Gang Zhang

Theoretical investigation of photophysical properties for a series of iridium(III) complexes with different substituted 2,5-diphenyl-1,3,4-oxadiazole

A quantum chemical investigation from structural and electronic properties and some charge-transport parameter viewpoints was performed on several homoleptic iridium complexes [(C∧N)2Ir(pic)] with the 2,5-diaryl-1,3,4-oxadia-zoles moiety in C∧N ligands, where pic represents the picolinate ancillary ligand. Complex 2 exhibits its blue phosphorescent emission with maxima at 485 nm. Furthermore, to obtain the mechanism of high phosphorescence yield in 2, we estimated the radiative rate constant kr, the contribution of 3MLCT in the T1 state, S1–T1 energy gap ΔES1–T1, and the transition dipole moment in the S0 → S1 transition μS1 for 2. Comparison of calculated results for the four complexes shows that the designed complex 2 may possess higher photoluminescent quantum efficiency than the others, making it a potential candidate as an efficient blue-emitting material.

Theoretical investigation of the effects of N-substitution on the photophysical properties of two series of iridium(III) complexes

Based on the complexes [Ir(dfb-pz)2(tfmtyp)] (1) and [Ir(tfmfb-pz)2(tfmtyp)] (2) [dfb-pz = 2,4-difluorobenzyl-N-pyrazole; tfmtyp = 2-(5-trifluoromethyl-[1,2,4]triazol-3-yl)-pyridine; tfmfb-pz = 2-tri-fluoromethyl-5-fluorobenzyl-N-pyrazole], two series of Ir(III) complexes have been designed by substituting “CH” groups with the N atom at -a, -b, -c, and -d positions on the pyridine moiety in N^N ligands. The electronic structure, absorption and emission spectra as well as phosphorescence efficiency of all these Ir(III) complexes were investigated by using density functional theory (DFT) and time-dependent DFT (TDDFT) methods. The calculated results show that the assumed complexes 1a and 2a may possess a higher photoluminescent quantum efficiency than other complexes and are potential candidates as efficient blue-emitting materials. This study shows that the N substitution can tune the emission color of 1 and 2 and enhance the photoluminescence quantum efficiency.

Theoretical study and rate constant calculation of the CH2O+CH3 reaction

The potential energy surface of the CH2O+CH3 reaction is explored at the MP2/6-311++G(d,p), MP4SDQ/6-311G(d,p), and QCISD(T)/6-311+G(3df,2p) (single point) levels of theory. Theoretical calculations suggest that the major product channel (R1) is the hydrogen abstraction leading to the product P1u2009CHO+CH4 (R1), while the addition process leading to P2H+CH3CHO (R2) appears to be negligibly small. The calculated enthalpies and dissociation activation energies for CH3CH2O and CH3OCH2 radicals involved in the reaction are in line with the experimental values. Dual-level dynamics calculation is carried out for the direct hydrogen abstraction channel. The energy profile of (R1) is refined with the interpolated single-point energies (ISPE) method at the QCISD(T)//MP2 level. The rate constants, which are evaluated by canonical variational transition-state theory (CVT) including small-curvature tunneling (SCT) correction, are in good agreement with the available experimental data. It is shown that tunneling effect p...

Shedding light on the photophysical properties of iridium(III) complexes with a dicyclometalated phosphate ligand via N-substitution from a theoretical viewpoint

The geometrical structures and phosphorescence efficiency of two series of iridium(III) complexes with wide-range color tuning have been focused on in this work. A DFT/TDDFT (density functional theory/time-dependent density functional theory) investigation on the electronic structure in the ground and lowest triplet excited states, the frontier molecular orbitals, the absorption spectra, and phosphorescence properties of 1–1d and 2–2d has been performed to get a better understanding of the relationship between the structure and property. Importantly, the nature of the N-substituents can influence the electron density distributions of frontier molecular orbitals and their energies, resulting in a change in transition character and emission color, while the attached –CF3 or –C(CH3)3 group on the triazole moiety has an impact on the radiative decay constants of all the complexes. The higher quantum yields of 1a, 1c, 2a, and 2c compared to 1b, 1d, 2b, and 2d can be explained by their larger separation between 3MLCT/π → π* and 3MC d–d states, and the designed 1a and 2a with high quantum efficiency are considered to be potential candidates for deep blue and blue-emitting materials, respectively.

Theoretical investigation on the electronic structures and phosphorescent properties of a series of cyclometalated platinum(II) complexes with different substituted N-heterocyclic carbene ligands

ABSTRACT A series of substituted platinum(II) complexes with a chelating N-heterocyclic carbene (NHC) ligand and a bidentate monoanionic auxiliary ligand (acetylacetone) have been investigated by using the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods, to explore their electronic structures, absorption and emission properties, and phosphorescence quantum efficiency. The influence of different substituted groups on photophysical properties of complexes studied has been detailedly analyzed. The lowest energy absorption and emission wavelengths calculated are comparable to the available experimental values. In addition, ionization potential (IP), electron affinities (EA), and reorganization energy (λ) were obtained to evaluate the charge transfer and balance properties between hole and electron. The calculated results also show that, due to a lower , larger3MLCT contribution, and higher value, the complex 5 owns possibly the largest kr value among these complexes. The theoretical studies could provide useful information for the candidated phosphorescent platinum(II) material for use in the organic light-emitting diodes.

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

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 complexes 1−7 are localised at 552, 559, 549, 517, 627, 788, and 574 nm, respectively, at CAM-B3LYP level. For complexes 1 and 3, the calculated results showed a lower and larger 3MLCT contributions and higher values, which could result in the larger kr 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.

Theoretical Investigation on the Electronic Structures and Optoelectronic Properties of a Series of Platinum(II) Complexes with Different Substituent Groups

A theoretical investigation was performed on a series of platinum(II) complexes with the dipivaloylmethane as ancillary ligand and tetrahydroquinolines with different substituent group (–CF3, –CN, –H, –CH3, and –OCH3) as C^N cyclometalating ligand. The geometry structures, electronic structures, absorption, and phosphorescent properties of these platinum(II) complexes have been investigated. Ionization potential and electron affinity were calculated to evaluate the injection abilities of holes and electrons into these complexes. The lowest energy absorption wavelengths are located at 362 nm for 1, 372 nm for 2, 361 nm for 3, 361 nm for 4, and 355 nm for 5, respectively. The lowest energy emissions of these complexes are localized at 520, 544, 513, 519, and 523 nm, respectively, for complexes 1–5, simulated in CH2Cl2 medium at M062X level. The calculated results indicate that the complex 2 possibly possesses the largest kr value among the five complexes. It is expected that the study can be useful for designing and synthesizing the new phosphorescent OLEDs materials.

Theoretical Studies on the Electronic Structures and Phosphorescence Properties of Three Heteroleptic Cyclometalated Iridium(III) Complexes

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 in 3 also 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).

Theoretical study on the electronic structures and phosphorescent properties of four Ir(III) complexes with different substituents on the ancillary ligand

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 –CF3 has no obvious effect on absorption and emission properties, while the substitutive group –N(CH3)2 with 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.

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

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 1a, 446 nm for 1b, 385 nm for 2a, and 399 nm for 2b, respectively, in good agreement with the energy gap (ΔEL-H) trend because the HOMO–LUMO transition configurations are predominantly responsible for the S0→S1 transition. 2b 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. [Supplemental materials are available for this article. Go to the publishers online edition of Molecular Crystals and Liquid Crystals to view the free supplemental file.]