Self-complementary tetracationic cyclophanes containing 4,4′-bipyridinium and 2,5-dimethoxy-1,4-xylyl subunits

4,4'-Bipyridinium-based tetracationic cyclophanes containing a 2,5-dimethoxy-1,4-xylyl unit were synthesized by using either m-terphenyl building blocks or incorporating a 4-hydroxy benzyl spacer between the complementary subunits. The cyclophanes show weak intramolecular charge-transfer (CT) bands in the visible region and one of the cyclophanes formed a green-coloured CT complex with ferrocene with an association constant (K-a) of 6.3 M-1. The electrochemical parameters obtained for the cyclophanes indicate that all the redox processes are reversible.