Molecular recognition directed self-assembly of tubular liquid crystalline and crystalline supramolecular architectures from taper shaped (15-crown-5)methyl 3,4,5-tris(p-alkyloxybenzyloxy)benzoates and (15-crown-5)methyl 3,4,5-tris(p-dodecyloxy)benzoate

Abstract

The syntheses and characterization of a series of (15-crown-5)methyl 3,4,5-tris(p-alkyloxybenzyloxy)benzoatest with alkyl tails of four 25, six 26, and twelve 27 carbon atoms and of (15-crown-5)methyl 3,4,5-tris(p-dodecyloxybenzoate)28 are described. Complexation of the crown ether endo-receptor with NaCF₃SO₃ destabilizes the crystalline phase of 25, 26, 27 and 28 and induces for the case of 27 and 28 the self-assembly of a supramolecular cylindrical channel-like architecture which displays a thermotropic hexagonal columnar (Φ_h) mesophase. Most remarkably, in the crystalline phase of the complexes of 27 with NaCF₃SO₃ the cylindrical structure of the Φ_n mesophase is maintained. Characterization of these supramolecular architectures was performed by a combination of differential scanning calorimetry (DSC), thermal optical polarized microscopy, X-ray scattering and molecular modelling. A model is proposed in which a stratum of the column is formed by six molecules of 27 and 28 with the crown ether receptors residing in the column centre and the alkyl tails radiating toward the column periphery. endo-Recognition generated via the (15-crown-5)methyl receptor upon complexation, and exo-recognition provided by the tapered 3, 4, 5tris(p-dodecyloxybenzyloxy)benzoate and 3, 4, 5-tris(p-dodecyloxy)benzoate fragments of 27 and 28 provide the driving force for the self-assembly of this cylindrical supramolecule.