Effect of Co-Crystal Formers on the Supramolecular Patterns and Luminescence Properties of Co-Crystals Comprising Fenbufen and Diverse N-Heterocycles

Abstract

Four co-crystals [(2-apy)·(Fbf)] (1), [(2-apz)·(Fbf)] (2), [(4,4′-bipy)·2(Fbf)] (3), and [(4,4′-bpe)·2(Fbf)] (4) (Fbf = fenbufen, 4-(4-biphenylyl)-4-oxobutyric acid, 2-apy = 2-aminopyridine, 2-apz = 2-aminopyrazine, 4,4′-bipy = 4,4′-bipyridine, 4,4′-bpe = trans-1,2-bis(4-pyridyl)ethene) have been obtained from the reaction of Fbf and different N-heterocycles by either liquid-assisted grinding method or solution evaporation, and characterized by elemental analysis, infrared spectroscopy, differential scanning calorimetry, photoluminescence spectroscopy, and powder- and single-crystal X-ray diffraction. Structural analyses indicate that conformations of Fbf molecules are highly related to the lone pair···π, C–H···π, or C–H···O interactions, which lead to the formation of different dihedral angles in the four planes in Fbf. With these non-covalent interactions, Fbf presents trans conformation in compounds 1, 3, 4, and cis conformation in compound 2. Interestingly, the packing diagrams of compounds 1 and 2 are very similar to the different trigonometric functions. Compounds 3 and 4 exhibit discontiguous packing diagrams with short snake-shaped chains owing to the higher symmetry of 4,4′-bipy and 4,4′-bpe molecules. Moreover, the differential scanning calorimetry analyses indicate the lower melting point of all compounds when compared with that of free Fbf. Luminescence investigation shows that only compound 1 exhibits strong blue emission in the solid state at room temperature.