esters in two series were observed to form a single hexagonal columnar phase, except for Tp4-1 having four β-butyloxy and two adjacent β-methoxycarbonyl chains which displays two columnar mesophase behaviours with a transition from the columnar plastic phase to hexagonal columnar phase. A significant difference between the two mesophase was observed in the variable temperature X-ray diffraction studies, and the mesophase assignment was also confirmed by polarising optical microscopy and differential scanning calorimetry. Moreover, the prepared esters in each series display the general trend of decreasing clearing temperature upon increasing alkoxy or alkoxycarbonyl chains length. The intermediate triphenylene 2,3-dicarboxylic acids were also found not only to exhibit columnar hexagonal mesophase over a narrower temperature range by maintaining high melting and clearing points but also to form organogel on mixing with toluene or dichloromethane with the assistance of hydrogen bonding.

GRAPHICAL ABSTRACT

KEYWORDS:

• Hexasubstituted triphenylene2
• 3-dicarboxylic ester
• discotic liquid crystal
• columnar plastic phase
• hydrogen bonding

Acknowledgements

This work was supported by the National Natural Science Foundation of China: [Grant Numbers 21072140, 51273133 and 21402187]; the Key Research and Development Projects in Sichuan Province: [Grant Number 2017SZ0075]; and the Sichuan Province Higher Education System Key Laboratory of Advanced Functional Materials: [Grant Number KFKT2014-03].

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by the Key Research and Development Projects in Sichuan Province: [Grant Number 2017SZ0075]; the Sichuan Province Higher Education System Key Laboratory of Advanced Functional Materials: [Grant Number KFKT2014-03]; and the National Natural Science Foundation of China: [Grant Numbers 21072140, 21402187, 51273133].