Luminescent iridium(III) complexes featuring cyclometalated 2-phenylbenzimidazole and bipyridine-based ancillary ligands were developed for the simultaneous and rapid detection of F⁻ and Al³⁺ ions in aqueous media. These probes exhibited excellent sensitivity, selectivity, reversibility, and reusability underscoring their potential as efficient sensors for the target ions.

Abstract

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.