Intense UV Absorption Research Articles

Metallocene-Naphthalimide Derivatives: The Effect of Geometry, DFT Methodology, and Transition Metals on Absorption Spectra.

In the present paper, the photophysical properties of metallocene-4-amino-1,8-naphthalimide-piperazine molecules (1-M2+), as well as their oxidized and protonated derivatives (1-M3+, 1-M2+-H+, and 1-M3+-H+), where M = Fe, Co, and Ni, were studied via DFT and TD-DFT, employing three functionals, i.e., PBE0, TPSSh, and wB97XD. The effect of the substitution of the transition metal M on their oxidation state, and/or the protonation of the molecules, was investigated. The present calculated systems have not been investigated before and, except for the data regarding their photophysical properties, the present study provides important information regarding the effect of geometry and of DFT methodology on absorption spectra. It was found that small differences in geometry, specifically in the geometry of N atoms, reflect significant differences in absorption spectra. The common differences in spectra due to the use of different functionals can be significantly increased when the functionals predict minima even with small geometry differences. For most of the calculated molecules, the main absorption peaks in visible and near-UV areas correspond mainly to charge transfer excitations. The Fe complexes present larger oxidation energies at 5.4 eV, whereas Co and Ni complexes have smaller ones, at about 3.5 eV. There are many intense UV absorption peaks with excitation energies similar to their oxidation energies, showing that the emission from these excited states can be antagonistic to their oxidation. Regarding the use of functionals, the inclusion of dispersion corrections does not affect the geometry, and consequently the absorption spectra, of the present calculated molecular systems. For certain applications, where there is a need for a redox molecular system including metallocene, the oxidation energies could be lowered significantly, to about 40%, with the replacement of the iron with cobalt or nickel. Finally, the present molecular system, using cobalt as the transition metal, has the potential to be used as a sensor.

Alkali-Niobate aluminosilicate glasses: Structure and properties

K0.5Na0.5NbO3 (KNN) based ceramics are considered optimal candidates to replace the toxic Pb-based piezoelectric materials; nonetheless, they are quite difficult to process. Therefore, obtaining an efficient glass-ceramic (GC) will have several advantages in lead-free piezoelectric production. The first step to developing advantageous functional GCs is to determine an adequate glass matrix and the network connectivity of the different structural entities depending on the bulk chemistry. Here, we investigated the structural variations occurring in aluminosilicate systems having Na2O/Al2O3 molar ratios from 1 to 5.7 upon the addition of KNN (0.4 up to 30 mol%) to understand how the bulk composition influences KNN incorporation and the properties of the glasses.Our study shows that more depolymerized aluminosilicate systems incorporate a larger amount of KNN because the Nb structural environment's evolution strongly depends on glass polymerization and the availability of charge compensator ions. No strong crosslinking between [SiO4], [AlO4], and [NbO6] structural entities was found, and there is an evolution from a heterogeneous environment with isolated [NbO6] units having different degrees of distortion to Nb–O–Nb linkages, up to the formation of clusters composed of corner-shared slightly distorted [NbO6]. All glass series tend to move toward these 3D clusters whenever the starting structure includes different entities or a more homogeneous environment. The evolution of the different niobate entities marks the changes in the properties that show non-linear variations with KNN content. Furthermore, the glass chemistry influences the crystallization kinetics, with activation energies for crystallization that vary from ∼300 ± 10 kJ/mol to ∼220 ± 10 kJ/mol depending on the alkali/Al2O3 molar ratios.The developed niobo-aluminosilicate glasses show high refractive indices, high transparency in the visible– NIR region and intense UV absorption. Therefore, these glasses are excellent candidates for photonic applications and optoelectronic devices. The stabilization of a perovskite-like phase upon crystallization confirms the potentiality for use as electro-optical glass-ceramics.

Detailed investigations on structural, spectroscopic, and optoelectronic properties of Ethyl Nile Blue thin films

Here, we highlight the interrelation between constitutional and spectroscopical properties of Ethyl Nile Blue thin films. The deposited films are amorphous with a homogenous and smooth surface profile. Spectrophotometrically, films show high IR transparency with intense UV and visible light absorption. Moreover, ENB films exhibit an indirect energy gap and Urbach energy ∼2.77 eV and 63 meV, respectively. The dispersion behavior of the films is inspected in correspondence to the single-effective-oscillator model. Referring to the thermal emissivity and the surface resistance characteristics of ENB film, impressive IR features have been discovered displaying the validity of ENB film in IR thermal emission applications. The nonlinear properties of ENB film like nonlinear optical susceptibility, nonlinear refractive index, and nonlinear absorption coefficient are evaluated. Comparison of the optical parameters of ENB and other conjugated organic dyes, it is highly recommended to possess high potentiality in UV–visible optoelectronics and optical switching applications.

Investigation on structural, morphological, and optical studies of multiphase titanium dioxide nanoparticles

Multiphase titanium dioxide (TiO2) nanoparticles were successfully synthesized using the hydrothermal method. The as-prepared nanoparticles were subjected to different annealing temperatures (Ta) to investigate their effects on the structural, morphological, and opto-chemical properties using X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), Scanning electron microscopy (SEM), Energy dispersive x-ray (EDX) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), and Ultraviolet-visible spectrometry (UV–Vis) techniques. As Ta is increased from 200 to 1200 °C, the TiO2 nanoparticles appear to have a stable tetragonal crystal structure throughout the various Ta. XRD measurements indicate an extended presence of mixed anatase-rutile phase composition with a slow phase transformation mechanism. The crystalline size of both the anatase and rutile phase increases from 19 to 38 nm and 18 -57 nm, respectively. The behaviour in the lattice parameter indicates that increasing Ta forces the crystalline structure in both phases to expand. Images from TEM and SEM micrographs reveal a similar morphology in agreement with XRD measurements. The micrographs reveal that increasing Ta increases material porosity and the dispersion of well-defined TiO2 nanostructure. The EDX spectroscopy confirms the successful synthesis of TiO2 nanoparticles with the absence of impurities after annealing. FT-IR confirms vibrational modes and bond behaviour associated with the expected titanium and oxygen elements with Ta. The UV–Vis spectroscopy characterizes changes in the multiphase TiO2 optical properties as the Ta is increased. An intense UV absorption is reported in the results section and its importance in solar cell applications is stated in the conclusion.

Theoretical investigation of the structural, electronic, magnetic and spectral properties of CumXn (X = Se, Te; m + n = 5) clusters

Based on the density functional theory (DFT), the geometric structures, relative stability as well as electronic, magnetic and spectral properties of CumXn (X = Se, Te; m + n = 5) clusters are systematically investigated with Gaussian 09. The ground state structures of CumXn clusters are found to be largely similar for X = Se and Te with minor differences. Characterized by energy gap, the stability of the CumXn clusters increases with increasing the number of Cu-X bonds and reaches the maximum for Cu2Se3 or Cu3Te2 (with the ratio m/n closest to unity). The electronic properties of CumXn clusters are related to the geometrical structures and the value of m. Particularly, Cu3Te2 cluster is found to exhibit superalkali nature with very low vertical electron affinity of 0.94eV. The magnitudes of local magnetic moments are more than 99.99% and less than 0.01% for X and Cu atoms, respectively. The equivalent Cu or X atoms with respect to the symmetrical axis of the CumXn clusters demonstrate the same local magnetic moments due to the symmetry of the electron angular momentum related to the symmetrical axis. The IR and Raman spectra of CumXn clusters exhibit similarity for X = Se and Te. The intense UV absorption peaks at 200–250nm for Cu4X and Cu3×2 clusters may reveal that they can act as potential UV absorption materials.

Influence of solvothermal growth condition on morphological formation of hematite spheroid and pseudocubic micro structures and its magnetic coercivity

Influence of solvothermal growth condition on morphological formation and population of defects of hematite spheroid and pseudocubic micro structures and its magnetic properties were studied. Spheroid shaped crystals with different size were obtained from growth solution made of methanol, methanol-water, propanol and pseudocubic crystallites with dimension of 1.281μm size were obtained with propanol-water solution combination at a growth temperature of 200°C. UV absorption and magnetic properties of spheroid and pseudocubic micro structures were size and shape dependant. Spheroid shaped sample grown from precursor solution made of methanol gives intense UV absorption peaks at 360nm and high coercivity (5.23 KOe) at room temperature. Reduction in magnetic coercivity and remanence of all samples at 5K with respect to 300K is attributed to antiferromagnetic nature of hematite with spheroid and pseudocubic morphology. High coercivity (6.2 KOe) at room temperature was observed from micro pseudocubic sample grown with propanol-water combination which is contributed to high aspect ratio, inter particle interaction and crystalline defects.

Synthesis, in vitro and in silico antimalarial activity of 7-chloroquinoline and 4H-chromene conjugates.

A new series of chloroquinoline-4H-chromene conjugates incorporating piperizine or azipane tethers were synthesized and their anti-malarial activity were evaluated against two Plasmodium falciparum strains namely 3D7 chloroquine sensitive (CQS) and K1 chloroquine resistant (CQR). Chloroquine was used as the standard and also reference for comparison. The conjugates exhibit intense UV absorption with λmax located at 342 nm (log ε=4.0), 254 nm (log ε=4.2), 223 nm (log ε=4.4) which can be used to spectrometrically track the molecules even in trace amounts. Among all the synthetic compounds, two molecules namely 6-nitro and N-piperazine groups incorporated 7d and 6-chloro and N-azapane incorporated 15b chloroquinoline-4H-chromene conjugates showed significant anti-malarial activity against two strains (3D7 and K1) of P. falciparum. These values are lesser than the values of standard antimalarial compound. Molecular docking results suggested that these two compounds showing strong binding affinity with P. falciparum lactate dehydrogenase (PfLDH) and also they occupy the co-factor position which indicated that they could be the potent inhibitors for dreadful disease malaria and specifically attack the glycolytic pathway in parasite for energy production.

Hydrothermal synthesis of ZnO decorated reduced graphene oxide: Understanding the mechanism of photocatalysis

ZnO nanomaterials are grown in-situ on graphene oxide (GO) materials by a facile hydrothermal method at a temperature of 100°C. These ZnO–graphene composite materials display a strong and broad absorption in the visible region besides an intense UV absorption peak. The enhanced fluorescent quenching observed for the graphene hybrids compared to ZnO, indicates the photoinduced electron transfer between ZnO and graphene layers, which in-turn reduces the recombination of charge carriers. In order to understand the mechanism of improved photocatalytic properties, reagents such as a radical scavenger t-BuOH and a hole scavenger EDTA-2Na were employed. The addition of t-BuOH did not show any appreciable changes in the photo-degradation properties of the ZnO–graphene hybrids. However, the addition of EDTA-2Na significantly reduced the photocatalytic activities of the ZnO–graphene hybrids indicated that photo-generated holes are the main reactive oxidative species responsible for the photocatalytic reaction. It has been concluded that the excellent absorption range, efficient charge transportation and separation and high surface area make the ZnO–graphene hybrids a better photocatalyst under UV and visible light.

Electron dynamics in complex environments with real-time time dependent density functional theory in a QM-MM framework.

This article presents a time dependent density functional theory (TDDFT) implementation to propagate the Kohn-Sham equations in real time, including the effects of a molecular environment through a Quantum-Mechanics Molecular-Mechanics (QM-MM) hamiltonian. The code delivers an all-electron description employing Gaussian basis functions, and incorporates the Amber force-field in the QM-MM treatment. The most expensive parts of the computation, comprising the commutators between the hamiltonian and the density matrix-required to propagate the electron dynamics-, and the evaluation of the exchange-correlation energy, were migrated to the CUDA platform to run on graphics processing units, which remarkably accelerates the performance of the code. The method was validated by reproducing linear-response TDDFT results for the absorption spectra of several molecular species. Two different schemes were tested to propagate the quantum dynamics: (i) a leap-frog Verlet algorithm, and (ii) the Magnus expansion to first-order. These two approaches were confronted, to find that the Magnus scheme is more efficient by a factor of six in small molecules. Interestingly, the presence of iron was found to seriously limitate the length of the integration time step, due to the high frequencies associated with the core-electrons. This highlights the importance of pseudopotentials to alleviate the cost of the propagation of the inner states when heavy nuclei are present. Finally, the methodology was applied to investigate the shifts induced by the chemical environment on the most intense UV absorption bands of two model systems of general relevance: the formamide molecule in water solution, and the carboxy-heme group in Flavohemoglobin. In both cases, shifts of several nanometers are observed, consistently with the available experimental data.

Novel iridium complexes containing alkylfluorene functionalized picolinic acid ancillary ligand: Synthesis, optophysics and electroluminescence properties

Two novel green-emitting cyclometalated iridium complexes of (Buppy)2Ir(Tfl-pic) and (Buppy)2Ir(Brfl-pic) were synthesized and characterized, in which Buppy is 2-(4-tert-butylphenyl)pyridine, Tfl-pic is 6-(6′-(9″-octyl-2″,7″-bi(9,9-dioctylfluoren-2-yl)fluoren-9″-yl)hexyloxy) picolinic acid and Brfl is 6-(6′-(2″,7″-di-bromo-9″-octylfluoren-9″-yl)hexyloxy) picolinic acid. Their thermal property, dispersibility and optophysical properties were investigated. Both iridium complexes present intense UV absorption bands and photoluminescence performance in CH2Cl2. Single-emissive-layer polymer light-emitting devices using (Buppy)2Ir(Tfl-pic) and (Buppy)2Ir(Brfl-pic) as a single dopant and a blend of poly(vinylcarbazole) and 2-(4-biphenyl)-5-(4-tert-butyl-phenyl)-1,3,4-oxadiazole as the host matrix were fabricated. The (Buppy)2Ir(Tfl-pic)-doped devices exhibited a maximum current efficiency of 2.44 cd A−1. As expected, the phase separation and concentration quenching of these iridium complexes in the devices are efficiently suppressed due to appending bulky fluorene derivatives on the picolinic acid unit by a non-conjugated connection.

Novel blue-emitting carboxyl-functionalized poly(arylene ether nitrile)s with excellent thermal and mechanical properties

A series of novel carboxyl-functionalized poly(arylene ether nitrile)s (CPAENs) were synthesized via nucleophilic substitution polycondensation reactions of 2,6-dichlorobenzonitrile with carboxyl-functionalized phenolphthalin and diphenol compounds, using N-methyl-2-pyrrolidone (NMP) as solvent in the presence of anhydrous potassium carbonate. The resulting CPAENs exhibited high glass transition temperatures ranging from 181 °C to 251 °C, and were thermally stable up to 400 °C under either nitrogen or air atmospheres. The incorporation of phenolphthalin-units into the polymer chain imparted an improved solubility of CPAENs in organic solvents, such as NMP, N,N-dimethylformamide, and tetrahydrofuran. The CPAENs were amorphous and can be readily cast into transparent films with a tensile strength of 75.1–104.7 MPa and a tensile modulus of 2.6–3.2 GPa. All CPAENs displayed a highly intense UV absorption in the wavelength range of 280–330 nm and a characteristic blue-emitting fluorescence under the UV irradiation.

Synthesis and Photochromic Properties of M<sub>O</sub>O<sub>3</sub> Nanosheets Crystallites

Layered Molybdenum trioxide MOO3, with a two-dimensional (2D) structure was successfully delaminated into colloidal nanosheets in n-butanol via a soft-chemical process involving intercalation of dodecylamine. X-ray diffration (XRD) showd that: after intercalation spacing of the layered material expend to 2.69nm from 1.38nm, and Characterizations by transmission electron microscopy (TEM) and scan electron microscopy (TEM) confirmed the formation of unilamellar 2D nanosheet crystallites with an average lateral size of 400 nm. The obtained nanosheets exhibited photochromic properties upon UV-VIS excitation. The chromogenic nanosheet obtained in this study features the intense UV absorption and optically switchable Visible-to-IR absorption, which may be useful for window applications such as heat-absorbing films.

Characterization of ZnO Nanopowder and Antibacterial Response against <i>Staphylococcus aureus </i>under UVA Illumination

In this study, we study the physical property and antibacterial bioactivity of ZnO nanopowder towards Staphylococcus Aureus. Transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), FTIR, Raman spectroscopy and UV-Vis were used to characterize the ZnO nanopowder. The major morphology consists of nanorods which have length 70-200 nm and width 30-120 nm. FTIR spectra performed a well-synthesis of ZnO that has Zn-O stretching bond (482 cm-1). UV-Vis absorption spectra showed an intense UV absorption at 387 nm, corresponding to optical bandgap 3.24 eV. Raman spectroscopy exhibited a prominent peak in E2high mode located at 435 cm-1. The antibacterial response of ZnO was performed toward Staphylococcus aureus. Higher concentration of ZnO had caused higher inhibition of the bacteria. Besides, the increment of capability of ZnO towards the bacteria was observed under UV radiation. It was believed that the irradiation had induced oxygen to be released from the surface of the ZnO and caused the increasing of reactive oxygen species, which enhance the bacteria inhibition.

Furoic and mefenamic acids as new matrices for matrix assisted laser desorption/ionization-(MALDI)-mass spectrometry

The present study introduces two novel organic matrices for matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS) for the analysis of small molecules. The first matrix is “2-amino-4,5-diphenylfuran-3-carboxylic acid” (also called furoic acid, FA) which was synthesized and then characterized by ultraviolet (UV), infrared (FTIR), nuclear magnetic resonance NMR (1H and 13C) and mass spectrometry. The compound has organic semiconductor properties and exhibits intense UV-absorption which is suitable for the UV-MALDI laser (N2 laser, 337nm). The second matrix is mefenamic acid (MA). The two matrices can be successfully applied for various classes of compounds including adenosine-5′-triphosphate (ATP, 0.5µL(10.0nmol)), spectinomycin (spect, 0.5µL(14.0nmol)), glutathione (GSH, 0.5µL(9.0nmol)), sulfamethazole (SMT, 0.5µL(2.0nmol)) and mixture of peptides gramicidin D (GD, 0.5µL (9.0nmol)). The two matrices can effectively absorb the laser energy, resulting in excellent desorption/ionization of small molecules. The new matrices offer a significant enhancement of ionization, less fragmentation, few interferences, nice reproducibility, and excellent stability under vacuum. Theoretical calculations of the physical parameters demonstrated increase in polarizability, molar volume and refractivity than the conventional organic matrices which can effectively enhance the proton transfer reactions between the matrices with the analyte molecules. While the reduction in density, surface tension and index of refraction can enhance homogeneity between the two new matrices with the analytes. Due to the sublimation energy of mefenamic acid is (1.2 times) higher than that of the DHB, it is more stable to be used in the vacuum.

Highly efficient near-infrared emission from binuclear cyclo-metalated platinum complexes bridged with 5-(4-octyloxyphenyl)-1,3,4-oxadiazole-2-thiol in PLEDs

A novel near-infrared-emitting binuclear platinum complex of (piq)2Pt2(μ-C8OXT)2 was synthesized and characterized, in which piq is 1-phenylisoquinolinato and C8OXT is a bridging ancillary ligand of 5-(4-octyloxyphenyl)-1,3,4-oxadiazole)-2-thiol. Its optophysical, electrochemical and electroluminescent characteristics were primary studied. This binuclear platinum complex exhibited an intense UV absorption at about 493nm from the metal–metal-to-ligand charge transfer transition and a bright near-infrared emission at 721nm in chloromethane. Using (piq)2Pt2(μ-C8OXT)2 as a single dopant, its single-emissive-layer polymer light-emitting devices presented a high-efficiency near-infrared emission peaked at 702nm with the maximum external quantum efficiency of 6.3% at 7.6mAcm−2. This work provides an efficient approach to realize high-efficiency near-infrared emission by binuclear platinum complexes.

Photochromogenic Nanosheet Crystallites of Tungstate with a 2D Bronze Structure

Layered rubidium tungstate, Rb(4)W(11)O(35), with a two-dimensional (2D) bronze-type tunnel structure was successfully delaminated into colloidal nanosheets via a soft-chemical process involving acid exchange and subsequent intercalation of tetrabutylammonium ions. Characterizations by transmission electron microscopy and atomic force microscopy confirmed the formation of unilamellar 2D nanosheet crystallites with a unique thickness of ∼3 nm and an average lateral size of 400 nm. The obtained nanosheets exhibited reversible color change upon UV-light excitation via an optical band gap of 3.5 eV. The ultimate 2D aspect ratio favorable for an adsorption of charge-compensating cations to trapped electrons working as a color center is presumably responsible for highly efficient photochromic behavior. Its coloration mainly consists of a broad band at a wavelength of 1800 nm and longer, which is much different from that of the common tungstate nanomaterials. Thus, the chromogenic nanosheet obtained in this study features the intense UV absorption and optically switchable visible-to-IR absorption, which may be useful for window applications such as cutoff filters and heat-absorbing films.

Electron Donor–Acceptor Interactions with Flanking Purines Influence the Efficiency of Thymine Photodimerization

Quantum yields for thymine photodimerization (Φ(TT)) have been determined for a series of short DNA single-strand and base-paired hairpin structures possessing a single thymine-thymine step with flanking purines. Values of Φ(TT) are strongly dependent upon the oxidation potential of the flanking purine, decreasing in the order: inosine > adenine > guanine > deazaguanine. The dependence of Φ(TT) on the ionization potential of the flanking purine is more pronounced when the purine of lower oxidation potential is located at the 5'- versus 3'-position in either a single strand or a hairpin. Molecular dynamics simulations for hairpin structures indicate that the TT step is π-stacked with both the 5' and 3' purine, but that there is little π-stacking with either purine in single-strand structures. The observation of moderately intense long-wavelength UV absorption features for hairpins having 5'-Z or G flanking purines suggests that excitation of ground state donor-acceptor complexes may account for more extensive quenching of dimerization by 5'- versus 3'-purines. The "purine effect" on Φ(TT) is attributed to a combination of ground state conformation, ground state electron donor-acceptor interactions, and excited state exciplex formation.

Tetrapalladium(II) Bisazobenzene and Azoazoxybenzene Complexes: Syntheses, Electronic Structures, and Optical Properties

Three new tetranuclear, chloride-bridged PdII complexes have been prepared by using 1,4-bis[(E)-phenylazo]benzenes (BPABs) and an azoazoxybenzene derivative. The latter was obtained unexpectedly by reacting N,N-dimethyl-4-nitrosoaniline with 2,3,5,6-tetramethylphenylenediamine in glacial acetic acid. Characterization includes 1H NMR and UV–vis spectroscopies, and single-crystal X-ray structures have been obtained for two of the proligands and one complex. As expected, the methyl groups on the central aryl rings cause severe departures from planarity. The proligands show an intense UV absorption (λmax ≈ 350 nm) due to π → π* intramolecular charge transfer, together with weaker n → π* bands in the visible region. The complexes display an intense visible band (λmax = 449–475 nm) and multiple near-UV absorptions. While the electronic absorption spectra of the BPAB complexes are quite similar, the azoazoxybenzene complex shows a doubly intense visible band. Dichroic ratios (DRs) measured in two different liqui...

Zeolite Confined Ti(OH)4 Nanoparticles in Highly Active and Selective Oxidation Catalyst

Some highly active, hydrophilic, MFI structured titanium silicate catalysts are characterized by an intense UV absorption centered in the 213–233 nm (43000–47000 cm−1) range. The assignment of this band to a specific molecular structure has remained unclear unlike the well published 233 nm UV bands of higher coordinated Ti-atoms at lattice defects or in variously agglomerated extra lattice Ti x O y (OH) z species. To decipher the structural origin of this intermediate UV band, we used Time-Dependent Density Functional Theory (TD-DFT) to compute the UV spectra of various model compositions and show in this paper that only one model, in which isolated tetrahedral Ti(OH)4 molecules reside in the zeolite channels without any covalent bond to the framework, fits the experimental UV spectrum. Hence these confined tetrahedral Ti(OH)4 nanoparticles may account for the enhanced activity and selectivity of some MFI type titanium silicate catalysts.

Synthesis, optophysical and electrochemical properties of bipolar-transporting europium(III) complexes with carbazole and oxadiazole units

A series of bipolar-transporting europium(III) complexes containing carbazole and oxadiazole units were synthesized and characterized. Two intense UV absorption bands at around 286 nm and 352 nm, and sharply red emissions peaked at 614 nm were observed for these europium complexes in dichloromethane. Importantly, the bipolar-transporting europium(III) complexes exhibited higher thermal stability, more intense UV absorption at 286 nm and twofold increased photoluminescent quantum yield compared to the reported red chromophore of tri(dibenzoylmethane) (1,10-phenanthroline) europium(III).