Sodium ion chemosensor of 3-oxo-3H-benzo[f]chromene-2-carboxylic acid: An experimental and computational study

A fluorescence compound with the typical skeleton of benzocoumarin was synthesized and its interaction with various metal ions was evaluated. The synthesis was performed via Knoevenagel condensation whereas identification of the product was accomplished by various spectroscopic techniques. The chemosensor test against representative metal ions was monitored by fluorescence spectrophotometry. A density functional theory calculation (DFT, functional/basis set; M06/6-31G (d, p)) was also performed to clarify the experimental results and to confirm the mechanism of interaction. 3-Oxo-3H-benzo[f]chromene-2-carboxylic acid 1 was obtained as a yellow solid in 60 % chemical yield. Melting point; 235.6-236.7 degrees C and lambda(max) UV/Vis, lambda(em) and Stokes shift (MeOH, nm) of 374, 445 and 71 nm, respectively. The structure of the compound was identified based on spectroscopic data and literature comparison. Compound 1 exhibited a chelation quenched fluorescence (CHQF) phenomenon selectively toward the Na+, with a binding stoichiometry (1:2) and LoD and LoQ of 0.14 and 0.48 mg/L, respectively. Based on DFT calculations, compound 1 chelated Na+ through mechanism of oxidative (1:1 equivalent) and reductive (2:1 equivalent) photoinduced electron transfer (PET), correspondingly.