Visible-light-switchable azobenzenes: Molecular design, supramolecular systems, and applications

Abstract

Photocontrol of functional molecules and supramolecular systems provides promising directions for the development of innovative materials and technologies. Reversible photoswitches that can isomerize among different states play a vital role in such photoresponsive systems. However, the commonly used UV light for triggering the isomerization of photoswitches such as azobenzene (AB) has limited their applications in functional material systems because UV light penetrates poorly and causes damage to materials or biological tissues. Accordingly, tremendous endeavors have been devoted to the development of visible-light-switchable molecules and expand their new applications in various fields. Herein, we highlight the strategies of molecule design for visible-light-switchable ABs by discussing the effects of benzene substituents on the absorption spectrum. Based on this, visible-light-responsive supramolecular systems with metal–organic frames, cyclodextrins, nanoparticles, and biomolecules (DNAs, peptides, and proteins) are elaborated. Then, the light-responsive mechanical properties and their emerging applications in actuators, biological systems, information storage, energy storage, nonlinear optical devices, and photoswitchable adhesives are discussed. Finally, a summary of the challenges and perspective on visible-light-switchable ABs are outlined. Key points: Structural design strategies for visible-light-responsive azobenzenes Visible-light-responsive supramolecular azobenzene systems in different research areas ranging from chemistry to biology Their light-responsive mechanical properties and emerging applications.