Theoretical Design Study on the Electronic Structures and Phosphorescent Properties of Four Iridium(III) Complexes

<div><p>The geometry structures, electronic structures, absorption, and phosphorescent properties of four Ir(III) complexes have been investigated using the density functional method. Calculations of ionization potential (IP) and electron affinity (EA) were used to evaluate the injection abilities of holes and electrons into these complexes. The result also indicates that the –CF₃ substituent group on the ligand not only change the character of transition but affect the rate and balance of charge transfer. The lowest energy absorption wavelengths are located at 428 nm for <b>1a</b>, 446 nm for <b>1b</b>, 385 nm for <b>2a</b>, and 399 nm for <b>2b</b>, respectively, in good agreement with the energy gap (Δ<i>E</i>_L-H) trend because the HOMO–LUMO transition configurations are predominantly responsible for the <i>S</i>₀→<i>S</i>₁ transition. <b>2b</b> has the 433 nm blue emission, which might be a potential candidate for blue emitters in phosphorescent dopant emitters in organic light emitting diodes (OLEDs). The study could provide constructive information for designing novel OLEDs materials in the future.</p><p><i>[Supplemental materials are available for this article. Go to the publisher's online edition of Molecular Crystals and Liquid Crystals to view the free supplemental file.]</i></p></div

DFT and TD-DFT Study on the Electronic Structures and Phosphorescent Properties of a Series of Heteroleptic Iridium(III) Complexes

The electronic structures and phosphorescent properties of a series of heteroleptic iridium­(III) complexes (mpmi)₂Ir­(dmpypz) (<b>1</b>; mpmi = 1-(4-tolyl)-3-methylimidazolium, dmpypz = 3,5-dimethyl-2-(pyrazol-3-yl)­pyridine), (bpmi)₂Ir­(dmpypz) (<b>2</b>; bpmi = 1-biphenyl-4-yl-3-methylimidazole), (dfmi)₂Ir­(dmpypz) (<b>3</b>; dfmi = 1-(2,6-difluorobiphenyl)-3-methylimidazole), (mtmi)₂Ir­(dmpypz) (<b>4</b>; mtmi = 1-methyl-3-(4′-(trifluoromethyl)­biphenyl-4-yl)­imidazole), (fmmi)₂Ir­(dmpypz) (<b>5</b>; fmmi = 1-(fluoren-2-yl)-3-methylimidazole), and (mhmi)₂Ir­(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^∧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 ³MLCT (%) contribution, smallest Δ<i>E</i>_S₁–T₁ and higher μ_S₁ values, and larger ³MC–³MLCT energy gap for <b>3</b> ensure its higher quantum yield in comparison with that of other complexes

Theoretical study on the electronic structures and phosphorescent properties of a series of iridium(III) complexes with N^C^N-coordinating terdentate ligands

<p>The geometry structures, electronic structures, absorption, and phosphorescent properties of a series of iridium(III) complexes with the structure Ir(N^C^N)(N^C)Cl, (N^C^N represents a terdentate coordination with different substituent groups C₂H₅ (<b>1</b>), NH₂ (<b>2</b>), CH₃ (<b>3</b>), H (<b>4</b>), CN (<b>5</b>), NO₂ (<b>6</b>), and CF₃ (<b>7</b>), N^C is 2-phenylpyridine) have been investigated using the density functional theory and time-dependent density functional theory. Calculations of ionisation potential and electron affinity were used to evaluate the injection abilities of holes and electrons into these complexes. The lowest energy absorption wavelength calculated is in good agreement with the experimental value. The lowest energy emissions of complexes <b>1</b>−<b>7</b> are localised at 552, 559, 549, 517, 627, 788, and 574 nm, respectively, at CAM-B3LYP level. For complexes <b>1</b> and <b>3</b>, the calculated results showed a lower and larger ³MLCT contributions and higher values, which could result in the larger <i>k</i>_r value than those of other complexes. It is anticipated that the theoretical studies can provide useful information for designing and synthesising the candidated phosphorescent material for use in the organic light-emitting diodes.</p