Electrogenerated chemiluminescence of cyclometalated iridium(III) complexes with derived β-acetylacetone as ancillary ligand

Abstract

Two cyclometalated iridium(III) complexes, (pq)2Ir(sa) and (pq)2Ir(psa), with 2-phenylquinoline (pq) as the C^N main ligand and succinylacetone (sa) or 4,6-dioxo-6-phenylhexanoic acid (psa) as the O^O ancillary ligand, were synthesized at first time. The solubility was reached down to 0.1mM for (pq)2Ir(sa) and 10μM for (pq)2Ir(psa) in acetonitrile-water (v/v=5:95) solution. The photophysical, electrochemical and electrogenerated chemiluminescence (ECL) properties of (pq)2Ir(sa) and (pq)2Ir(psa) in acetonitrile were mainly investigated. The oxidation peak potential of (pq)2Ir(sa) and (pq)2Ir(psa) appears at +0.79V and +0.8V vs SCE. (pq)2Ir(sa) and (pq)2Ir(psa) display orange ECL emission with a maximum wavelength at 621nm and 610nm, respectively. ECL efficiencies of (pq)2Ir(sa) and (pq)2Ir(psa) in acetonitrile containing tripropylamine were calculated to be 21.3-folds and 35.4-folds higher than that of Ru(bpy)32+. It was surprised to find that small amount of water can greatly increase the ECL intensity of these two complexes in acetonitrile containing tripropylamine. The ECL methods for the determination of trace water in organic solvent were developed in the range from 0.02 to 4.0% (v/v) and 0.05 to 4.0% (v/v) with detection limit of 0.01% and 0.03% for (pq)2Ir(sa) and (pq)2Ir(psa), respectively. It was found that the O^O ancillary ligand played a key function in the water-enhanced ECL emission. A double coreactant ECL pathway is proposed for the water-enhanced ECL emission. This work demonstrates that (pq)2Ir(sa) and (pq)2Ir(psa) have lower potential and high ECL coefficient, which are promising for the effective use as ECL emitter in analytical application.