title: Dethreading of a Photoactive Azobenzene-Containing Molecular Axle from a Crown Ether Ring: A Computational Investigation.
abstract: Pseudorotaxanes formed by a dibenzo[24]crown-8 ring (R) and a dialkylammonium axle bearing either two E- or two Z-azobenzene units (EE-A or ZZ-A) revealed useful for the construction of light-powered molecular machines and motors, as they provide the opportunity of photocontrolling self-assembly/disassembly processes. The potential energies profiles for the dethreading of these complexes have been investigated by adopting a combination of first-principles molecular dynamics, metadynamics and quantum-chemical geometry optimization approaches. While the dethreading of the EE-A axle is associated with a monotonic energy increase, for that of the ZZ-A axle a transition state and an intermediate structure, in which the components are still threaded together, are found. The rate determining step for the dethreading of the ZZ axle has a higher energy barrier than that of the EE axle, in agreement with the experimental kinetic data. Moreover, the results suggest that the elliptic shape of the ring cavity is important for discriminating between the E and Z terminal azobenzene during dethreading.
authors.affiliation: Dipartimento di Scienza ed Alta Tecnologia and INSTM, Università dell'Insubria, Via Valleggio 11, I-, 22100, Como, Italy.
authors.forename: Gloria
authors.initials: G
authors.lastname: Tabacchi
authors.affiliation: Photochemical Nanosciences Laboratory and Interuniversity Center for the Chemical Conversion of Solar Energy, Dipartimento di Chimica "G. Ciamician", Università di Bologna, Via Selmi 2, I-40126, Bologna, Italy.
authors.forename: Serena
authors.initials: S
authors.lastname: Silvi
authors.affiliation: Photochemical Nanosciences Laboratory and Interuniversity Center for the Chemical Conversion of Solar Energy, Dipartimento di Chimica "G. Ciamician", Università di Bologna, Via Selmi 2, I-40126, Bologna, Italy.
authors.forename: Margherita
authors.initials: M
authors.lastname: Venturi
authors.affiliation: Photochemical Nanosciences Laboratory and Interuniversity Center for the Chemical Conversion of Solar Energy, Dipartimento di Chimica "G. Ciamician", Università di Bologna, Via Selmi 2, I-40126, Bologna, Italy. alberto.credi@unibo.it.
authors.forename: Alberto
authors.initials: A
authors.lastname: Credi
authors.affiliation: Dipartimento di Scienza ed Alta Tecnologia and INSTM, Università dell'Insubria, Via Valleggio 11, I-, 22100, Como, Italy. ettore.fois@uninsubria.it.
authors.forename: Ettore
authors.initials: E
authors.lastname: Fois
keywords: metadynamics; molecular dynamics; molecular machines; rotaxane; supramolecular chemistry