Comparison of Electron-Transfer and Charge-Retention Characteristics of Porphyrin-Containing Self-Assembled Monolayers Designed for Molecular Information Storage

The redox kinetics for a variety of porphyrin-containing self-assembled monolayers (SAMs) on Au are reported. The measurements probe both the rate of electron-transfer (k0) for oxidation (in the presence of applied potential) and the rate of charge dissipation after the applied potential is disconnected (characterized by a charge-retention half-life (t1/2)). The porphyrins include (1) monomeric Zn complexes that contain phenylmethylene linkers wherein the number of methylene spacers varies from 0 to 3, (2) monomeric Zn complexes that contain different ethynylphenyl-derived linkers, and (3) a triple-decker lanthanide sandwich complex with a phenylethynylphenyl linker. The k0 values for all the porphyrin SAMs are in the range of 104−105 s-1. The k0 values for the monomeric ethynylphenyl-linked porphyrin SAMs are generally faster than those for the monomeric phenylmethylene-linked SAMs. The rates for the latter SAMs decrease as the number of methylene spacers increases. The rates for the triple-decker SAM ar...