COMPETITIVE SELF-ASSEMBLY AND ELECTROCHEMISTRY OF SOME FERROCENYL-N-ALKANETHIOL DERIVATIVES ON GOLD

Three ferrocenyl-alkanethiol derivatives with different functional gro ups linking ferrocene to an alkanethiol chain have been synthesized an d characterized electrochemically in bulk solution and in self-assembl ed monolayer films on gold electrodes. Relative affinities of the ferr ocenyl-alkanethiols and of the corresponding n-alkanethiols for the el ectrode surface were evaluated by the competitive self-assembly method . The affinity of the ferrocenyl-alkanethiols for the surface, relativ e to that of the corresponding alkanethiols, is a function of the pola rity of the functional group linking ferrocene to the alkanethiol chai n. In general, nonpolar linking groups (methylene) show a stronger aff inity for the surface than do polar groups (carboxamides) and especial ly charged groups (quaternary ammonium salts). It is postulated that e lectrostatic effects are critically important during self-assembly. Re dox potentials for the three ferrocenyl-alkanethiol derivatives scale approximately with the electron donating/withdrawing effects of the fu nctional groups on the cyclopentadiene rings. However, redox potential s for the surface-confined molecules are consistently more positive th an for the identical molecules in bulk solution.