Electrochemical and spectroscopic characterisation of structural reorganisation in N,N′–dialkylpyridinium cation radical deposits

The electrochemical reduction to form a deposit of the radical cation salt for a series of n-alkyl asymmetrically substituted viologens and the corresponding anodic oxidation processes have been investigated using electrochemical methods in in situ uv-visible reflectance spectroscopy. Particular attention was focussed on the nature of the restructuring involved in the ageing of the deposit. The use of both p- and s-polarised radiation clearly showed that initially the viologen units were deposited with the major molecular axis parallel to the electrode and on ageing they reorganised into a preferred orientation perpendicular to the electrode. The viologens with the larger substituents were initially deposited as aggregates of mixed micelles containing both cation radical and dication units. The latter were reduced at a well defined potential, the process being seen as a highly-reversible sharp current spike on the linear sweep voltammograms.