The reaction of a methyl-substituted benzylazide on the silicon (001) surface was investigated by means of X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and density functional theory (DFT)-based computations. It was found that the reaction takes place via an intermediate state, which could be experimentally observed at low temperatures. XPS analysis showed that at temperatures of 150 K and above, the azide further reacts on the silicon surface via abstraction of N 2 . The final state sees the remaining nitrogen atom of the adsorbate binding covalently to the surface. In the STM images, this final state is associated with two different adsorption configurations. In comparison with DFT calculations, these two configurations are assigned to the molecule being bound via the nitrogen atom only and to a configuration with the molecule bound to the substrate via the nitrogen atom and carbon ring simultaneously.

An additive-free chemoselective ligation of dual clickable building blocks is demonstrated. The challenge of balancing reactivity and stability was achieved by employing a small, electron-deficient tetrazine bearing an azido group and an enol ether functionalized cyclooctyne. The chemoselective sequence of strain-promoted azide−alkyne cycloaddition (SPAAC) and inverse-electron-demand Diels−Alder (IEDDA) reaction is demonstrated with a cholic acid derived triazide as a molecular surface model for layer-by-layer synthesis.

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.

Synthesis of organic bilayers on silicon was realized by a combination of surface functionalization under ultrahigh vacuum (UHV) conditions and solution-based click chemistry. The silicon (001) surface was prepared with a high degree of perfection in UHV and functionalized via chemoselective adsorption of ethynyl cyclopropyl cyclooctyne from the gas phase. A second organic layer was then coupled in acetonitrile via the copper-catalyzed alkyne−azide click reaction. The samples were directly transferred from UHV via the vapor phase of the solvent into the solution of reactants and back to UHV without contact to ambient conditions. Each reaction step was monitored by means of X-ray photoelectron spectroscopy in UHV; the N 1s spectra clearly indicated the click reaction of the azide group in the two test molecules employed, i.e., methyl-substituted benzyl azide and azide-substituted pyrene. In both cases, up to 50−60% of the ethynyl cyclopropyl cyclooctyne molecules on the surface were reacted.

Ether cleavage on the silicon (001) surface was investigated for a well-defined configuration of the ether group with respect to the underlying Si substrate. In order to maintain the reactants in a fixed orientation with respect to each other, cyclooctyne ether was chemoselectively attached on Si(001) via the strained triple bond of cyclooctyne. In this configuration, the ether group of this bifunctional molecule remains intact and its geometry with respect to the substrate is given by the cyclooctyne ring as a linker. The kinetics of the further reaction of the ether group at elevated temperatures was then investigated by means of real-time X-ray photoelectron spectroscopy using synchrotron radiation. A low activation barrier was deduced, which is interpreted in terms of the controlled configurations realized in the experiment in correlation with the underlying reaction mechanism.