Highly-strained cyclophanes bearing both photo- and electro-active constituents

The synthesis of a highly-strained cyclophane comprising azobenzene and methyl viologen units was achieved by coupling 3,3′-dihydroxy-4,4′-bipyridine with azobenzoic acid in CH2Cl2. The molecular structure, determined by single-crystal X-ray crystallography, shows that the azobenzene NN unit adopts the trans conformation and that the bipyridinium unit is twisted. The cyclic voltammogram recorded for the target compound displays an irreversible wave at −0.37 V vs Ag/AgCl, associated with the one-electron reduction of the bipyridinium subunit. A further wave is seen at E1/2 = −1.52 V versus Ag/AgCl and is assigned to one-electron reduction of the azobenzene group. Visible light illumination of the azobenzene chromophore in CH3CN triggers trans to cis isomerization but the process is irreversible.