Search results for "PHOTOCHEMISTRY"
showing 10 items of 2034 documents
Isomer effects in fragmentation of Polycyclic Aromatic Hydrocarbons
2015
We have observed significant differences in the fragmentation patterns of isomeric Polycyclic Aromatic Hydrocarbon (PAH) cations following collisions with helium atoms at center-of-mass energies around 100 eV. This is in contrast to the situation at other collision energies or in photo-absorption experiments where isomeric effects are very weak and where the lowest-energy dissociation channels (H- and C2H2-loss) domihate in statistical fragmentation processes. In the 100 eV range, non-statistical fragmentation also competes and is uniquely linked to losses of single carbon atoms (CHx-losses). We find that such CHx-losses are correlated with the ionic ground state energy within a given group…
A Highly Luminescent Nitrogen-Doped Nanographene as an Acid- and Metal-Sensitive Fluorophore for Optical Imaging.
2021
Dibenzo[hi,st]ovalene (DBOV) has excellent photophysical properties, including strong fluorescence and high ambient stability. Moreover, the optical blinking properties of DBOV have enabled optical super-resolution single-molecule localization microscopy with an imaging resolution beyond the diffraction limit. Various organic and inorganic fluorescent probes have been developed for super-resolution imaging, but those sensitive to pH and/or metal ions have remained elusive. Here, we report a diaza-derivative of DBOV (N-DBOV), synthesized in eight steps with a total yield of 15%. Nitrogen (N)-bearing zigzag edges were formed through oxidative cyclization of amino groups in the last step. UV-v…
ChemInform Abstract: A Photochemical One-Pot Three-Component Synthesis of Tetrasubstituted Imidazoles.
2015
α-(alkylideneamino)nitriles generated in situ from α-aminonitriles and aldehydes react with acylaziridines formed in situ by photochemical ring transformation of isoxazoles.
Influence of hydrogen on paramagnetic defects induced by UV laser exposure in natural silica
2005
Diffusion limited reactions of point defects were investigated in amorphous SiO2 exposed to UV laser light. Electron spin resonance and in situ absorption measurements at room temperature evidenced the annealing of E' centers and the growth of H(II) centers both occurring in the post-irradiation stage and lasting a few hours. These transients are caused by reactions involving molecular hydrogen H2, made available by dimerization of radiolytic H0.
Diffusion and Reactions of Hydrogen inF2-Laser-IrradiatedSiO2Glass
2002
The diffusion and reactions of hydrogenous species generated by single-pulsed F2 laser photolysis of SiO-H bond in SiO2 glass were studied in situ between 10 and 330 K. Experimental evidence indicates that atomic hydrogen (H0) becomes mobile even at temperatures as low as approximately 30 K. A sizable number of H0 dimerize by a diffusion-limited reaction into molecular hydrogen (H2) that may migrate above approximately 200 K. Activation energies for the diffusion, inherently scattered due to the structural disorder in glass, are separated into three bands centered at approximately 0.1 eV for free H0, approximately 0.2 eV presumably for shallow-trapped H0, and approximately 0.4 eV for H2.
In-situ formation, thermal decomposition, and adsorption studies of transition metal carbonyl complexes with short-lived radioisotopes
2014
Abstract We report on the in-situ synthesis of metal carbonyl complexes with short-lived isotopes of transition metals. Complexes of molybdenum, technetium, ruthenium and rhodium were synthesized by thermalisation of products of neutron-induced fission of 249Cf in a carbon monoxide-nitrogen mixture. Complexes of tungsten, rhenium, osmium, and iridium were synthesized by thermalizing short-lived isotopes produced in 24Mg-induced fusion evaporation reactions in a carbon monoxide containing atmosphere. The chemical reactions took place at ambient temperature and pressure conditions. The complexes were rapidly transported in a gas stream to collection setups or gas phase chromatography devices.…
Kinetics of Anionic Living Copolymerization of Isoprene and Styrene Using in Situ NIR Spectroscopy: Temperature Effects on Monomer Sequence and Morph…
2019
The living anionic copolymerization of isoprene (I) and styrene (S) can afford a variety of different polymer microstructures that strongly depend on experimental parameters such as solvent, counte...
Molecules Forced to Interact: Benzene and Pentafluoroiodobenzene
2020
The in situ low-temperature (co)crystallization of liquids and gases, followed by a detailed structural study, represents an approach to engineer and discover novel materials that are not formed under ambient conditions. Single-crystal X-ray diffraction revealed dimorphism along with a hierarchy of particular interactions in pentafluoroiodobenzene, C6F5I(1), and its benzene cocrystal (C6F5I)(2)center dot C6H6 (2). There are four polymorphs, two of 1, 1-I and 1-II, and two of 2, 2-I and 2-II, and they all are principally dominated by I center dot center dot center dot F and F center dot center dot center dot F halogen interactions. The nature and the contribution of different interactions we…
Connecting Electron-Deficient and Electron-Rich Aromatics to Support Intermolecular Interactions in Crystals
2015
Five compounds bearing electron-deficient pentafluorophenyl as well as electron-rich (salicylate or indole) aromatic moieties connected by amide or ester linkages were investigated by X-ray diffraction. In the crystals, various interactions (π–π, lone pair–π) between the different aromatic units are important structure controlling factors in addition to the stronger inter- or intramolecular hydrogen bonds induced by the amide and ester moieties. The hydrogen bonding leads to polymeric and macrocyclic assembly of the molecular building blocks.
Cross-Dehydrogenative Couplings between Indoles and beta-Keto Esters: Ligand-Assisted Ligand Tautomerization and Dehydrogenation via a Proton-Assiste…
2014
Cross-dehydrogenative coupling reactions between β-ketoesters and electron-rich arenes, such as indoles, proceed with high regiochemical fidelity with a range of β-ketoesters and indoles. The mechanism of the reaction between a prototypical β-ketoester, ethyl 2-oxocyclopentanonecarboxylate, and N-methylindole has been studied experimentally by monitoring the temporal course of the reaction by (1)H NMR, kinetic isotope effect studies, and control experiments. DFT calculations have been carried out using a dispersion-corrected range-separated hybrid functional (ωB97X-D) to explore the basic elementary steps of the catalytic cycle. The experimental results indicate that the reaction proceeds v…