Controlling the Molecular Shuttling of pH‐Responsive [2]Rotaxanes with Two Different Stations

Abstract

A novel synthesis of degenerate [2]rotaxanes with two different amine stations is presented. Variable‐temperature 1H NMR and rotating‐frame nuclear Overhauser effect correlation spectroscopy experiments revealed that the addition of trifluoroacetic acid initiates molecular shuttling. The activation barrier for the motion remained constant even when the amine in the outer station was changed. Conversely, the addition of camphorsulfonic acid caused a rotational motion, which was demonstrated by synthesizing a new [2]rotaxane without an outer station and examining its molecular behavior in the presence of acid.

Acid–base responsive molecular switching of a [2]rotaxane incorporating two different stations in an axle component

“…Previously, we focused on the synthesis of hydrogen-bond templated rotaxanes 24–26 as well as the incorporation of π–π interactions for the purpose of developing new rotaxanes for molecular switching. We chose a neutral phenanthroline derivative interpenetrated in the cavity of a macrocycle having an isophthalic bisamide skeleton without metal cation templates.…”

“…This rotaxane was shown to serve as a reversible pH-controlled molecular switch between two stations on the phenanthroline and the protonated aniline site. 25,26…”