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

Abstract

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.

Quantum-chemical studies of homoleptic iridium(III) complexes in OLEDs: fac versus mer isomers

“…It is known that frontier molecular orbitals (FMO) of complex ground state S 0 are related to its spectral properties [86]. Emission color of iridium(III) complexes can be adjusted by changing their HOMO-LUMO bandgap, which can be achieved on the course of ligand functionalization with electron-donating and electronwithdrawing substituents [86], and values of HOMO-LUMO gaps predicted for Ir(III) complexes by DFT methods showed surprisingly good correlation with the experimentally recorded values of energies of emitted photons even in the case of phosphorescence, see for example [21,22,[83][84][85][87][88][89][90]. Contour plots of frontier orbitals of both [Ir(bzq) 3 ] isomers are depicted in Fig.…”

Co‐Reactant and Annihilation Electrogenerated Chemiluminescence of [Ir(df‐ppy)2(ptb)]+ Derivatives

“…All structures are minima with no imaginary frequencies. Molecular orbitals were calculated at the BP86/def2‐TZVP level of theory, which has previously been demonstrated to produce reliable results . Molecular orbital analysis was carried out with the QMForge program…”

Water-Soluble Iridium(III) Complexes Containing Tetraethylene-Glycol-Derivatized Bipyridine Ligands for Electrogenerated Chemiluminescence Detection

“…Figure 8 shows the ECL intensities relative to that of the [Ru(bpy) 3 ] 2+ complex under the same conditions. The co-reactant ECL intensities of iridium(III) complexes relative to [Ru(bpy) 3 ] 2+ can be highly dependent on instrumental and chemical conditions (Chen et al, 2017). Using an applied potential pulse at [E ox p + 0.1 V] for 0.1 s, the co-reactant ECL intensities of most of the [Ir(C ∧ N) 2 (N ∧ N)] + complexes were greater than that of [Ru(bpy) 3 ] 2+ ( Figure 8A), but when the pulse time was increased to 0.5 s ( Figure 8B) the intensities were below that of [Ru(bpy) 3 ] 2+ .…”

“…Numerous cyclometalated iridium(III) complexes have been synthesized and many have shown impressive annihilation and/or co-reactant ECL intensities in organic media (Bruce and Richter, 2002;Kapturkiewicz et al, 2004;Kim et al, 2005). For example, we recently re-examined a promising series of heteroleptic iridium(III) complexes containing an acetylacetonate anion (acac) ligand, with several exhibiting much greater ECL intensities than [Ru(bpy) 3 ] 2+ (with tri-n-propylamine (TPrA) co-reactant in acetonitrile solution), although the relative intensities were highly dependent on reaction conditions (Chen et al, 2017).…”