engleski

Aromatic hydrazones derived from nicotinic acid hydrazide as fluorimetric pH sensing molecules: structural analysis by computational and spectroscopic methods in solid phase and in solution

Structural analyses of aroylhydrazones were performed by computational and spectroscopic methods (solid state NMR, 1 and 2D NMR spectroscopy, FT-IR (ATR) spectroscopy, Raman spectroscopy, UV-Vis spectrometry and spectrofluorimetry) in solid state and in solution. The studied compounds were N'-(2, 3- dihydroxyphenylmethylidene)-3- pyridinecarbohydrazide (1), N'-(2, 5- dihydroxyphenylmethylidene)-3- pyridinecarbohydrazide (2), N'-(3-chloro-2- hydroxy-phenylmethylidene)-3- pyridinecarbohydrazide (3), and N'-(2-hydroxy- 4-methoxyphenyl-methylidene)-3- pyridinecarbohydrazide (4). Both in solid state and in solution, all compounds were in ketoamine form (form I, –CO–NH–N=C–), stabilized by intramolecular H-bond between hydroxyl proton and nitrogen atom of the C=N group. In solid state, the C=O group of 1–4 were involved in additional intermolecular H- bond between closely packed molecules. Among hydrazones studied, the chloro- and methoxy- derivatives have shown pH dependent and reversible fluorescence emission connected to deprotonation/protonation of salicylidene part of the molecules. All findings acquired by experimental methods (NMR, IR, Raman, and UV- Vis spectra) were in excellent agreement with those obtained by computational methods.

1D and 2D NMR ; FT-IR ; Raman ; UV-Vis spectroscopy ; fluorescence ; computational study ; fluorimetric pH sensors

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