UV Vis Absorption Bands Research Articles

Preparation and characterization of nanofibers of polyvinyl alcohol/polyaniline-montmorillonite clay

This work describes the preparation of polyvinyl alcohol/polyaniline-montmorillonite clay (PVA/PANI-OMMT) nanofibers through electrospinning. Initially, for improving the compatibility of the clay towards the organic polymer, the montmorillonite (MMT) was submitted to an organophilization process using hexadecyltrimethylammonium bromide (CH3(CH2)15N(Br)(CH3)3). The PANI-OMMT composite, which was obtained after the in situ polymerization of aniline in presence of the organophilic clay (ratio of ≈1:3 in weight), was then placed in a matrix of PVA (weight ratio of 1:7 of composite:PVA) for the production of the PVA/PANI-OMMT composite fibers through electrospinning. We used several characterization techniques (X-ray diffraction (XRD); infrared absorption spectroscopy (FTIR), ultraviolet visible absorption spectroscopy (UV–Vis), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS)) to analyze the different samples produced. The clay organophilization was confirmed after observing the (001) plane displacement from 5,6° to 4,7° and absorption bands in 2924 cm−1, 2853 cm−1 and 1479 cm−1, as analyzed by XRD and FTIR, respectively. The presence of polyaniline in its emeraldine salt was identified by the presence of the characteristic UV–Vis absorption bands in 360 nm, 430 nm and 822 nm, while the formation of the PANI/OMMT nanocomposite was confirmed by observing the characteristic FTIR bands of each individual component. From the SEM images, we could establish that the resulting nanocomposite mats were composed by uniform fibers with an average diameter of 240 nm and presented good surface quality. We have found that EIS is an efficient technique for the evaluation of changes in the electric properties of the nanofibers after their exposure to vapors of methanol. We suggest that this organic-inorganic composite may find useful applications in the preparation of several devices based on polymers, such as heavy metal filtration membranes and gas sensors.

Synthesis and optoelectronic properties of novel alternate copolymers based on diketopyrrolopyrrole and triarylamine units spaced by flexible chain

A series of alternate copolymers D‑co‑Ts named P(DPP‑TA) P(DPP‑Cz) and P(DPP‑DB) consisting of both diketopyrrolopyrrole (DPP) and different triarylamine (TAA) units, were synthesized by Stille cross-coupling reaction in which DPP acts as an acceptor and TAA acts as a donor. These D‑co‑Ts show good thermal stability in nitrogen (N2) atmosphere. The solutions of D‑co‑Ts have strong UV–vis absorption bands in the range of 313 nm to 344 nm and have fluorescence (PL) peaks at from 415 nm to 496 nm with high quantum efficiency. The highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) energy levels and Eg were combined with via cyclic voltammograms (CV) as −5.19 eV to −5.41 eV, −3.77 eV to −3.80 eV, and 1.42 eV to 1.62 eV, respectively. The P(DPP‑TA) film shows the evident color changes from original yellow to brownish to blue. New absorption peaks of P(DPP‑TA) appear at 412 nm and 938 nm with increasing voltage in the UV–vis spectrophotometer, indicating D‑co‑Ts can be promising electrochromic materials. The highest coloration efficiency reaches up to be 270 cm2 C−1 for the P(DPP‑Cz). The memory performances of the ITO/polymer/Al sandwich devices were also studied, in which D‑co‑Ts exhibit the typical nonvolatile rewritable flash memory characteristics. The device of P(DPP‑DB) shows an ON/OFF current ratio of 5.80 × 104 under a threshold voltage of −1.80 V. Furthermore, in the explosive detection tests, the copolymer shows new emission band at 570 nm with addition of TNT, and the PL quenching efficiency goes up to be 82%.

Determination of kinetic parameters of the enzymatic reaction between soybean peroxidase and natural antioxidants using chemometric tools

The oxidation of eugenol, isoeugenol and vanillin natural antioxidants catalyzed by the soybean peroxidase enzyme was studied using uv–vis spectroscopy. An experimental design was used to optimize the different variables. The multivariate curve resolution method was used to obtain the profiles of antioxidant absorbance’s as a function of time due to uv–vis absorption bands of both antioxidants and the enzymatic reaction product/s show a strong overlap. From these results, apparent Michaelis-Menten constants as well as the kinetic parameters k1 and k3 involved in the catalytic cycle of peroxidases were calculated. The antioxidant apparent acidity constants were also determined at different pH’s from uv–vis spectrophotometric measurements. Values of k1 were (0.6 ± 0.1) × 105 M−1 s−1, (2.0 ± 0.2) × 105 M−1 s−1 and (7.0 ± 0.5) × 106 M−1 s−1 and k3 (4.0 ± 0.2) × 105 M−1 s−1, (6.0 ± 0.6) × 105 M−1 s−1 and (6.0 ± 0.9) × 106 M−1 s−1 for eugenol, isoeugenol and vanillin, respectively.

A fluorometric sensing method for sensitive detection of trypsin and its inhibitor based on gold nanoclusters and gold nanoparticles.

In this work, a facile, label-free, and sensitive fluorometric strategy for detection of trypsin and its inhibitor was established on the basis of the fluorescence resonance energy transfer (FRET) between mercaptoundecanoic acid functionalized gold nanoclusters (AuNCs) and gold nanoparticles (AuNPs) via protamine as a bridge. Protamine can trigger the aggregation of AuNPs and link AuNCs with aggregated AuNPs through electrostatic interaction. Compared with monodisperse AuNPs, the UV-vis absorption band of aggregated AuNPs overlapped considerably with the emission spectrum of AuNCs. Thus, the fluorescence of AuNCs was obviously quenched by the aggregated AuNPs through FRET. In the presence of trypsin, protamine was hydrolyzed into small fragments, leading to the deaggregation of AuNPs and breaking of the short distance between AuNPs and AuNCs, so the FRET process was inhibited, and the fluorescence of AuNCs was recovered. The increase in the fluorescence intensity of AuNCs was directly related to the amount of trypsin. Hence trypsin can be determined on the basis of the variation of fluorescence intensity, with a linear range of 5-5000 ng mL-1 and a detection limit of 1.9 ng mL-1. In addition, this system was used for the detection of trypsin inhibitor by application of the inhibitor isolated from soybean as a model. The sensing method was applied for trypsin detection in human urine and commercial multienzyme tablet samples with satisfactory results. Graphical abstract ᅟ.

Green Synthesis of AgNPs Coated Mesoporous Silica Nanoparticles Using Tyrosine as Reducing/Stabilising Agent

A novel, simple and environmental friendly approach to fabricate silver nanoparticles (AgNPs) on mesoporous silica nanoparticles (MSNs) using tyrosine (Tyr) as biological reducing agent was developed. The functionalization of Tyr with MSNs (Tyr-MSNs) (150 nm in length) by the sol-gel process was confirmed by the characteristic peaks of amino, carboxyl and silanol groups appeared in FTIR spectrum and the change of the zeta potential from 0 mV at pH 2 to-60 mV at pH 12. Then, AgNPs were formed on the surface of Tyr-MSNs (Tyr-MSN@AgNPs) via only reducibility from phenolic group of Tyr and catalytic activity from base at room temperature. TEM images and UV-Visible absorption band at 420 nm supported the obtained AgNPs (18 nm at pH 11) were tightly bound to Tyr-MSNs even after centrifugation at high speed. These Tyr-MSN@AgNPs would be potentially used as drug carrier in biomedical applications.

Synthesis and Characterization of Fully Conjugated Ladder Naphthalene Bisimide Copolymers.

Fully conjugated ladder copolymers have attracted considerable attention due to their unique fused-ring structure and optoelectronic properties. In this study, two fully conjugated ladder naphthalene diimide (NDI) copolymers, P(NDI-CZL) and P(NDI-TTL) with imine-bridged structures are presented in high yields. Both of the two copolymers have good solubility and high thermal stability. The corresponding compounds with the same structure as the copolymers were synthesized as model system. The yields for each step of the synthesis of the model compounds are higher than 95%. These results suggest that P(NDI-CZL) and P(NDI-TTL) can be synthesized successfully with fewer structural defects. The structures and optoelectronic properties of compounds and copolymers are investigated by NMR, fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-vis), and cyclic voltammetry (CV). Both in solution and as a thin film, the two copolymers show two UV-vis absorption bands (around 300–400 nm and 400–750 nm) and a very weak fluorescence. The collective results suggest that the two fully conjugated ladder copolymers can be used as potential acceptor materials.

Tuning the molecular/electronic structure of new substituted pyrazoles: Synthesis, biological trials, theoretical approaches and Hammett correlations

The high yield synthesis, characterization and biological trials of a family of compounds containing the pyrazole core (E)-3,5-dimethyl-1-(4-R-phenyl)-4-(phenyldiazenyl)-1H-pyrazoles (with R = 4-CH3O (1), 4-CH3 (2), 4-H (3), 4-F (4), 4-Cl (5), 4-CF3 (6), 4-CN (7), 4-NO2 (8), 3-Cl (9), 3-NO2 (10), 2-Cl (11) and C6F5 (12)) are reported. Hammett correlations were found for the experimental and theoretical computed data, showing the dependence of all the obtained results on the donor or acceptor nature of the R substituent. In this sense, the absorption wavelength does decrease as the electron-withdrawing character of the substituent increases. Furthermore, the wavelength intensity does follow a Hammett correlation with the sigma donor character of the substituents. The compounds were characterized using MP, EA, UV–vis, FT-IR, 1H NMR, 13C NMR including bidimensional NMR experiments (HMBC and HMQC). The structures of 4, 5 and 8 were successfully elucidated by means of X-Ray diffraction. Pyrazole based dyes are known in pharmacological areas. Therefore, biological activity of all these structures were tested against cancer cell lines over a wide library of cell lines (60), including leukemia, colon and brain cancer, showing that the compounds have anticancer activity, which expands the knowledge of this kind of dyes as targets for this critical application. Finally, quantum calculations were carried out in order to give a rational explanation to the observed UV–vis absorption bands and FT-IR signals. As shown, it is possible to tune the molecular/electronic structure of the synthesized dyes by means of changing the R substituent in the structure.

Synthesis and mesomorphic properties of benzoxazole derivatives with lateral multifluoro substituents

ABSTRACTFluorinated aromatics is generally chosen as mesogenic cores to design novel liquid crystal compounds. Here, a series of benzoxazole derivatives with laterally multifluorinated biphenyl units, 2-(3′,3-difluoro −4′-alkoxy-1,1′-biphenyl-4-yl)-benzoxazole derivatives (coded as nPF(3)PF(3)Bx), are synthesized and characterized, where methyl and nitro moieties are selected as terminal groups to investigate the effects of different polar substituents on the liquid crystal properties. The compounds nPF(3)PF(3)Bx show enantiotropic mesophases with mesophase ranges of 0–40°C and 0–63°C on heating and cooling for hydrogen-terminated derivatives (nPF(3)PF(3)BH), 43–93°C and 54–123°C for methyl-terminated ones (nPF(3)PF(3)BM), 60–108°C and 74–152°C for nitro terminated ones (nPF(3)PF(3)BN), respectively. They exhibit photoluminescence emission peaks at 390–392 nm and UV–vis absorption bands with maxima at 327–330 nm, respectively. The results reveal that lateral multifluoro substituents lead to a decrease in melting/clearing points, while electron-withdrawing terminal nitro moiety results in increases in both melting point and mesophase range.

Experimental and Theoretical Study on the Interaction of P-Aminophenol Hydrochloride with H2O

Abstract UV-Vis absorption spectra, cyclic voltammetry and 1H nuclear magnetic resonance (1H NMR) spectra were applied to explore the hydrogen bond interactions of p-aminophenol hydrochloride (PAH) with H2O. The results indicated the hydrogen bonds were formed in PAH–H2O system. The anodic/cathodic peak potentials and UV-Vis absorption bands of PAH in H2O could be affected due to the interactions. The results of density functional theory, atoms in molecules theory and natural bond orbital analyses further confirmed the existence of hydrogen bonds between the phenolic hydroxyl, –NH3 + protons and Cl− of PAH and H2O. Furthermore, the π-π stacking was suggested between PAH benzene rings from the 1H NMR spectra at higher concentrations.

Application of indoline dyes attached with strongly electron-withdrawing carboxylated indan-1,3-dione analogues linked with a hexylthiophene ring to dye-sensitized solar cells

An indoline dye attached with a carboxylated indan-1,3-dione moiety linked with a hexylthiophene ring exhibited the highest conversion efficiency among six analogues and D205. This result comes from the bathochromic UV–vis absorption band, suitable energy levels, good stability for redox process, and sufficiently long excited-state lifetime.

Synthesis of a porphyrin-hexaarylbenzene-hexabenzocoronene triad

The synthesis of a triad consisting of porphyrin and hexabenzocoronene (HBC) units, which are connected via a central hexaarylbenzene (HAB) core, is presented. The ortho substitution pattern at the core results in a close proximity of the two chromophores, which influences their properties such as the intensity ratio of UV-vis absorption bands.

Comparison of gold nanoparticles biosynthesized by cell-free extracts of Labrys, Trichosporon montevideense, and Aspergillus.

Biosynthesis of gold nanoparticles (AuNPs) by microbes has received much attention as an efficient and eco-friendly process. However, the characteristics of AuNPs biosynthesized by different microbial cell-free extracts are rarely comparatively studied. In this study, three locally isolated strains, i.e., bacteria Labrys sp. WJW, yeast Trichosporon montevideense WIN, and filamentous fungus Aspergillus sp. WL-Au, were selected for AuNPs biosynthesis. UV-Vis absorption bands at 538, 539, and 543nm confirmed the formation of AuNPs by these strains. Transmission electron microscopy and selected area electron diffraction analyses revealed that the as-synthesized AuNPs were crystalline with spherical or pseudo-spherical shapes. However, the average sizes of these AuNPs were diverse, which were 18.8, 22.2 and 9.5nm, respectively. The biomolecules involved in nanoparticles stabilization were demonstrated by Fourier transform infrared spectroscopy analysis. Four common functional groups such as -N-H, -C=C, -N=O, and -S=O groups were detected in these AuNPs, while a distinct -C=O group was involved in WL-Au-AuNPs. The catalytic rate of WL-Au-AuNPs toward 4-nitrophenol reduction (0.37min-1) was much higher than those of others (WJW-AuNPs 0.27min-1 and WIN-AuNPs 0.23min-1). This research would provide useful information for exploring efficient microbial candidates to synthesize AuNPs with excellent performances.

Microencapsulation of Three-Component Thermochromic System for Reversible Color Change and Thermal Energy Storage

In this study, poly(methyl methacrylate)/thermochromic system (PMMA/TS) and poly(methyl methacrylate-comethacrylic acid)/thermochromic system (P(MMA-co-MA)/TS) microcapsules were prepared by using emulsion polymerization method. The thermochromic system was consisting of crystal violet lactone (CVL) as a leuco dye, bisphenol-A (BPA) as a color developer, and 1-tetradecanol (TD) as a solvent. Microcapsules with different ratio of core/shell were synthesized to examine the effect of core/shell ratio on the properties of microcapsules. Phase transition temperatures and enthalpies, morphology, and particle size distributions of the microcapsules were analyzed using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and particle size analyzer instruments, respectively. FT-IR spectroscopy was used to prove the presence of the thermochromic system in the microcapsules. UV-Vis absorption bands of the thermochromic system (TS) and microencapsulated thermochromic system (MTS) at both below and above the melting temperature of the solvent were obtained by using a UV-Vis spectrophotometer. The visible color change depending on temperature was monitored for each microcapsule individually by using a digital camera. Spherical morphology and unimodal particle size distribution of the microcapsules were determined by means of SEM photographs and particle size distribution curve analysis. The mean particle sizes of the produced microcapsules varied in a range of 16.0-35.2 μm. The digital camera photographs and the UV-Vis absorbance curves proved that color changed between dark blue and light blue depending upon the temperature change. Meanwhile, the produced microcapsules were proven for an excellent heat storage capacity for thermal energy storage owing to phase changing of the tetradecanol solvent used in the thermochromic system. The melting enthalpy of the microcapsules ranged from 145.5 J/g to 193.4 J/g.

Zinc and copper complexes of stilbene iminopyridine ligands with η2-Olefin binding mode

Two stilbene based iminopyridine ligands (L1-L2) synthesized by a condensation reaction between N,N-Dimethyl-4,4′-azodianiline and 2-pyridinecarboxaldehyde or 2,6-pyridinedicarboxaldehyde, with 73% and 65% yield, are described. The two ligands have been characterized by elemental analysis and spectroscopic techniques. The complexation of ligand L1 with ZnCl2 afforded neutral tetrahedral zinc(II) metal complex C1 formulated as [ZnL1Cl2] with a 2D supramolecular architecture reinforced by π···π stacking and hydrogen bonding in the solid state. Interestingly in the case of copper(I) complex C2, ligand L1 acts as a ditopic ligand since it coordinates one Cu(I) with an iminopyridyl fragment and a second metal center with an η2-olefin binding mode giving rise to a 1D-polymeric structure. The coordination sphere is completed with an acetonitrile solvent molecule leading to a distorted tetrahedral geometry around copper cation and the resulting coordination polymer can be formulated as {[Cu(L1)2CH3CN]BF4}. In addition complexation of L2 with zinc chloride afforded complex C3 formulated as [ZnL2Cl2]. DFT and TDDFT computations permitted to investigate the frontier MOs of all species and to assign their UV–visible absorption bands.

SERS-active multi-channel fluorescent probe for NO: Guide to discriminate intracellular biothiols

We explored a rational design and synthesis of a Raman-active small molecular fluorescent probe (S1/Int-1) to acquire multicolor fluorescence-images based on intracellular nitric oxide (NO) in cancer cells. A new UV–vis absorption band centered at λab 510 nm for S1 was appeared in the presence of NO. Similarly, with increasing concentration of NO, the emission signal centered at 527 nm increased gradually. The probe S1 reacted with NO to form benzotriazole derivative Int-1 which showed characteristic intense Raman band centered at 1440 cm-1 for NN-. Individually, GSH and Cys reacted with Int-1 to offer a pair of new fluorophore 2 and 3 with different emission band centered at λem = 482 nm and λem = 453 nm respectively. Furthermore, the non-toxic probe S1 facilitated the monitoring of intracellular NO based dual colored imaging in the green and blue channel which intern allowed differentiating the intracellular GSH and Cys levels. Moreover, its cellular “off-on-off” response in the SERS spectral mode indicates that S1 can be a noninvasive tool to detect endogenous NO, GSH/Cys. Therefore, probe (S1/Int-1) could allow us monitoring of intracellular NO formation through dual channel fluorescence imaging with synchronous discrimination of thiols.

Influence of annealing temperature on the structural and optical properties of nanocrystalline zirconium oxide

Nanocrystalline zirconium oxide powder was prepared by sol-gel method using zirconyl chloride octahydrate (ZrOCl2·8H2O) and ethylenediaminetetraacitic acid (EDTA) in ammonium hydroxide (NH4OH) solution. The as-synthesized complex product was annealed at 650°C, 750°C and 850°C for 2h to get fine ZrO2 powder. These samples were further analyzed by Scanning electron microscopy (SEM), X- ray diffraction (XRD), Energy-dispersive X- ray spectroscopy (EDX), UV-vis analysis, Fourier transform infrared (FT-IR) spectroscopy, Photoluminescence spectroscopy (PL) and Raman Spectroscopy to study their structural and optical properties. The structural studies revealed that nanocrystalline ZrO2 powder exhibits monoclinic phase with variation in crystallite size with annealing temperature. The UV–vis absorption band edge of ZrO2 decreases from 514nm to 451nm as annealing temperature rises from 650°C to 750°C. It seems that the drastic reduction in band gap energy may be one of the novel unexpected characteristics of ZrO2. The FTIR analyses further confirmed the formation of nanocrystalline monoclinic ZrO2. PL analysis revealed the novel emission peaks at 305 and 565nm. The Raman spectroscopy confirmed the transformation of amorphous zirconium hydroxide to m-ZrO2 with increase in temperature from 650°C to 850°C.

Synthesis, vibrational and UV–visible studies of sodium cadmium orthophosphate

In this paper, NaCdPO4 orthophosphate was prepared by solid-state reaction technique at high temperature. Structural, vibrational and optical properties have been investigated. X-ray powder diffraction analysis revealed that the titled compound crystallizes in the orthorhombic system with Pmnb space group. Vibrational study by means of Raman and FTIR spectroscopies confirms the existence of the (PO4)3− functional group. Optical properties were recorded at room temperature using UV–visible spectroscopy in the spectral range (200–800) nm. The UV–Vis absorption bands are attributed to the charge transfer from the oxygen ligands to the central phosphate atom inside the PO4 3− groups. The optical absorbance was measured also to determinate the optical band gap using Kubelka–Munk function. The dispersion parameters (E0 and Ed) of this compound were estimated using the Wemple Di-Domenico model.

Interpretation of Raman Spectra of Oxide Materials: The Relevance of Absorption Effects

When using Raman spectra for structural characterization of solid powder materials such as catalysts, the interpretation needs to take into account the possible absorption of radiation. For example, the reduction of oxide materials may result in new UV–vis absorption bands and therefore affect the Raman intensity. In resonance Raman spectroscopy, the absorption correction of Raman intensity based on the Kubelka–Munk theory is widely established. In contrast, in Raman spectroscopy, typically no absorption correction or normalization by a phonon mode is applied. Using a combined approach of Raman and UV–vis spectroscopy, this study examines the effect of absorption on Raman spectra as well as the usefulness of different absorption corrections for Raman spectroscopy. The results show that a change in absorption of about 10% may result in a decrease in Raman intensity of up to one-third. Corrections based on the Kubelka–Munk theory predict large intensity changes for small changes in the low-absorption region...

Synthesis and characterization of stable electrochromic polyimides with quinolin-8-yloxy-substituted triphenylamine units

Herein, three kinds of electrochromic aromatic polyimides (PIs) were synthesized from 4,4′-diamino-4″-(quinolin-8-yloxy) triphenylamine (DAQTPA) with different dianhydrides, respectively. These PIs showed good thermostability below 450°C even in air atmosphere. The maximum UV–vis absorption bands of PIs located at 321–338nm for solid films. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of the PIs were calculated from the cyclic voltammetry (CV) test as −5.42 to −5.44eV and −3.53 to −3.85eV, respectively. These PIs performed stable reversible electrochromic properties with optical transmittance change (ΔT) around 28–43% and coloration efficiency (η) around 74–117cm2C−1.

Synthesis and optoelectronic properties of new polyarylates with 2-naphthyldiphenylamine units

Herein, five kinds of soluble electrochromic polyarylates were synthesized from the reaction of N,N'-bis(4-carboxyphenyl)-N,N'-di-2-naphthyl-1,4-phenylenediamine with five bisphenols via direct polycondensation process, respectively. These new materials showed no significant decomposition below 400°C in nitrogen atmosphere. The maximum UV–vis absorption bands of these polyarylates located at 328–348nm and 327–353nm for solid films and DMSO solution, respectively. The polyarylate 6a, as an example, exhibited not only aggregation-induced emission (AIE) effect in different fraction tetrahydrofuran/water solution, but also solvatochromism in various polar solvents, markedly. Two reversible pairs of distinct redox peaks were associated with noticeable color changed from original colorless to yellowish orange and green for polymeric film could be observed in the cyclic voltammetry (CV) test. New absorption peaks emerged in near–infrared (NIR) region with increasing voltage in the UV–vis spectra, which indicates these polyarylates can be used as NIR electrochromic materials. These polyarylates performed high contrast of optical transmittance change around 42–53% with the highest coloration efficiency up to 236cm2C−1.