We have prepared novel tetraazacyclotetradecane derivatives, functionalised at nitrogen with a pendant thiophene or oligothiophene group, for electropolymerisation. Square planar Ni(II) complexes of these ligands, [Ni(L)](ClO4)2, have been prepared, and their electropolymerisation has been examined. The terthiophene-bearing complex was electrooxidised in CH3CN–0.2 M Et4NBF4 to give soluble oligomers, which are likely to be the products of dimerisation (sexithiophenes). However, by employing a more positive potential limit, they are electropolymerised, to afford polythiophene films on indium-doped tin oxide (ITO)-coated glass or platinum electrodes, and the Ni(II)/Ni(III) wave is superimposed upon the polythiophene redox process. Attempts to isolate films of the dimerised terthiophene by the oxidation of neutral [NiCl2(L)] complexes in less polar media were unsuccessful. A polymer film could not be generated from the thiophene-bearing complex alone, even though a ‘spacer’ of five carbon atoms was incorporated between the thiophene and the bulky metal centre. However, copolymerisation with 3-methylthiophene successfully gave polythiophene copolymers incorporating the nickel(II) complex. In situ FTIR reflectance spectroelectrochemistry shows that in the early stages of film oxidation, the film behaves as a conventional polythiophene, but at higher potentials, the electronic band attributable to the transition from the valence band to the first intergap state undergoes some very unusual changes. Possible explanations for these are suggested.
- This article is part of the themed collection: Metal-organic conductors (enriched issue)