Supramolecular mesomorphic structures based on 2,5-dialkoxyterephthalicacid derivatives

Abstract

Self-assembly of 2,5-di-n-alkoxyterephthalic acids (C_nOTpA) and 2,5-di-n-hexylterephthalic acid (C₆TpA) as bifunctional hydrogen bond donors with bifunctional acceptors 1,3-diaminopropane (Dap), piperazine (Pip) and 4,4′-bipyridine (Bipy) has been investigated, both in the crystal lattice and in the mesophase. Stoichiometric mixtures of compounds C_nOTpA with diamine Dap form mesophases with a lamellar-type structure and constitute, to the best of our knowledge, the first examples of the generation of mesophases from 2,5-di-n-alkoxyterephthalic acids and bifunctional diamines. The liquid crystalline behaviour of these mixtures was characterized using X-ray scattering, DSC and polarizing microscopy. The self-assembly of complexes C₆TpA·Bipy and C₆TpA·Pip in the crystal lattice was characterized using single crystal X-ray structural analysis. In the crystal lattice of C₆TpA·Bipy, only hydrogen bonding interactions between the neutral acid and the base were observed. However, in the crystal structure of cocrystals of C₆TpA with Pip, an ionic interaction was observed due to proton transfer from the acid group to the basic nitrogen atoms of the base.