The role of intramolecular association in the electrochemical reduction of viologen dimers and trimers

The electrochemical reduction of several viologen dimers (D) and trimers (T) was studied by absorption spectroscopy and differential pulse polarography in N,N-dimethylformamide. The viologen dimer and trimer linked by a propane chain (D3 and T3) exhibited efficient intramolecular association between two viologen radial cations, while the association in other viologens having longer alkyl spacer chains was less efficient. For D3 and T3, reduction of the second viologen group proceeded at a more positive potential compared with that of the first one, indicating that the association of the radical cations facilitated the reduction processes. For the viologens which showed inefficient intramolecular association, the four (for dimers) and six (for trimers) formal potentials were explained by taking statistical factors into account. The effects of the chemical structure of the viologens on both their spectroscopic and electrochemical behavior were also discussed.