Adjustable current-responsive photoswitches based on azobenzene derivatives

Abstract Azobenzene (AB) undergoes a light-driven trans/cis (E/Z) isomerization, molecular shape and polarity changes making it a prominent molecular photoswitch. However, the challenges in quantitative measuring its shape and polarity change have limited the development of these photoswitches to applications in binary outputs. In this work, we show that the E-to-Z isomerization promotes the diffusion of Z-AB, leading to an increase of the diffusion-limited steady-state current (iL) in chronoamperometric processes. Moreover, the magnitude of iL and current transition rates could be fine-tuned by varying the substituents at the 4 and 4' position on the azobenzene. Based on this discovery, we design and synthesize a series of azobenzene derivatives. These compounds exhibit a variety of current response amplitudes (50–220 µA) and switching times (20–60 seconds to reach equilibrium). Molecular Dynamics simulations and Density Functional Theory calculations indicate that the more polar Z isomer has a stronger interaction with the solvent molecules, which enables better solvation and ultimately, promotes faster diffusion. It is envisaged that these multilevel azobenzene photoswitches could provide a platform for future applications in (photo)electrochemical catalysis and sensors.