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 ](PF 6 ) 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 ](PF 6 ) 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.