Density functional study of the O2 binding to [CuI(TPAR)]+ (TPA = tris(2-pyridylmethyl)amine) in THF and EtCN

Density functional theory using the B3LYP hybrid functional has been employed to study the formation of [Cu(II)(TPA(H))(O2-)]+ and [Cu(II)(TPA(MeO))(O2-)]+ (TPA = tris(2-pyridylmethyl)amine) in two different solvents, THF and EtCN. The thermodynamics of solvent coordination as well as that of the overall reactions with O2 has been computed. The formations of [Cu(II)(TPA(H))(O2-)]+ in THF and of [Cu(II)(TPA(MeO))(O2-)]+ in both THF and EtCN are found to be initiated from the [Cu(I)(TPA(R))]+ species, that is, the Cu complex possessing an empty coordination site. In contrast, the formation of [Cu(II)(TPA(H))(O2-)]+ in EtCN is found to be initiated from the [Cu(I)(TPA(H))(EtCN)]+ species, that is, one solvent molecule being coordinated to Cu(I). In general, good agreement is found between theoretical and experimental results. The high accuracy of the B3LYP functional in reproducing experimental thermodynamic data for the present type of transition metal complexes is demonstrated by the fact that the differences between measured and computed thermodynamic parameters (DeltaG degree, DeltaH degrees , and -TDeltaS degree, in most cases are less than 2.0 kcal mol(-1). An attempt was made to investigate the kinetics of the formation of [Cu(II)(TPA(H))(O2-)]+ in THF and EtCN. Computed free energies of activation, DeltaG, are in good agreement with experimental results. However, an analysis of the partitioning of the free energy barriers in enthalpic and entropic contributions indicates that the computationally studied reaction pathway might differ from the one observed experimentally.     

Effects of conjugation in length and dimension on spectroscopic properties of fluorene-based chromophores from experiment and theory

A series of one-photon absorption spectra for fluorene-based donor-pi-acceptor molecules is presented and spectroscopically assigned, based upon the results obtained from time-dependent density functional theory. The computed excitation energies were generally shown to be in good agreement with experiment, particularly when compared to results from measurements carried out in a nonpolar solvent, which were available for some molecules. The computed oscillator strengths may resolve discordant experimental values in some cases, for example, for AF-380, AF-270, and AF-295. However, a quantitative comparison between computed and observed oscillator strengths is complicated by band overlapping. Thus, the computed extinction coefficients obtained by summing over the Gaussian bands are useful in such cases.     

Multipolar symmetric squaraines with large two-photon absorption cross-sections in the NIR region

The two-photon absorption (TPA) properties of two extended symmetric squaraine dyes are thoroughly characterized from the experimental and quantum-chemical point of view. The two molecules are specially engineered to have a multipolar structure with increasing complexity, D-π-A-π-D and A'-π-D-π-A-π-D-π-A', respectively. The experimental TPA spectra, measured by means of the Z-scan technique in the femtoseconds regime, display considerably high values of TPA cross sections (σ(TPA)) for both molecules. In particular, the squaraine with the more extended structure shows the highest value of σ(TPA) ever reported for this class of molecules. CIS and TDDFT calculations of the one and two-photon absorption properties are carried out to clarify the origin of the observed TPA properties and fully characterize the electronic properties of these compounds. The calculations, in good agreement with the experimental data, suggest that the origin of this exceptionally high σ(TPA) can be ascribed to the presence of a peripheral A' group, that increases the density of excited states involved in the TPA process.     

Density functional calculations on electronic circular dichroism spectra of chiral transition metal complexes

Time-dependent density functional theory (TD-DFT) has for the first time been applied to the computation of circular dichroism (CD) spectra of transition metal complexes, and a detailed comparison with experimental spectra has been made. Absorption spectra are also reported. Various Co(III) complexes as well as [Rh(en)(3)](3+) are studied in this work. The resulting simulated CD spectra are generally in good agreement with experimental spectra after corrections for systematic errors in a few of the lowest excitation energies are applied. This allows for an interpretation and assignment of the spectra for the whole experimentally accessible energy range (UV/vis). Solvent effects on the excitations are estimated via inclusion of a continuum solvent model. This significantly improves the computed excitation energies for charge-transfer bands for complexes of charge +3, but has only a small effect on those for neutral or singly charged complexes. The energies of the weak d-to-d transitions of the Co complexes are systematically overestimated due to deficiencies of the density functionals. These errors are much smaller for the 4d metal complex. Taking these systematic errors and the effect of a solvent into consideration, TD-DFT computations are demonstrated to be a reliable tool in order to assist with the assignment and interpretation of CD spectra of chiral transition metal complexes.     

Strong two photon absorption and photophysical properties of symmetrical chromophores with electron accepting edge substituents

Two photon absorption (TPA) and photophysical properties of three new symmetrical chromophores with electron accepting phthalimide edge substituents have been studied. The three chromophores contain fluorene, alcoxy-substituted divinyl benzene, and carbazole moieties as central cores, respectively. The femtosecond time-resolved fluorescence upconversion spectroscopy and two photon excited fluorescence technique have been carried out. The effect of solvent polarity on TPA and on photophysics has also been determined. Ultrafast fluorescence dynamics, with decay times ranging from 1 to 13 ps, are revealed in polar solvents. This is attributed to the relaxation of the chromophores to the intramolecular charge transfer state. The chromophore bearing fluorene central core, being of the type A-pi-A, is the most efficient concerning TPA. Strong TPA, with a cross section value as high as 2100 GM at an excitation wavelength of 770 nm is found in acetophenone which is a solvent of intermediate polarity. The TPA spectra were also reproduced using a sum over states three-state model. A study of the TPA induced photobleaching of the fluorene molecule, doped in a solid poly(methyl-methacrylate) film, has shown that this material is very promising for efficient TPA optical data storage.     

Raman-spectroscopic investigations of ion—solvent interactions in concentrated solutions of LiCl in formic acid

Raman spectra of concentrated solutions of LiCl in HCOOH containing mainly ion pairs and single solvated ions prove to be suitable for an approximate experimental estimation of the influence of the ion on the HCOOH molecule. Remarkable changes in the CO, CO and CH bonds of the solvent molecule due to this influence are observed. These observations are shown to be in good agreement with calculated frequency shifts, obtained by semi-empirical molecular orbital methods applied to simple solvation models.     

Toward the complete prediction of the 1H and 13C NMR spectra of complex organic molecules by DFT methods: application to natural substances

The NMR parameters (1H and 13C chemical shifts and coupling constants) for a series of naturally occurring molecules have been calculated mostly with DFT methods, and their spectra compared with available experimental ones. The comparison includes strychnine as a test case, as well as some examples of recently isolated natural products (corianlactone, daphnipaxinin, boletunone B) featuring unusual and/or crowded structures and, in the case of boletunone B, being the subject of a recent revision. Whenever experimental spectra were obtained in polar solvents, the calculation of NMR parameters was also carried out with the Integral Equation-Formalism Polarizable Continuum Model (IEF-PCM) continuum method. The computed results generally show a good agreement with experiment, as judged not only by statistical parameters but also by visual comparison of line spectra. The origin of the remaining discrepancies is attributed to the incomplete modeling of conformational and specific solvent effects.     

Role of donor-acceptor strengths and separation on the two-photon absorption response of cytotoxic dyes: a TD-DFT study

Time-dependent density functional theory (TD-DFT) is applied to model one-photon (OPA) and two-photon (TPA) absorption spectra in a series of conjugated cytotoxic dyes. Good agreement with available experimental data is found for calculated excitation energies and cross sections. Calculations show that both OPA and TPA spectra in the molecules studied are typically dominated by two strong peaks corresponding to different electronic states. We find that donor-acceptor strengths and conjugated bridge length have a strong impact on the cross-section magnitudes of low- and high-frequency TPA maxima, respectively. These trends are analyzed in terms of the natural transition orbitals of the corresponding electronic states. Observed structure-property relationships may have useful implications on design of organic conjugated chromophores with tunable two-photon absorption properties for photodynamic therapy applications.     

UV-vis spectra of <Emphasis Type="Italic">p</Emphasis>-benzoquinone anion radical in solution by a TD-DFT/PCM approach

Excited electronic states of the anion radical of para-benzoquinone were studied by time dependent density functional theory (TD-DFT) including bulk solvent effects by the polarizable continuum model (PCM). The computed vertical excitation energies for the first four low-lying doublet states are in good agreement with previous post-Hartree–Fock computations. Geometry optimization of excited states and inclusion of solvent effects lead to a remarkable agreement between computed adiabatic transition energies and experimental band maxima. Together with their specific interest, the results point out the reliability of TD-DFT/PCM approach for valence excitations and the need to take geometry relaxation and solvent effects into the proper account for a meaningful comparison between computed and experimental absorption spectra.     

Hybrid density functional theory/molecular mechanics calculations of two-photon absorption of dimethylamino nitro stilbene in solution

The dimethylamino nitro stilbene (DANS) molecule is studied for exploring solvent effects on two-photon absorption using the quantum mechanical/molecular mechanical (QM/MM) response theory approach, where the quantum part is represented by density functional theory. We have explored the role of geometrical change of the chromophore in solution, the importance of taking a dynamical average over the sampled structures and the role of a granular representation of the polarization and electrostatic interactions with the classically described medium. The line shape function was simulated by the QM/MM technique thereby allowing for non-empirical prediction of the absolute two-photon cross section. We report a maximum in the TPA cross section for a medium of intermediate solvent polarity (i.e. in chloroform) and provide the grounds for an explanation of this effect which recently has been experimentally observed for a series of charge transfer species in solvents of different polarity. The calculations of absorption energies reproduce well the positive solvatochromic behavior of DANS and are in good agreement with experimental spectra available for the chloroform and DMSO solvents. In line with recent development of the QM/MM response technique for color modeling, we find this methodology to offer a versatile tool to predict and analyze two-photon absorption phenomena taking place within a medium.     

几个荧光蛋白发色团双光子吸收性质的理论研究

实验测得的荧光蛋白的单、双光子吸收光谱在低频和高频区域都表现出明显不同的特征。为了揭示这些不同点的起源和研究荧光蛋白的构–效关系,我们详细研究了三种荧光蛋白发色团(一种增强型蓝绿色荧光蛋白的中性发色团和两种红色荧光蛋白的阴离子发色团)的单、双光子吸收特性,分别计算了纯的和振动分辨的电子谱。计算结果表明：光谱线形与计算采用的交换相关密度泛函及谱截面计算所采用的近似关系密切;如果在计算光谱截面时,我们利用长程修正的交换相关泛函CAM-B3LYP来计算几何和电子结构参数,然后把Franck-Condon (FC)效应和包含Herzberg-Teller (HT)效果的电-声耦合效应都考虑进去,理论计算的光谱与实验测定的光谱可以很好地符合;对于两种离子态的发色团,HT电-声耦合效应使得对应于基态到第一激发态跃迁的双光子吸收最强峰相对于单光子吸收的最强峰发生了蓝移,但HT电-声耦合效应对高频的双光子吸收谱没有太大的影响;分子内电荷转移是导致高频区的双光子吸收明显强于单光子吸收的主要原因。     

A combined experimental and theoretical study on the conformational behavior of a calix[6]arene

An experimental and theoretical study on the conformational behavior of the 1,3,5-OMe-2,4,6-OCH(2)CONHOH-p-tert-butylcalix[6]arene has been carried out. In particular, semiempirical (AM1) and density functional theory (DFT) calculations have been performed in order to identify the possible conformers. The obtained results show that the cone structure is the most stable conformer at any level of theory, even if significant differences have been obtained for the other species. The inclusion of solvent effect, through a continuum model, also points out the relevant role played by the solvent in the stabilization of the cone structure in solution. These latter results have been confirmed by NMR experiments, which clearly show the presence of only the cone conformer in a polar solvent, such as DMSO. Finally, (1)H and (13)C NMR spectra on model systems, i.e., two successive phenol rings (Ar(1)-CH(2)-Ar(2)), have been computed at the DFT level and compared with the experimental spectra of the complete molecule. The results show an overall good agreement with the experimental data, thus leading to an unambiguous assignment of the experimental spectra.     

含三苯胺类富勒烯吡咯烷衍生物的合成、表征及理论计算

N-Methyl-2-（4-N,N-diphenylaminophenyl）fulleropyrrolidine and N-methyl-2-（4-di-p-tolylaminophenyl）fulleropyrrolidine were synthesized via the 1,3-dipolar cycloaddition reactions under microwave irradiation. The molecular structures were identified and characterized by MS, UV-Vis, FT-IR, ^1H NMR and fluorescence spectra. Photoinduced intramolecular electron transfer process from C60 moiety to triphenylamine moiety have been studied by nanosecond laser flash photolysis. The optimized structure and the distribution of the frontier molecular orbitals for C60-TPA were obtained by using DFT method at B3LYP/6-31G（d） level. The results indicated that the intramolecular photoinduced electron transfer could occur in these compounds, which were in excellent agreement with the nanosecond transient absorption spectra observed experimentally in polar solvent. The electronic spectrum of the compound C60-TPA was studied by ZINDO method on the basis of the optimized geometrics, which was essentially consistent with experimental values.     

Density functional calculation of the electronic circular dichroism spectra of the transition metal complexes [M(phen)3]2+ (M = Fe, Ru, Os)

The circular dichroism spectra of the tris-bidentate metal complexes Lambda-[M(phen)3]2+, with M = Fe, Ru, Os and phen = 1,10-tris-phenanthroline, are investigated computationally, employing time-dependent density functional theory. Good agreement with experimental spectra is obtained for Ru and Os. The Lambda-[Os(phen)3]2+ spectrum is analyzed in detail. It is shown how relativistic effects red shift CD bands where the Os 5d-orbital participates to a large extent in the excitations. Further, the participation of the metal in the ligand pi --> pi exciton CD is determined to be of the order of 10%. Though solvent effects can have a noticeable effect on individual transitions and rotatory strengths, they are demonstrated to have only a very small overall effect on the resulting simulated CD spectra. For Lambda-[Fe(phen)3]2+, the results are shown to be rather sensitive to the choice of the applied hybrid and nonhybrid density functionals, and the optimized geometries based thereupon. In particular, the sign pattern of the lower-energy part (up to 33 x 10(3) cm(-1)) of the Lambda-[Fe(phen)3]2+ CD spectrum is difficult to reproduce. Some combinations of functionals and geometries yield good agreement with experiment, but no "best" approach can be devised based on the available results. Possible sources of errors in the spectrum of Lambda-[Fe(phen)3]2+ due to deficiencies in the functionals and the exchange-correlation kernels are investigated.     

Solvatochromic and thermochromic shifts of electronic spectra of polar solute molecules in a mixture of polar and nonpolar solvent; the role of solvent-solvent interactions

A theoretical model is proposed to describe the influence of the concentration of a polar solvent and the temperature of a solution on the electronic spectra of a polar solute in a binary solvent mixture. It is shown that the interaction between molecules of the polar solvent in the first solvation shell makes the significant contribution to the formation of absorption and fluorescence bands of the solute. An experimental study of solvatochromic and thermochromic shifts of steady-state fluorescence spectra of 3-amino-N-methylphthalimide in decalin--propanol mixture for different values of propanol mole fraction is carried out. Good qualitative agreement between the experimental data and calculation results is observed.     

呋喃查尔酮结构与电子光谱的密度泛函理论研究

在密度泛函理论的PBE1PBE/6-31G(d)水平上对呋喃查尔酮及其衍生物的几何结构进行优化计算.在获得基态稳定结构的基础上,应用含时密度泛函理论计算其电子吸收光谱,探讨了取代基和溶剂对电子吸收光谱的影响,计算结果与实验结果吻合很好,平均绝对偏差仅为3.3nm(0.04eV).结果表明,取代基的引入和溶剂极性的增大均使光谱发生红移.通过前线轨道分析,揭示了该类化合物的主要吸收峰均源自分子中HOMO→LUMO电子跃迁.     

DFT, ab initio and FT-IR studies of the structure of sulfonamide triazenes

We present an in-depth investigation of the structural, infrared spectra and visible spectra of various triazenes with a sulfonamide moiety. The preparation of 4-sulfonyl amide benzenediazonium chloride with cyclic amines of various ring sizes (pyrrolidine, piperidine, 4-methylpiperidine, N-methylpiperazine, morpholine and hexamethyleneimine) are theoretically investigated using the density functional theory (DFT) and Hartree-Fock (HF) levels of theory with the standard 6-31G* basis set. The calculated vibrational frequencies are evaluated via comparison with experimental values. The vibrational spectral data obtained from solid-phase FT-IR spectra are assigned modes based on the results of the theoretical calculations. The UV-Vis spectrum of each compound is measured in various solvents with a wide range of polarity to examine the role of solvent chemistry on observed spectral changes. The calculated spectra are in good agreement with the experimental spectra.     

Two-photon-induced intramolecular excited-state proton transfer process and nonlinear optical properties of HBI in ethanol solution

The two-photon-induced excited state intramolecular proton transfer (ESIPT) process of 2-(2′-hydroxyphenyl) benzimidazole (HBI) in ethanol solution has been investigated. We focused on the calculation of TPA coefficient and nonlinear refraction index of HBI, and found that the theoretical calculated results were in good agreement with the experimental ones. By establishing the two-photon-induced ESIPT kinetic model for HBI, the TPA cross section was determined to be 2.09 × 10⁴ GM. For their large TPA cross section, HBI is a promising TPA candidate material for their potential application in many fields.     

Solvent effects on IR and VCD spectra of helical peptides: DFT-based static spectral simulations with explicit water

Simulations of IR and VCD spectra are carried out for model alpha-helical, 3(10)-helical, and 3(1)-helical (polyProII-like) oligopeptides, with up to 21 amide groups, and including explicit consideration of effects of directly hydrogen-bonded solvent (water). Parameters used were obtained from ab initio density functional theory (DFT) computations of force field, atomic polar and axial tensors for oligopeptides of 5 to 7 amides, whose structures were constrained in (phi,psi) to target the secondary structure type but otherwise fully optimized. By comparison with experimental data as well as with calculations for identical but isolated (gas phase) peptides, the computed effects of an inner shell of aqueous solvent on the vibrational spectra of helical oligopeptides are illustrated. The interaction with solvent causes significant frequency shifts of the amide bands, but only minor changes in the characteristic IR intensity distributions and splittings and the VCD band shapes. Better agreement with experimental band shapes is achieved for the alpha-helical amide I' (N-deuterated) VCD by inclusion of explicit solvent in the calculations. Some improvements are also observed in theoretical VCD predictions for 13C labeled alpha-helical peptides when solvated models are used. However, the qualitative isotopic splitting patterns are preserved and just shifted in frequency due to consistent, solvent independent interamide coupling constants. The critical match of experiment and theory for relative positions of transitions in peptides with specifically separated 13C=O labels, including and neglecting solvent, confirms the stability of the coupling interactions. Despite these solvation effects, the calculated VCD band shape of the amide I mode is shown to be a reliable conformational probe, since it remains basically insensitive to frequency shifts caused by environment. Thus theoretical VCD simulations, even vacuum calculations, are shown to provide useful spectral predictions for solution-phase peptides.     

Three‐dimensional reference interaction site model self‐consistent field analysis of solvent and substituent effects on the absorption spectra of Brooker's merocyanine

Solvent and substituent effects on the absorption spectra of Brooker's merocyanine (BM) are investigated using the three‐dimensional reference interaction site model self‐consistent field method and time‐dependent density functional theory. The π–π* excitation energies are computed for BM and its derivative 2,6‐di‐tert‐butyl (di‐t‐Bu) BM. The behaviors of the computed excitation energies with increasing solvent polarity are in good agreement with those of the corresponding experimental measurements. In addition, analysis of the solute–solvent interaction energies and spatial distribution functions reveals that the effects of the solvent on the absorption spectra are reduced by the steric hindrance of the t‐Bu groups. Furthermore, from the difference in the solute–solvent interaction energies of BM and di‐t‐Bu BM, it is shown that the effect of the t‐Bu substituents on the absorption spectrum is greater in high‐polarity solvents. © 2015 Wiley Periodicals, Inc.