Calculation Of Electronic Absorption Spectra Research Articles

SPECTRAL CHARACTERISTICS OF CONFORMATION ISOMERS OF MESO-OCTAMETHYL-CALIX(4)PYRROLE BASED ON QUANTUM-CHEMICAL CALCULATIONS

The structure optimization and calculation of electronic absorption spectra of meso-octa-methylcalix(4)pyrrole conformers was performed by density- functional theory using hybrid B3LYP functional in cc-pVTZ basis set of Gaussian 09 package. Analysis of experimental UV-Vis spectra of solutions of calix(4)pyrrole was carried out in various solvents. The conclusion on the existence of a dynamic equilibrium between conformers in solutions of meso-octamethylcalix(4)pyrrole was made.

Correction to Efficient Calculation of Electronic Absorption Spectra by Means of Intensity-Selected Time-Dependent Density Functional Tight Binding.

ADVERTISEMENT RETURN TO ISSUEPREVErratumNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to Efficient Calculation of Electronic Absorption Spectra by Means of Intensity-Selected Time-Dependent Density Functional Tight BindingRobert Rüger*, Erik van Lenthe, You Lu, Johannes Frenzel, Thomas Heine, and Lucas Visscher*Cite this: J. Chem. Theory Comput. 2017, 13, 7, 3424–3425Publication Date (Web):June 8, 2017Publication History Published online8 June 2017Published inissue 11 July 2017https://doi.org/10.1021/acs.jctc.7b00564Copyright © 2017 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views686Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (582 KB) Get e-Alerts Get e-Alerts

Calculation of Electronic Absorption Spectra with Account of Thermal Geometry Fluctuations

An influence of thermal fluctuations of molecule's geometry on calculated electronic-absorption Vis/Uv spectra is considered. Paper presents the quantum chemical modeling of the electronic-absorption spectra for the collection of graphene samples (44, 56, 60, 68 atoms). The calculations were performed by time dependent density functional theory (TDDFT) method in combination with molecular dynamics (MD) simulation at T=300 K. The noticeable changing of spectra relative to single point TDDFT calculation was discovered for two of four structures. We associate achieved results with perturbation of hydrogen and carbon atoms on the edges of the structures. We believe that suggested methodology will be useful in application engineering researches of novel molecules and molecular complexes.

Efficient calculation of electronic absorption spectra by means of intensity-selected time-dependent density functional tight binding.

During the last two decades density functional based linear response approaches have become the de facto standard for the calculation of optical properties of small- and medium-sized molecules. At the heart of these methods is the solution of an eigenvalue equation in the space of single-orbital transitions, whose quickly increasing number makes such calculations costly if not infeasible for larger molecules. This is especially true for time-dependent density functional tight binding (TD-DFTB), where the evaluation of the matrix elements is inexpensive. For the relatively large systems that can be studied the solution of the eigenvalue equation therefore determines the cost of the calculation. We propose to do an oscillator strength based truncation of the single-orbital transition space to reduce the computational effort of TD-DFTB based absorption spectra calculations. We show that even a sizable truncation does not destroy the principal features of the absorption spectrum, while naturally avoiding the unnecessary calculation of excitations with small oscillator strengths. We argue that the reduced computational cost of intensity-selected TD-DFTB together with its ease of use compared to other methods lowers the barrier of performing optical property calculations of large molecules and can serve to make such calculations possible in a wider array of applications.

Synthesis, structural and spectral analysis of 1-(pyrazin-2-yl) piperidin-2-ol by density functional theory

The organic compound 1-(pyrazin-2-yl) piperidin-2-ol (abbreviated as PPOL) has been synthesized and characterized by IR, Raman, 1H NMR and UV–Vis spectroscopy. The Fourier-transform Raman (3500–50cm−1) and infrared spectra (4000–400cm−1) were recorded in the solid state and interpreted by comparison with theoretical spectra derived from density functional theory (DFT) calculations. The optimized geometry, frequency and intensity of the vibrational bands of the compound was obtained by the density functional theory using 6-31G(d,p) basis set. In the optimized geometry results shows that geometry parameters are good agreement with XRD values. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. In calculation of electronic absorption spectra, TD-DFT calculations were carried out in the both gas and solution phases. 1H NMR chemical shifts were calculated by using the gauge-invariant atomic orbital (GIAO) method. 1H NMR analysis is evident for O–H⋯O intermolecular interaction of the title molecule. The thermodynamic properties of the title compound have been calculated at different temperatures and the results reveal that the standard heat capacities (Cp,m), standard entropies (Sm) and standard enthalpy changes (Hm) increase with rise in temperature. In addition, HOMO and LUMO energies and the first-order hyperpolarizability have been computed.

Quantum-chemical calculations of electronic-absorption spectra of aromatic amino acids in aqueous solution

Quantum-chemical methods are used to calculate electronic-absorption spectra, dipole moments, and atomic-charge distributions of aromatic amino acids in aqueous solutions at various concentrations. The electronic-absorption spectra are analyzed and compared with the spectra that are calculated for gas phase. The bathochromic shift of the spectral position is shown for the long-wavelength absorption peak of the singlet-singlet transition for aqueous solutions of amino acids.

Crystal structure, spectroscopic characterization and density functional studies of (E)-1-((3-methoxyphenylimino)methyl)naphthalen-2-ol

The Schiff base compound (E)-1-((3-methoxyphenylimino)methyl)naphthalen-2-ol was synthesized from the reaction of 2-hydroxy-1-naphthaldehyde with 3-methoxyaniline. The structural properties of the compound has been characterized by using FT-IR, UV–vis and X-ray single-crystal methods. According to X-ray diffraction result, the title compound exists in the phenol-imine tautomeric form. The molecular geometry, vibrational frequencies of the compound in the ground state have been calculated using the density functional theory (DFT/B3LYP) method with the 6-311++G(d,p) basis set, and compared with the experimental data. The obtained results show that the optimized molecular geometry is well reproduce the crystal structure. The theoretical vibrational frequencies are in good agreement with the experimental values. The calculations of electronic absorption spectra of tautomeric forms of the compound were performed by using TD-DFT calculations both in the gas phase and ethanol solvent. To investigate the tautomeric stability, optimization calculations at the B3LYP/6-311++G(d,p) level were performed for the phenol-imine and keto-amine forms of the compound. According to calculated results, the OH form is more stable than NH form. In addition, molecular electrostatic potential (MEP), frontier molecular orbital analysis (HOMO–LUMO), thermodynamic and, non-linear optical (NLO) properties of the compound were investigated using same theoretical calculations.

Synthesis, spectroscopic characterization and computational studies of (Z)-1-((5,6,7,8-tetrahydronaphthalen-1-ylamino)methylene)naphthalen-2(1H)-one

The Schiff base compound (Z)-1-((5,6,7,8-tetrahydronaphthalen-1-ylamino)methylene)naphthalen-2(1H)-one has been synthesized and characterized by IR, UV–Vis and single-crystal X-ray diffraction. The title compound exist as NH tautomeric form in solid state. Molecular geometry and vibrational frequencies of the compound in the ground state have been calculated using the density functional method (DFT) with 6-31G(d,p) basis set and compared with the experimental data. The calculated results show that the optimized geometry can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies are in good agreement with the experimental values. In calculation of electronic absorption spectra, TD-DFT calculations were carried out in the both gas and solution phases. The energetic behavior of the compound in solvent media has been examined using B3LYP method with the 6-31G(d,p) basis set by applying the polarizable continuum model (PCM). The total energy of the compound decreases with increasing polarity of the solvent. Besides, molecular electrostatic potential (MEP), non-linear optical (NLO) properties of the compound were investigated using theoretical calculations.

Wavelet-based linear-response time-dependent density-functional theory

Linear-response time-dependent (TD) density-functional theory (DFT) has been implemented in the pseudopotential wavelet-based electronic structure program BigDFT and results are compared against those obtained with the all-electron Gaussian-type orbital program deMon2k for the calculation of electronic absorption spectra of N2 using the TD local density approximation (LDA). The two programs give comparable excitation energies and absorption spectra once suitably extensive basis sets are used. Convergence of LDA density orbitals and orbital energies to the basis-set limit is significantly faster for BigDFT than for deMon2k. However the number of virtual orbitals used in TD-DFT calculations is a parameter in BigDFT, while all virtual orbitals are included in TD-DFT calculations in deMon2k. As a reality check, we report the X-ray crystal structure and the measured and calculated absorption spectrum (excitation energies and oscillator strengths) of the small organic molecule N-cyclohexyl-2-(4-methoxyphenyl)imidazo[1,2-a]pyridin-3-amine.

Synthesis, spectroscopic characterization and computational studies of (Z)-4-methyl-N-[2-((2-oxonaphthalen-1(2H)-ylidene)methylamino)ethyl]-benzenesulfonamide

Abstract The Schiff base compound (Z)-4-methyl-N-[2-((2-oxonaphthalen-1(2H)-ylidene)methylamino)ethyl]-benzenesulfonamide has been synthesized and characterized by IR, UV–Vis and single-crystal X-ray diffraction. Molecules of the title compound exist as NH tautomeric form in solid state. Molecular geometry and vibrational frequencies of the compound in the ground state have been calculated using the density functional theory (DFT) with 6-31G(d,p) basis set and compared with the experimental data. The calculated results show that the optimized geometry can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies are in good agreement with the experimental values. In calculation of electronic absorption spectra, TD-DFT calculations were carried out in the both gas and solution phases. The energetic behavior of the compound in solvent media has been examined using B3LYP method with the 6-31G(d,p) basis set by applying the polarizable continuum model (PCM). The total energy of the compound decreases with increasing polarity of the solvent. Besides, molecular electrostatic potential (MEP) and non-linear optical (NLO) properties of the title compound were investigated using theoretical calculations.

Study of the structure and spectral properties of dianions of Zn complexes of porphyrins by the method of density functional theory

The structure, solvation energies, and electronic absorption spectra of products corresponding to the second stage of reduction of Zn porphin (Zn-P) with metallic sodium are calculated using methods of density functional theory. Calculated solvation energies of free and bound ions make it possible to assume that, in commonly used aprotic solvents, reduction products form [2Na+ · Zn-P2−] anion-cation contact complexes. The relative energies of the four stable isomers [2Na+ · Zn-P2−] detected in the gas phase and solvents are considerably different. The arrangement of Na+ on different sides of the macrocycle and along the NN axis favors the interaction with the solvent and stabilization in the solution. This conclusion is consistent with the data of calculations of electronic absorption spectra and of modeling of the spectral manifestations of the electron photodetachment from dianions of Zn-tetraphenylporphyrin (Zn-TPP) in frozen matrices. The behavior of the calculated transitions in the series of neutral and charged forms of Zn-P and Zn-TPP is well consistent with experimental data. Despite the fact that the spectral properties of the neutral and dianionic forms of Zn-P and Zn-TPP in the visible range are similar, the nature of their excited states is different.

Density functional theory study of tautomerization of 2‐aminothiazole in the gas phase and in solution

AbstractThe amino/imino tautomeric equilibrium in the isolated, mono‐, di‐, and trihydrate forms and dimer of 2‐aminothiazole, and the effects of hydration or self‐assistance on the transition state structures corresponding to proton transfer from the amino to imino form, have been investigated by the B3LYP method in conjunction with 6‐31+G(d,p) and 6‐311+G(3df,2p) basis sets in the gas phase and in solution. The amino form has been found to be the predominant tautomer. The tautomeric barrier heights for water‐ and self‐assisted tautomerization reactions are significantly lower than that from the amino to imino form by the intramolecular proton transfer, showing the catalytic effect of water molecule(s) and the important role of 2‐aminothiazole itself for intermolecular proton transfer. Comparison between the tautomeric barriers demonstrates that the self‐association tautomerization through the dimerization is the most favorable pathway. Bulk solvent effects have been taken into account using the polarizable continuum model (PCM) of water and CCl4. The polar medium is favorable for the population of the imino form. The amino/imino equilibrium is also analyzed using the aromaticity index nucleus‐independent chemical shift (NICS); the NICS values for the amino form (about −10 ppm) are more negative than the imino species (about −8 ppm), showing that the amino form is more stable. The time‐dependent density functional theory (TDDFT) calculations of electronic absorption spectra suggest that the λmax of dimer is 255 nm. The oscillator strength of the imino forms is less than the amino form, and increases with the polarity of the solvents. All calculations for the tautomerization of 2‐aminothiazole are in reasonable line with the available experiments. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Ab initio calculation of electronic absorption spectra and ionization potentials of C3H3 radicals

C3H3 isomers play a major role in combustion chemistry and are of fundamental interest in understanding photodissociation processes of hydrocarbons. Nevertheless, their electronic and ionization spectra are largely unknown. This study presents the first extended investigation of the electronically excited states and ionization potentials of the four most stable isomers, namely propargyl, 1-propynyl, cycloprop-2-enyl, and cycloprop-1-enyl. Electronic spectra are studied by ab initio calculations of the vertical excitation energies at the multi-reference configuration interaction (MRCI) level of theory. Vertical and adiabatic ionization energies are determined by coupled-cluster (RCCSD(T)) and multi-reference perturbation theory (CASPT2). The obtained results are suitable to aid the experimental detection of the different C3H3 isomers. Most of all, the calculations show that the assignment of an experimentally observed absorption at 242 nm to the propargyl radical was erroneous. Therefore, some recent experiments, based on this assignment, also need to be re-interpreted because this absorption is due to a yet unknown species.

THE IMPACT OF THE PHENYL SPACER ON THE ELECTRONIC STRUCTURE AND SPECTRA OF PORPHYRIN DIMERS

Quantum-chemical investigation of the electronic structure and properties of the excited states of porphyrin dimers, in which monomeric subunits are linked by the phenyl spacer, is performed by semiempirical methods. The molecular orbitals of the monomeric subunits are shown to interact with each other via molecular orbitals of the phenyl ring. Comparison of the experimental absorption data and quantum-chemical calculations of electronic absorption spectra for different conformations of Zn-tetraphenylporphyrin dimer is performed and the main conformation of the dimer in a solution at 295 K, in which the planes of tetrapyrrole macrocycles are located at an angle of about 60°, is substantiated.

DFT/MRCI calculations on the excited states of porphyrin, hydroporphyrins, tetrazaporphyrins and metalloporphyrins

A combination of density functional theory and multi-reference configuration interaction methods (DFT/MRCI) has been applied to the calculation of electronic absorption spectra in a series of porphyrin-type molecules. The calculated excitation energies and oscillator strengths for free-base porphyrin ( PH 2) are in excellent agreement with experiment for both lower and higher excited states which are characterized by a significant contribution of double excitations (>20%). The 41 B 2 u , 41 B 3 u , and 51 B 2 u states are assigned to the L-band and the 71 B 3 u state to the M-band. The results for the hydroporphyrins chlorin ( CH 2) and bacteriochlorin ( BH 2) are in agreement with the experimentally observed increase in intensity for the Q-bands relative to PH 2. For BH 2 we predict a red shift of the Q x -band (0.2 eV) and a blue shift of the B-band (0.5–0.7 eV) in comparison to both PH 2 and CH 2. For porphyrazine ( PzH 2) and the commercial pigment phthalocyanine ( PcH 2) the calculated oscillator strengths of the Q- and B-bands are of comparable size explaining the intense color of PcH 2. For the metalloporphyrins with magnesium ( PMg ) and zinc ( PZn ), the x- and y-polarized components of the Q- and B-bands collapse, due to the higher D4 h symmetry of the molecules. The calculations reproduce the slight, experimentally observed increase in the oscillator strength of the Q-band and the decrease for the B-band. These effects are ascribed to the electropositive nature of the metals relative to hydrogen. Except for the Q-bands, which are adequately described by the 'four-orbital model,' it is essential to account for excitations outside the four frontier orbitals as well as double and triple excitations for accurate reproduction of experimental data. We compare our results both with experiment and, where available, recent first-principle SAC-CI, MRMP, and TDDFT calculations.

Photocolouration of 2,4,4,6-Tetraaryl-4H-pyrans and Their Heteroanalogues: Importance of Hypervalent Photoisomers

Molecular geometries of 2,4,4,6-tetraphenyl-4H-pyran (Ia), 4,4-(biphenyl-2,2e-diyl)-2,6-diphenyl-4H-pyran (Ib) and their heterocyclic isomers II-V were optimized by the PM3 method and used for the calculation of electronic absorption spectra by the CNDO/S-CI procedure. Comparison of the theoretical data with experimental UV-VIS absorption spectra made possible to select hypervalent molecules IIIa, IIIb, IVa and IVb being responsible for the photocolouration of 4H-pyrans Ia, Ib, while compounds Va, Vb, VI and VII come into account as possible photodegradation products. The bleaching process of the UV illuminated compound Ia is analyzed in terms of dispersive first-order reaction kinetics.

System–bath relaxation theory approach to nonadiabatic coupling effects on condensed phase electronic absorption spectra

Separation of a many-body system into a primary system plus a bath of background modes enables approximate calculation of electronic absorption spectra and zero-temperature resonance Raman scattering cross sections in cases where there is nonadiabatic coupling between two or more Born–Oppenheimer excited-state potential surfaces. In particular, the low-resolution optical line shape theory recently developed to describe curve-crossing phenomena [D. G. Evans and R. D. Coalson, J. Chem. Phys. 99, 6264 (1993)] is extended to systems where there is a primary nuclear coordinate mode that is characterized by large excited-state displacements and an ensemble of weakly displaced bath modes. The accuracy of the resulting approximation scheme is illustrated using the spectroscopic spin-boson model, in which all surfaces are harmonic, and path integral techniques can be used to obtain exact results. Application to more complicated systems is discussed.

Photocolouration of 2,4,4,6-Tetraaryl-4H-thiopyrans: A Semiempirical Quantum Chemical Study

Molecular geometries of 4H-thiopyrans Ia, Ib and their possible photoisomers IVa - VIIa and IVb - VIIb were optimized by the AM1 and PM3 method and used for the calculation of electronic absorption spectra by the CNDO/S-CI procedure. Comparison of the theoretical data with experimental UV-VIS absorption spectra made it possible to postulate two probable mechanisms of the photocolouration of Ia, Ib caused by sunlight or UV-illumination.