Pagoda[ n ]arenes ( n = 4, 5): Extremely Strong Binders for the Tropylium Cation.

Herein, host-guest complexation between pagoda[ n ]arenes ( n = 4, P4 ; n = 5, P5 ) and tropylium cation ( G ) was investigated in detail. It was found that both P4 and P5 showed surprisingly strong binding affinities toward the tropylium cation with association constants of more than 10 7 M -1 for the 1:1 host-guest complexes. The theoretical calculations showed different host-guest complexion ways for complexes G @ P4 and G @ P5 and the strong π···π interactions and multiple C-H···π interactions play a very important role in the formation of these stable complexes, respectively. Moreover, the switchable processes of guest binding and release in the complexes can be effectively controlled by redox stimuli, and they can be also visible by the color and fluorescence changes.