ELECTRON-TRANSFER REACTIONS OF EXTENDED O-QUINONE, P-QUINONE - VOLTAMMETRIC AND EPR ENDOR SPECTROSCOPIC INVESTIGATIONS/

The electrochemical properties of four ortho-, para-extended quinones/ quinonemethides dagger 1-4 have been investigated using cyclic voltamm etry (CV) and normal pulse voltammetry (NPV), The species are reduced by addition of two, four or six electrons to form a dianion (1), tetra anions (2, 3) and a hexaanion (4), all of which can be re-oxidized to the corresponding quinonoid species, These compounds, thus, exhibit a multistep redox behaviour, acting as good (quasi) reversible electron accepters with well separated potential steps, some of them correspond ing to a formal two-electron transfer. The radical anions 1 radical an ion-4 radical anion and the radical trianion 3(.3-), prepared electroc hemically in the first and third reduction steps, are persistent for s everal hours in the absence of air, They have been characterized by EP R and ENDOR spectroscopy, revealing a delocalization of the odd electr on, The areas of preferential spin residing, however, are quite differ ent in radical trianion 3(.3-) as compared to radical monoanion 3 radi cal anion, indicating a strong influence of the charge state in these radical anions.