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Ice surfaces are widely present in our environment and participate in many important chemical reactions. We study the adsorption of acetone, a typical polar small organic molecule, on ice by combin...

Accurate measurements of semiconductor nanocrystal (NC) emission quantum yields (QYs) are critical to condensed phase optical refrigeration. Of particular relevance to measuring NC QYs is a longstanding debate as to whether an excitation energy-dependent (EED) QY exists. Various reports indicate existence of NC EED QYs, suggesting that the phenomenon is linked to specific ensemble properties. We therefore investigate here the existence of EED QYs in two NC systems (CsPbBr3 and CdSe) that are possible candidates for use in optical refrigeration. The influence of NC size, size-distribution, surface ligand, and as-made emission QYs are investigated. Existence of EED QYs is assessed using two approaches (an absolute approach using an integrating sphere and a relative approach involving excitation spectroscopy). Altogether, our results show no evidence of EED QYs across samples. This suggests that parameters beyond those mentioned above are responsible for observations of NC EED QYs.

Studies of biosorption and bioaccumulation of heavy metals deal mostly with challenging, inhomogeneous, and complex materials. Therefore, most reports describe only application studies, while fundamental research is limited to indirect methods and speculations on the binding mechanisms. In this study, we describe a method for detecting and isolating heavy metal-binding biomolecules directly from crude extracts. The underlying principle is terbium sensitization and fluorescence excitation spectroscopy used offline after a chromatographic run. Compounds interacting with metal ions inevitably change the coordination sphere of terbium, which is reflected in the excitation spectrum leading to metal-specific luminescence. Main advantages of our approach include simple, fast, and inexpensive experiment design, nondestructive measurements, and detection limits far below 1 mg. Here, we have applied our method for three promising biosorbents (green algae, moss, and cyanobacterium) and obtained first information on the character of active compounds isolated from each species.

One of the most fascinating questions in chemistry is why nature chose CGAT as the alphabet of life. Very likely, such selection was the result of multiple factors and a long period of refinement. Here, we explore how the intermolecular interactions influenced such process, by characterizing the formation of dimers between adenine, theobromine and 4-aminopyrimidine. Using a combination of mass-resolved excitation spectroscopy and DFT calculations, we determined the structure of adenine-theobromine and 4-aminopyrimidine-theobromine dimers. The binding energy of these dimers is very close to the canonical adenine-thymine nucleobases. Likewise, the dimers are able to adopt Watson-Crick conformations. These findings seem to indicate that there were many options available to build the first versions of the informational polymers, which also had to compete with other molecules, such as 4-aminopyrimidine, which does not have a valid attaching point for a saccharide. For some reason, nature did not select the most strongly-bonded partners or if it did, such proto-bases were later replaced by the nowadays canonical CGAT., We thank MICIU (PGC2018-098561-B-C21) and the Basque Government (IT1162-19) for financial support. A.C. thank the Basque Government for a pre-doctoral fellowship.

Accepted: 2021-10-05, PA2210048000

This study investigates the significantly different luminescent and chiroptical properties of tetracycline (TC) when coordinated to Eu(III). The approach involves understanding the 1) speciation of TC and 2) conformation and species formed between Eu(III) and TC in a ratio of 1 : 1 in a dimethylformamide (DMF) solution and as a function of the pH value. By identifying the conformational changes of the various 1 : 1 Eu(III) : TC species, the results from this study explain information on the local microenvironment about the Eu(III) metal center. In particular, 5 D0 ←7 F0 Eu(III) laser excitation spectroscopy was employed to distinguish the different types of species found in solution in order to understand the interaction between Eu(III) and TC. On the other hand, circularly polarized luminescence (CPL) spectroscopy was used to understand the structural changes within the 1 : 1 Eu(III) : TC complex that could be related to the chirality of the Eu(III)-containing species. The CPL spectrum serves as a "fingerprint" to indicate the conformational changes within the 1 : 1 Eu(III) : TC complex as a result of the chiroptical signal arising from the various Eu(III) : TC species.

Surface THz emission from GaSe and three transition metal dichalcogenide layered bulk crystals were measured as a function of the photoexciting optical pulse wavelength. The nonequilibrium carrier dynamics was additionally characterized by the optical pump – THz probe experiments. The obtained results were discussed in terms of the electron energy band structures and the details of the THz emission mechanisms.

The newly designed polythiophene chemosensors (PT1 and PT2) were synthesized via the Suzuki–Miyaura polymerization with appropriate yields. The photophysical properties of PTs thus obtained were examined by means of UV/vis, fluorescence, excitation spectroscopy, and time-correlated single-photon-counting method. The π–π* transitions around 400–600 nm and the emissions in the range of 400–650 nm were observed. The binding behavior of PTs was also investigated upon the interaction of tetrabutylammonium or tetrabutylphosphonium isophthalate, affording the binding constants (K) of 5790–8310 M−1, which were quite smaller than those observed in the corresponding repeating unit. The comprehensive analyses of the UV/vis data and theoretical calculation supports revealed the origins of scope and limitation toward signal-amplification sensing. The present results obtained herein will guide the development of new amplification chemosensors.

Fluorescence Excitation Spectroscopy (FES) analyses the emission of light from a sample in order to provide biochemical information and may be used as a measurement in the quality assessment of food systems. An introduction into the method of FES is presented, including the historical background of the development of the methodology based on Gurwitsch’s and Popp’s research into mitogenetic radiation and biophotons, as well as a description of the measurement devices. Food produce grown under organic, biodynamic and conventional farming systems are compared from three scientifically controlled field experiments (wheat in Switzerland, cocoa beans in Bolivia and apples in the Netherlands). The results are used to explain the epistemology and the specific quality criteria which may be evaluated by FES, including product-specific or species-specific emission spectra, expression of specific maturation, plant development stages, organisational performance, and aspects of the integrity of the plant and its resilience to stay healthy.

The measuring devices which are used for measuring delayed luminescence by Fluorescence Excitation Spectroscopy (FES) are described. Results are given to show the measured emission of food samples in relation to farming practices (biodynamic, organic, or conventional) and growing conditions. This overview points to the special food-quality aspects which could be evaluated by FES. A relation to molecular structures, the physiological status, or possible physiological processes are discussed as important for the characteristic delayed luminescence after colour- (wavelength-) specific excitation.

Ionizing irradiation is used to preserve foodstuffs and improve food safety, but it is not permitted for organic products, with the exception for using low doses (less than 500 mGy) for detection p...

The rare earth materials have attracted intensive attention due to their strong luminescent characteristic. However, the split fine Stark levels are difficult to be determined. Here we report a room-temperature detection for Stark levels of YNbO4: Er3+ using established laser-induced spectroscopy system with dye laser of superhigh resolution of wavelength at 0.005 nm. From excitation spectra, six split Stark levels of 4G11/2 (Er3+) were directly detected. Moreover, nonradiative relaxations of 4G9/2→4G11/2 and 4G11/2→2H11/2/ 4S3/2 have been observed with weighed lifetimes of 0.70 μs and 6.15 μs, and characteristic green emission of Er3+ (@555 nm) yields lifetime of 31.78 μs.

International audience

The plasmonic properties of tip-substrate composite systems are of vital importance to near-field optical spectroscopy, in particular tip-enhanced Raman spectroscopy (TERS), which enables operando studies of nanoscale chemistry at a single molecule level. The nanocavities formed in the tip-substrate junction also offer a highly tunable platform for studying field-matter interactions at the nanoscale. While the coupled nanoparticle dimer model offers a correct qualitative description of gap-mode plasmon effects, it ignores the full spectrum of multipolar tip plasmon modes and their interaction with surface plasmon polariton (SPP) excitation in the substrate. Herein, we perform the first tip-enhanced Raman excitation spectroscopy (TERES) experiment and use the results, both in ambient and aqueous media, in combination with electrodynamics simulations, to explore the plasmonic response of a Au tip-Au substrate composite system. The gap-mode plasmon features a wide spectral window corresponding to a host of tip plasmon modes interacting with the plasmonic substrate. Simulations of the electric field confinement demonstrate that optimal spatial resolution is achieved when a hybrid plasmon mode that combines a multipolar tip plasmon and a substrate SPP is excited. Nevertheless, a wide spectral window over 1000 nm is available for exciting the tip plasmon with high spatial resolution, which enables the simultaneous resonant detection of different molecular species. This window is robust as a function of tip-substrate distance and tip radius of curvature, indicating that many choices of tips will work, but it is restricted to wavelengths longer than ∼600 nm for the Au tip-Au substrate combination. Other combinations, such as Ag tip-Ag substrate, can access wavelengths as low as 350 nm.

We show that ultrasonication extracts inner tubes from double-wall carbon nanotubes (DWCNT), and characterize the process by density gradient ultracentrifugation (DGU) combined with in situ spectroscopic characterization in the density gradient. Our observations also cast new light on the question whether or not the inner tubes of DWCNTs fluoresce, which has been the subject of a long-standing debate, even though single‐DWCNT experiments have already shown drastic PL‐quenching for the inner CNT [1]. Indeed, in previous studies to characterise the PL from DWCNTs, they were typically solubilised using sonication, while here we see that upon sonication, the extraction of the inner tubes from the DWCNTs leads to much more, efficiently fluorescing SWCNTs. First, the DWCNTs were purified from SWCNTs and bundles using density gradient ultracentrifugation (DGU). Then, sonication is applied, after which the extracted inner tubes were separated from the DWCNTs by DGU and characterised by in situ resonant Raman and PL‐spectroscopy as a function of height in the centrifuge tube [2]. These subsequent in situ DGU experiments unambiguously prove the extraction of inner SWCNTs from DWCNTs, even by very brief sonication, and sonication-time-dependent measurements show that the process quickly saturates. [1] D. Levshov, R. Parret, H.-N. Tran, T. Michel, T.T. Cao, V.C. Nguyen, R. Arenal, V.N. Popov, S.B. Rochal, J.-L. Sauvajol, A.-A. Zahab, M. Paillet, Phys. Rev. B 96, 195410 (2017). [2] S. Cambré, P. Muyshondt, R. Federicci, W. Wenseleers, Nanoscale 7, 20015 (2015).

Single-wall carbon nanotubes (SWCNTs) possess unique electronic and optical properties that depend strongly on their exact chiral structure. Recent progress in the structure sorting of specific SWCNT chiralities, with increasing chiral purity[1], demands an effective characterization methodology to be developed to accurately determine the chiral composition of any SWCNT chirality. Very often, optical spectroscopy is used to assess the chiral composition of a sample, but absorption cross-sections, PL quantum efficiencies and Raman cross-sections are all depending on the exact chiral structure,[2] and can be strongly influenced by other factors such as the specific internal and external environment of the SWCNTs.[3] In this work, we systematically compare the chirality distribution obtained from 3 different optical spectroscopic techniques, i.e. absorption, wavelength-dependent Raman and fluorescence-excitation spectroscopy with the chirality distribution obtained from high-resolution transmission electron microscopy for both chirality-sorted and unsorted SWCNT samples. This combined approach demonstrates the importance of using a multi-technique characterization strategy for a reliable determination of SWCNT chirality distribution.[4] [1] J.A. Fagan, Nanoscale Adv. 1, 3307 (2019) and references therein [2] V.N. Popov, Nano Lett. 4, 1795 (2004) [3] S. Cambré et al, Angew. Chem. – Int Ed. 50, 2764 (2011); ACS nano 6, 2649 (2012) [4] A. Castan et al, Carbon 171, 968 (2021)

In situ and operando spectroscopic techniques are crucial for our understanding of complex heterogeneously catalyzed reactions. Under actual reaction conditions, however, many phenomena such as adsorption, (by)-product formation, and desorption of various species in different phases occur simultaneously, leading to crowded spectra that are difficult to interpret. About 15 years ago, modulation excitation spectroscopy (MES) was introduced to the heterogeneous catalysis community and has been increasingly applied since then. The periodic perturbation of a given system, in combination with phase-sensitive detection (PSD) analysis, significantly reduces noise, distinguishes between active and spectator species, and enables extraction of kinetic information. In this review article, we discuss the origin and theory of MES, summarize different application examples (with an emphasis on heterogeneous catalysis), and suggest future developments of the technique.

Ruby is a gem variety of corundum (α-Al2O3) that is colored red by trivalent chromium (Cr3+) substituting for Al3+ in the corundum structure. Recently, the beryllium (Be) heat treatment has been practiced as a technique to enhance the color of ruby. The ruby will turn orange to be an orange sapphire as a result of the enhancement. Some advanced technics to identify the Be heat-treated orange sapphire have been developed such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), secondary ion mass spectrometry (SIMS) and laser-induced breakdown spectroscopy (LIBS). We studied the effect of Be atoms in the corundum structure using the red, green, blue and purple laser excitation spectroscopy with the wavelengths of 634 nm, 545 nm, 452 nm and 408 nm respectively. The fluorescence spectra were analyzed for unheated, normal heat treatment and Be heat treatment synthetic ruby samples. The fluorescence intensity of the Be-heated samples was lowest compared to the unheated and normal treated ones for both high and low Cr content.

Inverse temperature crystallization of two‐dimensional organic–inorganic hybrid perovskites and systematic studies on their excitonic states by two‐photon excitation spectroscopy are reported. The exciton binding energies are similar for C4PI nanosheets and bulk crystals due to the weak interlayer coupling. Furthermore, dark excitonic 2p states are also observed.

The authors declare no competing financial interests. The author CH Tan thanks Malaysian Government MyBrainSc for the funding and also Matthew Davies from Swansea University for providing PL excitation spectroscopy instrument. Funding from the KAUST project OSR-2015-CRG-2572 is gratefully acknowledged. The authors also thank KAUST for financial support and acknowledge EC FP7 Project SC2 (610115), EC H2020 (643791), and EPSRC Projects EP/G037515/1 and EP/M005143/1.

The reactive surface sites of MoS2 hydrotreating catalysts (unpromoted as well as Co- and Ni-promoted) supported on MgAl2O4 spinel were investigated with respect to the substitution of sulfur by oxygen using in situ XAS coupled with modulation excitation spectroscopy (MES). Specifically, MES experiments were carried out by periodically cycling between a H2O and H2S containing hydrogen gas mixture at 400 °C. Due to the low fraction of S–O exchange, conventional XANES and EXAFS data hardly showed any changes when these catalysts were exposed to increasing ratios of H2O to H2S in an H2 atmosphere. XANES and EXAFS data extracted at the Mo K-edge by MES analysis showed that for approximately 1% of the Mo atoms, sulfur atoms are replaced by oxygen atoms when exposed to H2O, causing partial oxidation of these active sites. The reaction is reversible and Mo returns to its initial sulfide phase when H2O is removed and H2S is supplied in the feed. In the case of Co- and Ni-promoted catalysts, the magnitude of S–O exchange was found to be reduced, indicating the beneficial effect of promotion. MES at the Ni K-edge showed that Ni was oxidized during H2O exposure, which in turn delayed the Mo oxidation in the Ni-promoted catalyst. The structures of these catalysts under S–O exchange were modeled using density functional theory (DFT) calculations, showing that the edge atoms are affected strongly. For all three catalysts, OH substitution is more favorable, while O substitution could be possible at high H2O pressure for unpromoted MoS2. Mo K-edge XANES spectra calculated using these simulated structures support the results obtained from the MES experiments. The presented approach using MES in combination with XAS and supported by DFT can be extended in general to catalysts under operando conditions and is thus a useful tool for determination of the active site on an atomic-scale.

Intermolecular interactions are difficult to model, especially in systems formed by multiple interactions. Such is the case of caffeine-phenol. Structural data has been extracted by using mass-resolved excitation spectroscopy and double resonance techniques. Then the predictions of seven different computational methods have been explored to discover structural and energetic discrepancies between them that may even result in different assignments of the system. The results presented herein highlight the difficulty of constructing functionals to model systems with several competing interactions, and raise awareness of problems with assignments of complex systems with limited experimental information that rely exclusively on energetic data.

The underlying Michelson-Morley experiment [12.1] was made possible in an interferometer designed by Michelson for atomic spectroscopy in his attempt to establish a new meter standard using a suitably narrow spectral line, the red-line singlet not doublet of cadmium, via measuring visibility of a resultant two-beam interference pattern (see Chap. 3): \( {\text{V}} = \left( {{\text{I}}_{\hbox{max} } {-}{\text{I}}_{\hbox{min} } } \right)/\left( {{\text{I}}_{\hbox{max} } + {\text{I}}_{\hbox{min} } } \right) \).

We investigate the basis set requirements for calculating properties corresponding to removing core electrons by the Δ self-consistent-field approach using Hartree-Fock and density functional theory. Standard contracted basis sets are shown to produce large errors and the improved performance of core-augmented basis sets is traced to the fact that the core-augmenting functions effectively create an auxiliary set of uncontracted functions in the core region. We propose two specific basis sets of double and triple-ζ quality based on exponent interpolation of the polarization consistent basis sets, denoted pcX-1 and pcX-2, that display significantly lower basis set errors compared to other alternatives. These are suitable for both nonrelativistic and relativistic calculations of the Douglas-Kroll-Hess type, with typical basis set errors of 0.1 and 0.01 eV, respectively, and they can be used in a mixed basis set approach with only a minor degradation in performance. The versions augmented with diffuse functions (aug-pcX-1 and aug-pcX-2) are shown to perform better than other alternatives for X-ray absorption spectroscopy. When used in connection with range-separated hybrid density functional methods and relativistic corrections, the pcX -n basis sets can in favorable cases reproduce experimental results to within a few tenths of an eV.

Phytoplankton play a vital role as primary producers in aquatic ecosystems. One common approach to classifying phytoplankton is fluorescence excitation spectroscopy, which leverages the variation in types and concentrations of pigments among different phytoplankton taxonomic groups. Here, we used a fluorescence imaging photometer to measure excitation ratios (“signatures”) of single cells and bulk cultures of seven differently pigmented phytoplankton species as they progressed from nitrogen N-replete to N-depleted conditions. Our objective was to determine whether N depletion alters the fluorescence excitation signature of each species and, if so, how quickly they recover when N (as nitrate) was resupplied, because these factors affect our ability to classify the species correctly. Of the seven species studied, only Proteomonas sulcata, a marine cryptophyte, showed measurable changes in single-cell fluorescence excitation ratios and bulk fluorescence excitation spectra. These changes were likely due to decreases in the cellular concentration of phycoerythrin, a N-rich pigment, as N became scarce. Within 3 h of resupply of N, fluorescence signatures began returning to pre-depletion values and were indistinguishable from N-replete cells by 80 h after resupply. These data suggest that our classification approach is robust for non-PE containing phytoplankton. PE-containing phytoplankton might exhibit systematic changes in their signatures depending on their level of N depletion, but this could be detected and the phytoplankton re-classified following a few hours of incubation in N replete conditions.

Over the past 25 years, single-molecule spectroscopy has developed into a widely used tool in multiple disciplines of science. The diversity of routinely recorded emission spectra does underpin the strength of the single-molecule approach in resolving the heterogeneity and dynamics, otherwise hidden in the ensemble. In early cryogenic studies single molecules were identified by their distinct excitation spectra, yet measuring excitation spectra at room temperature remains challenging. Here we present a broadband Fourier approach that allows rapid recording of excitation spectra of individual molecules under ambient conditions and that is robust against blinking and bleaching. Applying the method we show that the excitation spectra of individual molecules exhibit an extreme distribution of solvatochromic shifts and distinct spectral shapes. Importantly, we demonstrate that the sensitivity and speed of the broadband technique is comparable to that of emission spectroscopy putting both techniques side-by-side in single-molecule spectroscopy., In single-molecule spectroscopy typically only emission spectra are recorded. Here, the authors develop a technique to record single-molecule excitation spectra under ambient conditions, which is robust against blinking and bleaching, and reveals a large distribution of spectra across the molecule ensemble.

We report the measurement of transition frequencies of Rb85 atoms in a room-temperature vapor cell to nP1/2 (n=34–53) and nP3/2 (n=34–87) Rydberg levels by observing single-photon Rydberg excitation spectroscopy. Based on the spectroscopic data, we determine quantum defects that are in good agreement with previous measurements of low-lying Rydberg states. Furthermore, the residuals between observed and calculated values of fine-splitting intervals in our experiments are found to be less than 10 MHz.

International audience; Studies on human norovirus are severely hampered by the absence of a cell culture system until the discovery of murine norovirus (MNV). The cell membrane domains called lipid rafts have been defined as a port of entry for viruses. This study is conducted to investigate murine norovirus binding on the mouse leukemic monocyte macrophage cell line. Lipid raft related structures are extracted from cells by detergent treatment resulting detergent-resistant membrane (DRMs) domains. The real-time polymerase chain reaction technique is performed to detect the viral genome, thereby the MNV binding on the DRMs. The interactions between MNV and DRMs are investigated by high-speed atomic force microscopy (HS-AFM) combined with surface-enhanced Raman spectroscopy (SERS). The inoculation of the virus onto cells results in the aggregations of detergent-resistant membrane domains significantly. The characteristic Raman band of MNV is found in inoculated samples. To be sure that these results are originated from specific interactions between DRM and MNV, methyl-a-cyclo-dextrin (MaCD) is applied to disrupt lipid rafts. The MNV binding on DRMs is precluded by the MaCD treatment. The cholesterols chains are defined as a key factor in the interactions between norovirus and DRMs. The authors conclude that the MNV binding involves the presence of DRMs and cholesterol dependent.

E-mail: bhboo@cnu.ac.krReceived August 23, 2012, Accepted October 28, 2012Key Words : 5,8-Dihydroxy-1,4-naphthoquinone, Fluorescence, Fluorescence excitation, TD DFT, Orbitalpopulation analysisExcited-state intramolecular proton transfer (ESIPT) hasbeen a research topic of incessant and wide interest becauseof its importance in many photophysical

3+1 Resonance-enhanced multiphoton ionization and photofragment excitation spectroscopy have been used to identify NH X(3)Σ(-) as a primary product of methylamine photodissociation after state-specific excitation to the S1 state. On the basis of standard thermochemical data, NH X(3)Σ(-) can be formed only in conjunction with closed-shell CH4 coproducts, indicating that dissociation must occur on the T1 surface. It is proposed that the mechanism for the formation of triplet NH and CH4 involves intramolecular abstraction between frustrated radical products and is an example of roaming-mediated intersystem crossing.