DFT and TD-DFT Study on the Electronic Structures
and Phosphorescent Properties of a Series of Heteroleptic Iridium(III)
Complexes
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Abstract
The
electronic structures and phosphorescent properties of a series
of heteroleptic iridium(III) complexes (mpmi)<sub>2</sub>Ir(dmpypz)
(<b>1</b>; mpmi = 1-(4-tolyl)-3-methylimidazolium, dmpypz =
3,5-dimethyl-2-(pyrazol-3-yl)pyridine), (bpmi)<sub>2</sub>Ir(dmpypz)
(<b>2</b>; bpmi = 1-biphenyl-4-yl-3-methylimidazole), (dfmi)<sub>2</sub>Ir(dmpypz) (<b>3</b>; dfmi = 1-(2,6-difluorobiphenyl)-3-methylimidazole),
(mtmi)<sub>2</sub>Ir(dmpypz) (<b>4</b>; mtmi = 1-methyl-3-(4′-(trifluoromethyl)biphenyl-4-yl)imidazole),
(fmmi)<sub>2</sub>Ir(dmpypz) (<b>5</b>; fmmi = 1-(fluoren-2-yl)-3-methylimidazole),
and (mhmi)<sub>2</sub>Ir(dmpypz) (<b>6</b>; mhmi = 1-methyl-3-phenanthren-2-ylimidazole)
have been investigated by using density functional theory (DFT) and
time-dependent density functional theory (TDDFT) methods. The influence
of different substituent groups and π-conjugation degrees on
the optical and electronic properties of Ir(III) complexes was also
explored by introducing phenyl, fluorophenyl, (trifluoromethyl)phenyl,
and rigid construction on the phenylimidazole moiety of a cyclometalated
ligand (C<sup>∧</sup>C) in complex <b>1</b>. The calculated
results show that the lowest energy absorption wavelengths of complexes <b>1</b>–<b>6</b> are 387, 380, 378, 375, 391, and 384
nm, respectively. The introduction of different substituent groups
leads to different degrees of red shift for complexes <b>2</b>–<b>6</b> in emission spectra in comparison with that
of complex <b>1</b>. It is believed that the highest triplet
metal to ligand charge transfer <sup>3</sup>MLCT (%) contribution,
smallest Δ<i>E</i><sub>S<sub>1</sub>–T<sub>1</sub></sub> and higher μ<sub>S<sub>1</sub></sub> values,
and larger <sup>3</sup>MC–<sup>3</sup>MLCT energy gap for <b>3</b> ensure its higher quantum yield in comparison with that
of other complexes
