Crown ether-containing N-salicylidene aniline derivatives: synthesis, characterization and optical properties

15-Crown-5 ether-containing N-salicylidene aniline derivatives of the common formula benzo-15-crown-5-NCH–(2-OH-aryl) [aryl = C6H4 (1), 5-ClC6H3 (2), 5-BrC6H3 (3), C10H6 (4)] have been synthesized and characterized by elemental analysis, NMR, diffuse reflectance, fluorescence, IR and Raman spectroscopies. The crystal structure of 1, elucidated by X-ray diffraction, is stabillized by an intramolecular hydrogen bond and intermolecular π⋯π stacking interactions. Molecules 1–3 are thermochromic and show the presence of a mixture of enol and cis-keto forms in the solid state at room temperature. Compound 1 displays photochromism upon irradiation at 546 nm, which is reversible and exhibits relatively quick back thermal relaxation.