3<Emphasis Type="Italic">H</Emphasis>-Benzo[<Emphasis Type="Italic">a</Emphasis>]imidazo[4,5-<Emphasis Type="Italic">j</Emphasis>]acridine as a new fluorescent heterocyclic system: synthesis,spectral studies,and quantum chemical investigation

The synthesis, spectral studies, and theoretical calculations of a new fluorescent heterocyclic system are described. New 3H-benzo[a]imidazo[4,5-j]acridines were obtained in high yields by the reaction of 1-alkyl-5-nitro-1H-benzimidazoles with (naphthalen-1-yl)acetonitrile via nucleophilic substitution of hydrogen, and their structures were established by spectral (UV-Vis, FT-IR, 1H and 13C NMR) and analytical data. Study of the optical and solvatochromic properties of the dyes revealed their high molar absorption coefficients and high fluorescence quantum yields which in some cases exceeded quantum yields of well-known fluorescent dyes such as fluorescein. Density functional theory (DFT) calculations using the B3LYP hybrid functional and 6-311++G(d,p) basis set were performed to obtain optimized geometries and frontier orbital structures of the synthesized compounds. The electronic absorption spectra were also simulated by the time-dependent density functional theory (TD-DFT) method.     

Experimental, theoretical and biological activity study on 1-(4,5-dihydro-3-arylpyrazol-1-yl)-2-(1H-1,2,4-triazol-1-yl)-ethanone

Four compounds have been synthesized and characterized by¹H NMR spectroscopy and elemental analyses, among which 1-(4,5-dihydro-3-phenyl-pyrazol-1-yl)-2-(1H-1,2,4-triazol-1-yl)ethanone 3a was further confirmed by X-ray crystallographic analysis. The biological activities of these compounds were tested, with the result that they displayed moderate fungicidal activities. In addition, a MO calculations using density functional theory (DFT) at B3LYP/6-31G^* level have also been carried out, and the structure–activity relationships for these compounds are discussed.     

Microwave‐assisted Synthesis,Characterization, and Density Functional Theory Study of Biologically Active Ferrocenyl Bis‐pyrazoline and Bis‐pyrimidine as Organometallic Macromolecules

Organometallic macromolecules such as ferrocenyl bis‐pyrazoline ( 2 , 3 ) and bis‐pyrimidine ( 4 , 5 ) derivatives were synthesized by reacting ferrocenyl bis‐chalcone 1 with thiosemicarbazide/phenylhydrazine/guanidine hydrochloride/thiourea, respectively, under microwave irradiation. Ferrocenyl bis‐chalcone 1 was synthesized by reacting acetyl ferrocene with terephthalaldehyde. Synthesized compounds were characterized by using IR, ¹H NMR, ¹³C NMR, EI‐MS, and elemental analysis. In vitro antibacterial activity against two Gram‐negative and two Gram‐positive bacteria was determined by the disc diffusion assay. Moreover, minimum inhibition concentrations were also measured with reference to chloramphenicol. Thioamide functionally containing ferrocenyl bis‐pyrazoline derivative 2 shows the best antibacterial activity on Escherichia coli and Salmonella typhimurium, among all tested compounds including the reference drug chloramphenicol. The structure–activity relationship is also developed by using computational calculations with density functional theory (DFT)/B3LYP method.     

Diaza-18-crown-6 based chromophores for modulation of two-photon absorption cross-section by metal ions

Two chromophores with diaza-18-crown-6 as receptor have been synthesized in high yields. The electronic structure, one-photon absorption (OPA) spectra, and two-photon absorption (TPA) properties have been studied in detail. When no metal ion is added as input, both show negligible TPA cross-section (σ₂). However, in the presence of Zn(II)/Cd(II)/Mg(II)/Ca(II) ion, each exhibits large TPA cross-section value. Binding of metal ion in the receptor increases the symmetric charge transfer leading to large σ₂ values. Theoretical calculations at the B3LYP functional with 6-31G^∗ and LanL2DZ mixed basis set under DFT formalism support experimental results.     

2-[(1H-benzimidazol-2-ylmethyl)-amino]-benzoic acid methyl ester: crystal structure, DFT calculations and biological activity evaluation

In the present study, structural properties of 2-[(1H-benzimidazol-2-ylmethyl)-amino]-benzoic acid methyl ester have been studied extensively by spectral methods and X-ray crystallography. Quantum mechanical calculations of energies, geometries, vibrational wavenumbers, NMR and electronic transitions were carried out by DFT using B3LYP functional combined with 6-31G(d) basis set. Natural bond orbitals (NBO) analysis and frontier molecular orbitals were performed at the same level of theory. DFT calculations showed good agreement between the theoretical and experimental values of optimized and X-ray structure as well as between the vibrational and NMR spectroscopy. The title compound was screened for its antibacterial activity referring to Tetracycline as standard antibacterial agent.     

Synthesis,spectral properties,and solvatochromism of merocyanine dyes based on bis(2,2,3,3,4,4,5,5-octafluoropentyl)-4,5-dinitro-9H-fluorene-2,7-disulfonate

Di-, tetra-, and hexamethine merocyanines containing heterocyclic fragments with different electron-donor abilities have been synthesized on the basis of bis(2,2,3,3,4,4,5,5-octafluoropentyl)-4,5-dinitro-9H-fluorene-2,7-disulfonate. Their electronic absorption spectra in solvents with different polarities have been studied, and their electronic structure and electronic transitions have been analyzed by DFT and TDDFT quantum chemical calculations using B3LYP functional and 6-31G(d,p) basis set. The electronic structure of the synthesized merocyanines changes from neutral polyene to polymethine and dipolar polyene, depending on the electron-donor ability of the heterocyclic fragment, length of the polymethine chain, and solvent polarity. Therefore, these merocyanines display positive, negative, and reverse solvatochromism.     

Molecular modeling of 3,4-pyridinedicarbonitrile dye sensitizer for solar cells using quantum chemical calculations

The geometries, electronic structures, polarizabilities, and hyperpolarizabilities of organic dye sensitizer 3,4-pyridinedicarbonitrile was studied based on Hartree–Fock (HF) and density functional theory (DFT) using the hybrid functional B3LYP. Ultraviolet–visible (UV–Vis) spectrum was investigated by time dependent DFT (TD-DFT). Features of the electronic absorption spectrum in the visible and near-UV regions were assigned based on TD-DFT calculations. The absorption bands are assigned to π → π1 transitions. Calculated results suggest that the three lowest energy excited states are due to photoinduced electron transfer processes. The interfacial electron transfer between semiconductor TiO₂ electrode and 3,4-pyridinedicarbonitrile is due to electron injection process from excited dye to the semiconductor’s conduction band. The role of cyanine in 3,4-pyridinedicarbonitrile in geometries, electronic structures, and spectral properties were analyzed.     

Investigation of the structure, the optical properties, and the photophysics of some indolocarbazoles having terminal aromatic rings

Structures, optical properties, and photophysics of ladder indolo[3,2-b]carbazoles substituted symmetrically by phenylene and thiophene rings have been investigated theoretically and experimentally. The ground state optimized structures were obtained using the density functional theory (DFT) as approximated by the B3LYP functional and employing the 6-31G^* basis set. All derivatives were found nonplanar in their electronic ground states. The character and the energy of the singlet–singlet electronic transitions have been investigated by applying the time-dependent density functional theory (TDDFT) to the correspondingly optimized-ground-state geometries. The ab initio restricted configuration interaction (singles) method (RCIS/6-31G^*) was adopted to obtain the first singlet excited-state structures (S₁) of the molecule. TDDFT calculations performed on the S₁ optimized geometries was used to obtain emission energies. UV–vis and fluorescence spectroscopies were analyzed in conjunction with theoretical calculations. The computed excitation and emission energies were found in reasonable agreement with the experimental absorption and fluorescence spectra. Finally, the photophysical behavior of the indolocarbazoles have been studied by means of steady state and time resolved fluorescence. The overall data have allowed the determination of the rate constants for the radiative and nonradiative decay processes. Both theoretical and experimental data show that the replacement of phenylene rings by thiophene units induces a red shift in the absorption and fluorescence spectra. This behavior is interpreted in terms of the electron donor properties of the thiophene ring. On the other hand, the change of the substitutional pattern, from 2,8 to 3,9, causes a significant hypsochromic shift of the absorption and fluorescence bands.     

Benzoid–Quinoid tautomerism of schiff bases and their structural analogs: LVII. 2-[(3-oxo-5-phenylpyrazolidin-1-yl)methylidene]-1<Emphasis Type="Italic">H</Emphasis>-indene-1,3(2<Emphasis Type="Italic">H</Emphasis>)-dione

Potentially tautomeric azomethine imide, 2-[(3-oxo-5-phenylpyrazolidin-1-yl)methylidene]-1H-indene- 1,3(2H)-dione, has been synthesized by condensation of 5-phenylpyrazolidin-3-one with 2-(hydroxymethylidene)-1H-indene-1,3(2H)-dione. According to the IR, ¹H and ¹³C NMR, and electronic absorption spectroscopy data and DFT B3LYP/6-311++G(d,p) quantum chemical calculations, the title compound in solution exists as planar tricarbonyl tautomer stabilized by intramolecular hydrogen bond between the NH proton of the pyrazolidine fragment and carbonyl oxygen atom of the indene fragment. Its crystal structure was determined by X-ray analysis.     

3-Alkylsulfanyl-2-arylazo-3-(pyrrolidin-1-yl)-acrylonitriles as masked 1,3-dipoles

Reaction of 3-alkylsulfanyl-2-arylazo-3-(pyrrolidin-1-yl)acrylonitriles with maleimides, dimethyl maleate and dimethylacetylene dicarboxylate were carried out to give octahydro-pyrrolo[3,4-a]pyrrolizin-4-ylidenes, hexahydro-pyrrolizines and 6,7-dihydro-5H-pyrrolizines. The formation of the synthesized compounds is explained by a 1,3-dipolar cycloaddition of an in situ generated azomethine ylide. The mechanisms of the formation of these active intermediates were discussed with the aid of density functional theory methods with the B3LYP functional 6-31G⁺ calculations using the STQN method and chemical experiments.     

Theoretical Study and Experimental Analysis on 2-(1-Ethyl-4-hydroxy-2-oxo-1,2-dihydroquinolin-3-yl)-2-oxoacetic Acid (<Emphasis Type="Bold">3</Emphasis>) Using the DFT Approach

Riley oxidation of 3-acetyl-4-hydroxyquinolin-2(1H)-one (1) with selenium dioxide furnished the unexpected product 2-(1-ethyl-4-hydroxy-2-oxo-1,2-dihydroquinolin-3-yl)-2-oxoacetic acid (3). The expected product 2-(1-ethyl-4-hydroxy-2-oxo-1,2-dihydroquinolin-3-yl)-2-oxoacetaldehyde (2) was excluded based on the spectral data. The elemental analysis and spectral data (IR, and ¹H NMR) was used to deduce the structure of compound 3. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations of the electronic structure at the B3LYP/6-311G (d,p) level of theory have been employed for compound 3 to investigated its geometry, linear polarizability 〈Δα〉, first-order hyperpolarizability 〈β〉, natural bonding orbital (NBO), molecular electrostatic potential contours (MEP and ESP), electrophilicity, and UV–Vis spectra in both ethanol and dioxane solvents. The geometrical and energetic parameters have been extensively investigated to reveal the reason behind the selective formation of compound 3, rather than the expected product 2. FT-IR spectra in the solid phase were recorded for compound 3. The thermo-chemical parameters, harmonic vibration frequencies, and the equilibrium geometries have been calculated at the DFT/B3LYP/6-311G (d,p) level. Time-dependent density functional theory (TD-DFT) was used to calculate the excited states of compound 3. Changes in the solvent cause changes in the band intensities and in the positions of the band maxima (λ_max). The excited state was identified and contributes to the electronic configurations, and it was characterized in terms of the relevant MOs. The theoretical spectra were computed using the Coulomb-attenuating method (CAM-B3LYP), using the basis set 6-311G (d,p) in the gas phase, and the polarizable continuum model (PCM) in dioxane and ethanol. The results indicate good agreement with the observed spectra.     

Theoretical Investigation by DFT and Molecular Docking of Synthesized Oxidovanadium(IV)-Based Imidazole Drug Complexes as Promising Anticancer Agents

Vanadium compounds have been set in various fields as anticancer, anti-diabetic, anti-parasitic, anti-viral, and anti-bacterial agents. This study reports the synthesis and structural characterization of oxidovanadium(IV)-based imidazole drug complexes by the elemental analyzer, molar conductance, magnetic moment, spectroscopic techniques, as well as thermal analysis. The obtained geometries were studied theoretically using density functional theory (DFT) under the B3LYP level. The DNA-binding nature of the ligands and their synthesized complexes has been studied by the electronic absorption titrations method. The biological studies were carried with in-vivo assays and the molecular docking method. The EPR spectra asserted the geometry around the vanadium center to be a square pyramid for metal complexes. The geometries have been confirmed using DFT under the B3LYP level. Moreover, the quantum parameters proposed promising bioactivity of the oxidovanadium(IV) complexes. The results of the DNA-binding revealed that the investigated complexes bind to DNA via non-covalent mode, and the intrinsic binding constant (K_b) value for the [VO(SO₄)(MNZ)₂] H₂O complex was promising, which was 2.0 × 10⁶ M⁻¹. Additionally, the cytotoxic activity of the synthesized complexes exhibited good inhibition toward both hepatocellular carcinoma (HepG-2) and human breast cancer (HCF-7) cell lines. The results of molecular docking displayed good correlations with experimental cytotoxicity findings. Therefore, these findings suggest that our synthesized complexes can be introduced as effective anticancer agents.     

Theoretical investigation of carotenoid ultraviolet spectra

We have determined the π band‐gaps of the main carotenoids present in poly(methyl)methacrylate/buriti blends, namely, trans‐β‐carotene, 13‐cis‐β‐carotene, 9‐cis‐β‐carotene, phytofluene, and zeaxanthin. Semiempirical, model Hamiltonian, and density functional calculations were carried out to study these structures. The geometries were fully optimized using AM1, PM3, and B3LYP/6‐31G(d,p) methods. The TD‐DFT and ZINDO/S methods were applied for the calculation of the electronic absorption spectra of the optimized B3LYP geometries. The calculated spectra using the polarizable continuum model for the solvent effects were compared with the available experimental. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Fluorene-based oligomers as red light-emitting materials: a density functional theory study

The electronic structures, charge injection and transport, absorption and emission spectra, properties of two series of fluorene-based oligomers {2-[2-{2-[5-(9H-Fluoren-3-yl)-thiophen-2-yl]-vinyl}-6-(2-thiophen-2-yl-vinyl)-pyran- 4-ylidene]-malononitrile} _n (FTPM) _n and {2-{2-{2-[5-(9H-Fluoren-2-yl)-2-hydroxy- 3-methoxy-phenyl]-vinyl}-6-[2-(2-hydroxy-3-methoxy-phenyl)-vinyl]-pyran-4- ylidene}-malononitrile} _n (FOOPM) _n (n = 1–4) have been investigated by the density functional theory (DFT) approach. The ground-state geometries of (FTPM)₄ and (FOOPM)₄ optimized at B3LYP/6-31G(d) level exhibited zigzag arrangements. The energies of HOMO and LUMO, HOMO–LUMO energy gaps (ΔE _H–L ) of (FTPM) _n and (FOOPM) _n (n = ∞) were obtained by linear extrapolation method. Moreover, the calculations of ionization potential (IP), electronic affinity (EA), and reorganization energy (λ) were used to evaluate the charge injection and transport abilities. For (FTPM)₄ and (FOOPM)₄, the TDDFT calculations revealed that the absorption peaks can be characterized as π–π* transition and couple with the location of electron density distribution changes in different repeat units. All the earlier theoretical investigations are intended to establish the structure–property relationships, which can provide guidance to design the organic light-emitting diodes (OLEDs) with high performance.     

Spectral,luminescent, and photophysical properties of dipyrrolylbenzenes

Dipyrroles with a phenylene bridge, 1,4-bis(pyrrol-2-yl)benzene, 4-(1-vinylpyrrol-2-yl)-1-(pyrrol-2-yl)benzene, and 1,4-bis(1-vinylpyrrol-2-yl)benzene, show intense room-temperature fluorescence in solutions. Analysis of electronic absorption spectra, fluorescence spectra, and results of B3LYP, TD B3LYP, and CIS quantum chemical calculations showed that the introduction of a bulky substituent in position 1 of the pyrrole ring makes the ground-state structures of dipyrrolylbenzenes less planar. Excited-state geometries of all molecules relax to more planar conformations. An increase in the probability of nonradiative transitions has little effect on the quantum yields of fluorescence (Φ_f) of dipyrrolylbenzenes. Even for 1,4-bis(1-vinylpyrrol-2-yl)benzene, where the pyrrole rings deviate from the benzene ring plane by 44°, the fluorescence efficiency remains high enough (Φ_f = 0.7). Substitution at nitrogen atoms has little effect on positions of fluorescence band maxima. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1433–1438, July, 2008.     

Synthesis,crystal structure and photoluminescence of 3-(4-(anthracen-10-yl)phenyl)-benzo[5,6]coumarin

A new coumarin derivative, 3-(4-(anthracen-10-yl)phenyl)-benzo[5,6]coumarin, was synthesized and characterized by FT-IR, ¹H NMR, element analysis and single crystal X-ray crystallography. The dihedral angle of benzo[5,6]coumarin ring and phenyl group is 36.15°, and the dihedral angle of phenyl group and anthracene skeleton is 89.37°. The UV–vis absorption and photoluminescence of the compound were discussed. The result shown that the compound exhibits high fluorescence quantum yield (Φ_F), large Stokes shift and green emission (508 nm). The molecular structure of the compound was optimized using density functional theory (DFT) at B3LYP/6-31G(d) level, and the HOMO and LUMO levels of the compound were deduced.