A Water-Soluble pH-Triggered Molecular Switch

A bistable donor–acceptor
[2]­catenane, which is composed
of a crown ether containing a hydroquinone unit and a 1,5-diaminonaphthalene
unit, interlocked mechanically by cyclobis­(paraquat-p-phenylene) as its tetrachloride, exists as a mixture of translational
isomers, both in the solid state and in aqueous solution. UV/vis and 1H NMR spectroscopies demonstrate that this isomeric mixture
can be switched in water in the presence of hydrochloric acid to afford
a single diprotonated derivative in which only the hydroquinone unit
resides inside the cavity of the tetracationic cyclophane. Treatment
with 1,4-diazabicyclo[2.2.2]­octane resets the molecular switch.