Ionic liquid adsorbate enhanced electrogenerated chemiluminescence of ruthenium, osmium, and iridium complexes in water

The electrochemistry, UV–vis absorption, photoluminescence (PL) and coreactant electrogenerated chemiluminescence (ECL) of Ru(bpy)32+ (where bpy = 2,2′-bipyridine), (bpy)2Ru(DM-bpy)2+ (DM-bpy = 4,4′-dimethyl-2,2′-bipyridine), (bpy)2Ru(DC-bpy)2+ (DC = 4,4′-dicarboxy-2,2′-bipyridine), Os(phen)2(dppene)2+ (phen = 1,10-phenanthroline; dppene = 1,2-cis-bis-2-diphenylphosphinoethylene), and Ir(ppy)3 (ppy = 2-phenylpyridine) have been obtained in aqueous solution containing the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([emim][EtSO4]). Tri-n-propylamine (TPrA) was used as the oxidative–reductive ECL coreactant. Minor shifts in the RuII/RuIII oxidation potential and no shifts in UV–vis absorbance and photoluminescence emission maxima are observed in the presence of 0.3% (v/v) [emim][EtSO4]. However, dramatic increases in ECL intensities between 2.4 and 3.5-fold are observed when [emim][EtSO4] is present for the ruthenium systems. Experiments indicate that adsorption of the IL occurs at the electrode surface, favoring the co-localization of luminophore and coreactant within the adsorbate layer (solid-phase co-extraction), leading to higher ECL intensities. Ir(ppy)3 and Os(phen)2(dppene)2+ are poorly soluble in aqueous solution. However, when these compounds are placed in aqueous solution containing trace amounts of [emim][EtSO4], adsorption onto the electrode takes place, yielding ECL intensity increases of ∼27- and 5-fold, respectively.

► A water soluble ionic liquid (IL) enhances electrogenerated chemiluminescence (ECL).
► Adsorption of the IL on the electrode occurs, allowing Reagent pre-concentration.
► Both water soluble and relatively insoluble luminophores display enhanced ECL.