Dimerisation of organic radical ions and redox reactions of dimers as studied by temperature-dependent in situ ESR/UV-vis-NIR spectroelectrochemistry

The kinetic and structural consequences of dimerisation as one of the main chemical follow-up reactions in electron transfer in organic molecules is v ery often not understood. As electrochemical methods result in an indirect description of dimerisation processes following electron transfer steps, sp ectroelectrochemical methods are needed for direct evidence of dimerisation . The triple in situ experimental technique for the simultaneous measuremen t of ESR and UV-vis-NIR spectra in electrochemical experiments at different temperatures, including a special TE102 optical ESR cavity and Bruker temp erature control system, is presented in its application to redox reactions of dimeric structures and dimerisation reactions following an electron tran sfer. As redox systems, Wurster's reagent and thianthrene are used for refe rence work. The triple spectroelectrochemical method is successfully applie d to extended organic pi -conjugated systems like end-capped quarter-thioph ene and dimeric fullerene C-120 where the dimeric structures have been char acterised in detail. (C) 2001 Elsevier Science B.V. All rights reserved.