Improved and Controlled Complexation of Paraquat Derivatives by the Formation of a Bis(m-phenylene)-26-Crown-8-Based Lariat Ether

A novel bis(m-phenylene)-26-crown-8-based lariat ether (i.e., 3b) was synthesized and characterized. It can bind paraquat derivatives more strongly than bis(m-plaenylene)-26-crown-8 in solution. It forms pseudorotaxanes with two paraquat derivatives in the solid state. N-Methyl substitution was found to play an important role on the binding strength of lariat ether 3b. Furthermore, due to the introduction of two benzyloxy groups, its binding to paraquat derivatives can be switched off (and back on) by adding K+ (and then dibenzo-18-crown-6), and the disassociation percentage depends on the concentration of the added K+ ions.