I. Tabakovic et al., REACTIVITY OF OXIDIZED OLIGOTHIOPHENES SUBSTITUTED WITH METHOXY AND THIOALKYL GROUPS, Journal of electroanalytical chemistry [1992], 424(1-2), 1997, pp. 35-42
alpha-Oligothiophenes with one to five rings, substituted with beta-me
thoxy groups and terminated with either (2-hydroxyethyl)thio (1-5) or
(2-acetoxyethyl)thio groups (1a-5a) were synthesized. Cyclic voltammet
ry, coulometry and vis spectroscopy were used to investigate the react
ivity of the cation radicals and dications. The cation radicals, even
the 'monothiophene cation radical' 3-methoxy-2,5-bis(hydroxyethylthio)
thiophene (1(+)), were somewhat stable in acetonitrile. The dications
of the acetoxy derivatives 2a-5a were also stable on this time scale.
Dications 1a(2+) and 1(2+)-5(2+) were not stable. The instability of 2
(2+)-5(2+) is attributed to an intramolecular reaction between the ter
minal hydroxy groups and the oxidized thiophene units. This reaction l
ed to the isolation of an unusual spiro product from a preparative sca
le oxidation of bithiophene 2. Several of the cation radicals precipit
ated on the electrode surface. The unusual shape of the voltammograms
which resulted was investigated, and evidence for the formation of two
different salts, one fully oxidized and one mixed valence, was obtain
ed.