Solar E→Z photoisomerization of azo switches

By absorbing light energy, molecular photoswitches can undergo structural changes, store chemical energy, and perform dynamic work, which has profound impacts on the development of stimuli-responsive systems, energy storage/conversion materials, artificial molecular machines, etc. Developing photoswitches that can be fueled by natural sunlight will bring great benefits to their applications in the context of carbon neutrality. Here, we show that solar photoswitching can be realized by reshaping the absorption spectral profile, i.e., rendering the absorption of parent isomer overwhelmingly stronger than that of metastable isomer across the UV–Vis spectra. Solar E→Z photoisomerization of azo molecules—the most widely used class of photoswitches—are achieved by implementing this spectral tuning principle. A simple yet tunable molecular design strategy to meet this spectral requirement is established and a variety of solar photoisomerizable heteroaryl-based azo-switches are developed. Photoswitching under natural sunlight in place of the traditional artificial lights represents a crucial step towards sustainable light-driven processes.