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Electron-transport properties of ethyne-bridged diphenyl zinc-porphyrin molecules

We investigate the electron-transport properties of ethyne-bridged diphenyl zinc-porphyrin molecules suspended between gold (111) electrodes by first-principles calculations within the framework of density functional theory. It is found that the conductance of a molecular junction in which phenyl and porphyrin rings are perpendicular is reduced by three orders of magnitude compared with that of a junction in which the phenyl and porphyrin rings are coplanar. In the coplanar configuration, electrons are transmitted through $π$ states, which extend over the whole molecule. In the perpendicular configuration, the conductance is suppressed because of the reduction of electron hopping between $π$ states of the phenyl ring and $σ$ states of the porphyrin ring.