Structural electronic study via XPS and TEM of sub-nanometric gold particles protected by calixarenes

In the last years, substituted ferrocenes have been investigated as active redox molecules, able to tune the response of a functionalized electrode (especially gold and silicon) on which they are adsorbed, due to their attractive electrochemical characteristics: fast electron-transfer rate, low oxidation potential, and two stable redox states [1]. Ferrocene derivatives present also the advantage of a facile tunability of their redox potential via substitution of one or more H atoms of the cyclopentadyenil (Cp) ring with distinct functional groups. We present the results of an experimental and theoretical investigation on pure ethyl-, vinyl and ethynylferrocene in the gas phase by means of NEXAFS at the C K-edge, and XPS of the C 1s region, and by DFT calculations. Such a combination probes both the state of charge of the C atoms of the substituent group of the three molecules, and the extent of conjugation of the C-C arm with the Cp ring. A reliable assignment of the characteristic NEXAFS features associated to double and triple C-C bond of the lateral substituents of such closely related molecules may offer the fingerprint of the preservation or loss of the unsaturation in the anchoring arm upon its reaction with a surface, as well as shed light on the reaction mechanism for the surface anchoring on Si with different recipes, which is an actively investigated, yet still open, issue.