Dual-Responsive Luminescent Iridium(III) Complex-Based Sensors for Simultaneous and Selective Detection of Fluoride...

In this study, we report the design and synthesis of two luminescent polypyridyl iridium(III) complexes, [Ir(C^N)₂(N^N)]Cl (Ir1 and Ir2), for the simultaneous detection of Al³⁺ and F^- ions. In these complexes, C^N represents a cyclometalated 2-phenylbenzimidazole (Ph-benz) ligand, while N^N corresponds to 2,2'-bipyridine derivatives, specifically, 2,2'-bipyridine-4,4'-dicarboxylic acid in Ir1 and diethyl[2,2'-bipyridine]-4,4'-dicarboxylate in Ir2. The interaction of the ─NH group of Ph-benz and the ─COOH group of the bipyridine ligand with F^- and Al³⁺ ion induces distinct photoluminescence changes, enabling selective and sensitive detection of both analytes. Ir1 and Ir2 exhibit detection limits of 0.09 µM and 0.44 µM for F^-, and 0.008 µM and 0.06 µM for Al³⁺, respectively. Mechanistic investigations, supported by computational analysis, reveal that F^--induced deprotonation of the Ph-benz ─NH and bipyridine ─COOH groups modulates the lowest-energy electronic transitions, thereby altering the photophysical properties. Additionally, Al³⁺ binds at distinct coordination sites on Ir1 and Ir2, leading to divergent photoluminescence responses. Both probes exhibit excellent luminescence reversibility upon sequential addition of F^- and Al³⁺, underscoring their reusability and cost-effectiveness. Notably, Ir1 displays visible luminescence switching observable by the naked eye. These findings establish Ir1 as promising dual-ion luminescent sensors for potential applications in environmental monitoring and biomedical diagnostics.