Bernadette Divisia-Blohorn

Conjugated polyrotaxanes: improvement of the polymer properties by using sterically hindered coordinating units

A new conjugated copper-complexed polyrotaxane has been prepared by electropolymerization of a thiophene derivative; the rings are threaded onto a multi-1,10-phenanthroline (phen) axle, copper(I) acting as a template. The presence of CH3 groups ortho to the nitrogen atoms of the phen nuclei belonging to the conjugated backbone has a profound effect on the stability of the polymer, on its electrochemical properties and on its ability to be remetallated once the template metal centre (copper(I)) has been removed.

Preparation and spectroelectrochemical behaviour of a new alternate copolymer of 3,3′-di-n-octyl-2,2′-bithiophene and fluoren-9-one

The synthesis and spectroelectrochemical behaviour of a new solution processible conjugated polymer, namely poly[{5,5′-(3,3′-di-n-octyl-2,2′-bithiophene)}-alt-(2,7-fluoren-9-one)] (abbreviated as PDOBTF), are described. PDOBTF can be considered as the first member of a new family of conjugated copolymers—poly(oligothiophene-alt-fluoren-9-one)s—whose properties can be tuned by changing the length of the oligothiophene segments and their regiochemistry. PDOBTF can be obtained by oxidative polymerisation of 2,7-bis(4-octylthien-2-yl)-fluoren-9-one or by condensation polymerisation of 2,7-bis(5-bromo-4-octylthien-2-yl)-fluoren-9-one using a modification of Yamamoto coupling. Both preparation methods lead to a mixture of polymeric and oligomeric species and require post-polymerisation fractionating if high molecular fractions are to be obtained. Oxidative polymerisation gives product of a higher molecular weight (Mn = 41.0 kDa, Mw/Mn = 1.81 for the highest molecular weight fraction) as compared to the one prepared by Yamamoto condensation polymerisation (Mn = 13.3 kDa, Mw/Mn = 1.45 for the highest molecular weight fraction). Electrochemical oxidation of PDOBTF in an nonaqueous electrolyte (0.1 M Bu4NBF4/acetonitrile) gives rise to an anodic peak at E = 835 mV, which can be ascribed to the p-type doping of the copolymer. The extension of the potential to E = 1500 mV results in the oxidative degradation of the copolymer and induces total loss of its electroactivity. UV-Vis-NIR and Raman spectroelectrochemical data are consistent with the oxidative doping. The latter technique enables the monitoring of the doping-induced changes in both structural sub-units of the copolymer: the bithiophene sub-unit and the fluoren-9-one one.

Electrode-deposited films of polyrotaxanes: electrochemically induced gliding motion

Using the three-dimensional template effect of copper(I) or copper(II), a macrocycle incorporating two different chelating units was threaded by a coordinating molecular fragment whose two ends bear pyrrole nuclei; after electropolymerization, an electroactive film was obtained that clearly showed pirouetting of the ring induced by reducing the five-coordinate copper(II) complex to copper(I). The motion is driven by the difference in the stereoelectronic preferences of copper(I) and copper(II). The present system allows motions of the monovalent complex only.

Electroactive polymer films of silver complexes with intertwinedand interlocked ligands: the AgI–Ag0 redoxcouple as a topological probe

The electrochemical properties of bis(2,9-diaryl-1,10-phenanthroline)silver complexes are reported. The redox potentials of the coordinated metal centre are strongly dependent on the topology of the organic backbone surrounding the metal centre and its set of ligands. This particular property can be used for the evaluation of the topological characteristics of different polypyrrole matrices built around entwined 2,9-diaryl-1,10-phenanthroline moieties.

Solvent effects on the electrochemical properties of IrCl2(bpy)2

Abstract To investigate the solvent dependence of the d-d contribution to the redox orbital of the cis-dichloro- bis-(s,2′-bipyridine) iridium(III) ion, the first reduction electron transfer has been studied in various non-aqueous and aqueous solvents by cyclic voltammetry and spectroelectrochemistry. Totally irreversible electrochemical processes and chloride release have been observed in water, methanol and formamide, which are consistent with the proposed pre-dominantly metallic nature of the redox orbital in these solvents. In other solvents the electron reduction sequence and the low chemical reaction rate of chloride release suggest a strong interaction between the ligand and metal-centered redox orbitals. Correlation of the reduction potential with the Gutmanns acceptor number and dielectric constant of the solvents indicates that chloride release depends strongly upon the dissociative properties of the solvent. The electrochemical behaviour and photochemical observations are compared.

Electroactive films of [Cu(dpp)2]+ covalently attached to polypyrrole (dpp = 2,9-diphenyl-1,10-phenanthroline)

A copper(I) complex containing two entwined dpp ligands (dpp = 2,9-diphenyl-1,10-phenanthroline), each covalently linked to a pyrrole sub-unit, has been synthesized; electropolymerization of the complex generates a conductive film on platinum or glassy carbon, which can be reversibly de- and re-metallated.