Co-reactant Electrogenerated Chemiluminescence of Iridium(III) Complexes Containing an Acetylacetonate Ligand

We examine the electrogenerated chemiluminescence (ECL) of three Ir(C<^>N)(2)(acac) complexes, where acac=acetylacetonate anion and C<^>N=2-phenylpyridine (ppy), 2-phenylbenzothiazole (bt), or 2-phenylquinoline (pq) anions, with tri-n-propylamine co-reactant in acetonitrile under a range of chemical and instrumental conditions; this follows somewhat conflicting recent claims of the ECL intensities from complexes of this type. Relevant electrochemical, spectroscopic, and ECL properties are evaluated in direct comparison with those of Ir(ppy)(3) and [Ru(bpy)(3)](PF6)(2), as well as data from previous publications. DFT calculations on the Ir(C<^>N)(2)(acac) complexes show the HOMOs to be composed of both the metal and the C<^>N ligand, and the LUMOs almost exclusively on the C<^>N ligand. The ECL intensities of the Ir(C<^>N)(2)(acac) complexes (relative to [Ru(bpy)(3)](PF6)(2)) were dependent on experimental conditions and, in some cases, the ECL intensities reported for iridium complexes may have been derived using conditions that unintentionally disadvantaged the reference electrochemiluminophore.