PREPARATION AND CHARACTERIZATION OF THIENONAPHTHOQUINONES AND THEIR RADICAL IONS

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.