as disclosed in ep 0901176 and ep 0947123 or polyaniline as disclosed in u s pat no 5 723 873 and u s pat no 5 798 170 the cathode is selected in order that electrons are efficiently injected into the device and as such may comprise a single conductive material such as a layer of aluminium alternatively it may comprise a plurality of metals for example a bilayer of calcium and aluminium as disclosed in wo 98 10621 or a thin layer of dielectric material such as lithium fluoride to assist electron injection as disclosed in for example wo 00 48258 the device is preferably encapsulated with an encapsulant to prevent ingress of moisture and oxygen suitable encapsulants include a sheet of glass films having suitable barrier properties such as alternating stacks of polymer and dielectric as disclosed in for example wo 01 81649 or an airtight container as disclosed in for example wo 01 19142 in a practical optoelectronic device at least one of the electrodes is semi transparent in order that light may be absorbed in the case of a photoresponsive device or emitted in the case of a pled where the anode is transparent it typically comprises indium tin oxide examples of transparent cathodes are disclosed in for example gb 2348316 where the polymer of the invention is used in a switching device such as a field effect transistor it will be appreciated that all of the electrodes may be opaque a monomer of formula.