Self‐ordered states derived from 2‐benzoyloxy‐ and 2‐benzoylamino‐5‐cyanotroponoids and their corresponding benzenoids: formation of hexagonal self‐assembly of liquid crystalline 2‐trialkoxybenzoylamino‐5‐cyanotroponoids in gel states through intramolecular hydrogen bonding and π–π interaction*

*. Dedicated to the late Professor Naomi Miyazima.

Abstract

Two ring systems constructed by a cyanotropone ring and a benzoyl group with a mono‐, di‐, and tri‐alkoxyl group, linked by an ester or amide group, and the corresponding benzenoids were synthesised to investigate mesomorphic properties. Both troponoid esters and amides with a monoalkoxybenzoyl group and the corresponding benzenoids had smectic A phases. Troponoid esters and amides with a di‐ and trialkoxybenzoyl group exhibited smectic A and hexagonal columnar phases, respectively. However, the corresponding benzenoids with a di‐ and trialkoxybenzoyl group did not exhibit any mesophases. Interestingly, only the mesomorphic troponoid amides with a trialkoxybenzoyl group showed gelling ability. Non‐mesomorphic troponoid amides with a trialkoxybenzoyl group, troponoid amides with mono‐ and dialkoxyl groups, all troponoid esters and all benzenoid esters and amides were not gelators. It was observed that gel formation is strongly related to the formation of a hexagonal columnar phase. An X‐ray diffraction study of octanol gels showed that hexagonal packing is involved in gel formation. NMR titration experiments and IR spectral observation of octanol gels supported the fact that intramolecular hydrogen bonding between the tropone carbonyl and the NH group made the core part flat to induce effective π–π interactions, which are driving forces of gelling ability.

*. Dedicated to the late Professor Naomi Miyazima.

Keywords:

• gel formation
• intramolecular hydrogen bonding
• π–π interaction
• troponoid derivatives
• hexagonal columnar phase

Notes

*. Dedicated to the late Professor Naomi Miyazima.