Electrochemical, spectroelectrochemical and EPR properties of poly(pyrrole-viologens)

Chemical doping to control the in-situ formed doping structure in light-emitting electrochemical cells

The initial operation of a light-emitting electrochemical cell (LEC) constitutes the in-situ formation of a p-n junction doping structure in the active material by electrochemical doping. It has been firmly established that the spatial position of the emissive p-n junction in the interelectrode gap has a profound influence on the LEC performance because of exciton quenching and microcavity effects. Hence, practical strategies for a control of the position of the p-n junction in LEC devices are highly desired. Here, we introduce a "chemical pre-doping" approach for the rational shifting of the p-n junction for improved performance. Specifically, we demonstrate, by combined experiments and simulations, that the addition of a strong chemical reductant termed "reduced benzyl viologen" to a common active-material ink during LEC fabrication results in a filling of deep electron traps and an associated shifting of the emissive p-n junction from the center of the active material towards the positive anode. We finally demonstrate that this chemical pre-doping approach can improve the emission efficiency and stability of a common LEC device.

Multichromophoric electrochromic polymers: colour tuning of conjugated polymers through the side chain functionalization approach

Organic electrochromic materials have gained constantly increasing interest over the years with respect to their inorganic counterpart due to essentially two distinctive characteristics: their processability through solution based low cost processes and their wide colour palette. Such characteristic features enabled their application in displays, smart windows, electronic paper and ophthalmic lenses. Alongside the established concept of donor-acceptor polymers, side chain functionalized multichromophoric polymers are gaining attention as a highly performing and synthetically feasible alternative, particularly relevant to applications requiring a complete colourlessness in one of the accessible redox states of the material. The primary aim of the present article is to review all the results involving the tuning of the native electrochromic properties of simple conjugated polymers through the introduction of a discrete electrochromic molecule as a side chain substituent.

Viologens as charge carriers in a polymer-based battery anode

Viologens, either as anions in solution or as pendant substituents to pyrrole, were incorporated as dopants to electrodeposited films of polypyrrole. The resulting polymer films exhibited redox activity at -0.5 V vs Ag/AgCl. The film consisting of polypyrrole with pendant viologens exhibited the best charge-discharge behavior with a maximum capacity of 55 mAh/g at a discharge current of 0.25 mA/cm(2). An anode consisting of polypyrrole (pPy) doped with viologen (V) was coupled to a cathode consisting of pPy doped with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) to yield a polymer-based battery with a cell electromotive force (emf) of 1.0 V, maximum capacity of 16 mAh/g, and energy density of 15 Wh/kg.