# pH-Controlled isomerization kinetics of ortho-disubstituted benzamidines: E/Z isomerism and axial chirality

## TL;DR

This paper explores how pH can control the structural changes in a new type of molecular switch based on benzamidine.

## Contribution

The study introduces ortho-disubstituted benzamidine as a novel pH-responsive molecular switch.

## Key findings

- Protonation of the amidine moiety suppresses C–N bond rotation.
- pH adjustment can control isomerization kinetics via rotational barriers.
- ortho-Disubstituted benzamidine shows potential as a pH-responsive system.

## Abstract

pH-Responsive molecular switches and motors are a class of organic molecules whose three-dimensional structure can be changed by acid–base stimuli. To date, pH-responsive molecular switches have been developed using various functional groups, but further advances require expanding the range of pH-responsive systems and discovering new molecular architectures. Here, we investigate the pH-responsive behavior of ortho-disubstituted benzamidine, which generates atropisomers and E/Z isomers. The amidine moiety allows modulation of the C–N and C–N/C–C rotational barriers by protonation, providing a novel approach to control the kinetics of isomerization via pH adjustment. The results showed that protonation of the amidine moiety significantly suppresses both C–N bond rotation and C–N/C–C concerted rotation, demonstrating the potential of ortho-disubstituted benzamidine derivatives as a novel pH-responsive molecular switch.