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Your search keyword '"Grass, Stéphane"' showing total 23 results
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23 results on '"Grass, Stéphane"'

1. Growth Dynamics and Electron Reflectivity in Ultrathin Films of Chiral Heptahelicene on Metal (100) Surfaces Studied by Spin‐Polarized Low Energy Electron Microscopy

Author

Baljozović, Miloš, Cauduro, André L Fernandes, Seibel, Johannes, Mairena, Anaïs, Grass, Stéphane, Lacour, Jérôme, Schmid, Andreas K, and Ernst, Karl-Heinz

Subjects
Condensed Matter Physics, Quantum Physics, Nanotechnology, Applied Physics
Abstract

Interaction of electrons with chiral matter gives rise to interesting phenomena such as the chirality-induced spin selectivity. The interdependence of reflectivity of spin-polarized low energy electrons and the absolute handedness of chiral molecules is investigated. First, the growth of homochiral films of helical aromatic hydrocarbons, so-called helicenes, on a Cu(100) surface is studied by means of low energy electron microscopy and scanning tunneling microscopy in ultrahigh vacuum. As soon as the coverage exceeds one monolayer, double-layer nucleation and growth is favored such that depletion in the first layer occurs. Spatially resolved work function measurements show that second-layer patches have a lower work function than first-layer areas. Reflectivity spectra of spin-polarized electrons do not show any asymmetry between homochiral films of the enantiomers. Laterally resolved work function measurements do not confirm work function differences such as those reported earlier for photoelectron studies of chiral peptide films on ferromagnetic substrates.

Published
2021

2. Spin- and angle-resolved photoemission spectroscopy study of heptahelicene layers on Cu(111) surfaces

Author

Baljozović, Miloš; https://orcid.org/0000-0002-2728-8142, Arnoldi, Benito, Grass, Stéphane; https://orcid.org/0000-0002-6598-3904, Lacour, Jerome; https://orcid.org/0000-0001-6247-8059, Aeschlimann, Martin; https://orcid.org/0000-0003-3413-5029, Stadtmüller, Benjamin; https://orcid.org/0000-0001-8439-434X, Ernst, Karl-Heinz; https://orcid.org/0000-0002-2077-4922, Baljozović, Miloš; https://orcid.org/0000-0002-2728-8142, Arnoldi, Benito, Grass, Stéphane; https://orcid.org/0000-0002-6598-3904, Lacour, Jerome; https://orcid.org/0000-0001-6247-8059, Aeschlimann, Martin; https://orcid.org/0000-0003-3413-5029, Stadtmüller, Benjamin; https://orcid.org/0000-0001-8439-434X, and Ernst, Karl-Heinz; https://orcid.org/0000-0002-2077-4922

Abstract

It has been demonstrated previously that electrons interact differently with chiral molecules depending on their polarization. For enantiomeric pure monolayers of heptahelicene, opposite asymmetries in spin polarization were reported and attributed to the so-called chirality-induced spin selectivity effect. However, these promising proof-of-concept photoemission experiments lack the angular and energy resolution that could provide the necessary insights into the mechanism of this phenomenon. In order to fill in the missing gaps, we provide a detailed spin- and angle-resolved photoemission spectroscopy study of heptahelicene layers on a Cu(111) substrate. Throughout the large accessible energy and angle range, no chirality induced spin asymmetry in photoemission could be observed. Possible reasons for the absence of signatures of the spin-dependent electron transmission through the chiral molecular layer are briefly discussed.

Published
2023

11. Enantiopure encaged Verkade's superbases: Synthesis, chiroptical properties, and use as chiral derivatizing agent

Author

Yang, Jian, primary, Chatelet, Bastien, additional, Hérault, Damien, additional, Dufaud, Véronique, additional, Robert, Vincent, additional, Grass, Stéphane, additional, Lacour, Jérôme, additional, Vanthuyne, Nicolas, additional, Jean, Marion, additional, Albalat, Muriel, additional, Dutasta, Jean‐Pierre, additional, and Martinez, Alexandre, additional

Published
2019
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13. Configurationally Stable Doubly-Bridged Biphenyl Azocines via Cu-Catalyzed Double Carbene Insertions into Corresponding Azepines

Author

Harthong Steven, Brun Elodie, Grass Stéphane, Besnard Céline, Bürgi Thomas, and Lacour Jérôme

Abstract

Doubly bridged biphenyl azocines can be prepared in a single step via copper catalyzed reactions of a doubly bridged biphenyl azepine and diazodiester reagents. Double [12] Stevens rearrangements occur at 100 °C to afford doubly tethered 8 membered rings (49 to 61) as trans and cis regioisomers (1:1 ratio). These products present an axial chirality. ECD and VCD analyses of the separated enantiomers (CSP HPLC) were used to assign the absolute configuration. High configurational stability is observed for both regioisomers as racemization does not occur after 1 week of heating at 208 °C in dodecane (?G‡ > 41 kcal/mol). Interestingly reactions performed at 40 °C retain a certain level of enantiospecificity (82 86) avoiding for the most part the thermal racemization of the starting material.

Published
2016
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14. Electrogenerated chemiluminescence of cationic triangulene dyes

Author

Adam Catherine, Wallabregue Antoine, Li Haidong, Gouin Jérôme, Grass Stéphane, Bosson Johann, Bouffier Laurent, Lacour Jérôme, and Sojic Neso

Abstract

Trianguleniums are fascinating conjugated hexacyclic cations that exhibit interesting electronic and optical properties. Herein the electrogenerated chemiluminescence (ECL) emission of this family of fluorescent dyes is reported for the first time. Redox behavior and fluorescence properties of eight cationic triangulene luminophores with different heteroatom patterns in the core structure and various pending substituents were examined to rationalize the ECL. Clearly the more electron rich the carbocations the more efficient the corresponding ECL and two very distinct classes of triangulenes can be drawn from these studies using an ECL wall sufficiency formalism.

Published
2015
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16. Enantiopure encaged Verkade's superbases: Synthesis, chiroptical properties, and use as chiral derivatizing agent.

Author

Yang, Jian, Chatelet, Bastien, Hérault, Damien, Dufaud, Véronique, Robert, Vincent, Grass, Stéphane, Lacour, Jérôme, Vanthuyne, Nicolas, Jean, Marion, Albalat, Muriel, Dutasta, Jean‐Pierre, and Martinez, Alexandre

Subjects
CIRCULAR dichroism, AZIDES, CHIRALITY, SPECTROMETRY
Abstract

Verkade's superbases, entrapped in the cavity of enantiopure hemicryptophane cages, have been synthesized with enantiomeric excess (ee) superior to 98%. Their absolute configuration has been determined by using electronic circular dichroism (ECD) spectroscopy. These enantiopure encaged superbases turned out to be efficient chiral derivatizing agents for chiral azides, underlining that the chirality of the cycloveratrylene (CTV) macrocycle induces different magnetic and chemical environments around the phosphazide functions. [ABSTRACT FROM AUTHOR]

Published
2020
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19. Asymmetric Synthesis of Dihydrofurans via Rh(II)-catalzed Cyclopropanation-Rearrangement of Enol Ethers with Silanyloxyvinyl Diazoacetates

Author

Muller, Paul, Bernardinelli, Gérald Hugues, Allenbach, Yves, Ferri, Maria, and Grass, Stéphane

Subjects
ddc:540, Carbenes, Diazo compounds, Stereoselectivity, Transition metals, Catalysis
Abstract

The cyclopropanation of dihydrofuran and dihydropy­ran with methyl 1-(silanyloxy)vinyl diazoacetates in the presence of chiral Rh(II)-catalysts affords cyclopropanes with high diastereo- and enantioselectivitiy. The cyclopropanes, in turn, rearrange to ­dihydrofurans upon desilylation with TBAF.

Published
2005

23. Merging polyacenes and cationic helicenes: from weak to intense chiroptical properties in the far red region.

Author

Duwald R, Bosson J, Pascal S, Grass S, Zinna F, Besnard C, Di Bari L, Jacquemin D, and Lacour J

Abstract

A series of helical tetracenes and pentacenes was synthesized from cationic [6] and [4]helicene precursors. These colorful acenes fluoresce in the far red region. While [4]helicene-based pentacenes exhibit chiroptical properties mainly in the UV region, [6]helicene-derived tetracenes show enhanced ECD in the visible range, in addition to clear CPL responses. This difference is rationalized using first principles., Competing Interests: Authors declares no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

Published
2019
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