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Abstract: We have reported a theoretical analysis of a series of heteroleptic iridium(III) complexes (mpmi)2Ir(pybi) [mpmi=1-(4-tolyl)-3-methyl-imidazole, pybi=2-(pyridin-2-yl)-benzo[d]imidazole] (1a), (fpmi)2Ir(pybi) [fpmi=1-(4-fluoro-phenyl)-3-methyl-imidazole] (1b), (tfpmi)2Ir(pybi) [tfpmi=1-methyl-3-(4-trifluoromethyl-phenyl)-imidazole] (1c), (pypmi)2Ir(pybi) [pypmi=3-(3-methyl-imidazol)-pyrazole] (2a), (phpymi)2Ir(pybi) [phpymi=3-(3-methyl-imidazol)-5-phenyl-pyrazole] (2b), and (inpymi)2Ir(pybi) [inpymi=3-(3-methyl-imidazol)-indeno[1,2-c]pyrazole] (2c) by using the density functional theory (DFT) method to investigate their electronic structures and photophysical properties and obtain further insights into the phosphorescent efficiency mechanism. By changing cyclometalated ligands, the conjugation length, and substituents of the cyclometalated ligands, one can tune the emission color from green (λ em=520nm) to orange (λ em=592nm). Complexes 1a, 1b, 2a, and 2b have the almost identical emission wavelength about 550nm, while 592nm for 1c and 520nm for 2c are red shifted and blue shifted, respectively, relative to 1a. The calculated results indicate that, for 1b and 1c, the substituents of −F and −CF3 at the phenyl moiety cause a poor hole-injection ability compared with that of 1a. For all these complexes studied, the hole-transporting performances are better than the electron-transporting ones. The difference between reorganization energies for hole transport (λ ih) and reorganization energies for electron transport (λ ie) for complex 1c are relatively smaller, indicating that the hole and electron transfer balance could be achieved more easily in the emitting layer. The alteration of cyclometalated ligands with different conjugation lengths and substituents has an impact on the optoelectronic properties of these complexes. It is believed that the larger metal to ligand charge transfer (MLCT) character, the highest and values, and the smallest value could result in the larger phosphorescent quantum efficiency for 2c than other complexes. [Copyright &y& Elsevier]

Theelectronic structures and phosphorescent properties of a seriesof heteroleptic iridium(III) complexes (mpmi)2Ir(dmpypz)(1; mpmi = 1-(4-tolyl)-3-methylimidazolium, dmpypz =3,5-dimethyl-2-(pyrazol-3-yl)pyridine), (bpmi)2Ir(dmpypz)(2; bpmi = 1-biphenyl-4-yl-3-methylimidazole), (dfmi)2Ir(dmpypz) (3; dfmi = 1-(2,6-difluorobiphenyl)-3-methylimidazole),(mtmi)2Ir(dmpypz) (4; mtmi = 1-methyl-3-(4′-(trifluoromethyl)biphenyl-4-yl)imidazole),(fmmi)2Ir(dmpypz) (5; fmmi = 1-(fluoren-2-yl)-3-methylimidazole),and (mhmi)2Ir(dmpypz) (6; mhmi = 1-methyl-3-phenanthren-2-ylimidazole)have been investigated by using density functional theory (DFT) andtime-dependent density functional theory (TDDFT) methods. The influenceof different substituent groups and π-conjugation degrees onthe optical and electronic properties of Ir(III) complexes was alsoexplored by introducing phenyl, fluorophenyl, (trifluoromethyl)phenyl,and rigid construction on the phenylimidazole moiety of a cyclometalatedligand (C∧C) in complex 1. The calculatedresults show that the lowest energy absorption wavelengths of complexes 1–6are 387, 380, 378, 375, 391, and 384nm, respectively. The introduction of different substituent groupsleads to different degrees of red shift for complexes 2–6in emission spectra in comparison with thatof complex 1. It is believed that the highest tripletmetal to ligand charge transfer 3MLCT (%) contribution,smallest ΔES1–T1and higher μS1values,and larger 3MC–3MLCT energy gap for 3ensure its higher quantum yield in comparison with thatof other complexes. [ABSTRACT FROM AUTHOR]