Effect of ancillary ligands on the electronic structures, DNA-binding and spectral properties of [Co(L)2(pip)] (L = phen, bpy, en, tap)

Studies on the electronic structures and related properties of a series of Co(Ш) complexes have been carried out, using the density functional theory (DFT) at the B3LYP/LanL2DZ level. The effect of the ancillary ligands on their electronic structures, DNA-binding affinities and spectra was revealed. The results show that an ancillary ligand has quite important effect on electronic structures and DNA-binding properties of these Co(Ш) complexes. The ancillary ligand possessing a great conjugated structure can effectively improve the DNA-binding affinity of the complex. Meanwhile, introducing a stronger electronegative N atom on the skeleton of ancillary ligand can obviously reduce the LUMO energy of the complex. Based on these findings, a designed complex 4 can be expected to have the greatest K_b value in complexes 1–4. So it may be able to control the interaction between the complex and DNA-base-pairs via varying ancillary ligands. In addition, the electronic absorption spectra of these complexes were calculated and simulated in aqueous solution using the time-dependent DFT (TDDFT) method and the effect of the ancillary ligands on the spectra was also explored. The calculated absorption spectra of these complexes in aqueous solution are in a satisfying agreement with the experimental results, and the properties of experimental absorption bands were theoretically explained in detail.     

Calculation of optical rotatory dispersion and electronic circular dichroism for tris-bidentate groups 8 and 9 metal complexes, with emphasis on exciton coupling

The optical rotatory dispersion (ORD, both non-resonant and resonant) and the electronic circular dichroism (CD) of tris-bidentate transition metal complexes of the form [M(L)(3)](n+) (M = Fe, Ru, Os, Co, Rh, Ir; n = 2, 3; L = 1,10-phenanthroline, 2,2'-bipyridine) are calculated using time-dependent density functional theory (TDDFT). The exciton CD band resulting from the coupling of ligand π-to-π* transitions is investigated in detail and analyzed in terms of exciton coupling of long-axis transitions using a dipole coupling model that takes TDDFT data for a single ligand as input. Results of the coupling model agree well with the full TDDFT CD spectra. The usefulness and reliability of this model is discussed. The resonant ORDs calculated directly from analytical damped linear TDDFT response compare well with Kramers-Kronig transformations of the calculated CD spectra. For comparisons of resonant ORD with experiment, one needs to consider wavelength shifts.     

Highlighting the role of the medium in DFT analysis of the photophysical properties of ruthenium(II) polypyridine-type complexes

In order to test the pertinence of the density functional theory to interpret the photophysical properties of ruthenium(II) polypyridine-type complexes, DFT and TDDFT calculations are performed both on the isolated molecule and in solution media described by the dielectric-like polarized continuum model (PCM). This study is focused on three isoelectronic complexes: [Ru(bpy)(2)(PhenImHPh)](2+) (II), where PhenImHPh represents the 2-(3,5-ditertbutylphenyl)imidazo[4,5-f][1,10]phenanthroline ligand, as well as [Ru(bpy)2(PhenImPh)]+ (I), and [Ru(bpy)(2)(PhenImH2Ph)](3+) (III), obtained by changing the protonic state of the imidazole ring. The structural and electronic properties of the ground and lowest triplet states are fully characterized in vacuo and in water solution, and the absorption spectra in the visible region are also investigated by TDDFT. The theoretical data are compared to the electrochemistry, UV-visible, and photophysical experiments to assess the validity and limits of each type of calculation. The choice of the functional is also discussed.     

DFT Study on Methanofullerene Derivative [6,6]-Phenyl-C61 Butyric Acid Methyl Ester

Density functional theory (DFT) and time-dependent density functional theory (TDDFT) with hybrid functional B3LYP were used to investigate several physical and chemical properties of [6,6]-phenyl-C₆₁ butyric acid methyl ester (PCBM), including the geometry, electron structure, charge population, bond properties, as well as IR, Raman and electronic absorption spectra. The analysis of the natural bond orbital (NBO) suggested that there were about 0.11 electrons transferred from moiety phenyl and butyric acid methyl ester group of PCBM to fullerene cage. The strongest IR and Raman peaks came from different modes with the frequencies of 1773 and 1492 cm⁻¹, respectively. The calculated isotropic polarizability, polarizability anisotropy invariant, and hyperpolarizability were 577.7, 96.9, and −22.8 a.u., respectively. Based on TDDFT, the electronic absorption spectra of PCBM were calculated and analyzed. The calculated absorption band near 349 nm agreed well with the experimental measurement.     

Experimental and Theoretical Studies of Charge Delocalization in Biruthenium–Alkynyl Complexes Bridged by Thiophenes

A series of binuclear ruthenium–alkynyl complexes that are bridged by thiophene groups (thiophene, bithiophene, and terthiophene) have been synthesized. All of these complexes have been well‐characterized by NMR spectroscopy, X‐ray diffraction, and elemental analysis. The electronic properties of these complexes have been examined by using cyclic voltammetry, UV/Vis/NIR and IR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and density functional theory (DFT) calculations. Electrochemical results showed that the potential difference (ΔE) and comproportionation constant (K_c) decreased with increasing size of the thiophene bridging unit. The UV/Vis/NIR spectra and TDDFT calculations of the monocations indicated that the NIR transitions displayed aromatic bridging character. EPR studies of the mono‐oxidized radical species further demonstrated that the unpaired electron/hole was delocalized over both metals and the bridging ligand and established significant participation in the ligand oxidation.     

黄曲霉素B1在银团簇表面吸附的表面增强拉曼光谱

采用密度泛函理论(DFT)的B3LYP方法和6-311g(d, p)(C, H, O)/LanL2DZ(Ag)基组, 优化得到黄曲霉素分子AFB₁与Ag小团簇形成的复合物AFB₁-Ag_n (n=2, 4, 6)的稳定结构, 并计算了三种复合物的表面增强拉曼光谱(SERS)和预共振拉曼光谱(SERRS), 与实验结果相一致. 计算结果显示: 三种复合物表面增强拉曼光谱中C＝O伸缩振动模的增强因子约为10²-10³, 是由于极化率改变引起的静化学增强. 根据含时密度泛函理论(TDDFT)方法计算得到的吸收光谱, 分别选择407.5、446.2和411.2 nm作为入射光, 计算三种复合物的共振拉曼光谱, 发现在SERRS光谱中, Ag―O伸缩振动的增强因子达到10⁴量级, 主要是由电荷转移产生的共振增强引起的.     

Electronic structure of the complexes of fullerene C60 with polyaromatic molecules

Electronic structure of the complexes of fullerene C₆₀ with triphenylene (TP) and 9,10-diphenylantracene (DPA) has been studied by an X-ray fluorescent spectroscopy. The C Kα spectrum of a complex was shown to be almost an additive sum of the C Kα spectra measured for fullerene and organic ligand. The quantum-chemical calculation of a DPA·C₆₀ structural unit using density functional theory (DFT) revealed a slight charge transfer from DPA molecule to the C₆₀ cage. The intermolecular interaction in the complex was found to proceed through quit energy deep molecular orbitals.     

Structure of Zinc and Nickel Histidine Complexes in Solution Revealed by Molecular Dynamics and Raman Optical Activity

The histidine residue has an exceptional affinity for metals, but solution structure of its complexes are difficult to study. For zinc and nickel complexes, Raman and Raman optical activity (ROA) spectroscopy methods to investigate the link between spectral shapes and the geometry were used. The spectra were recorded and interpreted on the basis of ionic equilibria, molecular dynamics, ab initio molecular dynamics, and density functional theory. For zwitterionic histidine the dominant tautomer was determined by the decomposition of experimental spectra into calculated subspectra. An octahedral structure was found to prevail for the ZnHis₂ complex in solution, in contrast to a tetrahedral arrangement in the crystal phase. The solution geometry of NiHis₂ is more similar to the octahedral structure found by X-ray. The Raman and ROA structural determinations of metal complexes are dependent on extensive computations, but reveal unique information about the studied systems.     

Physical, photophysical and structural properties of ruthenium(II) complexes containing a tetradentate bipyridine ligand

The focus of this report is the synthesis and properties of two new analogues of ruthenium(ii) tris-bipyridine, a monomer and dimer. The complexes contain the ligand 6,6'-(ethan-1,2-diyl)bis-2,2'-bipyridine (O-bpy) which contains two bipyridine units bridged in the 6,6' positions by an ethylene bridge. Crystal structures of the two complexes formulated as [Ru(bpy)(O-bpy)](PF6)2 and [(Ru(bpy)2)2(O-bpy)](PF6)4 reveal structures of lower symmetry than D3 which affects the electronic properties of the complexes as substantiated by density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. The HOMO lies largely on the ruthenium center; the LUMO spreads its electron density over the bipyridine units, but not equally in the mixed O-bpy-bpy complexes. Calculated Vis/UV spectra using TDDFT methods agree with experimental spectra. The lowest lying triplet excited state for [Ru(bpy)(O-bpy)](PF6)2 is 3MC resulting in a low emission quantum yield and a large chloride ion photosubstitution quantum yield.     

Theoretical study on contribution of charge transfer effect to surface-enhanced Raman scattering spectra of pyridine adsorbed on Ag(n) (n = 2-8) clusters

We investigate surface-enhanced Raman scattering (SERS) spectra of pyridine–Ag_n (n = 2–8) complexes by density functional theory (DFT) and time-dependent DFT (TDDFT) methods. In simulated normal Raman scattering (NRS) spectra, profiles of pyridine–Ag_n (n = 2–8) complexes are analogical with that of isolated pyridine. Nevertheless, calculated pre-SERS spectra are strongly dependent on electronic transition states of new complexes. Wavelengths at 335 nm, 394.8 nm, 316.9 nm and 342.6 nm, which are nearly resonant with pure charge transfer excitation states, are adopted as incident light when simulating pre-SERS spectra for pyridine–Ag_n (n = 2–8) complexes, respectively. We obtain enhancement factors from 10³ to 10⁵ in pre-SERS spectra compared with corresponding NRS spectra. The obvious increase in Raman intensities mainly result from charge transfer resonance Raman enhancement. A charge difference densities (CDDs) methodology is adopted in describing chemical enhancement mechanism. This methodology aims at visualizing charge transfer from Ag_n (n = 2–8) clusters to pyridine on resonant electronic transition, which is one of the most direct evidences for chemical enhancement mechanism.     

Time-Dependent Density Functional Theory Study on Excited-State Hydrogen Bonding Dynamics of Acetic Acid Hydrates

The time-dependent density functional theory (TDDFT) method was performed to investigate the hydrogen-bonding dynamics of acetic acid (AA) hydrates in aqueous solution. For AA, it tends to be both active hydrogen acceptor and donor and denote double H-bonds as O_A···H_W and H_A···O_W, resulting in ring structure hydrates. The ground-state geometry optimizations and electronic transition energies and corresponding oscillation strengths of the low-lying electronically excited states for the isolated AA monomer and the hydrogen-bonded ring structure hydrates are calculated by the density functional theory and TDDFT methods, respectively. Different types of intermolecular hydrogen bonds are formed between one AA molecule and water molecules. According to Zhao’s rule on the excited-state hydrogen bonding dynamics, it can be found that the intermolecular hydrogen bonds O_A···H_W and H_A···O_W are strengthened in electronically excited states of the hydrogen-bonded ring structure hydrates, with the excitation energy of a related excited state being lowered and electronic spectral redshifts being induced. Moreover, the hydrogen bond strengthening in the electronically excited state is crucial to the photophysics and photochemistry of hydrates with AA in aqueous solution.     

Time‐dependent density functional theory study on the electronic excited‐state hydrogen‐bonding dynamics of 4‐aminophthalimide (4AP) in aqueous solution: 4AP and 4AP–(H2O)1,2 clusters

The time‐dependent density functional theory (TDDFT) method has been carried out to investigate the excited‐state hydrogen‐bonding dynamics of 4‐aminophthalimide (4AP) in hydrogen‐donating water solvent. The infrared spectra of the hydrogen‐bonded solute?solvent complexes in electronically excited state have been calculated using the TDDFT method. We have demonstrated that the intermolecular hydrogen bond C? O···H? O and N? H···O? H in the hydrogen‐bonded 4AP?(H₂O)₂ trimer are significantly strengthened in the electronically excited state by theoretically monitoring the changes of the bond lengths of hydrogen bonds and hydrogen‐bonding groups in different electronic states. The hydrogen bonds strengthening in the electronically excited state are confirmed because the calculated stretching vibrational modes of the hydrogen bonding C?O, amino N? H, and H? O groups are markedly red‐shifted upon photoexcitation. The calculated results are consistent with the mechanism of the hydrogen bond strengthening in the electronically excited state, while contrast with mechanism of hydrogen bond cleavage. Furthermore, we believe that the transient hydrogen bond strengthening behavior in electroniclly excited state of chromophores in hydrogen‐donating solvents exists in many other systems in solution. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2010     

亚甲基富勒烯衍生物[6,6]-苯基-C61丁酸甲酯的密度泛函研究

运用密度泛函理论和含时密度泛函理论研究了亚甲基富勒烯衍生物[6,6]-苯基-C61丁酸甲酯(PCBM)的几种物理化学性质, 包括几何结构、电子结构、电荷布居与成键, 以及IR、Raman和电子吸收光谱. 自然键轨道方法的结果表明, 大约有0.11个电子通过成键由分子的一部分苯基和丁酸甲酯基团(电子给体)转移到富勒烯笼(电子受体). 最强的IR和Raman谱峰来自于不同的振动模式, 分别位于1773和1492 cm-1处. 计算的各向同性极化率、极化率各向异性不变量以及超极化率分别是577.7、96.9、-22.8 a.u.. 基于含时密度泛函理论计算并分析了PCBM的电子吸收谱, 在349 nm处的吸收峰与实验结果符合很好.     

TDDFT Study of the Electronic Structure,Absorption and Emission Spectra of the Light Emitters of the Amazing Firefly Bioluminescence and Solvation Effects on the Spectra

The ground and excited state properties of luciferin (LH₂) and oxyluciferin (OxyLH₂), the bioluminescent chemicals in the firefly, have been characterized using density functional theory (DFT) and time dependent DFT (TDDFT) methods. The effects of solvation on the electronic absorption and emission spectra of luciferin and oxyluciferin were predicted with a self‐consistent isodensity polarized continuum model of the solvent using TDDFT. The S₀→S₁ vertical excitation energies in the gas phase and in water were obtained. Optimizations of the excited state geometries permitted the first predictions of the fluorescence spectra for these biologically important molecules. Shifts in both of the absorption and emission spectra on proceeding from the gas phase to aqueous solution were also predicted.     

Synthesis,spectroscopic characterization,crystal and molecular structure of [ReOX2(bopyH)(PPh3)] complexes: DFT calculations for [ReOCl2(bopyH)(PPh3)]

The reactions of [ReOX₃(PPh₃)₂] (X = Cl, Br) with benzoylpyridine (bopy) have been examined and novel [ReOX₂(bopyH)(PPh₃)] oxocompounds have been obtained. The complexes were structurally and spectroscopically characterised. In the both structures two-electron reduced form of benzoylpyridine is coordinated to the central ion. The electronic structure of [ReOCl₂(bopyH)(PPh₃)] has been calculated with the density functional theory (DFT) method, and additional information about binding has been obtained by NBO analysis. The UV–Vis spectrum of the [ReOCl₂(bopyH)(PPh₃)] has been discussed on the basis of TDDFT calculations.     

A sequential molecular mechanics/quantum mechanics study of the electronic spectra of amides

We report gas-phase electronic spectra of formamide, N-methyformamide, acetamide, and N-methylacetamide at 300 K calculated using a combination of classical molecular dynamics and time-dependent density functional theory (TDDFT). In comparison to excitation energies computed using the global minima structures, the valence npi* and pi(nb)pi* states show a significant red-shift of 0.1-0.35 eV, while smaller shifts are found for the n3s and pi(nb)3s Rydberg states. In this work, we have identified the physical origin of these shifts arising from variations of the molecular structure. We present simple relationships between key geometrical parameters and spectral shifts. Consequently, electronic spectra can be generated directly from ground-state structures, without additional quantum chemical calculations. The electronic spectrum of formamide in aqueous solution is computed using TDDFT using an explicit solvent model. This provides a quantitative determination of the condensed-phase spectrum. In general, this study shows that temperature effects can change the predicted excitation energies significantly and demonstrates how electronic spectra at elevated temperatures can be computed in a computationally efficient way.     

DFT studies of structural preference of coordinated ethylene in W(CO)3(PX3)2(CH2CH2) (X=H, CH3, F, Cl, Br, and I)

A set of phosphine complexes of the type W(CO)₃(PX₃)₂(CH₂CH₂) (X=H, CH₃, F, Cl, Br, and I) were investigated by density functional theory method (BP86) to examine the effect of the substituent X on the orientation of C-C vector of the ethylene ligand with respect to one of the metal-ligand bonds as well as the donation and the backdonation in the bonding ligands of phosphine and ethylene. When X=CH₃, H, F, and Cl, the ethylene C-C vector prefers to be coplanar with metal-phosphine bonds, while for the ethylene complexes containing PBr₃ and PI₃ ligands, the structural preference is coplanarity of the ethylene and the metal-carbonyl bonds. The molecular orbital calculations and natural bond orbital analysis were used to examine the structural consequences derived from these complexes. It can be concluded that the structural preferences in the complexes have a clear relation to electronic effects of phosphine ligands. Our calculations for halide phosphine complexes, particularly for PBr₃ and PI₃, allow us to conclude that in addition to electronic effects, steric factors can also affect the orientation of the ethylene ligand in complexes.     

Group-6 metal carbonyl complexes of pyridylbenzoxazole and pyridylbenzothiazole: Synthesis, structure, electrochemistry, photophysical property and DFT calculations

Cr, Mo and W tetracarbonyl complexes of 2-(2-pyridyl)benzoxazole (PBO) and 2-(2-pyridyl)benzothiazole (PBT) are spectroscopically characterised. The confirmatory structure of [Mo(CO)₄(PBO)] has been determined by X-ray crystallography. The complexes show negative solvatochromic effect, with increasing solvent polarity the MLCT band is shifted to longer wavelength region. Cyclic voltammetry shows M(I)/M(0) redox response and also exhibit fluorescence spectra at room temperature. The electronic structures of the complexes are calculated by density functional theory (DFT) and time dependent-DFT calculated results are used to explain redox property and electronic transitions.     

Ab initio and DFT study of the electronic structures and spectroscopic properties of pyrene ligands and their cyclometalated complexes

Two ligands 1‐diphenylphosphinopyrene (1‐PyP) ( L ₁ ), 1,6‐bis(diphenylphosphino)‐pyrene (1,6‐PyP) ( L ₂ ) and their cyclometalated complexes [Pt(dppm)(1‐PyP‐H)]⁺ ( 1 ), [Pt₂(dppm)₂(1,6‐PyP‐H₂)]²⁺ (dppm = bis(diphenylphosphino)methane ( 2 ), and [Pd(dppe)(1‐PyP‐H)⁺ (dppe = bis(diphenylphosphino)ethane) ( 3 ) are investigated theoretically to explore their electronic structures and spectroscopic properties. The ground‐ and excited‐state structures are optimized by the density functional theory (DFT) and single‐excitation configuration interaction method, respectively. At the time‐dependent DFT (TDDFT) and B3LYP level, the absorption and emission spectra in solution are obtained. As revealed from the calculations, the lowest‐energy absorptions of 1 and 3 are attributed to the mixing ligand‐to‐metal charge transfer (CT)/intraligand (IL)/ligand‐to‐ligand CT transitions, while that of 2 is attributed to the IL transition. The lowest‐energy phosphorescent emissions of the cyclometalated complexes are attributed to coming from the ³ILCT transitions. With the increase of the spin‐orbit coupling effect, the phosphorescence intensities and the emissions wavelength are correspondingly increased. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011