Luminescent Eu(III) and Gd(III) trisbipyridine cryptates: experimental and theoretical study of the substituent effects.

Synthesis, absorption spectra and luminescebce properties of a series of lanthanide trisbipyridine cryptates Ln within R-Bpy x R-Bpy x R-Bpy, where Ln = Eu, Gd and R = H, COOH, COOCH3, CONH(CH2)2NH2 are described. Comparison of the unsubstituted parent compound with the substituted compounds shows that bipyridine substitution doesn't alter significantly the photophysical properties of the lanthanide cryptate. The absorption maximum is slightly red-shifted when three bipyridines are substituted, whereas substituting one bipyridines has a negligible effect on the absorption spectra. The experimental triplet state energy is between 21600 and 22 100 cm(-1) for the series of compounds and the luminescence lifetimes at 77 K are between 0.5 and 0.8 ms in HO2 and equal to 1.7 ms in D2O. The experimental characterizations are completed by DFT and TD-DFT calculations to assess the ability of these approaches to predict absorption maxima, triplet state energies and structural parameters of lanthanide cryptates and to characterize the electronic structure of the excited states. The calculations on the unsubstituted parent and substituted compounds show that absorption maxima and lowest 3pipi* triplet state energies can be accurately determined from density functional theory (DFT) and time-dependent (TD) DFT calculations.     

A density functional theory (DFT) and time-dependent density functional theory (TDDFT) study on optical transitions in oligo(p-phenylenevinylene)-fullerene dyads and the applicability to resonant energy transfer

The optical transitions of three different size oligo(p-phenylenevinylene)-fullerene dyads (OPV(n)-MPC(60); n = 2-4) and of the corresponding separate molecules are studied using density functional theory (DFT) and time-dependent density functional theory. The DFT is used to determine the geometries and the electronic structures of the ground states. Transition energies and excited-state structures are obtained from the TDDFT calculations. Resonant energy transfer from OPV(n) to MPC(60) is also studied and the Fermi golden rule is used, along with two simple models to describe the electronic coupling to calculate the energy transfer rates. The hybrid-type PBE0 functional is used with a split-valence basis set augmented with a polarization function (SV(P)) in calculations and the calculated results are compared to the corresponding experimental results. The calculated PBE0 spectra of the OPV(n)-MPC(60) dyads correspond to the experimental spectra very well and are approximately sums of the absorption spectra of the separate OPV(n) and MPC(60) molecules. Also, the absorption energies of OPV(n) and MPC(60) and the emission energies of OPV(n) are predicted well with the PBE0 functional. The PBE0 calculated resonant energy transfer rates are in a good agreement with the experimental rates and show the existence of many possible pathways for energy transfer from the first excited singlet states of the OPV(n) molecules to the MPC(60) molecule.     

Application of density functional theory for studies of excited states and phosphorescence of platinum(II) acetylides

The electronic states of different conformations of platinum acetylides Pt(PH3)2(C[triple bond]C-Ph)2 and Pt(PH3)2(C[triple bond]C-PhC[triple bond]C-Ph)2 (PE1 and PE2) were calculated with density functional theory (DFT) using effective core potential basis sets. Time dependent DFT calculations of UV absorption spectra showed strong dependence of the intense absorption band maxima on mutual orientation of the phenyl rings with respect to the P-Pt-P axis. Geometry optimization of the first excited triplet state (T1) indicates broken symmetry structure with the excitation being localized in one ligand. This splits the two substitution ligands into a nondistorted aromatic ring with the C[triple bond]C-Ph bonds for one side and into a quinoid structure with a cumulenic C=C=C link on the other side. Quadratic response (QR) calculations of spin-orbit coupling and phosphorescence radiative lifetime (tauR) indicated a good agreement with experimental tauR values reported for solid PE1 and PE2 and PE2 capped with dendrimers in tetrahydrofuran solutions. The QR calculations reproduced an increase of tauR upon prolongation of pi chain of ligands and concommittant redshift of the phosphorescence. Moreover, it is shown how the phosphorescence borrows intensity from sigma-->pi* transitions localized at the C[triple bond]C-Pt-P fragments and that there is no intensity borrowing from delocalized pi-->pi* transitions.     

Testing computational models of hyperpolarizability in a merocyanine dye using spectroscopic and DFT methods

The structural and electronic properties of a highly solvatochromic merocyanine dye, 2-(3-cyano-5,5-dimethyl-4-(3-(1-octadecylpyridin-4(1H)-ylidene)prop-1-enyl)furan-2(5H)-ylidene)malononitrile (pyr3pi), have been investigated using UV-vis, NMR, hyper-Rayleigh scattering, and Raman spectroscopies and further interpreted using computational chemistry. Spectroscopic data indicate that pyr3pi exists in its zwitterionic form even in low polarity solvents with electronic absorption spectra showing a hypsochromic shift with an increase in solvent polarity and NMR experiments indicating an increasingly zwitterionic structure in chloroform as the temperature is lowered. Raman spectra in increasingly polar solvents show small variations of the structure that are consistent with a change toward a structure with more zwitterionic character. However, comparison of the calculated and experimental vibrational energies and intensities and comparison of NMR coupling constants with calculated bond order indicate that calculations underestimate the amount of charge separation seen in low polarity solvents. Although for this system density functional theory (DFT) calculations and the two-state model qualitatively reproduce negative solvatochromism, they fail to reproduce the trends in hyperpolarizability seen experimentally. This is attributed to solvent field DFT calculations underestimating the degree of charge separation in reaction fields representing low polarity solvents.     

FT-IR and FT-Raman spectral investigation, computed IR intensity and Raman activity analysis and frequency estimation analysis on 4-chloro-2-bromoacetophenone using HF and DFT calculations

In this work, the experimental and theoretical spectra of 4-chloro-2-bromoacetophenone (4C2BAP) are studied. FT-IR and FT-Raman spectra of title molecule have been recorded in the region 4000-100 cm(-1). The structural and spectroscopic data of the molecule in the ground state have been calculated by using Hartree-Fock and density functional method (B3LYP) with the 6-31G (d, p) and 6-311G (d, p) basis sets. The vibrational frequencies are calculated and scaled values are compared with the experimental FT-IR and FT-Raman spectra. The DFT (B3LYP/6-311G (d, p)) calculations are more reliable than the ab initio HF/6-311G (d, p) calculations for the vibrational study of 4C2BAP. The optimized geometric parameters (bond lengths and bond angles) are compared with experimental values of the molecule. The alteration of vibrational bands of the carbonyl and acetyl groups due to the presence of halogens (Cl and Br) in the base molecule is also investigated from their characteristic region of linked spectrum.     

Electronic spectroscopy and computational studies of glutathionylco(III)balamin

We have studied glutathionylcobalamin (GS-Cbl) by optical spectroscopy and with density functional theory (DFT) and time-dependent DFT (TD-DFT) electronic structure methods of truncated geometric models. We examined the geometric structure of the models by comparison of DFT calculations with recent high-resolution experimental X-ray structure data ( Hannibal, L. et al. Inorg. Chem. 2010, 49, 9921) for GS-Cbl, and we examined the TD-DFT excitation simulations by comparison of the models with measured optical spectra. The calculations employed the B3LYP hybrid functional and the nonhybrid BP86 functional in both vacuum and water (conductor polarized continuum model (cpcm)) with the 6-311G(d,p) basis set. The optimized geometric structure calculations for six truncated models were made by varying the chemical structure, solvent model, and the two DFT functionals. All showed similar geometry. Charge decomposition analysis (CDA) and extended charge decomposition analysis (ECDA), especially with BP86 shows the similar charge transfer nature of the Co-S bond in GS-Cbl and the Co-C bond in CH(3)Cbl. Mayer and Wiberg bond orders illustrate the similar covalent nature of the two bonds. Finally, absolute optical spectral simulation calculations were compared with the experimental UV-visible extinction spectrum and the electronic circular dichroism (ECD) differential extinction spectrum. The BP86 method shows more spectral features, and the best fit was found for a GS-Cbl model with 5,6-dimethylbenzimidazole at the BP86/6-311G(d,p) level with a water cpcm solvent model. The excited state transitions were investigated with Martin's natural transition orbitals (NTOs). The BP86 calculations also showed π bonding interactions between Co and the axial S of the GS- ligand in the molecular orbitals (MOs) and NTOs.     

Structural and spectroscopic characterization of 2,3-difluorobenzoic acid and 2,4-difluorobenzoic acid with experimental techniques and quantum chemical calculations

In this study, the molecular conformation, vibrational and electronic transition analysis of 2,3-difluorobenzoic acid and 2,4-difluorobenzoic acid (C7H4F2O2) were presented using experimental techniques (FT-IR, FT-Raman and UV) and quantum chemical calculations. FT-IR and FT-Raman spectra in solid state were recorded in the region 4000-400 cm(-1) and 4000-5 cm(-1), respectively. The UV absorption spectra of the compounds that dissolved in ethanol were recorded in the range of 200-800 nm. The structural properties of the molecules in the ground state were calculated using density functional theory (DFT) and second order M?ller-Plesset perturbation theory (MP2) employing 6-311++G(d,p) basis set. Optimized structure of compounds was interpreted and compared with the earlier reported experimental values. The scaled vibrational wavenumbers were compared with experimental results. The complete assignments were performed on the basis of the experimental data and total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. A study on the electronic properties, such as absorption wavelength, excitation energy, dipole moment and frontier molecular orbital energy, were performed by time dependent DFT (TD-DFT) approach. Based on the UV spectra and TD-DFT calculations, the electronic structure and the assignments of the absorption bands of steady compounds were discussed. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecules.     

Experimental and computational investigation of thiolate alkylation in Ni(II) and Zn(II) complexes: role of the metal on the sulfur nucleophilicity

The biologically relevant S-alkylation reactions of thiolate ligands bound to a transition metal ion were investigated with particular attention paid to the role of the metal identity: Zn(II) versus Ni(II). The reactivity of two mononuclear diamine dithiolate Zn and Ni complexes with CH(3)I was studied. With the [ZnL] complex (1) (LH(2) = 2,2'-(2,2'-bipyridine-6,6'-diyl)bis(1,1-diphenylethanethiolate)), a double S-methylation occurs leading to [ZnL(Me2)I(2)] (1(Me2)), while with [NiL] (2), only the mono-S-methylated product [NiL(Me)]I (2(Me)) is formed. Complexes 1 and 1(Me2) have been characterized by X-ray crystallography, while the structures of 2 and 2(Me) have been previously described. The kinetics of the first S-methylation reaction, investigated by (1)H NMR, is found to follow a second-order rate law, and the activation parameters, ΔH(?) and ΔS(?), are similar for both 1 and 2. S K-edge X-ray absorption spectroscopy measurements have been carried out on 1, 2, and 2(Me), and a TD-DFT approach was employed to interpret the data. The electronic structures of 1 and 2 calculated by DFT reveal that the thiolate-metal bond is predominantly ionic in 1 and covalent in 2. However, evaluation of the molecular electrostatic potential minima around the lone pairs of the thiolate sulfur atoms gives similar values for 1 and 2, suggesting a comparable nucleophilicity. The DFT-optimized structures of the mono-S-methylation products have been calculated for the Zn and Ni complexes. Molecular electrostatic potential analysis of these products shows that (i) the nucleophilicity of the remaining thiolate sulfur atom is partly quenched for the Ni complex while it is conserved in the Zn complex and, more importantly, (ii) that the accessibility for the methyl transfer agent to the remaining thiolate is favored for the mono-S-methylated Zn complex compared to the Ni one. This explains the absence of a double S-methylation process in the case of the Ni complex at room temperature.     

Density functional theory studies on the structure,spectra (FT-IR,FT-Raman,and UV) and first order molecular hyperpolarizability of 2-hydroxy-3-methoxy-N-(2-chloro-benzyl)-benzaldehyde-imine: Comparison to experimental data

The infrared and Raman spectra of 2-hydroxy-3-methoxy-N-(2-chloro-benzyl)-benzaldehyde-imine (HMCBI) have been recorded and analyzed. Density functional calculations at B3LYP/6-311++G(d,p) level were carried out to study the equilibrium geometries and vibrational spectra of HMCBI. The calculations revealed that the optimized geometry closely resembled the experimental XRD data. The calculated vibrational spectra were analyzed on the basis of the potential energy distribution (PED) of each vibrational mode, which allowed us to obtain a quantitative as well as qualitative interpretation of IR and Raman spectra. The ¹H nuclear magnetic resonance (NMR) chemical shifts of the molecule in the ground state were calculated by Gauge independent atomic orbital (GIAO) method. Information about size, shape, charge density distribution and site of chemical reactivity of the molecules has been obtained by mapping electron density isosurface with electrostatic potential surface. Based on optimized ground state geometries, the NBO analysis has been done to study donor–acceptor (bond–antibond) interactions. The TD-DFT method has been used to calculate energies, oscillator strengths of electronic singlet–singlet transitions and the absorption wavelengths. Solvent effects were considered using the polarizable continuum model (PCM). Good consistency is found between the calculated results and experimental data for the electronic absorption. The calculated first hyperpolarizability may be attractive for further studies on non-linear optical properties of materials.     

Excited-state hydrogen bonding and deprotonation of esculetin in solution: a DFT/TDDFT study

The combined density functional theory (DFT) and time-dependent density functional theory (TDDFT) method was used to study the electronic spectral properties of different deprotonated forms of esculetin. By comparing the experimental absorption and fluorescence bands with the calculated electronic spectra, it is evidently demonstrated that the minor absorption and fluorescence bands observed at slightly longer wavelengths than the principal bands in experiments are predominantly from the de-H3 form of the esculetin monomer. Furthermore, we clarified the relationship between electronic spectral shifts and electronic excited-state intramolecular hydrogen bonding changes: the strengthening of intramolecular hydrogen bond can induce an electronic spectral blueshift while the intramolecular hydrogen bond weakening can result in an electronic spectral redshift.     

Spectroscopic, quantum chemical DFT/HF study and synthesis of [2.2.1] hept-2'-en-2'-amino-N-azatricyclo [3.2.1.0(2,4)] octane

The compound 4-N-bicyclo [2.2.1] hept-2'-en-2'-amino-N-azatricyclo [3.2.1.0(2,4)] octane (2) has been synthesized and characterized by elemental analysis, IR, UV-vis, mass and NMR. Density functional theory (DFT) and Hartree-Fock (HF) calculations have been carried out for the title compound by using the standard 6-31G* basis set. The calculated results show that the predicted geometry can well reproduce the structural parameters. Predicted vibrational frequencies have been assigned and compared with experimental IR spectra and they complement each other. The theoretical electronic absorption spectra have been calculated by using CIS, TD-DFT and ZINDO methods. The (13)C NMR and (1)H NMR of compound (2) have been calculated by means of Becke 3-Lee-Yang-Parr (B3LYP) density functional method with 6-31G* basis set. Comparison between the experimental and the theoretical results indicates that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties. On the basis of vibrational analyses, the thermodynamic properties of the title compound at different temperatures have been calculated.     

Optical properties and delocalization of excess negative charges on oligo(phenylenevinylene)s: a quantum chemical study

A quantum chemical study of the electronic structure of negatively charged phenylenevinylene (PV) oligomers and methoxy-substituted derivatives is presented. The geometries of the PV oligomers were optimized using density functional theory. The geometry deformations are found to be delocalized along the entire oligomer chain without indication of polaron formation. The optical absorption spectra of the negatively charged PVs were calculated using both time-dependent density functional theory (TDDFT) and the singly excited configuration interaction method with an intermediate neglect of differential overlap reference wave function (INDO/s-CIS). The available experimental optical absorption energies are reproduced by the calculations. Introduction of methoxy substituents reduces the transition energies, while this does not have a strong effect on the charge distribution along the chain. DFT calculations yield a more delocalized excess negative charge than that of INDO/s-CIS calculations.     

Unraveling the Electronic Structure,Spin States,Optical and Vibrational Spectra of Malaria Pigment

A detailed knowledge of the electronic structure and magnetic and optical properties of hemozoin, the malaria pigment, is essential for the design of effective antimalarial drugs and malarial diagnosis. By employing state‐of‐the‐art electronic structure calculations, we have performed an in‐depth investigation of the malaria pigment. Specifically, molecular bond lengths and spin states of the two Fe^III heme centers and their exchange interaction, the UV/Vis absorption spectrum, and the IR vibrational spectra were calculated and compared with available experimental data. Our density functional theory (DFT)‐based calculations predict a singlet ground spin state that stems from an S=5/2 spin state on each of the Fe heme centers with a very weak antiferromagnetic exchange interaction between them. Our theoretical UV/Vis and IR spectra provide explanations for various spectroscopic studies of hemozoin and β‐hematin (a synthetic analogue of hemozoin). A good comparison of calculated and measured properties demonstrates the convincing unveiling of the electronic structure of the malaria pigment. Based on the predicted vibrational spectra, we propose a unique spectral band from the nuclear resonance vibrational spectroscopy (NRVS) results that could be used as a key fingerprint for malarial detection.     

MP2, DFT and ab initio calculations on thioxanthone

Density functional theory (DFT), HF and MP2 calculations have been carried out to investigate thioxanthone molecule using the standard 6-31+G(d,p) basis set. The results of MP2 calculations show a butterfly structure for thioxanthone. The calculated results show that the predicted geometry can well reproduce the structural parameters. The predicted vibrational frequencies were assigned and compared with experimental IR spectra. A good harmony between theory and experiment is found. The theoretical electronic absorption spectra have been calculated using CIS method. ¹³C and ¹H NMR of the title compound have been calculated by means of B3LYP density functional method with 6-31+G(d,p) basis set. The comparison of the experimental and the theoretical results indicate that density functional B3LYP method is able to provide satisfactory results for predicting NMR properties.     

Gold atoms and dimers on amorphous SiO(2): calculation of optical properties and cavity ringdown spectroscopy measurements

We report on the optical absorption spectra of gold atoms and dimers deposited on amorphous silica in size-selected fashion. Experimental spectra were obtained by cavity ringdown spectroscopy. Issues on soft-landing, fragmentation, and thermal diffusion are discussed on the basis of the experimental results. In parallel, cluster and periodic supercell density functional theory (DFT) calculations were performed to model atoms and dimers trapped on various defect sites of amorphous silica. Optically allowed electronic transitions were calculated, and comparisons with the experimental spectra show that silicon dangling bonds [[triple bond]Si(.-)], nonbridging oxygen [[triple bond]Si-O(.-)], and the silanolate group [[triple bond]Si-O(-)] act as trapping centers for the gold particles. The results are not only important for understanding the chemical bonding of atoms and clusters on oxide surfaces, but they will also be of fundamental interest for photochemical studies of size-selected clusters on surfaces.     

Experimental and computational studies on zwitterionic (E)-2-(1-(2-(4-methylphenylsulfonamido)ethyliminio)ethyl) phenolate

The Schiff base compound (E)-2-(1-(2-(4-methylphenylsulfonamido)ethyliminio)ethyl) phenolate has been synthesised and characterized by IR, UV–Vis, and X-ray single-crystal determination. Ab initio calculations have been carried out for the title compound using the density functional theory (DFT) and Hartree–Fock (HF) methods at 6-31G(d) basis set. The calculated results show that the DFT/B3LYP and HF can well reproduce the structure of the title compound. Using the TD-DFT and TD-HF methods, electronic absorption spectra of the title compound have been predicted and a good agreement with the TD-DFT method and the experimental ones is determined. Molecular orbital coefficient analyses reveal that the electronic transitions are mainly assigned to n → π* and π → π* electronic transitions. To investigate the tautomeric stability, optimization calculations at B3LYP/6-31G(d) level were performed for the NH and OH forms of the title compound. Calculated results reveal that the OH form is more stable than NH form. In addition, molecular electrostatic potential and NBO analysis of the title compound were performed at B3LYP/6-31G(d) level of theory.