Ja. Crayston et al., PREPARATION AND CHARACTERIZATION OF THIENONAPHTHOQUINONES AND THEIR RADICAL IONS, Perkin transactions. 2, (9), 1993, pp. 1589-1595
Three naphtho[2,3-c]thiophene-4,9-diones (thienonaphthoquinones) have
been prepared and their redox properties studied by chemical, electroc
hemical and EPR spectroscopic methods. All three quinones were readily
reduced electrochemically to the corresponding radical anions and sub
sequently to dianions. The cyclic voltammograms showed evidence of ion
pairing of the dianions. All three quinones were also electrochemical
ly oxidised to radical cations. The structures and thermodynamic prope
rties of the quinones, the radical cations, radical anions and dianion
s were studied by the semi-empirical AM1 method. The experimental redo
x potentials were found to correlate with the computed energies of the
appropriate frontier MOs. The electrochemically generated radical ani
ons were observed by EPR spectroscopy and shown to decay with second-o
rder kinetics. The rate constants increased as the electron-releasing
character of the substituents in the benzene ring increased. The only
EPR spectroscopically detectable radical cation was that from the 6,7-
dimethoxynaphtho[2,3-c]thiophene-4,9-dione. Attempts by electrochemica
l and chemical methods to polymerise the thienonaphthoquinones were un
successful.