Conductivity measurements in single-molecule junctions: Meta-substituted benzene

Abstract

The conductance of substituted benzene molecules is measured in metal-molecule-metal junctions formed by breaking gold point contacts. In a previous study, we could see a clear peak in the conductance histogram of 1,4-benzenediamine but not in that of 1,3-benzenediamine. To understand this difference and to obtain a clear peak in meta-substituted molecule, we screen the molecules with different end groups and find methyl selenide and diphenylphosphine are measurable groups. 1,3-Bis(methylseleno)benzene shows a peak in the conductance histogram, whereas tetrahydrobenzo[1,2-b:5,4-b']diselenophene does not. In addition, 1,3-bis(diphenylphosphino)benzene reveals a sharper peak than 1,3-bis(methylseleno)benzene. We hypothesize the specific conformation of the end groups relative to the phenyl ring enables the favorable alignment of non-pair electrons for the electron tunneling through the molecule. The relative energies of conformers are being calculated.