Crystal structures of cocrystals of 2,7-dihydroxynaphthalene with isoniazid and piracetam

Cocrystals of 2,7-dihydroxynaphthalene (DHN, or naphthalene-2,7-diol) with isoniazid (pyridine-4-carbohydrazide) (INH), denoted DHN–INH [C10H8O2·C6H7N3O, (I)], and piracetam [2-(2-oxopyrrolidin-1-yl)acetamide] (PIR), denoted DHN–PIR [C10H8O2·C6H10N2O2, (II)], were obtained by the solvent-assisted grinding method and characterized by IR spectroscopy, powder X-ray diffraction and single-crystal X-ray diffraction. Cocrystal (I) crystallized in the triclinic space group P\overline{1} and showed a 2:2 stoichiometry. DHN and INH molecules are connected by O—H...N(pyridine) and O—H...N(hydrazide) hydrogen bonds. Cocrystal (II) crystallized in the space group Pca21 with a 1:1 stoichiometry. DHN and PIR molecules are connected by O—H...O=C hydrogen bonds. The supramolecular architecture of cocrystal (I) showed interlinked supramolecular tapes; meanwhile, in cocrystal (II), interlinked supramolecular sheets were observed.

A strategy to construct fluorescent non-aromatic small-molecules: hydrogen bonds contributing to the unexpected fluorescence

Propanedioyl dihydrazide (PDH), traditionally believed to be non-fluorescent, was first discovered to emit substantial fluorescence in both the solid state and solvents.

Stacking among the clips of the poly-aromatic rings of phenazine with hydroxy-aromatics and photophysical properties

Clip-like arrangements of molecules in the cocrystals of phenazine with hydroxy-aromatics in their respective self-assemblies and photophysical properties were presented. Phenazine cocrystals with 1,2-dihydroxybenzene provided assembly with butterfly-like arrangements. In these cocrystals, the phenazine molecules occurred in parallel pairs having extensive π-stacking. The clip-like cocrystals with 1,3-dihydroxybenzene also exhibited parallel pairs of phenazine molecules that were parallel cofacial π-stacked. The hydrated cocrystals of phenazine with 1,2,3-trihydroxybenzene had chains of parallel cofacial phenazine rings having three distinguishable π-separation distances among the centroids of the phenazine rings. Also, 2,7-dihydroxynaphthalene formed a clip-like cocrystal with phenazine, which encapsulated an additional molecule of phenazine. This cocrystal also provided chain-like parallel arrangements of the phenazine molecules. The emission and quantum yields of the cocrystals were determined by the integrating sphere method, which indicated that only the cocrystal of phenazine with 2,7-dihydroxynaphthalene showed monomer-like emission of phenazine and the rest of the cocrystals were in a quenched state. In the solution phase, quenching of the emission of hydroxynaphthalene was observed when phenazine was added to an independent solution of 2,7-dihydroxynaphthalene or another hydroxynaphthalene. However, when hydroxybenzenes were added to a solution of phenazine, fluorescence enhancements of phenazine occurred due to photo-electron transfer.

π-Stackings control the photoluminescence efficiencies in solids, whereas in solutions, the ON or OFF processes are dependent on the hydroxyaromatics.