Developing long-lifetime luminescent Ir(III) complexes for facile detection of pesticide residue in complex matrices

To develop long-lifetime luminescent Iridium(III) [Ir(III)] complexes, two novel series (a1-a4 and b1-b4) were designed and synthesized, and their structure-photophysical property relationships were systematically investigated. Notably, introducing a sulfur (S) atom simultaneously extends the luminescence lifetime and enhances the quantum yield of these complexes. Among them, b3 stands out as an exceptional time-resolved emission spectroscopy (TRES) probe due to its prolonged lifetime and high quenching efficiency by polydopamine (PDA). By leveraging dual mechanisms, PDA-mediated quenching of b3 and thiocholine (TCh)-inhibited dopamine (DA) polymerization, a sensitive luminescent platform for malathion (MAL) detection was developed. The resulting detection platform achieves an ultra-low limit of detection (LOD) 0.32 nM within a linear range of 0.001-15.0 μM. Notably, the long-lived b3 (τ = 1.665 μs) permits effective MAL detection even in a highly fluorescent RhB matrix using TRES (LOD = 13.2 nM), whereas steady-state emission spectra (SSES)-based detections fail under such conditions. The successful application of b3 in real-sample analysis demonstrates the great potential of Ir(III) complexes in TRES-based detection. This work not only expands the repertoire of TRES probes but also presents a highly effective luminescent platform for pesticide detection.