Electrochemically Induced Reversible and Irreversible Coupling of Triarylamines

The electrochemical coupling and dimerization behavior of the low molecular compounds triphenylamine (TPA) and 9-phenylcarbazole (PHC) in comparison to tri-p-tolylamine ( p -TTA) with para-blocked methyl groups has been investigated in detail. In contrast to the unsubstituted radical cations of TPA and PHC, the radical cations of p -TTA are stable in the radical cation state and do not undergo any further coupling reactions. However, we found that the dicationic state of p -TTA does undergo two different competitive reaction pathways: (1) an irreversible intramolecular coupling reaction which leads to phenylcarbazole moieties and (2) a reversible intermolecular dimerization leading to charged σ-dimers. The σ-dimers become decomposed upon discharging at low potentials (E pc = −0.97 V vs Fc/Fc+) so that the starting monomer p -TTA is partially regenerated. In particular, the reversible dimerization reaction has not been described in literature so far. Polymeric systems containing para-methyl blocked triarylamines in the side chain exhibit similar coupling behavior upon electrochemical doping.