Synthesis and study of three hydroxypyrazole-based ligands: A ratiometric fluorescent sensor for Zn(II)

The coordination and photochemical properties of three hydroxypyrazole-based ligands - tert-butyl 2-[1-[3-(4-cianophenyl)-5-hydroxy-1-phenyl-1H-pyrazol-4-yl]ethylidene]hydrazinecarboxylate (L1), tert-butyl 2-[1-[3-(3,5-bis(trifluoromethyl)phenyl)-5-hydroxy-1-phenyl-1H-pyrazol-4-yl]ethylidene]hydrazinecarboxylate (L2), and tert-Butyl 2-[1-[3-(phenantrene-9-yl)-5-hydroxy-1-phenyl-1H-pyrazol-4-yl]ethylidene]hydrazinecarboxylate (L3) - are reported. The ligands are fluorescent and able to coordinate a Zn(II) ion in a water/acetonitrile solvent with concomitant keto-enol tautomerism, giving rise to large Stokes shifts in the emission spectra. Ligand L1 has a peculiar double emission and can be exploited as a ratiometric fluorescent sensor.