title: Reversible mechanical switching of magnetic interactions in a molecular shuttle.
abstract: An acid-base switchable molecular shuttle based on a [2]rotaxane, incorporating stable radical units in both the ring and dumbbell components, is reported. The [2]rotaxane comprises a dibenzo[24]crown-8 ring (DB24C8) interlocked with a dumbbell component that possesses a dialkylammonium (NH2 (+)) and a 4,4'-bipyridinium (BPY(2+)) recognition site. Deprotonation of the rotaxane NH2 (+) centers effects a quantitative displacement of the DB24C8 macroring to the BPY(2+) recognition site, a process that can be reversed by acid treatment. Interaction between stable 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radicals connected to the ring and dumbbell components could be switched between noncoupled (three-line electron paramagnetic resonance (EPR) spectrum) and coupled (five-line EPR spectrum) upon displacement of the spin-labelled DB24C8 macroring. The complete base- and acid-induced switching cycle of the EPR pattern was repeated six times without an appreciable loss of signal, highlighting the reversibility of the process. Hence, this molecular machine is capable of switching on/off magnetic interactions by chemically driven reversible mechanical effects. A system of this kind represents an initial step towards a new generation of nanoscale magnetic switches that may be of interest for a variety of applications.
authors: Dipartimento di Chimica "G. Ciamician", Università di Bologna Via Selmi 2, 40126 Bologna (Italy).
authors: Valentina
authors: V
authors: Bleve
authors: Dipartimento di Chimica "G. Ciamician", Università di Bologna Via Selmi 2, 40126 Bologna (Italy).
authors: Christian
authors: C
authors: Schäfer
authors: Dipartimento di Chimica "G. Ciamician", Università di Bologna Via Selmi 2, 40126 Bologna (Italy).
authors: Paola
authors: P
authors: Franchi
authors: Dipartimento di Chimica "G. Ciamician", Università di Bologna Via Selmi 2, 40126 Bologna (Italy).
authors: Serena
authors: S
authors: Silvi
authors: Dipartimento di Chimica "G. Ciamician", Università di Bologna Via Selmi 2, 40126 Bologna (Italy).
authors: Elisabetta
authors: E
authors: Mezzina
authors: Dipartimento di Chimica "G. Ciamician", Università di Bologna Via Selmi 2, 40126 Bologna (Italy).
authors: Alberto
authors: A
authors: Credi
authors: Dipartimento di Chimica "G. Ciamician", Università di Bologna Via Selmi 2, 40126 Bologna (Italy).
authors: Marco
authors: M
authors: Lucarini
keywords: EPR; molecular devices; rotaxane; spin labelling; supramolecular chemistry