A Solvatochromic Luminescence Color Switchable Iridium(III) Complex of a Click-generated Ligand for Nitroaromatic Explosive Detection

Abstract

Chemosensors exhibiting tunable luminescence are of considerable interest for advanced sensing applications.In this work, we report the design and synthesis of a highly orange-emissive Ir(III) complex, 1[PF₆], incorporating a click-generated triazole-based substituted phenanthroline ligand that enables selective and sensitive detection of the nitroaromatic explosive picric acid (PA). The ligand and the complex have been characterized by 1D NMR (1H, 13C) and 2D NMR (1H-1H COSY), ESI-HRMS, and single-crystal X-ray diffraction. Compound 1[PF6] exhibits pronounced solvatochromic behaviour, where upon increasing the solvent polarity, a bathochromic luminescence shifting from green to orange-red is observed. The red shifting of PL maxima of 1[PF6] in highly polar/polar protic solvents is attributed to the alteration of energy of the 3LLCT, 3LC and 3MLCT excited states. Theoretical calculations have been carried out to assign electronic transitions responsible for the observed transition bands in both the ground and excited states. Furthermore, the highly luminescent complex 1[PF6] was successfully employed for the luminescence turn-off detection of nitroaromatic explosive picric acid. Moreover, a low limit of detection (LOD) of 3.89 nM was obtained for 1[PF6]. For 1[PF6], the Stern–Volmer plot displayed a dynamic nature which was supported with emission lifetime measurements. Theoretical studies were carried out to get insight into the electronic transitions responsible for non-raditive emission in presence of PA.