Phosphorescent Chemosensor Based on Iridium(III) Complex for the Selective Detection of Cu(II) Ion in Aqueous Acetonitrile

Abstract

Cu(II) ion has two sides. In one side, Cu(II) ion is an important cofactor in nearly 20 metalloenzymes and an essential micronutrient for all living systems. But, in other side, Cu(II) ion is one of significant metal pollutants and toxic to living cells if present in slightly high concentrations, causing neurodegenerative diseases such as Menkes and Wilson’s disease. In this instance, the selective detection of Cu(II) ion in environment and in living systems is very important. Consequently, various fluorescent chemosensors for the highly sensitive and selective detection of Cu (II) ion have been developed. Phosphorescent chemosensors for the selective detection of Cu(II) ion are also attractive because long-lived phosphorescence can be discriminated readily from scattered light and short-lived background fluorescence normally present in biological samples. However, phosphorescent chemosensors for the selective detection of Cu(II) ion have been only sparingly reported. In phosphorescent chemosensors, heavymetal complexes have been widely utilized as effective phosphors. Especially, cyclometalated iridium(III) complexes, which are known as efficient phosphorescent dopants in organic light emitting diodes (OLEDs), bonded to appropriate receptors have been utilized as phosphorescent chemosensors for the selective detection of Ca(II), Hg(II) or fluoride ion. Very recently, an iridium(III) complex containing one 2-(2'-benzo[b]thienyl)pyridine (btp), two cyclometalating 2-phenylpyridine (ppy) ligands and a di(2-picolyl)amine (DPA) receptor tethered to the btp ligand by a methylene linker was reported to be an effective phosphorescent chemosensor for Cu(II) ion. In this study, we wish to prepare another iridium(III) complex-based phosphorescent chemosensor for the selective detection of Cu(II) ion. Previously, iridium(III) complex containing 3,9-dithia-6-azaundecane receptor tethered to the 2,2'-bipyridine ligand was reported to be quite successful for the selective detection Hg(II) ion. 3,9-Dithia-6-azaundecane receptor tethered to the 2,2'-bipyridine ligand in complex 1 has been proposed to be an effective receptor for Hg(II) ion. Similarly, by replacing the 3,9-dithia-6-azaundecane receptor of the previously reported complex with a DPA receptor, which has been used as an effective receptor for Zn(II) or Cu(II) ion, the resulting complex 1 (Fig. 1) was expected to be a good phosphorescent chemosensor for the selective detection of Cu(II) ion. Complex 1 was prepared as shown in Figure 1. By treating iridium(III) complex containing two cyclometalating 2-phenylpyridine (ppy) ligands and 4,4'-bis(bromomethyl)-2,2'bipyridine, which was prepared according to the procedure