Catechol-Based Macrocyclic Rods: En Route to Redox-Active Molecular Switches

The design and synthesis of the macrocyclic turnstile 1 comprising a terminally sulfur-functionalized molecular rod and a redox-active catechol subunit is described. The shape-persistent macrocyclic scaffold consists of alternating arylene and ethynylene units. A freely rotating 2,6-diethynyl-catechol subunit is clamped between both terminal arylene subunits as molecular turnstile. While the electrochemical switching between the catechol and the quinone form of this catechol subunit is displayed by cyclic voltammetry, conformational rearrangements by favoring and disfavoring the formation of intramolecular hydrogen bonds are the subject of current investigations. Terminal acetyl-protected sulfur anchor groups enabled the immobilization of the macrocycle between an Au tip and an Au substrate of a STM set-up. Preliminary single-molecule transport investigations of the turnstile 1 display comparable values as for the parent molecular rod. An electrochemically-controlled single-molecule transport experiment to investigate redox-state-dependent transport properties is currently under way. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)