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 (Δ H pp of ca. 265 G) and that due to unpaired spins of the polymer backbone (Δ H pp 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).