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The ground (S(0)) and excited triplet (T(1)) electronic states and corresponding optical spectra of a series of cationic complexes [RuH(CO)L(PPh(3))(2)](+) (L=2,2´-bipyridyl) (Rubpy), 4,4´-dicarboxylic-2,2´-bipyridyl (Rudcbpy), bis-4,4’-(N-methylamide)-2,2´-bipyridyl (Rudamidebpy), bis-4,4’-(methyl)-2,2´-bipyridyl (RudMebpy), [Ru(CO)(2)dcbpy(PPh(3))(2)](2+) (Ru(2CO)dcbpy), and [Ru(H)(2)dcbpy(PPh(3))(2)] (Ru(2H)dcbpy) have been studied by combined Density Functional/Time-Dependent Density Functional (DFT/TDDFT) techniques using different combinations of DFT exchange-correlation functionals and basis sets. PBE0/LANL2DZ provided more accurate geometries to describe S(0) whereas B3LYP/LANL2DZ predicted spectral energies that correlated better with the available experiment data. The Ru (II) complexes with different substituents emit photons ranging from 560–610 nm in the series RudMebpy, Rubpy, Rudamidebpy, Rudcbpy. The calculations predicted a maximum emission at about 540 nm for the complex constructed from two carbonyl π-acceptors ligands trans to the dcbpy, while an emission in the far infrared region is calculated when two H σ-donor ligands trans to the dcbpy. Our calculation results show correlations between HOMO-LUMO energy gap, Stokes shift, and T(1) distortion, which reflect the different effects of electron-withdrawing and donating groups. We proposed that these correlations can be used to predict the photophysical properties for new complexes.

Made available in DSpace on 2019-10-04T12:38:15Z (GMT). No. of bitstreams: 0 Previous issue date: 2019-09-15 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) The solvent-induced Stokes' shift, which describes the response at different solvents (acetonitrile, chloroform, dichloromethane, 1,4-dioxane, N,N-dimethylformamide, ethanol, heptanol, tetrahydrofuran, and toluene) to a sudden change in the charge distribution of excited 4-(Dicyanomethylene)-2-tert-butyl-6- (1,1,7,7-tetramethyljulolidin-4-yl-vinyl)-4H-pyran (DCJTB) molecule, was studied through absorption and emission spectra and TD-DFT calculations; the solvent effect was studied trough the IEF-PCM model. The application of IEF-PCM model with TD-DFT methods to obtain the absorption energies provided excellent match with the experimental results. The results observed, for solvents effects on the positions of maxima absorption and emission between experimental data and theoretical calculations, have average absolute deviations of only 0.03 eV and 0.22 eV, respectively. A systematic error was observed by comparing the theoretical and experimental maxima for the emission energies. However, the application of the Lippert-Mataga and Bilot-Kawski equations to the TD-DFT-simulated Stokes' shifts values resulted in excellent correlation coefficients: Lippert-Mataga, R-2 = 0.9982, Bilot-Kawski, R-2 = 0.9908 and R-2 = 0.9795. (C) 2019 Elsevier B.V. All rights reserved. Univ Estadual Campinas, UNICAMP, Inst Chem, Dept Phys Chem, BR-13083861 Campinas, SP, Brazil Sao Paulo State Univ, UNESP, Fac Sci, Dept Chem, BR-17033360 Bauru, SP, Brazil Sao Paulo State Univ, UNESP, Fac Sci, Dept Chem, BR-17033360 Bauru, SP, Brazil FAPESP: 2016/20549-5 FAPESP: 2015/22338-9 FAPESP: 308480/2016-3 FAPESP: 2016/04963-6 FAPESP: INCT.Bio.Nat 2014/50926-0 CNPq: 302793/2016-0 CNPq: 306975/2013-0 CNPq: 305541/2017-0 CNPq: 440503/2014-0

Two free base meso-tetraphenylporphyrin-fullerene dyads, H2PMe-C60, H2POMe-C60, and their zinc complexes, ZnPMe-C60 and ZnPOMe-C60, which the para positions of the meso-tetrasubstituted phenyl groups of the porphyrin core were substituted by methyl(-Me) and methoxyl(-OMe) groups respectively, were synthesized. The porphyrin unit in the synthesized dyads is directly linked to the fullerene entity through the pyrrole-β- position rather than through the traditionally meso-substituted phenyl group, which may be more favorable for electron communication between the donor and the acceptor. They are fully characterized by mass spectrometry, nuclear magnetic resonance, infrared spectroscopy and ultraviolet visible spectroscopy. Experimental results obtained from steady-state fluorescence spectroscopy and cyclic voltammetry show that the coordination of the zinc ions lead to an increase in the singlet excited state energy of the metallated porphyrin unit by about 0.15 eV, and to a reduce in the HOMO level and in the HOMO-LUMO energy gap. The molecular reorganization energy decreases after the electron-donating groups of -Me or -OMe attaching to the para position of the meso-phenyl group of the porphyrin moiety. The results of the energy calculations show that photoinduced electron transfer is thermodynamically favorable for the synthesized porphyrin-C60 dyads. There exists a competition between the photoinduced electron transfer and energy transfer processes from the first singlet excited state of porphyrin core to fullerene moiety. The photoinduced electron transfer rate constant of the dyads were calculated according to Marcus theory. The results indicate that the coordination of metal zinc ions lead to great increase in the electron transfer rate constant. Further, the photoinduced electron transfer rate constant increases in the order ZnP-C60, ZnPMe-C60, ZnPOMe-C60.

A novel semicarbazone O2N donor ligand, HL, was synthesized by condensation of 2-aminochromone-3-carboxaldehyde with semicarbazide hydrochloride. The HL ligand is allowed to react with several copper(II) salts namely: AcO–, NO3–, SO42– and Cl–, in absence and presence of secondary ligand (SCN-, 8-HQ and 1,10-phen), forming binary and ternary copper complexes. Characterization of the compounds has been done using various techniques like elemental analyses, magnetic moments, conductance measurement, thermogravimetry and FT-IR, UV-Vis, 1H and 13C NMR, EPR and mass spectroscopy. The HL ligand acts as monoanionic O2N tridentate in most complexes, forming Cu(II) complexes with an octahedral and square planar geometrical arrangements. The compounds exhibit luminescence property; promising interesting potential applications as photoactive materials. The ground state (µg) and excited state (µe) dipole moments are estimated from solvatochromic shifts of absorption and fluorescence spectra as a function of the dielectric constant (Ɛ) and refractive index (n) by using Bilot–Kawski, Lippert–Mataga, Bakhshiev, Kawski–Chamma–Viallet and Reichardt correlation methods. Excited state dipole moment is observed as larger than the ground state dipole moment. The molecular structural parameters of the ligand and its Cu(II)- complexes have been calculated on the basis of DFT level implemented in the Gaussian 09 program at the B3LYP/6-31G(d,p) level and the theoretical data are correlated with the experimental data. The antibacterial properties of the ligand and its complexes have been screened against selected kinds of bacteria and fungi.

The potential functions of internal rotation V(φ) (PFIR) of methacryloyl fluoride (MAF) in the ground (S0) and excited (S1) electronic states were reconstructed using the TORSIO program from experimental energy levels of the torsional transitions in the s-trans- and s-cis isomers. The energy levels were obtained from the analysis of the vibrational structure in the high-resolution gas-phase UV spectrum. The (S0) and (S1) equilibrium geometries of the s-trans- and s-cis rotational isomers of MAF as well as structural parameters for a set of points along the relaxed geometry scans, which were used to find expansion coefficients of kinematic function F(φ) in the Fourier series, were calculated using extended multiconfiguration quasi-degenerate perturbation theory, XMCQDPT2/SA(2)-CASSCF(6,5)/aug-cc-pVTZ. The ground (S0) state calculations were also done at the MP2 level of theory. In (S0) state, parameters Vn., barriers of internal rotation ΔH‡ and ΔH of MAF isomers were calculated using two theories. The calculated values of Vn, ΔH‡, ΔH in (S0) state are in good agreement with those derived from the vibrationally resolved UV spectrum of MAF in the gas phase. Within the one-dimensional model, the experimentally derived barrier heights that hinder internal rotation in MAF were found to be 2100 ± 50 cm−1 and 4950 ± 250 cm−1 in the (S0) and (S1) states, respectively. The parameters Vn and ΔH‡ in (S1) state are determined for first time.

Synthetic dyes having high photostability on hydrophobic fibers such as poly(ethylene terephthalate) (PET) are of interest for use on textile substrates for outdoor applications. While much is known about photostable dyes developed for PET in the 1980s, owing to their viability for use in automobile interiors, little has been published on currently viable photostable disperse dyes. As part of an effort to help fill this void and to facilitate future photostable disperse dye design, the present study involved the use of experimental measurements and modelling studies to help characterize the molecular structures of commercially viable dyes for producing photostable colors on PET fibers, beginning with a pair of blue dyes. With the aid of HR-MS, 500 MHz 1H NMR, and X-ray crystallography, it was established that the two dyes are structural isomers having 1,5-(OH)2-anthraquinone (AQ) and 1,8-(OH)2-AQ base structures. It is proposed that the photostability of these dyes arises from the presence of multiple OH/NH groups ortho to the AQ C O groups which enables them to dissipate excited state energy through intramolecular proton transfer. Further, using DFT-based molecular modelling studies, it was shown that the dye having the 1,5-(OH)2-AQ base structure has a lower ESOP than the isomeric dye having the 1,8-(OH)2-AQ base structure. Similarly, results from calculating Frontier HOMO and LUMO isosurfaces indicated that the LUMO lobes of the latter dye are larger, suggesting that this dye undergoes excitation faster than the 1,5-(OH)2-AQ isomer.

A trio of 1,4-diaryl-1,3-butadiynes with methoxy and trifluoromethoxy substituents in the 4- and 4′-positions were prepared in useful yields (42% for one, 95+% for the others), their structures determined and their purity ascertained. Analysis of the single crystal X-ray data for the three compounds revealed that two were mostly planar with small dihedral angles of 6–9° between their aryl rings, while one existed in a twisted conformation with a dihedral angle of approximately 53° between it's aryl rings. The solid-state absorption spectra of all three compounds were similar, with structured absorptions at approximately 340 nm. One of the compounds had absorption bands at 263 and 457 nm. Two of the compounds had similar emission bands with maxima that ranged from 440 to 450 nm, while the other was quite different, with a broad emission band with a maximum at 564 nm. Each of the three compounds had excited state decay traces that were fit to tri-exponential curves which yielded three lifetimes: a longer one attributed to aggregate emission, a shorter one arising from an intermolecular charge transfer transition, and a medium one that is assigned to a locally excited transition.

Single crystals of an organic charge-transfer compound, 4-nitrobenzyl isoquinolinium picrate, [4NO2BzIQl][PIC](1), were grown by slow evaporation technique at room temperature. Single crystal XRD and powder XRD studies conform the crystal structure and crystalline nature. In the title compound, the [4NO2BzIQl]+ cations and the [PIC]- anions stack into a columnar structure through π···π and C H···π interactions. The FT-IR and Raman spectra were recorded and analyzed with the aid of density functional theory calculations in order to make a suitable assignment of the observed bands. The simulated spectrum satisfactorily coincides with the experimental UV–visible spectrum. Thermal stability and the major gaseous products of decomposition at 293 °C were examined by TG-DTA-MS technique. The material shows three main emission peaks about 385, 467 and 538 nm upon excitation at 241 nm in solid state at room temperature. The excited state energy from theoretical UV–vis spectra, the total energy of intramolecular interactions and nonlinear optical properties were studied using DFT calculations.

Pyrene and its OH, NH2, and CN substituted derivatives were investigated experimentally by using UV/Vis absorption spectroscopy, steady state and time-resolved fluorescence spectroscopy in different polarity solvents. The computational part includes investigation of Pyrene and derivatives in excited S1 state in gas phase and in solution. Calculations were carried out with density functional theory (DFT) and time-dependent density functional theory (TDDFT) at B3LYP/6-311++G(d,p) level. Both ground and excited state geometries were fully optimized in gas phase and in solution. Solution calculations were carried out with Polarizable Continuum Model (PCM). Current results indicate that solvent polarity did not affect Py and its derivatives except PyNH2. Solvent has minor effects on PyCN and PyOH. Although PyNH2 has he smallest HOMO-LUMO energy gap, it is not the best candidate due to its shortest fluorescence lifetime. On the other hand, PyOH and PyCN have longer lifetimes. Therefore, it is concluded that investigated molecules are appropriate candidates for photosensitive applications in the order of PyNH2

Understanding electronic structures and excitation properties is a fundamental issue to develop novel electron donor (D) and acceptor (A) molecular dyad that can be applied in optoelectronic systems. Here, the geometry, electronic structures, and excitation properties of three meso-pentafluorophenyl substituted zinc porphyrin fullerene ((F15P)ZnP C60) dyad were analyzed based on density functional theory (DFT) and time dependent DFT (TDDFT) calculations. The geometrical parameters provide the D-A distance is about 18.19 A. The electronic structure analysis indicates that the highest occupied molecular orbital and the lowest unoccupied molecular orbital are localized in porphyrin core and C60, respectively. The transition configurations and the MOs suggest the excited states at the absorption maxima are local excited states, while the charge transfer (CT) states are transient intermediates. The population analysis supports the first singlet/triplet excited states are local excitations in porphyrin (LEP). Quasi-degeneracy of excited states between LEP and local excitation in C60 (LEC) enable the partial delocalization of eigenstates and excitation-energies over the D and A in dyad, while the quasi-degeneracy between CT and LEP generate synergistic enhancement effects for CT. The results of this work could be helpful to understand optoelectronic properties of (F15P)ZnP C60 dyad.

Since acenaphthene isolated in an Ar matrix at 15 K emits green-yellow phosphorescence for ∼10 s after stopping UV-light irradiation, its transient IR spectrum is expected to be measured with an FTIR spectrometer during UV irradiation. The transient spectrum observed is found to be consistent with the simulated spectrum of acenaphthene in the lowest electronically excited triplet (T1) state calculated at the B3LYP/6–31++G(d,p) level. The spectral pattern obtained using the B3LYP functional, which is the most popular DFT hybrid functional, reproduces the observed spectrum more satisfactorily than that obtained using the recently proposed M06-2x functional, although the optimized geometrical parameters in the both calculations are not so different from each other. The IR-band assignments of the T1 state and the structural changes from the S0 state to the T1 state are discussed based on the results of B3LYP calculation.

The radiationless decay of the isothiazole and thiazole molecules in the gas phase is investigated by a combination of static MS-CASPT2 computations with dynamics simulations, and some deactivation pathways are identified leading from the lowest excited singlet (S1) state back to the electronic ground (S0) state. The dominant relaxation pathway of the excited isothiazole is found to involve out-of-plane ring deformation (ring puckering) at the C4=C5(H8) S1 moiety, while the excited-state decay of thiazole can proceed through the ring puckering and S1 C2 bond cleavage pathways both of which happen at the S1 C2(H6) = N3 moiety. On the basis of the calculation results, we suggest that both ring-puckering and ring-opening routes should play rather important roles in the photophysics and photochemistry of heterocyclic molecules, and the position of the N atom in the heterocyclic ring has an effect on the excited state deactivation.

In the present study Ca2P2O7:Ce3+ pyrophosphate phosphor was synthesized by modified solid state diffusion. Materialization of crystalline phases were recognized by X ray diffraction pattern and their photoluminescence properties were studied using excitation and emission spectra under ultraviolet ray excitation ranging from 250 to 400 nm. The Ca2P2O7:Ce3+ phosphor was excited at 298 nm, the emission spectrum exhibited two intense bands at 362 nm and 390 nm emission due to 5d → 4f transitions of Ce3+ ions. The morphological investigations of Ca2P2O7 pyrophosphate have been carried out by scanning electron microscopy and fourier transform infrared spectra at room temperature was also examined. Stoke's shift, type of interaction between activator and the influences of the doping concentration of Ce3+ on the luminescence characteristics are discussed from photoluminescence excitation and emission spectra.

Two novel molecules (SCLPY-MeO and SCLPY-CN) are designed based on the N-salycilidene-5-chloroaminopyridine (SCLPY) via introducing the methoxyl (-OCH3) and cyano (-CN) groups at the meta-position of the chlorine atom, respectively, to explore the effect of the substitution of electron-withdrawing and donating groups on the excited-state intramolecular proton transfer (ESIPT) mechanism and photophysical properties of SCLPY, employing the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. The significant calculated structural parameters associated with the intramolecular hydrogen bonds (IHBs) have demonstrated that the IHBs intensity is enhanced in the excited state and SCLPY is endowed with the strongest IHB. The partial quenching of the short-wavelength fluorescence in SCLPY-CN has been satisfactorily explained by calculating the transition electric dipole moment and the long-wavelength fluorescence of that exhibits the largest Stokes shifts relative to the other molecules. Moreover, introducing the -OCH3 group has evidently enhanced the luminescent intensity of SCLPY. On account of the potential energy curves (PECs), scanning with gradually elongating the O1-H2 bond, it can be known that the forward proton transfer process is more readily to occur in the S1 state due to the relatively lower energy barriers compared with the ground state. Moreover, SCLPY is provided with the lowest energy barrier, implying that the ESIPT behavior is most likely inclined to proceed in SCLPY. Therefore, it is well illustrated that the introductions of -OCH3 and –CN groups indeed have an impact on the ESIPT process and photophysical properties of SCLPY.

The three Schiff base-type Cu(I) complexes [Cu(POP)(N^N)]PF6, N^N = N,N-diphenyl-4-(6-((phenylimino)methyl)pyridin-3-yl)aniline (P1), N-((5-(4-(diphenylamino)phenyl)pyridin-2-yl)methylene)naphthalen-2-amine (P2), N-((5-(4-(diphenylamino)phenyl)pyridin-2-yl)methylene)adamantan-1-amine (P3), were prepared and characterized. The photophysical properties of these Cu(I) complexes is tuned by the addition of different substituents such as phenyl, naphthyl and adamantanyl groups into the backbone of Schiff base ligand. The resulting complexes exhibit high absorption ability in the visible region with molar extinction coefficients of up to 3 7400 M−1 cm−1. The emissions in CH2Cl2 solution are in the range of 551–552 nm with lower quantum yields of 1.1–2.0% and short-lived excited lifetimes of 2.78–3.09 ns for all the complexes at room temperature. The photophysical properties were further explained by DFT and TDDFT methods.

A zinc complex with a N2O2 donor diamine is synthesized and its fluorescence property is explored. The hydrogen bonding environment in its solid state structure is well supported qualitatively and quantitatively with the help of Reduced Density Gradient (RDG) based NCI (non-covalent interactions) index calculation and AIM analyses. Also, the physical nature of other weak non-covalent interactions in the complex is examined. The absorption and emission properties of the complex are explained using density functional theory (DFT) calculations. Analysis of the natural transition orbitals (NTO) shows that the excited state can be mainly characterized by an intra-ligand charge transfer (ILCT) transition within a diamine from the highest-occupied NTO (hole) to the lowest-unoccupied NTO (electron).

The molecular, spectroscopic, and excited state properties of synthetic dyes for fiber-based outdoor materials continue to be of commercial interest. Early developments in this area were reported in the 1980s, when the need for dyes for polyester (PET)-based automobile interiors gave rise to commercially viable nitrodiphenylamine yellow, anthraquinone red and blue, and azo red dyes. To augment that initial knowledge base, the present study involved the use of experimental and theoretical methods to help establish the molecular structures and excited state properties of some more recent dyes for producing photostable colors on PET fibers. Having completed the characterization of present-day scarlet, blue, and yellow disperse dyes for PET-based fibers used outdoors, our attention turned to commercially available red and violet dyes. In this regard, HPLC analysis showed that the red product was a mixture containing four components, while the violet product contained only one component. Results from 1H NMR, HRMS, and single crystal X-ray diffraction analyses indicated that the principal components were dyes having a 1-amino-4-hydroxyanthraquinone base structure. The presence of an –OH group alpha to an anthraquinone C=O moiety provides for intramolecular H-bonding and a subsequent opportunity for intramolecular proton transfer in the excited state – as a photostabilizing mechanism. Further, for both dyes, results from the analysis of Frontier HOMO and LUMO isosurfaces indicated strong HOMO-LUMO overlap without molecular gaps and were consistent with strong excited state energy dissipation in a non-destructive way.

LnIII coordination compounds were synthesized with two benzimidazolic ligands, 2 pb = 2-(2-pyridyl)benzimidazole and 4tb = 2-(4-thiazolyl)benzimidazole, with Eu, Gd, Tb and Dy, namely: [Ln (NO3)3 (Ln)2]⋅S, where Ln = 2 pb, 4tb and S = solvent. They were characterized by IR, 1D and 2D 1H and 13C NMR, solid state UV–Vis–NIR absorption and emission and EPR spectroscopies, X-ray powder diffraction, elemental analyses, electrical conductivity and magnetic susceptibility. The compounds of EuIII with 2 pb and 4tb, TbIII and DyIII with 4tb showed luminescence at RT in the solid state; their emission life time ranged from 0.026 to 1.82 ms. 2 pb and 4tb sensitized lanthanides luminescence. Results of DFT theoretical calculations for the ligand (H2L) are used to assign the ligand singlet and triplet excited state energy levels. Additionally, a full analysis of the X-band EPR spectra in the solid state gave the following results, at 297 K for [Gd(NO3)3 (2 pb)2]·CH3COCH3, g = 1.990, |D| = 0.0687 cm−1, E = 0.0165 cm−1 and λ = |E/D| = 0.240; for [Gd(NO3)3 (4tb)2]⋅CH3COCH3, g = 2.000; |D| = 0.0670 cm−1, E = 0.000 cm−1 and λ = |E/D| = 0.000. At lower temperature, 128 K, compounds showed an increase of the rhombicity as the temperature decreased.

This work was part of an investigation aimed at characterizing the molecular and excited state properties of currently available disperse dyes developed to provide stability to extensive sunlight exposures when adsorbed on poly(ethylene terephthalate) (PET) fibers. Having completed the characterization of yellow, magenta, and cyan disperse dyes for PET-based fabrics used outdoors, our attention turned to the colors designed to enhance the color gamut of a standard 4-member (cyan/yellow/magenta/black) color set. The present study pertained specifically to the characterization of commercially available scarlet dyes. In this regard, HPLC analysis showed that a scarlet product used for PET coloration was mainly a 70/30 mixture of dyes, and the use of HRMS and single crystal X-ray diffraction analyses indicated that these two dyes were azo compounds derived from isomeric pyridine-based couplers which differed in the location of the primary amino ( NH2) and anilino ( NHPh) groups attached to the pyridine ring. One dye structure has the NHPh group para to the azo group (Sc2), while the other has that group in the ortho position (Sc3). The presence of either ortho substituent provides photostabilization through intramolecular H-bonding with the azo moiety. Further, results from molecular modeling studies showed that the lower excited state oxidation potential of Sc3 relative to that of Sc2 allows Sc3 to function as an energy quencher for the excited state of Sc2 – through thermodynamically favorable electron transfer.

Non- and dinitro 4-bromomethyl-7-methyl coumarins and new mono- and trinitro 4-bromomethyl-7-methyl coumarins have been synthesized. Effect of nitro groups on the photophysical properties of the parent 4-bromomethyl-7-methyl coumarin has been reported. Their ground and excited state dipole moments have been estimated by solvatochromic method using nine solvents. A reasonable agreement has been observed between calculated and observed dipole moments. Reduction in dipole moment has been observed for mono- and dinitro compounds where as the trinitro compound was found to have higher dipole moment in the excited state.

In the present work, the molecular structures of two new azomethine dyes: Download : Download high-res image (99KB) Download : Download full-size image have been predicted and investigated using Density Functional Theory (DFT) in dimethylformamide (DMF). The geometries of the azomethine dyes were optimized by B3LYP/6-31+G* level of theory. The electronic spectra of these azomethine dyes in a DMF solvent was carried out by using TD-B3LYP/6-31+G* method. After quantum-chemical calculations two new azomethine dyes for optoelectronic applications were synthesized. FT-IR spectra of the title compounds are recorded and discussed. The computed absorption spectral data of the azomethine dyes are in good agreement with the experimental data, thus allowing an assignment of the UV/Vis spectra. On the basis of polyvinyl alcohol (PVA) and the new synthesized azomethine dyes polarizing films for visible region of spectrum were developed. The main optical parameters of the polarizing PVA-films (Transmittance, Polarization Efficiency and Dichroic Ratio) have been measured and discussed. Anisotropy of thermal and electrical conductivity of the PVA-films have been studied and explained.

New hetero-stilbene derivatives, namely cis/trans-2/3/4-(2-vinylstyryl)pyridines, have been synthesized by Wittig reaction from the diphosphonium salt of α, α′-o-xylenedibromide, formaldehyde and 2/3/4-pyridinecarbaldehydes. The 2/3/4-(2-vinylstyryl)pyridines afforded, by photochemical intramolecular cycloaddition and cyclization reactions, diverse new polycyclic products with the pyridine ring integrated into the polycyclic skeletons. All of the new benzobicyclo[3.2.1]octadiene, benzobicyclo[2.1.1]hexene and vinyl- benzoquinoline products were identified and characterized by spectroscopic methods. Isomerized dihydro- intermediates *Revised Manuscript Click here to view linked References 2 (DHQs), that formed as a result of [1, n-H] shifts were also isolated, identified and characterized. DHQ intermediate isomers were never isolated in these conditions before.

Various concentrations of Er3+ (0.3, 0.5, 1.0 and 1.5 mol %) doped lithium fluoro zinc borate glasses were synthesized by a traditional melt quenching method. XRD, FTIR and FESEM have been employed to analyze the structural, compositional and morphological analysis respectively. Judd–Ofelt theory has been employed to analyze the intensity parameters (Ωλ, λ = 2, 4 and 6) which can be used to estimate the radiative properties of fluorescent levels of Er3+. We have been observed a strong NIR emission peak at 1.53 μm (4I13/2 → 4I15/2) under the excitation of 980 nm from Er3+: LBZ glasses. Nevertheless, the NIR emission is remarkably enhanced by increasing the Er3+ ions concentration until the optimized concentration of 0.5 mol%. The lifetime of the excited level of 4I13/2 in the NIR emission transition is evaluated and it is found to be1.22 ms from the decay analysis of 0.5 mol% Er3+: LBZ glass. Apart from the NIR emission, a bright up-conversion green emission is observed at 544 nm (4S3/2 → 4I15/2) along with an intense red emission at 659 nm (4F9/2 → 4I15/2) and a weak blue emission (2H9/2 → 4I15/2) under the excitation of 980 nm. Up-conversion emission features were significantly enhanced with increasing the Er3+ concentration up to 1.0 mol%. The combination of the obtained up-conversion emission colors of green, red and blue could generate white light emission. The cool white-light emission from the optimized glass sample has been confirmed from the Commission International de I'Echairage (CIE) 1931 chromaticity diagram analysis and their correlated color temperature (CCT) values. Based on the NIR and up-conversion emission features, Er3+: LBZ glasses could be suggested as promising candidates for optical amplifiers, optical telecommunication windows and white light photonic applications.

Terpyridines containing substituted o-iminophenolic groups were synthesized. The obtained compounds possess two emission bands: with normal (at 480–495 nm) and anomalous Stokes shifts (at 509–569 nm) generated by the fast intramolecular O→N proton transfer in the singlet excited state (ESIPT effect). They represent bifunctional chromogenic “naked-eye” chemosensors for Cu2+ and Ni2+ due to their complexation with o-hydroxyimine fragment (change of the solution color from colorless to bright yellow) and for Fe2+ - due to complexation with the terpyridine moiety (colorless to violet).

Two free base porphyrins, 5,10-bis(4-aminophenyl)-15,20-diphenylporphyrin ( cis -DATPP), 5,15-bis(4-aminophenyl)-10,20-diphenylporphyrin ( trans -DATPP), and their zinc metalated analogues ( cis -ZnDATPP and trans -ZnDATPP) were synthesized. A series of their corresponding polyimides were obtained by the condensed polymerization of the respective monomeric isomer DATPP with a 1:1 ratio of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB) and 4,4′-hexafluoroisopropylidenediphthalic anhydride (6FDA). The inclusion of PFMB and 6FDA into the polymeric backbone causes the polymers to be moderately to highly soluble in organic polar solvents. The molar content of the respective DATPP monomer varied between 5 and 30%. All compounds were structurally characterized by 1 H NMR and ATR-IR spectroscopy and the porphyrin content in the polyimides was determined by UV–Visible absorption spectroscopy. Photophysical properties consisted of measuring both the UV–Visible (ground state) absorption and fluorescence (excited state) spectra, fluorescence quantum yields (Φ f ), and fluorescence lifetimes (τ f ) in dichloromethane and N,N-dimethylacetamide. Fluorescence quenching was also measured and observed by the Stern-Volmer relationship, using 9,10-anthraquinone (AQ) as the quencher molecule. Both the bimolecular rate constant of fluorescence quenching (k q ) and the Stern-Volmer constant (K Q ) were calculated from this relationship. Furthermore, deviations from linearity depicted in the Stern-Volmer plots for TPP and ZnTPP at higher concentrations of AQ were also measured as a means of examining and explaining the simultaneous occurrence of dynamic (collisional) quenching and static quenching in the mechanisms of fluorescence quenching. It was found in this work that the significantly larger values in the static quenching constant (K S ) than in the dynamic quenching constant (K D ) are indicative that static quenching and ground state complex formation between the fluorophore and quencher is the dominant mechanism of fluorescence quenching of these systems at higher quencher concentrations.

In present work, Polarization, Excited States, FT-IR, 1 H, 13 C NMR, Trans–Cis ( E → Z ) Isomerization Properties and Anisotropy of Thermal and Electrical Conductivity of the three new Azomethines dyes such as: 4-((E)-((4-((E)-phenyldiazenyl)phenyl)imino)methyl)benzoic acid ( I ), 5-phenyl-N-(pyrimidin-2-yl)isoxazole-3-carboxamide ( II ) and (Z)-1-(4-((E)-((4-phenylcyclopenta-1,4-dien-1-yl)methylene)amino)phenyl)ethanone oxime ( III ) in the presence of polyvinyl alcohol (PVA) matrix were studied. The absorption spectrum of the I , II and III in dimethylformamide (DMF) solution was calculated. The nature of absorption peaks of the dyes in the UV/Vis spectral regions was interpreted. The molecular HOMO-LUMO, excitation energies and oscillator strengths for E and Z isomers of the I , II and III have also been calculated and presented. Optical Properties of the PVA-films containing these new synthesized dyes have investigated. Polarizing Efficiency (PE) of obtained PVA-film is 97–98% at Stretching Degree (R s ) 3.5. Anisotropy of thermal and electrical conductivity of the PVA-films containing the title compounds was also measured and discussed.

In this contribution, we report the synthesis of benzofuranyl-derived flavylium salts whose structure have been confirmed by mass spectrometry and by NMR. Their structural and electronic properties have been studied by absorption and fluorescence spectroscopies and DFT calculations. Theoretical structural parameters of the calculated compounds were validated by the experimentally obtained X-Ray structure of 2-(2-benzofuranyl)-7-hydroxy-1-benzopyrylium perchlorate. The absorption spectra of the benzofuranyl-derived flavylium salts were simulated with good accuracy with respect to the experimental data. In equilibrated buffered solutions, the pH-driven multi-state evolution reaction of novel benzofuranyl-flavyliums afforded trans-chalcone and chalconate derivatives as the predominant species. The elusive nature of the species formed in solution was corroborated by chemical quantum calculations. The fluorescence bands of the flavylium, trans-chalcone and chalconate forms were assigned to their fluorophoric units by selective excitation of each one of the species present in solution. Fluorescence spectroscopy strongly suggests that 2-(2-benzofuranyl)-7-hydroxy-1-benzopyrylium perchlorate displays excited state proton transfer (ESPT).

Vacuum ultraviolet photoabsorption spectra of pentane (C5H12) structural isomers (n-pentane and isopentane) are recorded in the 6–11.5 eV region using a synchrotron light source. The photoabsorption spectra for both the pentane isomers showed a continuum, beginning at about 7.5 eV and increasing in intensity up to 10.5 eV with few broad peaks devoid of discernible structures. Quantum chemical calculations using the DFT methodology predicted the optimized ground geometry and fundamental frequencies for neutral and cationic pentane isomers. The excited electronic state vertical energies are computed using time-dependent DFT and allied to construe the experimental spectra. From theory, the electronic spectra of pentane isomers encompass mostly valence-Rydberg mixed type transitions, converging to the first four ionization potentials while isopentane at 9.62 eV predicted a uni-molecular dissociation to C2H5• and C3H7• radicals. The plot of potential energy curves for the first few excited states facilitated understanding the spectral features UV region and its photodissociation mechanism for both pentanes. The broad continuum spectra in both isomers may be attributed to strong valence - Rydberg interactions along with a contribution from the presence of conformers, low torsional modes and Rydberg series converging to close-lying ionization potentials. Gas phase infrared spectra of pentane isomers in the 500–4000 cm−1 region were revisited and DFT calculations clarified few vibrational assignments. The present study provides a comprehensive understanding of the absorption spectra in the VUV and IR regions of n-pentane and isopentane.

6-Aminouracils have extensively been used as precursors for synthesizing numerous uracil derivatives of biological and pharmaceutical significance. This study describes an application of 1,3-dimethyl-5-(arylazo)-6-aminouracils (Uazo: Uazo1-Uazo4, precursors) for an efficient synthesis of a series of 8-substituted-azapurins (AP), namely 1,3-dimethyl-8-(aryl)-azapurin-2,6-diones (aryl = p-HC6H4 (AP1), -MeC6H4 (AP2), ClC6H4 (AP3), and SO2NH2C6H4 (AP4)) following an oxidation method in the presence of copper (II) nitrate and in alkaline medium. The obtained compounds were isolated in good yields as crystalline air-stable products and have been fully characterized in the solution by UV–vis and NMR spectroscopy, as well as in the solid state by FT-IR spectroscopy, elemental analysis, and single-crystal X-ray diffraction (for AP2 and AP4). UV–vis study evidences that the conversion of the 6-aminouracil precursors occurs via an intermediate, Cu(II)-complex and a plausible mechanism for the formation of AP1-AP4 has been proposed. Unlike AP2 the crystal structure of AP4 reveals the formation of interdigitated 1D H-bonded chains that has been topologically classified within the 2C1 type. The 1H NMR spectra of the products have proton signals that completely devoid of hydrazone ( NH ) and imine (=NH) signals of their parent Uazo derivatives, thus confirming their full conversion and a stability of the AP1-AP4 in solution. The excitation and emission spectra of AP1-AP4 were also recorded in solution, revealing electronic transitions between similar vibrational energy levels of S0 (singlet ground state) and S1 (singlet first excited state).

Intra-molecularly hydrogen bonded compound 2-(1,4-dioxo-1,4-dihydronaphthalen-2-yl-amino)benzoic acid (ANQ) shows emission at single wavelength upon excitation in UV-region whereas it shows dual fluorescence emissions on excitation in visible region. Such emissions depend on solvent, concentration and pH. Solvent dependent structural changes of ANQ are reflected in solution studies carried out by 1 HNMR, UV–visible and fluorescence spectroscopy. DLS study has showed that in addition to monomers, self-assemblies with 415 nm average sized particles are formed in DMF solution. HOMO-LUMO of three tautomeric forms of the compound was calculated by DFT using CAMB3LYP/6-31 + G(d,p) as basis set shows that naphthoquinone form has about 86.30 kJ/mol higher stability over an imino-quinone form. From various studies relating concentration dependence, pH, life-time, study on dual-emissions caused by visible excitation has established the observed emissions to originate from aggregation contributing as charge-transfer and deprotonated species. Whereas the single emission caused by UV-excitation occurs through excited state intra-molecular proton transfer.

In the present work, the quantum theoretical calculations of the molecular structures of the four new synthesized azomethine dyes such as: 1. ( E )- N -(4-butoxybenzylidene)-4-(( E )-phenyldiazenyl)aniline (PAZB-6), 2. ( E )- N -(4-(benzyloxy)benzylidene)-4-(( E ))-phenyldiazenyl)aniline (PAZB-7), 3. 4-(( E )-4-(( E )-phenyldiazenyl)phenyl)imino)methyl)phenol (PAZB-8), 4. ( E )- N -(4-methoxybenzylidene)-4-(( E ))-phenyldiazenyl)aniline (PAZB-9) have been predicted using Density Functional Theory in the solvent Dimethylformamide. The geometries of the azomethine dyes were optimized by PBE1PBE/6-31+G* level of theory. The electronic spectra of the title compounds in the solvent DMF was carried out by TDPBE1PBE/6-31+G* method. FT-IR spectra of the title compounds are recorded and discussed. Frontier molecular orbitals, molecular electrostatic potential, electronic properties, natural charges and Natural Bond Orbital (NBO) analysis of the mentioned compounds were investigated and discussed by theoretical calculations. The azomethine dyes were synthesized after quantum chemical modeling for optical applications. A new study of anisotropy of thermal and electrical conductivity of the colored stretched PVA-films have been undertaken.

The UV–vis absorption and steady state fluorescence spectra of phenyl salicylate (abbreviated as PS) have been recorded in a series of non-polar, polar protic and polar aprotic solvents at room temperature and the obtained spectral data are used to determine the solvatochromic behavior and the ground and excited state dipole moments. Basis set sensitive molecular structure along with X-ray crystal data are evaluated. The ground state and excited state dipole moments are determined by using Lippert-Mataga, Bakhshiev, Bilot-Kawski and Reichardt solvatochromic shift methods as a function of dielectric constant ( e ) and refractive index ( n ) of the solvents. The larger excited state dipole moment value indicates the more polar PS in the excited state. The rate of μ e / μ g is found as 2.4239. Solvatochromic behavior of PS is enlightened by using Kamlet-Taft and Catalan models. Kamlet-Taft solvatochromic model indicates that non-specific solute solvent interactions are controlled by solvent dispersion-induction forces and specific interactions are directed by hydrogen-bond donor capacity of solvent. Catalan solvatochromic model designates that solute-solvent interactions are governed by solvent polarizability. Ground and excited state dipole moments are found theoretically by using DFT/B3LYP/6–311++G(d, p) and TDDFT/B3LYP/6–31++G(d, p) methods. External electric field effect on LUMO-HOMO band gap and dipole moment have been investigated by using B3LYP/6–311++G(d, p) method.

The reaction of 1-isocyanatonaphthalene with hydrazine hydrate in presence of acetone resulted in the formation of napthyl based semicarbazone (1). The compound has been characterized using UV–Visible, FT-IR, NMR, mass spectroscopic and single crystal X-ray diffraction (XRD) tools. The interaction between 1 and fluoride ion has been investigated by means of UV–Visible and fluorescence spectra. The fluoride ion sensing mechanism of 1 has been studied by hybrid density functional theory (DFT) and time dependent DFT (TD-DFT) methods. The added fluoride ion formed intermolecular hydrogen bonds with the protons of N1 H1 and N2 H2 groups of 1 in the ground state. The N1 H1 proton which is closer to naphthalene moiety prefers to bind fluoride anion in the excited state after deprotonation, which lead to excited state proton transfer (ESPT). The fluoride ion sensing process shows a moderate (31.99 kcal/mol) Gibbs free energy. To understand the dynamic features, the transition state (TS) calculation is performed and the change in entropy is found to be −0.6259 kJ/mol, which shows that the sensing process is thermodynamically allowed.

In this present work, first time interaction between new synthesized derivative of the 4-((E)-((4-((E)-phenyldiazenyl)phenyl)imino)methyl)benzoic acid (E-PABA) and the BN(6,6-7) Nanotube for medical applications were studied. The geometries of the compounds E-PABA, the BN(6,6-7) Nanotube and the Complex BN(6,6-7)/E-PABA were optimized by Density Functional Theory (DFT) in the gas phase. The adsorption effect of the compound E-PABA on the electronic properties, chemical shift tensors and natural charge of the BN(6,6-7) Nanotube was investigated and discussed. The electronic spectra of the E-PABA and the Complex BN(6,6-7)/E-PABA in the gas phase carried out by Time Dependent Density Functional Theory (TD-DFT) for the foundation adsorption effect on maximum wavelength of the E-PABA.

The molecules based on the excited state intramolecular proton transfer (ESIPT) process are widely used in the fluorescent probes, organic light-emitting diodes and other fields due to their unique optical properties. However, the relationship between the structures and optical properties of ESIPT-based molecules still needs to be further explored. Herein, the effects of different functional groups embedded with the benzene ring on the ESIPT properties and electronic spectra of 2-(1H-Benzimidazol-2-yl)phenol (HBYP)-based derivatives (DPYP, HAYP and HIYP) were explored by using the density functional theory and time-dependent density functional theory methods. Utilizing theoretical calculations, the geometric parameters, including bond lengths and bond angles, infrared vibration spectra, frontier molecular orbitals, potential energy curves as well as topological analysis of the bond critical point of the molecules in the ground and excited states were acquired. The results manifest that the ESIPT process is facile to occur for HBYP and its three derivatives upon the photo-excitation, which can be confirmed by comparing the crucial geometric parameters, IR stretching vibration peaks and energy barriers between the S0 and S1 states. It is worth noting that the molecule HAYP exhibits the largest proton transfer barrier at the S1 state among the studied molecules, and the fluorescence peaks corresponding to its enol and keto forms show the most obvious Stokes shifts of 260 nm and 284 nm, respectively. Therefore, we can deduce that the fluorescence properties can be further affected by regulating the ESIPT characteristics of molecules via the functional group substitution.

New near-infrared broad-band emission with λmax~920 nm was detected in 2,5-bis(2′-benzoxazolyl)hydroquinone (BBHQ), a molecule known to undergo the single proton transfer in the ESIPT reaction and to emit the fluorescence with λmax ~600 nm. The new emission was attributed to the fluorescence of the product of double proton transfer in the excited BBHQ. The attribution was based on the qualitative agreement verifying the theoretical predictions and on the behaviour of the two properly chosen derivatives: the diethyl-BBHQ independently showing the same broad-band IR fluorescence, and the monomethoxy-BBHQ, a “negative witness”- a structure with one of two ESIPT reactivity sites eliminated, showing no trace of the new emission.

Aggregation behavior of push-pull salen-type schiff base (BIHyDE) in different solvents at ground and excited state, has been investigated. At ground state, lower energy absorption band is suppressed during concentration dependent UV-Vis study in CHCl3 solution. The broadening of lower energy emission band is observed during concentration dependent fluorescent study in CHCl3 solution. Interestingly, fluorescence life time of BIHyDE in solution is also altered during concentration dependent fluorescence study in CHCl3 solvent. Similar aggregation is also observed at ground and excited state in ACN solvent. Dipolar state and intermolecular dipolar interaction of BIHyDE molecule highly influence towards strong aggregation process and orientation of molecule in solution. Ground state and excited state optical properties are highly influenced by concentration of push-pull salen-type schiff base (BIHyDE) in different solvents.

The inter- and intramolecular interactions of benzo[h]quinoline and 10-hydroxybenzo[h]quinoline have been studied using quantum-chemical methods. Here, we report on results of monomeric and dimeric forms obtained on the basis of Density Functional Theory (DFT) in its classical formulation as well as using its Time-Dependent extension (TD-DFT). The simulations were performed in the gas phase and with solvent reaction field using toluene and acetonitrile as solvents. Symmetry-Adapted Perturbation Theory (SAPT) and Atoms in Molecules (AIM) were employed to characterize interactions and forces present in the studied compounds with special attention paid to the presence of inter- and intramolecular hydrogen bonds. It was found that spontaneous proton transfer phenomenon was not preferable in the electronic ground state. However it was noticed in the excited electronic state. The presence of the polar environment lowers the energy profile of the proton reaction path and slightly influences the electronic structure and aromaticity of the compounds. The results of the SAPT analysis showed that the O-H... N intermolecular hydrogen bond in the dimer 1 is only ca. twice stronger than the C-H... O and C-H... π contact present in the dimers formed by 10-hydroxybenzo[h]quinoline.

Two Schiff base ligands (2a and 2b) and their zinc complexes (3a and 3b) have been designed and facilely synthesized through simple condensation reactions using compound 1 derived from natural dehydroabietic acid as the precursor. The larger dihedral angles of the ligands shown by the single crystal X-ray diffraction analysis indicate their stronger molecular motion, which is in consistence with their low fluorescence efficiency that is verified by the photophysical measurements. After coordination with zinc ions, the fluorescence intensity of the zinc complexes is larger, which might be explained by the structural rigidification via coordination, thereby reducing the energy loss from molecular motion. Furthermore, complex 3b exhibits a specific negative solvatochromic effect, and the absorption of its maximum wavelength shows a hypsochromic shift with increased polarity. Such solvatochromic phenomena can be explained by the synergy of intramolecular charge transfer and the proximity effect that may increase the energy difference between the ground state and the excited state in polar solvents. This work not only discusses their relationship between photophysical properties and structures, but also provides a new natural source for further research in fluorescent materials.

The FT-Raman and FT-IR spectra of N -(adamantan-1-yl)-1,2,3,4-tetrahydroisoquinoline-2-carbothioamide were recorded and investigated. The DFT/M06-2X/6-311++G(d,p) method was used to compute the vibrational wavenumbers. The effect of solvents (water, carbon tetrachloride and chloroform) on the dipole moment and polarizability has been evaluated. UV–Vis spectrum of the title compound was recorded and compared with the theoretical spectrum calculated by TD-DFT approach. To investigate the movement of electrons within the system when excited, the difference of the excited and ground state densities has also been plotted. The molecular docking studies reveals that the investigated compound may exhibit HIV-1 Protease inhibitory activity.

We present fluorescence emission spectra of the 2-tolunitrile dimer and the 2-tolunitrile water cluster through various vibronic bands in the electronically excited state. From the transition dipole moments in the individual monomers, the 2-TN dimer has shown to form J-aggregates, which is why the one-photon allowed transition is the S1 state in this cluster in contrast to other symmetric dimers, which tend to form H-aggregates. The changes of the molecular structures upon electronic excitation have been determined from a fit of the intensities in various fluorescence emission spectra. The excited state structure of the 2-TN dimer has been found to be asymmetric, in contrast to the ground state structure. Thus, emission takes place from one of the locally excited monomer moieties in the 2-tolunitrile dimer.

In the present work, Polarization, Excited States, Trans–Cis ( E → Z ) Isomerization Properties and Anisotropy of Thermal and Electrical Conductivity of the 4-(phenyldiazenyl)aniline in the presence of polyvinyl alcohol (PVA) matrix were studied. DFT, UV/Vis, IR-Spectroscopies and Indicator Method were used for Determination of Thermal Conductivity of polymer films. The absorption spectra of the 4-(phenyldiazenyl)aniline in dimethylformamide (DMF) solvent and in aqueous medium were calculated. The nature of absorption peaks of the 4-(phenyldiazenyl)aniline in the UV/Vis spectral regions were interpreted. The solvent effect on the absorption spectrum of the 4-(phenyldiazenyl)aniline has established. The molecular HOMO-LUMO, excitation energies and oscillator strengths for E and Z isomers of the 4-(phenyldiazenyl)aniline have also been calculated and presented. Optical Properties of the PVA-films containing 4-(phenyldiazenyl)aniline have been also investigated. Polarizing Efficiency (PE) of obtained PVA-film is 98–99% at Stretching Degree (R s ) 3.5. Anisotropy of thermal and electrical conductivity of PVA-films containing E and Z isomers of the 4-(phenyldiazenyl)aniline was also measured and discussed.

Electronic absorption and fluorescence spectra of two Rhodamine dyes (Rhodamine B and Rhodamine 6G) in binary solutions are studied in this paper. The excited state dipole moments have been computed using the correlation coefficients obtained by linear solvation energy relationship (LSER) applied to electronic spectra and the values of the dipole moments in the ground state of Rhodamines computed by HyperChem 8.0.6. The nature and the contributions of each type of interactions to the spectral shifts from visible range are established based on solvatochromic analysis.

Employing chiral bis-bidentate N-donor ligand, (+)-2,5-bis(4,5-pinene-2-pyridyl) pyrazine (L), as a bridging ligand for Er(dbm) 3 H 2 O, and depending on the ratio control of reactants, two mono- and dinuclear homochiral Er III complexes with the formulae Er(dbm) 3 L·2H 2 O ( 1 ) (dbm ─ = dibenzoylmethanate) and Er 2 (dbm) 6 L·6H 2 O ( 2 ) have been synthesized and structurally characterized. Circular dichroic (CD) spectra verify their chiroptical activities. Investigations on the luminescent properties of complexes 1 and 2 demonstrate that they exhibit characteristic near-infrared (NIR) luminescence of the Er III ion at around 1533 nm and the emission intensity of the mononuclear complex 1 is much larger than that of dinuclear species 2 , the reason of which is elucidated in this work. In addition, the measurements of magnetic properties indicate that the direct-current (dc) magnetic behaviors of complexes 1 and 2 mainly result from the thermal depopulation of the excited M J sublevels of the Er III ions. Notablely, complex 2 is the first example of chiral polynuclear lanthanide complexes with NIR-luminescence property.

The optimization of geometrical parameters and calculation of the force fields of trans -acrolein (CH 2 CHCHO) in the ground S 0 and lowest excited triplet (T 1 ) and singlet (S 1 ) electronic states are performed at the CASPT2/def2-TZVPP theoretical level. Co-assignments of the vibrational frequencies calculated from the corresponding force fields are validated by calculations of the analogs of the Duschinsky matrix for the pairs of the (S 0 , T 1 ) and (S 0 , S 1 ) electronic states. The results obtained by comparing the vibrational frequencies calculated from the scaled force fields with the experimental vibrational frequencies made it possible to corroborate some details of the molecular structure in these electronic states.

In the present work, intermolecular interactions between triphenylphosphine oxide (TPPO) and benzamide (BZM) has been studied in solid state by Positron Annihilation Lifetime Spectroscopy (PALS) and supported by several analytical techniques (in solid state and in solution) and by computational modeling (in gaseous phase). Isothermal Titration Calorimetry (ITC) in ethyl acetate solvent showed that complexation is a stepwise process, with 2:1 and 1:1 TPPO/BZM stoichiometries, both driven by entropy. HPLC analysis of isolated single crystal confirmed the existence of a 2:1 TPPO/BZM crystalline complex in solid state. The results of thermal analysis (TGA, DTA and DSC) and FTIR spectroscopy showed that the interactions in the complexes are relatively weaker than those found in pure precursors. Finally, PALS showed higher positronium formation probability ( I 3 ) at [TPPO 0.62 ·BZM 0.38 ] and [TPPO 0.25 ·BZM 0.75 ] molar fractions, corroborating the existence of two stoichiometries for the TPPO/BZM system and suggesting greater electronic availability of n - and π -electrons in heterosynton complexes, as resulting of interactions, bring forward new evidences of the participation of electronic excited states on the positronium formation mechanism.

In the present communication, quantitative interpretation and assignments of the electronic absorption spectra, vibrational and one- and two-dimensional NMR spectra of alloxan, are detailed. A synergic analysis based on DFT and TD-DFT calculations and the experimental findings are performed. Attempt is made to relate these spectral findings to the electronic structure of alloxan. The computed electronic spectrum predicted three well defined bands. Natural transition orbital analysis indicate an intramolecular charge transfer from npπ orbital of the water oxygen atom resulting in the short wavelength nπ* at ∼200 nm. Furthermore, UV-photoabsorption cross section for alloxan and its monohydrate are simulated. The spectrum, composed of 10 excited states, was simulated with the nuclear ensemble approximation, sampling a Wigner distribution with 300 points. The FT-IR spectrum of alloxan, measured in the solid state as KBr pellets is reported and is computed at the DFT/B3LYP/6-311++G** level of theory. All observed vibrations are assigned. The 600 MHz one- and two-dimensional COSY, 1H NMR spectra of alloxan, measured in DMSO, are reported and analyzed and computed theoretically using the GIAO method. Hydrogen-bond interactions are responsible for remarkable downfield shift of 1H NMR peaks for alloxan.

A combined theoretical and experimental study was performed in order to clarify the mechanisms of phototransformations of a quinaldic acid solution in acetonitrile when exposed to UV radiation. The theoretical calculations were performed at the BLYP/aug-cc-pVDZ level. It was established that the most stable isomer of the compound in the solution is the one with an intramolecular H-bond between the H atom from the carboxylic group and the N atom from the quinoline ring. The major photoprocess is the breaking of the intramolecular H-bond, i.e. the rotation around the C OH bond of the carboxylic group through the specroscopically active 1 ππ* excited state. Rietveld method was applied to refine the crystal structure of the compound. The refinement lead to the following unit cell parameters: a = 9.76754 A, b = 6.02724 A, c = 28.11714 A, β = 90.495°; and a space Group of P 2/c (Z = 4). The cell volume is 1655.23 A 3 .

The fluorescence quenching of fluorenone in protic solvent has been extensively investigated, and the intermolecular hydrogen bond was found to play a crucial role. Unfortunately, the mechanism at atomic level is still not clear. In the present work, we theoretically put forward the charge transfer along the hydrogen bond in the excited states. The vertical excitation energies of the fluorenone-methanol complex as well as the potential energy profiles and surfaces of the vertical excited states and charge transfer states were calculated by using the ab initio electronic-structure methods. The photochemical reactions occurring in the diverse charge transfer states were compared and their decisiveness to the fluorescence quenching was discussed in the paper.

Syntheses of 5-nitro-2-(2-phenylhydrazinyl)pyridine (5-nitro-2-phenylhydrazopyridine), 3-methyl-5-nitro-2-(2-phenylhydrazinyl)pyridine (3-methyl-5-nitro-2-phenylhydrazopyridine), 4-methyl-5-nitro-2-(2-phenylhydrazinyl)pyridine (4-methyl-5-nitro-2-phenylhydrazopyridine) and 6-methyl-5-nitro-2-(2-phenylhydrazinyl)pyridine (6-methyl-5-nitro-2-phenylhydrazo-pyridine) have been described. Electronic absorption and emission spectra of the compounds in the solid state and in various solvents have been measured at room temperature and discussed in terms of DFT quantum chemical calculations. The molecular structures and energy sequences of the singlet and triplet states have been determined in the B3LYP/6-311G(2d,2p) approximations. The Mulliken analysis and non-bonding orbital approach have been used in characterization of the studied compounds. It has been shown that the HOMO-LUMO transition of the studied compounds is observed in the range 23,900 ÷ 29,300 cm −1 and in this excitation the π-electrons of phenyl ring are transferred to nitro group of pyridine ring. In such a transition the hydrazo-bridge should take part as a mediator. The luminescence of the studied hydrazo-compounds is weak, not measureable in the solid state but measureable in solution.