Tuning Single‐Molecule Conductance in Metalloporphyrin‐Based Wires via Supramolecular Interactions

Abstract

Nature hasd eveloped supramolecular constructs to delivero utstanding charge-transport capabilities usingm etalloporphyrin-baseds upramoleculara rrays. Herein we incorporate simple,n aturally inspired supramolecular interactions via theaxial complexation of metalloporphyrinsintothe formation of as ingle-molecule wire in an anoscale gap. Smalls tructural changesi nt he axialc oordinatingl inkers result in dramatic changesi nt he transportp ropertieso ft he metalloporphyrinbasedw ire. Thei ncreased flexibilityo fapyridine-4-yl-methanethiol ligand duet oa ne xtra methyl group, as compared to am orer igid 4-pyridinethioll inker, allows thep yridine-4-ylmethanethiol ligand to adopta nu nexpectedh ighlyc onductive stackeds tructure betweent he twoj unctione lectrodesa nd the metalloporphyrin ring.D FT calculations reveal am olecular junction structurec omposedo fashifteds tack of thet wo pyridiniclinkers andthe metalloporphyrin ring.Incontrast, the more rigid4-mercaptopyridineligandpresentsamore classical lifted octahedral coordinationo ft he metalloporphyrin metal center,l eading to al ongere lectronp athway of lowerc onductance. This worksopens to supramolecular electronics, aconcept alreadyexploited in naturalorganisms.

Room‐Temperature Spin‐Dependent Transport in Metalloporphyrin‐Based Supramolecular Wires

“…The three previously reported conductance features I‐III for the [Co II (DPP)]/PyrMT system, [29] are also identified in all four studied metal porphyrins (Co, Ni, Cu, Zn). In all cases, the low conductance features II and III display small variations upon inversion of the Ni tip magnetization direction, within narrow conductance ranges of 0.8–1×10 −2 G o and 2–3×10 −3 G o for II and III, respectively.…”

“…In all cases, the low conductance features II and III display small variations upon inversion of the Ni tip magnetization direction, within narrow conductance ranges of 0.8–1×10 −2 G o and 2–3×10 −3 G o for II and III, respectively. These two conductance features have been previously ascribed to junction configurations arising from direct pyridinyl/DPP ring interactions via π–π stacking or/and hydrogen bonding with little or no orbital contribution from the metal center [29] . Likewise, the high conductance feature I has been univocally assigned to the pyridinyl coordination of the metal center [20] and it is observed that its conductance value depends on both the metal center (M II =Co, Ni, Cu and Zn) and the Ni magnetization sign (α, β) (Figure 2).…”

“…Figure 2 shows the three conductance features (high I, medium II and low III) previously characterized for this system corresponding to different supramolecular junction configurations as the interelectrode distance is increased [29] . Alpha/Beta labeled curves shows individual traces under opposite Ni electrode magnetizations along the main molecular junction axis.…”

“…The metalloporphyrin is supramolecularly trapped in a nanoscale gap by functionalizing both junction electrodes with pyridine‐4‐yl‐methanethiol (PyrMT) coordinating ligands in a magnetically modified version of a scanning tunneling microscope (STM) break‐junction system (Figure 1) [20, 21] using both dynamic or tapping (monitoring the induced pulling of the molecular junction) [26, 27] and static or blinking (monitoring the spontaneous molecular junction formation) [26, 28] working modes. Our results reveal several new charge transport properties in a single‐molecule junction: (i) among the different identified supramolecularly generated electron pathways through these molecular junctions, [29] the spin‐dependent transport is exclusively observed in those where metal orbitals are directly participating in the junction formation. (ii) The observed spin‐dependent transport is not limited to one direction of the current through the molecular junction (typically from the spin‐polarized electrode to the diamagnetic metal electrode), but also observed in the opposite direction of the current flow between both junction electrodes.…”

Porphyrins as building blocks for single-molecule devices

“…More recently, they investigated the effect of different linkers (for electrode coating) on the configurations of supramolecular junctions using the same technique with an applied bias voltage of 7.5 mV. 63 They used pyridine-4-thiol ( PyrT ) and the previously used pyridin-4-ylmethanethiol ( PyrMT ) as electrode coating materials to study junctions after exposition to porphyrin 40 , 5,15-bisphenyl porphyrin 41 , and their Co complexes 42 and 43 , respectively (see Fig. 15(a) ).…”