Formation of charge-transfer complexes based on a tropylium cation and 2,6-helic[6]arenes: a visible redox stimulus-responsive process.

Charge-transfer (CT) complexes formed from 2,6-helic[6]arene hosts and a tropylium cation are described in detail. In particular, it was found that the binding and release processes of the guest in the complexes could be efficiently controlled by a redox stimulus, and the responsive process could be visually observed by the color change of the solution. To our knowledge, this represents the first visible redox stimulus-responsive host-guest system formed from the tropylium cation.