A highly selective and sensitive ratiometric chemodosimeter for Hg2+ ions based on an iridium(iii) complex viathioacetal deprotection reaction

Abstract

A novel luminescent biscyclometalated iridium(III) complex [Ir(C^N)₂bpy]PF₆ (Ir-S, bpy = 2,2′-bipyridine) containing two 2-phenylpyridine (ppy) cyclometalating ligands (C^N) functionalized with 1,3-dithiane for the detection of Hg²⁺ ions has been synthesized and characterized by spectroscopic and photophysical measurements. The luminescence of Ir-S exhibits a ratiometric response upon the addition of Hg²⁺ ions. The absorption, emission, ¹H NMR and ESI mass spectral changes of Ir-S in the absence and presence of Hg²⁺ ions have all demonstrated the Hg²⁺-promoted thioacetal deprotection reaction of Ir-S and the generation of a complex [Ir(pba)₂bpy]PF₆ (Ir-CHO, Hpba = 4-(pyridin-2-yl)benzaldehyde). DFT calculation studies suggest that the dominant participation of the 1,3-dithiane group in the HOMO of Ir-S leads to different excited states and distinct excited energies of Ir-S and Ir-CHO and consequently results in their different emission properties. The titration and competition experiments significantly reveal the highly sensitive and selective properties of Ir-S as a promising indicator for Hg²⁺ ions over other metal cations.