Département de chimie moléculaire

We report the study of stimuli-responsive Zn(II) and Fe(II) coordination polymers (MC34+ or MC24+ with M = Fe2+ or Zn2+). These soluble metallopolymers were formed spontaneously by reaction of an organic ligand (C34+ or C24+) with one molar equivalent of metal ions. The C34+ and C24+ ligands incorporate two chelating terpyridine groups bridged by a redox responsive hinge featuring two viologen units (viologen = N,N'-dialkyl-4,4'-bipyridinium) linked either through propyl (C34+) or ethyl (C24+) chains. The viologen units in the polymer chains were reduced (1e per viologen group) either by bulk electrolysis or by visible-light irradiation carried out in the presence of a photosensitizer. The 1e reduction of the viologen units in the MC24+ polymers induced a slight decrease in the viscosity of the solutions due to a modification of the overall charge carried by the metallopolymers. In contrast, reduction of coordination polymers involving propyl linkers (MC34+) led to a remarkable increase ({\~{}}+400{%}) in observed viscosity. This reversible effect was attributed to a folding of the polymer chains triggered by $π$-dimerization of the photo-generated viologen cation radicals.