Single molecule vs. large area design of molecular electronic devices incorporating an efficient 2-aminepyridine double anchoring group

Herrer, L. and Ismael, A. and Martín, S. and Milan, D. C. and Serrano, J. L. and Nichols, R. J. and Lambert, C. and Cea, P. (2019) Single molecule vs. large area design of molecular electronic devices incorporating an efficient 2-aminepyridine double anchoring group. Nanoscale, 11 (34). pp. 15871-15880. ISSN 2040-3364

Abstract

When a molecule is bound to external electrodes by terminal anchor groups, the latter are of paramount importance in determining the electrical conductance of the resulting molecular junction. Here we explore the electrical properties of a molecule with bidentate anchor groups, namely 4,4′-(1,4-phenylenebis(ethyne-2,1-diyl))bis(pyridin-2-amine), in both large area devices and at the single molecule level. We find an electrical conductance of 0.6 × 10-4G0 and 1.2 × 10-4G0 for the monolayer and for the single molecule, respectively. These values are approximately one order of magnitude higher than those reported for monodentate materials having the same molecular skeleton. A combination of theory and experiments is employed to understand the conductance of monolayer and single molecule electrical junctions featuring this new multidentate anchor group. Our results demonstrate that the molecule has a tilt angle of 30° with respect to the normal to the surface in the monolayer, while the break-off length in the single molecule junction occurs for molecules having a tilt angle estimated as 40°, which would account for the difference in their conductance values per molecule. The bidentate 2-aminepyridine anchor is of general interest as a contact group, since this terminal functionalized aromatic ring favours binding of the adsorbate to the metal contact resulting in enhanced conductance values.