Component Analysis of the Visible Absorption Spectra of I2 and Br2 in Inert Solvents: A Critique of Band Decomposition by Least-Squares Fitting

Capture of Gaseous Iodine in Isoreticular Zirconium-Based UiO-n Metal-Organic Frameworks: Influence of Amino Functionalization, DFT Calculations, Raman and EPR Spectroscopic Investigation

A series of Zr-based UiO-n MOF materials (n=66, 67, 68) have been studied for iodine capture. Gaseous iodine adsorption was collected kinetically from a home-made set-up allowing the continuous measurement of iodine content trapped within UiO-n compounds, with organic functionalities (-H, -CH₃ , -Cl, -Br, -(OH)₂ , -NO₂ , -NH₂ , (-NH₂ )₂ , -CH₂ NH₂ ) by in-situ UV-Vis spectroscopy. This study emphasizes the role of the amino groups attached to the aromatic rings of the ligands connecting the {Zr₆ O₄ (OH)₄ } brick. In particular, the preferential interaction of iodine with lone-pair groups, such as amino functions, has been experimentally observed and is also based on DFT calculations. Indeed, higher iodine contents were systematically measured for amino-functionalized UiO-66 or UiO-67, compared to the pristine material (up to 1211 mg/g for UiO-67-(NH₂ )₂ ). However, DFT calculations revealed the highest computed interaction energies for alkylamine groups (-CH₂ NH₂ ) in UiO-67 (-128.5 kJ/mol for the octahedral cavity), and pointed out the influence of this specific functionality compared with that of an aromatic amine. The encapsulation of iodine within the pore system of UiO-n materials and their amino-derivatives has been analyzed by UV-Vis and Raman spectroscopy. We showed that a systematic conversion of molecular iodine (I₂ ) species into anionic I^- ones, stabilized as I^- ⋅⋅⋅I₂ or I₃ ^- complexes within the MOF cavities, occurs when I₂ @UiO-n samples are left in ambient light.

Photochromism and photocatalysis of organic–inorganic hybrid iodoargentates modulated by argentophilic interactions

A series of organic–inorganic hybrid iodoargentates exhibit photochromic and photocatalytic properties, which could be effectively modulated by argentophilic interactions.

Photochromic and luminescent switchable iodoargentate hybrids directed by solvated lanthanide cations

A series of photochromic and luminescent switchable iodoargentate hybrids have been constructed by using solvated lanthanide cations as SDAs.

Polymerization of acetylene: polyynes, but not carbyne

Polymerization of acetylene in the presence of sterically-hindered endgroups leads to polyynes, but with lengths shorter than by stepwise syntheses.

Development and integration of block operations for data invariant automation of digital preprocessing and analysis of biological and biomedical Raman spectra

High-throughput information extraction from large numbers of Raman spectra is becoming an increasingly taxing problem due to the proliferation of new applications enabled using advances in instrumentation. Fortunately, in many of these applications, the entire process can be automated, yielding reproducibly good results with significant time and cost savings. Information extraction consists of two stages, preprocessing and analysis. We focus here on the preprocessing stage, which typically involves several steps, such as calibration, background subtraction, baseline flattening, artifact removal, smoothing, and so on, before the resulting spectra can be further analyzed. Because the results of some of these steps can affect the performance of subsequent ones, attention must be given to the sequencing of steps, the compatibility of these sequences, and the propensity of each step to generate spectral distortions. We outline here important considerations to effect full automation of Raman spectral preprocessing: what is considered full automation; putative general principles to effect full automation; the proper sequencing of processing and analysis steps; conflicts and circularities arising from sequencing; and the need for, and approaches to, preprocessing quality control. These considerations are discussed and illustrated with biological and biomedical examples reflecting both successful and faulty preprocessing.

Fully automated decomposition of Raman spectra into individual Pearson's type VII distributions applied to biological and biomedical samples

Rapid technological advances have made the acquisition of large numbers of spectra not only feasible, but also routine. As a result, a significant research effort is focused on semi-automated and fully automated spectral processing techniques. However, the need to provide initial estimates of the number of peaks, their band shapes, and the initial parameters of these bands presents an obstacle to the full automation of peak fitting and its incorporation into fully automated spectral-preprocessing workflows. Moreover, the sensitivity of peak-fit routines to initial parameter settings and the resultant variations in solution quality further impede user-free operation. We have developed a technique to perform fully automated peak fitting on fully automated preconditioned spectra-specifically, baseline-corrected and smoothed spectra that are free of cosmic-ray-induced spikes. Briefly, the tallest peak in a spectrum is located and a Gaussian peak-fit is performed. The fitted peak is then subtracted from the spectrum, and the procedure is repeated until the entire spectrum has been processed. In second and third passes, all the peaks in the spectrum are fitted concurrently, but are fitted to a Pearson Type VII model using the parameters for the model established in the prior pass. The technique is applied to a synthetic spectrum with several peaks, some of which have substantial overlap, to test the ability of the method to recover the correct number of peaks, their true shape, and their appropriate parameters. Finally the method is tested on measured Raman spectra collected from human embryonic stem cells and samples of red blood cells.

Analysis of the visible absorption spectrum of I2 in inert solvents using a physical model

Absorption spectra of I(2) dissolved in n-heptane and CCl(4) are analyzed with a quantum gas-phase model, in which spectra at four temperatures between 15° and 50 °C are least-squares fitted by bound-free spectral simulations to obtain estimates of the excited-state potential energy curves and transition moment functions for the three component bands--A ← X, B ← X, and C ← X. Compared with a phenomenological band-fitting model used previously on these spectra, the physical model (1) is better statistically, and (2) yields component bands with less variability. The results support the earlier tentative conclusion that most of the ~20% gain in intensity in solution is attributable to the C ← X transition. The T-dependent changes in the spectrum are accounted for by potential energy shifts that are linear in T and negative (giving red shifts in the spectra) and about twice as large for CCl(4) as for heptane. The derived upper potentials resemble those in the gas phase, with one major exception: In the statistically best convergence mode, the A potential is much lower and steeper, with a strongly varying transition moment function. This observation leads to the realization that two markedly different potential curves can give nearly identical absorption spectra.

Least-squares analysis of overlapped bound-free absorption spectra and predissociation data in diatomics: the C(1Πu) state of I2

Absorption spectra are recorded at low resolution but high quantitative precision for I(2) vapor at 35 °C and 64 °C. These and literature spectra are analyzed by least-squares quantum spectral simulation of the overlapped A ← X, B ← X, and C((1)Π(u)) ← X transitions, with the aid of a pseudocontinuum model for the discrete regions of the A ← X and B ← X spectra. The analysis yields improved descriptions of the small-R regions of the A- and B-state potentials, which are known precisely at larger R from discrete spectroscopy. The C potential is determined at small R from its C ← X absorption, at intermediate R from literature data for B → C predissociation, and at large R from its known van der Waals well. The estimates of the electronic transition moment function ∣μ(e)(R)∣ for the B-X transition expand upon precise results from a recent determination by a different method. For the C-X and A-X transitions, the R-dependence of the transition moment functions resembles that found previously for these systems in Br(2). Of the spectroscopic properties, the C ← X spectrum is most altered from the previous analysis, being now ∼20% weaker. For B → C predissociation, no derived C potential has yielded computed rates in adequate statistical agreement with the analyzed experimental data.

From monomer to bulk: appearance of the structural motif of solid iodine in small clusters

Formation of iodine clusters in a solid krypton matrix was studied using resonance Raman spectroscopy with a 1 cm(-1) resolution. The clusters were produced by annealing of the solid and recognized by appearance of additional spectral transitions. Two distinct regions, red-shifted from the fundamental vibrational wavenumber of the isolated I(2) at 211 cm(-1), were observed in the signal. The intermediate region spans the range 196-208 cm(-1), and the ultimate region consists of two peaks at 181 and 190 cm(-1) nearly identical to crystalline I(2). The experimental results were compared to DFT-D level electronic structure calculations of planar (I(2))(n) clusters (n = 1-7). The dimer, trimer, and tetramer structures, where the I(2) molecule is complexed from one end, were found to exhibit vibrational shifts corresponding to the intermediate size clusters. The larger, bulklike shift appears when the iodine molecule is coordinated from two opposite directions as in the case of a pentamer and higher clusters. Starting from the pentamer, the structural motif of crystalline iodine is clearly recognized in the clusters.

Spectroscopic Signatures of Halogens in Clathrate Hydrate Cages. 1. Bromine

We report the first UV-vis spectroscopic study of bromine molecules confined in clathrate hydrate cages. Bromine in its natural hydrate occupies 51262 and 51263 lattice cavities. Bromine also can be encapsulated into the larger 51264 cages of a type II hydrate formed mainly from tetrahydrofuran or dichloromethane and water. The visible spectra of the enclathrated halogen molecule retain the spectral envelope of the gas-phase spectra while shifting to the blue. In contrast, spectra of bromine in liquid water or amorphous ice are broadened and significantly more blue-shifted. The absorption bands shift by about 360 cm-1 for bromine in large 51264 cages of type II clathrate, by about 900 cm-1 for bromine in a combination of 51262 and 51263 cages of pure bromine hydrate, and by more than 1700 cm-1 for bromine in liquid water or amorphous ice. The dramatic shift and broadening in water and ice is due to the strong interaction of the water lone-pair orbitals with the halogen sigma* orbital. In the clathrate hydrates, the oxygen lone-pair orbitals are all involved in the hydrogen-bonded water lattice and are thus unavailable to interact with the halogen guest molecule. The blue shifts observed in the clathrate hydrate cages are related to the spatial constraints on the halogen excited states by the cage walls.

Quenched by ice: Transient grating measurements of vibronic dynamics in bromine-doped ice

In both water and in ice, the absorption spectra of bromine are dramatically broadened and blueshifted, and all fluorescence is quenched. Time resolved, electronically resonant transient grating measurements are carried out to characterize the vibronic dynamics of the trapped molecule in its electronic B(3Pi0u) state in ice. Independent of the initial excitation energy, after the first half-period of motion, a vibrational packet is observed to oscillate near the bottom of the potential, near nu=1. The oscillations undergo a chirped decay to a terminal frequency of 169 cm(-1) on a time scale of taunu=1240 fs, to form the stationary nu=0 level. The electronic population in the B state decays in taue=1500 fs. Adiabatic following to the cage-compression coordinate is a plausible origin of the chirp. Analysis of the absorption spectrum is provided to recognize that solvent coordinates are directly excited in the process. The observed blueshift of the absorption is modeled by considering the Br2-OH2 complex. Two-dimensional simulations, that explicitly include the solvent coordinate, reproduce both the time data and the absorption spectrum. The observed sharp vibrational recursions can be explained by overdamped motion along the solvent coordinate, and wave packet focusing by fast dissipation during the first half-period of motion of the molecular coordinate.