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Your search keyword '"Wegner, Hermann A."' showing total 98 results
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98 results on '"Wegner, Hermann A."'

22. A Long‐Lived Azafullerenyl Radical Stabilized by Supramolecular Shielding with a [10]Cycloparaphenylene

Author

Stergiou, Anastasios, Rio, Jérémy, Griwatz, Jan H., Arčon, Denis, Wegner, Hermann A., Ewels, Christopher P., and Tagmatarchis, Nikos

Subjects
Steric effects, long-lived radicals, Fullerene, Materials science, Radical, Supramolecular chemistry, host–guest complexes, 010402 general chemistry, Photochemistry, 01 natural sciences, Catalysis, law.invention, Radical Chemistry, Paramagnetism, law, photoinduced radical generation, Electron paramagnetic resonance, Hyperfine structure, Research Articles, azafullerenes, [10]cycloparaphenylene, 010405 organic chemistry, General Medicine, General Chemistry, 0104 chemical sciences, Unpaired electron, Research Article
Abstract

A major handicap towards the exploitation of radicals is their inherent instability. In the paramagnetic azafullerenyl radical C59N., the unpaired electron is strongly localized next to the nitrogen atom, which induces dimerization to diamagnetic bis(azafullerene), (C59N)2. Conventional stabilization by introducing steric hindrance around the radical is inapplicable here because of the concave fullerene geometry. Instead, we developed an innovative radical shielding approach based on supramolecular complexation, exploiting the protection offered by a [10]cycloparaphenylene ([10]CPP) nanobelt encircling the C59N. radical. Photoinduced radical generation is increased by a factor of 300. The EPR signal showing characteristic 14N hyperfine splitting of C59N.⊂ [10]CPP was traced even after several weeks, which corresponds to a lifetime increase of >108. The proposed approach can be generalized by tuning the diameter of the employed nanobelts, opening new avenues for the design and exploitation of radical fullerenes., A radical shielding approach based on supramolecular complexation exploits the protection offered by a [10]cycloparaphenylene ([10]CPP) nanobelt encircling C59N. to stabilize this radical. The EPR signal of C59N.⊂[10]CPP showing characteristic 14N hyperfine splitting was observed even several weeks after its generation.

Published
2019
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23. Exploring London Dispersion and Solvent Interactions at Alkyl–Alkyl Interfaces Using Azobenzene Switches

Author

Strauss, Marcel A. and Wegner, Hermann A.

Subjects
spectroscopy, solvent effects, 010402 general chemistry, 01 natural sciences, London dispersion force, Catalysis, chemistry.chemical_compound, Dispersion Interactions, molecular probes, Alkyl, chemistry.chemical_classification, 010405 organic chemistry, Chemistry, Communication, Intermolecular force, General Chemistry, Communications, 0104 chemical sciences, Crystallography, Azobenzene, Intramolecular force, London dispersion, Solvent effects, azobenzenes, Isomerization, Two-dimensional nuclear magnetic resonance spectroscopy
Abstract

Interactions on the molecular level control structure as well as function. Especially interfaces between innocent alkyl groups are hardly studied although they are of great importance in larger systems. Herein, London dispersion in conjunction with solvent interactions between linear alkyl chains was examined with an azobenzene‐based experimental setup. Alkyl chains in all meta positions of the azobenzene core were systematically elongated, and the change in rate for the thermally induced Z→E isomerization in n‐decane was determined. The stability of the Z‐isomer increased with longer chains and reached a maximum for n‐butyl groups. Further elongation led to faster isomerization. The origin of the intramolecular interactions was elaborated by various techniques, including 1H NOESY NMR spectroscopy. The results indicate that there are additional long‐range interactions between n‐alkyl chains with the opposite phenyl core in the Z‐state. These interactions are most likely dominated by attractive London dispersion. This work provides rare insight into the stabilizing contributions of highly flexible groups in an intra‐ as well as an intermolecular setting., An azobenzene setup was used to examine London dispersion in conjunction with solvent interactions between linear alkyl chains. 1H NOESY NMR analysis indicated additional long‐range interactions with the opposite phenyl core in the Z‐isomer. This work provides rare insight into the stabilizing contributions of highly flexible groups in an intra‐ as well as an intermolecular setting.

Published
2019
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