We report a detailed experimental and theoretical study on high-order harmonic generation of a femtosecond Ti-sapphire laser focused at an intensity of around 1015 W cm−2 onto a high-pressure (50–210 mbar) neon gas cell of variable length (1–3 mm). Using thorough three-dimensional simulations, we discuss the interplay between the different factors influencing the harmonic-generation efficiency, i.e. phase matching determined by the electronic and atomic dispersions, re-absorption of the harmonics by the medium and refraction of the generating laser beam. Generically, we find that, in our generation conditions, the emission yield of harmonics from the plateau region of the spectrum is absorption limited, whereas the emission from harmonics in the cut-off is strongly reduced due to both electron dispersion and ionization-induced refraction of the laser beam. A good agreement between the numerical results and the experimental data is obtained for the harmonic yield dependence on the various generation parameters (gas pressure, medium length and laser intensity).
A time-resolved study of core-level chemical shifts in a monolayer of aromatic molecules reveals complex photoinduced reaction dynamics. The combination of electron spectroscopy for chemical analysis and ultrashort pulse excitation in the extreme ultraviolet allows performing time-correlated 4d-core-level spectroscopy of iodine atoms that probe the local chemical environment in the adsorbate molecule. The selectivity of the method unveils metastable molecular configurations that appear about 50 ps after the excitation and are efficiently quenched back to the ground state.
Here we present detailed investigations of UV-photoinduced dimerization of anthracene substructures without solvent environment at the level of molecular monolayers prepared on a surface. Monolayers prepared on silicon(100) substrates were analyzed by means of X-ray photoelectron spectroscopy (XPS) in the valence band region revealing significant changes in the carbon C 2s region (11-20 eV). SVWN DFT calculations were performed to understand the influence of the structural changes by dimerization. The geometric structure of the functionality was retrieved through B3LYP DFT calculations, which were performed ahead of the SVWN DFT ones, and the result of these calculations matches with the measured vibration signature. FTIR investigations of polybutadiene (PBD) volume backboned functionality were performed before and after irradiation.
An organic-inorganic hybrid polymer, composed of poly(methylsilsesquioxane) (PMSSQ) and poly(4-vinyl benzaldehyde) (PStCHO), is prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization of 4-vinyl benzaldehyde (StCHO) using a macro-chain transfer agent (CTA) based on PMSSQ. The obtained PMSSQ-PStCHO is spin-coated on substrates such as silicon wafers or copper plates to afford aldehyde-functionalized surfaces. Successful Kabachnik-Fields post-polymerization modifi cation (KF-PMR) of the aldehyde-functionalized surfaces is conducted with amines and dialkyl phosphonates, and characterized by surface analysis techniques including IR, energy-dispersive X-ray (EDX), and X-ray photoelectron spectroscopy (XPS) measurements, documenting the installation of α-amino phosphonates onto surfaces with practically quantitative conversion of aldehydes. In addition, the generated α-amino phosphonates are successfully deprotected to afford the corresponding α-amino phosphonic acids on surfaces, which make this route a reliable tool-enabling surface functionalization with α-amino phosphonic acids.surfaces. To expand the scope of functional materials featuring designed surface characteristics, a number of highly reactive and selective reactions, so-called "click reactions", have been employed. This includes Cu(I)-catalyzed and metal-free 1,3-dipolar cycloaddition (CuCAAC) reaction of organo-azides and alkynes, [ 1,2 ] thiol-ene, thiol-maleimide, [ 3 ] nucleophile-isocyanate, [ 4 ] and activated ester-amine reactions, which all realize a facile functionalization of substrate surfaces. [5][6][7][8] In spite of the fact that these click reactions have been employed in surface modifi cation chemistry, the intrinsic drawbacks of these conventional "click reactions" are: 1) only one functionality per one reaction can be achieved and 2) no functionality owing to linkages that are generated via reactions. In order to target material surfaces featuring more sophisticated functionalities, chemists need to propose a synthetic strategy realizing installation two or more functional molecules per single reactive site accompanied with a generation of an attracting linkage.
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