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 107 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 pi center dot center dot center dot pi interactions and multiple C-H center dot center dot center dot pi 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.

Automated summary

In this study, the host-guest complexation between pagoda[n]arenes and the tropylium cation was investigated. Both P4 and P5 showed strong binding affinities towards the tropylium cation, with association constants of more than 107 M-1 for the 1:1 host-guest complexes. Theoretical calculations revealed different complexation modes for G@P4 and G@P5, with pi center dot center dot center dot pi and C-H center dot center dot center dot pi interactions playing important roles.