Conjugated Polymetallorotaxanes: In-Situ ESR and Conductivity Investigations of Metal−Backbone Interactions

Electrochemical studies of polymetallorotaxane films of a general formula poly[1,3,M n + ] where M n + is copper(I), cobalt(II), zinc(II), or lithium(I) are reported for both metalated and demetalated (poly[1,3,-]) forms. Cyclic voltammograms (CV) recorded for polymetallorotaxanes containing redox-active metals, with an exception of the Li one, in addition to the electroactivity of the complexing metal exhibit two redox couples associated with the consecutive oxidation/reduction of the oligothienylene units in the wiring polymer. For poly[1,3,Cu + ], the CV studies are completed by ESR spectroelectrochemical investigations combined with in-situ conductivity measurements as a function of the electrode potentials. In the ESR response, two signals of different origin can be distinguished: a broad signal originating from Cu(II) paramagnetics ions (ΔHpp of ca. 265 G) and that due to unpaired spins of the polymer backbone (ΔHpp of ca. 21 G). Potential dependencies of these two signals as well as potential-induced conductivity variations are consistent with the postulate of two independent conductivity processes occurring via mixed-valence Cu(II)/Cu(I) moieties and through bipolaron-type charge carriers. For comparison, ESR and conductivity responses to the working electrode potential change were measured for poly[1] and poly[2], i.e., thienylene unit-based polymers constituting wiring backbones in the polymetallorotaxanes studied. The comparison of these results clearly indicates that metal-complexed rings constitute barriers which lower charge-carrier mobility. As a result, poly[1] and poly[2] exhibit significantly higher electronic conductivity (σ of ca. 5 × 10-3 S/cm) as compared to the conductivity of the corresponding polymetallorotaxanes (σ of ca. 2 × 10-5 S/cm).