Tuning radical interactions in trisradical tricationic complexes by varying host-cavity sizes

Although host-guest pairing interactions between bisradical dicationic cyclobis(paraquat- p -phenylene) ( BB 2( &z.rad; +) ) and the bipyridinium radical cation ( BIPY&z.rad; + ) have been studied extensively, host molecules other than BB 2( &z.rad; +) are few and far between. Herein, four bisradical dicationic cyclophanes with tunable cavity sizes are investigated as new bisradical dicationic hosts for accommodating the methyl viologen radical cation ( MV&z.rad; + ) to form trisradical tricationic complexes. The structure-property relationships between cavity sizes and binding affinities have been established by comprehensive solution and solid-state characterizations as well as DFT calculations. The association constants of the four new trisradical tricationic complexes are found to range between 7400 and 170 000 M −1 , with the strongest one being 4.3 times higher than that for [MV⊂BB] 3( &z.rad; +) . The facile accessibility and tunable stability of these new trisradical tricationic complexes make them attractive redox-controlled recognition motifs for further use in supramolecular chemistry and mechanostereochemistry. Although host-guest pairing interactions between bisradical dicationic cyclobis(paraquat- p -phenylene) ( BB 2( &z.rad; +) ) and the bipyridinium radical cation ( BIPY&z.rad; + ) have been studied extensively, host molecules other than BB 2( &z.rad; +) are few and far between.