Tubular and lamellar hydrogen-bonding molecular assemblies of isophthalic acid derivatives bearing a –CONHCnH2n+1 chain

Abstract

Isophthalic acid derivatives (CnIP), bearing alkylamide chains (–CONHC_nH_2n+1: n = 6, 10, 14, and 18) at the 5-position that can participate in hydrogen bonding, were prepared and evaluated for their hydrogen-bonding molecular assembly structures for organogelation and liquid crystal formation. The hydrogen-bonding carboxylic acid (–COOH) groups form a ring-shaped (CnIP)₆ hexamer or a one-dimensional (1D) zig-zag (CnIP)_∞ chain. Although neither organogelation nor liquid crystal formation was observed in the isophthalic acid derivative bearing an alkoxy (–OC₁₄H₂₉) chain, C14IP and C18IP derivatives could form both organogel and liquid crystal states through intermolecular N–H⋯O = amide-type hydrogen-bonding interactions. A discotic hexagonal columnar liquid crystal (Col_h) phase was observed in hydrated (C14IP)₆·(H₂O)_n and (C18IP)₆·(H₂O)_n, whereas a lamella-type liquid crystal (L_a) phase was confirmed in the unhydrated C18IP. In the Col_h phase, O–H⋯O hydrogen-bonding ring-shaped (C14IP)₆ and (C18IP)₆ hexamers assembled to form the tubular molecular assembly stabilized by intermolecular–N–H⋯O = hydrogen-bonding interactions along the tube growth direction, where H₂O molecules were contained within the hydrophilic space. On the other hand, the N–H⋯O = hydrogen-bonding interactions between the 1D zig-zag (CnIP)_∞ chains formed a layer-type molecular assembly of the L_a-phase in the absence of water molecules.