Vibrational Overtone Research Articles

Atomic and microstructural origin of banded colours in purple-blue variety of agate from Yozgat Province, Turkey

Agates from Yozgat province are appreciated on the gem market for their white and purple-blue banded colours. In this study, we present a detailed investigation aimed at the identification of the atomic and structural origin of this peculiar colouration of chalcedony. X-ray diffraction and Raman spectroscopy revealed the presence of fine grains of quartz and moganite with a preferential accumulation of the latter in the blue bands. Near-infrared diffuse absorption spectra show overtones of hydroxyls vibrations at 1425, 1900, and 2250 nm. In the visible, the broad absorption at about 500 nm, as well as its behaviour at low temperatures, is compatible with the optical activity of iron impurities in quartz matrices, such as that observed in amethysts. Peak intensities and shapes are very similar for spectra collected in blue and white bands. Accordingly, trace-element composition from laser ablation inductively coupled mass spectrometry confirmed that the two regions have similar Fe content. The perceived changes in band colours are indeed originated by differences in microstructural arrangement and size of the grains visualised through scanning electron microscopy. White and blue stripes have grains of about 5 µm and 300 nm in size, respectively, resulting in an accentuated scattering component for the white bands. Therefore, the unique purple-blue shades typical of Yozgat agates are a combination of iron-related colour centres and scattering effect.

Superior Iodine Uptake Capacity Enabled by an Open Metal-Sulfide Framework Composed of Three Types of Active Sites

Superior Iodine Uptake Capacity Enabled by an Open Metal-Sulfide Framework Composed of Three Types of Active Sites

High-resolution spectra of [formula omitted] overtone of trans-formic acid in the supersonic jet

First high-resolution low-temperature spectrum of the 2νOH overtone of trans-formic acid have been measured using direct-absorption laser spectroscopy. The supersonic cooling in the jet expansion to 37 K has dramatically simplified the complex ro-vibrational structure of the band due to the thermal depopulation of higher-lying rotational states. Altogether, 597 lines have been measured with a line-position accuracy better than 0.001 cm−1, and 441 of them have been reliably assigned using a custom-build program for a line-by-line assignment using the ground state combination differences. In total, 39 low-lying upper rotational states of the overtone vibration have been calculated from these line assignments. Moreover, some additional states have been also identified and tentatively assigned to a bath of dark states present in this spectral region. A global fit using A-reduced Watson’s type Hamiltonian in Ir representation has been performed to obtain several ro-vibrational constants for the 2νOH vibration. In addition, the fit demonstrates the effect of numerous perturbations in the rotational structure.

Intramolecular vibrational redistribution in formic acid and its deuterated forms.

The intramolecular vibrational relaxation dynamics of formic acid and its deuterated isotopologues is simulated on the full-dimensional potential energy surface of Richter and Carbonnière [J. Chem. Phys. 148, 064303 (2018)] using the Heidelberg MCTDH package. We focus on couplings with the torsion vibrational modes close to the trans-cis isomerization coordinate from the dynamics of artificially excited vibrational mode overtones. The bright C-O stretch vibrational mode is coupled to the out-of-the plane torsion mode in HCOOH, where this coupling could be exploited for laser-induced trans-to-cis isomerization. Strong isotopic effects are observed: deuteration of the hydroxyl group, i.e., in HCOOD and DCOOD, destroys the C-O stretch to torsion mode coupling whereas in DCOOH, little to no effect is observed.

Spectrochemical and stable isotopic characteristics of magnesite deposits in Salem, Southern India: CO2 repository through supergene processes

Magnesite (MgCO3), a carbonate mineral, is considered as a carbon dioxide repository in geological formations and has important industrial applications. Magnesite can form through the alteration of magnesium-rich rocks in marine and non-marine geological settings. We investigated the magnesite deposits of the Salem mafic–ultramafic Complex (SMUC) in southern India through chemical and spectroscopic techniques. We characterize the magnesite mineralization based on visible-near infrared reflectance spectroscopic analyses, XRD, laser Raman analysis, and stable C-O isotope methods. Hyperspectral data show paired absorption at 2.3 and 2.5 µm, attributed to C-O bond vibration overtones and combination tones of C-O stretching and bending. The FTIR spectrum brings out frequencies of vibrations between the atomic bonds. The Laser Raman data show peaks at or near 212, 332, 735, 1096, and 1460 cm−1. The stable isotope data indicate that the magnesite mineralization resulted from the alteration of the ultramafic rocks by low-temperature (49 ± 3.3 °C) fluids. The source of carbon is correlated to the decarboxylation or dissolution of marine limestone. We propose a genetic model that invokes the percolation of meteoric water through weak planes and fractures into the ultramafic rocks.Our results provide a typical example of magnesite as a natural CO2 repository formed through supergene processes.

Classical Intermolecular Hydrogen Bonding Motifs of Heterocyclic rac-2-Amino-3-carbonitrile Derivatives: Linking Hirshfeld Surface Analysis, CT-DNA Binding Affinity, and Molecular Docking

Four 2-amino-4-(aryl)-7,7-dimethyl-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile (Series I) and three 2-amino-1-phenyl-7,7-dimethyl-5-oxo-4-(aryl)-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (Series II) derivatives were formed via multicomponent microwave reactions as racemic mixtures. The solid-state IR spectra revealed bands in the region between 3190 and 3414 cm–1 attributed to the amino functional group’s asymmetric, symmetric, and bending overtone vibration modes. Furthermore, the IR spectra of some of the compounds in each series were similar and this served as an indication of similar structural features in the solid state. This was confirmed via single-crystal X-ray diffraction. A detailed survey of the related 2-amino-3-carbonitrile derivatives in the Cambridge Structural Database revealed 12 classical intermolecular hydrogen-bonding motifs involving the amino functional group. The vast variation in the hydrogen bonding motifs was found to be caused by the type of group bonded to the 4H-pyran (in Series I) or dihydropyridine (in Series II) moiety. In this work, an unprecedented hydrogen bonding motif comprising a non-classical hydrogen bond acceptor was found in one instance. For both Series I and II, the N–H···N and N–H···O hydrogen bonds were investigated using noncovalent interaction (NCI) plots and molecular pairwise energy calculations. The contributions of reciprocal N···H and O···H contacts (attributed to N–H···N and N–H···O, respectively) toward the Hirshfeld surface range between 9.9 and 15.3% in Series I and between 10.8 and 15.0% in Series II. In addition, the compounds showed moderate to good binding affinity to calf thymus DNA (CT-DNA) with intrinsic binding constants (Kb) between 8.00 × 104 and 5.00 × 105 M–1 for Series I compounds and between 6.60 × 104 and 1.45 × 105 M–1 for Series II. A relationship was established between the reciprocal N···H to O···H contributions ratio from the Hirshfeld surface analysis and Kb. Molecular docking studies of each compound’s respective enantiomers into DNA were done using canonical–DNA dodecamer (B-DNA) as a model for CT-DNA. The compounds were found to interact with DNA via a minor groove-binding mode. The S-enantiomer for most of the compounds bound favorably compared to their respective R-enantiomers. The ratio of calculated ΔG for the DNA binding of the R-enantiomer to that of the S-enantiomer (ΔGR/ΔGS) follows the same positive trend as the experimental Kb value for each compound in Series I while a negative trend was observed for Series II. Finally, a relationship between the Hirshfeld surface analysis and calculated ΔG values was also established in this work.

Torsional motions of the free and H-bonded hydroxyl groups of the catechol molecule

Torsional vibrations of free and hydrogen-bonded hydroxyl groups of the 1,2-dihydroxybenzene molecule are analyzed within the harmonic and anharmonic approximations, as well as by constructing a 2D potential energy surface formed by varying the torsional coordinates of the two OH groups. Calculation of the vibrational spectrum of the molecule in the harmonic and anharmonic approximations was performed at the MP2/acc-pVTZ level of theory. Calculations of the 2D potential energy surface were performed at the MP2/acc-pVTZ, MP2/CBS(T,Q), and CCSD(T)/acc-pVDZ levels of theory. Calculations of the 2D surfaces of dipole moment components and kinetic coefficients were performed at the MP2/cc-pVTZ and MP2/acc-pVTZ levels of theory. In the latter case, the formalism of Wilson’s s→ vectors was used. The energies of the first 100 stationary torsional levels are calculated and classified by irreducible representations of the molecular symmetry group C2V(M). Furthermore, the analysis of wave functions allowed us to assign most of the torsional states to the fundamentals, combinations, and overtones of the torsional vibrations of the hydroxyl groups of two conformers that have the point symmetry groups CS (I) and C2V (II). The tunneling frequencies between equivalent configurations of conformer I in the ground and excited torsional states are estimated. The calculated values of the frequencies of fundamental torsional vibrations of two OH groups and the tunneling splitting value of the first excited torsional state of the free hydroxyl group of conformer I are compared with the experimental data presented in a recently published work [J. Bruckhuisen et al., Molecules 26 (2021) 3645]. Torsional IR spectra of the molecule are modeled at different temperatures.

Multilayer Polymer Photonic Aegises Against Near-Infrared Solar Irradiation Heating.

Preventing solar heating is nowadays of paramount interest in energy savings and health preservation. For instance, in building thermalization solar heating consumes an excess of energy leading to harmful CO2 emissions, while in food and beverage packaging it may lead to variation of organoleptic properties or even health issues. The phenomenon is attributed to the large presence of moieties with highly absorbing vibrational overtones and combination bands in the near-infrared spectral region that induces heating in water, moisture, and in polymers used in packaging. Thus, reducing and controlling the light absorbed by these materials with effective low-cost passive systems can play a major role in energy saving and health preservation. In this work, different polymer dielectric mirrors are reported, made of poly(N-vinylcarbazole) and either cellulose acetate or poly(acrylic acid), and able to selectively reflect near-infrared radiation while maintaining high transparency in the visible range. To this end, simple, tandem, and superperiodic mirrors are used to shield radiation impinging on samples of water and paraffin, demonstrating shielding efficiencies up to 52% with respect to unshielded references, promising a new paradigm to solve thermal management issues.

Gasoline octane number prediction from near-infrared spectroscopy with an ANN-based model

In this study, determination model for research octane numbers (RONs) of gasoline fuels has been developed based on near-infrared (NIR) spectroscopy and artificial neural networks (ANN). Input features were the partial least squares (PLS) factors extracted from the NIR spectra, and their size number was set from 30 to 46 with a step size of 4. 200 gasoline fuels collected from different regions in China were used to validate the prediction model, and their RONs varies from 90 to 100. The optimal prediction result shows that about 94% of residuals between the predicted and experimental RONs distribute within the experimental error range. It demonstrates that the proposed ANN-NIR model has the potential to predict RONs of real gasoline fuels from various regions in China. Additionally, the contributions of the NIR spectra to the PLS factors could be obtained using the partial least squares regression method, and the results show that the selected PLS factors generally contain the C–H bond vibration information, e.g. the first vibrational overtone of C–H bond, the second vibrational overtone of C–H bond, and the vibrational combination of C–H bond.

Local and Remote Conformational Switching in 2-Fluoro-4-Hydroxy Benzoic Acid

In this work, 2-F-4-OH benzoic acid was isolated in Ar matrices and conformational changes were induced by near-IR irradiating the sample. Upon deposition, three conformers could be observed in the matrix, denoted as A1, A2, and D1, respectively. A1 and A2 are trans carboxylic acids, i.e., there is an intramolecular H bond between the H and the carbonyl O atoms in the COOH group, whereas D1 is a cis carboxylic acid with an intramolecular H bond between the F atom and the H atom in the COOH group, which otherwise has the same structure as A1. The difference between A1 and A2 is in the orientation of the carbonyl O atom with regard to the F atom, i.e., whether they are on the opposite or on the same side of the molecule, respectively. All three conformers have their H atom in their 4-OH group, facing the opposite direction with regard to the F atom. The stretching overtones of the 4-OH and the carboxylic OH groups were selectively excited in the case of each conformer. Unlike A2, which did not show any response to irradiation, A1 could be converted to the higher energy form D1. The D1 conformer spontaneously converts back to A1 via tunneling; however, the conversion rate could be significantly increased by selectively exciting the OH vibrational overtones of D1. Quantum efficiencies have been determined for the ‘local’ or ‘remote’ excitations, i.e., when the carboxylic OH or the 4-OH group is excited in order to induce the rotamerization of the carboxylic OH group. Both ‘local’ and ‘remote’ conformational switching are induced by the same type of vibration, which allows for a direct comparison of how much energy is lost by energy dissipation during the two processes. The experimental findings indicate that the ‘local’ excitation is only marginally more efficient than the ‘remote’ one.

Optically pumped and matrix‐assisted anti‐Stokes Raman spectroscopy

AbstractAnti‐Stokes Raman spectroscopy is an excellent method to suppress optical backgrounds from Raman scatters and surrounding materials, even in electronic resonance conditions. The upshift of scattered light can avoid the fluorescence or phosphorescence that is usually red‐shifted with respect to the excitation wavelength. However, this method's competence is circumscribed by its low scattering efficiency, which results from an insufficient population of upper vibrational states that obey temperature‐dependent Boltzmann statistics. To overcome this limitation, we propose that the mode‐selective absorption of overtone or combination vibrations leads to enhanced anti‐Stokes Raman scattering under simultaneous optical pumping and Raman excitation. In this work, we applied near‐infrared (NIR) pumping resonant with vibrational overtones of nonfluorescent systems. Vibrationally resonant pumping is efficient for population transfer, and the excess energy is thermodynamically distributed over all fundamental vibrations. Furthermore, we present that NIR absorbing molecules can be employed as matrices to amplify anti‐Stokes Raman signals of weak scattering targets.

Rate Constants and Branching Ratios for the Self-Reaction of Acetyl Peroxy (CH3C(O)O2•) and Its Reaction with CH3O2

The self-reaction of acetylperoxy radicals (CH3C(O)O2•) (R1) as well as their reaction with methyl peroxy radicals (CH3O2•) (R2) have been studied using laser photolysis coupled to a selective time resolved detection of three different radicals by cw-CRDS in the near-infrared range: CH3C(O)O2• was detected in the Ã-X˜ electronic transition at 6497.94 cm−1, HO2• was detected in the 2ν1 vibrational overtone at 6638.2 cm−1, and CH3O2• radicals were detected in the Ã-X˜ electronic transition at 7489.16 cm−1. Pulsed photolysis of different precursors at different wavelengths, always in the presence of O2, was used to generate CH3C(O)O2• and CH3O2• radicals: acetaldehyde (CH3CHO/Cl2 mixture or biacetyle (CH3C(O)C(O)CH3) at 351 nm, and acetone (CH3C(O)CH3) or CH3C(O)C(O)CH3 at 248 nm. From photolysis experiments using CH3C(O)C(O)CH3 or CH3C(O)CH3 as precursor, the rate constant for the self-reaction was found with k1 = (1.3 ± 0.3) × 10−11 cm3s−1, in good agreement with current recommendations, while the rate constant for the cross reaction with CH3O2• was found to be k2 = (2.0 ± 0.4) × 10−11 cm3s−1, which is nearly two times faster than current recommendations. The branching ratio of (R2) towards the radical products was found at 0.67, compared with 0.9 for the currently recommended value. Using the reaction of Cl•-atoms with CH3CHO as precursor resulted in radical profiles that were not reproducible by the model: secondary chemistry possibly involving Cl• or Cl2 might occur, but could not be identified.

Two-color resonance enhanced multiphoton ionization spectroscopy of o-hydroxybenzonitrile and Franck-Condon simulation

The cyano group is a typical electron-withdrawing group, which has aroused the interest of relevant researchers. Many papers reported the dispersed fluorescence spectra of o-hydroxybenzonitrile, its dimers, and complexes with small molecules, aiming to study the intermolecule hydrogen bond and the vibration features of the electronic ground state. There are also reports on using fluorescence excitation spectra to study excited state vibrations, but no report on the systematical analyzing of the vibration features of excited state spectra. Compared with fluorescence spectroscopy, resonance enhanced multiphoton ionization (REMPI) spectroscopy detects ions to obtain excited state energy level data, which has mass-resolution capability, and eliminates the interference of impurities with different charge-to-mass ratios. The strong electron-withdrawing ability of cyano group results in higher ionization energy for molecules containing cyano groups. Many REMPI experiments on benzonitrile derivatives require two-color lasers. In this paper, two-color resonance enhanced two-photon ionization experiment is performed by using a home-made linear time-of-flight mass spectrometer, and the vibration-resolved REMPI spectrum of o-hydroxybenzonitrile is obtained for the first time. Combining the high-precision density functional theory calculations with the Franck-Condon spectral simulations, the spectral characteristics are analyzed in detail, and a large number of fundamental, overtone and combined vibrations are found. The spectral assignment is carried out as accurately as possible. Most of the fundamental vibrations located at ring are assigned to the in-plane distortion or swing of the ring, which is related to the expansion of the ring during the molecular excitation. Theoretical and experimental results show that the low-frequency signal of REMPI spectrum is strong, the background is low, the band is less, and the resolution is good. As the vibration frequency increases, the signal changes in the worse direction. This is because the low-frequency spectrum mainly comes from the low-frequency fundamental vibrations and a little contribution from overtones. As the vibration frequency increases, the contributions from overtone and combined vibrations gradually increase, resulting in dense bands and low resolution. Theoretical calculations show that the high-order vibration and combination of multi-mode vibrations usually have a lower Franck-Condon factor, so the signal gradually becomes weak as the frequency increases, and the signal-to-noise ratio becomes worse.

Contribution of vibrational overtone excitations to positron annihilation rates for benzene and naphthalene

Positron-electron annihilation spectra of benzene, deuterated benzene, and naphthalene were theoretically calculated as a function of positron collision energy using Feshbach vibrational resonance energies and widths, which can be obtained from the correlation-polarization-potential model. We found that the contribution of overtone excitations to the annihilation spectrum becomes large for the vibrational mode, where structural deformation along the corresponding vibrational coordinate significantly changes the positron binding energy and polarizability. This behavior occurs for the ${\ensuremath{\nu}}_{2}$ vibrational mode in benzene and deuterated benzene, corresponding to symmetric ring stretching. Since the incoming positron is dominantly attracted by the \ensuremath{\pi} electrons of benzene, we conclude that the ring stretching vibration largely affects the \ensuremath{\pi}-electron density of the benzene ring.

Rate Constant and Branching Ratio for the Reactions of the Ethyl Peroxy Radical with Itself and with the Ethoxy Radical

The self-reaction of the ethyl peroxy radical (C2H5O2) (1) has been studied using laser photolysis coupled to a selective time-resolved detection of two different radicals by continuous-wave cavity ring-down spectroscopy (cw-CRDS) in the near-infrared range: C2H5O2 was detected in the Ã-X̃ electronic transition at 7596 cm–1 and HO2 was detected in the 2ν1 vibrational overtone transition at 6638.2 cm–1. Radicals were generated from pulsed 351 nm photolysis of the C2H6/Cl2 mixture in the presence of O2. The reaction can proceed via a radical propagation channel, leading to two C2H5O radicals (1a) or to stable products (1b/1c). Because C2H5O radicals react subsequently with O2, leading to HO2, which in turn reacts rapidly with C2H5O2, knowledge of the branching ratio is indispensable for retrieving the rate constant. A strong disagreement exists about the rate constant and the branching ratio of (1) between the recommendation of the IUPAC (Atkinson et al., Atmos. Chem. Phys. 2006, 3625) or JPL (Publication 19-5, 2020) and a recent, more direct measurement (Noell et al., J. Phys. Chem. A 2010, 6983). The rate constant for the self-reaction has been found here to be k1 = (1.0 ± 0.2) × 10–13 cm3 s–1 with the branching fraction of the C2H5O radical channel being α = (0.31 ± 0.06), being in contradiction with the recommendations, but confirming the most recent measurement and indicating that the current recommendation for this reaction should be revised. The reaction of C2H5O2 with the ethoxy radical (C2H5O) can also be involved in the reaction mechanism, and its rate constant is also extracted from modeling. It is found to be k9 = (7 ± 1.5) × 10–12 cm3 s–1, two times slower than the only available measurement from Noell et al. J. Phys. Chem. A 2010, 6983.

Vibration fault identification of a turbojet engine based on cepstrum analysis

A vibration fault identification method based on vibration state characteristics of a turbojet engine and cepstrum analysis technology was proposed in this paper, and the application of cepstrum in vibration analysis of an aero-engine was also discussed. The vibration data of the turbojet engine in three different test cases of 0.8 rated state, max power state, and afterburning state were analyzed using the cepstrum analysis method. The periodic components and the characteristics of multi-component side-frequency complex signals in the dense overtone vibration signals were separated and extracted, which reflected the sensitivity of the positions of the compressor casing and the turbine casing to the harmonic vibration components of high- and low-pressure rotors and the characteristic difference of different vibration parts. Thus, effective identification of vibration faults was achieved. The results shows that the cepstrum analysis technique applied to the vibration analysis of the turbojet engine can better identify the sideband components of the frequency domain modulated signal and enhance the recognition capability of the fault frequency component, which is helpful to identify the engine vibration fault quickly and accurately.

Near-Infrared Spectroscopy Study of Serpentine Minerals and Assignment of the OH Group

Three different kinds of serpentine mineral samples were investigated using Fourier transform near-infrared spectroscopy (FTNIR). The results show that there are obvious differences in the characteristic infrared spectra of the three serpentine group minerals (lizardite, chrysotile, and antigorite), which can easily be used to identify these serpentine minerals. The combination of weak and strong peaks in the spectrum of lizardite appears at 3650 and 3690 cm−1, while the intensities of the peaks at 4281 and 4301 cm−1 (at 7233 and 7241 cm−1, respectively) are similar. A combination of weak and strong peaks in chrysotile appears at 3648 and 3689 cm−1 and at 4279 and 4302 cm−1, and a single strong peak appears at 7233 cm−1. In antigorite, there are strong single peaks at 3674, 4301, and 7231 cm−1, and the remaining peaks are shoulder peaks or are not obvious. The structural OH mainly appears as characteristic peaks in four regions, 500–720, 3600–3750, 4000–4600, and 7000–7600 cm−1, corresponding to the OH bending vibration, the OH stretching vibration, the OH secondary combination vibration, and the OH overtone vibration, respectively. In the combined frequency vibration region, the characteristic peak near 4300 cm−1 is formed by the combination of the internal and external stretching vibrations and bending vibrations of the structural OH group. The overtone vibrations of the OH stretching vibration appear near 7200 cm−1, and the practical factor is about 1.965. The near-infrared spectra of serpentine minerals are closely related to their structural differences and isomorphous substitutions. Therefore, near-infrared spectroscopy can be used to identify serpentine species and provides a basis for studies on the genesis and metallogenic environment of these minerals.

On the “Matsubara heating” of overtone intensities and Fermi splittings

Classical molecular dynamics (MD) and imaginary-time path-integral dynamics methods underestimate the infrared absorption intensities of overtone and combination bands by typically an order of magnitude. Plé et al. [J. Chem. Phys. 155, 2863 (2021)] have shown that this is because such methods fail to describe the coupling of the centroid to the Matsubara dynamics of the fluctuation modes; classical first-order perturbation theory (PT) applied to the Matsubara dynamics is sufficient to recover most of the lost intensity in simple models and gives identical results to quantum (Rayleigh-Schrödinger) PT. Here, we show numerically that the results of this analysis can be used as post-processing correction factors, which can be applied to realistic (classical MD or path-integral dynamics) simulations of infrared spectra. We find that the correction factors recover most of the lost intensity in the overtone and combination bands of gas-phase water and ammonia and much of it for liquid water. We then re-derive and confirm the earlier PT analysis by applying canonical PT to Matsubara dynamics, which has the advantage of avoiding secular terms and gives a simple picture of the perturbed Matsubara dynamics in terms of action-angle variables. Collectively, these variables "Matsubara heat" the amplitudes of the overtone and combination vibrations of the centroid to what they would be in a classical system with the oscillators (of frequency Ωi) held at their quantum effective temperatures [of ℏΩi coth(βℏΩi/2)/2kB]. Numerical calculations show that a similar neglect of "Matsubara heating" causes path-integral methods to underestimate Fermi resonance splittings.

Anharmonic Vibrational Spectrum and Experimental Matrix Isolation Study of Thioformic Acid Conformers—Potential Candidates for Molecular Cloud and Solar System Observations?

Abstract Thioformic acid (TFA) is the sulfur analog of formic acid, the simplest organic acid. It has three analogs, HCOSH, HCSOH, and HCSSH, each of them having two rotational isomeric (rotameric) forms: trans and cis where the trans form is energetically more stable. In this article, we study computational energetics and anharmonic vibrational spectrum of TFA, including overtone and combination vibrations. We also studied experimental photoisomerization and photodecomposition channels of HCOSH molecules with different wavelengths. We suggest that TFA is a potential sulfur-containing candidate molecule for interstellar and planetary observations and discuss these in light of different radiation environments in space. More generally, we discuss that infrared radiation-driven photoisomerization reactions may be a common phenomenon in such environments and can affect the chemical reaction pathways of organic and other interstellar molecules.

A hybrid erbium(III)-bacteriochlorin near-infrared probe for multiplexed biomedical imaging.

Spectrally distinct fluorophores are desired for multiplexed bioimaging. In particular, monitoring biological processes in living mammals needs fluorophores that operate in the 'tissue-transparent' near-infrared (NIR) window, that is, between 700 and 1,700 nm. Here we report a fluorophore system based on molecular erbium(III)-bacteriochlorin complexes with large Stokes shift (>750 nm) and narrowband NIR-to-NIR downconversion spectra (full-width at half-maximum ≤ 32 nm). We have found that the fast (2 × 109 s-¹) and near-unity energy transfer from bacteriochlorin triplets to the erbium(III) 4I13/2 level overcomes the notorious vibrational overtones quenching, resulting in bright and long-lived (1.73 μs) 1,530 nm luminescence in water. We demonstrate the excitation/emission-multiplexed capability of the complexes in the visualization of dynamic circulatory and metabolic processes in living mice, and through skull tracking of cancer cell metastases in mouse brain. This hybrid probe system facilitates robust multiplexed NIR imaging with high contrast and spatial resolution for applications ranging from fluorescence-guided surgery, diagnostics and intravital microscopy.