Effects of a semi-fluorinated side chain and a lateral polar group on mesomorphic properties of 5-cyanotroponoids and benzonitriles

Abstract

A semi-fluorinated side chain and a lateral polar group were introduced into 5-cyanotroponoids and benzonitriles to investigate effects on their thermal behaviours. The semi-fluorinated side chain induced mesophases when the corresponding non-fluorinated derivatives were non-mesomorphic, changed the kind of mesophases and/or made mesomorphic compounds non-mesomorphic. A formyl group at the C-3 position of the benzonitrile ring of 4-benzoylaminobenzonitrile derivatives made thermal behaviours almost identical to those of 2-benzoylamino-5-cyanotroponoids, where intramolecular hydrogen bonding between the amide proton and the tropone carbonyl group took part in formation of the flat core structure. The intramolecular hydrogen bonding between the lateral formyl group and the amide proton of 4-benzoylaminobenzonitriles restricted the free rotation around the C–N bond between the nitrogen atom and the benzonitrile ring to make the molecule structure flat, which enhanced the lateral overlap between neighbouring molecules to induce and enhance mesomorphic properties.

Keywords:

• 5-cyanotroponoid and benzonitrile liquid crystals
• semi-fluorinated side chains
• lateral polar substituents
• intramolecular hydrogen bonding