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This study provides a complete analysis of the electronic and photophysical properties of orotic (OA) and isoorotic (IOA) azo dyes. The ability of the dye to work as an excited state intramolecular proton transfer (ESIPT) was investigated by using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TD-DFT) methods. The effect of electron-donating substituents (CH3 and NMe2) and an electron-withdrawing one (NO2) was examined. In addition, the effect of the solvent polarity on the ESIPT process is studied. All the geometrical structures in the singlet ground (S0) and excited (S1) states, were optimized using B3LYP/6-311+G** level of theory. The intramolecular hydrogen bond parameters (IHBs), and the Infra-Red vibrational analysis of the O-H bond show that the IHBs are enhanced in the S1 state. Furthermore, the absorption spectra were simulated and the values of stokes shifts were observed. The PAIOA derivative with an electron withdrawing group shows large stokes shift compared with those having electron-donating ones. Therefore, we can safely conclude that the substitutents groups and the different solvents are extremely impactful on the ESIPT process.

Colorectal cancer (CRC) is the second most common cause of death worldwide, affecting approximately 1.9 million individuals in 2020. Therapeutics of the disease are not yet available and discovering a novel anticancer drug candidate against the disease is an urgent need. Thymidylate synthase (TS) is an important enzyme and prime precursor for DNA biosynthesis that catalyzes the methylation of deoxyuridine monophosphate (dUMP) to deoxythymidine monophosphate (dTMP) that has emerged as a novel drug target against the disease. Elevated expression of TS in proliferating cells promotes oncogenesis as well as CRC. Therefore, this study aimed to identify potential natural anticancer agents that can inhibit the activity of the TS protein, subsequently blocking the progression of colorectal cancer. Initially, molecular docking was implied on 63 natural compounds identified from

The present study presents a thorough theoretical analysis of the electronic structure and conformational preference of the Schiff’s base ligand N,N-bis(2-hydroxybenzilidene)-2,4,6-trimethyl benzene-1,3-diamine (H2L) and its metal complexes with Zn2+, Cu2+ and Ag+ ions. The study aims to investigate the behavior of H2L and the binuclear Zn2+ complex (1), as fluorescent probes for the detection of metal ions (Zn2+, Cu2+ and Ag+) using Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT). The six conformers of the H2L ligand were optimized using B3LYP/6-311++G** level of theory, while the L-2-metal complexes were optimized by applying B3LYP functional with LANL2DZ/6-311++G** mixed basis set. The gas-phase and solvated Enol-cis isomer (E-cis) was found to be the most stable species. The absorption spectra of E-cis isomer and its metal complexes were simulated using B3LYP, CAM-B3LYP, M06-2X and ωB97X functionals with a 6-311++G** basis set for C, O, N and H atoms and LANL2DZ basis set for the metal ions (Zn2+, Cu2+ and Ag+). The computational results of B3LYP functional were in excellent agreement with the experimental ones. Hence, it has been adopted for performing the emission calculations. The results indicated that, the metal complex (1) can act as a fluorescent chemosensor, for the detection of Ag+ and Cu2+ ions through the mechanism of the Intermolecular Charge Transfer (ICT) and as a molecular switch “On-Off-On” via the replacement of Cu2+ by Ag+ ions, as proved experimentally.

The present study presents a thorough theoretical analysis of the electronic structure and conformational preference of Schiff's base ligand N,N-bis(2-hydroxybenzilidene)-2,4,6-trimethyl benzene-1,3-diamine (H

The gas-phase hydroaminoalkylation reaction of propene catalyzed by group 4 (M = Ti, Zr and Hf) metal amido complexes [(≡Si-O-)(M(-NMe

The gas-phase thermal tautomerization reaction between imidazole-4-acetic (I) and imidazole-5-acetic (II) acids was monitored using the traditional hybrid functional (B3LYP) and the long-range corrected functionals (CAM-B3LYP and ?B97XD) with 6-311++G** and aug-cc-pvdz basis sets. The roles of the long-range and dispersion corrections on their geometrical parameters, thermodynamic functions, kinetics, dipole moments, Highest Occupied Molecular Orbital–Lowest Unoccupied Molecular Orbital (HOMO–LUMO) energy gaps and total hyperpolarizability were investigated. All tested levels of theory predicted the preference of I over II by 0.750–0.877 kcal/mol. The origin of predilection of I is assigned to the H-bonding interaction ( ). This interaction stabilized I by 15.07 kcal/mol. The gas-phase interconversion between the two tautomers assumed a 1,2-proton shift mechanism, with two transition states (TS), TS1 and TS2, having energy barriers of 47.67–49.92 and 49.55–52.69 kcal/mol, respectively, and an sp3-type intermediate. A water-assisted 1,3-proton shift route brought the barrier height down to less than 20 kcal/mol in gas-phase and less than 12 kcal/mol in solution. The relatively high values of total hyperpolarizability of I compared to II were interpreted and discussed. The long-range correction is quite essential for total hyperpolarizability DFT evaluation as the traditional hybrid functional overestimate it. Finally, the computation of tot values is basis set independent.

Funding sources from the King Abdulaziz University and the King Abdullah University of Science and Technology, Thuwal, Saudi Arabia. Computation for the work presented in this paper was supported by KAU's High Performance Computing Center (Aziz Supercomputer) (http://hpc.kau.edu.sa) and by the KAUST Super-computing Laboratory (KSL) at KAUST.

The main purpose of the present study is to investigate the role of 1,12-diaminododecane and 4,4′-diaminobiphenyl, as bifunctional amino derivatives, on the properties of poly(methyl methacrylate) (PMMA). Cross-linked PMMA derivatives of different degrees (2, 5, 10, 20, 30, 50, and 70 mass%) were synthesized by the interaction of neat PMMA with these two cross-linking agents through a polycondensation technique. FT-IR probes the possible interaction between the carbonyl (C=O) group of PMMA and the amino group of the diamine compounds. The change in the degree of crystallinity from one polymer to another is affected by the ratio and type of cross-linking. The surface morphology is dramatically changed by increasing the degree of cross-linking as evidenced from the SEM images. A major mass loss between 209 and 471 °C was observed from the TG curve of C-PMMA-H2, whereas C-PMMA-ph2 showed a major mass loss between 223 and 538 °C. A significant change in the thermal degradation behavior of cross-linked polymers was investigated at high cross-linking degrees. All products showed a final decomposition temperature (FDT) higher than pure PMMA. Considering the best result, FDT increased from 390 °C for pure PMMA to 577 °C for C-PMMA-H4 and 607 °C for C-PMMA-ph7. Moreover, a theoretical thermochemical analysis of the monomeric cross-linked isodesmic reaction was performed using density functional theory (DFT). The heat of formation of reactants and products was calculated and analyzed. The study, also, showed that the reactions are endothermic and spontaneous in the reverse direction at all temperatures.

A one-pot multi-component synthesis of 4,5,-diphenyl-2-(pyren-1-yl)-1H-imidazole (DPI) chromophore was performed by the reaction of benzil, pyrene-1-carboxaldehyde and ammonium acetate in acetic acid. Structure elucidation of DPI chromophore was confirmed by spectroscopic techniques (FT-IR, 1H NMR, 13C NMR and mass spectra). The physicochemical and photophysical parameters of DPI chromophore such as extinction coefficient, oscillator strength, dipole moment, stokes shift and fluorescence quantum yield were calculated experimentally and theoretically on the basis of the different solvents polarity to see the effect of the solvents on DPI chromophore. DPI chromophore was also applicable for determination of critical micelle concentration (CMC) of cationic and anionic surfactant such as cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS).

The functionality of the proton-coupled electron transfer (PCET) model was tested on a squaraine-sensitized solar cell. The geometrical parameters, excitations, and electronic structures of free and Ti+4-bound squaraine dye were monitored using a set of pure and hybrid density functional theory (DFT) functionals with diffuse and polarization functions. The infrared spectra showed the dye-metal proton transfer. The UV-Vis spectra of unbound and bound squaraine dye using the pure functional (PBEPBE) are in excellent agreement with the experimental ones. The first photoexcited state charge transfer enhanced the charge density around the anchoring group of neat and bound squaraine dye. The injection of electronic charge into the titanium complex was confirmed by density of states (DOS) and natural bond orbital (NBO) analyses. The comparatively high total hyperpolarizability of the squaraine dye is indicative of a potent nonlinear optical (NLO) devise.

(4Z)-4-[(9-Ethyl-9H-carbazol-3-yl)methylidene]-2-phenyl-1,3-oxazol-5(4H)-one (ECPO) was prepared by the one-pot multi-component reaction of 9-ethyl-9H-carbazole-3-carbaldehyde, hippuric acid, anhydrous sodium acetate and acetic anhydride under microwave irradiation. The structure of ECPO was confirmed by elemental analysis and spectral studies (1H and 13C NMR, FT-IR) and theoretically by Density Functional Theory (DFT). The experimental and simulated electronic absorption and fluorescence spectra of ECPO have been studied in solvents of different polarities. They are in good agreement with each other. The data were used to study solvatochromic properties such as excitation coefficient, Stokes shift, oscillator strength, transition dipole moment, and fluorescence quantum yield. The wavelength maxima showed red shifts with increasing solvent polarity from n-hexane to DMSO. ECPO undergoes solubilization in different micelles and may be used as a probe for determining the critical micelle concentration (CMC) of CTAB and SDS. The interaction of colloidal silver nanoparticles (AgNPs) with ECPO dye was studied in ethanol and ethylene glycol using steady state fluorescence quenching measurements. The Stern–Volmer quenching rate constant (Ksv) was calculated to be 5.28 × 107 M−1 and 3.48 × 107 M−1 in ethanol and ethylene glycol, respectively. ECPO's highly promising NLO character was complemented by NBO investigation.

(2 E )-3-(3,4-dimethoxyphenyl)-1-(2-hydroxyphenyl)prop-2-en-1-one (DMHP) was synthesized by the reaction of 3,4-dimethoxy benzaldehyde with 1-(2-hydroxyphenyl) ethanone under microwave irradiation. The structure of DMHP was established experimentally by EI-MS, FT-IR, 1 H and 13 C NMR spectral studies and elemental analysis and theoretically. Electronic absorption and emission spectra of DMHP were studied in different solvents on the basis of polarities, and the obtain data were used to determine the solvatochromic properties such as extinction coefficient, oscillator strength, transition dipole moment, stokes shift, fluorescence quantum yield and photochemical quantum yield. The absorption and emission maxima were red-shifted when the polarity of the solvent was increased from dioxan to DMSO; in excellent agreement the DFT findings. The DMHP experimental intramolecular charge transfer (ICT) was complemented by a natural bond orbital (NBO) analysis. Fluorescence intensities of DMHP were increase and decrease in presence of CTAB and SDS, so DMHP was used to find out the critical micelle concentration (CMC) of CTAB and SDS.

An efficient and novel method for the synthesis of a series of 11-aryl-10,12-dihydrodiindino[1,2- b‘,2′,1′- e]pyridine via one-pot multi-component reactions of aldehydes, indan-1-one and ammonium acetate has been delineated. All prepared compounds were structurally elucidated by IR, UV-Vis, 1H and 13C NMR and X-ray diffraction techniques. The molecules adopted monoclinic crystal system with P21/ c space group and almost similar unit cell dimensions. The X-ray molecular geometries of the studied compounds were in excellent agreement with those computed by B3LYP/6-311++G(d,p) level of theory. The energies of the frontier orbitals calculated by B3LYP/6-311++G(d,p) level of theory enabled monitoring the reactivity and stability of the title molecules. The non-linear optical properties (NLO) and pNA were also computed and discussed. Compounds have shown broad spectrum cytotoxic activity against some human tumour cell lines; two of them rendering the most profound effect.

In this work, a unique network core-shell structure based poly(Pyrrole-co-O-Toluidine) (PPCOT) - NiFe2O4 (NF) nanoparticles (NPs) and decorated with cross-linked single-walled carbon nanotubes (C-SWCNTs) has been synthesized as an electrochemical sensor for Fe3+ ions. The results revealed that the electrochemical properties and sensitivity of the ternary PPCOT/NF/C-SWCNT nanocomposites (NCs) were considerably better than the individual properties of copolymer PPCOT, binary PPCOT/NF NCs or NF NPs. The improved properties were attributed to the 3D structure of C-SWCNTs, which offer a large specific surface area that improves the electrical conductivity of the ternary PPCOT/NF/C-SWCNT NCs. DFT calculations for the heat of formation of monomers (PT, PP and TT) were also carried out. The heats of formation of the standard states of the monomers are exothermic and spontaneous at all temperatures. Here, the NCs of the synthesized 3D network core-shell were coated on a working electrode of an electrochemical sensor; the current collector is a glassy carbon electrode. The fabricated sensor is displayed good sensitivity and lower limit of detection of 11.0158 μA μM−1 cm−2 and 97.08 ± 4.85 pM, respectively. By the increasing of PPCOT, it is significantly increased the electrochemical interactions among the matrices of PPCOT, C-SWCNTs and NF. The Fe3+ sensor showed a preference towards Fe3+, which was linear for concentrations ranging from 0.1 nM to 0.01 mM. Moreover, the sensor’s analytical parameters, such as reproducibility and response time, were outstanding. Thus, the assembled sensor is highly effective and useful for Fe3+ ions detection in real environmental samples.

The optical absorption and emission properties of (E,E)-2,5-bis[2-(1-methyl-1H-pyrrole-2-yl)-vinyl] pyrazine (BMPVP) have been studied in different solvents. The BMPVP dye shows strong solvatochromic emission upon changing the solvent polarity from nonpolar to polar; indicating that the emission state is of intramolecular charge transfer (ICT) character. The solvent effect on the spectral properties such as singlet absorption, molar absorptivity, oscillator strength and fluorescence quantum yield of BMPVP have been studied in detail. The Lippert-Mataga and Reichardt correlations were used to estimate the difference between the excited and ground state dipole moments (Δm). Electronic excited states in different solvents were investigated using TD-DFT. The intramolecular charge transfer was analyzed by the NBO technique. The BMPVP dye is highly photostable in polar protic and polar aprotic solvents, while it displays photodecomposition in chloromethane solvents via formation of a contact ion pair. The photochemical quantum yield depends on the electron affinity of the solvent. A solution of (8 × 10−5 M) BMPVP in THF, dioxane, CH3CN or DMSO gives laser emission when pumped by a nitrogen laser pulse (λex = 337.1 nm) of 800ps duration and 1.48 mJ pulse energy. The BMPVP dye displays fluorescence quenching by colloidal silver nanoparticles (AgNPs) in ethanol with a fluorescence quenching rate constant of 1.40 × 109 M−1. The fluorescence data revealed that the dynamic quenching and the energy transfer play major roles in the fluorescence quenching mechanism.

We present a comprehensive investigation, via first-principles density functional theory (DFT) calculations, of various surface terminations of magnetite, Fe3O4 (111), a major iron oxide that also has a number of applications in electronics and spintronics. We compare the thermodynamic stability and electronic structure among the different surfaces terminations. Interestingly, we find that surfaces modified with point defects and adatoms are close in surface energy and that they can be more stable than bulk-like terminations in the oxygen-rich and -poor regimes. These surfaces show different surface chemistry and electronic structures as well as distinctive spin polarization features near the Fermi level with regard to those previously considered in the literature. Our studies provide an atomic level insight for magnetite surfaces, which is a necessary step to understanding their interfaces with organic layers in OLEDs and spintronic devices.

The present study aims at a fundamental understanding of bonding characteristics of the C–Br and O–Br bonds. The target molecular systems are the isomeric CH3OBr/BrCH2OH system and their decomposition products. Calculations of geometries and frequencies at different density functional theory (DFT) and Hartree–Fock/Møller–Plesset (HF/MP2) levels have been performed. Results have been assessed and evaluated against those obtained at the coupled cluster single-double (Triplet) (CCSD(T)) level of theory. The characteristics of the C–Br and O–Br bonds have been identified via analysis of the electrostatic potential, natural bond orbital (NBO), and quantum theory of atoms in molecules (QTAIM). Analysis of the electrostatic potential (ESP) maps enabled the quantitative characterization of the Br σ-holes. Its magnitude seems very sensitive to the environment and the charge accumulated in the adjacent centers. Some quantum topological parameters, namely Ñ2ρ, ellipticity at bond critical points and the Laplacian bond order, were computed and discussed. The potential energy function for internal rotation has been computed and Fourier transformed to characterize the conformational preferences and origin of the barriers. NBO energetic components for rotation about the C–Br and O–Br bonds as a function of torsion angle have been computed and displayed.

We aim at providing better insight into the parameters that govern the intramolecular charge transfer (ICT) and photo-injection processes in dyes for dye-sensitised solar cells (DSSC). Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations are utilized to study the geometry, electronic structure, electrostatic potential (ESP) and absorption spectrum, for a representative donor-π bridge-acceptor (D–π–A) dye for DSSC. The coplanar geometry of the dye (D1) facilitates strong conjugation and considerable delocalization originating the π CT interaction from donor to acceptor orbitals and the hyper-conjugative interactions involving Rydberg states. A model simulating the adsorption of the dye on the TiO2 surface is utilized to estimate binding energies. The effect of fluorine substituents in the π-spacer on the quantum efficiency of DSSCs was investigated. Gibb’s free energy values, redox potentials, excited state lifetime, non-linear optical properties (NLO) and driving forces for D1 and its fluorinated derivatives were computed.

The gas-phase FTIR study of the pyrolysis products of iminodiacetonitrile, (N≡CCH2)2NH has revealed the existence of C-cyanomethanimine, N≡CCH═NH, and ketenimine, CH2═C═NH. The former has two isomers: Z and E; while the later readily taumerizes to acetonitrile, CH3C≡N. A trapping/revaporization system has been used to purify C-cyanomethanimine. The analysis of the rotational structures of the IR medium resolution C-type CNH bend, ν6, and C═N torsional mode, ν10, has led to a conformational characterization of these isomers. The Z-isomer was shown to be the major product. This conjecture was supported by ab initio MO calculations that confirmed the relative total energy stability of the Z-isomer over its E-counterpart by 0.173 to 2.326 kJ/mol. The K values indicated that the equilibrium concentration of Z-C-cyanomethanimine amounts to up to three times that of E-C-cyanomethanimine. A further investigation using NBO technique proved the predilection of the Z-isomer. In addition it relates its provenance of preference to the remote nN6 → σ*C4-N5 interaction that stabilized it by 1.10 kcal/mol. A thorough theoretical investigation of the tautomerization reaction between ketenimine and acetonitrile will be published in a separate contribution.

The linear and nonlinear optical (NLO) properties of methoxybenzylidene (1) and thiophen-2-ylmethylidene (2) tetrahydronaphthalone derivatives are studied using long-range corrected density functional theory (LC-DFT). The calculated hyperpolarisabilities indicate that both compounds have measurable NLO properties (approximately one to two times the hyperpolarisability of p-nitroaniline). Charge-transfer indices and time-dependent DFT calculations suggest that the NLO properties are a result of a charge-transfer excitation, which is typical in conjugated donor–acceptor structures. The ultraviolet–visible spectra of 1 and 2 are also predicted using gap-fitting schemes, and these data are used to assess how accurately the hyperpolarisabilities of 1 and 2 could be estimated by the solvatochromic method.

The gas phase conformational and nonlinear optical properties of cis-N-phenylbenzohydroxamic acid (cis-NPBHA) keto and enol forms were studied applying traditional hybrid and long-range-corrected Density Functional Theory (DFT) and time-dependent density functional (TD-DFT) methods. The calculated geometrical parameters for the two isomers agreed satisfactorily with literature ones. The keto form was predicted to be more stable than the enol counterpart by 10.70–12.60 kcal/mol, and the Gibb’s free energies for the conversion: enol⇌keto were found to be 11.14 kcal/mol (B3LYP/6-311+G**), 12.53 kcal/mol (CAM-B3LYP/6-311+G**) and 13.28 kcal/mol (ωB97XD/6-311+G**). All the selected functionals have computed larger total hyperpolarizabilities for the enol tautomer compared to those of the keto rival. The traditional hybrid functional yielded higher total hyperpolarizabilities than those of the long-range-corrected ones. The total hyperpolarizabilities were nicely correlated with HOMO–LUMO energy gaps and absorption maxima. The support of these molecular properties by natural bond orbital (NBO) calculations was evaluated and discussed.

Solvent-assisted linker exchange (SALE) has recently emerged as an attractive strategy for the synthesis of metal-organic frameworks (MOFs) that are unobtainable via traditional synthetic pathways. Herein we present the first example of selective SALE in which only the benzimiadazolate-containing linkers in a series of mixed-linker zeolitic imidazolate frameworks (ZIF-69, -78, and -76) are replaced. The resultant materials (SALEM-10, SALEM-10b, and SALEM-11, respectively) are isostructural to the parent framework and in each case contain trifluoromethyl moieties. We therefore evaluated each of these materials for their hydrophobicity in condensed and gas phases. We expect that selective SALE will significantly facilitate the design of improved, and potentially complex, MOF materials with new and unusual properties.

The photochromic and nonlinear optical (NLO) properties of three isomers of the fulgide dicyclopropyl-methylene-(2,5-dimethyl-3-furylethylidene)-succinic anhydride (1-Z, 1-E and 1-C) were studied usinghybrid and range separated density functional theory (DFT) methods. Theoretical spectroscopic data(k max ) is compared to experiment; the DFT calculations are capable of qualitatively, but not quantita-tively, predicting the photochromic properties of 1-E. Large changes in the k max of 1-E upon irradiationof light are also predicted to be accompanied by a substantial increase in hyperpolarizability. 2013 Elsevier B.V. All rights reserved. 1. IntroductionThe use of photochromic compounds (i.e., compounds thatundergo a reversible chemical transformation resulting in spectralchanges upon absorption of light) for data storage was first pro-posed by Hirshberg in the 1950s [1]. More recently, the possibilityof 3D optical data storage and the demand for improved high-capacity data storage media devices has led to a renewed interestin photochromic organic compounds [2–5]. Among these are fulg-ides; derivativesof dimethylenesuccinic anhydridethatcan exhibitphotochromism and possess properties that allow for practicalapplications [6–8]. A specific example of a fulgide having proper-ties suitable for application in optical data storage devices is 1-E[8] (see Fig. 1).The optical properties of 1-E have been studied experimentallyby Asiri and coworkers [8,9]. These studies confirmed the photo-chromic properties of 1-E, which were attributed to a conrotatoryisomerization of 1-E into 1-C upon irradiation with UV light. Deter-mining such properties a priori by computational techniqueswould certainly be useful for experimentalists, saving resourcesand aiding in rational design of optical materials.Along with photochromism, the nonlinear optical (NLO) proper-ties of the fulgides are also of interest in electro-optic and datastorage applications [10–12]. At the molecular level, NLO behavioris relatedwith the hyperpolarizabilityb of the materialthroughtherelation (Einstein summation convention assumed)

Ab initio molecular orbital calculations using MP2 and DFT/B3LYP methods at the 6-311++G(d,p) and aug-cc-pvdz basis sets were applied to characterise the kinetics of the thermal dissociation of HC≡CCH2NHX [where X = OH(I), F(II) and Cl(III)] to produce Z- and E-prop-2-ynylideneamines (HC≡CCH=NH) (IV and V, respectively), which tautomerise to vinyl cyanide (CH2=CHC≡N) (VI). The optimised geometries and electronic energies of reactants, transition states and products were estimated and discussed. A concerted proton migration and HX abstraction mechanism was proposed for the imine formation. The reliance of these properties on the elected levels of theory was discussed. The activation energies and barrier heights for the Z- and E-forms and their vinyl cyanide tautomers were estimated and analysed. The Z-form was computed to be more stable than the E-form. Using natural bond orbital calculations, the origin of the preference of the Z-form was attributed mainly to the N lone pair delocalisations. Vinyl cyanide...

The transition structures and the activation energies for the possible thermal elimination of H2O, HF and HCl from ethane-1,2-diol, 2-fluoroethanol and 2-chloroethanol respectively, were investigated. The relative stabilities and associated barrier heights of syn and anti vinyl alcohol isomers and their acetaldehyde tautomer were estimated. HF, DFT/B3LYP and MP2 methods at 3-21G, 6-31+G(d), 6-311++G(d,p) and aug-cc-pvdz basis sets were applied to identify the stationary points of the studied systems. The optimized geometries and electronic energies of reactants, transition states and products were analyzed. The dependence of these properties upon the theoretical level was discussed. A concerted proton release and a hydroxide or halide ion expulsion mechanism was proposed to account for the thermal rearrangement of reactants to products. A thorough understanding of syn vinyl alcohol preference is provided by performing natural bond orbital (NBO) analysis. The oxygen atom lone pair (LP) and periplanar hyper...

The structure, reactivity, natural bond orbital (NBO), linear and nonlinear optical (NLO) properties of three thiazole azo dyes (A, B and C) were monitored by applying B3LYP, CAM-B3LYP and ωB97XD functionals with 6-311++G** and aug-cc-pvdz basis sets. The geometrical parameters, dipole moments, HOMO-LUMO (highest occupied molecular orbital, lowest unoccupied molecular orbital) energy gaps, absorption wavelengths and total hyperpolarizabilities were investigated in carbon tetrachloride (CCl4) chloroform (CHCl3), dichloromethane (CH2Cl2) and dimethlysulphoxide (DMSO). The donor methoxyphenyl group deviates from planarity with the thiazole azo moiety by ca. 38°; while the acceptor dicyanovinyl, indandione and dicyanovinylindanone groups diverge by ca. 6°. The HOMOs for the three dyes are identical. They spread over the methoxyphenyl donor moiety, the thiazole and benzene rings as π-bonding orbitals. The LUMOs are shaped up by the nature of the acceptor moieties. The LUMOs of the A, B and C dyes extend over the indandione, malononitrile and dicyanovinylindanone acceptor moieties, respectively, as π-antibonding orbitals. The HOMO-LUMO splittings showed that Dye C is much more reactive than dyes A and B. Compared to dyes A and B, Dye C yielded a longer maximum absorption wavelength because of the stabilization of its LUMOs relative to those of the other two. The three dyes show solvatochromism accompanied by significant increases in hyperpolarizability. The enhancement of the total hyperpolarizability of C compared to those of A and B is due to the cumulative action of the long π-conjugation of the indanone ring and the stronger electron-withdrawing ability of the dicyanovinyl moiety that form the dicyanovinylindanone acceptor group. These findings are facilitated by a natural bond orbital (NBO) technique. The very high total hyperpolarizabilities of the three dyes define their potent nonlinear optical (NLO) behaviour.

Diarylidenecyclopentanone compound namely, 2,5-bis[4-choloroacetyl-(thiophen-2-ylmethylene)]cyclopentanone (BCTCP) was firstly synthesized using the normal condition of Friedel-Crafts method by reacting 2,5-bis(thiophen-2-ylmethylene)cyclopentanone (BTCP) with chloroacetyl chloride in the presence of aluminum chloride anhydrous. The structure of this compound was confirmed by elemental and spectral analyses including FT-IR, 1H–NMR, 13C–NMR and mass spectrometry. The electronic absorption and emission properties of BCTCP were studied in different solvents. BCTCP displays a slight solvatochromic effect of the absorption and emission spectrum, indicating a small change in dipole moment of BCTCP upon excitation. BCTCP displayed photodecomposition in chlorinated solvents upon irradiating with 365 nm light. Ground and excited states electronic geometric optimizations were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively. A DFT natural bond orbital (NBO) analysis complemented the intramolecular charge transfer (ICT). The simulated maximum absorption and emission wavelengths are in line the observed ones in trend, and were proportionally red-shifted with the increase of the solvent polarity. The stability, hardness and electrophilicity of BCTCP in different solvents were correlated with the polarity of the elected solvents.

Novel heterocyclic azomethine dyes were prepared by the reaction of anthracene-9-carbaldehyde with different heterocyclic amines under microwave irradiation. Structures of the azomethine dyes were confirmed by the elemental analysis, mass spectrometry and several spectroscopic techniques. We studied absorbance and fluorescence spectra of the azomethine dyes in various solvents. They are found to be good absorbers and emitters. We also report photophysical properties like, extinction coefficient, oscillator strength, stokes shift and transition dipole moment. This reflects physicochemical behaviors of synthesized dyes. In addition, their intramolecular charge transfer and nonlinear optical properties, supported by natural bond orbital technique, were also studied computationally by density functional theory. The negative nonlinear refractive index and nonlinear absorption coefficient were measured for these dyes using the closed and open aperture Z-scan technique with a continuous wave helium-neon laser. These are found to vary linearly with solution concentration.

A new macromolecule pyrimido[l,2-a]benzimidazole derivative named 1,4-bis(2-(2-phenylpyrimido[1,2-a]benzimidazol-4-yl)phenoxy)butan (BPPB) has been synthesized in accepted yield using microwave assistance. The new compound BPPB has been formed by the interaction of 3,3'-((butane-1,4-diylbis(oxy))bis(2,1-phenylene))bis(1-phenylprop-2-en-1-one) (3) with 2- aminobenzimidazole (4) in the presence of potassium hydroxide as a basic catalyst in dimethylformamide (DMF) under microwave radiation for 20 min. The chemical structure of this novel compound was elucidated by elemental and spectral techniques including: FT-IR, (1)H-NMR, (13)C-NMR and mass spectra. The electronic absorption and emission spectra of BPPB were measured in different solvents. BPPB displayed a solvatochromic effect of the emission spectrum that is reflected by red shifts of its fluorescence emission maxima on increasing the solvent polarity, indicating a change of electronic charge distribution upon excitation. BPPB crystalline solids gave excimer-like emission at 535 nm with a bandwidth of ca. 60 nm. Ground and excited states electronic geometry optimizations using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively, complemented these spectral findings. The intramolecular charge transfer was investigated by natural bond orbital (NBO) technique.

The gas-phase decomposition mechanism of the photochemical and thermal reaction of cyclopropenone leading to carbon monoxide and acetylene has been investigated theoretically. We employed the B3LYP, MP2, and CASSCF methods with the 6-311 + G** basis set to determine the pathways and the potential energy surface (PES) of this reaction. PES minima were characterized by the absence of any imaginary frequencies and compared with the transition states that contained single imaginary frequencies. The intrinsic reaction coordinate (IRC) method was used to find the minimum energy paths in which reactants and products were connected to the transition states. Activation barrier, thermodynamic, and IRC analyses were performed using the above three methods. Our computations indicated that the decomposition of cyclopropenone proceeds through a stepwise mechanism containing two transition states (TS1 and TS2) and an intermediate. The results show that TS1, the critical transition state, determines the rate of the cyclo...

E,E-2,5-bis[2-(3-pyridyl)ethenyl]pyrazine (BPEP) has been prepared by aldol condensation between 2,5-dimethylpyrazine and pyridine-3-carboxaldehyde. It is characterized by IR, (1)H NMR, and (13)C NMR. The electronic absorption and emission properties of BPEP were studied in different solvents. BPEP displays a slight solvatochromic effect of the absorption and emission spectrum, indicating a small change in dipole moment of BPEP upon excitation. The dye solutions (1 × 10(-4) M) in CHCl3, EtOH and dioxane give laser emission in blue region upon excitation by a 337.1 nm nitrogen pulse (λ = 337 nm). The tuning range, gain coefficient (α) and emission cross - section (σe) have been determined. Ground and excited states electronic geometric optimizations were performed using density functional theory (DFT) and time-dependent density functional theory (TD-DFT), respectively. A DFT natural bond analysis complemented the ICT. The simulated maximum absorption and emission wavelengths are in line the observed ones in trend, and are proportionally red-shifted with the increase of the solvent polarity. The stability, hardness and electrophilicity of BPEP in different solvents were correlated with the polarity of the elected solvents. BPEP dye displays fluorescence quenching by colloidal silver nanoparticles (AgNPs). The fluorescence data reveal that radiative and non-radiative energy transfer play a major role in the fluorescence quenching mechanism.

The gas-phase thermal tautomerization reaction between imidazole-4-acetic (I) and imidazole-5-acetic (II) acids was monitored using the traditional hybrid functional (B3LYP) and the long-range corrected functionals (CAM-B3LYP and ωB97XD) with 6-311++G** and aug-cc-pvdz basis sets. The roles of the long-range and dispersion corrections on their geometrical parameters, thermodynamic functions, kinetics, dipole moments, Highest Occupied Molecular Orbital–Lowest Unoccupied Molecular Orbital (HOMO–LUMO) energy gaps and total hyperpolarizability were investigated. All tested levels of theory predicted the preference of I over II by 0.750–0.877 kcal/mol. The origin of predilection of I is assigned to the H-bonding interaction (nN8→σ*O14–H15). This interaction stabilized I by 15.07 kcal/mol. The gas-phase interconversion between the two tautomers assumed a 1,2-proton shift mechanism, with two transition states (TS), TS1 and TS2, having energy barriers of 47.67–49.92 and 49.55–52.69 kcal/mol, respectively, and an sp3-type intermediate. A water-assisted 1,3-proton shift route brought the barrier height down to less than 20 kcal/mol in gas-phase and less than 12 kcal/mol in solution. The relatively high values of total hyperpolarizability of I compared to II were interpreted and discussed.

The photophysical parameters such as electronic absorption spectra, molar absorptivity(ε), fluorescence spectra and fluorescence quantum yield (φf) of a new dye namely 2,7-diacetyl-9-((dimethylamino)methylene)-9H-fluorene (DMMF) were determined in different solvents. The electronic absorption are less sensitive to medium polarity. A bathochromic shift was observed in emission spectra(ca. 50 nm) upon increase of solvent polarity, which indicates that the singlet excited state (S1) of DMMF is more polar than the singlet ground state (So). Solid crystals of DMMF exhibit intense yellow fluorescence maximum at 550 nm with bandwidth equal 64 nm upon excitation at wavelength 365 nm. The change in dipole moment value (Δμ) was calculated by using the variation of Stokes shift with solvent polarizability (Δf) (Lippert - Mataga plot) and was found to be 7.22 and 5.5 Debye for higher and lower energy of So - S1 (π-π*) H-1 → L and So - S1 (π-π*) H → L, respectively. These results show that, the excited state is more polar than the ground state. The net photochemical quantum yields of photodecomposition of DMMF (φc) were calculated as 7.2 × 10(-5), 1.14 × 10(-4), 1.44 × 10(-4) and 2.11 × 10(-4) in different solvents such as MeOH, CH2Cl2, CHCl3 and CCl4, respectively. DFT/TD-DFT methods were used to study the geometric and electronic structures of DMMF in different solvents. A good agreement was found between the experimental and theoretical results.

Long-range corrected hybrid density functionals (LC-DFT), with range separation parameters optimally tuned to obey Koopmans’ theorem, are used to calculate the first-order hyperpolarizabilities of prototypical charge-transfer compounds p-nitroaniline (PNA) and dimethylamino nitrostilbene (DANS) in the gas phase and various solvents. It is shown that LC-DFT methods with default range separation parameters tend to underestimate hyperpolarizabilities (most notably in solution) and that the tuning scheme can sharply improve results, especially in the cases when the standard LC-DFT errors are largest. Nonetheless, we also identify pathological cases (two pyrrole derivatives) for which LC-DFT underestimates the hyperpolarizabilities, regardless of tuning. It is noted that such pathological cases do not follow the usual inverse relation between the hyperpolarizability and amount of exact exchange, and thus this behavior may serve as a diagnostic tool for the adequacy of LC-DFT.

MP2, DFT and CCSD methods with 6-311++G** and aug-cc-pvdz basis sets have been used to probe the structural changes and relative energies of E-prop-2-ynylideneamine (I), Z-prop-2-ynylideneamine (II), prop-1,2-diene-1-imine (III) and vinyl cyanide (IV). The energy near-equivalence and provenance of preference of isomers and tautomers were investigated by NBO calculations using HF and B3LYP methods with 6-311++G** and aug-cc-pvdz basis sets. All substrates have Cs symmetry. The optimized geometries were found to be mainly theoretical method dependent. All elected levels of theory have computed I/II total energy of isomerization (ΔE) of 1.707 to 3.707 kJ/mol in favour of II at 298.15 K. MP2 and CCSD methods have indicated clearly the preference of II over III, while the B3LYP functional predicted nearly similar total energies. All tested levels of theory yielded a global II/IV tautomerization total energy (ΔE) of 137.3–148.4 kJ/mol in support of IV at 298.15 K. The negative values of ΔS indicated that IV is favoured at low temperature. At high temperature, a reverse tautomerization becomes spontaneous and II is preferred. The existence of II in space was debated through the interpretation and analysis of the thermodynamic and kinetic studies of this tautomerization reaction and the presence of similar compounds in the Interstellar Medium (ISM).

The nonlinear optical (NLO) properties of N-ethyl dicyanocarbazole (1), N-ethyl cyanoethylacetatecarbazole (2), and N-ethyl dimethylacetatecarbazole (3) are studied with traditional hybrid and long-range corrected (LC) density functional theory (DFT) methods. The carbazoles are predicted to have planar structures with a high degree of π-conjugation and charge transfer, resulting in measurable NLO responses. The DFT data here calculated allow us to refine and correct previously reported experimental hyperpolarizabilities for these compounds. Experimental UV–vis absorption bands (related to hyperpolarizabilities estimated via solvatochromism) are also accurately reproduced by LC-DFT when using gap fitting schemes. The effects of different functionals on the HOMO–LUMO energy gaps and eventually on the total hyperpolarizabilities are discussed.

The gas phase properties of the Z- and E-isomers of 4-(p-N,N-dimethyl-aminophenylmethylene)-2-phenyl-5-oxazolone (DPO) and 4-(2,5-dimethoxyphenylmethylene)-2-phenyl-5-oxazolone (DMPO) are studied using traditional hybrid and long-range-corrected density functional theories (LC-DFT). Excellent agreement is found between the optimized molecular geometries and the experimental crystal structures. Our calculations predict both DPO and DMPO to have significant nonlinear optical (NLO) susceptibilities. These results are compared with data for the prototypical NLO chromophore p-nitroaniline, and the effect of the range separation parameter on LC-DFT hyperpolarizabilities is also analyzed.

The FTIR spectra of a series of 1H- and 2H- 1,2,3- and 1,2,4- triazoles and benzotriazoles were measured in the solid state. Assignments of the observed bands were facilitated by computation of the spectra using the density functional B3LYP method with the 6-311++G** basis set. The theoretical spectra show very good agreement with experiment. Rigorous normal coordinate analyses have been performed, and detailed vibrational assignment has been made on the basis of the calculated potential energy distributions. Several ambiguities and contradictions in the previously reported vibrational assignments have been clarified. "Marker bands" characterize the triazole ring were identified. The effect of substituents, the nature of the characteristic "marker bands" and quenching of intensities of some bands are discussed. Comparison of the topology of the charge density distribution, and the electric response properties of the 1H-, and 2H- isomers of both 1,2,3- and 1,2,4 triazole have been made using the quantum theory of atoms-in-molecules (QTAIM) by calculating the Laplacian of the electron density (∇²ρ(r)). Analysis of the contour plots and relief maps of ∇²ρ(r) reveals that 1,2,3- and 1,2,4-triazoles show completely different topological features for the distribution of the electron density. Thus, while the 1,2,3-isomer is a very polar molecule, the 1,2,4-isomer is much more polarizable. Bonding characteristics show also different features. This would thus underlie the different features of their vibrational spectra. The reported vibrational assignment can be used for further spectroscopic studies of new drugs and biological compounds containing the triazole ring.

The gas-phase thermal tautomerization reaction between 2-hydroxypyridine (2-HPY) and 2-pyridone (2-PY) was investigated by applying 6-311++G** and aug-cc-pvdz basis sets incorporated into some density functional theory (DFT) and coupled cluster with singles and doubles (CCSD) methods. The geometrical structures, dipole moments, HOMO-LUMO energy gaps, total hyperpolarizability, kinetics and thermodynamics functions were monitored against the effects of the corrections imposed on these functionals. The small experimental energy difference between the two tautomers of 3.23 kJ/mol; was a real test of the accuracy of the applied levels of theory. M062X and CCSD methods predicted the preference of 2-HPY over 2-PY by 5-9 kJ/mol; while B3LYP functional favoured 2-PY by 1-3 kJ/mol. The CAM-B3LYP and omega B97XD functionals yielded mixed results depending on the basis set used. The source of preference of 2-HPY is the minimal steric hindrance and electrostatic repulsion that subdued the huge hyperconjugation in 2-PY. A 1,3-proton shift intramolecular gas-phase tautomerization yielded a high average activation of 137.152 kJ/mol; while the intermolecular mixed dimer interconversion gave an average barrier height of 30.844 kJ/mol. These findings are boosted by a natural bond orbital (NBO) technique. The low total hyperpolarizabilities of both tautomers mark out their poor nonlinear optical (NLO) behaviour. The enhancement of the total hyperpolarizability of 2-HPY over that of 2-PY is interpreted by the bond length alternation.