Influence of polar substituents and flexible chain length on mesomorphism in non-mesogenic linear hydrogen bonded complexes

• Published in: Journal of molecular liquids 2021-08, Vol.336, p.116313, Article 116313
• Main Authors: Bhagavath, Poornima, Mahabaleshwara, S., Bhat, Sangeetha G., Potukuchi, D.M., Shetty, Prakasha, Maddasani, Srinivasulu
• Format: Article
• Language: English
• Subjects: Dihalobenzoic acids; Hydrogen bonding; Induced mesomorphism; Linear HB complexes; Polar substituents; Pyridyl units; Smectic phases
• ISSN: 0167-7322
• DOI: 10.1016/j.molliq.2021.116313

•The dihalobenzoic acids and the pyridyl units are non-mesogenic but their 1:1 binary mixtures are mesogenic.•The dihalobenzoic acid HB complexes are rich in mesomorphism than the corresponding monohalobenzoic acid complexes.•The PyBnA:4Cl2FBA complexes are rich in mesomorphism than the corresponding PyBnA:2,4-diClBA complexes.•The size of the halo substituent at ortho position influences the induced mesomorphism. Liquid Crystalline (LC) behavior is observed in the mixtures of low molecular weight dihalobenzoic acids viz., 2,4-dichlorobenzoic acid and 4-chloro-2-fluorobenzoic acid and the Schiff’s base pyridyl units, viz., (4-pyridyl)-benzylidene-4ʹ-n-alkyl anilines (heptyl, decyl, dodecyl, tetradecyl and hexadecyl homologues, PyBnA) in 1:1 M ratio. The dihalobenzoic acids and the pyridyl moieties are non-mesogenic, but their equimolar (1:1) mixtures exhibit liquid crystalline behavior through intermolecular hydrogen bonding (HB), which is characterized by the infrared spectroscopy. The dihalobenzoic acids are the proton donors, while the pyridyl units are proton acceptors and are found to undergo self-assembly. The dihalobenzoic acid HB complexes are found to exhibit higher liquid crystallinity than the corresponding mono halo substituted benzoic acid HB complexes with the same pyridyl units. The 4-chloro-2-fluorobenzoic acid HB complexes exhibit large mesomorphic state than the 2,4-dichlorobenzoic acid HB complexes with the same pyridyl moieties. The thermal range of the HB complexes are found to exhibit an increasing trend initially, followed by a decreasing tendency with the increase of chain length of the proton acceptors. The HB complexes of the decyl homologue of the proton acceptor (PyB10A) is found to show high liquid crystallinity in both the series. The influence of the moieties on melting and clearing temperatures is discussed in the wake of results in other liquid crystalline series.