A Porous Aromatic Framework Functionalized with Luminescent Iridium(III) Organometallic Complexes for Turn-On Sensing of ⁹⁹TcO₄^–

Contamination of ⁹⁹TcO₄^–, a problematic radioactive anion in the nuclear fuel cycle, in groundwater has been observed in a series of legacy nuclear sites, representing a notable radiation hazard and environmental concern. The development of convenient, rapid, and sensitive detection methods is therefore critical for radioactivity control and remediation tasks. Traditional detection methods suffer from clear demerits of either the presence of large interference from coexisting radioactive species (e.g., radioactivity counting methods) or the requirement of extensive instrumentation and analysis procedure (e.g., mass spectrometry). Here, we constructed a luminescent iridium­(III) organometallic complex (Ir­(ppy)₂(bpy)⁺; ppy = 2-phenylpyridine, bpy = 2,2^′-bipyridine)-grafted porous aromatic framework (Ir-PAF) for the first time, which can be utilized for efficient, facile, and selective detection of trace ReO₄^–/TcO₄^– in aqueous solutions. Importantly, the luminescence intensity of Ir-PAF is greatly enhanced in the presence of ReO₄^–/TcO₄^–, giving rise to a distinct turn-on sensor with the detection limit of 556.9 μg/L. Such a superior detection capability originates from the highly selective and strong interaction between ReO₄^–/TcO₄^– and Ir­(ppy)₂(bpy)⁺, leading to an efficient pre-enrichment of ReO₄^–/TcO₄^– during analysis and subsequently a much weaker nonradiative decay of the luminescence of Ir­(ppy)₂(bpy)⁺, as illustrated by density functional theory (DFT) calculation as well as quantum yield and fluorescence lifetime measurements. Successful quantification of trace ReO₄^– in simulated Hanford low-activity waste (LAW) solution containing large excess of Cl^–, NO₃^–, and NO₂^– was demonstrated, highlighting the bright future of luminescent PAFs in the area of chemical sensing.