Near-infrared Absorption Band Research Articles

Femtosecond Two-Photon Ionization and Solvated Electron Geminate Recombination in Liquid-to-Supercritical Ammonia

The first-ever femtosecond pump-probe study is reported on solvated electrons that were generated by multiphoton ionization of neat fluid ammonia. The initial ultrafast ionization was carried out with 266 nm laser pulses and was found to require two photons. The solvated electron was detected with a femtosecond probe pulse that was resonant with its characteristic near-infrared absorption band around 1.7 μm. Furthermore, the geminate recombination dynamics of the solvated electron were studied over wide ranges of temperature (227 K ≤ T ≤ 489 K) and density (0.17 g cm(-3) ≤ ρ ≤ 0.71 g cm(-3)), thereby covering the liquid and the supercritical phase of the solvent. The electron recombines in a first step with ammonium cations originating from the initial two-photon ionization thereby forming transient ion-pairs (e(am)(-)·NH(4)(+)), which subsequently react in a second step with amidogen radicals to reform neutral ammonia. The escape probability, i.e., the fraction of solvated electrons that can avoid the geminate annihilation, was found to be in quantitative agreement with the classical Onsager theory for the initial recombination of ions. When taking the sequential nature of the ion-pair-mediated recombination mechanism explicitly into account, the Onsager model provides a mean thermalization distance of 6.6 nm for the solvated electron, which strongly suggests that the ionization mechanism involves the conduction band of the fluid.

Advantages of immobilization of Pt nanoparticles protected by dendrimers on multiwalled carbon nanotubes

Pt nanoparticles (PtNPs) were synthesized in the presence of a NH(2)-terminated fourth generation poly(amido amine) (PAMAM) dendrimer as a stabilizer at different molar ratios (M:D) of metal precursor to amine terminal group of dendrimer. Subsequently, PtNPs protected by dendrimers (DENPtNPs) were covalently immobilized on multiwalled carbon nanotubes (MWCNTs) by using a condensing agent for amide bond formation between acid-treated MWCNTs and DENPtNPs and the product CNT/DENPtNPs were characterized. PtNPs on MWCNTs increased quantitatively in content with M:D and dispersed with same aspect as the dispersion of DENPtNPs in water: PtNPs homogeneously dispersed at low M:D ratio and slightly aggregated at high ratio. The decomposition of CNT/DENPtNPs occurred at the lower temperature owing to the catalytic effect of PtNPs. A near-infrared absorption band around 2083 nm, which is extremely weak for MWCNTs, was intensified and D, D' and G Raman bands were slightly downshifted when DENPtNPs were attached. These phenomena can be attributed to the electron transfer from DENPtNPs to MWCNTs. Remarkable advantage is apparent from the enhanced electrochemical behavior of CNT/DENPtNPs loaded on gold electrode. PtNPs promoted the electron transfer of MWCNTs and dendrimers contributed to uptake of redox materials.

Calibration of near-infrared absorption band for a sun-photometer

Calibration of near-infrared absorption band for a sun-photometer

Bleaching of plasmon-resonance absorption of gold nanorods decreases efficiency of cell destruction

When irradiated with nanosecond laser pulses, gold nanoparticles allow for manipulation or destruction of cells and proteins with high spatial and temporal precision. Gold nanorods are especially attractive, because they have an up-to-20-fold stronger absorption than a sphere of equal volume, which is shifted to the optical window of tissue. Thus, an increased efficiency of cell killing is expected with laser pulses tuned to the near infrared absorption peak of the nanorods. In contrast to the higher-absorption, experiments showed a reduced efficacy of cell killing. In order to explain this discrepancy, transient absorption of irradiated nanorods was measured and the observed change of particle absorption was theoretically analyzed. During pulsed irradiation a strong transient and permanent bleaching of the near-infrared absorption band occurred. Both effects limit the ability of nanorods to destroy cells by nanocavitation. The existence of nanocavitation and transient bleaching was corroborated by optoacoustic measurements.

Photophysical Properties and Electronic Structure of Stable, Tunable Synthetic Bacteriochlorins: Extending the Features of Native Photosynthetic Pigments

Bacteriochlorins, which are tetrapyrrole macrocycles with two reduced pyrrole rings, are Nature's near-infrared (NIR) absorbers (700-900 nm). The strong absorption in the NIR region renders bacteriochlorins excellent candidates for a variety of applications including solar light harvesting, flow cytometry, molecular imaging, and photodynamic therapy. Natural bacteriochlorins are inherently unstable due to oxidative conversion to the chlorin (one reduced pyrrole ring) or the porphyrin. The natural pigments are also only modestly amenable to synthetic manipulation, owing to a nearly full complement of substituents on the macrocycle. Recently, a new synthetic methodology has afforded access to stable synthetic bacteriochlorins wherein a wide variety of substituents can be appended to the macrocycle at preselected locations. Herein, the spectroscopic and photophysical properties of 33 synthetic bacteriochlorins are investigated. The NIR absorption bands of the chromophores range from ∼700 to ∼820 nm; the lifetimes of the lowest excited singlet state range from ∼2 to ∼6 ns; the fluorescence quantum yields range from ∼0.05 to ∼0.25; and the yield of the lowest triplet excited state is ∼0.5. The spectroscopic/photophysical studies of the bacteriochlorins are accompanied by density functional theory (DFT) calculations that probe the characteristics of the frontier molecular orbitals. The DFT calculations indicate that the impact of substituents on the spectral properties of the molecules derives primarily from effects on the lowest unoccupied molecular orbital. Collectively, the studies show how the palette of synthetic bacteriochlorins extends the properties of the native photosynthetic pigments (bacteriochlorophylls). The studies have also elucidated design principles for tuning the spectral and photophysical characteristics as required for a wide variety of photochemical applications.

Optical and near-infrared velocity dispersions of early-type galaxies★

We have carried out a systematic, homogeneous comparison of optical and near-infrared dispersions. Our magnitude-limited sample of early-type galaxies in the Fornax cluster comprises 11 elliptical and 11 lenticular galaxies more luminous than MB = -17. We were able to determine the central dispersions based on the near-infrared CO absorption band head for 19 of those galaxies. The velocity dispersions range from less than 70 km/s to over 400 km/s. We compare our near-infrared velocity dispersions to the optical dispersions measured by Kuntschner (2000). Contrary to previous studies, we find a one-to-one correspondence with a median fractional difference of 6.4%. We examine the correlation between the relative dust mass and the fractional difference of the velocity dispersions, but find no significant trend. Our results suggest that early-type galaxies are largely optically thin, which is consistent with recent Herschel observations.

Temperature imaging of water in a microchannel using thermal sensitivity of near-infrared absorption

This paper presents a remote and preparation-free method of temperature imaging of aqueous solutions in microchannels of microfluidic chips. The principle of this method is based on the temperature dependency of the near-infrared (NIR) absorption band (ν(2) + ν(3) band) of water. Temperature images were constructed from absorbances in a narrow wavelength range including 1908 nm, the most sensitive to temperature in the band, measured by using an NIR camera and an optical narrow-bandpass filter. Calculation and calibration results demonstrated a linear relationship between the absorption coefficient and temperature with a temperature coefficient of 1.5 × 10(-2) K(-1) mm(-1). Temperature images of 50 μm thick water in a Y-shaped PDMS microchannel locally heated by a neighboring hot wire were obtained, in which thermal diffusion processes in the microchip were visualized. Temperature resolution was estimated to be approximately 0.2 K according to the temperature coefficient and noise level.

Molecular logic circuit based on a multi-state mononuclear platinum(ii) terpyridyl complex

A new type of multi-state platinum(ii) terpyridyl acetylide complex: platinum(ii) 4'-(4-dimethylaminophenyl)-2,2' : 6',2''-terpyridyl ferrocenyl acetylide (1), together with its reference complexes: platinum(ii) 4'-(4-methylphenyl)-2,2' : 6',2''-terpyridyl ferrocenyl acetylide (2), platinum(ii) 4'-(4-dimethylaminophenyl)-2,2' : 6',2''-terpyridyl phenyl acetylide (3) and platinum(ii) 4'-(4-methylphenyl)-2,2' : 6',2''-terpyridyl phenyl acetylide (4), are designed and synthesized. UV-vis-NIR absorption and electrochemical studies demonstrate that complex 1 possesses three ordered intraligand charge transfer (ILCT), ligand-to-ligand charge transfer (LLCT) and metal-to-ligand charge transfer (MLCT) states, and the successive modulation of the intramolecular ILCT, LLCT and MLCT states in a single mononuclear platinum(ii) complex 1 is well evidenced by their reference complexes 2-4. More interestingly, a near-infrared absorption band ranging from 720-1000 nm was clearly observed for complexes 1 and 2 upon oxidation of the σ-bonded ferrocene-ethynyl group by Fe(ClO(4))(3), which was tentatively assigned to platinum(ii)-disturbed ligand-to-metal charge transfer (LM'CT) of the ferrocenium group. These promising features allow us to integrate the multiple states to reproduce basic logic operations at the molecular level. A four-state (LLCT, ILCT, MLCT and LM'CT) molecular switch of complex 1 that responds to the stimulation of H(+), Fe(ClO(4))(3) and Zn producing four outputs has been encoded in binary digits. The logic function executed by complex 1 is equivalent to that of a combinational logic circuit integrating seven or eight logic functions as AND, OR, NOT. A three-input-four-output molecular logic circuit has been established.

Temperature-Induced Molecular Structural Changes of Linear Poly(ethylene imine) in Water Studied by Mid-Infrared and Near-Infrared Spectroscopies

The chain conformation and hydration structure of an aqueous solution of linear poly(ethylene imine) (LPEI) have been studied by the use of mid-infrared (mid-IR) and near-infrared (NIR) spectrometries to explore the molecular mechanism of an upper critical solution temperature (UCST)-type solubility change. When LPEI was dissolved in water, the solution became a gel at room temperature. Mid-IR and NIR absorption bands of the LPEI gel appeared at the same positions as the bands of the dihydrate crystal of LPEI in a film, which suggested that LPEI formed dihydrate crystallite in water at room temperature. This means that LPEI is in a planar-zigzag structure even in water at room temperature. When the gel was heated, it was changed to a transparent aqueous solution. Both mid-IR and NIR bands of an LPEI aqueous solution above 64 degrees C exhibited a broader bandwidth than those at room temperature. Judging from the change of the bandwidth, the LPEI chain in water was disordered by heating to take a random-coil form. In addition, band locations of the CH stretching first-overtone vibration bands in a NIR spectrum of the solution above 64 degrees C were higher than those of melted dry LPEI, which was reasonably understandable that the disordered LPEI chains in the aqueous solution were in a highly hydrated state. These spectral results have revealed that the change from the planar-zigzag form to the random-coil one in water is a trigger to begin the UCST-like solubility change on heating followed by hydration.

A Five-Center Redox System: Molecular Coupling of Two Noninnocent Imino-o-benzoquinonato-Ruthenium Functions through a π Acceptor Bridge

Combining the concepts of noninnocent behavior of metal/ligand entities and the coupling of redox-active moieties via an electronically mediating bridge led to the synthesis and the structural, electrochemical, and spectroscopic characterization of [Cl(Q)Ru(mu-tppz)Ru(Q)Cl](n) where Q(o) is 4,6-di-tert-butyl-N-phenyl-o-iminobenzoquinone and tppz(o) is 2,3,5,6-tetrakis(2-pyridyl)pyrazine, the available oxidation states being Ru(II,III,IV), Q(o,*-,2-), and tppz(o,*-,2-). One-electron transfer steps between the n = (2-) and (4+) states were studied by cyclic voltammetry and by EPR, UV-vis-NIR spectroelectrochemistry for the structurally characterized anti isomer of [Cl(Q)Ru(mu-tppz)Ru(Q)Cl](PF(6))(2), 2(PF(6))(2), the only configuration obtained. The combined investigations reveal that 2(2+) is best described as [Cl(Q(*-))Ru(III)(mu-tppz(o))Ru(III)(Q(*-))Cl](2+) with antiferromagnetic coupling between the ruthenium(III) and the iminosemiquinone components at each end. A metal-based spin as evident from large g factor anisotropy (EPR) and an intense intervalence absorption band at 1850 nm in the near-infrared (NIR) suggest that oxidation occurs at both iminosemiquinones to yield two Ru(II,III)-bonded quinones, implying redox-induced electron transfer. Reduction takes place stepwise at the metal centers yielding iminosemiquinone complexes of Ru(III,II) as evident from radical complex EPR spectra with small (99,101)Ru hyperfine contributions. After complete metal reduction to ruthenium(II) the bridging ligand tppz is being reduced stepwise as apparent from typical NIR absorption bands around 1000 nm and from small g anisotropy of the monoanion [Cl(Q(*-))Ru(II)(mu-tppz(*-))Ru(II)(Q(*-))Cl](-). A structure-based DFT calculation confirms the Ru-Cl character of the HOMO and the iminoquinone-dominated LUMO and illustrates the orbital interaction pattern of the five electron transfer active components in this new system.

NIR Absorbance Characteristics of Deoxynivalenol and of Sound and Fusarium-Damaged Wheat Kernels

The near infrared (NIR) absorption spectra of deoxynivalenol (DON) and single wheat kernels with or without DON were examined. The NIR absorption spectra of 0.5–2000 ppm of DON in acetonitrile were recorded in the 350–2500 nm range. Second derivative processing of the NIR spectra and spectral subtractions showed DON absorption bands at 1408 nm, 1904 nm and 1919 nm. NIR spectra of sound and Fusarium-damaged kernels were also acquired using two instruments. Subtraction of average absorption spectra and second derivative spectra were evaluated to identify different NIR signatures of the two types of kernel. Differences in peak height and positions of the NIR absorption bands of the kernels were noted. At 1204 nm, 1365 nm and 1700 nm, the differences were in the heights of the absorption peaks. Such differences may be attributed to changes in the levels of grain food reserves such as starches, proteins and lipids and other structural compounds. Shifts in absorption peak positions between the two types of kernels were observed at 1425–1440 nm and 1915–1930 nm. These differences may arise from other NIR active compounds, such as DON, which are not common for the two types of kernel. Since the NIR absorption of DON may have contributed to the shifts between sound and Fusarium-damaged kernels, this study indicates the potential for NIR spectrometry to evaluate Fusarium damage in single kernels based on the DON levels.

Heterologous synthesis and assembly of functional LHII antenna complexes from Rhodovulum sulfidophilum in Rhodobacter sphaeroides mutant

The light harvesting complexes, including LHII and LHI, are the important components of photosynthetic apparatus. Rhodovulum (Rdv.) sulfidophilum and Rhodobacter (R.) sphaeroides belong to two genera of photosynthetic bacteria, and they are very different in some physiological characteristics and light harvesting complexes structure. The LHII structural genes (pucBsAs) from Rdv. sulfidophilum and the LHI structural genes (pufBA) from R. sphaeroides were amplified, and cloned into an expression vector controlled by puc promoter from R. sphaeroides, which was then introduced into LHI and LHII-minus R. sphaeroides mutants; the transconjugant strains synthesized heterologous LHII and native LHI complexes, which played normal roles in R. sphaeroides. The Rdv. sulfidophilum LHII complex from pucBsAs had near-infrared absorption bands at ~801-853 nm in R. sphaeroides, and was able to transfer energy efficiently to the native LHI complex. The results show that the pucBsAs genes from Rdv. sulfidophilum could be expressed in R. sphaeroides, and the functional foreign LHII and native LHI were assembled into the membrane of R. sphaeroides.

Relationship between Sensory Scores and near Infrared Absorptions in Characterising Bitto, an Italian Protected Denomination of Origin Cheese

Historically, specific types of cheese are made in certain geographic areas. Often they have unique flavour characteristics. Studies have suggested the role of local pastures in determining cheese aroma. Bitto is a protected denomination of origin cheese produced in summer in Valtellina (Lombardy, Italy). The aim of this paper was to study the relationship between sensory scores assigned to Bitto cheese by a highly trained panel of experts and near infrared (NIR) data in verifying the NIR ability in predicting sensory characteristics. Bitto moulds (39), with assigned sensory scores, were analysed in the whole NIR range by an Fourier transform-NIR spectrometer. Grated cheese spectra (156) were recorded in reflectance mode. Spectra were grouped in two independent sets (calibration/prediction set = 30 samples; test set = nine samples). PLS1 and PLSD were applied. PLS1 results allowed a satisfactory prediction of total sensory score ( RMSEP 2.53; bias 1.2; slope 0.814) and an acceptable prediction of “Taste and Flavour” score ( RMSEP 0.60; bias 0.51; slope 0.565) for the nine samples in the test set. An acceptable preliminary classification of samples into three “quality classes” was also obtained applying PLSD. Factor loadings plots allowed the identification of some NIR absorption bands related to the development of cheese taste and flavour.

Composition, particle size, and near-infrared irradiation effects on optical properties of Au–Au2S nanoparticles

Near-infrared (NIR)-absorbing nanoparticles synthesized by the reduction of tetrachloroauric acid (HAuCl4) using sodium sulfide (Na2S) exhibited absorption bands at ∼530 nm and at the NIR region of 650−1100 nm. A detailed study on the structure and microstructure of as-synthesized nanoparticles was reported previously. The as-synthesized nanoparticles were found to consist of amorphous AuxS (x = ∼2), mostly well mixed within crystalline Au. In this work, the optical properties were tailored by varying the precursor molar ratios of HAuCl4 and Na2S. In addition, a detailed study of composition and particle-size effects on the optical properties was discussed. The change of polarizability by the introduction of S in the form of AuxS (x = ∼2) had a significant effect on NIR absorption. Also, it was found in this work that exposure of these particles to NIR irradiation using a Nd:YAG laser resulted in loss of the NIR absorption band. Thermal effects generated during NIR irradiation had led to microstructural changes that modified the optical properties of particles.

Near-infrared (NIR) spectroscopy. A new method for arthroscopic evaluation of low grade degenerated cartilage lesions. Results of a pilot study

BackgroundArthroscopy is a highly sensitive method of evaluating high-grade cartilage lesions but the detection of low-grade lesions is often is unreliable. Objective measurements are required. A novel NIRS (near-infrared-spectroscopy) device for detection of low-grade cartilage defects was evaluated in a preliminary clinical study.MethodsIn 12 patients who had undergone arthroscopy, the cartilage lesions within the medial knee compartment were classified according to the ICRS protocol.With a NIR spectrometer system and an optical probe, similar in design to a hook used for routine arthroscopy, the optical properties of cartilage were measured during arthroscopy.ResultsThe mean ratio of 2 NIR absorption bands of intact cartilage 3.8 (range 2.3 to 8.7).was significantly lower than that of cartilage with grade 1 lesions (12.8, range 4.8 to 19.6) and grade 2 lesions (13.4, range 10.4 to 15.4).No differences were observed between grade 1 and grade 2 lesions.ConclusionNIRS can be used to distinguish between ICRS grade 1 lesions and healthy cartilage during arthroscopic surgeries. The results of this clinical study demonstrate the potential of NIRS to objectify classical arthroscopic grading systems.

The First Detection of Near-Infrared CN Bands in Active Galactic Nuclei: Signature of Star Formation

We present the first detection of the near-infrared CN absorption band in the nuclear spectra of active galactic nuclei (AGNs). This feature is a recent star formation tracer, being particularly strong in carbon stars. The equivalent width of the CN line correlates with that of the CO at 2.3 μm as expected in stellar populations (SPs) with ages between ~0.2 and ~2 Gyr. The presence of the 1.1 μm CN band in the spectra of the sources is taken as unambiguous evidence of the presence of young/intermediate SPs close to the central source of the AGNs. Near-infrared bands can be powerful age indicators for star formation connected to AGNs, the understanding of which is crucial in the context of galaxy formation and AGN feedback.

Spectroscopy of synthetic Mg‐Fe pyroxenes I: Spin‐allowed and spin‐forbidden crystal field bands in the visible and near‐infrared

Abstract— Understanding the fundamental crystal chemical controls on visible and near‐infrared reflectance spectra of pyroxenes is critical to quantitatively assessing the mineral chemistry of pyroxenes viewed by remote sensing. This study focuses on the analysis of spectroscopic measurements of a comprehensive set of synthetic Mg‐Fe pyroxenes from the visible through the near‐infrared (0.3–2.6 μm) to address the constraints of crystal structure and Fe2+ content on spin‐forbidden and spin‐allowed crystal field absorptions in Ca‐free orthopyroxenes. The chemistry and oxidation state of the synthetic pyroxenes are characterized. Coordinated Mössbauer spectroscopy is used to determine site occupancy of Fe2+ in the M1 and M2 crystallographic sites. Properties of visible and near‐infrared absorption bands of the synthetic pyroxenes are quantified using the modified Gaussian model. The 1 and 2 μm spin‐allowed crystal field absorption bands move regularly with increasing iron content, defining a much tighter trend than observed previously. A spin‐allowed crystal field absorption band at 1.2 μm is explicitly verified, even at low total iron contents, indicating that some portion of Fe2+ resides in the M1 site. The 1.2 μm band intensifies and shifts to longer wavelengths with increasing iron content. At visible wavelengths, spin‐forbidden crystal field absorptions are observed in all iron‐bearing samples. The most prominent absorption near 506 nm, attributed to iron in the M2 site, shifts to slightly longer wavelengths with iron content. The purity and extent of this pyroxene series allows visible wavelength absorption bands to be directly assigned to specific transitions of Fe2+ in the M1 and M2 sites.

Photochromism and polaronic photocharge localization in diluted KTa1−xNbxO3

Ultraviolet (UV)-light-induced optical absorption in the near infrared (NIR) region was observed in diluted KTa1−xNbxO3 single crystals (x=0,0.004,0.007,0.012,0.07) at low temperatures. Illumination by wideband light (3.10–4.13eV, 300–400nm) is accompanied by the appearance of a broad NIR absorption band with the position of the maxima varying in the 0.69–0.8eV (1.54–1.79μ, T=1.3K) region for different Nb concentrations. This UV-light-induced absorption is absent in nominally pure KTaO3, as well as in all Nb diluted specimens at elevated temperatures. The centers responsible for the photochromic NIR absorption bands are tied to interband optical transitions of pair Nb4+ electronic polarons. The photochromic experimental data, supplemented by luminescence studies in the visible range, evidence the strong localization of the photocharge carriers by pair Nb4+ polarons at low temperatures. It is suggested that namely the strong localization of the photocarriers plays a crucial role in photoinduced gigantic dielectric effects and possible phase transitions, which have been recognized recently in incipient ferroelectrics at low temperatures.

Near-infrared observations of water-ice in OH/IR stars

A search for the near-infrared water-ice absorption band was made in a number of very red OH/IR stars which are known to exhibit the 10 μm silicate absorption. As a by-product, accurate positions of these highly reddened objects are obtained. We derived a dust mass loss rate for each object by modelling the spectral energy distribution and the gas mass loss rate by solving the equation of motion for the dust drag wind. The derived mass loss rates show a strong correlation with the silicate optical depth as well as that of the water-ice. The stars have a high mass loss rate (>10 -4 M ⊙ yr -1 ) with an average gas-to-dust mass ratio of 110. In objects which show the 3.1 μm water-ice absorption, the near-IR slope is much steeper than those with no water-ice. Comparison between our calculated mass loss rates and those derived from OH and CO observations indicates that these stars have recently increased their mass loss rates.

The determination of the degree of cure in epoxy paints by infrared spectroscopy

The goal of this paper is to present a method to determine the time evolution of epoxy conversion for epoxy/amine and epoxy/amide formulations in heterogeneous systems such as paints by means of near infrared (NIR) spectroscopy. The cure reaction involves a simple addition mechanism between the oxirane ring and the amine/amide hydrogen functional groups. The extent of the reaction was calculated from the NIR absorption band at around 4530 cm −1 which depends on the oxirane rings concentration. The NIR spectroscopic method, which has the advantage of real time analysis over other techniques such as chemical titration, can be employed with most of the usual, modern FTIR spectrometers.