Density functional theory investigation of Eu(III) complexes with beta-diketonates and phosphine oxides: model complexes of fluorescence compounds for ultraviolet LED devices

The density functional theory was employed to investigate Eu(III) complexes with three beta-diketonates and two phosphine oxides (complex M1: Eu(bdk)3(TPPO)2, complex M2: Eu(bdk)3(TMPO)2, and complex M3: Eu(bdk)3(TPPO)(TMPO)) deemed to be the model complexes of the fluorescence compounds for the ultraviolet LED devices we have recently developed. For each complex, two minimum energy points corresponding to two different optimized geometries (structures A and B) have been found, and the difference of the energy between two minimum energy points is found to be quite small (less than 1 kcal/mol). Vertical excitation energies and oscillator strengths for each complex at two optimized geometries have been obtained by the time-dependent density functional theory, and the character of the excited states has been investigated. For complex M3, the absorption edge is red-shifted, and the oscillator strengths are relatively large. The efficiency of intersystem crossing and energy transfer from the triplet excited state to the Eu(III) ion is considered by calculating DeltaE(ISC) (the energy difference between the first singlet excited state and the first triplet excited state) and DeltaE(ET) (the difference between the excitation energy of the complex for the first triplet excited state and the emission energy of the Eu(III) ion for 5D to 7F).     

Strongly photoluminescent Eu(III) tetrazolate ternary complexes with phosphine oxides as powerful sensitizers

The Eu(III) cation forms electrically neutral photoluminescent complex with 5-(2-pyridyl-1-oxide)tetrazolate (PTO) anion. Although the photoluminescence properties of such tertiary Eu(III) and Tb(III) complexes were not as high (13 and 31% photoluminescence quantum yield, respectively) as reported for other diketonate lanthanide complexes probably because of high number of nitrogen atoms involved in PTO which leads to attachment of water molecules, reducing the luminescence quantum yield with vibrational and rotational quenching. Here, we report the removal of quencher molecules from the coordination sphere of tris–europium tetrazolate oxide complex by replacing them with various phosphine oxides which leads to improved photoluminescence quantum yield for the complexes by acting as auxiliary co-ligands with that of the main antenna 5-(2-pyridyl-1-oxide)tetrazolate. The coordination sphere in these complexes can be complemented by aromatic phosphine oxides to provide highly photoluminescent Eu(III) complexes. The highest quantum yield was 38% in 3 [Eu(PTO)₃·DPEPO](H₂O)₅ containing bis(2-(diphenylphosphino)phenyl) ether oxide (DPEPO) as compared to tris–europium complex with 5-(2-pyridyl-1-oxide)tetrazolate.     

Density functional theory insight into Eu(III) and Am(III) complexes with two 2,6-dicarboxypyridine diamide-type ligands

Extraction complexes of Eu(III) and Am(III) with two 2,6-dicarboxypyridine diamide-type ligands L–A and L–B (Fig. 1) are studied by density functional theory (DFT). At both B3LYP/6-31G(d)/RECP and MP2/6-31G(d)/RECP levels of theory, the geometrical optimizations of the structures of the complexes can achieve the same accuracy and obtain the same geometrical configuration. At the B3LYP/6-311G(d,p)/RECP level of theory Eu³⁺ and Am³⁺ prefer to form [ML]³⁺ complexes under the solvation conditions, and the Am(III) complexes with L–A are more stable than the corresponding Eu(III) complexes. In the system with the ligand L–B, both [ML]³⁺ and [ML(NO₃)₃] species are very unstable.     

Gallium(III) halide complexes with phosphines,arsines and phosphine oxides – a comparative study

The phosphine oxide complexes [GaX₃(Me₃PO)] and [(GaX₃)₂{μ-o-C₆H₄(CH₂P(O)Ph₂)₂}] have been prepared and characterised by microanalysis, IR and multinuclear NMR (¹H, ¹³C{¹H}, ³¹P{¹H} and ⁷¹Ga) spectroscopy. The structures of [GaCl₃(Me₃PO)], [(GaBr₃)₂{μ-o-C₆H₄(CH₂P(O)Ph₂)₂}] and of the ionic product [GaI₂(Me₃PO)₂][GaI₄] have been determined and show that the Lewis acidity of the gallium halides towards phosphinoyl ligands diminishes as the halogen becomes heavier. The [GaX₃(Ph₃E)] (X = Cl, Br or I; E = P or As) and [(GaX₃)₂{μ-o-C₆H₄(CH₂PPh₂)₂}] (X = Br or I) have been prepared and their structural and spectroscopic properties compared with those of the phosphinoyl complexes. The results, and competitive solution NMR studies, show that Ga(III) binds the hard R₃PO in preference to the softer phosphine or arsine ligands. Hydrolysis of gallium(III) phosphines is shown to lead to [R₃PH][GaX₄], but in contrast to some other p-block halides, GaX₃ do not promote air-oxidation of R₃P to R₃PO.     

Density functional study on zerovalent lanthanide bis(arene)-sandwich complexes

Several zerovalent lanthanide bis(arene)-sandwich complexes, Ln(η⁶-C₆H₆)₂, Ln = La, Ce, Eu, Gd and Lu, have been studied by means of density functional theory. The calculated geometries are in good agreement with experiment. The calculated dissociation energies of the bond Ln-(η⁶-C₆H₆) may be considerably underestimated, but they correctly reveal the variation regularity. The bonding in these molecules can be described in terms of a relatively weak π-electron donation from benzene to Ln and a stronger electron back-donation from Ln 5d to the benzene π* orbitals. During bond formation, there is electron promotion from Ln 6s to 5d instead of from 4f to 5d, in opposition to the proposal of Anderson et al. The relativistic effect only slightly influences the molecular geometry, but decreases the bonding energy considerably through lowering the Ln 6s level and raising the 5d level. It enhances the trend of the bonding energy to decrease along the lanthanide series. Received: 22 June 1998 / Accepted: 9 September 1998 / Published online: 17 December 1998     

Density functional theory study on the bridge structure in dimeric aluminum (III) water complexes

Density-functional theory methods were used to investigate the structure of dimeric aluminum (III) water complexes as a function of bridging group. The possibilities of oxygen, water, and hydroxyl bridge ligands and a variety of structural arrangements, such as cis/trans, with respect to the relative position of hydroxyl ligands, were considered. Within the limit of our computational level, we found that electrostatic repulsion between hydroxyls is important in deciding the polyaluminum structure. Although the structures of aluminum-hexaaquo predominate, species with small number of charges or a large number of hydroxyl ligands have a tendency toward a five-coordinate trigonal bipyramidal configuration. Because water is electronically neutral, it cannot provide enough negative charges as a bridge ligand to stabilize two Al(III) molecules. The energy differences among many configurational isomers of hydroxyl Al are so small that they may coexist and convert into each other easily at room temperature.     

Density functional theory investigation of the redox properties of tricyclopentadienyl- and phospholyluranium(IV) chloride complexes

The redox behavior of tricyclopentadienyl- and phospholyluranium(IV) chloride complexes L(3)UCl with L = C(5)H(5) (Cp), C(5)H(4)Me (MeCp), C(5)H(4)SiMe(3) (TMSCp), C(5)H(4)(t)Bu ((t)BuCp), C(5)Me(5) (Cp*), and C(4)Me(4)P (tmp), has been investigated using relativistic density functional theory calculations, with the solvent being taken into account using the conductor-like screening model. A very good linear correlation (r(2) = 0.99) has been obtained between the computed electron affinities of the L(3)UCl complexes and the experimental half-wave reduction potentials E(1/2) related to the U(IV)/U(III) redox systems. From a computational point of view, our study confirms the crucial importance of spin-orbit coupling and solvent corrections and the use of an extended basis set in order to achieve the best experiment-theory agreement. Considering oxidation of the uranium(IV) complexes, the instability of the uranium(V) derivatives [L(3)UCl](+) is revealed, in agreement with experimental electrochemical findings. The driving roles of both the electron-donating ability of the L ligand and the U 5f orbitals on the redox properties of the complexes are brought to light. Interestingly, we found and explained the excellent correlation between variations of the uranium Hirschfeld charges following U(IV)/U(III) electron capture and E(1/2). In addition, this work allowed one to estimate theoretically the half-wave reduction potential of [Cp*(3)UCl].     

Interactions of Rh(III)-dihydrido-bis(phosphine) complexes with semicarbazones

Interaction of cis,trans,cis-[Rh(H)2(PR3)2(acetone)2]PF6 complexes (R = aryl or R3 = Ph2Me, Ph2Et) under H2 with E-semicarbazones gives the Rh(III)-dihydrido-bis(phosphine)-semicarbazone species cis,trans-[Rh(H)2(PR3)2{R'(R' ')C=N-N(H)CONH2}]PF6, where R' and R' ' are Ph, Et, or Me. The complexes are generally characterized by elemental analysis, 31P{1H} NMR, 1H NMR, and IR spectroscopies, and MS. X-ray analysis of three PPh3 complexes reveals chelation of E-semicarbazones by the imine-N atom and the carbonyl-O atom. In contrast, the corresponding reaction of [Rh(H)2(PPhMe2)2(acetone)2]PF6 with acetophenone semicarbazone gives the ortho-metalated-semicarbazone species cis-[RhH(PPhMe2)2{o-C6H4(Me)C=N-N(H)CONH2}]PF6. The X-ray structure of E-propiophenone semicarbazone is also reported. Rhodium-catalyzed, homogeneous hydrogenation of semicarbazones was not observed even at 40 atm H2.     

Vibrational spectra of mixed (phthalocyaninato)(porphyrinato) yttrium(III) double-decker complexes: Density functional theory calculations

The vibrational (IR and Raman) spectra of neutral and reduced mixed (phthalocyaninato)(porphyrinato) yttrium(III) double-decker complexes Y(Pc)(Por) and [Y(Pc)(Por)]⁻ [the simplified models of mixed (phthalocyaninato)(porphyrinato) rare earth(III) complexes] are studied using density functional theory (DFT) calculations. The simulated IR and Raman spectra of Y(Pc)(Por) are compared with the experimental IR spectrum of Tb(Pc)(TClPP) and Raman spectrum of Y(Pc)(TClPP), respectively, and many bands can acceptably fit in spite of the different species. On the basis of comparison with the simulated spectra of PbPc and PbPor together with the assistance of normal coordinate analysis, the calculated frequencies in their IR and Raman spectra are identified in terms of the vibrational mode of different ligand for the first time. The calculated frequency at 1048 cm⁻¹ in the IR spectrum of [Y(Pc)(Por)]⁻ with contribution from both Pc and Por vibrational modes is the characteristic IR vibrational mode of the reduced double-decker, while the characteristic IR vibrational mode of Y(Pc)(Por) attributed from the vibration of phthalocyanine monoanion radical Pc⁻ appears at 1257 cm⁻¹. In line with our previous experimental findings that the Raman spectra of M(Pc)(TPP) and M(Pc)(TClPP) are dominated by the Pc vibrational modes, theoretical calculations indicate that most of the Raman vibrational modes contributed from Por ring are covered up by those of Pc ring and thus are hard to be recognized in the Raman spectra of [Y(Pc)(Por)]⁻ and Y(Pc)(Por) due to their much weaker intensity in comparison with that of Pc ligand. Comparison in the IR and Raman spectra between [Y(Pc)(Por)]⁻ and Y(Pc)(Por) also suggests the localization of hole on the Pc ring in the neutral double-decker Y(Pc)(Por). The present work, representing the first detailed DFT study on the vibrational spectra of mixed (phthalocyaninato)(porphyrinato) rare earth(III) double-decker complexes, is useful in helping to understand the vibrational spectroscopic properties of this series of mixed tetrapyrrole ring complexes.     

Ytterbium-catalyzed dual intermolecular hydrophosphination: synthesis of bis(phosphinyl)dienes and bis(alkenyl)phosphine oxides

Dual intermolecular hydrophosphination of conjugated diynes with 2 equiv of diphenylphosphine was catalyzed by ytterbium complexes, Yb(η²-Ph₂CNPh)(hmpa)₃ (1) and Yb[N(SiMe₃)₂]₃(hmpa)₂ (2), to give the corresponding 1,4-bis(diphenylphosphinyl)buta-1,3-dienes in high yields after oxidative work-up. Distribution of the four possible stereoisomers sharply depended on substituents of the substrates. (Z,Z)-Isomers were predominantly obtained from the disubstituted diynes, together with minor (Z,E)-isomers. On the other hand, the reaction of the terminal diynes provided major (E,Z) and minor (E,E)-butadienes. 1,4-Di-tert-butylbuta-1,3-diyne was exclusively converted to an allenic compound. Moreover, the dual hydrophosphination using phenyphosphine was also performed with 1 and 2. Thus, the reaction of 2 equiv of aromatic alkynes with PhPH₂ and subsequent oxidation gave bis(alkenyl)phosphine oxides in preference of the (Z,Z)-stereoisomers.     

Density functional theory investigation of decamethyldizincocene

A density functional investigation into the structure and vibrational properties of the recently synthesized, novel, Zn(I)-containing species decamethyldizincocene has been performed. Our analysis is in agreement with the general structural properties of the experimental results. We have corroborated the experimental geometry as a true minimum on the global molecular energy surface, confirmed the experimental hypothesis that the Zn atoms are in a Zn(I) state, and provided a detailed analysis of the experimentally undefined Zn-dominant IR and Raman spectral bands of this unusual Zn(I) species.     

Synthesis of Eu(III) and Tb(III) complexes with novel pyridine dicarboxamide derivatives and their luminescence properties

A novel ligand, N2,N6-bis[2-(3-methylpyridyl)]pyridine-2,6-dicarboxamide (L2) and the corresponding Eu(III) and Tb(III) hydrochlorate complexes have been synthesized and characterized in detail based on elemental analysis, IR and NMR. The crystal and molecular structure of the complexes was determined by X-ray crystallography. The Eu(III) and Tb(III) ions were found to coordinate to the amido nitrogen atoms and pyridine nitrogen atoms. The luminescence properties of lanthanide complexes in solid state, in different solutions and in different pH value were investigated. The result shows that Tb(III) complexes exhibit more efficient luminescence than Eu(III) complexes, and the ligand (L2) is an excellent sensitizer to Tb(III) ion.     

Density functional theory investigation of benzenethiol adsorption on Au(111)

We have studied the adsorption of benzenethiol molecules on the Au(111) surface by using first principles total energy calculations. A single thiolate molecule is adsorbed at the bridge site slightly shifted toward the fcc-hollow site, and is tilted by 61 degrees from the surface normal. As for the self-assembled monolayer (SAM) structures, the (2 square root of 3 x square root of 3)R30 degrees herringbone structure is stabilized against the (square root 3 x square root 3)R30 degrees structure by large steric relaxation. In the most stable (2 square root 3 x square root 3)R30 degrees SAM structure, the molecule is adsorbed at the bridge site with the tilting angle of 21 degrees, which is much smaller compared with the single molecule adsorption. The van der Waals interaction plays an important role in forming the SAM structure. The adsorption of benzenethiolates induces the repulsive interaction between surface Au atoms, which facilitates the formation of surface Au vacancy.     

Density functional study on Am(III)/Eu(III) selectivity using crown ether type ligands

Journal of Radioanalytical and Nuclear Chemistry - Density functional theory calculations were applied to understand the selectivity between Am3+ and Eu3+ ions with the crown ethers type ligands....     

Enhanced lasing properties of dissymmetric Eu(III) complex with bidentate phosphine ligands

The luminescent and lasing properties of Eu(III) complexes were enhanced by using an dissymmetric Eu(III) complex. The photophysical properties (the emission spectral shapes, the emission lifetimes, the emission quantum yields, and the stimulated emission cross section (SEC)) were found to be dependent on the geometrical structures of Eu(III) complexes. The geometrical structures of Eu(III) complexes were determined by X-ray single crystal analyses. The symmetrical group of Eu(hfa)3(BIPHEPO) (tris(hexafluoroacetylacetonato)europium(III) 1,1'-biphenyl-2,2'-diylbis(diphenylphosphine oxide)) was found to be C1, which was more dissymmetric than Eu(hfa)3(TPPO)2 (tris(hexafluoroacetylacetonato)europium(III) 1,2-phenylenebis(diphenylphosphine oxide): C2 symmetry) and Eu(hfa)3(OPPO)2 (tris(hexafluoroacetylacetonato)europium(III) 1,2-phenylenebis(diphenylphosphine oxide): C2 symmetry). The analytical data were supported by Judd-Ofelt analysis. The most dissymmetrical Eu(III) complex, Eu(hfa)3(BIPHEPO), showed large electron transition probability and large SEC (4.64 x 10(-20) cm2). The SEC of Eu(hfa)3(BIPHEPO) was superior to even the values of Nd-glass laser for practical use (1.6-4.5 x 10(-20) cm2). The lasing properties of Eu(III) complexes in polymer thin film were measured by photopumping of a Nd:YAG laser (355 nm). The threshold energy of lasing oscillation was found to be 0.05 mJ. The increasing rate of the lasing intensity of Eu(hfa)3(BIPHEPO) as a function of the excitation energy was much larger than that of Eu(hfa)3(TPPO)2 and Eu(hfa)3(OPPO)2. The dissymmetrical structure of Eu(hfa)3(BIPHEPO) promoted the enhancement of the lasing property.     

Highly improved electroluminescence from a series of novel Eu(III) complexes with functional single-coordinate phosphine oxide ligands: tuning the intramolecular energy transfer, morphology, and carrier injection ability of the complexes

The functional single-coordinate phosphine oxide ligands (4-diphenylaminophenyl)diphenylphosphine oxide (TAPO), (4-naphthalen-1-yl-phenylaminophenyl)diphenylphosphine oxide (NaDAPO), and 9-[4-(diphenylphosphinoyl)phenyl]-9H-carbazole (CPPO), as the direct combinations of hole-transporting moieties, and electron-transporting triphenylphosphine oxide (TPPO) were designed and synthesized (amines or carbazole), together with their Eu(III) complexes [Eu(tapo)(2)(tta)(3)] (1), [Eu(nadapo)(2)(tta)(3)] (2), and [Eu(cppo)(2)(tta)(3)] (3; TTA: 2-thenoyltrifluoroacetonate). The investigation indicated that by taking advantage of the modification inertia of the phosphine oxide ligands, the direct introduction of the hole-transport groups as chromophore made TAPO, NaDAPO, and CPPO obtain the most compact structure and mezzo S(1) and T(1) energy levels, which improved the intramolecular energy transfer in their Eu(III) complexes. The amorphous phase of 1-3 proved the weak intermolecular interaction, which resulted in extraordinarily low self-quenching of the complexes. The excellent double-carrier transport ability of the ligands was studied with Gaussian calculations, and the bipolar structure of TAPO and CPPO was proved. The great improvement of the double-carrier transport ability of 1-3 was shown by cyclic voltammetry. Their HOMO and LUMO energy levels of around 5.3 and 3.0 eV, respectively, are the best results for Eu(III) complexes reported so far. A single-layer organic light-emitting diode of 2 had the impressive brightness of 59 cd m(-2) which, to the best of our knowledge, is the highest reported so far. Both of the four-layer devices based on pure 1 and 2 had a maximum brightness of more than 1000 cd m(-2), turn-on voltages lower than 5 V, maximum external quantum yields of more than 3 % and excellent spectral stability.     

Synthesis of Eu(III) and Tb(III) complexes with novel pyridine dicarboxylic acid derivatives and their fluorescence properties

Starting from pyridine-2,6-dicarboxylic acid (DPA), a series of novel pyridine-2,6-dicarboxylic acid derivatives were synthesized. In these compounds, 4-(hydroxymethyl)pyridine-2,6-dicarboxylate (4-HMDPA) and 4-[(bis-carboxymethyl-amino)-methyl]-pyridine-2,6-dicarboxylic acid (4-BMDPA) were used as multifunctional ligands to coordinate with Tb(III) and Eu(III) and the complexes were prepared. The fluorescence properties of the solid complexes and their solutions were investigated in detail. The results indicated that the weak election-withdrawing group 4-hydroxymethyl in 4-position of pyridine in 4-HMDPA could weaken the fluorescence intensity of the lanthanide complexes. The contradistinctive experimental results showed that the fluorescence intensities of these complexes are related to pH values of the aqueous solutions and the dipole moments of solvent molecules: in the neutral aqueous solutions, the fluorescence intensities of these complexes were strongest, while the dipole moments were lower when the fluorescence intensities were stronger. 4-BMDPA is the better sensitizer and may be used as time-resolved fluoroimmunoassay. __________ Translated from Chemical Journal of Chinese Universities, 2006, 27(3) (in Chinese)     

Density functional theory calculations of novel Rh(I) diphosphinite catalysts

Novel Rh(I) diphosphinite catalysts [Rh((R,R)-3,4-(bis(O-diphenylphosphino)-1,2,5,6-tetra-O-methyl-chiro-inositol)]+ ([Rh-CANDYPHOS]+) and [Rh((R,R)-3,4-(bis(O-diphenylphosphino)-1,2,5,6-tetra-O-ethyl-chiro-inositol)]+ ([Rh-EtCP]+) have been prepared utilizing naturally-occurring resources. Potential energy surfaces for the catalyzed asymmetric hydrogenation of the prochiral enamides methyl-(Z)-α-acetamido cinnamate, methyl-(Z)-α-acetamido cinnamic acid and dimethyl itaconate have been surveyed using density function theory (DFT) methods. Key transition states were identified from previous [Rh((R,R)-DUPHOS)]+ studies for the two diastereoisomeric manifolds 1 and 2. Transition state energies were found starting from models based on (1) the X-ray structure of the active complex (CANDYPHOS)(η⁴-(Z,Z)-cyclo-octa-1,5-diene)-rhodium(I) tetrafluoroborate CHCl₃ solvate [3] and (2) models in which the complex (without substrate) started with C2 molecular symmetry. The difficulties encountered in calculations of the transition state energies of large cations are outlined and limitations noted. Transition state enthalpy values are compared with the observed experimental free energy differences results and previous studies 1 and 2. The predictive aspects of the calculations appear to be limited with the starting models playing an important part in the absolute value of the final energies.     

Neutral bis(pentafluorophenyl)triphenylarsinegold(III) complexes

The complexes XAu(C₆F₅)₂AsPh₃ have been prepared by substitution of chloro- or perchlorato-bis(pentafluorophenyl)triphenylarsinegold(III) with alkali or with silver salts MX (X = NO₃, CH₃COO, NO₂, CF₃COO, CN, SCN, N₃ and C₆H₅COO). Decomposition of the nitrato or acetato complex leads to C₆F₅AuAsPh₃.