Water-Soluble Iridium(III) Complexes Containing Tetraethylene-Glycol-Derivatized Bipyridine Ligands for Electrogenerated Chemiluminescence Detection

Four cationic heteroleptic iridium(III) complexes containing a 2,2′-bipyridine (bpy) ligand with one or two tetraethylene glycol (TEG) groups attached in the 4 or 4,4′ positions were synthesized to create new water-soluble electrogenerated chemiluminescence (ECL) luminophores bearing a convenient point of attachment for the development of ECL-labels. The novel TEG-derivatized bipyridines were incorporated into [Ir(C(∧)N)(2)(R-bpy-R′)]Cl complexes, where C(∧)N = 2-phenylpyridine anion (ppy) or 2-phenylbenzo[d]thiazole anion (bt), through reaction with commercially available ([Ir(C(∧)N)(2)(μ-Cl)](2) dimers. The novel [Ir(C(∧)N)(2)(Me-bpy-TEG)]Cl and [Ir(C(∧)N)(2)(TEG-bpy-TEG)]Cl complexes in aqueous solution largely retained the redox potentials and emission spectra of the parent [Ir(C(∧)N)(2)(Me-bpy-Me)]PF(6) (where Me-bpy-Me = 4,4′methyl-2,2′-bipyridine) luminophores in acetonitrile, and exhibited ECL intensities similar to those of [Ru(bpy)(3)](2+) and the analogous [Ir(C(∧)N)(2)(pt-TEG]Cl complexes (where pt-TEG = 1-(TEG)-4-(2-pyridyl)-1,2,3-triazole). These complexes can be readily adapted for bioconjugation and considering the spectral distributions of [Ir(ppy)(2)(Me-bpy-TEG)](+) and [Ir(ppy)(2)(pt-TEG)](+), show a viable strategy to create ECL-labels with different emission colors from the same commercial [Ir(ppy)(2)(μ-Cl)](2) precursor.