Theoretical Studies of the Spectroscopic Properties of [Pt(trpy)C⋮CR]+ (trpy = 2,2‘,6‘,2‘ ‘-Terpyridine; R = H, CH2OH, and C6H5)

THEORETICAL COMPUTATIONAL STUDIES ON ELECTRONIC STRUCTURES, SPECTROSCOPIC PROPERTIES AND NITROGEN HETEROATOM EFFECT OF A SPECIES OF ASYMMETRICAL DIIMINE LIGAND PLATINUM(II) COMPLEXES

Electronic structures and spectroscopic properties of a series of platinum(II) complexes based on the C-linked asymmetrical diimine ligand (2-pyridyl-pyrazole (1), 2-pyridyl-1,2,4-triazole (2), 2-pyridyl-tetrazole (3), 2-pyrazine-pyrazole (4) have been studied by the time-dependent density functional theory calculations with polarizable continuum model. The ground- and excited-state structures were optimized by the density functional theory and single-excitation configuration interaction methods, respectively. The calculated structures and spectroscopic properties are in agreement with the corresponding experimental data. The results of the spectroscopic investigations revealed that the lowest-energy absorptions have1,3metal-to-ligand charge transfer (MLCT)/1,3single ligand centered charge transfer (ILCT) mixing characters. The highest-occupied molecular orbitals (HOMOs) of 1–4 are composed of Pt ( d yz) and azole, while the lowest-unoccupied molecular orbitals (LUMOs) are mainly localized upon the pyridyl-azolate ligand (70% on the pyridine segment). From 1 to 3, the molecular orbital (MO) energies of HOMO and LUMO are decreased and the HOMO energies are changed more remarkably. This is caused by that the conjugation of the azolate segment of the ligand are enhanced through introducing more N heteroatoms into this segment. As a result of MO energy change, the lowest-energy absorptions are blue-shifted in the order 1 < 2 < 3. With the replacement of pyridyl by pyrazine, the HOMO energy of 4 is comparable to 1, but the LUMO energy is decreased by 0.8 eV, and the lowest-energy absorptions are red-shifted to 2.36 eV. Otherwise, the phosphorescent emissions of these complexes have the 3MLCT/3ILCT characters, and should originate from the lowest-energy absorptions. The emissions of 1–4 are red-shifted in the order 3 < 2 < 1 < 4. The heteroatom effect is suitable for tuning the spectra of this kind of materials.

Ab initio and DFT study of luminescent cyclometalated N-heterocyclic carbene organogold(III) complexes

The structures of versatile N-heterocyclic carbene-containing Au(III) complexes in the ground and low-lying excited states have been optimized at the B3LYP functional and the single-excitation configuration interaction (CIS) method, respectively. The spectral properties are predicted with time-dependent density functional theory (TDDFT). In addition, the charge transport quality has been estimated approximately by the predicted reorganization energy (λ). As revealed from the calculations, the introduction of methyl has a bigger influence on the spectral properties than phenyl. Furthermore, we find that changing the auxiliary ligand could tune the charge transfer properties.

DFT/TD-DFT investigation on Ir(III) complexes with N-heterocyclic carbene ligands: geometries, electronic structures, absorption, and phosphorescence properties

Iridium(III) complexes with N-heterocyclic (NHC) ligands including fac-Ir(pmb)(3) (1), mer-Ir(pmb)(3) (2), (pmb)(2)Ir(acac) (3), mer-Ir(pypi)(3) (4), and fac-Ir(pypi)(3) (5) [pmb = 1-phenyl-3H-benzimidazolin-2-ylidene, acac = acetoylacetonate, pypi = 1-phenyl-5H-benzimidazolin-2-ylidene; fac = facial, mer = meridional] were investigated theoretically. The geometry structures of 1-5 in the ground and excited state were optimized with restricted and unrestricted DFT (density functional theory) methods, respectively (LANL2DZ for Ir atom and 6-31G for other atoms). The HOMOs (highest occupied molecular orbitals) of 1-3 are composed of d(Ir) and pi(phenyl), while those of 4 and 5 are contributed by d(Ir) and pi(carbene). The LUMOs (lowest unoccupied molecular orbitals) of 1, 2, 4, and 5 are localized on carbene, but that of 3 is localized on acac. The calculated lowest-lying absorptions with TD-DFT method based on Perdew-Burke-Erzenrhof (PBE) functional of 1 (310 nm), 2 (332 nm), and 3 (347 nm) have ML(carbene)CT/IL(phenyl-->carbene)CT (MLCT = metal-to-ligand charge transfer; ILCT = intraligand charge transfer) transition characters, whereas those of 4 (385 nm) and 5 (389 nm) are assigned to ML(carbene)CT/IL(carbene-->carbene)CT transitions. The phosphorescences calculated by TD-DFT method with PBE0 functional of 1 (386 nm) and 2 (388 nm) originate from (3)ML(carbene)CT/(3)IL(phenyl-->carbene)CT excited states, but those of 4 (575 nm) and 5 (578 nm) come from (3)ML(carbene)CT/(3)IL(carbene-->carbene)CT excited states. The calculated results showed that the carbene and phenyl groups act as two independent chromophores in transition processes. Compared with 1 and 2, the absorptions of 4 and 5 are red-shifted by increasing the effective pi-conjugation groups near the C(carbene) atom. We predicated that (pmb)(2)Ir(acac) is nonemissive, because the LUMO of 3 is contributed by the nonemissive acac ligand.

Theoretical Studies on Structures and Spectroscopic Properties of a Series of Novel Cationic [trans-(C∧N)2Ir(PH3)2]+ (C∧N = ppy, bzq, ppz, dfppy)

The geometries, electronic structures, and spectroscopic properties of a series of novel cationic iridium(III) complexes [trans-(C/N)(2)Ir(PH(3))(2)]+ (C/N = 2-phenylpyridine, 1; benzoquinoline, 2; 1-phenylpytazolato, 3; 2-(4,6-difluorophenyl)pyridimato, 4) were investigated theoretically. The ground- and excited-state geometries were optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ levels, respectively. The optimized geometry structural parameters agree well with the corresponding experimental results. The unoccupied molecular orbitals are dominantly localized on the C/N ligand, while the occupied molecular orbitals are composed of Ir atom and C/N ligand. Under the time-dependent density functional theory (TDDFT) level with the polarized continuum model (PCM) model, the absorption and phosphorescence in acetonitrile (MeCN) media were calculated based on the optimized ground- and excited-state geometries, respectively. The calculated results showed that the lowest-lying absorptions at 364 nm (1), 389 nm (2), 317 nm (3), and 344 nm (4) are all attributed to a {[d(yz)(Ir) + pi(C/N)] --> [pi*(C/N)]} transition with metal-to-ligand and intraligand charge transfer (MLCT/ILCT) characters; moreover, the phosphorescence at 460 (1) and 442 nm (4) originates from the 3{[d(yz)(Ir) + pi(C/N)] [pi*(C/N)]} (3)MLCT/(3)ILCT excited state, while that at 505 (2) and 399 nm (3) can be described as originating from different types of (3)MLCT/(3)ILCT excited state (3){[d(xy)(Ir) + pi(C/N)] [pi*(C/N)]}. The calculated results also revealed that the absorption and emission transition character can be altered by adjusting the pi electron-withdrawing groups and, furthermore, suggested that the phosphorescent color can be tuned by changing the pi-conjugation effect of the C/N ligand.

Highly Efficient Blue Photoexcitation of Europium in a Bimetallic Pt–Eu Complex

We report the preparation and characterization of dinuclear Pt-Ln complexes constructed from a square-planar Pt(II) core bearing an ethynyl-terpyridine residue connected to platinum by the ethynyl bond. Complexation of the neutral Eu(hfac)3 (hfac = hexafluoroacetylacetonate) fragment to free terpyridine (terpy) gives a stable bimetallic complex (log beta = 6.7). In the crystal structure, the flat Pt[triple bond]terpy core coordinates to Eu(III), which is nonacoordinated with the three nitrogen atoms of the terpy subunit and six oxygen atoms of the three hfac ligands. These atoms form a distorted monocapped square antiprism with a pseudo-C2 symmetry axis passing through the nitrogen atom of the central pyridine ring and the Eu atom. Spectroscopic measurements showed that irradiation with visible light of wavelength up to 460 nm in the 1MLCT state of the Pt subunit resulted in a quantitative energy transfer to the Eu center, which strongly luminesces in the red with an overall luminescence quantum yield of 38%. The energy-transfer process is quantitative and not sensitive to oxygen, and the complexation of Eu to the Pt metallosynthon allows the recovery of the energy lost due to triplet-oxygen quenching of the 3MLCT state observed in the uncomplexed Pt precursor.

Synthesis, structures and properties of a new series of platinum–diimine–dithiolate complexes

The new square-planar platinum-diimine-dithiolate compounds [Pt(mesBIAN)SS] have been synthesised {mesBIAN = bis(mesityl)biazanaphthenequinone; SS = 1,2-dithiooxalate (dto) , maleonitriledithiolate (mnt) , 1,2-benzenedithiolate (bdt) , 3,4-toluenedithiolate (tdt) and 1,3-dithia-2-thione-4,5-dithiolate (dmit) }, and the X-ray crystal structures of and determined. Cyclic voltammetry reveals that all the compounds form stable anions, and ESR spectroscopy of these anions shows that the SOMO is based upon the mesBIAN ligand; compounds also show a reversible oxidation wave in their CV. Computational studies reveal that charge-transfer processes from orbitals that are combinations of metal and dithiolate ligand to a mesBIAN pi-based LUMO are responsible for the low energy absorptions seen in the UV/visible spectra of these compounds, and that the reverse process is responsible for the observed room-temperature solution luminescence of [Pt(mesBIAN)Cl(2)] and , and . Compounds and , containing aromatic thiolates, were not found to luminesce under the same conditions. Resonance Raman experiments have shown the origin of band-broadening of the lowest-energy absorption band in the absorption spectra of to be due to vibronic structure within one electronic transition.

Theoretical studies on structures and spectroscopic properties of a series of novel mixed-ligand Ir(iii) complexes [Ir(Mebib)(ppy)X]

The series of novel mixed-ligand iridium(III) complexes Ir(Mebib)(ppy)X (Mebib = bis(N-methylbenzimidazolyl)benzene and ppy = phenylpyridine; X = Cl, 1; X = -C[triple band]CH, 2; X = CN, 3) have been investigated theoretically to explore their electronic structures and spectroscopic properties. The ground and excited state geometries have been fully optimized at the B3LYP/LANL2DZ and CIS/LANL2DZ levels, respectively. The optimized geometry structural parameters agree well with the corresponding experimental results. The HOMO of 1 and 3 are mainly localized on the Ir atom, Mebib, and ppy ligand, but that of 2 has significant X ligand composition. Absorptions and phosphorescences in CH2 Cl2 media have been calculated using the TD-DFT level of theory with the PCM model based on the optimized ground and excited state geometries, respectively. The lowest lying absorptions of 1 and 3 at 444 and 416 nm are attributed to a {[d(yz)(Ir) + pi(Mebib) + pi(ppy)] --> [pi*(Mebib)]} transition with metal-to-ligand, ligand-to-ligand, and intra-ligand charge transfer (MLCT/LLCT/ILCT) character, whereas that of 2 at 458 nm is related to a {[d(yz)(Ir) + pi(Mebib) + pi(ppy) + pi(C[triple band]CH)] --> [pi*(Mebib)]} transition with MLCT/LLCT/ILCT and X ligand-to-ligand charge transfer (XLCT) transition character. The phosphorescence of 1 and 3 at 565 and 543 nm originates from the 3{[dy(yz)(Ir) + pi(Mebib) + pi(ppy)] [pi*(Mebib)]} excited state, while that of 2 at 576 nm originates from the 3{[d(yz)(Ir) + pi(Mebib) + pi(ppy) + pi(C[triple band]CH)] [pi*(Mebib)]} excited state. The calculation results show that the absorption and emission transition character can be changed by altering the pi electron-withdrawing ability of the X ligand and the phosphorescent color can be tuned by adjusting the X ligand.