The Effect of Oxygen Heteroatoms on the Single Molecule Conductance of Saturated Chains

Single molecule conductance measurements on alkanedithiols and alkoxydithiols (dithiolated oligoethers) were performed using the STM-controlled break junction method in order to ascertain how the oxygen heteroatoms in saturated linear chains impact the molecular conductance. The experimental results show that the difference in conductance increases with chain length, over the range studied. Comparisons with electronic structure calculations and previous work on alkanes indicate that the conductance of the oligoethers is lower than that of alkane chains with the same length. Electronic structure calculations allow the difference in the conductance of these two families of molecules to be traced to differences in the spatial distribution of the molecular orbitals that contribute most to the conductance. A pathway analysis of the electronic coupling through the chain is used to explain how the difference in conductance between the alkane and oligoether molecules depends on the chain length.