Molecular orientation and reactions probed via SERS

Abstract

Surface enhanced Raman spectroscopy (SERS) can be combined with electrochemical techniques (EC-SERS) to allow the in situ analysis of electrode surfaces, including understanding the fundamental interactions between the electrode and adsorbed molecules, and identifying the intermediates, products and mechanisms of electrochemical reactions. In this work, the potential dependent orientation of ortho-, meta- and para- nitrile substituted benzenethiol self assembled monolayers (SAMs) has been investigated on Au sphere segment void (SSV) substrates by analysis of the in plane and out of plane SERS vibrational band intensities, peak positions and the selection rules. The electroreduction of p-nitrothiophenol (PNTP) and electrooxidation of p-aminothiophenol (PATP) SAMs have also been probed. By using density functional theory (DFT) calculated Raman spectra evidence of new intermediate species has been discovered for both reactions, including a different oxidation mechanism for PATP in acidic and alkaline media. Furthermore, the adsorption and orientation of thioamide terminated molecular wires, an interesting new species for molecular electronics, has been investigated by examining both the absence of expected vibrations and the most intense SERS bands. Finally, further understanding of glycerol electrooxidation has important applications in direct liquid fuel cells (DLFCs), but has a complex reaction mechanism with many intermediates. By careful analysis of the peak pattern of in situ SERS spectra, intermediate species have been identified and the reaction mechanism uncovered.

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Identifiers

ORCID for Andrea E. Russell: orcid.org/0000-0002-8382-6443

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