Development of renewable energy technologies has been a significant area of research amongst scientists with the aim of attaining a sustainable world society. Solar thermal fuels that can capture, convert, store, and release solar energy in the form of heat through reversible photoisomerization of molecular photoswitches such as azobenzene derivatives are currently in the limelight of research. Herein, we provide a state-of-the-art account on the recent advancements in solar thermal fuels based on azobenzene photoswitches. We begin with an overview on the importance of azobenzene-based solar thermal fuels and their fundamentals. Then, we highlight the recent advances in diverse azobenzene materials for solar thermal fuels such as pure azobenzene derivatives, nanocarbon-templated azobenzene, and polymer-templated azobenzene. The basic design concepts of these advanced solar energy storage materials are discussed, and their promising applications are highlighted. We then introduce the recent endeavors in the molecular design of azobenzene derivatives toward efficient solar thermal fuels, and conclude with new perspectives on the future scope, opportunities and challenges. It is expected that continuous pioneering research involving scientists and engineers from diverse technological backgrounds could trigger the rapid advancement of this important interdisciplinary field, which embraces chemistry, physics, engineering, nanoscience, nanotechnology, materials science, polymer science, etc.

Soft robots that can move like living organisms and adapt to their surroundings are currently in the limelight from fundamental studies to technological applications, due to their advances in material flexibility, human-friendly interaction, and biological adaptation that surpass conventional rigid machines. Light-fueled smart actuators based on responsive soft materials are considered to be one of the most promising candidates to promote the field of untethered soft robotics, thereby attracting considerable attention amongst materials scientists and microroboticists to investigate photomechanics, photoswitch, bioinspired design, and actuation realization. In this review, we discuss the recent state-of-the-art advances in light-driven bimorph soft actuators, with the focus on bilayer strategy, i.e., integration between photoactive and passive layers within a single material system. Bilayer structures can endow soft actuators with unprecedented features such as ultrasensitivity, programmability, superior compatibility, robustness, and sophistication in controllability. We begin with an explanation about the working principle of bimorph soft actuators and introduction of a synthesis pathway toward light-responsive materials for soft robotics. Then, photothermal and photochemical bimorph soft actuators are sequentially introduced, with an emphasis on the design strategy, actuation performance, underlying mechanism, and emerging applications. Finally, this review is concluded with a perspective on the existing challenges and future opportunities in this nascent research Frontier.

Hydrogel-based sensors have attracted significant attention owing to their promising applications in artificial intelligence. However, developing robust hydrogel conductors with customizable functionality and excellent sensor properties is challenging. In this study, a new class of sponge-like porous hydrogel conductors integrating self-healing ability, multiple sensations, and excellent mechanical properties is proposed. These attractive comprehensive properties result from liquid metal-created multiple structures. Using acrylic acid as a reactive monomer, liquid metals not only promote the formation of self-healing supramolecular hydrogel networks, but also enable the reduction of graphene oxide to form electronic conductive networks and create macroporous structures in the hydrogel. These structures allow hydrogel conductors to be used as soft sensors with high compressive sensitivity (up to 0.85 kPa⁻¹), a wide range of strain sensitivities (more than 400%), and other multiple sensations such as high sensitivity to temperature evolution, response to solvent change, and sensing atmospheric negative pressure (vacuum). Furthermore, their excellent self-healing ability can further enhance their durability. Such unique multiple sensations are expected to provide novel prospects for the development of sophisticated artificial flexible devices.

This review provides a state-of-the-art account on the design and properties of advanced functional carbon dots and their emerging applications ranging from optical and energy to biomedical fields.