title: A multistate switchable [3]rotacatenane.
abstract: Rotacatenanes are exotic molecular compounds that can be visualized as a unique combination of a [2]catenane and a [2]rotaxane, thereby combining both the circumrotation of the ring component (rotary motion) and the shuttling of the dumbbell component (translational motion) in one structure. Herein, we describe a strategy for the synthesis of a new switchable [3]rotacatenane and the investigation of its switching properties, which rely on the formation of tetrathiafulvalene (TTF) radical π-dimer interactions-namely, the mixed-valence state (TTF(2) )(+.) and the radical-cation dimer state (TTF(+.) )(2) -under ambient conditions. A template-directed approach, based on donor-acceptor interactions, has been developed, resulting in an improved yield of the key precursor [2]catenane, prior to rotacatenation. The nature of the binding between the [2]catenane and selected π-electron-rich templates has been elucidated by using X-ray crystallography and UV/Vis spectroscopy as well as isothermal titration microcalorimetry. The multistate switching mechanism of the [3]rotacatenane has been demonstrated by cyclic voltammetry and EPR spectroscopy. Most notably, the radical-cation dimer state (TTF(+.) )(2) has been shown to enter into an equilibrium by forming the co-conformation in which the two 1,5-dioxynaphthalene (DNP) units co-occupy the cavity of tetracationic cyclophane, thus enforcing the separation of TTF radical-cation dimer (TTF(+.) )(2) . The population ratio of this equilibrium state was found to be 1:1. We believe that this research demonstrates the power of constructing complex molecular machines using template-directed protocols, enabling us to make the transition from simple molecular switches to their multistate variants for enhancing information storage in molecular electronic devices.
authors.affiliation: Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA.
authors.forename: Gokhan
authors.initials: G
authors.lastname: Barin
authors.forename: Ali
authors.initials: A
authors.lastname: Coskun
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Friedman
authors.forename: Mark A
authors.initials: MA
authors.lastname: Olson
authors.forename: Michael T
authors.initials: MT
authors.lastname: Colvin
authors.forename: Raanan
authors.initials: R
authors.lastname: Carmielli
authors.forename: Sanjeev K
authors.initials: SK
authors.lastname: Dey
authors.forename: O Altan
authors.initials: OA
authors.lastname: Bozdemir
authors.forename: Michael R
authors.initials: MR
authors.lastname: Wasielewski
authors.forename: J Fraser
authors.initials: JF
authors.lastname: Stoddart