Search

To investigate the influence of the different substituents in the main ligands on the electronic structures, phosphorescent properties, and organic light-emitting devices (OLEDs) performance, three iridium(III) complexes 1, 2, and 3 are studied by means of the density functional theory/time-dependent density functional theory (DFT/TDDFT). Ionization potential, electron affinities, and reorganization energy have also been obtained to evaluate the charge transfer and balance properties between hole and electron for the three complexes. The lowest energy absorption wavelength calculated for complex 1 is in very good agreement with the experimental value. The lowest energy emissions of complexes 1, 2, and 3 are localised at 492, 565, and 510 nm, respectively, at M052X level. It is expected that this work might provide a way to develop potential iridium(III) phosphors with good electroluminescent performance. [ABSTRACT FROM AUTHOR]

A DFT/TDDFT investigation has been conducted on two series of cyclometalated iridium(III) complexes to shed light on the effects of structure and steric factors on the photophysical properties. The results reveal that the nature of the N substitution can influence the electron density distributions of the frontier molecular orbitals and their energies, resulting in a change in transition character and emission color. The absorption spectra of the complexes are similar to each other, with 2a- 5a and 2b- 5b presenting a slight redshift compared with their parent complexes. Again, on the basis of the calculations, the higher radiative rate constants ( kr) of 1a- 5a with respect to 1b- 5b can be explained by a larger metal contribution to the excited states (MLCT%) and larger S0-S1 transition electric dipole moments ( µ [ABSTRACT FROM AUTHOR]

The electronic and photophysical properties of a series of iridium(III) complexes based on amidate ancillary ligand have been investigated using the density functional theory (DFT) and time-dependent density functional theory (TDDFT). Ionization potential (IP), electron affinities (EA) and reorganization energy ( λ hole/electron ) have also been obtained to evaluate the charge transfer and balance properties between hole and electron. The absorption and emission properties can be altered by the different electron-withdrawing and electron-donating substituents in the N-acetylaniline. The calculated lowest energy emissions for 1 – 6 are localized at 542, 538, 535, 557, 538, and 495 nm, respectively. It can also be seen that the complex 4 and 6 have possibly the largest and smallest k r values than among these complexes. It is anticipated that the theoretical work can be useful for designing promising phosphorescent materials for use in the organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

The electronic structures and phosphorescence efficiency for two series of Ir(III) complexes with different substituent groups were theoretically investigated by using density functional theory (DFT) and time-dependent DFT (TDDFT) methods. The results reveal that the nature of the different substituents can influence the electron density distributions of frontier molecular orbitals and their energies, resulting in the change of transition character and emission color, while the different number of –(CH 2 CH 2 O)– units have an impact on the HOMO and LUMO energy levels of the designed complexes 2a – 6a and 2b – 6b . It can be speculated that the complexes 1a – 4a and 1b – 5b are considered to be potential candidates as blue-emitting materials. The assumed complexes 6a and 6b also are the potential candidate as an efficient green-emitting material with high photoluminescent quantum yield. [ABSTRACT FROM AUTHOR]

The geometry structures, electronic structures, absorption and phosphorescent properties of a series of iridium(III) complexes with the different N-substitution cyclometalating ligand and the same benzyldiphenylphosphine auxiliary ligand have been theoretically investigated by using the density functional theory method. The lowest energy absorption wavelengths are located at 378 nm for A , 430 nm for B , 411 nm for C , 436 nm for D , and 394 nm for E . The introduction of N atom substitution at 1-, 2-, 3-, and 4-positions on the pyridyl moiety of complex A leads to an obvious redshifted absorption. The lowest energy emissions for complexes A – E are localized at 450, 409, 438, 483, and 429 nm, respectively, simulated in CH 2 Cl 2 medium at M052X level. Ionization potential and electron affinity have been calculated to evaluate the injection abilities of holes and electrons into these complexes. For complex C , the calculated results showed that it can possibly possess the larger radiative decay rate ( k r ) value than those of other four complexes. It is anticipated that the theoretical studies can provide valuable information for designing new phosphorescent metal complexes of organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

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]

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(1), NH2(2), CH3(3), H (4), CN (5), NO2(6), and CF3(7), 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 complexes1−7are localised at 552, 559, 549, 517, 627, 788, and 574 nm, respectively, at CAM-B3LYP level. For complexes1and3, the calculated results showed a lowerand larger3MLCT contributions and highervalues, which could result in the largerkrvalue 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. [ABSTRACT FROM AUTHOR]

Highlights: [•] Five Ir(III) complexes have been theoretically investigated. [•] The different substituents affect the charge transfer rate and balance. [•] The calculated photophysical properties have a good agreement with the experimental data. [Copyright &y& Elsevier]

Highlights: [•] Seven tris-cyclometalated iridium(III) complexes have been theoretically studied. [•] The substituted groups have the important effect on the photophysical properties. [•] Complex 5 possibly possesses the largest k r value among the seven complexes. [ABSTRACT FROM AUTHOR]

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 –CF3substituent 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 for1a, 446 nm for1b, 385 nm for2a, and 399 nm for2b, respectively, in good agreement with the energy gap (ΔEL-H) trend because the HOMO–LUMO transition configurations are predominantly responsible for theS0→S1transition.2bhas 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. [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.] [ABSTRACT FROM PUBLISHER]

The geometry structures, electronic structures, absorption, and phosphorescence properties of three heteroleptic cyclometalated iridium(III) complexes have been theoretically investigated by the density functional theory (DFT) method. The highest occupied molecular orbital (HOMO) of the three complexes has the similar distributions on two main ligands. However, the lowest unoccupied molecular orbital (LUMO) of the three complexes has different distributions on different ligand fragments. Especially for 3, the LUMO is mainly composed of the picolinate auxiliary ligand. The lowest lying absorptions were calculated to be at 409, 473, and 414 nm for 1–3, respectively. By changing the conjugation length of the main ligand from 1 to 2, one can tune the emission color from green to red. The addition of sterically bulky phenolic substituents in3also results in an obvious red shift of the emission wavelength. The calculated results show that the absorption and emission transition character can be changed by altering the main ligands. Calculations of ionization potential (IP) and electron affinity (EA) were used to evaluate the injection abilities of holes and electrons into these complexes. The theoretical work should provide a suitable guide to the future design and synthesis of novel phosphorescent materials for use in the organic light-emitting diodes (OLEDs). [ABSTRACT FROM AUTHOR]

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]

We have reported a theoretical analysis of a series of heteroleptic iridium(iii) complexes (mpmi)2Ir(fppi) [mpmi = 1-(4-tolyl)-3-methyl-imidazole, fppi = 4-fluoro-2-(pyrrol-2-yl)-pyridine] (1a), (mpmi)2Ir(dfpi) [dfpi = 4-fluoro-2-(3-fluoro-pyrrol-2-yl)-pyridine] (1b), (mpmi)2Ir(tfpi) [tfpi = 2-(pyrrol-2-yl)-4-trifluoromethyl-pyridine] (1c), (mpmi)2Ir(priq) [priq = 1-(pyrrol-2-yl)isoquinoline] (2a), (mpmi)2Ir(isql) [isql = 1-(indol-2-yl)-isoquinoline] (2b), and (mpmi)2Ir(biql) [biql = 1-(benzoimidazol-2-yl)-isoquinoline] (2c) by using the density functional theory (DFT) method to investigate their electronic structures, photophysical properties, and the phosphorescent efficiency mechanism. The results reveal that the nature of the ancillary ligands can affect the electron density distributions and energies of frontier molecular orbitals, resulting in changes of charge transfer performances and emission color. It is found that the studied complex 1c with the –CF3 substituent at the pyridine moiety results in the lower HOMO–LUMO energy gap and LUMO energy level, which will lead to a rich electron injection ability compared with that of 1a. For each complex studied (except 2b), the hole-transporting performance is better than the electron-transporting performance. In addition, for complexes 2a and 2b, the differences between reorganization energies for hole transport (λih) and reorganization energies for electron transport (λie) are relatively smaller, indicating that the hole and electron transfer balance could be achieved more easily in the emitting layer. It is believed that the largest metal to ligand charge transfer (MLCT) character, the higher μS1 and ET1 values, as well as the smallest ΔES1–T1 value could result in higher phosphorescent quantum efficiency for 1b than those of other complexes. [ABSTRACT FROM AUTHOR]

The geometry structures, electronic structures, absorption and phosphorescent properties of four Ir(III) complexes {[(F2-ppy)2Ir(pta-X)], where F2-ppy = (2,4-difluoro)phenylpyridine; pta = pyridine-1,2,4-triazole;X= –CF3; –H; –CH3; –N(CH3)2}, are investigated using the density functional method. The results reveal that the electron-accepting group –CF3has no obvious effect on absorption and emission properties, while the substitutive group –N(CH3)2with strong electron-donating ability has obvious effect on the emission properties. The mobility of hole and electron were studied computationally based on the Marcus–Hush theory. Calculations of ionisation potential and electron affinity were used to evaluate the injection abilities of holes and electrons into these complexes. We hope that this theoretical work can provide a suitable guide to the future design and synthesis of novel phosphorescent materials for use in the organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

The geometry structures, electronic structures, absorption, and phosphorescence properties of four tris-cyclometalated iridium(III) complexes IrL3, that is, 1 (L = 2-(4,6-difluorophenyl)pyridinato,N,C2′), 2 (L = 2-(4,6-difluorophenyl)pyridinato,N,C2′-5-phenyl), 3 (L = 2-(4,6-difluorophenyl)pyridinato,N,C2′-5-( p-tolyl)), and 4 (L = 2-(4,6-difluorophenyl) benzo[ h]isoquinoline), have been investigated under the framework of the time-dependent density functional theory approach. For assumed 2 and 3, the emission energies are nearly the same, consistent with their similar HOMO−LUMO energy gaps. The calculated lowest energy emissions are localized at 523, 605, 616, and 642 nm for 1, 2, 3, and 4, respectively. Calculations of ionization potential and electron affinity were used to evaluate the injection abilities of holes and electrons into these complexes. For 2, the calculated results evidenced a larger 3MLCT contribution (27.0%), a large S0 → S1 transition dipole moment () of 1.43 D, and a small S1−T1 splitting energy () of 0.33 eV, which could result in a large radiative decay rate ( kr). We hope that this theoretical work can provide a suitable guide to the future design and synthesis of novel phosphorescent materials for use in the organic light-emitting diodes. [ABSTRACT FROM AUTHOR]

Abstract: We report a quantum-chemistry study of electronic structures and spectral properties of four Ir(III) complexes Ir[2-(2,4-di-X-phenyl)pyridine]2(picolinate), where X=–CH3 (1), –H (2), –CN (3), –NO2 (4). The absorption and emission spectra were calculated based on the optimized ground state and excited state geometries, respectively, by means of the time-dependent density functional theory (TDDFT). The effect from the electron-withdrawing and electron-donating substituents on charge injection, transport, absorption, and phosphorescent properties has been investigated. The absorption and emission properties can be altered by the different electron-withdrawing and electron-donating groups. Besides, ionization potential (IP), electron affinities (EA) and reorganization energy (λ hole/electron) were obtained to evaluate the charge transfer and balance properties between hole and electron. The calculated results show that the different substitute groups affect the charge transfer rate and balance. It can be anticipated that the complexes 3 and 4 have good charge transport rates and balance between the hole and electron. [Copyright &y& Elsevier]

Abstract: We report a quantum-chemistry analysis of four heteroleptic iridium(III) complexes (tfmppy)2Ir(tpip) [tfmppy=4-trifluoromethylphenylpyridine, tpip=tetraphenylimido-diphosphinate] (1), (tfmpyN3)2Ir(tpip) [tfmpyN3 =4-trifluoromethylphenyl-[1,2,3]-triazole] (2), (CN-pyN3)2Ir(tpip) [CN-pyN3 =4-cyanophenyl-[1,2,3]-triazole] (3) (ph-pta)2Ir(tpip) [ph-pta=2-(5-phenyl-[1,2,4]-triazol-3-yl)-pyridine] (4), which have been studied by using density functional theory (DFT) and time-dependent DFT (TDDFT) methods, to investigate their electronic structures, injection and transport properties, absorption and phosphorescence mechanism. The results reveal the different cyclometalated ligands have a large impact on the charge transfer performances of the studied complexes. The complex 4 possess better charge transfer abilities and balanced charge transfer rates, which is a potential candidate as blue-emitting material. [Copyright &y& Elsevier]

The influence of different substituent groups and π-conjugation degree on the optical and electronic properties of six Ir(III) complexes has been theoretically studied. The injection abilities of holes and electrons into these complexes have been evaluated with the ionization potential and electron affinity. The lowest energy absorption wavelengths calculated for these complexes are in good agreement with the available experimental values. The lowest energy emissions of these complexes are localized at 569, 584, 634, 554, 569, and 851 nm, respectively. The study could provide good information for designing the potential phosphorescent material for use in the organic light-emitting diodes. [ABSTRACT FROM AUTHOR]