Département de chimie moléculaire

The ability of three bis-viologen cyclophanes to act as redox-triggered contractile switches is investigated. Odd/even effects in the formation of cyclic bis-viologens are circumvented by the use of a Zincke salt intermediate and a tetrathiafulvalene template to prep. a flexible cyclophane with hexyl linkers. Comparative spectro-electrochem. studies of this macrocycle with two other pentyl- or heptyl-linked cyclic bis-viologens show that the development of intramol. interactions in aq. soln. depends on the length of the bridges. This dependence is confirmed by EPR and DFT studies of the magnetic coupling in the diradical dication species. The anti-ferromagnetic or ferromagnetic nature of the coupling depend, resp., on the odd or even no. of methylene groups in the spacer. [on SciFinder(R)]