CAM-B3LYP Levels Research Articles

Chalcone as Potential Nonlinear Optical Material: A Combined Theoretical, Structural and Spectroscopic Study.

In this work, we propose the synthesis of a novel bromine chalcone (E)-3-(2-bromophenyl)-1-(2phenylsulfonylamine)-phenyl)prop-2-en-1-one (BRC) that has been crystallized by slow evaporation technique. The second order molecular optical scattering and two-photon absorption(2PA) spectrumof the BRC molecule dissolved in Dimethyl Sulfoxide (DMSO) were evaluated by using Hyper Rayleigh Scattering and femtosecond tunable Z-Scan techniques. The first order hyperpolarizability of BRC dissolved in DMSO was estimated by using a simplified two-level model, in which one- and two-photon absorption parameters were used as input information to the model. The BRC crystal was characterized from single crystal X-ray diffraction (DRX) and spectroscopy analyzes. Also, the thermogravimetric analyses and the fluorescence spectra were obtained. In addition, an ab-initio calculation method, which includes the Møller-Plesset Perturbation Theory (MP2) and the Density Functional Theory (DFT) at CAM-B3LYP level,was used to estimate the crystal linear refractive index and the third-order electric susceptibility. Also, the average first hyperpolarizability of BRC molecules dissolved in DMSO was calculated and compared with the experimental results. The obtained values are good and qualify BRC crystal as a potential candidate for application in nonlinear optical devices.

DFT investigation of the electronic structure and nonlinear optic properties (NLO) of 3-amino-4-(Boc-amino)pyridine

The molecular geometrical parameters, vibrational frequencies, electronic properties and nonlinear optical (NLO) behavior of 3-amino-4-(Boc-amino)pyridine have been evaluated using the B3LYP, CAM-B3LYP and B3PW91 levels of density functional theory (DFT). The dipole moment (μ) and first hyperpolarizability (β) values of the title complex show that the molecule can be a good candidate as NLO material. The energy of HOMO and LUMO levels and the HOMO–LUMO energy gap, hardness, softness and electronegativity have been analyzed using DFT/B3LYP method with the 6-31+G(d,p) basis set. To understand the effect of the different media (gas phase and in methanol solvent) in electronic transitions, the UV–Vis computations of the molecule have been performed using time-dependent DFT (TD-DFT)/6-31+G(d,p) by applying the integral equation formalism-polarized continuum model. The second-order interaction energies of 3-amino-4-(Boc-amino)pyridine have been calculated using natural bond orbital analysis.

Electrochemical Properties of Al Doped Polypyrrole Composite Polymer: Mott-Schottky Approximation and Density Functional Theory

Polypyrrole and Al doped polyprrole thin films were synthesized by electrochemical deposition method. FTIR spectroscopic studies confirm the formation of PPy and Al:PPy thin films. From the FESEM crosssectional images, film thickness were measured as 393.9 and 425.0 nm for the PPy and Al doped PPy thin film, respectively. Electrochemical properties of the deposited polymers are studied by Mott-Schottky analysis and electrochemical impedance spectroscopy. The calculated acceptor concentration is 5.03 × 1018 m−3 and 5.14 × 1018 m−3 for PPy and Al:PPy thin film, respectively. EIS analysis are performed to find out the effect of aluminum doping on PPy matrix. An equivalent circuit model is fitted to the EIS data to understand the behavior of coating/electrolyte interface and to determine the values of the circuit elements. Time-dependent self-consistent field and density functional theory based on CAM-B3LYP level with 6-311G(d,p) basis set are used to compute electronic properties such as HOMO and LUMO energies, ionization potential, electron affinity, electronegativity, hardness, softness. Electronic energy levels of the synthesized polymers are represented using the results of Mott-Schottky studies, and the frontier energy levels are also illustrated in this energy diagram to give more detailed explanation.

Experimental and computational VUV photoabsorption study of dimethyl carbonate: A green solvent

VUV photoabsorption spectrum of dimethyl carbonate in the energy region 7–11 eV and its complete spectral analysis with the aid of quantum chemical calculations is reported for the first time. The spectrum recorded using synchrotron radiation comprises of weak bands overlapping a broad intense continuum. With a view to interpret possible vibronic structure, gas phase infrared spectrum in the region 500–4000 cm−1 is revisited. Density functional theory (DFT) and time dependent DFT (TDDFT) methodologies are used to obtain ground state geometry, vibrational frequencies and vertical excitation energies of dimethyl carbonate. The intense broad features in the spectrum could be attributed to valence transitions. Based on quantum defect calculations, energy ordering and symmetry, weak bands are designated as ns, np and nd type Rydberg transitions converging to the first five ionization potentials. The highest occupied molecular orbital is nonbonding in nature and largely localized on the oxygen atom of carbonyl group and quantum defect values obtained are consistent with excitation from oxygen lone pair. Excellent correlation is obtained between theoretically predicted (CAM-B3LYP levels of theory) and experimentally observed excited state energies. Potential energy curves of ground and first few excited states generated with a view to provide additional insights into their nature and further describe the observed spectra. The present study provides a comprehensive experimental and computation analysis of the VUV photoabsorption spectroscopy of dimethyl carbonate.

Spectroscopy of diethyl carbonate, a green solvent: An experimental and theoretical study

The electronic spectra of diethyl carbonate (DEC) based on photoabsorption spectroscopy using synchrotron radiation are investigated in the 6.8-11.5 eV region. The VUV photo absorption spectrum reported here for the first time comprises broad features in the 7-11 eV region with few weak overriding spectral peaks. The broad peaks could be assigned to valence excitations, while the weak ones correspond to the Rydberg series of ns, np, and nd types, thus converging to the first five ionization potentials. Quantum defect values obtained are consistent with the excitation of an electron from oxygen lone pair. Infrared bands of DEC were revisited in the 600-3100 cm−1 region. The observed infrared bands of DEC could be assigned by DFT calculations. The TDDFT methodology is used to compute the vertical excited state energies, valence/Rydberg nature, and oscillator strengths of the excited electronic states. A good agreement using the CAM-B3LYP level of theory is achieved between the theoretically predicted values and experimental observations. In the ionic limit of DEC, the lengthening of the CO and CO–C2H5 bond lengths is predicted. The potential energy curves of the first few excited states assisted in additional insights on the nature of the excited states and their role in photo dissociation dynamics. This study gives a first comprehensive report on the analysis of absorption spectra of DEC in the VUV region and the complete spectral assignments in the VUV and IR regions by quantum chemical calculations.

The effect of different conjugated structures in main ligand on the photophysical properties for a series of iridium(III) complexes from a theoretical perspective

The electronic structure and photophysical properties of five iridium(III) complexes have been studied using the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The influence of different conjugated structures on their photophysical properties has been explored. Ionization potentials, electron affinities and reorganization energy have also been obtained to evaluate the charge transfer and balance properties between hole and electron. The lowest energy emissions from the CAM-B3LYP level for these complexes are localized at 472, 503, 523, 635 and 699 nm, respectively. The theoretical investigation would be useful to design potential phosphorescent materials for application in the organic light-emitting diodes.

Isoprene-Derived Organosulfates: Vibrational Mode Analysis by Raman Spectroscopy, Acidity-Dependent Spectral Modes, and Observation in Individual Atmospheric Particles.

Isoprene, the most abundant biogenic volatile organic compound (BVOC) in the atmosphere, and its low-volatility oxidation products lead to secondary organic aerosol (SOA) formation. Isoprene-derived organosulfates formed from reactions of isoprene oxidation products with sulfate in the particle phase are a significant component of SOA and can hydrolyze forming polyols. Despite characterization by mass spectrometry, their basic structural and spectroscopic properties remain poorly understood. Herein, Raman microspectroscopy and density functional theory (DFT) calculations (CAM-B3LYP level of theory) were combined to analyze the vibrational modes of key organosulfates, 3-methyltetrol sulfate esters (racemic mixture of two isomers), and racemic 2-methylglyceric acid sulfate ester, and hydrolysis products, 2-methyltetrols, and 2-methylglyceric acid. Two intense vibrational modes were identified, ν(RO-SO3) (846 ± 4 cm-1) and νs(SO3) (1065 ± 2 cm-1), along with a lower intensity δ(SO3) mode (586 ± 2 cm-1). For 2-methylglyceric acid and its sulfate esters, deprotonation of the carboxylic acid at pH values above the pKa decreased the carbonyl stretch frequency (1724 cm-1), while carboxylate modes grew in for νs(COO-) and νa(COO-) at 1413 and 1594 cm-1, respectively. The ν(RO-SO3) and νs(SO3) modes were observed in individual atmospheric particles and can be used in future studies of complex SOA mixtures to distinguish organosulfates from inorganic sulfate or hydrolysis products.

Acid-Base Properties of Xanthohumol: A Computational and Experimental Investigation.

UV-vis spectrophotometry has been applied to determine acid dissociation constants of the prenylated chalcone xanthohumol. The pKa values were compared with those derived from pH-metric titrations. The order of the deprotonation site in the xanthohumol molecule was estimated by quantum mechanical calculations as 2'-OH, 4'-OH, and 4-OH. Furthermore, the electronic and spectroscopic properties of xanthohumol have been investigated on the basis of the time-dependent density functional theory (TDDFT). The TDDFT method, combined with a hybrid exchange-correlation functional using the B3LYP and CAM-B3LYP levels of theory in conjunction with the SMD solvation model, was used to optimize all geometries and predict the excitation energies of the neutral form and ionized species of the chalcone depending on pH value. The computed results were in good agreement with the experimental data. Consideration of the acid-base profile in conjunction with other molecular properties has a great importance and has the potential to be used to further improve the bioavailability of xanthohumol.

Investigation of carboxylation of carbon nanotube in the adsorption of anti-cancer drug: A theoretical approach

Nowadays, an important process applied in the design of novel composite materials and drug delivery fields is the carboxylation of carbon nanotubes. In this work, we study the interaction of the anti-cancer drug hydroxyurea with carboxyl-functionalized zigzag carbon nanotubes (CNTs) by employing the method of the density functional theory (DFT) at B3LYP and CAM-B3LYP levels in gas and solvent phases. The results show that all complexes are energetically favorable, especially in the aqueous phase. The enthalpy energy values are negative in all cases, which indicate their exothermic adsorption nature. The presence of COOH groups would create enough free space on the nanotube surface for the adsorption between interacting atoms. Thus, these can increase the activity of CNTs. Data indicates that adsorption is dependent on the carboxyl sites of the nanotube as well as on the sites of the drug. Furthermore, the hydrogen-bonding interactions between drug and COOH-CNTs play an important role for the different kinds of adsorption observed.

Spectroscopic, optical, DNA, antimicrobial and density functional theory studies of 5-Bromo-2-(trifluoromethyl)pyridine

The spectroscopic characterization of 5-Bromo-2-(trifluoromethyl)pyridine was performed by the applying of Fourier Transform-Infrared (FT-IR) and 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopies. The optimized geometric structure of 5-Bromo-2-(trifluoromethyl)pyridine was searched by density functional theory (DFT) on employing B3LYP, CAMB3LYP, and B3PW91 functional. The vibrational frequencies and chemical shift values were calculated by using B3LYP, CAMB3LYP, and B3PW91 levels with the 6–31++G(d, p) basis set. The non-linear optical (NLO) properties of 5-Bromo-2-(trifluoromethyl)pyridine were determined using the same methods The HOMO-LUMO energies were examined by applying time-dependent DFT (TD-DFT) method with integral equation formalism-polarized continuum model (IEF-PCM). The second-order interaction energies of the title molecule were derived from Natural Bond Orbital (NBO) analysis. The effect of the molecule on pBR322 plasmid DNA was monitored by agarose gel electrophoresis experiments. The antimicrobial activities were tested by using minimal inhibitory concentration method (MIC).

Role of N-Heterocyclic Carbenes as Ligands in Iridium Carbonyl Clusters

The low-energy isomers of Irx(CO)y(NHC)z (x = 1, 2, 4) are investigated with density functional theory (DFT) and correlated molecular orbital theory at the coupled cluster CCSD(T) level. The structures, relative energies, ligand dissociation energies, and natural charges are calculated. The energies of tetrairidium cluster are predicted at the CAM-B3LYP level that best fit the CCSD(T) results compared with the other four functionals in the benchmark calculations. The NHC's behave as stronger σ donors compared with CO's and have higher ligand dissociation energies (LDEs). For smaller isomers, the increase in the LDEs of the CO's and the decrease in the LDEs of the NHC's as more NHC's are substituted for CO's are due to π-back-bonding and electron repulsion, whereas the trend of how the LDEs change for larger isomers is not obvious. We demonstrate a μ3-CO resulting from the high electron density of the metal centers in these complexes, as the bridging CO's and the μ3-CO's can carry more negative charge and stabilize the isomers. Comparison of calculations for a mixed tetrairidum cluster consisting of two calixarene-phosphine ligands and a single calixarene-NHC ligand in the basal plane demonstrated good agreement in terms of both the ligand substitution symmetry (C3v derived), as well as the infrared spectra. Similar comparisons were also performed between calculations and experiment for novel monosubstituted calixarene-NHC tetrairidium clusters.

Effect of H-bonding interactions of water molecules in the self assembly of supramolecular architecture-joint experimental and computational studies

A new {[Cu(4,4′-BP)2.(H2O)4].2,6-NDC.3(H2O)} complex has been synthesized by refluxing Cu(NO3)2, 2,6-NDC and 4,4′-BP (1:1:1 ratio) (2,6-NDC = 2,6-Naphthalene Dicarboxylic acid, 4,4′-BP = 4,4'-bipyridine) in methanol/ammonia mixture and characterized by various spectroscopic techniques. The geometry around Cu2+ ion is typical octahedral in cationic complex, while the deprotonated 2,6-NDC act as a charge balancing counter anionic part. Water molecules (lattice and coordinated) also play important role in the self-assembly by forming H bonded supramolecular architecture involving strong inter/intramolecular secondary interactions. The luminescence property and thermogravimetric analyses were also investigated. Both the intermolecular interactions of molecular and crystal structures of this complex were compared and discussed using Hirshfeld surface analysis and 2D-fingerprint plots. Hirshfeld surface analysis indicates that H⋯H, O⋯H and π···π contacts can account for 40.4, 19.3 and 7.7% respectively of the total Hirshfeld surface area. The DFT calculation at the CAM-B3LYP level of theory revealed the existence of three hydrogens binds in the complex. These hydrogen bonds exist between the oxygen atom of ligand and the hydrogen of coordinated water molecules.

Catalytic promiscuity of mononuclear copper(II) complexes in mild conditions: Catechol and cyclohexane oxidations

Two copper(II) mononuclear complexes were synthesized and investigated as promiscuous oxidative catalysts: [Cu(pymimi)Cl2]: [(2-(pyridyl-2-yl)ethyl)((1-methylimidazol-2-yl)methyl)imine](bischlorido)copper(II), C1, and [Cu(pymima)Cl2]: [(2-(pyridyl-2-yl)ethyl)((1-methylimidazol-2-yl)methyl)amine] (bischlorido)copper(II), C2. Both complexes were characterized by the following techniques: X-ray crystallography, decomposition point, elemental analysis, IR, UV–Vis and EPR spectroscopies, conductimetric analysis and electrochemistry. DFT calculations at the B3LYP level were carried out to corroborate structural, vibrational and spin Hamiltonian parameters (gx, gy and gz). TDDFT electronic spectra were calculated at CAMB3LYP level. Cyclohexane peroxidation promoted by C1 and C2 yielded the following overall conversions/turnover numbers: 48%/531s−1 and 46%/508s−1, respectively. Both complexes also catalyze the conversion of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylquinone (3,5-DTBQ) with turnover numbers of 6.0×10−2s−1 for C1 and 11.0×10−2s−1 for C2. Complexes C1 and C2 can be classified as substrate promiscuous catalysts due to their ability to promote the oxidation of two different substrates, in the presence of distinct oxidants (O2, for catechol and H2O2 for cyclohexane).

Comparison of different hybrid DFT methods on structural, spectroscopic, electronic and NLO parameters for a potential NLO material

The molecular geometrical, vibrational frequency, molecular static polarizability and hyperpolarizability parameters, as well as HOMO-LUMO energies of 4-Aminopyridinium monophthalate (4-APMP) as potential nonlinear optical (NLO) material in the ground state were examined using hybrid GGA, meta-GGA, range-separated hybrid and long-range (LR) corrected models (B3LYP, B3PW91, M062X, HSEh1PBE, CAM-B3LYP, LC-BLYP and ωB97XD levels of density functional theory) with 6-311G(d,p) basis set in order to analyze the effects of different percentage of HF exchange. TD-DFT computations with the PCM (polarizable continuum model) within methanol solvent based on implicit/explicit model and gas phase in the excited state were employed to investigate UV–vis absorption and fluorescence emission wavelengths. Furthermore, by regarding the potential energy distribution (PED), a detailed vibrational study was fulfilled by using VEDA program. Experimental values of structural and spectroscopic parameters of 4-APMP were used to display the effects of the different theoretical methods on the spectroscopic and structural properties. To display the agreement and accuracy of among selected DFT levels and experimental data, the linear correlation coefficients (R2), mean absolute deviation (MAD), overall mean percent deviation (MPD), optimal scaling factor (λ) and overall root mean square (RMS) deviation for structural and vibrational frequency parameters were presented. The NLO parameters indicated that 4-APMP exhibits significant molecular nonlinearity.

Experimental and computational studies of 4-(Trifluoromethyl)pyridine-2-carboxylic acid

The vibrational spectrum of 4-(Trifluoromethyl)pyridine-2-carboxylic acid was recorded using Fourier transform infrared spectrometer in the range 4000–400 cm−1. The optimized geometric structure of 4-(Trifluoromethyl)pyridine-2-carboxylic acid was searched by B3LYP, CAMB3LYP, and PBEPBE levels of density functional theory (DFT). The vibrational wavenumbers of the title molecule in the ground state were computed by using B3LYP, CAMB3LYP, and PBEPBE methods with the 6-31G (d) basis set. NMR chemical shifts of the title compound were calculated using the gauge-independent atomic orbital (GIAO) method. The solvent effect on the UV–Vis absorption spectrum of the molecule was also examined using the B3LYP method by applying the integral equation formalism-polarized continuum model (IEF-PCM). The nonlinear optical (NLO) properties were measured by means of hyperpolarizability calculation. The electric dipole moment, the mean polarizability and the mean first hyperpolarizability were calculated by using the DFT method with B3LYP, CAMB3LYP, and PBEPBE levels.

Improvement of photovoltaic performance by substituent effect of donor and acceptor structure of TPA-based dye-sensitized solar cells.

We report a computational study of a series of organic dyes built with triphenylamine (TPA) as an electron donor group. We designed a set of six dyes called (TPA-n, where n = 0-5). In order to enhance the electron-injection process, the electron-donor effect of some specific substituent was studied. Thus, we gave insights into the rational design of organic TPA-based chromophores for use in dye-sensitized solar cells (DSSCs). In addition, we report the HOMO, LUMO, the calculated excited state oxidized potential E(dye*)(eV) and the free energy change for electron-injection ΔGinject(eV), and the UV-visible absorption bands for TPA-n dyes by a time-dependent density functional theory (TDDFT) procedure at the B3LYP and CAM-B3LYP levels with solvent effect. The results demonstrate that the introduction of the electron-acceptor groups produces an intramolecular charge transfer showing a shift of the absorption wavelengths of TPA-n under studies. Graphical Abstract Several organic dyes TPA-n with different donors and acceptors are modeled. A strong conjugation acrros the donor and anchoring groips (TPA-n) bas been studied. Candidate TPA-3 shows a promising results.

Bicarbonate and Alkyl Carbonate Radicals: Structural Integrity and Reactions with Lipid Components.

The elusive neutral bicarbonate radical and the carbonate radical anion form an acid/conjugate base pair. We now report experimental studies for a model of bicarbonate radical, namely, methyl carbonate (methoxycarbonyloxyl) radical, complemented by DFT computations at the CAM-B3LYP level applied to the bicarbonate radical itself. Methyl carbonate radicals were generated by UV irradiation of oxime carbonate precursors. Kinetic EPR was employed to measure rate constants and Arrhenius parameters for their dissociation to CO2 and methoxyl radicals. With oleate and cholesterol lipid components, methyl carbonate radicals preferentially added to their double bonds; with linoleate and linolenate substrates, abstraction of the bis-allylic H atoms competed with addition. This contrasts with the behavior of ROS such as hydroxyl radicals that selectively abstract allylic and/or bis-allylic H atoms. The thermodynamic and activation parameters for bicarbonate radical dissociation, obtained from DFT computations, predicted it would indeed have substantial lifetime in gas and nonpolar solvents. The acidity of bicarbonate radicals was also examined by DFT methods. A noteworthy linear relationship was discovered between the known pKa's of strong acids and the computed numbers of microsolvating water molecules needed to bring about their ionization. DFT computations with bicarbonate radicals, solvated with up to eight water molecules, predicted that only five water molecules were needed to bring about its complete ionization. On comparing with the correlation, this indicated a pKa of about -2 units. This marks the bicarbonate radical as the strongest known carboxylic acid.

Computational studies on structure and spectroscopic properties of 4-(Boc-amino) pyridine

The molecular modeling of 4-(Boc-amino) pyridine was carried out using B3LYP, CAMB3LYP and PBE1PBE levels of density functional theory (DFT). The vibrational frequencies of the title molecule in the ground state were computed by using B3LYP, CAMB3LYP and PBE1PBE methods with the 6-31G + (d, p) basis set. Gauge-independent atomic orbital (GIAO) 1H and 13C nuclear magnetic resonance (NMR) chemical shift values of the 4-(Boc-amino) pyridine were calculated by using the DFT/B3LYP with 6-31G + (d, p) basis set. The solvent effect on the NMR spectra of the molecule was also examined using the B3LYP method by applying the integral equation formalism-polarized continuum model (IEF-PCM). The electronic properties, such as HOMO-LUMO energies, absorption wavelengths and excitation energy, were investigated by time dependent DFT (TD-DFT) method with IEF-PCM. The mulliken charges on the atoms and second-order interaction energies were derived from NBO analysis. To investigate the nonlinear optical (NLO) properties of the title molecule, the electric dipole moment, the mean polarizability and the mean first hyperpolarizability were computed by using the DFT method with B3LYP, CAM-B3LYP and PBE1PBE levels.

Prediction of ROA and ECD Related to Conformational Changes of Astaxanthin Enantiomers.

ECD, ROA, and VCD were used to characterize astaxanthin conformers that differ in their arrangements of the β-ionone ring in respect to the chain. We obtained ECD spectra experimentally, and the ECD, ROA, and VCD spectra of both individual conformers and conformation-averaged mixtures were predicted using quantum-chemical calculations at the CAM-B3LYP level of theory using the PCM solvation model. The chiroptical methods employed (particularly ECD and ROA) were considerably more sensitive to conformational changes of astaxanthin compared to "mono-signed" conventional Raman spectroscopy. Strikingly, conformers that are the same optical isomers (e.g., of 3S,3'S-astxanthin), while geometrically nearly mirror images, exhibited sign-inversed ECD and ROA spectra. The conformational sensitivity of these chiroptical methods makes them a promising tool in the study of carotenoids in the natural environment (for instance, in de novo algal or yeast astaxanthin sources).

Theoretical analysis of excited states and energy transfer mechanism in conjugated dendrimers

Published in Journal of Computational Chemistry 2015, 36, 151–163; DOI: 10.1002/jcc.23778 The additional corrections were to delete the red cross for the excitation energy at the BH&HLYP and CAM-B3LYP levels in Figure 7. Low-lying excited states with different computational levels and experimental data. The blue, green, and red colors represent the 3→3 LE transition, the CT (2→3, 3→2) transitions, and the 2→2 LE, respectively. The solid lines and crosses denote the major and secondary electronic characters of each excited state. Furthermore, in the discussion of electronic character for the S3 state in Table S3 (Supporting Information), the “HOMO-1→LUMO(21%) 2→2” should be corrected to “HOMO-1→LUMO(21%) 2→3”. We apologize for any inconvenience caused by above misprints. Additional Supporting Information may be found in the online version of this article. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.