Role of the extent of -electron conjugation in visible-light assisted molecular anchoring on Si(111) surfaces

• Published in: Superlattices and microstructures Vol. 46; no. 1-2; pp. 30 - 33
• Main Authors: Boccia, A., Decker, F., Marrani, A.G., Stranges, S., Zanoni, R., Cossi, M., Iozzi, M.F.
• Format: Journal Article
• Language: English
• Published: 01.08.2009
• Subjects: Anchoring; Carbon-carbon composites; Conjugation; Electrode potentials; Electrodes; Semiconductors; Silicon; Wafers
• ISSN: 0749-6036
• DOI: 10.1016/j.spmi.2008.11.005

The first theoretical and experimental study is reported of the hybrid species resulting from a selected series of differently substituted ferrocenes anchored on Si(111) with their lateral arm. Si functionalized wafers were produced following extra-mild conditions, by exposing H-Si(111) surfaces, brought in contact with each molecular species under controlled conditions, to visible-light. It has been reported in the literature that vinylferrocene molecules adopt preferential arrangements when exposed to Si(100) from the gas phase, resulting in a peculiar self-assembling geometry. Nothing was known, however, on the same system on the Si model surface (111). Ethylferrocene, vinylferrocene and ethynylferrocene were anchored on Si(111) and the resulting hybrids were characterized by XPS and tested as semiconductor electrodes in a cell. We were motivated by our previous results on the same molecules, where we found that the conjugation of the C-C lateral arm with the ferrocene moiety plays a role in the electronic structure of the free molecules and in the electrochemical response of the corresponding hybrids on Si(100). Distinct experimental values of redox potentials were reproducibly shown by the hybrids, which calls for different arrangements of the tethering arms bound to Si. A linear relationship is found between the redox potentials obtained from the functionalized wafers used as electrodes in a cell and the values of the first ionization energy observed for the free molecules in the gas-phase, previously explored by synchrotron radiation photoemission. On the basis of our previous findings, the reproducibly distinct values of redox potentials displayed by the hybrids hint at a preservation of the nature of the C-C bond present in the anchoring arm of the precursor upon addition to silicon.