RESUMO
The additive-free tetrazine/enol ether click reaction was performed in ultra-high vacuum (UHV) with an enol ether group covalently linked to a silicon surface: Dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate molecules were coupled to the enol ether group of a functionalized cyclooctyne which was adsorbed on the silicon (001) surface via the strained triple bond of cyclooctyne. The reaction was observed at a substrate temperature of 380â K by means of X-ray photoelectron spectroscopy (XPS). A moderate energy barrier was deduced for this click reaction in vacuum by means of density functional theory based calculations, in good agreement with the experimental results. This UHV-compatible click reaction thus opens a new, flexible route for synthesizing covalently bound organic architectures.
RESUMO
The reaction of methyl enol ether functionalized cyclooctyne on the silicon (001) surface was investigated by means of X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT). Three different groups of final states were identified; all of them bind on Si(001) via the strained triple bond of cyclooctyne but they differ in the configuration of the methyl enol ether group. The majority of molecules adsorbs without additional reaction of the enol ether group; the relative contribution of this configuration to the total coverage depends on substrate temperature and coverage. Further configurations include enol ether groups which reacted on the silicon surface either via ether cleavage or enol ether groups which transformed on the surface into a carbonyl group.
RESUMO
Selective adsorption of multifunctional molecules is rarely observed when the different functional groups react via nonactivated reaction channels. Although the latter is also the case for ether cleavage and the adsorption of C=C double bonds on the highly reactive Si(001) surface, we find that allyl ethers, which combine both functional groups, react on Si(001) selectively via the cleavage of the molecules' ether group. In addition, our XPS measurements at 90, 150, and 300 K indicate an increased reactivity of the ether group when compared to monofunctional ethers. STM investigations furthermore reveal different final adsorption configurations after ether cleavage of allyl methyl ether when compared to diethyl ether as the monofunctional reference molecule. The interaction of the two functional groups in one molecule thus leads to new reaction channels with higher reactivity for ether cleavage on Si(001). As a further consequence, the reactivity of the C=C double bond is suppressed up to room temperature, leading to the observed selective adsorption.
RESUMO
Desorption/ionization induced by neutral clusters (DINeC) in combination with mass spectrometry (MS) was used for the investigation of the molecular composition of the surface of ionic liquids (IL). Based on the surface sensitivity of DINeC-MS, accumulation of either cations or anions was discriminated on the surface of bulk IL depending on the molecular structure of the IL components. In particular, cations with long alkyl chains aggregate on the surface, but this tendency is more reduced the larger the respective anion is; in the case of larger anions and smaller cations, it can be even reversed. For thin layers of IL, the ratio between cations and anions as detected in the mass spectra was found to be further influenced by the substrate surface.