Absorption Spectroscopic Properties Research Articles

Synthesis, spectroscopic, and lead(II) binding behavior of three novel dibenzo-18-crown-6 hydrazones

Three novel hydrazonic derivatives of dibenzo-18-crown-6 were synthesized and their vibrational and electronic absorption spectroscopic properties thoroughly investigated. Their lead binding behaviors were also characterized and the observations rationalized by density functional theoretical modeling. All three cis-dihydrazonic compounds are of low overall molecular symmetry with their ether cavity adopting an open configuration at the global energy minima where the hydrazonic side-arms are electronically and vibrationally nonequivalent. Their optical absorption features are dominated by π → π * transitions where one side of the molecule exhibits Lewis acid behavior whereas the other behaves like a Lewis base. In addition to their sensitivity to pH, all three derivatives form stable 2:1 metal-ligand complexes with lead, due to coordination at the ether cavity, in addition to the hydrazone “backbone” and possibly the heterocyclic ring. The most stable lead complex is formed with the thiophene carboxylic acid hydrazide derivative due to favorable soft-soft interactions between lead and the ring-based sulfur atom.

SYNTHESIS AND PHOTOCHEMICAL PROPERTIES OF NOVEL AZOQUINOLINE CONTAINING POLYMERS

The development of modern technologies are constantly requires seeking new low-cost, efficient materials and establish new technical methods for application these materials. Synthesis of polymers with predicted and expected properties on the one hand and using specific features of interaction light with photoactive fragments in polymers, on the other hand, opens new prospects of application for new materials based on these polymers. The side chain methacrylic polymers with different active functional group have been well studied and widely applied in many fields, such as optoelectronics, nonlinear optics, optical storage materials, biochemicals, and medicine.
 The present work focused on synthesis new azostyrylcontaining methacrylic monomers and copolymers with methylmetacrylate (MMA) based on these monomers. The pre­sent study is a first reported notice of the synthesis and photochemical properties of methacrylic polymers with 6-azo-phenylquinoline frag­ments in side chain. Moreover in this work the features of syntheses have been described in detail for monomers and polymers based on new azocompounds. Absorption spectroscopic properties for new quinoline polymers with azo fragment were investigated with UV-Vi­sible spectrophotometry in THF solutions. All studi­ed polymers show a strong absorption band in the range of 300–375 nm resulting from π-π* electronic transition and a weak absorption band in the range of 400–490 nm assigned to n-π* transitions. Electron donating and electron withdrawing substituents at quinoline moity of azo-quinoline polymer solutions lead to bathochromic shift of the π-π*absorption band which agrees well with the result of work. We found that this red-shift increases with an increase of electron donating strength of the substituent as well as with an increase of electron withdrawing strength of the substituent. Based on of the result achieved we can suppose that irradiation of polymers with azo fragment lead to photoinduced trans-cis-isomerization.
 From the obtained and presented results one can conclude that novel quinoline polymers with azo fragment can be considered as promising materials for applications requiring photosensitivity in certain of range of wavelength.

Substitution Effect on Self-Assembly and the Resulting Fluorescence Efficiency of Triangular Azo Chromophores

To investigate the effect of substituents and substitution positions on absorption and fluorescence spectroscopic properties, and self-assembled structures, we designed triangular azo chromophores (1-3) in which three azo groups are connected to a central ring. 1 and 2 where electron-donating methoxy (MeO) groups are attached to para and meta positions, respectively, had different melting temperatures and colors. A dilute para-MeO (1) solution was redder than 3 with electron-withdrawing bromo (Br) groups and liquefied at lower temperatures. The elongated structure formed as a result of the one-dimensional (1D) assembly of 1 showed little fluorescence, whereas the chopstick-shaped structure and the entangled fiber assembled from 2 and 3, respectively, were brightly red fluorescent. Our investigation suggest that the molecular geometry and steric effects play important roles in self-assembly and the resulting fluorescence characteristics.

Adsorption behaviors and emission properties of p-sulfonatocalixarene/ammonium-based surfactant systems: A comparison between the effects of gemini surfactant and its corresponding monomeric surfactant

So far, the research on calixarene/surfactant systems has been mainly focused on their aggregation characteristics due to their potential applications as stimuli-responsive systems, while the reports about their absorption behavior and spectroscopic properties have been limited. Understanding basic properties of supra-amphiphilic molecules is of great significance to improve their application performance and expand their application potential. In the present study, the interactions of p-sulfonatocalix[n]arenes (SC[n], n = 4, 6 and 8) with the cationic surfactants (including dodecyltrimethyl ammonium bromide (DTAB), pentamethylene-1,5-bis (dimethyldodecyl ammonium bromide) (12-5-12), and octamethylene-1,8-bis(dimethyldodecyl ammonium bromide (12-8-12)) were studied by measuring surface tension, fluorescence spectra and 1H NMR spectra. It was found that SC[n] changed the absorption behaviors of 12-s-12 (s = 5 and 8) and DTAB at air/water surface in different ways. In the presence of SC[n], the value of γ for 12-s-12 remains almost constant until 12-s-12 content reaches C1, then decreases sharply until C2, followed by a slow decrease up to the CMC. The surface tension of DTAB/SC[n] solution begins to decrease at a very low concentration of DTAB until Ca, followed by a short plateau until Cb, and then, the surface tension increases sharply until Cc, after which, the surface tension curve gradually overlaps with that of single DTAB solution. Meanwhile, the binding of SC[n] with these surfactants makes SC[n] emit fluorescence, and the quantum yields for SC[n]/12-s-12 systems are higher than those for SC[n]/DTAB systems. Supra-amphiphiles have been expected as smart materials. This study may provide meaningful information for application of calixarene-based supra-amphiphiles.

Versatile Para-Substituted Pyridine Lanthanide Coordination Complexes Allow Late Stage Tailoring of Complex Function.

A series of cationic and neutral p-Br and p-NO2 pyridine substituted Eu(III) and Gd(III) coordination complexes serve as versatile synthetic intermediates. Nucleophilic aromatic substitution occurs readily at the para position under mild conditions, allowing C-N and C-C bond forming reactions to take place, permitting the introduction of azide, amino and alkynyl substituents. For Eu(III) complexes, this approach allows late stage tuning of absorption and emission spectral properties, exemplified by the lowering of the energy of an LMCT transition accompanied by a reduction in the Eu-Npy bond length. Additionally, these complexes provide direct access to the corresponding Eu(II) analogues. With the Gd(III) series, the nature of the p-substituent does not significantly change the EPR properties (linewidth, relaxation times), as required for their development as EPR spin probes that can be readily conjugated to biomolecules under mild conditions.

Sellmeier dispersion and spectroscopic properties of Er3+-doped lutetium gallium garnet single crystal

The authors report growth, refractive index dispersion, optical absorption and Judd-Ofelt spectroscopic properties of Er3+-doped lutetium gallium garnet (Lu3Ga5O12) single-crystal. The crystal was grown by Czochralski technique. The density of the crystal was measured by Archimedes method. Er3+ concentration in the crystal was measured by inductively coupled plasma atomic emission spectroscopy. The measurement results allow to reach that Er3+ ion in the crystal has a desired segregation coefficient ∼1.0. Refractive index of the crystal was measured as a function of wavelength in the range of 245–1553 nm using an ellipsometer and a prism coupler, and a Sellmeier equation is established for the crystal. Optical absorption of Er3+ in the crystal was studied in the wavelength range of 300–1700 nm and Er3+ absorption cross section spectrum was obtained. Based on the absorption cross section spectrum and the Sellmeier equation, Judd-Ofelt analysis was done for the crystal. Visible, near-infrared and mid-infrared fluorescence spectra and lifetimes of Er3+ in the crystal were measured, and emission characteristics are demonstrated. Spectroscopic knowledge of peaking absorption cross section, oscillator strength, Judd-Ofelt intensity parameters, radiative rate, fluorescence branch ratio, radiative and fluorescence lifetime, and quantum efficiency of some typical Er3+ emissions is obtained.

A Chemodosimetric Approach for Fluorimetric Detection of Hg2+ Ions by Trinuclear Zn(II)/Cd(II) Schiff Base Complex: First Case of Intermediate Trapping in a Chemodosimetric Approach.

The present work discloses the application of two fluorescent zinc and cadmium complexes (1 and 2) for sensing of Hg(II) ions through a chemodosimetric approach. The ligand under consideration in this work is a N2O donor Schiff base ligand (E)-4-bromo-2-(((2-morpholinoethyl)imino)methyl)phenol (HL), which has been harnessed to generate complexes [Zn3L2(OAc)4] (1) and [Cd3L2(OAc)4] (2). X-ray single crystal diffraction studies unveil the trinuclear skeleton of complexes 1 and 2. Both complexes have been found to be highly fluorescent in nature. However, the quantum efficiency of Zn(II) complex (1) dominates over the Cd(II) analogue (2). The absorption and emission spectroscopic properties of the complexes have been investigated by density functional theory. Complexes 1 and 2 can detect Hg2+ ions selectively by fluorescence quenching, and it is noteworthy to mention that the mechanism of sensing is unique as well as interesting. In the presence of Hg2+ ions, complexes 1 and 2 are transformed to mononuclear mercuric intermediate complex (3) and finally to a trinuclear mercuric complex (4) by hydrolysis. We have successfully trapped the intermediate complex 3, and we characterized it with the aid of X-ray crystallography. Transformation of complexes 1 and 2 to intermediate complex 3 and finally to 4 has been established by UV-vis spectroscopy, fluorescence spectroscopy, ESI-MS spectroscopy, 1H NMR spectroscopy, and X-ray crystallography. The spontaneity of the above conversion is well supported by thermodynamic aspects as reflected from density functional theoretical calculations.

Effect of Nd2O3 and Na2O concentration on physical and spectroscopic properties of TeO2–Bi2O3–ZnO–Na2O–Nd2O3 glasses

Two series of tellurite glasses with molar compositions of (55TeO2–2Bi2O3–(41-x) ZnO–2Na2O–xNd2O3 (x = 0.5, 1.0, 1.5, 2.0 and 2.5) and 55TeO2–2Bi2O3–(41-x) ZnO-xNa2O-2Nd2O3 (x = 1.0, 2.0, 3.0, 4.0, 5.0) were fabricated using melt quenching technique. Based on the measured densities, refractive indices and absorption spectra, physical and spectroscopic properties of these two-glass series are evaluated and compared. Whereas substitution of ZnO by Nd2O3 causes the values of density and refractive index increase, the substitution of ZnO by Na2O has been shown to impact the glass density and refractive index in the opposite manner. Molar volume of both series increases with an increase of either Nd2O3 or Na2O concentrations. In this regard, a dynamical model explaining the density and molar volume was proposed. Additionally, Judd-Ofelt theory was applied in order to predict the physical and laser properties of the two glasses series as a function of glass compositions, i.e., Judd-Ofelt parameters Ωt (t = 2, 4, 6), branching ratios (β), calculated lifetimes (τ), the emission to exited state absorption intensity ratio (Aem/AESA) and spectroscopic quality χ = Ω4/Ω6. Equations to relate χ with branching ratios for laser transitions 4F3/2 to 4IJ’ (with J′ = 9/2, 11/2, 13/2 and 15/2) were also derived.

Experimental (X-ray Diffraction, UV–Vis Spectroscopy) and DFT Studies of 1-Ethyl-3-methylquinoxaline-2-thione

In this paper, we present the experimental and theoretical investigation of 1-ethyl-3-methylquinoxaline-2-thione, molecule exhibiting an important biological activity. We used X-ray diffraction, UV-visible absorption spectroscopy and DFT calculations with 6-31G(d,p) basis sets. According to the results, the compound crystallizes in the monoclinic system, P21/c with eight molecules per unit cell (Z = 8, Z ' = 2) and with the lattice parameters (a = 7.7882(8) A, b = 15.964(2) A, c = 16.519(2) A, α = 90°, β = 94.413(11)°, γ = 90°), in which the two fused-rings adopt a planar geometry, and assumes a dihedral angle with the ethyl group, presenting the most stable conformation. UV–Vis absorption spectroscopic properties of 1-ethyl-3-methylquinoxaline-2-thione showed a redshift when the solvent polarity increases from ethanol to DMSO. Detailed analysis of intra and intermolecular interactions as such H-bonding, π–π stacking, electronic transitions, HOMO–LUMO patterns, molecular electrostatic potential maps and Mulliken charges distribution was carried out in order to investigate charge transfer within the molecule for the needs of biomedical applications.

Fluorescence analysis of natural dyes from Plumeria rubra (red and white) flowers

Eco-friendly aqueous dye is extracted from the flowers of Plumeria rubra (red and white). Absorption, luminescence and fluorescence spectroscopic properties of the extracted dyes are analyzed by respective spectroscopic techniques. Fluorescence quantum yields, Stoke’s shift, fluorescence life time, radiative and non-radiative rate constants are discussed with various excitation wavelengths in the range of 200–420 nm. Hence, a suitable excitation wavelength of the extracted dye is found to be in the range of 300–370 nm and the dye shows strong fluorescence in this range. Radiative and non-radiative rate constants and fluorescence life time results elucidate the effective fluorescence properties of the extracted dyes. It can be used as a potentially durable natural dye for fluorescence related applications.

The pH Dependent Protein Structure Transitions and Related Spin-State Transition of Cytochrome c′ from Alcaligenes xylosoxidans NCIMB 11015

Abstract The unusual magnetic/spectroscopic properties of Cytochrome c′ (Cyt c′) have been discussed, especially concerning the possibility of a quantum mechanically mixed-spin configuration of heme Fe(III). Here, four unique-spin species were identified from the magnetic circular dichroism (MCD) spectra of Cyt c′ from Alcaligenes xylosoxidans (AxCyt c′). The electrospray ionization mass spectrometric (ESI-MS) and circular dichroism (CD) spectroscopic data showed the overall conformation of AxCyt c′ was unchanged, in complete contrast to the drastic changes in the heme MCD spectra over the range of pH 3.5 and 11.8. The pH dependency of ESI-MS, electronic absorption, MCD, and CD spectroscopic properties of AxCyt c′ enabled us to reveal the undiscovered correlation between the protein-folding state and the electronic structure of the active site as a function of pH. The mechanism of alkaline spin-state transition through the rearrangement of the hydrogen-bonding linkage between Helix C and D is also proposed on the basis of atomic resolution crystal structure analyses (A. Takashina, M. Unno, T. Kohzuma, Chem. Lett. 2015, 44, 268).

Optical absorption and fluorescence properties of trivalent lanthanide chlorides in high temperature molten LiCl–KCl eutectic

The absorption and fluorescence spectroscopic properties of all series of lanthanide elements (La, Ce, …, Yb, Lu) were investigated in high temperature molten LiCl–KCl eutectic. Based on absorption spectra, the molar absorptivities for major absorption bands of lanthanides (Ln) were determined by analyzing the calibration curves at various concentrations. Moreover, the nephelauxetic parameters, β, for lanthanides in molten LiCl–KCl salt were evaluated by comparing those for aqueous lanthanide ions. In addition, fluorescence spectra and lifetimes of lanthanide elements were obtained at various Ln(III) concentrations, and this is the first to systematically present fluorescence spectroscopic properties of the whole lanthanide elements in high temperature molten LiCl–KCl salt. Such absorption and fluorescence spectra can provide a fundamental basis for the understanding and development of various pyrochemical processes in molten LiCl–KCl eutectic.

Experimental and theoretical investigations on spectroscopic properties of the imidazole-fused phenanthroline and its derivatives

Two phenanthroline derivatives, 1H-imidazo[4,5-f][1,10]phenanthroline (imPhen) and 2-(9H-fluoren-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (Flu-imPhen), have been synthesized and characterized and the corresponding absorption and emission spectroscopic properties have been studied in CH2Cl2 solution. The imPhen exhibits the main two absorption bands at 282nm and 229nm and these bands are assigned as the typical π→π*(Phen) state. In addition, the weak absorption bands at 313nm associated with a shoulder near 302nm were assigned to the π→π*(Phen) state with partial charge transfer (CT) character. A similar absorption spectra are observed in the case of the Flu-imPhen in the region of 200–300nm, while the region of 300–400nm of the spectra are dominated by the characteristic π→π* transition of the fluorene moiety. imPhen shows the typical ligand-centered 1π→π* emission, while Flu-imPhen emits from the mixed 1π→π*/CT states. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) were employed to rationalize the photophysical properties of these ligands studied. The theoretical data confirm the assignment of the experimental absorption spectra and the nature of the emitting states.

A theoretical analysis of the intrinsic light-harvesting properties of xanthopterin

Belonging to the family of pterins, which are common chromophores in several bio-organisms, xanthopterin has been shown experimentally (Plotkin et al., 2010) to have the ability of acting as a light-harvesting molecule. In the present study, multiconfigurational second-order perturbation theory is used to determine the stability of distinct amino/imino and lactam/lactim tautomers and the absorption and emission spectroscopic characteristics, electron donor and acceptor properties and the electron and charge transfer efficiencies via π-stacking. The lactam–lactam form 3H5H (and in a lesser extent 1H5H) is predicted to have the most appropriate intrinsic characteristics for the light-harvesting properties of xanthopterin, since it is the most stable isomer predicted for the gas phase and estimated for polar environments, absorbs solar light at longer wave lengths, has relatively low donor properties and the presence of the keto groups, instead of enol, increases the efficiency for energy transfer through excimer-like interactions.

Peptide-based FeS4 complexes: the zinc ribbon fold is unsurpassed to stabilize both the FeII and FeIII states

Whereas Zn(Cys)4 zinc fingers exist with different protein folds, only the zinc ribbon fold is found in rubredoxin Fe(Cys)4 sites. To assess the significance of this observation, we have investigated the binding and stability of Fe(2+) and Fe(3+) ions by a set of four peptides designed to model Zn(Cys)4 zinc fingers with various folds, i.e. zinc ribbon, treble clef and a loosened zinc ribbon fold. All peptides were shown by means of UV-Vis and CD spectroscopies to form stable 1 : 1 Fe(II)/peptide complexes with binding constants higher than 10(7) M(-1) at pH 7. Their oxidation into Fe(III) complexes and the stability of the latter were compared. The UV-Vis absorption and CD spectroscopic properties of the Fe(II) and Fe(III) complexes were analysed with respect to the structures of the zinc analogues in order to get insight into the local arrangement of the Fe(Cys)4 core around the metal ion. The chemical stability of these complexes was rationalized according to the shielding from the solvent provided by the various peptide folds to the FeS4 core. In addition, we showed that whereas UV-visible spectra inform only on the FeS4, the information derived from the corresponding CD spectra extend to the Cβ orientation and the peptide fold. The results presented here demonstrate that while the zinc ribbon fold is not strictly required to obtain a Fe(Cys)4 site, it affords a drastically superior protection of the site toward external redox agents. This finding brings new clues to engineer stable and redox-active Fe(Cys)4 sites in de novo proteins.

Cyclotriveratrylene–carbazole cage for self-assembly of C60

A novel open-bowl pyramidal compound cyclotriveratrylene–carbazole (CTV–CZ) was designed and synthesized. Its absorption and emission spectroscopic properties in different organic solvents were characterized. Three absorption peaks of CTV–CZ around 235nm, 260nm and 290nm were observed. The fluorescence emission peaks were at about 353nm and 368nm using a solution of ∼10−7M CTV–CZ. The intermolecular interaction between CTV–CZ and fullerene (C60) was studied in detail by UV–vis absorption and fluorescence spectra. CTV–CZ could associate with C60 to form supramolecular complex with 1:1 molar ratio and the binding constant was estimated to be 5.0(6)×104M−1 by fluorimetry. The formation of inclusion complex for CTV–CZ and C60 was further confirmed by 1H NMR and cyclic voltammetry. The downfield shift of protons of CTV–CZ in its 1H NMR spectrum and the decrease of redox currents on addition of C60 showed that photo induced electron transfer (PET) occurred from the electron donor CTV and CZ units to the electron acceptor C60.

Electrochemical and spectroscopic studies of Pu(IV) and Pu(III) in nitric acid solutions

Electrochemical and absorption spectroscopic properties of Pu(IV) and Pu(III) in nitric acid have been investigated by using cyclic voltammetry (CV) and UV–Visible spectroscopy. CV using a glassy carbon electrode suggested that the electrochemical reaction of Pu(IV) nitrate complexes were found to be a quasi-reversible reduction to Pu(III) species. The formal redox potentials (E 0) for Pu(IV)/Pu(III) couples were +0.721, +0.712, +0.706, +0.705, +0.704, 0.694, and +0.696 V (vs. Ag/AgCl) when nitric acid concentrations are 1–7 M nitric acid solutions, respectively. These results indicate that the reduction product of Pu(IV) is only Pu(III). Further details for reaction mechanism of Pu(IV) were discussed on the basis of digital simulation of the experimental cyclic voltammograms. The absorption spectroscopic properties of Pu(III) and Pu(IV) in nitric acid solutions were investigated with UV–Visible spectrophotometry. As a result, it was founds that the intensities of the characteristic absorption peaks of Pu(III) and Pu(IV) tend to decrease with increasing nitric acid concentration for 1–8 M, and the peaks positions shifted longer or shorter wavelengths depending on the complex-forming abilities of Pu(III) and Pu(IV) with an increase in the nitric acid concentration.

Absorption and Fluorescence Spectroscopic Properties of 1- and 1,4-Silyl-Substituted Naphthalene Derivatives

Silyl-substituted naphthalene derivatives at the 1- and 1,4-positions were synthesized and their UV absorption, fluorescence spectroscopic properties, and fluorescence lifetimes were determined. Analysis of the results shows that the introduction of silyl groups at these positions of the naphthalene chromophore/fluorophore causes shifts of the absorption maxima to longer wavelengths and increases in fluorescence intensities. Bathochromic shifts of the absorption maxima and increases in fluorescence intensities are also promoted by the introduction of methoxy and cyano groups at the naphthalene 4- and 5-positions. In addition, the fluorescence of 9,10-dicyanoanthracene is efficiently quenched by these naphthalene derivatives with Stern-Volmer plot calculated rate constants that depend on the steric bulk of the silyl groups.

Syntheses, Structural, and Spectroscopic Properties of Copper(II) Complexes of Constrained Macrocyclic Ligands

AbstractThe complexes [Cu(L1)(H2O)2](BF4)2·2H2O (1) [L1 = 5, 16‐dimethyl‐2, 6, 13, 17‐tetraazatricyclo(14, 4, 01.18,07.12)docosane] and 0.5[Cu(L2)(NO3)2][Cu(L2)](NO3)2 (2) [L2 = dibenzyl‐5, 16‐dimethyl‐2, 6, 13, 17‐tetraazatricyclo(14, 4, 01.18,07.12)docosane] were synthesized and characterized by single crystal X‐ray analyses. In these constrained macrocycles, the central copper(II) atoms are in a tetragonally distorted octahedral environment with four nitrogen atoms of the macrocyclic ligands in equatorial positions and oxygen atoms from either water molecules or nitrato groups in axial positions. The macrocyclic ligands in both complexes adopt the most stable trans‐III conformation. The Cu–N distances [1.999(7)–2.095(7) Å] are typical for such complexes, but the axial ligands are weakly coordinating Cu–OH2 bonds [2.693(3) Å] and Cu–ONO2 bonds [2.873(7) Å] due to the combination of the pseudo Jahn–Teller effect and strong in‐plane ligand field. The crystals are stabilized by a three‐dimensional network by hydrogen bonds that are formed among the secondary nitrogen hydrogen atoms, oxygen atoms of water molecules, fluorine atoms of BF4–, and oxygen atoms of NO3–. The electronic absorption and IR spectroscopic properties are also discussed.

Comparison of the Photophysical Properties of a Planar, PtOEP, and a Nonplanar, PtOETPP, Porphyrin in Solution and Doped Films

The absorption and emission spectroscopic properties of planar (2,3,7,8,12,13,17,18-octaethylporphyrinato)platinum(II) (PtOEP) and nonplanar (2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrinato)platinum(II) (PtOETPP) complexes have been studied at room temperature. Liquid solutions and doped films, in polystyrene (PS) and epoxy (EPO) polymers, have been investigated. In dilute liquid solution, the photophysical properties of the nonplanar complex are substantially perturbed compared to the planar analogue. Strong ligating solvents further affect the photophysical behavior of both Pt(II) complexes via axial ligation to the central metal ion. At high concentrations, ground state aggregation and excimer formation is observed for PtOEP films in PS and EPO hosts. Incorporation of the nonplanar PtOETPP complex in PS results in enhanced coplanarity of the meso-phenyl groups, leading to a more extended conjugation between the meso-substituents and the π-conjugated system of the macrocycle. A more planar conformer for the nonplanar PtOETPP is present in the EPO host.