On the Fluorescent, Steric and Electronic Factors Affecting the Detection of Metallic Ions Using an Imidazolyl-Phenolic Derived Fluorescent Probe

The imidazolyl-phenolic probe used at the present study has its photophysic properties regulated by a tautomeric equilibrium. After the absorption of a photon, an excited state intramolecular proton transfer process generates a ketonic species, responsible for the 440 nm emission (in CH₃CN/H₂O, 95:5, v/v). Addition of Cu²⁺, Al³⁺, Cr³⁺ and Fe³⁺ suppresses emission through a combination of dynamic and static-like quenching, as indicated by Stern-Volmer plots, with a higher sensitivity for Cu²⁺ (K_SV = 1.90 × 10⁵ and 2.40 × 10⁴ L mol^-1, respectively, for Cu²⁺ and Fe³⁺). The trivalent ions led to the formation of a locked-enol tautomer that emits at shorter wavelengths; this coordinated compound is also quenched at metallic ions concentrations above 20 µmol L^-1, due to a collisional process. When compared to another imidazolyl-phenolic probe, experimental and simulated data revealed that fluorescent, steric and electronic effects regulate their sensitivity towards the ions.

Keywords:
ESIPT; tautomerization; fluorescent sensor; copper(II); iron(III)