Strict steric requirements for the formation of helical mesophases consisting of H-bonded supramolecules

The possibility of achieving chiral helical superstructures in the columnar mesophase of H-bonded complexes of 2,4,6-triarylamino-1,3,5-triazines and chiral benzoic acids is pursued in this work. A series of heterodimeric complexes have been prepared and their mesomorphic states studied by polarized optical microscopy, differential scanning calorimetry, X-ray diffraction, and circular dichroism. It is concluded that steric requirements strongly influence the mesomorphism of these H-bonded complexes. Hence, well-defined columnar arrangements, characterized by high transition enthalpies and a large number of X-ray diffraction rings, are exhibited by complexes with a given number of peripheral tails and a steric compromise between the sizes of the triazine and the acid partners. Optical activity derived from a chiral columnar organization within the mesophase appears for these well-defined hexagonal columnar mesophases.