Strong Fermi level pinning induces a high rectification ratio and negative differential resistance in hydrogen bonding bridged single cytidine pair junctions†
We propose a high performance single molecule rectifier by sandwiching a deoxycytidine base pair between gold electrodes. The conductance of the single base pair junction can be controlled by its protonation status, with ON/OFF ratios between the protonated (pCC) and deprotonated (CC) junctions of 3–5 orders of magnitude. In the conducting pCC state, we observed a high rectification ratio of two orders of magnitude at bias voltage values around 0.1 V. This rectification ratio surpasses most of the theoretical designs for single molecular rectifiers, while the low working voltage implies significant energy efficiency. Negative differential resistance (NDR) was also witnessed in the protonated state, with a peak to valley ratio of 24. Both the rectifying and NDR effects originate from strong Fermi level pinning effects. The electronic performance offers these single base pair junctions potential applications as a unimolecular rectifier or switch with an NDR effect. The current–voltage response is unique compared with those of the reported canonical A–T and G–C pairs, and provides the possibility to be used for i-motif DNA structure recognition or sequencing.