DFT (LSDA, B3LYP and B3PW91) comparative vibrational spectroscopic analysis of alpha-acetonaphthone

Linear and Nonlinear Optical Responses of Nitrobenzofurazan-Sulfide Derivatives: DFT-QTAIM Investigation on Twisted Intramolecular Charge Transfer

In this study, we report on the green fluorescence exhibited by nitrobenzofurazan-sulfide derivatives (NBD-Si, i = 1-4). The optical responses of these studied compounds in a polar methanol solvent were simulated by the use of time-dependent density functional theory (TD-DFT) employing the Becke-3-Parameter-Lee-Yang-Parr (B3LYP) functional along with the 6-31G(d,p) basis set. The computed energy and oscillator strength (f) results complement the experimental results. The band gap was calculated as the difference between the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). Additionally, the density of states (DOS) was computed, providing a comprehensive understanding of the fundamental properties of these materials and further corroborating the experimental data. When the experimental data derived from ultraviolet/visible (UV/visible) and fluorescence spectroscopic techniques and those from simulated spectra are analyzed, the extracted values match up adequately. In addition, the NBD-sulfide compounds exhibit a large Stokes shift up to 85 nm in a polar methanol solvent. They are hypothesized to represent a novel paradigm of excited-state intramolecular charge transfer (ICT). To understand the intrinsic optical properties of NBD-Si materials, an ICT was identified, and its direction within the molecule was evaluated using the ratio of βvect and βtotal, values extracted from the computed nonlinear optical (NLO) properties. Moreover, the reduced density gradient (RDG)-based noncovalent interactions (NCIs) were employed to characterize the strength and type of NBD-Si interactions. Furthermore, noncovalent interactions were identified and categorized using the Quantum Theory of Atoms in Molecules (QTAIM) analysis. Ultimately, the combination of Hirshfeld surface analysis and DFT calculations was utilized to enhance the characterization and rationalization of these NCIs.

Design new organic material based on triphenylamine (TPA) with D-π-A-π-D structure used as an electron donor for organic solar cells: A DFT approach

Because of the increasing scarcity of fossil fuels and the growing need for energy, it has become necessary to research new renewable energy resources. In this study, five new high-performance materials (TP-FA₁F-TP - TP-FA₅F-TP) of the D-π-A-π-D configuration based on triphenylamine (TPA) were theoretically investigated by applying DFT and TD-DFT methods for future application as heterojunction organic solar cells (BHJ). The influence of the modification of the acceptor (A) of the parent molecule TP-FTzF-TP on the structural, electronic, photovoltaic and optical properties of the TP-FA1F-TP - TP-FA5F-TP organic molecules was investigated in detail. TP-FA₁F-TP - TP-FA₅F-TP showed E_gap in the interval of 1.44-2.01 eV with λ_abs in the range of 536-774 nm, open-circuit voltage (V_oc) values varied between 0.3 and 0.56 V and power conversion efficiencies (PCE) ranging from (3-6) %. Our results also show that the donor molecules suggested in this research exhibit an improved performance compared to the recently synthesized TP-FTzF-TP, such as a lowest HOMO energy, a smaller E_gap, and a greater absorption spectrum, and can lead to higher performance. Indeed, this theoretical research could lead to the future synthesis of better compounds as active substances used in BHJ.

New organic dye-sensitized solar cells based on the D-A-π-A structure for efficient DSSCs: DFT/TD-DFT investigations

Global energy consumption has increased due to population growth and economic development. Solar energy is one of the most important renewable energy sources for human consumption. In this research, four novel organic dyes (D2-D5) of the D-A-π-A structure based on triphenylamine (TPA) were studied theoretically using DFT and TD-DFT techniques for future usage as dye-sensitized solar cells (DSSCs). The effects of modifying the π-spacer of the reference molecule D1 on the structural, electronic, photovoltaic, and optical characteristics of the D2-D5 dyes were studied in detail. D2-D5 exhibited band gaps (E _gap) in the range from 1.89 to 2.10 eV with λ _abs in the range of 508 to 563 nm. The results obtained show that modifying the π-spacer of the dye D1 increased its hole injection and reinforced the intramolecular charge-transfer (ICT) impact, which resulted in a red-shifted ICT absorption with a greater molar extinction coefficient. The theoretically calculated open-circuit voltage (V _oc) values ranged from 0.69 to 1.06 eV, while the light-harvesting efficiency (LHE) values varied from 0.95 to 0.99. Indeed, this theoretical research could guide chemists to synthesize effective dyes for DSSCs.

Étude structurale des systèmes dissymétriques de structure D-π-A à base de thiénopyrazine destinés aux cellules solaires organiques de type « bulk heterojunction » (BHJ)

Onze nouvelles molécules organiques de structure donneurs-espaceur-accepteurs (D-π-A) utilisées pour les cellules solaires organiques (OSC) basées sur la thiénopyrazine et le thiophène ont été étudiées par la théorie de la densité fonctionnelle (DFT) et la théorie de la densité fonctionnelle dépendante de temps DFT (TD-DFT), pour expliquer comment l’ordre de conjugaison influe sur les performances des cellules solaires. Le groupe accepteur d’électrons (ancrage) était composé de 2-cyanoacrylique pour tous les composés, tandis que l’unité donneuse d’électrons était variée et que son influence fut étudiée. Les résultats théoriques ont montré que les calculs TD-DFT, avec une fonction hybride d’échange – corrélation utilisant la méthode d’atténuation de Coulomb (CAM-B3LYP) en conjonction avec un modèle de solvatation à cycle continu polarisable (modèle de continuum polarisable, PCM) combinée avec la base 6-31G(d,p), était raisonnablement capable de prédire les énergies d’excitation, les spectres d’absorption et d’émission des molécules étudiées. Les niveaux d’énergie des orbitales moléculaires frontières (orbitale moléculaire occupée de plus haute énergie (HOMO) et orbitale moléculaire inoccupée de plus basse énergie (LUMO) de ces composés peuvent avoir un effet positif sur le processus d’injection et de régénération d’électrons. La tendance des lacunes calculées HOMO-LUMO se compare bien avec les données spectrales. En outre, les valeurs estimées de photovoltage en circuit ouvert (Voc) pour ces composés ont été présentées. L’étude des propriétés structurelles, électroniques et optiques de ces composés pourrait aider à concevoir des matériaux organiques photovoltaïques fonctionnels plus efficaces.

The photophysical properties and electronic structures of bis[1]benzothieno[6,7-d:6′,7′-d′]benzo[1,2-b:4,5-b′]dithiophene (BBTBDT) derivatives as hole-transporting materials for organic light-emitting diodes (OLEDs)

The compounds with the D–π–A structure are found to be good candidates for blue-emitting materials.

Structures, Interconversions, and Spectroscopy of Iron Carbonyl Clusters with an Interstitial Carbide: Localized Metal Center Reduction by Overall Cluster Oxidation

The syntheses, interconversions, and spectroscopic properties of a set of iron carbonyl clusters containing an interstitial carbide are reported. This includes the low temperature X-ray structures of the six-iron clusters (Y)₂[Fe₆(μ₆-C)(μ₂-CO)₄(CO)₁₂] (1a-c; where Y = NMe₄, NEt₄, PPh₄); the five-iron cluster [Fe₅(μ₅-C)(CO)₁₅] (3); and the novel formulation of the five-iron cluster (NMe₄)₂[Fe₅(μ₅-C)(μ₂-CO)(CO)₁₃] (4). Also included in this set is the novel charge-neutral cluster, [Fe₆(μ₆-C)(CO)₁₈] (2), for which we were unable to obtain a crystallographic structure. As synthetic proof for the identity of 2, we performed a closed loop of interconversions within a family of crystallographically defined species (1, 3, and 4): [Fe₆]^2- → [Fe₆]⁰ → [Fe₅]⁰ → [Fe₅]^2- → [Fe₆]^2-. The structural, spectroscopic, and electronic properties of this "missing link" cluster 2 were investigated by IR, Raman, XPS, and Mössbauer spectroscopies-as well as by DFT calculations. A single ν_CO feature (1965 cm^-1) in the IR spectrum of 2, as well as a prominent Raman feature (ν_symm = 1550 cm^-1), are consistent with the presence of terminal carbonyls and a {(μ₆-C)Fe₆} arrangement of iron centers around the central carbide. The XPS of 2 exhibits a higher energy Fe 2p_3/2 feature (707.4 eV) as compared to that of 1 (705.5 eV), consistent with the two-electron oxidation induced by treatment of 1 with two equivalents of [Fc](PF₆) under CO atmosphere (for the two added CO ligands). DFT calculations indicate two axial and four equatorial Fe sites in 1, all of which have the same or similar oxidation states, for example, two Fe(0) and four Fe(+0.5). These assignments are supported by Mössbauer spectra for 1, which exhibit two closely spaced quadrupole doublets with δ = 0.076 and 0.064 mm s^-1. The high-field Mössbauer spectrum of 2 (4.2 K) exhibits three prominent quadrupole doublets with δ = -0.18, -0.11, and +0.41 mm s^-1. This indicates three pairs of chemically equivalent Fe sites. The first two pairs arise from irons of a similar oxidation state, while the last pair arises from irons in a different oxidation state, indicating a mixed-valent cluster. Variable field Mössbauer spectra for 2 were simulated assuming these two groups and a diamagnetic ground state. Taken together, the Mössbauer results and DFT calculations for 2 indicate two axial Fe(II) sites and four equatorial sites of lower valence, probably Fe(0). In the DFT optimized pentagonal bipyramidal structure for 2, the Fe(II)-C_carbide distances are compressed (∼1.84 Å), while the Fe(0)-C_carbide distances are elongated (∼2.05 Å). Analysis of the formulations for 1 (closo-square bipyramid) and 2 (nido-pentagonal bipyramid) is considered in the context of the textbook electron-counting rules of 14n+2 and 14n+4 for closo and nido clusters, respectively. This redox-dependent intracluster disproportionation of Fe oxidation states is concluded to arise from changes in bonding to the central carbide. A similar phenomenon may be promoted by the central carbide of the FeMoco cluster of nitrogenase, which may in turn stimulate N₂ reduction.

Quantum chemical and spectroscopic (FT-IR and FT-Raman) investigations of 3-methyl-3h-imidazole-4-carbaldehyde

FT-IR and FT-Raman spectra of 3-methyl-3h-imidazole-4-carbaldehyde (3M3HI4C) were recorded in the region 4000-400cm(-1) and 3500-50cm(-1), respectively. Optimized geometric parameters, conformational equilibria, normal mode frequencies, and corresponding vibrational assignments of 3M3HI4C were theoretically examined by quantum chemical methods for the first time. All vibrational frequencies were assigned in detail with the help of total energy distribution (TEDs). The experimental wavenumbers were compared with the scaled vibrational frequencies determined by DFT/B3LYP method. The results showed that the B3LYP/6-311++G(d,p) method predicts vibrational frequencies and the structural parameters effectively. The most stable conformer of the title compound was determined. The total electron density and molecular electrostatic potential surfaces of the molecule were constructed by using B3LYP/6-311++G(d,p) method to display electrostatic potential (electron+nuclei) distribution. The electronic properties HOMO and LUMO energies were measured. The lower energy band was assigned to the HOMO→LUMO transition. Natural bond orbital analysis of title molecule has been performed to indicate the presence of intramolecular charge transfer. Energies, relative stabilities, and dipole moments of title molecule were also compared and analyzed in the gas phase and in solvents. Furthermore, solvent effects on the geometry and vibrational frequency of 3M3HI4C were studied theoretically at the DFT/B3LYP level in combination with the conductor polarizable continuum model (C-PCM).

Synthesis, molecular structure, FT-IR, Raman, XRD and theoretical investigations of (2E)-1-(5-chlorothiophen-2-yl)-3-(naphthalen-2-yl)prop-2-en-1-one

A novel (2E)-1-(5-chlorothiophen-2-yl)-3-(naphthalen-2-yl)prop-2-en-1-one [C17H11ClOS] compound has been synthesized and its structure has been characterized by FT-IR, Raman and single-crystal X-ray diffraction techniques. The isomers, optimized geometrical parameters, normal mode frequencies and corresponding vibrational assignments of the compound have been examined by means of the density functional theory method, employing, the Becke-3-Lee-Yang-Parr functional and the 6-311+G(3df,p) basis set. Reliable vibrational assignments and molecular orbitals have been investigated by the potential energy distribution and natural bonding orbital analyses, respectively. The compound crystallizes in the monoclinic space group P2₁/c with the unit cell parameters a=5.7827(8)Å, b=14.590(2)Å, c=16.138(2)Å and β=89.987 (°). The CC bond of the central enone group adopts an E configuration. There is a good agreement between the theoretically predicted structural parameters and vibrational frequencies and those obtained experimentally.

An experimental and theoretical study on the novel (Z)-1-((naphthalen-2-ylamino)methylene)naphthalen-2(1H)-one crystal

A novel compound has been synthesized, and its structure has been characterized by IR, UV-vis, NMR and X-ray single-crystal determination techniques. The title compound crystallizes in the orthorhombic space group P212121 with a=6.2120(4)Å, b=10.8242(7)Å, c=22.3857(15)Å and Z=4. The crystal structure has intramolecular N-H···O hydrogen bond and C-H···Cg interaction. These hydrogen bonds and interactions are effective in crystal packing. The optimum molecular geometry, conformational analysis, normal mode wavenumbers, infrared and Raman intensities, corresponding vibrational assignments, chemical shift assignments, and thermo-dynamical parameters have been investigated with the help of Density Functional Theory (DFT). Detailed vibrational assignments have been made on the basis of potential energy distribution (PED). In order to understand the electronic transitions of the compound, time dependent DFT (TD-DFT) calculations were performed in gas phase. Also, the dipole moment, linear polarizabilities, anisotropy and first hyperpolarizabilities values have been computed.

FTIR, FT-Raman and NMR studies on 2,6-dichlorotoluene and 2-chloro-6-fluorotoluene based on density functional theory

In the present work, we reported a combined experimental and theoretical study on molecular structure and vibrational analysis of 2,6-dichlorotoluene (DCT) and 2-chloro-6-fluorotoluene (CFT). FTIR and FT-Raman spectra of the title compounds in the solid phase are recorded in the region 4000-400 cm(-1) and 4000-50 cm(-1) respectively. The structural and spectroscopic data of the molecules in the ground state is calculated using Hartree-Fock (HF) and density functional methods (B3LYP) with 3-21 and 6-31G* basis sets. The DFT (B3LYP/31G*) calculations have been giving energies, optimized structures, harmonic vibrational frequencies, IR intensities and Raman activities. The study is extended to the HOMO-LUMO analysis to calculate the energy gap, ionization potential, electron affinity, global hardness, chemical potential and thermodynamic properties of DCT and CFT. A complete vibrational assignment aided by the theoretical harmonic frequency analysis has been proposed. The calculated HOMO and LUMO energies show the charge transfer occurs in the molecule. The harmonic vibrational frequencies have been compared experimental FTIR and FT-Raman spectra. The observed and calculated frequencies are found to be in good agreement. The complete vibrational assignments are performed on the basis of the Total Energy Distribution (TED) of the vibrational modes calculated with scaled quantum mechanical (SQM) method. (13)C NMR chemical shifts results are compared with the experimental values. The experimental spectra also coincide satisfactorily with those of theoretically constructed spectrograms.

Theoretical structure and vibrational spectra of ciprofloxacin: density functional theory study

The molecular structure and vibrational spectra of ciprofloxacin(1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinolinecarboxylic acid) have been calculated using the different density functional theory (DFT) methods and various basis sets. This paper examines the comparative performance of different DFT methods at various basis sets in predicting molecular and vibrational spectra of ciprofloxacin. The calculation results show that SVWN/LANL2DZ level and SVWN/6-31G level offer the highest certainty to predict the structure and vibrational spectra of ciprofloxacin, respectively.

Density functional theory study on the molecular structure and vibration spectra of fenbufen

This paper examines the comparative performance of different density functional theory (DFT) methods at various basis sets in predicting molecular and vibration spectra of gamma-oxo-[1,1'-biphenyl]-4-butanoic acid (fenbufen). DFT methods including mPW1PW91, HCTH, SVWN, PBEPBE, B3PW91 and B3LYP were investigated. Different basis sets including LANL2DZ, SDD, LANL2MB, CEP-4G, CEP-31G, and CEP-121G were also considered. It is remarkable that the mPW1PW91/LANL2DZ and mPW1PW91/SDD levels are clearly superior to all of the remaining DFT levels in predicting the structure of fenbufen. The calculated results also indicate that SVWN/LANL2DZ level show better performance in the vibration spectra prediction of fenbufen comparing other DFT methods.

Hydrogen bond dynamics in crystalline β-9-anthracene carboxylic acid--a combined crystallographic and spectroscopic study

We compare results from single crystal X-ray diffraction and FTIR spectroscopy to elucidate the nature of hydrogen bonding in β-9-anthracene carboxylic acid (β-9AC, C(15)H(10)O(2)). The crystallographic studies indicate a disorder for the protons in the cyclic hydrogen bond. This disorder allows the determination of the energy difference between two proton sites along the hydrogen bond. The temperature dependent Fourier transform infrared spectroscopy (FTIR) underpins the crystallographic results. The combination of both methods allows the estimation of a one-dimensional potential curve describing the OH-stretching motion. The dynamical properties of the proton transfer along the hydrogen bond are extracted from this potential. The work presented here has profound implication on future studies of photochemical dynamics of crystalline β-9AC, which can deliver a deeper understanding of the mechanism of photochemical driven molecular machines and the optical and electronic properties of molecular organic semiconductors.

Vibrational spectroscopic and quantum chemical calculations of (E)-N-Carbamimidoyl-4-((naphthalen-1-yl-methylene)amino)benzene sulfonamide

FT-IR and FT-Raman spectra of (E)-N-Carbamimidoyl-4-((naphthalen-1-yl-methylene)amino)benzene sulfonamide were recorded and analyzed. The vibrational wavenumbers were computing at various levels of theory. The data obtained from theoretical calculations are used to assign vibrational bands obtained experimentally. The results indicate that B3LYP method is able to provide satisfactory results for predicting vibrational frequencies and structural parameters. The calculated first hyperpolarizability is comparable with reported values of similar derivatives and is an attractive object for future studies of non-linear optics. The geometrical parameters of the title compound are in agreement with that of similar derivatives.

FT-IR spectroscopy and DFT calculation study on the solvent effects of benzaldehyde in organic solvents

FT-IR spectra of benzaldehyde in 11 different organic solvents were recorded and analyzed. The density functional theory (DFT) B3LYP/6-31G* method was chosen to calculate the infrared spectrum of benzaldehyde in gaseous state. The electrostatic effects of different solvents in benzaldehyde solutions were calculated using DFT with the self-consistent isodensity polarizable continuum model (SCI-PCM). Two remarkable carbonyl (C=O) peaks of benzaldehyde were observed by FT-IR in alcohol solvents, which were caused by different hydrogen bond species and explained by ab initio calculation. The results showed that the combination of SCI-PCM model and ab initio calculation could give excellent agreements with FT-IR spectra of title compound in solutions.

FT-IR and FT-Raman vibrational analysis, ab initio HF and DFT simulations of isocyanic acid 1-naphthyl ester

The Fourier transform infrared and Fourier transform Raman spectra of isocyanic acid 1-naphthyl ester (C(11)H(7)NO) [ICANE] are recorded in solid phase, the harmonic vibrational frequencies, infrared intensities, Raman activities, bond length, bond angle and dihedral angle are calculated by HF and DFT methods by using different basis set. A detailed vibrational spectral analysis has been carried out and assignments of observed fundamental bands have been proposed on basis of peak positions and relative intensities. The scaled theoretical frequencies showed very good agreement with experimental values. A detailed interpretations of the infrared and Raman spectra of isocyanic acid 1-naphthyl ester are reported, the theoretical spectra for infrared and Raman spectrum of title molecule have been constructed. The effect due to the substitutions of isocyanato group is also investigated. A study on the electronic properties, such as excitation energies and wavelengths, are performed with different solvent by time-dependent DFT (TD-DFT) approach. HOMO and LUMO energies are calculated that these energies show charge transfer occurs within the molecule.