A Fluorenone Derived Schiff Base as a Selective Colorimetric Sensor for Copper Ions and its Applications

Abstract

AbstractIn this study, a naked‐eye colorimetric probe (L) was synthesized by condensation reaction of 9‐fluorenone with 2‐thiophene carboxylic acid hydrazide and characterized by various analytical techniques. The presence of O, N, and S heteroatoms in L would modulate the hard and soft characters, which is responsible for selective complexation of Cu2+ and fluorenone act as signalling unit. The sensing ability of L was studied with various metal ions by colorimetric, test paper strip, and UV‐visible spectrophotometry in DMSO: H2O (6 : 4, v/v). The colorless solution L turned green upon interacting with Cu2+ ions, while other ions did not change color. The probe L exhibits an absorbance band at 354 nm; upon interaction with Cu2+ ions, it exhibits a band at 413 nm due to ligand‐to‐metal charge transfer (LMCT). The probe L binds Cu2+ in a 2 : 1 stoichiometric ratio with an association constant of 3.76×107 M−2, established using Job's and BindFit methods. Further, binding mechanism is supported by EPR and ESI studies. The probe L can work in the pH range of 3.0 to 7.5 and detect as low as 93 nM (6 ppb) by spectrophotometry. Probe L demonstrates a promising potential for detecting Cu2+ ions in the semi‐aqueous medium.