Electron transfer rates of alkyl-ferrocene molecules forming incomplete monolayer on silicon electrodes

Abstract

This study shows the results obtained when binding alkyl ferrocene molecules on silicon surface forming incomplete monolayers. The electrodic surface functionalization is carried out by a two step procedure: First, a hydrosilytation reaction between a Si-H surface and an alkenyl bromide active by white light; and then, the reaction of this surface with a monolithio ferrocene solution. Alkenyl bromide with different numbers of carbon atoms (3, 5 and 10 carbon atoms) were employed in order to obtain propyl, pentyl and decyl ferrocene chains on the electrodic surface. The samples of modified silicon were analyzed by X-ray photoelectron spectroscopy (XPS) and electrochemical measurements confirming the presence of ferrocene molecules on the electrode surface. The results obtained show that in each and every case, there were incomplete monolayers on the silicon surface, ranging from 16% to 42 %, depending on the alkenyl bromide employed in the synthesis. AC voltammetry was employed to determine the kinetic of the electron transfer between ferrocene molecules and the silicon electrode. However, the rate constant is not influenced by the length of the alkyl chain, and is usually constant (2.01 s-1 - 3.66 s-1). The result above is due to the electron transfer process which is determine by electron hopping in a regime of bonded diffusion and not by a long-rate electron transfer such as in a full compact monolayer. © 2010.