Water-Soluble Iridium(III) Complexes Containing Tetraethylene-Glycol-Derivatized Bipyridine Ligands for Electrogenerated Chemiluminescence Detection
Ben Newman, Lifen Chen, Luke C. Henderson, Egan H. Doeven, Paul S. Francis, David J. Hayne
Abstract
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 (-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 (-Cl)] 2 precursor.