A Porphyrin-based NIR Fluorescent Probe for Bi³⁺ and Potential Applications

Herein, we have prepared a 5,10,15,20-Tetrakis(4-hydroxyphenyl) porphyrin (P) which acts as a probe for selective and sensitive detection of Bi³⁺ ions. Probe P was obtained by reacting pyrrole with 4-hydroxyl benzaldehyde and characterized by NMR, IR, and ESI-MS. All photo-physical studies of P were tested in DMSO:H₂O (8:2, v/v) media by spectrophotometry and spectrofluorometry respectively. The selectivity of P was tested with different metal ions in solution as well as in the solid phase, only Bi³⁺ showed red fluorescence quenching while with other metal ions, no such effect was observed. The Job's plot unveiled the 1:1 stoichiometric binding ratio of the probe with Bi³⁺ and anticipated association constant of 3.4 ×10⁵ M^-1, whereas the Stern-Volmer quenching constant was noticed to be 5.6 ×10⁵ M^-1. Probe P could detect Bi³⁺ down to 27 nM by spectrofluorometric. The binding mechanism of P with Bi³⁺ was well supported with NMR, mass, and DFT studies. Further, the P was applied for the quantitative determination of Bi³⁺ in various water samples and the biocompatibility of P was examined using neuro 2A (N2a) cells. Overall, probe P proves promising for the detection of Bi³⁺ in the semi-aqueous phase and it is the first report as a colorimetric and fluorogenic probe.