near-IR Absorption Spectra Research Articles

Anharmonic Aspects in Vibrational Circular Dichroism Spectra from 900 to 9000 cm-1 for Methyloxirane and Methylthiirane.

Vibrational circular dichroism (VCD) spectra and the corresponding IR spectra of the chiral isomers of methyloxirane and of methylthiirane have been reinvestigated, both experimentally and theoretically, with particular attention to accounting for anharmonic corrections, as calculated by the GVPT2 approach. De novo recorded VCD spectra in the near IR (NIR) range regarding CH-stretching overtone transitions, together with the corresponding NIR absorption spectra, were also considered and accounted for, both with the GVPT2 and with the local mode approaches. Comparison of the two methods has permitted us to better describe the nature of active “anharmonic” modes in the two molecules and the role of mechanical and electrical anharmonicity in determining the intensities of VCD and IR/NIR data. Finally, two nonstandard IR/NIR regions have been investigated: the first one about ≈2000 cm–1, involving mostly two-quanta bending mode transitions, the second one between 7000 and 7500 cm–1 involving three-quanta transitions containing CH-stretching overtones and HCC/HCH bending modes.

Development of neodymium (III) ions doped sodium fluoro-borate glass composite materials and study of the laser emission

Neodymium (III) ions doped sodium fluoro-borate (BCNF) glass materials have been prepared by the melt quenching method and Fourier transform infrared (FTIR) method was intended for the identification of the functional groups present in the BCNF host glass. X-ray diffraction (XRD) analysis is used for the study of structural details of the prepared glass composite materials. In order to study the spectroscopic properties of fabricated glasses, absorption, emission and decay measurements has been performed. Additionally, the spectroscopic properties of Nd3+ ions were analyzed using Judd-Ofelt theory. UV–Vis and Near-IR absorption spectra of glass composite samples reveal eleven significant peaks. Under the excitation of 808 nm laser diode, three near-IR emission bands are at around 876 nm, 1058 nm and 1331 nm from 4F3/2 → 4I9/2, 4I11/2 and 4I13/2 radiative transitions, respectively, were observed in the Nd3+ ions doped glass composite material. The lifetimes of this transition has been experimentally determined through decay profile studies. For all Nd3+ ion concentrations, the decay time curves of the 4F3/2 level were essentially single exponential.

Sandwich double-decker Er(iii) and Yb(iii) complexes containing naphthalocyanine moiety: synthesis and investigation of the effect of a paramagnetic metal center.

Novel heteroleptic Er(iii) and Yb(iii) naphthalocyaninato-phthalocyaninates containing an octa-phenyl or octa-phenoxysubstituted naphthalocyanine deck were synthesised and identified by 1H NMR, EPR and high resolution MALDI-TOF/TOF mass spectrometry. Direct synthesis of novel homoleptic Yb(iii) bis (octa-phenylnaphthalocyaninate) was carried out. Downfield lanthanide induced shifts of the aromatic protons in target compounds were observed compared with the corresponding diamagnetic Lu(iii) complexes. In the near-IR absorption spectra, an increase in ionic radius from Lu(iii) to Er(iii) resulted in a bathochromic shift of the intervalence band up to 1473 nm. This work presents the first experimental EPR study of Yb(iii) bis naphthalocyaninate, where a set of magnetic parameters and properties (including spin, magnitude and sign of magnetic anisotropy parameter D, increased splitting in a crystal field, ferromagnetic f-π interaction etc.) were determined and interpreted by both EPR and SQUID techniques and supported by theoretical considerations.

Chameleon diamonds: Thermal processes governing luminescence and a model for the color change

To date, the eponymous color-changing behavior of chameleon diamonds lacks an explanation in terms of an identified diamond defect structure or process. Well known, however, is that this color-change is driven by the influence of both light and heat. In this paper, we present observations of how luminescence emission in chameleon diamonds responds to temperature changes and optical pumping. Fluorescence, phosphorescence, and thermoluminescence experiments on a suite of natural chameleon diamonds reveal that a specific emission band, peaking near 550nm, may be stimulated by several different mechanisms. We have observed thermal quenching of the 550nm emission band with an activation energy of 0.135eV. The 550nm band is also observed in phosphorescence and thermoluminescence. Thermoluminescence spectra suggest the presence of low lying acceptor states at 0.7eV above the valence band. When excited with 270nm light, we observe emission of light in two broad spectral bands peaking at 500 and 550nm. We suggest that the 550nm emission band results from donor—acceptor pair recombination (DAPR) from low lying acceptor states at ca. 0.7eV above the valence band and donor states approximately 2.5 to 2.7eV above the valence band. We do not identify the structure of these defects. We propose a speculative model of the physics of the color change from ‘yellow’ to ‘green’ which results from increased broad-band optical absorption in the near-IR to visible due to transitions from the valence band into un-ionized acceptor states available in the ‘green’ state of the chameleon diamond. We report near-IR absorption spectra confirming the increased absorption of light in the near-IR to visible in the ‘green’ when compared to the ‘yellow’ state with a threshold at ca. 0.65eV, supporting the proposed model.

Homoleptic nickel(II) complexes of redox-tunable pincer-type ligands.

Different synthetic methods have been developed to prepare eight new redox-active pincer-type ligands, H(X,Y), that have pyrazol-1-yl flanking donors attached to an ortho-position of each ring of a diarylamine anchor and that have different groups, X and Y, at the para-aryl positions. Together with four previously known H(X,Y) ligands, a series of 12 Ni(X,Y)2 complexes were prepared in high yields by a simple one-pot reaction. Six of the 12 derivatives were characterized by single-crystal X-ray diffraction, which showed tetragonally distorted hexacoordinate nickel(II) centers. The nickel(II) complexes exhibit two quasi-reversible one-electron oxidation waves in their cyclic voltammograms, with half-wave potentials that varied over a remarkable 700 mV range with the average of the Hammett σ(p) parameters of the para-aryl X, Y groups. The one- and two-electron oxidized derivatives [Ni(Me,Me)2](BF4)n (n = 1, 2) were prepared synthetically, were characterized by X-band EPR, electronic spectroscopy, and single-crystal X-ray diffraction (for n = 2), and were studied computationally by DFT methods. The dioxidized complex, [Ni(Me,Me)2](BF4)2, is an S = 2 species, with nickel(II) bound to two ligand radicals. The mono-oxidized complex [Ni(Me,Me)2](BF4), prepared by comproportionation, is best described as nickel(II) with one ligand centered radical. Neither the mono- nor the dioxidized derivative shows any substantial electronic coupling between the metal and their bound ligand radicals because of the orthogonal nature of their magnetic orbitals. On the other hand, weak electronic communication occurs between ligands in the mono-oxidized complex as evident from the intervalence charge transfer (IVCT) transition found in the near-IR absorption spectrum. Band shape analysis of the IVCT transition allowed comparisons of the strength of the electronic interaction with that in the related, previously known, Robin-Day class II mixed valence complex, [Ga(Me,Me)2](2+).

Quantitative Analysis of Complex Formation in Acetone−Chloroform and Ethyl Acetate−Cyclohexane Solutions

The actual binary (double) solutions of “acetone–chloroform” and “ethyl acetate–cyclohexane” are simulated as ideal multi-component (triple, quadruple) mixtures, which consist of associates [Ap], [Bq], and complexes [AnBm]. The MCR-ALS method is used for the analysis of near-IR absorption spectra. Complexes of a single type [A1B1] are determined in an acetone–chloroform solution, and complexes of two types, [X1Y1] and [X5Y1], are determined in an ethyl acetate–cyclohexane solution. An auxiliary method for determining the number of complexes by analyzing the residual intensity in the IR spectra is proposed. Information about the number of complexes in solutions obtained by analyzing the residual intensity correlates with the MCR-ALS data. It is used for the interpretation of the formation of complexes in binary solutions.

Picosecond Pulse Radiolysis of the Liquid Diethyl Carbonate

The diethyl carbonate, DEC, is an ester that is used as a solvent in Li-ion batteries, but its behavior under ionizing radiation was unknown. The transient optical absorption spectra, the decay kinetics, and the influence of various scavengers have been studied by using the picosecond laser-triggered electron accelerator ELYSE. In neat DEC, the intense near-IR (NIR) absorption spectrum is assigned to the solvated electron. It is overlapped in the visible range by another transient but longer-lived and less intense band that is assigned to the oxidized radical DEC(-H). The solvated electron molar absorption coefficients and radiolytic yield evolution from 25 ps, the geminate recombination kinetics, and the rate constants of electron transfer reactions to scavengers are determined. The radiolytic mechanism, indicating a certain radioresistance of DEC, is compared with that for other solvents.

Dual Fluorescence of Graphene Oxide: A Time-Resolved Study

The fluorescence properties of graphene oxide (GO) was studied by recording the fluorescence lifetime, fluorescence emission, and excitation spectra, as well as UV-visible and near-IR absorption spectra. For the first time, we showed that a blue band (ca. 440 nm) and a long wavelength (LW) band (ca. 700 nm) are coexistent, which can be recorded simultaneously by controlling concentration, excitation wavelength, and pH values. Two bands are closely related by the protonation or deprotonation of GO. The blue band is favored by low GO concentration, short excitation wavelength, and high pH value, while the LW band is favored by low pH and long excitation wavelength. To reveal the nature of the dual emission of GO, the fluorescence lifetimes under various conditions were also measured. The blue band contains three emitting components; one of them has a lifetime as long as 10 ns, and its emitting intensity is fairly sensitive to pH, showing the potential for applications in sensing H(+) and fluorescence lifetime imaging. Combining the results under various conditions, we conclude that the electronic transition for this component is very likely due to n-π* transition. The LW band contains two main emitting components (0.2 and 2.1 ns) that also appear in the blue band as minor contributors; the related emission is assigned to π-π* transition. In summary, GO emission is of broadband (300-1250 nm), long-lived, pH sensitive, and excitation wavelength dependent. This makes it easily tailored for versatile applications.

Direct Calculations of Mid- and Near-IR Absorption and Circular Dichroism Spectra of Chiral Molecules Using QM/MM Molecular Dynamics Simulation Method

The infrared (IR) and vibrational circular dichroism (VCD) spectra of (1S)-(-)-β-pinene in the mid- and near- IR frequency regions are numerically simulated by using a time-correlation function theory and mixed quantum/classical simulation method. Anharmonic vibrational dynamics and fluctuating atomic partial charges of the chiral pinene were obtained by carrying out quantum mechanical/molecular mechanical (QM/MM) molecular dynamics (MD) simulations. Thus obtained time-correlation functions of electric and magnetic dipole moments are used to calculate the IR absorption and VCD spectra, and they are directly compared with experimental results. Not only the fundamental transition bands but also first overtone and combination bands in the near-IR frequency region are successfully simulated. It is shown that the polarizable nature of the solute is particularly important in quantitatively reproducing the near-IR spectra, whereas such polarization effects on dipole and rotational strengths of lower-frequency and large-amplitude vibrations are less critical. We anticipate that the present QM/MM MD method in combination with mixed quantum/classical time-correlation function theory to calculate both mid- and near-IR absorption and VCD spectra will be of critical use in interpreting vibrational optical activity properties of even conformationally flexible chiral molecules, such as proteins.

ChemInform Abstract: Near-IR Absorption Spectra for the Buckminsterfullerene Anions: An Experimental and Theoretical Study.

ChemInform Abstract: Near-IR Absorption Spectra for the Buckminsterfullerene Anions: An Experimental and Theoretical Study.

ChemInform Abstract: Sol-Gel Syntheses and Spectroscopic Characterization of Chromium-Doped Silicates and Germanates.

To avoid the technical difficulties encountered with high-temperature processing techniques, low-temperature sol−gel processes have been examined as routes to the Cr-doped olivine, Mg2SiO4, and the structural analogues Ca2SiO4 and Ca2GeO4. Gelation yields transparent, lightly colored gels that are converted to microcrystalline ceramic powders on heating to 850 °C. Initially doped with CrCl3·6H2O (0.01−1%), conversion to the ceramic is accompanied by changes in the coordination and oxidation state of the chromium. Consistent with size considerations, EPR, EXAFS, and XANES data indicate chromium exists principally as tetrahedrally coordinated Cr4+ in Ca2SiO4 and Ca2GeO4, and as a mixture of octahedrally coordinated Cr3+ and tetrahedrally coordinated Cr4+ in Cr-Mg2SiO4. Visible and near-IR electronic absorption and emission spectra reflect the composition of the material, and a comparison of the absorption of randomly oriented microcrystalline ceramics shows a surprising similarity in both band position and ...

Simulation of the absorption spectra of nanometallic Al particles with core–shell structure: size-dependent interband transitions

Nanoaluminum combined with an oxidizing polymer binder is representative of a new class of nanotechnology energetic materials termed “structural energetic materials” that can be laser initiated by near-infrared heating of the Al particles. The visible and near-IR absorption spectra of Al nanoparticles passivated by the native oxide Al2O3, embedded in nitrocellulose (NC) binder, are simulated numerically using a model for the metallic dielectric function that incorporates the effects of interband transitions. The effects of oxide thickness, nanoparticle size and size distribution, and particle shape on the absorption characteristics are investigated. The nanoparticle spectra evidence an absorption peak and valley in the 550–1,100 nm range that redshift with decreasing nanoparticle size. Calculations indicate that this peak-valley structure results from interband transitions, and the unusual redshift cannot be explained without using an interband transition onset frequency that varies with nanoparticle size.

“Mechanically Docked” Metallodendrimers about Single-Walled Carbon Nanotubes

We report experimental support for “mechanical docking” of an optically active rigid molecule, ruthenium metallodendrimer (decamer), to single-walled carbon nanotubes (SWNTs) with some diameter selectivity. Binding of these rigid metallodendrimers onto dispersed single-walled carbon nanotubes has been studied by Raman and UV−vis−near-infrared (NIR) absorption spectroscopy. Atomic force and scanning electron micrographs indicate strong binding of these molecules specifically to the ends of nanotubes and are consistent with the spectroscopic evidence for diameter selectivity presented here. Near-IR absorption and radial breathing mode Raman spectra of these “end-functionalized” SWNTs show preferential diameter-selective separation, along with a red shift of the optical transitions. A concentration-dependent red shift is observed for the NIR absorption for decamer-bound nanotubes. This indicates a strong interaction between selective SWNTs and the decamer, forming a mechanically docked supramolecular complex. Spectral shifts and intensity variations in specific radial breathing mode bands of the functionalized SWNTs are complementary to our observations of the UV−vis−NIR absorption spectra and atomic force microscopy data.

Regulation of the Near‐IR Spectral Properties of Individually Dissolved Single‐Walled Carbon Nanotubes in Aqueous Solutions of dsDNA

Two different single-walled carbon nanotubes (SWNTs), the so-called HiPco and CoMoCAT, have been individually dissolved in aqueous solutions of double-stranded DNA (dsDNA). Atomic force microscopy (AFM) revealed the fine structures of the dsDNA-wrapped SWNTs. The near-IR absorption and photoluminescence (PL) spectra of aqueous solutions of dsDNA-wrapped SWNTs were recorded and, in pure water, we observed only a single two-dimensional PL spot from (6,5) SWNTs for both HiPco and CoMoCAT. In sharp contrast, when Tris-EDTA (TE) buffer was used in place of pure water, the PL-mapping images of the solutions showed chirality indices of (6,5), (7,5), (7,6), (8,4), (9,4), and (10,2) for HiPco-SWNTs, and (6,5) and (7,5) for CoMoCAT-SWNTs. The first semiconducting bands in the near-IR absorption spectra of solutions of dsDNA-wrapped SWNTs are different. To explain the observed differences in the near-IR absorption and PL behavior we conducted several experiments and found that the near-IR optical properties of the SWNTs can be modulated by changing the pH of the solutions. The pH break-points for near-IR absorption bleaching and PL quenching are different and the phenomena are explained by differences in the numbers of holes generated on the SWNTs. These findings are important from both fundamental and applied viewpoints.

DFT/TDDFT study of lanthanide(III) mono- and bisporphyrin complexes.

The electronic structure, molecular structure, and electronic spectra of lanthanide(III) mono- and bisporphyrin complexes are investigated using a DFT/TDDFT method. These complexes include YbP(acac), YbP(2), [YbP(2)](+), YbHP(2), and [YbP(2)](-) (where P = porphine and acac = acetylacetonate). To shed some light on the origin of the out-of-plane displacement of Yb in YbP(acac), unligated model systems, namely, planar D(4h) and distorted C(4nu) YbP, were calculated. For comparison, the calculations were also extended to include the C and [Ce(IV)P(2) ](+) systems. Even without an axial ligand, the lanthanide atom lies considerably above the porphyrin plane; the distortion of the YbP molecular structure from a planar D(4h) to the nonplanar C(4nu) symmetry leads to a considerable energy lowering. The axial ligand makes the metal out-of-plane displacement even larger, and it also changes the redox properties of the lanthanide monoporphyrin. The ground-state configurations of YbP(2) and YbHP(2) were determined by considering several possible low-lying states. YbP(2) is confirmed to be a single-hole radical. The special redox properties of the bisporphyrin complexes can well be accounted for by the calculated ionization potentials and electron affinities. The TDDFT results provide a clear description of the UV-vis and near-IR absorption spectra of the various lanthanide porphyrins.

Charge Resonance Character in the Charge Transfer State of Bianthryls: Effect of Symmetry Breaking on Time-Resolved Near-IR Absorption Spectra

We study the effects of symmetry breaking on the photogenerated intramolecular charge transfer (CT) state of 9,9'-bianthryl (BA) with femtosecond time-resolved near-IR spectroscopy. The time-resolved near-IR spectra are measured in acetonitrile for a symmetric substituted derivative of 10,10'-dicyano-9,9'-bianthryl (DCBA) and asymmetric substituted derivatives of 10-cyano-9,9'-bianthryl (CBA) and 9-(N-carbazolyl)anthracene (C9A), as well as nonsubstituted BA. The transient near-IR absorption spectrum of each compound at 0 ps has a locally excited (LE) absorption band, which agrees with the transient absorption band of the corresponding monomer unit. At 3 ps after the photoexcitation, the symmetric compounds show a broad charge transfer (CT) absorption band, whereas no absorption peak appears in the spectra of the asymmetric compounds. The broad CT absorption at 1250 nm only observed for the symmetric compounds can be attributed to the charge resonance transition associated with two equivalent charge separated states.

Study of the NpO 2 2+ -H2O-CrO 4 2− System. The Synthesis, Crystal Structure, and Properties of the Neptunium(VI) Chromate [(NpO2)(CrO4)(H2O)] ⋅ 4H2O

A new neptunium(VI) complex [(NpO2)(CrO4)(H2O)] ⋅ 4H2O (I) was synthesized, its crystal structure was determined, and the IR and near-IR absorption spectra were measured. The unit cell parameters are: a = 8.634(4) A, b = 11.119(4) A, c = 9.410(3) A, β = 92.40(3)°, space group P21/c, Z = 4, V = 902.6(6) A3, R = 0.048, wR(F2) = 0.054. The crystal structure of the compound is composed of the [(NpO2)(CrO4)(H2O)]n layers and the crystal water molecules located between the layers. The coordination polyhedron of neptunium is a pentagonal bipyramid whose equatorial plane is formed by the oxygen atoms of two bridging water molecules and three chromate ions. The Np(VI) complexation with the chromate ions in an aqueous solution at μ = 1 was studied by spectrophotometry. The stability constants for 1 : 1 and 1 : 2 complexes were calculated, logβ1 = 3.19(2), logβ2 = 3.93(2), respectively.

Investigation of the Ultraviolet, Visible, and Near‐Infrared Absorption Spectra of Hydrogenated Polycyclic Aromatic Hydrocarbons and Their Cations

The formation and the presence of PAHs containing excess H atoms, or hydrogenated PAHs (Hn-PAHs) in interstellar clouds has recently been discussed. It has been suggested that Hn-PAHs contribute to the IR emission bands andthattheymightbeamongthemolecularprecursorsofthecarbonparticlesthatcausetheinterstellar UVextinction curve. The spectroscopy of Hn-PAHs is investigated, and the implications for interstellar spectra are discussed. The UV, visible, and near-IR absorption spectra of a series of Hn-PAHs and their photoproducts formed by vacuum UV irradiation were measured for the first time in inert-gas (neon) matrices at 5 K. It is shown that the spectra of both the neutral Hn-PAH and cationic Hn-PAH + species exhibit vibronic band systems with similar spectral positions and relative spectral intensities to their nonhydrogenated PAH chromophore counterparts. The results are discussed in the context of the nature of the origin of the diffuse interstellar bands. Subject headingg astrochemistry — ISM: lines and bands — ISM: molecules — methods: laboratory — molecular data — ultraviolet: ISM

Covalent Cross-Linked Polymer/Single-Wall Carbon Nanotube Multilayer Films

Layer-by-layer films have been constructed from a cationic diazoresin and poly(sodium 4-styrenesulfonate)-functionalized single-wall carbon nanotubes (SWNT). Raman and near-IR absorption spectra indicate that some diazonium ions reacted with SWNT during film construction. The ionic bonds in the film between diazonium ions and sulfonate ions converted to covalent bonds upon UV irradiation as shown by the disappearance of diazonium ion peaks in the UV and IR spectra and appearance of an arenesulfonate peak in the IR spectra. The resistance of the film toward etching by polar solvents increased significantly after irradiation.

Near-IR Absorption and Fluorescence Spectra and AFM Observation of the Light-Harvesting 1 Complex on a Mica Substrate Refolded from the Subunit Light-Harvesting 1 Complexes of Photosynthetic Bacteria Rhodospirillum rubrum

The subunit light-harvesting 1 (LH 1) complexes isolated from photosynthetic bacteria Rhodospirillum rubrum using n-octyl-beta-glucoside were reassociated and adsorbed on a mica substrate using spin-coat methods with the aim of using this LH complex in a nanodevice. The near-IR absorption and fluorescence spectra of the LH 1 complexes indicated that the LH 1 complex on the mica was stable, and efficient energy transfer from a carotenoid to a bacteriochlorophyll a was observed. Atomic force microscopy of the reassociated LH 1 complexes, under air, showed the expected ringlike structure. The outer and inner diameters of the ringlike structure of the LH 1 complex were approximately 30 and 8 nm, respectively, and the ringlike structure protruded by 0.2-0.6 nm.