Separation Of Absorption Bands Research Articles

Wavelength and polarisation dependence of pump-induced loss in Ti:sapphire

We use pump beam wavelength and polarisation to demonstrate that the phenomenon of pump-induced loss in Ti:sapphire is linked to simultaneous excitation of two separate absorption bands: the Ti3+ pump band and the parasitic 400 nm residual absorption. We find that the degree of pump-induced loss is linked to the relative absorption strengths of the residual absorption band and the Ti3+ pump band at the wavelength(s) of excitation.

Data-driven discovery of molecular photoswitches with multioutput Gaussian processes.

Photoswitchable molecules display two or more isomeric forms that may be accessed using light. Separating the electronic absorption bands of these isomers is key to selectively addressing a specific isomer and achieving high photostationary states whilst overall red-shifting the absorption bands serves to limit material damage due to UV-exposure and increases penetration depth in photopharmacological applications. Engineering these properties into a system through synthetic design however, remains a challenge. Here, we present a data-driven discovery pipeline for molecular photoswitches underpinned by dataset curation and multitask learning with Gaussian processes. In the prediction of electronic transition wavelengths, we demonstrate that a multioutput Gaussian process (MOGP) trained using labels from four photoswitch transition wavelengths yields the strongest predictive performance relative to single-task models as well as operationally outperforming time-dependent density functional theory (TD-DFT) in terms of the wall-clock time for prediction. We validate our proposed approach experimentally by screening a library of commercially available photoswitchable molecules. Through this screen, we identified several motifs that displayed separated electronic absorption bands of their isomers, exhibited red-shifted absorptions, and are suited for information transfer and photopharmacological applications. Our curated dataset, code, as well as all models are made available at https://github.com/Ryan-Rhys/The-Photoswitch-Dataset.

Synthesis of functionalized diazocines for application as building blocks in photo- and mechanoresponsive materials.

Seven symmetrically 3,3’-substituted diazocines were synthesized. Functional groups include alcohol, azide, amine and vinyl groups, which are suitable for polymer synthesis. Upon irradiation at 385 and 530 nm the diazocines perform a reversible, pincer-type movement switching the 3,3’-distance between 6.1 Å (cis, stable isomer) and 8.2 Å (trans, metastable isomer). Key reactions in the synthesis are an oxidative C–C coupling of 2-nitrotoluenes (75–82% yield) and a reductive ring closure to form the diazocines (56–60% yield). The cyclization of the dinitro compound to the azo compound was improved in yield and reproducibility, by over-reduction to the hydrazine and reoxidation to the azo unit. In contrast to 3,3’- and 4,4’-diaminodiazocine, which have been implemented in macromolecules for conformation switching, our compounds exhibit improved photophysical properties (photostationary states, separation of absorption bands in the cis and trans configuration). Hence they are promising candidates as molecular switches in photo and mechanoresponsive macromolecules and other smart materials.

Before Förster. Initial excitation in photosynthetic light harvesting.

Electronic 2D spectroscopy allows nontrivial quantum effects to be explored in unprecedented detail. Here, we apply recently developed fluorescence detected coherent 2D spectroscopy to study the light harvesting antenna 2 (LH2) of photosynthetic purple bacteria. We report double quantum coherence 2D spectra which show clear cross peaks indicating correlated excitations. Similar results are found for rephasing and nonrephasing signals. Analysis of signal generating quantum pathways leads to the conclusion that, contrary to the currently prevailing physical picture, the two weakly coupled pigment rings of LH2 share the initial electronic excitation leading to quantum mechanical correlation between the two clearly separate absorption bands. These results are general and have consequences for the interpretation of initially created excited states not only in photosynthesis but in all light absorbing systems composed of weakly interacting pigments where the excitation transfer is commonly described by using Förster theory. Being able to spectrally resolve the nonequilibrium dynamics immediately following photoabsorption may provide a glimpse to the systems' transition into the Förster regime.

A Low Radar Cross Section and Low Profile Antenna Co-Designed With Absorbent Frequency Selective Radome

A low radar cross section (RCS) and low profile antenna co-designed with absorbent frequency selective radome (AFSR) is investigated. A pair of circular slot resonators is embedded on surface of the AFSR to realize a transmission window in the vertical polarization, while the wide absorption band is still maintained in the horizontal polarization. When a patch antenna is etched within the AFSR, where the metal grounds of the patch antenna and AFSR are co-used, the co-designed antenna with low RCS and low profile is thus realized. For demonstration, an AFSR is designed with its transmission window has a minimal insertion loss of 0.45 dB at 8.9 GHz, and two separate absorption bands (a lower absorption band from 4.8 to 7.5 GHz and an upper absorption band from 10 to 13 GHz) in the vertical polarization, a wide absorption band (from 4.5 to 12.5 GHz) in the horizontal polarization. A patch antenna etched within the AFSR is optimized to operate at 8.9 GHz, then it is simulated and fabricated. The measured results demonstrate that the proposed antenna not only has good radiation patterns, but also obtains significant RCS reduction.

Multiphotochromism in an Asymmetric Ruthenium Complex with Two Different Dithienylethenes.

An asymmetric bis(dithienylethene-acetylide) ruthenium(II) complex trans-Ru(dppe)2(L1o)(L2o) (1oo) incorporating two different dithienylethene-acetylides (L1o and L2o) was designed to modulate multistate photochromism in view of the well separated ring-closing absorption bands between L1o and L2o. Upon irradiation with appropriate wavelengths of light, complex 1 undergoes stepwise photocyclization and selective photocycloreversion to afford four states (1oo, 1co, 1oc, and 1cc). As a contrast, symmetric complexes trans-Ru(dppe)2(L1o)2 (2oo) and trans-Ru(dppe)2(L2o)2 (3oo) with two identical dithienylethene-acetylides were synthesized, and the corresponding photochromic behavior was investigated. The photochromic properties of the oxidized species (1oo+/1co+/1oc+/1cc+, 2oo+/2co+/2cc+, and 3oo+/3co+/3cc+) were also investigated. The ring-closing absorption bands of one-electron oxidized species 1oo+, 2oo+, and 3oo+ show obvious blue shifts relative to those of 1oo, 2oo, and 3oo, respectively. The ring-closing absorption bands in both neutral and oxidized species grow progressively following oo → oc/co → cc and oo+ → oc+/co+ → cc+. As revealed by spectroscopic, electrochemical, and computational studies, complex 1 displays eight switchable states through stepwise photocyclization, selective cycloreversion, and a reversible redox process.

Conjugation in and optical properties of 1-R-1,2-diphospholes and 1-R-phospholes.

The strength of conjugation between the diene moieties of 1-R-1,2-diphospholes and 1-R-phospholes and exocyclic phenyl groups of these P-heteroles has been quantitatively characterized by the use of Raman activities of the bands of the phenyl substituents. It is shown that conjugation in both types of phospholes is very similar to the conjugation of phenyl groups with the diene system of cyclopentadiene. Introduction of substituents (-OMe, -C(═O)H, -NO2, -NMe2, and -CH═CH2) in the para-position of the phenyl groups of 1-R-1,2-diphospholes extends π-delocalization of exocyclic groups into the electronic system of the 1,2-diphosphole ring, producing bathochromic shifts of the absorption bands up to 63 nm. In contrast, hypsochromic shifts up to 40 nm can be achieved by introduction of SnMe3 or SiMe3 groups at the phosphorus(III) atom of the 1,2-diphosphole and concomitant increase of aromaticity of the P-heterole. Conjugation shifts the "centre of gravity" of the whole electronic absorption spectrum, whereas positions of separate absorption bands are not simply dependent on conjugation lengths.

Time-Resolved Dynamics of the OH Stretching Vibration in Aqueous NaCl Hydrate

We report on the first time-resolved study of the OH stretching vibration in NaCl dihydrate with the use of two-color IR spectroscopy. The sample is characterized by conventional FTIR spectroscopy. The water molecules bound in the hydrate show two well separated absorption bands at 3426 cm(-1) and 3541 cm(-1). The transient data display an ultrafast heating of the polycrystalline ice-hydrate samples after excitation of the OH stretching vibration and its transient relaxation. The relaxation time of the low-frequency OH stretching band in the NaCl hydrate is measured to be 6.8 +/- 1 ps. The dynamics are significantly slower than those measured in neat water. This fact, together with the reproducible crystalline environment reveals the potential of aqueous hydrates for a systematic investigation of the OH stretching vibration in varying hydrogen bonding environments.

Spectral observation of the galaxy Kaz 17

The results of a spectral study of the galaxy Kaz 17 are presented. 150 lines are identified in its spectrum, of which 21 are in emission while the rest are absorption lines. These lines belong to the following elements and ions:..... and FeI. Roughly 56% of the absorption lines belong to FeI. Of the absorption lines, 10 belonging to TiI and FeI are isolated. Because of the closeness of their wavelengths, the rest merge and form separate absorption bands. 10 lines, including 8 emission lines, are unidentified in the spectrum of Kaz 17. In all, 160 lines were observed in the spectrum of Kaz 17. In terms of the structure of the emission lines, Kaz 17 can be assigned to type Sy1, and in terms of the absorption lines, it more closely resembles a normal galaxy.

Charge transfer complexes of 9-vinyl-carbazole with π acceptors in homogeneous and in micellar solutions

The molecular association of 9-vinyl-carbazole (CBZ) with three electron acceptors, p-chloranil (CHL), 2,7-dinitro-9-fluorenone (FL), and tetracyano- p-quinodimethane (TCNQ), is studied in acetonitrile and in micellar aqueous solution of sodium dodecyl sulfate (SDS). In both media, stable charge transfer (CT) complexes are formed with association constants in the range of 8–500 M −1. CBZ and FL form a 1:2 complex in acetonitrile, but in SDS micelles the association is 1:1 due to size restriction and occupancy statistics in the host aggregates. The combination of absorption and fluorescence emission spectroscopy data indicates that the bimolecular CT complex of CBZ with TCNQ is stabilized in two distinct environments of the SDS micelles providing then two separated CT absorption bands.

Structures and UV‐Visible Absorption Properties of Unsymmetrical Bisdithiolene Nickel Complexes

AbstractA new unsymmetrical bisdithiolene nickel complex Ni(Et2dazdt)(mnt) was synthesized and structurally characterized, where Et2dazdt and mnt denote 1,4‐diethyl‐perhydrodiazepine‐2,3‐dithione and maleonitrildithiolate, respectively. Its crystal structure and absorption spectrum were determined and compared to those of Ni(Et2pipdt)(mnt), where Et2pipdt is 1,4‐diethyl‐piperazine‐2,3‐dithione. X‐ray diffraction analysis reveals that the Ni(S2C2)2 moiety of Ni(Et2dazdt)(mnt) is not planar due to the twist conformation of a seven‐member ring of Et2dazdt ligand. The twisting of Et2pipdt is less severe and NiS4 center of Ni(Et2pipdt)(mnt) possesses a closer to planar conformation than that of Ni(Et2dazdt)(mnt). Unlike Ni(Et2pipdt)(mnt), Ni(dazdt)(mnt) shows two major separated absorption bands in the visible and near‐IR region, although both absorption bands show negative solvatochromism similar to that of Ni(Et2pipdt)(mnt).

Spectroscopic study of rare earth chlorocomplexes in propylene carbonate

Absorption spectra of Et 4N +(ClO 4 −, Cl −) 0.18 M lanthanides in propylene carbonate (PC) solutions were investigated in the near UV, visible and near IR. The multiwavelength numerical treatment is based upon the optical density matrix rank analysis and an original optimization calculation, which leads to simultaneous determination of the overall stability constants and specific extinction coefficients of the complexes. The constitution of the rare earth chloride PC solutions, after testing several theoretical models, is limited to LnCl 2+ and LnCl 2+, the latter being the more substituted Ln(III)-chlorocomplex, as shown by the identical absorption bands assigned in the solid state and calculated in solution: the overall stability constants are 54, 92, 80 for LnCl 2+, 1.6 × 10 3, 5.2 × 10 3, 1.0 × 10 4 for LnCl 2 + where Ln is Pr, Nd, Sm respectively. Stabilization of the complexes with respect to the lower donor strength of propylene carbonate compared with methanol is found; however, the values of the calculated stability constants are consistent with the formation of weak complexes. The solvent effect upon the electronic spectra is also illustrated by better separated absorption bands in PC than in anhydrous methanol.

Multicomponent determination by flow injection analysis using PU 4021 diode array detector. A direct determination of lanthanoids

Flow injection analysis (FIA) using a multichannel UV-VIS diode array detector enables several components with sufficiently separate absorption bands to be determined simultaneously. The effects of the basic parameters of the FIA apparatus (geometry, flow rates, etc.), error of measurement of the analytical signal, mutual interactions between the components to be determined, and the data handling procedure on the accuracy and precision of the calculated concentrations of the components are demonstrated on a model case of binary and ternary mixtures of Cu(II), Ni(II), Co(II), and U(VI). The majority and minority components can be determined with relative errors of 1-3% and 2-20%, respectively, over the concentration region of 2 to 200 mmol l-1 at concentration ratios from 1:1 to 50:1. The method has been applied to a simultaneous determination of Pr(III), Sm(III), and Nd(III) in oxidic concentrates of rare earths over the region of 1 – 20 mg ml-1 at concentration ratios down to 1:10 with relative errors not exceeding 5%.

The Temperature Dependence of Band Maxima Molar Absorptivities of the Carbon-Bromine Stretching Modes in n-Butyl Bromide in the Liquid Phase

In the determination of energy differences of conformers in the fluid states by infrared spectroscopy it is nearly always assumed that the ratio of the molar absorptivities at the band maxima of two separate absorption bands is independent of temperature. This assumption has been tested by fitting the data obtained from n-butyl bromide to a mathematical model which can be iterated to convergence on a value of the energy difference between the trans and gauche isomers. The data utilized are the C-Br stretching modes of the two conformers at about 655 and 567 cm−1, respectively. It is shown that the assumption of temperature independence of the ratios of the molar absorptivities at the peak maxima is a good one, although both values are individually temperature dependent.

Langmuir-Blodgett films containing porphyrins in a well-defined environment

Mono- and multilayers of porphyrins containing aliphatic side chains are studied by optical spectroscopy and microscopy. These techniques are used to control the manipulation of monolayers at the air-water interface and to transfer the monolayers onto solid supports. It is shown that hydrogen-bonded aggregates can be formed and distinguished by separate absorption and fluorescence bands. Their establishment can be avoided by addition of Cd 2+ ions or enhanced by increasing the surface pressure. Homogeneity of the monolayers formed is checked by fluorescence microscopy. It is demonstrated that the films can be transferred onto solid supports without altering their optical properties.

Optical absorption and electron spin resonance in vanadium-containing phosphate and fluoride phosphate glasses

Two glass systems have been investigated: (100 − x)[12 Al(PO 3) 3 28.5 MgF 2 5 CaF 2 54.5 BaF 2] x V 2O 5 with x = 0, 0.5, 1, 2, 3, 5, 8 and compared with: (100 − x)[12 Al(PO 3) 3 33.5 Mg(PO 3) 2 54.5 Ba(PO 3) 2] x V 2O 5. While the pure phosphate glass system (OV) has a strong reducing action on vanadium, the fluoride-phosphate system (FV) favours higher oxidation states by the lower electron donor properties of fluorine compared with oxygen. As a consequence, in the OV-system V 3+-ions strongly dominate the line shape in the absorption spectra and prevent separation of the optical absorption bands. However, in the FV-system the separation succeeds for the absorption bands of all three valency conditions V 3+, V 4+ and V 5+, which is only possible by the presence of fluorine. The separated absorption bands indicate an orthorhombic symmetry for the V 4+-complexes, which is shifted to a tetragonal symmetry with increasing vanadium oxide and decreasing F/O-ratio. In contrast to an increase of ligand field strength, the ESR-spectra show a decrease of the g-factors within a certain concentration range. This decrease seems to be a result of an exchange of planar-coordinated fluorine by oxygen ligands, combined with a reduction of π-bonding contributions.

First reaction steps and intermediates of the oxidation of ascorbic acid by dioxygen. Catalysis by cobalt(II) tetrasulphophthalocyanine

The oxidation of ascorbic acid by dioxygen catalyzed by cobalt(II) tetrasulphophthalocyanine (CoTSP) has been studied by the stopped-flow method. Two reactive intermediates, [O2.CoTSP. ascorbic acid] and [O2.CoTSP], characterized by separate absorption bands at 570 nm and 634 nm, respectively, have been proved to form in the reaction. The individual steps of the reaction have been elucidated, and their rate constants have been determined or estimated.

Resonance Raman examination of axial ligand bonding and spin-state equilibria in metmyoglobin hydroxide and other heme derivatives.

Resonance Raman spectra and excitation profiles have been obtained within the 5700-6300-A absorption band of purified sperm whale metmyoglobin hydroxide (MbIIIOH) solutions. A large enhancement occurs for a Raman peak at 490 cm-1 which is shown by isotopic substitution of 18O for 16O to be almost purely an Fe-O stretch. The Fe-O vibration in MbIIIOH occurs 5 cm-1 to lower energy than the corresponding vibration at 495 cm-1 in human methemoglobin hydroxide (HbIIIOH) [Asher, S., Vickery, L., Schuster, T., & Sauer, K. (1977) Biochemistry 16, 5849], reflecting differences in ligand bonding between Mb(III) and Hb(III). A larger frequency difference (10 cm-1) exists between MbIIIF and HbIIIF for the Fe-F stretch. We do not observe separate Fe-O or Fe-F stretches from the alpha and beta chains of either HbIIIOH or HbIIIF. Excitation profile measurements for MbIIOH indicate that the 5700-6300-A absorption band is composed of two separate absorption bands which result from a high- and a low-spin form of MbIIIOH. The spin-state-sensitive Raman band at 1608 cm-1 reflects the high-spin species and has an excitation profile maximum at about 6000 A while the low-spin Raman band occurs at 1644 cm-1 and shows an excitation profile maximum at 5800 A. The Fe-O stretch at 490 cm-1 has an excitation profile maximum at about 6000 A. The differences in frequency and Raman cross section between the Fe-X vibrations in MbIIIX and HbIIIX (X = OH-, F-) can be related to increases in the out-of-plane iron distance for the high-spin species of MbIIIX. The shift in the 1644-cm-1 MbIIIOH low-spin state Raman band indicative of the heme core size to 1636 cm-1 in HbIIIOH indicates a larger heme core size in HbIIIOH. Raman frequency shifts are used to estimate differences in bond strain energies between MbIIIX and HbIIIX (X = OH-, F-). Previous resonance Raman excitation profile data can be interpreted in terms of separate contributions from different spin-state species.

Solvent Effects on Nuclear Magnetic Resonance Chemical Shifts

Abstract The basic nuclear magnetic resonance (NMR) experiment involves the subjection of a macroscopic assembly of atoms or molecules to the influence of a strong static magnetic field and of a much weaker one derived from a radiofrequency signal. If the magnitude of either the former field or the frequency of the latter is maintained constant and the other varied, conditions may be achieved where the combined interactions of the two fields with magnetic nuclei in the sample lead to discrete changes in the energy of the nuclei. These energy changes can be detected by various means [1,2] and a spectrum of nuclear resonance conditions may be recorded. At an early stage in the development of the technique it was discovered [3] that the resonance condition for a particular nuclide was influenced by its chemical environment. Subsequently, it was established that a compound containing several nuclei of the same type could produce a spectrum exhibiting separate absorption bands which were chemically shifted, depending on the environments of the nuclei. Moreover, it was found that the chemically shifted bands could be composed of multiplet lines [4] due to spin interactions between the various nuclei. A substantial proportion of the use of NMR has been devoted to the determination of chemical shifts (6) and spin-spin coupling constants (J) and their interpretation in terms of the functional group type of the nuclei involved, their dispositions, and their relative quantities. However, the appearance of NMR spectra is not influenced by intramolecular factors alone, but by intermolecular effects also which can modify chemical shifts significantly and, to a lesser extent coupling constants. Consequently, before NMR can be used to elucidate molecular structure unambiguously, the effects of the environment of a molecule on its spectrum must be understood. While this may be a satisfactory objective per se, it should not be forgotten that a full understanding of medium effects additionally may provide new tools for the determination of molecular structure and also new understanding of the behavior of the medium itself, which may have greater fundamental importance.

Ferric Oxide (α-Haematite?) in Interstellar Dust

Recent studies suggest that the 4430 A diffuse interstellar band represents the crystal-field field-independent transition 6A1⇐4A1E(G) in octahedral-Fe3+ ions located in oxide or Si-substituted silicate lattices1–3, with intensity considerations favouring the former (as α or γ-Fe2O3). Here, I point out that the 4430 A band halfwidth and a Racah B parameter calculated from the separation of absorption bands in spectra of type I supernovae, when interpreted in light of next-nearest neighbour interactions in terrestrial minerals, are not-inconsistent indicators of the presence of ferric oxides, possibly haematite (α-Fe2O3).