Tuning molecular assembly to enhance azobenzene-based solar thermal fuel efficiency

Abstract

Molecular solar thermal fuel (STF) systems harness solar energy from solar radiation and store it as chemical energy. The stored energy is released as heat in the presence of suitable stimuli. Recently, azobenzene and its several derivatives have largely been used to develop molecular solar thermal fuel systems. These molecules photoisomerize into a metastable state and store the solar energy. Various techniques are applied to tune the isomerization enthalpy, thermal back half-life and stability of the STF materials at the molecular level. In addition, the intermolecular assembly of the azo-molecules in an STF material plays an important role in altering the system's energy storage efficiency. A precise arrangement of photochromic compounds can be achieved by adjusting the chemical structures of the photoswitches, anchoring the photoswitches to a polymer/carbon-based material or attaching a phase-changing material to the photoswitches. These methodologies significantly alter the energy density and storage timing of the system. This review focuses on how suitable modulations of the molecular assembly nature of the photoswitches can be exploited to achieve highly efficient STF materials. Major factors, such as the structural design of the photochromes and different templating technologies, are addressed in detail. The proposed idea of tuning the molecular assembly in STF materials will provide rational guidance and facilitate the future development of efficient STF materials for large-scale applications in the field of renewable energy sources.