1 research outputs found
Determination of the Local Electric Field at Au/SAM Interfaces Using the Vibrational Stark Effect
A comprehensive
understanding of physical and chemical processes
at biological membranes requires the knowledge of the interfacial
electric field which is a key parameter for controlling molecular
structures and reaction dynamics. An appropriate approach is based
on the vibrational Stark effect (VSE) that exploits the electric-field
dependent perturbation of localized vibrational modes. In this work,
6-mercaptohexanenitrile (C5CN) and 7-mercaptoheptanenitrile (C6CN)
were used to form self-assembled monolayers (SAMs) on a nanostructured
Au electrode as a simple mimic for biomembranes. The Cî—¼N stretching
mode was probed by surface enhanced infrared absorption (SEIRA) spectroscopy
to determine the frequency and intensity as a function of the electrode
potential. The intensity variations were related to potential-dependent
changes of the nitrile orientation with respect to the electric field.
Supported by electrochemical impedance spectroscopy, molecular dynamics
simulations, and quantum chemical calculations the frequency changes
were translated into profiles of the interfacial electric field, affording
field strengths up to 4 × 10<sup>8</sup> V/m (C6CN) and 1.3 ×
10<sup>9</sup> V/m (C5CN) between +0.4 and −0.4 V (vs Ag/AgCl).
These profiles compare very well with the predictions of a simple
electrostatic model developed in this work. This model is shown to
be applicable to different types of electrode/SAM systems and allows
for a quick estimate of interfacial electric fields. Finally, the
implications for electric-field dependent processes at biomembranes
are discussed