Theoretical Density Functional Theory Study Research Articles

Theoretical Density Functional Theory Study of Electrocatalytic Activity of MN4-Doped (M = Cu, Ag, and Zn) Single-Walled Carbon Nanotubes in Oxygen Reduction Reactions.

The mechanism of oxygen reduction reaction (ORR) on transition metal-doped nitrogen codoped single-walled nanotubes, C114H24MN4 (MN4-CNT where M = Zn, Cu, or Ag; N = pyridinic nitrogen), has been studied with the density functional theory method at the ωB97XD/DGDZVP level of theory. The charge density analysis revealed two active sites of the catalyst toward ORR: the MN4 site and the C=C bond of the N–C=C–N metal-chelating fragment (C2 site). The structure of O-containing adsorbates (O2*, HOO*, O*, HO*, etc.) on the two sites and the corresponding adsorption energies were determined. The analysis of the free energy diagrams allows to conclude that the 4e– mechanism of ORR is thermodynamically preferable for all the studied catalysts. The probability of the 2e– mechanism of ORR with the formation of hydrogen peroxide decreases in the order Cu > Ag > Zn. The most and the least exergonic steps of the conventional 4e– mechanism of ORR on each active site of model catalysts as well as the electrode potentials of deceleration and of maximum catalytic activity in both acidic and alkaline media are determined. The relative catalytic activity toward ORR increases in the order Zn < Ag ≪ Cu and is mainly attributed to the C2 site rather than the MN4 site, while combined catalytic activity of the two sites (AgN4/C2 sites) is predicted for the AgN4-CNT catalyst.

Formation mechanism of HCN and NH3 during indole pyrolysis: A theoretical DFT study

Coal is a major contributor to the global emission of nitrogen oxides. The NOx formation during coal utilisation typically derives from thermal decomposition of N-containing compounds pyrrole, which usually combines with an aromatic ring in the form of indole. NH3 and HCN are common precursors of NOx from the decomposition of N-containing compounds. In this study, possible pathways of indole pyrolysis to form HCN and NH3 are investigated using the density functional theory (DFT) method. Calculation results indicate that indole pyrolysis has two type of possible initial reactions, which are internal hydrogen transfer and hydrogen homolysis reaction, respectively. The initial reaction mode of indole has a great impact on the subsequent pyrolysis pathway. Additionally, it is shown that indole can produce two nitrogen-containing products, i.e. HCN and NH3. Five pathways will result in the formation of HCN (path-1, path-3, path-a, path-b, path-c), and another two pathways will lead to the NH3 (path-2, path-4). Furthermore, among all the reaction mechanisms of indole pyrolysis, the path-1 is the optimal reaction pathway. During which, indole is converted to a diradical intermediate, then the intermediate undergoes a synergy ring-opening transition state to form a new intermediate. Afterwards, the new intermediate decomposes into CN by homolysis of the C–C bond.

Theoretical DFT study of R-phenyl alanine-S mandelate

Abstract The homodesmic reactions involving the donor-acceptor interactions and charge transfer mechanisms give low energy gap novel organic compounds having the high electrochemical activity and highly reactive materials. Internal charge transfer ability in amino acids give zwitterions. The amino acids also form the salt with organic acids. The donor-acceptor ability of the organic salts stabilises the structural arrangement through inter molecular hydrogen bonding. The title compound, R-phenyl alanine -S-mandelate (RPASMA) was synthesised, single crystal was grown by slow evaporation method, characterisation studies carried out , single crystal XRD analysis and MO6 Density Functional Theory (DFT) were also carried out. The crystal parameters of the title compound was compared with the theoretical DFT study and the inter molecular hydrogen bonding interactions stabilising the molecular sheet formation was also confirmed. the non-centrosymmetric structure indicating the presence of nonlinear optical activity (NLO) due to Second Harmonic Generation (SHG) property. The title compound showed twice the NLO activity of standard NLO material, Potassium Di hydrogen ortho Phosphate (KDP) and proved that the title compound can be used in device applications as a good NLO material.

Ni-CNT Chemical Sensor for SF₆ Decomposition Components Detection: A Combined Experimental and Theoretical Study.

SF6 decomposition components detection is a key technology to evaluate and diagnose the insulation status of SF6-insulated equipment online, especially when insulation defects-induced discharge occurs in equipment. In order to detect the type and concentration of SF6 decomposition components, a Ni-modified carbon nanotube (Ni-CNT) gas sensor has been prepared to analyze its gas sensitivity and selectivity to SF6 decomposition components based on an experimental and density functional theory (DFT) theoretical study. Experimental results show that a Ni-CNT gas sensor presents an outstanding gas sensing property according to the significant change of conductivity during the gas molecule adsorption. The conductivity increases in the following order: H2S > SOF2 > SO2 > SO2F2. The limit of detection of the Ni-CNT gas sensor reaches 1 ppm. In addition, the excellent recovery property of the Ni-CNT gas sensor makes it easy to be widely used. A DFT theoretical study was applied to analyze the influence mechanism of Ni modification on SF6 decomposition components detection. In summary, the Ni-CNT gas sensor prepared in this study can be an effective way to evaluate and diagnose the insulation status of SF6-insulated equipment online.

Interaction between polysaccharide monomer and SiO2/Al2O3/CaCO3 surfaces: A DFT theoretical study

In the present study, the interaction between a model polysaccharides monomer β-D-glucopyranose with different mineral solid surfaces, including hydroxylated (0 0 1) surface of SiO2, (0 0 0 1) surface of Al2O3 and (1 0 4) surface of CaCO3, were explored by theoretical calculations based on Density Functional Theory (DFT) under periodic boundary conditions. The adsorption geometry of the β-D-glucopyranose monomer (GM) at different solid surface and the interaction energies were analyzed in detail, and the interaction mechanism was determined via electron density differences iso-surface, Mulliken charge, as well as projected density states (PDOS) analysis. Very strong interaction was found between GM and Al2O3 (0 0 0 1) surface, which was mainly attributed to the formation of bridging AlO bonds and H-bonds. There was the bonding between H-1s and O-2p orbitals for the formed hydrogen bonds and hybridization between O-p states and Al-d states for the bridging AlO bonds. The interaction between GM and CaCO3 (1 0 4) surface was mainly attributed to the electrostatic interaction and hydrogen bonded interaction, and was fairly strong, too. But there was only hydrogen bonds between GM and SiO2 surface, which was relative weak. In all the three adsorbed systems, significant charge redistribution was observed which contributed to the interaction between them, though little electron transferred between them. The finding is very meaningful for providing theoretical direction in proceeding sufficient application of diverse kind of natural sugar-based functional substances in many fields.

Experimental and Atomic Modeling of the Adsorption of Acid Azo Dye 57 to Sepiolite

AbstractSepiolite is a hydrated magnesium silicate with a microporous and mesoporous structure. The fibrous morphology and the alternating blocks and tunnels along the fiber direction of sepiolite make it an ideal material to sequester a variety of organic and inorganic contaminants. The adsorption of various surfactants by organo sepiolites have been experimentally investigated. How this hydrophobic material adsorbs dye molecules at the atomic level, however, is a great mystery. For this reason, the present study focused on the adsorption of acid azo 57 dye molecules to modified sepiolite. For this purpose, the amenability of sepiolite to remove the anionic textile dye (acid azo red dye 57) was first studied in detail. Additionally, a typical cationic surfactant, hexadecyltrimethylammonium Br (HTAB), was used to modify sepiolite to increase the adsorption capacity. Zeta potential measurements on the sepiolite and the HTAB modified sepiolite were also carried out. Moreover, Density Functional Theory (DFT) studies were performed to understand the mechanism of the adsorption of dye molecules to natural and modified sepiolite surfaces. On the basis of the experimental studies, three general systems were theoretically examined: (i) HTAB molecules on sepiolite basal surfaces to represent four Si tetrahedra, (ii) neutral or charged acid azo red dye 57 molecules on sepiolite basal surfaces to represent four Si tetrahedra, and (iii) HTAB on the surface of neutral or charged acid azo red dye 57 molecules as a substrate. The results clearly indicated good agreement between the experimental studies and the theoretical computational DFT studies. For example, the double layer structure found in experimental studies was also demonstrated in DFT studies and confirmed increased adsorption in the presence of acid azo dye 57.

Reactivity of pyrazole derivatives with halomethanes: A DFT theoretical study

The N-alkylation reaction of pyrazole derivatives with halomethanes was studied using density functional theory (DFT). The hybrid method B3LYP was employed, along with an ECP basis set such as LANL2DZ for halogen atoms (X = Cl, Br, I) and the 6-311 + G(d,p) basis set for all other atoms. In order to predict the specific site at which the pyrazole derivatives interact with halomethanes, local reactivity descriptors such as the Fukui functions were calculated. Detailed analysis of transition-state energies showed that alkylation occurred at the nitrogen atom N2 in the pyrazole derivatives, in agreement with the chemical reactivity results. The reaction mechanisms were elucidated by performing intrinsic reaction coordinate (IRC) calculations that considered the effects of the solvent and the species of halogen in the halomethane.

Electronic nature of the emitting triplet in SF5-substituted cationic Ir(III) complexes

A theoretical density functional theory study has been performed on a family of cationic iridium(III) complexes of the form [Ir(C^N)2(dtBubpy)]+ (dtBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine), that incorporate 2-phenylpyridine (1, 2) and 1-phenylpyrazole (3, 4) cyclometallating C^N ligands functionalized with SF5 groups. The goal is to investigate the effect that the inclusion of SF5 groups in meta (1, 3) and para position (2, 4) with respect to the Ir–C bond has on the electronic nature of the emitting triplet state and the emission wavelength. The attachment of the electron-withdrawing groups induces the stabilization of the molecular orbitals localized on the C^N ligands and, in particular, of the highest-occupied molecular orbital (HOMO). This stabilization enlarges the energy gap between the HOMO and the lowest-unoccupied molecular orbital (LUMO), and shifts to higher energies the metal-to-ligand charge transfer (MLCT) triplet described by the HOMO → LUMO excitation. As a consequence, a triplet state of ligand-centered (LC) nature becomes the lowest-energy triplet excited state for all the four complexes. For complexes 1 and 2, the state is centered on the C^N ligands (3LCC^N) and the introduction of the SF5 groups in para causes a greater effect than their insertion in meta. Substitution of the pyridine ring by a pyrazole ring in complexes 3 and 4 destabilizes the 3LCC^N states and the lowest-energy triplet involves the diimine N^N ligand (3LCN^N). Theoretical calculations therefore predict that the electronic nature of the lowest-lying triplet drastically changes in passing from the unsubstituted complex (3MLCT) to complexes 1 and 2 (3LCC^N) and to complexes 3 and 4 (3LCN^N). These changes help to rationalize the aspect of the emission spectra and the shift to the blue of the emission wavelength. The appearance of low energy 3LC triplets centered on the ancillary ligand, whose energy is hardly affected by changes in the C^N ligands structure, constitutes a limit to blue-shift the phosphorescence emission in this kind of complexes.

Insight into the reactivity difference of two iron phthalocyanine catalysts in chromogenic reaction: DFT theoretical study

ABSTRACTChromogenic reaction catalyzed by metal phthalocyanine (MPc) complexes is a novel and practical method for the facile identification of phenolic pollutants. Exploring the catalytic reaction mechanism is the current concern in the investigation. In this work, tetranitro iron (II) phthalocyanine (TNFe(II)Pc) and iron (II) phthalocyanine (Fe(II)Pc) catalyzed chromogenic reactions were studied at the B3LYP level on the basis of the density functional theory (DFT) calculation. The molecular structure, atomic charge, and frontier molecular orbital of these two kinds of iron phthalocyanine complex were investigated. The calculation results demonstrate that no obvious difference for geometry structures of Fe(II)Pc and TNFe(II)Pc macrocycle can be found, while the atomic charge of Fe atom increases obviously with the four nitro groups substituted on the peripheral of macrocycle. By applying the descriptor of donor–acceptor molecular hardness, the difference of electron transfer from chlorophenol substrates to TNFe(II)Pc/Fe(II)Pc was well explained. Our investigations could provide a new strategy in designing various MPc catalysts for chromogenic identification of chlorophenol pollutants.

Theoretical (DFT) and experimental studies on multiple hydrogen bonded liquid crystals comprising between aliphatic and aromatic acids

Liquid crystalline complex has been designed from non-mesogenic citric acid (CA) and mesogenic 4-undecyloxybenzoic acid (11OBA) in different mole ratio by means of intermolecular hydrogen bond. Optimized geometry for CA+11OBA (1:1) HBLC complex using density functional theory (DFT) at B3LYP level with 6-311G (d, p) basis set has been studied. Highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), hydrogen bond length/angle, electrostatic potential (ESP) and Mulliken charge distribution for the HBLC complexes are theoretically determined. Further atomic, molecular properties and charge transfer capability of present HBLC complex is evaluated from HOMO/LUMO energies. Theoretically calculated vibration frequencies of HBLC complex is validated through experimentally recorded Fourier transform infrared (FT-IR) spectrum. Characteristic features of various textures by polarizing optical microscopy (POM) and temperature dependent of various thermodynamic properties of CA+11OBA complexes are carefully investigated. Enantiotropic nematogen and finger print smectic X textures along with their phase sequences are also analyzed. Structural and optical characteristics of present HBLC complexes are evinced by nuclear magnetic resonance (1H NMR) and UV–Vis spectrophotometer (for band gap) techniques. The impact of mesogenic ratio (11OBA) on CA+11OBA complex is also discussed. In this present work, a noteworthy observation of photocatalytic activity of CA+11OBA HBLC complex is noticed. Also, textural changes with phase transition temperature, induced smectic phases, thermal range, enthalpy, and tilt angle are reported. Presence of H-bond in the HBLC complex and experimentally obtained results are compared with theoretical DFT studies.

PBE–DFT theoretical study of organic photovoltaic materials based on thiophene with 1D and 2D periodic boundary conditions

Conjugated organic systems such as thiophene are interesting topics in the field of organic solar cells. We theoretically investigate π-conjugated polymers constituted by n units (n = 1–11) based on the thiophene (Tn) molecule. The computations of the geometries and electronic structures of these compounds are performed using the density functional theory (DFT) at the 6–31 G(d, p) level of theory and the Perdew–Burke–Eenzerhof (PBE) formulation of the generalized gradient approximation with periodic boundary conditions (PBCs) in one (1D) and two (2D) dimensions. Moreover, the electronic properties (HOCO, LUCO, Egap, Voc, and Vbi) are determined from 1D and 2D PBC to understand the effect of the number of rings in polythiophene. The absorption properties—excitation energies (Eex), the maximal absorption wavelength (λmax), oscillator strengths, and light harvesting—efficiency are studied using the time-dependent DFT method. Our studies show that changing the number of thiophene units can effectively modulate the electronic and optical properties. On the other hand, our work demonstrates the efficiency of theoretical calculation in the PBCs.

Structural characterization, solvent effects on nuclear magnetic shielding tensors, experimental and theoretical DFT studies on the vibrational and NMR spectra of 3-(acrylamido)phenylboronic acid

Structural elucidation of 3-(acrylamido)phenylboronic acid (C9H10BNO3) was carried out with 1H, 13C and HETCOR NMR techniques. Solvent effects on nuclear magnetic shielding tensors were examined with deuterated dimethyl sulfoxide, acetone, methanol and water solvents. The correct order of appearance of carbon and hydrogen atoms on NMR scale from highest magnetic field region to the lowest one were investigated using different types of theoretical levels and the details of the levels were presented in this study. Stable structural conformers and vibrational band analysis of the title molecule (C9H10BNO3) were studied both experimental and theoretical viewpoints using FT-IR, Raman spectroscopic methods and density functional theory (DFT). FT-IR and Raman spectra were obtained in the region of 4000–400 cm−1, and 3700–10 cm−1, respectively. Becke-3-Lee-Yang-Parr (B3LYP) hybrid density functional theory method with 6-31++G(d, p) basis set was included in the search for optimized structures and vibrational wavenumbers. Experimental and theoretical results show that after application of a suitable scaling factor density functional B3LYP method resulted in acceptable results for predicting vibrational wavenumbers except OH and NH stretching modes which is most likely arising from increasing unharmonicity in the high wave number region and possible intra and inter molecular interaction at OH edges those of which are not fully taken into consideration in theoretical processes. To make a more quantitative vibrational assignments, potential energy distribution (PED) values were calculated using VEDA 4 (Vibrational Energy Distribution Analysis) program.

FTIR, Raman and NMR spectroscopic and DFT theoretical studies on poly(N-vinylimidazole)

In this study where the FTIR, Raman, 1H NMR and 13C NMR spectra of poly(N-vinylimidazole) which can be abbreviated as poly(NVIM) are first reported, a comparison of the experimental and theoretical vibrational spectral data of monomer NVIM and water-soluble poly(NVIM) has been given; such a comparison over the vibrational modes and associated spectral data calculated at B3LYP/6-31+G(d) level of theory for NVIM and its stable dimer forms provided significant contributions for getting a reliable interpretation of the observed vibrational spectra of poly(NVIM). The obtained results revealed that the change from NVIM to poly(NVIM) should be characterized by the disappearance of the CH2CH bonds of the vinyl group and the appearance of the aliphatic CH and CH2 bonds. Besides this, the thermal properties of poly(NVIM) were elucidated by thermogravimetric analyses such as TGA, DTA and DSC, while some electronic structure parameters of the most stable dimers of NVIM were investigated through the structure calculations performed by using B3LYP method and 6-31+G(d) basis set within the density functional theory (DFT) methodology.

Aromaticity of benzene in condensed phases. A case of a benzene–water system

A theoretical Density Functional Theory study was performed for a benzene molecule in water cages. Two DFT functionals (B3LYP and BLYP) were employed. The optimized geometries of the studied clusters were used to calculate the aromaticity of benzene in a condensed phase using the aromaticity indices: HOMA, NICS, PDI, and H. The results were compared with aromaticity of a single benzene molecule in the gas phase and in the solvent environment provided by the PCM continuum model. It is argued that high aromaticity of benzene in the gas phase is retained in the water environment.

Fe as Hydrogen/Halogen Bond Acceptor in Square Pyramidal Fe(CO)5

Hydrogen bonded complexes formed between the square pyramidal Fe(CO)5 with HX (X = F, Cl, Br), showing X-H···Fe interactions, have been investigated theoretically using density functional theory (DFT) including dispersion correction. Geometry, interaction energy, and large red shift of about 400 cm(-1) in the HX stretching frequency confirm X-H···Fe hydrogen bond formation. In the (CO)5Fe···HBr complex, following the significant red-shift, the HBr stretching mode is coupled with the carbonyl stretching modes. This clearly affects the correlation between frequency shift and binding energy, which is a hallmark of hydrogen bonds. Atoms in Molecule (AIM) theoretical analyses show the presence of a bond critical point between the iron and the hydrogen of HX and significant mutual penetration. These X-H···Fe hydrogen bonds follow most but not all of the eight criteria proposed by Koch and Popelier (J. Phys. Chem. 1995, 99, 9747) based on their investigations on C-H···O hydrogen bonds. Natural bond orbital (NBO) analysis indicates charge transfer from the organometallic system to the hydrogen bond donor. However, there is no correlation between the extent of charge transfer and interaction energy, contrary to what is proposed in the recent IUPAC recommendation (Pure Appl. Chem. 2011, 83, 1637). The "hydrogen bond radius" for iron has been determined to be 1.60 ± 0.02 Å, and not surprisingly it is between the covalent (1.27 Å) and van der Waals (2.0) radii of Fe. DFT and AIM theoretical studies reveal that Fe in square pyramidal Fe(CO)5 can also form halogen bond with ClF and ClH as "halogen bond donor". Both these complexes show mutual penetration as well, though the Fe---Cl distance is closer to the sum of van der Waals radii of Fe and Cl in (CO)5Fe···ClH, and it is about 1 Å less in (CO)5Fe···ClF.

Hydrogen peroxide as oxidant in bio-mimetic catalysis by manganese porphyrin: Theoretical DFT studies

The aim of this study is to elucidate the geometry and electronic structure of various adducts that may be formed between manganese(III) (Mn(III)) porphyrin and hydrogen peroxide. Hydrogen peroxide may interact with Mn(III) porphyrin either as H2O2 or, after dissociation, as OOH–. In the former, it may decompose into two hydroxo groups, which acquire OH– character or an oxo group (=O) and a water molecule. Therefore, the following systems are considered: MnP(H2O2)+, MnP(H2O2)(OH), MnP(OH)3, [Formula: see text], MnPO+, MnPO(OH), MnP(OOH), MnP(OOH)(OH)–, and the possible transformations between them are taken into account. The reported studies are performed within the Density Functional Theory (DFT) method with the GGA-BP functional. The geometry and electronic structures of the structures found along the studied reaction pathways are discussed in terms of interatomic distances, valence angles, Mulliken charges, and spin densities. It was found that different active oxygen species may be formed in the reaction between Mn(III) porphyrin and hydrogen peroxide. As manganese is a transition metal, numerous possible spin states for each of the studied structures are found, where the relative energies of different multiplicities depend strongly on the ligands present in the complex. In view of the catalytic properties, all oxygen-containing ligands are negatively charged, which results in their behaviour as nucleophiles towards hydrocarbons. Finally, the analysis of charge and spin populations on different parts of the studied systems indicate the porphyrin ligand as active in charge transfer processes.

Computational study of Mg insertion into amorphous silicon: advantageous energetics over crystalline silicon for Mg storage

ABSTRACTWe show in a theoretical density functional theory study that amorphous Si (a-Si) has more favorable energetics for Mg storage compared to crystalline Si (c-Si). Specifically, Mg and Li insertion is compared in a model a-Si simulation cell. Multiple sites for Mg insertion with a wide range of binding energies are identified. For many sites, Mg defect formation energies are negative, whereas they are positive in c-Si. Moreover, while clustering in c-Si destabilizes the insertion sites (by about 0.1/0.2 eV per atom for nearest-neighbor Li/Mg), it is found to stabilize some of the insertion sites for both Li (by up to 0.27 eV) and Mg (by up to 0.35 eV) in a-Si. This could have significant implications on the performance of Si anodes in Mg batteries.

Differences in Nuclearity, Molecular Shapes, and Coordination Modes of Azide in the Complexes of Cd(II) and Hg(II) with a “Metalloligand” [CuL] (H2L =N,N′-Bis(salicylidene)-1,3-propanediamine): Characterization in Solid and in Solutions, and Theoretical Calculations

Two new heterometallic copper(II)-mercury(II) complexes [(CuL)Hg(N3)2]n (1) and [(CuL)2Hg(N3)2] (2) and one copper(II)-cadmium(II) complex [(CuL)2Cd(N3)2] (3) have been synthesized using "metalloligand" [CuL] (where H2L = N,N'-bis(salicylidene)-1,3-propanediamine) and structurally characterized. Complex 1 is a one-dimensional (1D) helical coordination polymer constructed by the joining of the dinuclear [(CuL)Hg(N3)2] units through a single μ-l,l azido bridge. In the dinuclear unit the Hg(II) is bonded with two phenoxido oxygen atoms of "metalloligand" [CuL] and two nitrogen atoms of azido ligands. Complex 2 is a linear trinuclear entity, in which two terminal "metalloligands" [CuL] are coordinated to central Hg(II) through double phenoxido bridges. The azido ligands link the central mercury atom with the terminal copper atoms via μ-l,3 bridges. In contrast, the trinuclear complex 3 is bent. Here, in addition to two double phenoxido bridges, central Cd(II) is bonded to two mutually cis nitrogen atoms of two terminal azido ligands. The variation in the coordination modes of the azido ligand seems to be responsible for the different molecular shapes of 2 and 3. Interestingly, bond distances between the Hg atoms and the central nitrogen atom of the azido ligands are 2.790(4) and 2.816(5) Å in 1 and 2.823(4) Å in 2. These bond distances are significantly less than the sum of van der Waals radii of mercury (2.04 Å) and nitrogen (1.55 Å) and considerably longer than the sum of their covalent radii (2.03 Å). However the distances are similar to reported Hg-N bond distances of some Hg(II) complexes. Therefore, we have performed a theoretical density functional theory study to know whether there is any interaction between the central nitrogen atom of the azido ligand and the mercury atoms. We have used the Bader's "atoms-in-molecules", energetic and orbital analyses to conclude that such interaction does not exist. The probable reason for different molecular shapes observed in trinuclear complexes of 2 and 3 also has been studied and explained by theoretical calculations and using the CSD. Electronic spectra, EPR spectra and ESI mass spectra show that all three complexes lose their solid state identity in solution.

Design, synthesis and evaluation of redox, second order nonlinear optical properties and theoretical DFT studies of novel bithiophene azo dyes functionalized with thiadiazole acceptor groups

Abstract Two series of novel thermally stable second-order nonlinear optical (NLO) heterocyclic azo dyes 4 – 5 have been designed and synthesized. The two series of compounds were based on different combinations of acceptor groups (thiadiazole or arylthiadiazole electron-deficient heterocycles) linked to bithiophene which acts at the same time as a donor group and as a π-conjugated bridge. The solvatochromic behavior of azo dyes 4 – 5 was investigated in several solvents of different polarity, while their thermal stability was evaluated using thermogravimetric analysis. Optimized ground-state molecular geometries and an estimation of the lowest energy single electron vertical excitation energies in DMF solutions were obtained using density functional theory (DFT). Their redox properties were studied by cyclic voltammetry, while hyper-Rayleigh scattering (HRS) was employed to evaluate their second-order nonlinear optical properties. The measured molecular first hyperpolarizabilities and the observed electrochemical behavior showed variations for the different acceptor systems used (thiadiazole or arylthiadiazole) and were also sensitive to the electronic acceptor strength of the substituents ( R ) linked to thiadiazole or arylthiadiazole heterocycles. Donor–acceptor arylthiadiazole-bithienyl diazenes exhibit the most promising thermal ( T d = 237–305 °C) and solvatochromic (Δ ν = 1117–2503 cm −1 ) properties and second order nonlinear optical response (136–226 × 10 −30 esu).

Experimental and theoretical DFT studies of structure, spectroscopic and fluorescence properties of a new imine oxime derivative

A new imine oxime, (1E,2E)-phenyl-[(1-phenylethyl)imino]-ethanal oxime (I), is synthesized and characterized. The title compound crystallizes in the monoclinic space group P21/c with a=12.3416(7), b=9.5990(6), c=11.9750(7), β=92.417(4) and Z=4. Crystallographic, vibrational (IR), and NMR (1H and 13C chemical shifts) data are compared with the results of density functional theory (DFT) method at the B3LYP/6-311++G(d,p) level. The structure of I is stabilized by intermolecular OH⋯N hydrogen bonds. The theoretical calculations show that the compound exhibits a number of isomers, and the molecular geometry of the most stable optimized isomer (s-trans-E,E) can well reproduce the X-ray structure. The calculated vibrational bands and NMR chemical shifts are consistent with the experimental results. The NBO/NPA atomic charges are performed to explore the possible coordination modes of the compound. The electronic (UV–vis) and photoluminescence spectra calculated using the TD-DFT method are correlated to the experimental spectra. The DMSO solutions of I are fluorescent at room temperature. The assignment and analysis of the frontier HOMO and LUMO orbitals indicates that both absorption and emission bands are originated mainly from the π–π* transitions.