Oligo(phenyleneethynylene) as a molecular lead for STM measurement of single molecule conductance of a helical peptide

Molecular conductance of a linear conjugate of a helical peptide and an oligo(phenyleneethynylene) (OPE) (8OPE) was analysed by scanning tunneling spectroscopy. 8OPE molecules were embedded in a self-assembled monolayer (SAM) of 1-decanethiol (C10) on gold substrate. I–V profiles of 8OPE showed an asymmetric character in terms of the bias dependence when the scanning tunneling microscopy (STM) tip was put closely on the molecule, while those of C10 retained a symmetric character irrespective of the STM tip position. The OPE moiety therefore acts as ‘molecular lead’ due to the strong electron coupling between the closely positioned tip and the π-conjugate system.