Sheathed Molecular Junctions for Unambiguous Determination of Charge-Transport Properties

Future applications of single-molecular and large-surface area molecular devices require a thorough understanding and control of molecular junctions, interfacial phenomena, and intermolecular interactions. In this contribution the concept of single-molecule junction and host-guest complexation to sheath a benchmark molecular wire-namely 4,4 '-(1,4-phenylenebis(ethyne-2,1-diyl))dianiline - with an insulating cage, pillar[5]arene 1,4-diethoxy-2-ethyl-5-methylbenzene is presented. The insertion of one guest molecular wire into one host pillar[5]arene is probed by H-1-NMR (nuclear magnetic resonance), whilst the self-assembly capabilities of the amine-terminated molecular wire remain intact after complexation as demonstrated by XPS (X-ray photoelectron spectroscopy) and AFM (atomic force microscopy). Encapsulation of the molecular wire prevents the formation of pi- pi stacked dimers and permits the determination of the true single molecule conductance with increased accuracy and confidence, as demonstrated here by using the STM-BJ technique (scanning tunneling microscopy- break junction). This strategy opens new avenues in the control of single-molecule properties and demonstrates the pillararenes capabilities for the future construction of arrays of encapsulated single-molecule functional units in large-surface area devices.