Redox-addressable single-molecule junctions incorporating a persistent organic radical

The integration of radical (open-shell) species into single-molecule junctions at non-cryogenic temperatures is a key to unlocking the potential of molecular electronics in further applications. While many efforts have been devoted to this issue, in the absence of a chemical or electrochemical potential the open-shell character is lost when in contact with the metallic electrodes. Here, the organic 6-oxo-verdazyl radical, which is stable at ambient temperatures and atmosphere, has been functionalised by aurophilic 4-thioanisole groups at the 1,5-positions and fabricated into a molecular junction using the scanning tunnelling microscope break-junction technique. The verdazyl moiety retains open-shell character within the junction even at room temperature, and electrochemical gating permits in-situ reduction of the verdazyl to the closed-shell anionic state in a single-molecule transistor configuration. In addition, the bias-dependent alignment of the open-shell resonances with respect to the electrode Fermi levels gives rise to purely electronically-driven rectifying behaviour. The demonstration of a verdazyl-based molecular junction capable of integrating radical character, transistor-like switching behaviour, and rectification in a single molecular component under ambient conditions paves the way for further studies of the electronic, magnetic, and thermoelectric properties of open-shell species.

Single-molecule junction spontaneously restored by DNA zipper

The electrical properties of DNA have been extensively investigated within the field of molecular electronics. Previous studies on this topic primarily focused on the transport phenomena in the static structure at thermodynamic equilibria. Consequently, the properties of higher-order structures of DNA and their structural changes associated with the design of single-molecule electronic devices have not been fully studied so far. This stems from the limitation that only extremely short DNA is available for electrical measurements, since the single-molecule conductance decreases sharply with the increase in the molecular length. Here, we report a DNA zipper configuration to form a single-molecule junction. The duplex is accommodated in a nanogap between metal electrodes in a configuration where the duplex is perpendicular to the nanogap axis. Electrical measurements reveal that the single-molecule junction of the 90-mer DNA zipper exhibits high conductance due to the delocalized π system. Moreover, we find an attractive self-restoring capability that the single-molecule junction can be repeatedly formed without full structural breakdown even after electrical failure. The DNA zipping strategy presented here provides a basis for novel designs of single-molecule junctions.