Shift In Absorption Spectra Research Articles

Copigmentation Effect of Some Phenolic Acids on Stabilization of Roselle (Hibiscus sabdariffa) Anthocyanin Extract

The present study aimed at utilization of copigmentation phenomenon to increase the stability of anthocyanin in roselle extract during storage at 10°C for 60 days by the addition of some phenolic acids (ferulic, cinnamic and coumaric) as a copigments and investigate the possibility of using copigmented extracts as a natural food colorants instead of harmful synthetic ones. The data obtained confirmed that addition of the aforementioned phenolic acids to roselle anthocyanin extracts resulted in an increment of anthocyanin and color stability during storage comparing with the control extract. At the end of storage period, the reduction in anthocyanin content were 31.53, 20.48, 9.31 and 5.52% for control and extracts copigmented with ferulic, cinnamic coumaric acids respectively. Addition of phenolic acids to roselle extract also attributed to a hyperchromic effect and bathochromic shift in visible absorption spectra of copigmented extracts compared to the control. Roselle anthocyanin extracts treated with phenolic acids showed a noticeable antioxidant and antimicrobial activities compared with control extract. Marshmallow prepared from studied copigmented roselle extracts as a natural colorants was highly accepted by panelists.

P-Sulfonatocalix[8]arene and vitamin C complexation: assessment of photophysical, pKa and antioxidant property

Mode of inclusion complexation of p-sulfonatocalix[8]arene and ascorbic acid in aqueous solution has been investigated in acidic pH based by UV–visible, fluorescence, FT-IR, 1H-NMR and HR-MS spectroscopic studies. Addition of ascorbic acid solution to p-sulfonatocalix[8]arene enhances the fluorescence intensity of p-Sulfonatocalix[8]arene with blue shift in absorption spectra. Hypsochromic shift in absorbance maxima and hyperchromic shift in emission maxima indicates that ascorbic acid experiences less polar microenvironment when bind with SCX8. Binding site and stoichiometry are examined by 1H-NMR and HR-MS techniques. Binding constant (K = 0.42 × 102 M−1) for the inclusion complex is calculated. For complexation, forces like electrostatic attraction, hydrogen bonding and hydrophobic environment of p-sulfonatocalix[8]arene cavity play important role. p-sulfonatocalix[8]arene shows upward pKa shift after binding with Ascorbic acid. The antioxidant property of ascorbic acid has been investigated which shows enhancement by 57% upon complexation with p-sulfonatocalix[8]arene.

A convenient colorimetric and ratiometric fluorescent probe for detection of cyanide based on BODIPY derivative in aqueous media

A convenient colorimetric and ratiometric fluorescent probe based on BODIPY derivative for cyanide detection has been synthesized, whose structural contains a dicyanovinyl group used as a sensing unit. Among the tested analytes, such as CN−, F−, Cl−, Br−, I−, ClO4−, AcO−, NO3−, H2PO4− HSO4−, S2− and N3−, only CN− could react with dicyanovinyl moiety by nucleophilic addition, which disrupted the π-conjugation of the probe and hindered the intramolecular charge transfer (ICT), leading a blue shift of absorption and fluorescence spectrum and a concomitant color change from yellow to light pink. The detection limit of this probe was calculated to be 0.98 μM, which is lower than the maximum concentration in drinking water (1.9 μM) permitted by the World Health Organization (WHO). Moreover, the probe showed excellent selectivity and anti-interference ability towards CN− over other anions. The reaction mechanism was fully supported by 1H NMR and MS spectrum.

Spectroscopic properties of diketopyrrolopyrrole derivatives with long alkyl chains

The diketopyrrolopyrrole derivatives with long alkyl chains were synthesised and spectrally characterised. Experimental spectroscopic techniques were supplemented by the DFT calculations of equilibrium geometries, normal mode frequencies and time-dependent DFT simulated UV–vis spectra. Comparison between the symmetrical and unsymmetrical substitution of alkyl chains resulted in some changes like bathochromic shift of absorption, excitation and emission spectra, significant reduction of molar absorption coefficient in UV–vis range, increase of fluorescence quantum yield, and slight increase of fluorescence lifetimes. The influence of the length of the alkyl chain on the properties of material was also discussed. The experimental spectroscopic data together with the calculated results show that presence of the alkyl substituent at the nitrogen atom influences more on the properties of the investigated DPPs than the length of attached chain.

Structural explanation of the spectral features of the nonsymmetrical complex {2,3,7,8,12,13,17,18-octaethyl-5-[(methylimino)methyl]porphyrinato-κ4N21,N22,N23,N24}palladium(II).

The features of porphyrins defining their functionality are related to their conformational flexibility. The degree of nonplanarity of metalloporphyrins depends directly on the number of substituents, their size and their location. The introduction of substituents in the meso positions of β-substituted porphyrins increases the steric interaction and leads to distortions of the porphyrin core. Increasing the distortion of the porphyrin core would augment the bathochromic (red) shift of the electronic absorption spectra. A new nonsymmetrical 2,3,7,8,12,13,17,18-octaethyl-5-[(methylimino)methyl]porphyrin complex of palladium(II), [Pd(C38H47N5)], was synthesized and characterized by NMR, mass spectrometry and X-ray analysis. The features of the electronic absorption spectrum of the synthesized complex are explained by the planarity of the porphyrin core and the π-system of the imino group orthogonal to it.

The study of metal binding properties and electronic transitions of dithienopyrole derivatives

Fluorescence chromophore (L) based on dithienopyrole derivatives (DPT) have been compared the binding site for detecting metal ions. There are consisting of methacryloyl amine (L1) and cyanoacrylic acid (L2) acceptor, respectively. Corresponding molecular geometries, orbital energies, electron contributions and absorption properties of the fluorescence sensor were investigated by using density functional theory (DFT) with B3LYP method of calculation. The DFT based studies with various solvation and absorption spectra were performed using time-dependent density functional theory (TD-DFT) with the polarized continuum model. Comparing with L2, the experimental L1 shows a red shift both absorption and emission spectra at 350 and 485 nm, respectively. The solvent environment exhibited slight shift in experimental and calculated absorption. An effect of various metal ions on absorption behavior was studied. Results indicate that the L1 and L2 exhibit excellent sensitivity for Pb2+ ion. The binding complex M-L1 and M-L2 (M: Cd, Cu, Hg, Pb, Zn) exhibited Pb<Cu<Zn<Mn<Cd<Hg.

Cyanidin-Based Novel Organic Sensitizer for Efficient Dye-Sensitized Solar Cells: DFT/TDDFT Study

Cyanidin is widely considered as a potential natural sensitizer in dye-sensitized solar cells due to its promising electron-donating and electron-accepting abilities and cheap availability. We consider modifications of cyanidin structure in order to obtain broader UV-Vis absorption and hence to achieve better performance in DSSC. The modified molecule consists of cyanidin and the benzothiadiazolylbenzoic acid group, where the benzothiadiazolylbenzoic acid group is attached to the cyanidin molecule by replacing one hydroxyl group. The resulting structure was then computationally simulated by using the Spartan’10 software package. The molecular geometries, electronic structures, absorption spectra, and electron injections of the newly designed organic sensitizer were investigated in this work through density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations using the Gaussian’09W software package. Furthermore, TDDFT computational calculations were performed on cyanadin and benzothiadiazolylbenzoic acid separately, as reference. The computational studies on the new sensitizer have shown a reduced HOMO-LUMO gap; bathochromic and hyperchromic shifts of absorption spectra range up to near-infrared region revealing its enhanced ability to sensitize DSSCs.

IR surface polariton spectroscopy as a method for studying the optical properties of ultra thin films

Experimental results of investigation of optical properties of MgO thin films (thickness 10, 30, 100 и 300 nm) and AlN films (thickness 40 и 400 nm) on sapphire substrate are discussed. The optical phonon frequencies of these films are located in frequency region of surface polariton of sapphire. Due to the resonance between them the splitting and the shift of absorption spectra of sapphire surface polariton appear. From these experimental data it is possible to reconstruct all constants of the permittivity of both the film and substrate, the film thickness, and to specify its structure.

BODIPY associates in organic matrices: Spectral properties, photostability and evaluation as OLED emitters

In the present study four BODIPY (boron dipyrromethene: 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes with π-extended substituents in C-8 position were investigated in solvents and polymer mediums. High aggregation degree was observed for the dyes in the solid state. Association and twisted intramolecular charge transfer processes were found to affect the spectral properties of the compounds causing bathochromic shifts in absorption and fluorescence spectra. The extension of substituent π-conjugation gains molecular association evoked presumably by π-π interaction between the substituents of the adjacent molecules. Photostability of the complexes in different forms was analyzed and the distorted form stabilized by polymer matrix was found to be the most stable. The substituent nature did not affect strongly the photostability of dyes. Displacement of monomer-associate equilibrium in hybrid materials with polymethylmethacrylate and poly(9-vinylcarbazole) was exploited for tuning spectral characteristics of the materials. Two dyes readily forming aggregates at the lowest concentrations were applied for the fabrication of organic light-emitting diodes. The fabricated devices exhibited electroluminescence in the appropriate spectral ranges with moderate efficiency.

Role of Ni2+ Ions in Magnetite Nano-particles Synthesized by Co-precipitation Method

In the present work, nickel-doped iron oxide (NixFe3−x O 4) nanoparticles with different concentration of nickel (x = 0, 0.05, 0.1, and 0.15) have been prepared by co-precipitation method. These prepared nanoparticles have been characterized by using x-ray diffractometer, thermo gravimetric analysis and differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, vibrating sample magnetometer, and UV-Visible spectroscopy to study their structural, thermal, morphological, magnetic, and optical properties, respectively. The x-ray diffraction confirms the formation of single-phase inverse spinel cubic structure of NiFe3 O 4 nanoparticles. Crystallite size has been estimated by the full width at half maximum of the most intense x-ray diffraction peak where vibrational and stretching modes of metal-oxygen bonds in 872 cm are shown in Fourier transform infrared spectra which confirms the formation of nanoparticles. The thermal analysis revealed that the transition temperature and stability increases with increasing Ni concentration. The surface morphology indicated that the particles are spherical in shape with some agglomeration. The magnetic measurement revealed that the coercivity and anisotropy increases with nickel doping in magnetite nanoparticles. The optical analysis revealed that direct and indirect both types of band gap increases when the particle size decreases because the absorption spectra shift toward smaller wavelength. The blue shift confirms the formation of nanoparticles.

Studies on optical properties of Si220 nanoclusters via time-dependent density functional theory calculations

The optical properties of bare and hydrogen passivated Si220 nanoclusters(NCs) in four typical motifs(i.e., bulk-like, onion-like, bucky-diamond and icosahedral motifs) were studied via time-dependent density functional theory(TD-DFT) calculations. The calculation results show that there is a significant blue shift in the optical absorption spectra when the Si NCs are passivated with hydrogen. A strong absorption peak in the visible light region appears for the hydrogenated bulk-like, onion-like and bucky-diamond Si NCs.

Two indole chalcone derivatives as chemosensor for cyanide anions

Two bromine substituted indole chalcone derivatives were synthesized via typical condensation reaction between 2-(hydroxyl)-4-bromine acetophenone and 3-indolealdehyde (1) or N-ethyl-3-indolealdehyde (2) in good yields. Their recognition properties for cyanide anions were investigated. The results indicate that the compounds exhibit quick and obvious color and fluorescence turn-on changes to cyanide anions with color changes from yellow to red (1) or from light yellow to deep yellow (2). Mechanism studies suggest that hydrogen bonding reaction between cyanide anions and NH moiety of compound 1 occurs, which leads to the red shift of absorption spectra and the deepening of color. To compound 2, bonding mechanism is typical Michael reaction mechanism.

Influence of ligand donor-acceptor properties on the structure, optical, and electrochemical characteristics of Ir(III) complexes with cyclometallated 2-phenylbenzotiazole

The cis-C,C-structure of a series of cyclometallated Ir(III) complexes with 2-phenylbenzotiazole was determined by the methods of X-ray diffraction (XRD) analysis, 1H, 13C, 31P NMR, and IR spectroscopy. Long-wave absorption bands, phosphorescence, and processes of electrochemical oxidation and reduction of the complexes were assigned to the transfer of electrons presumably located on dπ and π* orbitals of cyclometallated 2-phenylbenzotiazole. The decrease in donor and acceptor properties of the ligands leads to the blue shift of absorption spectra and phosphorescence and to the anodic shift of oxidation and reduction potentials of the complexes.

Pictet–Spengler Synthesis of Quinoline‐Fused Porphyrins and Phenanthroline‐Fused Diporphyrins

AbstractDoubly and quadruply quinoline‐fused porphyrins were effectively synthesized through a reaction sequence consisting of Suzuki–Miyaura coupling of β‐borylated porphyrins with 2‐iodoaniline and subsequent Pictet–Spengler cyclization. These quinoline‐fused porphyrins display red‐shifted absorption bands and higher electron‐accepting abilities. This synthetic protocol also allowed the synthesis of phenanthroline‐fused porphyrin dimers, which bound either a NiII or ZnII cation. The resultant metal complexes displayed further red shifted absorption spectra and molecular twists to effect an almost perpendicular arrangement of the two porphyrins.

Pictet-Spengler Synthesis of Quinoline-Fused Porphyrins and Phenanthroline-Fused Diporphyrins.

Doubly and quadruply quinoline-fused porphyrins were effectively synthesized through a reaction sequence consisting of Suzuki-Miyaura coupling of β-borylated porphyrins with 2-iodoaniline and subsequent Pictet-Spengler cyclization. These quinoline-fused porphyrins display red-shifted absorption bands and higher electron-accepting abilities. This synthetic protocol also allowed the synthesis of phenanthroline-fused porphyrin dimers, which bound either a NiII or ZnII cation. The resultant metal complexes displayed further red shifted absorption spectra and molecular twists to effect an almost perpendicular arrangement of the two porphyrins.

The effects of polyvinylpyrrolidone and thermal annealing on red shifts for absorption spectra of the nanoparticle Au/TiO2 thin film with different Au ratios

Plasmonic solar cell efficiency strongly depends on parameters of Au/TiO2 nanoparticles (NPs) embedded system including Au sizes, distribution, aggregation, and dielectric environment—polymer encapsulated around Au/TiO2 NPs. This paper briefly outlines the technological developments for preparation of the nanoparticles Au/TiO2 solutions with different Au ratios, in presence of 200, 500 mg PVP and in absence of polyvinylpyrrolidone (PVP). After that from the obtained solutions, the Au/TiO2 thin films are prepared by spin coating method aiming to get different Au nanoparticles (Au NPs) sizes with uniform dispersion. The next step, the Au/TiO2 thin films samples have been annealed at different temperatures, the absorption spectra of the different Au/TiO2 NPs thin films are investigated using the UV–Vis spectroscopy techniques. The obtained experiment results show that the absorption spectra in the case of not thermal annealing is blue shift meanwhile in the case of thermal annealing, the absorption spectra are red shifted, enhanced depending on the annealing temperatures, Au sizes, ratios and PVP amounts. The enhancement and red shifts of absorption spectra for each case of Au/TiO2 NPs thin films have been discussed and explained by interaction between PVP and Au NPs features at different annealing temperatures.

Influence of structural and solvation factors on the spectral-fluorescent properties of alkyl-substituted BODIPYs in solutions

The spectral-fluorescent properties of alkyl-substituted BODIPYs 1–5 in organic solvents were investigated. The alkyl-substituted BODIPYs 1–5 exhibit intense chromophoric properties (lgε=4.60–5.00). Relative fluorescence quantum yield of studied compounds reaches 66–100% and weakly dependent on the structural and solvation effects. Introduction of methyl, propyl, amyl and heptyl substituents in the 2,6-positions of the pyrroles the results in a significant red shift (22–29nm) in the electronic absorption and fluorescence spectra.

Density functional theory studies on the structural and physical properties of Cu-doped anatase TiO2(101) surface

Structure and physical properties of anatase TiO2 (101) surface doped with copper have been studied by using density functional theory. Results show that Cu@Ti and Cu@O systems behave as p and n type semiconductors, respectively. Anatase TiO2 (101) surface exhibits a blue shift in optical absorption spectra compared with pure TiO2 bulk materials. Enhanced photocatalytic activity at wavelength around 400nm could be contributed by the change in electronic structure.

Electronic and optical properties of beryllium sulfide monolayer: Under stress and strain conditions

Electronic and optical properties of two-dimensional graphene-like structure of beryllium sulfide (BeS) have been studied in the framework of the density functional theory. Different values of stress and strain are exerted for tuning electronic and optical parameters. The electronic results show that both biaxial stress and strain effects cause band gap reduction with different rates. Also, we have red and blue shifts in the optical absorption spectrum peaks by applying strain and stress, respectively. Our results express that BeS monolayer can be the promising candidate for the future nano-devices.

Spectroscopic and laser properties of bulk iron doped zinc magnesium selenide Fe:ZnMgSe generating at 4.5 - 5.1 µm.

The Fe:Zn(1-x)Mg(x)Se (x = 0.19, 0.27, and 0.38) solid solutions spectroscopic properties were investigated and laser oscillations were achieved for the first time. The increase of the magnesium concentration in the Fe:ZnMgSe crystal was shown to result in an almost similar long wavelength shift of both absorption and fluorescence spectra of about 60 nm per each 10% of magnesium. With the Fe:ZnMgSe crystal temperature decrease, the fluorescence spectrum maximum shifts towards shorter wavelength resulting mainly from strong narrowing of the longest wavelength fluorescence line. Laser radiation wavelength dependence on the magnesium concentration as well as on temperature was observed. The Fe:ZnMgSe x = 0.38 laser oscillation wavelength increased from 4780 nm at 80 K to 4920 nm at 240 K using the optical resonator without any intracavity spectrally-selective element. In comparison with the Fe:ZnSe laser operating in similar conditions, these wavelengths at both temperatures were shifted by about 500 nm towards mid-IR region.