Using X-ray induced photoelectron spectroscopy, the influence of Brønsted acids, namely sulfuric, nitric, and hydrochloric acid on the electronic properties of single-walled carbon nanotubes (SWCNTs) was investigated. Doping effects were monitored by changes in binding energy of the C 1s core level of the nanotubes. For all three acids, an acceptor type doping of the SWCNTs was observed by a shift of the C 1s core level towards lower binding energies. The inferred change of the Fermi-level position was 0.5 eV in the case of H 2 SO 4 , 0.2 eV in the case of HNO 3 , and 0.1 eV in the case of HCl. For HNO 3 and HCl the doping was found to be unstable. The S 2p, N 1s, and Cl 2p core level spectra of the corresponding acid showed spectral features which can be attributed to the respective oxidation state of these anions in the acid, indicating that doping was induced by intercalation.
Geriist sind bemerkenswert regioselektiv[" 'I; durch sukzessive Cyclopropanierung aquatorialer (e) 6-6-Doppelbindungen entsteht das T,-symmetrische Hexaaddukt C,,(COOEt),, lr2, 'I. Der bevorzugte Angriff von 6-6-Doppelbindungen, die sich in e-Positionen (Abb. 1) zu bereits gebundenen Addenden befinden, la& sich rnit einer kombi-R2
We describe for the first time the full reaction coordinate regarding the photoisomerization of red-absorbing norbornadienes (NBDs) to quadricyclanes (QCs). Our studies go beyond steady-state investigations by using an arsenal of timeresolved techniques. Importantly, the red absorption of NBDs is made possible by a different charge-transfer character; adjusting its strength enables control over the photoreversibility of the rearrangement. In the case of strong charge-transfer character (a weakly electron-withdrawing ester and a strongly electron-donating dimethylaniline), photoirradiation with visible light into the delocalized charge-transfer absorption of NBD affords QC reversibly. In stark contrast, UV photoirradiation into the NBD localized excited state leads to a photoinduced degradation and cannot be back-isomerized to NBD under any circumstances. If the charge-transfer character is weak (a weakly electron-withdrawing ester and a weakly electron-donating phenyl), reversibility is seen independently of the photoirradiation light.
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