Intense Redox-Driven Chiroptical Switching with a 580 mV Hysteresis Actuated Through Reversible Dimerization of an Azoniahelicene

Molecular switches are of interest for the construction of molecular-scale memory devices. Switches based on redox-triggered helicenes can achieve intense chiroptical read-out values but most systems only display a small potential difference between the “ON” and the “OFF” switch states (redox hysteresis). Although a larger hysteresis could be achieved by coupling the electron transfer to a fast follow-on reaction, this approach has been limited to the intramolecular ring-opening of helicene-like systems to axially chiral biaryls. Here, we present the first intermolecular follow-on reaction: an azoniahelicene system that dimerises upon reduction, leading to intense, reversible chiroptical switching with a >500 mV hysteresis and a >300 mV “read-only” potential range. The reported helicene dimerization is supported by detailed electrochemical investigations and the comparison of experimental and calculated electronic circular dichroism (ECD) spectra.