Modulation of Electronic Coupling through Self-Assembled Monolayers via Internal Chemical Modification

Self-assembled monolayers of ˆ-hydroxyalkanethiols at Au electrodes are used to probe the structural dependence of long-range electron transfer. The electron transfer rates for ferricyanide and osmium(III) tris(bipyridyl) are measured at Au electrodes coated with self-assembled monolayers of HO(CH2)n-X-(CH2)mSH where X denotes an ether, olefin, or alkyne function. Each of these modifications decreases the electronic coupling across the monolayers. Ab initio calculations of the neutral diradical splitting energies for modified and unmodified alkanes correctly predict these decreases in electronic coupling.