Electrochimica Acta, Vol.305, 378-387, 2019
Potential dependent orientation of sulfanylbenzonitrile monolayers monitored by SERS
The change in orientation of 2-, 3-, and 4-sulfanylbenzonitrile (SBN) self assembled monolayers (SAMs) with respect to electrochemical potential was studied using surface-enhanced Raman spectroscopy (SERS). Being able to understand monolayer orientation under potential control has important applications in both sensors and molecular electronics, where orientation can affect sensitivity and electron transfer respectively. We characterise the vibrations of all three monolayers using a combination of experimental and density function theory (DFT) calculated spectra. The results reveal that the SERS intensities of both in plane (IP) and out of plane (OOP) modes of the aromatic ring and nitrile group are reversibly changed by potential, indicating an orientation change via variations in the tilt and/or twist angles. At more negative potentials the nitrile group of all three SAMs is more perpendicular to the electrode surface and at more positive potentials it is more parallel, governed by an electrostatic interaction between the nitrile group and the electrode surface. Additional effects of the applied potential are observed for the orientation of the ring with respect to the electrode surface through aromatic ring-surface pi interactions, confirmed by examination of the effects of the applied potential on the peak width of the C-C ring breathing mode. (C) 2019 Elsevier Ltd. All rights reserved.