Theoretical study of molecular rectification in porphyrin dimer

Carrying out theoretical calculations using the density functional method for nonequilibrium electron transport, we investigated the electric conductibility of a porphyrin dimer coupled to gold electrodes by thiolate bonds. A porphyrin with four electron-donating amino groups in the dimer is connected to a porphyrin with four electron-withdrawing cyano groups by a dimethylene bridge. The calculations demonstrated that this dimer allows more flow of electrons from the first porphyrin (donor) to the second porphyrin (acceptor) than in the opposite direction. This means that the porphyrin dimer has favorable rectifier characteristics that are accounted for by the mechanism of not Aviram and Ratner [Chem. Phys. Lett. 29 (1974) 277] but of Stokbro, et al. [J. Am. Chem. Soc. 125 (2003) 3674].