Red-orange emissive cyclometalated neutral iridium(III) complexes and hydridoiridium(III) complex based on 2-phenylquinoxaline : Structure, photophysics and reactivity of acetylacetone towards cyclometalated iridium dimer

Abstract

A new series of heteroleptic cyclometalated iridium(III) complexes has been synthesized and characterized by absorption, emission and cyclic voltammetry studies: (pqx) 2Ir(acac) (1), (dmpqx) 2Ir(acac) (2) and (dfpqx)2Ir(acac) (3) where pqx=2-phenylquinoxalinate, dmpqx=2-(2,4- dimethoxyphenyl)quinoxalinate, dfpqx=2-(2,4-difluorophenyl) quinoxalinate and acac=acetylacetonate anion. The reaction of excess acetylacetone with μ- chloride-bridged dimeric iridium complex, [(C∧N) 2Ir(μ-Cl)] 2, gives a complex 1 and an unusual hydridoiridium(III) complex, (pqx)IrH(acac) 2 (4). The complex 1, 2 and 3 show their emissions in an orangered region (λ PL,max = 583-616 nm), and the emission maxima can be tuned by the change of substituent at phenyl ring of 2-phenylquinoxaline ligand. The phosphorescent line shape indicates that the emissions originate predominantly from 3MLCT states with little admixture of ligand-based 3(π-π *) excited states. The structures of complex 3 and 4 are additionally characterized by a single crystal X-ray diffraction method. The complex 3 shows a distorted octahedral geometry around iridium(III) metal ion. A strong trans influence of the phenyl ring is examined. In complex 4, there are two discrete molecules which are mirror images each other at the ratio of 1:1 in an unit cell. We propose that the phosphorescent complex 1, 2 and 3 are possible candidates for the phosphors in OLEDs applications.