Ionic iridium complexes with conjugated phenyl substituent: Synthesis and DFT calculation on the electrochemical and electrochemiluminescent properties

Two ionic iridium complexes, (bpq)(2)Ir(bpy)+PF6- (1) and (bpq - OCH3)(2)Ir(bpy)+PF6- (2), where bpq is 6-methyl-2,4-diphenyl quinolone anion, bpy is 2,2'-bipyridine, were synthesized and structurally characterized. Their photophysical, electrochemical and electrochemiluminescence properties were investigated. With the conjugated phenyl substitution, the pi-pi ligand center transitions in the emission process were enhanced, resulting in a broad and strong photoluminescence emission. The photoluminescence quantum yields were measured to be 0.214, 0.209, respectively for complex 1 and 2. The complex 1 also exhibited greater electrochemiluminescence efficiency than the complex 2. To further elucidate the influence of different structures on the electrochemical and electrochemiluminescence properties, the density functional theory calculations were performed on the complexes 1, 2 along with other four well documented bis-cyclometalated iridium complexes. The calculation revealed that about 90% electronic density in the lowest unoccupied molecular orbital were distributed in N boolean AND N auxiliary ligand for ionic complexes, whereas most electronic density were distributed in C boolean AND N main ligand for neutral complexes. (C) 2014 Elsevier Ltd. All rights reserved.