Click reactions such as the most prominent alkyne azide coupling are generally performed in the presence of a catalyst dissolved in an adequate solvent. On the other hand, highly reactive surfaces such as the technologically most important Si(001) surface, are typically prepared and stored under UHV conditions in order to guarantee a high level of cleanliness and structural perfection. The direct application of solution-based click chemistry schemes to such vacuum-processed surfaces thus seems as an experimental contradiction. However, this combination could open the route to synthesizing new organic molecular architectures, e.g., with tailored optical or physicochemical properties, within the framework of vacuum-based technologies.<br/><br/>Here we use surface functionalization based on substituted cyclooctynes and their chemoselective reactivity on Si(001) in combination with a direct transfer from UHV into solution in order to apply solution-based click chemistry on a silicon surface prepared and functionalized under UHV conditions.<br/><br/>The UHV-based functionalization of the silicon (001) surface was realized via chemoselective adsorption of ethinyl cyclopropyl cyclooctyne (ECCO) from the gas phase. The second organic layer was then coupled in acetonitrile solution via the copper-catalyzed alkyne azide click reaction. For the latter step, the samples were directly transferred from UHV via the vapor phase of the solvent into the azide solution 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 benzylazide and azide substituted pyrene. Using optimized copper(I) catalysts, effective reaction yields of up to 75 % were measured. With pyrene substituted azide as reactant for the alkyne azide coupling of the second layer, an optically active molecular structure was covalently attached to silicon in a controlled manner. This demonstrates the potential of our strategy for a wide range of applications.

Solution-based alkyne azide coupling on functionalized Si(001) prepared under UHV conditions

ACS Spring Meeting 2021

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