Tailoring Thermotropic Mesophase Morphologies by Molecular Recognition and Fluorophobic Effect

An alkoxyphenyl-substituted melamine derivative has been investigated in binary mixtures with two-chain and three-chain semiperfluorinated benzoic acids. Equimolar mixtures of the melamine with the complementary benzoic acids form discrete hydrogen-bonded heterodimers with elongated central core. The dimeric supermolecules involving two-chain partially fluorinated acids organize to infinite bilayer ribbons composed of distinct lipophilic, H-bonded polar aromatic and fluorinated regions, respectively. The two-dimensional lattice symmetry of the ribbon phases, rectangular or oblique, are defined by the positions of the fluorinated chains at the phenyl ring of the acid component. Heterodimers of the melamine with a three-chain partially fluorinated benzoic acid display a hexagonal columnar phase consisting of extended columnar aggregates with circular shape with a distinct lipophilic region in the center surrounded by side-by-side arranged H-bonded polar rodlike segments and, finally, by a shell of fluorinated fragments. Additionally, a cubic phase is observed at more elevated temperatures above the Col h phase. Docking of 2 or 3 equiv. of the two-chain benzoic acids to the melamine core leads to the formation of cylindrical aggregates with a polar hydrogen-bonded aromatic center surrounded by lipophilic alkyl segments and an outer sphere of fluorinated molecular blocks. The aggregates organize to hexagonal columnar mesophases.