IN-SITU ELECTROCHEMICAL EPR STUDIES OF CHARGE-TRANSFER ACROSS THE LIQUID LIQUID INTERFACE/

The in situ measurement of EPR spectra of radical ions generated at th e polarized liquid/liquid interface is described in relation to the 7, 7,8,8-tetracyanoquinodimethane (TCNQ), 2,3,5,6-tetrachloro-p-benzoquin one (TCBQ) and 2,3,5,6-tetrafluoro-p-benzoquinone (TFBQ) radical anion s and the tetrathiafulvalene (TTF) radical cation. TCNQ and TTF were c hosen as model compounds with which to quantify the performance of a n ovel liquid/liquid electrochemical EPR cell. The anion radical of TCNQ and the cation radical of TTF in 1,2-dichloroethane (DCE) were produc ed at the water interface by electron transfer from/to the aqueous-pha se ferricyanide/ferrocyanide redox couple by applying a potential diff erence between the two phases with a four-electrode potentiostat. The EPR signal intensity (at constant magnetic field) of the resultant org anic radicals was monitored during potential step experiments which in dicated that the EPR data could be modeled in terms of diffusional tra nsport. TCBQ and TFBQ were chosen as compounds to model the electron t ransfer behavior of biologically important quinones at the oil/water i nterface. The EPR and voltammetric data obtained from TCBQ/TCBQ(-.) an d TFBQ/TFBQ(-.) indicated unambiguously that the two semiquinones are stable at the DCE/water interface and do not undergo immediate protona tion.