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.

Solar thermal fuel (STF) technology based on azobenzene (Azo) compounds represents a novel approach for the capture, conversion, and storage of solar energy. Azos can store energy by isomerization between their thermodynamically stable trans-isomers and higher energy, metastable cis-isomers. The energy barrier to Azo isomerization must be overcome in order to store and release energy using these materials. Generally, this is achieved using heat, light, or catalysis. Heating is the most frequently used strategy to overcome the energy barrier and release the stored energy in Azo-based STFs (Azo-STFs). However, heating Azos is not economical in practical STF applications. A notable target is the development of strategies for the construction of STFs that operate at room temperature. In this study, polyvinyl alcohol (PVA) polymer-templated, gold nanoparticle (AuNP) doped, 1,3,5-tris(arylazo)benzene (tri-Azo)-based STFs (PVA/Azo@AuNP STFs) are presented. The heat storage and release behavior of these composites can be controlled completely using light alone at room temperature. Light at a wavelength of 365 nm is effective for charging the PVA/Azo@AuNP STFs, while light at 520 nm induces the release of energy from the samples. Temperature increases of up to 8.8 °C were observed during the discharge of the PVA/Azo@AuNP STFs. The significant heat output can be attributed to three cooperative effects. First, irradiation at 520 nm irradiation triggers cis-to-trans isomerization of tri-Azo. Second, light irradiation at 520 nm stimulates the plasmonic photothermal effect in the AuNPs, releasing heat, which stimulates the cis-to-trans isomerization reaction. Finally, the AuNPs act as catalysts, accelerating the cis-to-trans isomerization reaction. Through these multiple stimulation modes, heat is released rapidly from the charged PVA/Azo@AuNP STFs. The mechanism and design principles for such novel Azo-STFs are discussed. This work provides a new strategy for the design of efficient Azo-STFs that operate at room temperature.

In this work, we present a pair of chiral PEDOT derivatives named poly((R)-2-(chloromethyl)-2,3-dihydrothieno[3,4-b][1,4]dioxine) ((R)-PEDTC) and poly((S)-2-(chloromethyl)-2,3-dihydrothieno[3,4-b][1,4]dioxine) ((S)-PEDTC), which were employed as excellent chiral recognition materials for fabricating chiral sensors and then discriminating between 3,4-dihydroxyphenylalanine (DOPA) enantiomers. Importantly, the mechanism of the stereospecificity of the interaction between the DOPA enantiomers and chiral polymers was discussed specifically. A series of performances of corresponding polymers were characterized in some detail using different strategies including CV, CD, FT-IR, UV-vis, SEM, and TG. The CD spectrum indicated that (R)-PEDTC and (S)-PEDTC are mirror symmetric. CV shows that the polymers had superior redox reversibility in CH₃CN–Bu₄NPF₆. Finally, different electrochemical methods including CV, square wave voltammetry (SWV) and differential pulse voltammetry (DPV) were introduced for the discrimination of DOPA enantiomers. Satisfactory measurement results demonstrated that (R)-PEDTC/GCE and (S)-PEDTC/GCE exhibited excellent enantioselectivity of DOPA enantiomers and the tendency was for anisotropic interaction between (R)-PEDTC and L-DOPA, and (S)-PEDTC and D-DOPA. This implied that the obtained polymer films could be promising candidates as enantioselective materials in the electrochemical sensor field.