Structure, spectral-luminescent and ionochromic properties of hydroxyaryl(hetaryl)idene azomethine imines

Abstract A series of stable, potentially prototropic and ionochromic azomethine imines based on the 5-phenylpyrazolidine-3-one was synthesized and investigated. According to 1H, 13C, 15N NMR spectroscopy and X-ray diffraction data compounds containing 2,3-dihydroxynaphthalene 1, 2-hydroxynaphthalene 4 and 3-hydroxybenzo[b]thiophene 5 substituents exist in the enol E form, whereas compounds with 3-methyl-5-phenylpyrazole-1-one 3 and indan-1,3-dione 6 substituents prefer keto K tautomeric forms. The DFT B3LYP/6-31++G (d,p) calculations of relative stability of tautomers of the studied azomethine imines are in agreement with the experimental findings. Azomethine imines 1, 4 and 5 represent ion-active “naked-eye” switches of spectral properties in the presence of F−, AcO− and H2PO4− anions.