Measurements of the Potential Dependence of Electric Field Magnitudes at an Electrode Surface Using Fluorescent Probes in a Self-Assembled Monolayer.

This report details the measurement of the dependence of the electric field magnitude on applied potential in two regions of the electrical double layer, inside the Outer Helmholtz Plane OHP, i.e. inside the monolayer, and in the diffuse layer, for a metalorganic thin filmelectrolyte system. The self-assembled monolayers SAMs used in these experiments were formed from n-alkyl thiols on roughened Ag and roughened or smooth Au electrodes. The electric field magnitudes were calculated from the Stark shifts of a cationic fluorescent probe, an aminostyrylpyridinium derivative, that was immobilized in the SAM. The chain lengths of these alkyl thiols were varied to control the distance of the probe from the OHP and thus the relative position of the probe in the electrical double layer. Two cases were examined, one in which the probe was embedded within the SAM, and another in which the probe was external to the SAM. The composition of the monolayers and the orientation of the probe and n-alkyl thiol molecules within them were characterized using ex situ reflection-absorption Fourier transform infrared spectroscopy RA-FTIR. jg p3