AIE active Schiff base derived Pd(II) complex as a ratiometric sensor for fluoride ion

A tripodal AIE active Schiff base (L4) was synthesized and utilized along with pyridine for the synthesis of Pd(II) metal complex (MH1) using a two-step process. X-ray diffraction studies were performed to establish the molecular geometry of the synthesized ligand (L4) and its metal complex (MH1), which revealed square planar geometry for the Pd(II) complex. DFT studies revealed a reduction in HOMO-LUMO gap upon complexation of the ligand with Pd(II) ion. The compound L4 displayed aggregation induced emission and viscosity induced emission enhancement was observed in MH1. The developed metal complex was utilized for the sensitive and selective recognition of F⁻ ion through a ligand exchange reaction. A ratiometric “turn-off” response along with colorimetric change are the characteristic features of the Pd(II) complex (MH1). The probe revealed a binding constant of 1.4 * 10⁷ M⁻¹ as calculated using Benesi-Hildebrand equation. Moreover, the binding stoichiometry in the MH1-F⁻ complex was found to be 1:1. The sensing mechanism was established using mass spectrometry as the presence of fluoride incorporated complex was noticed. The structure of the resulting complex was also established using DFT based studies.