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

Abstract

Molecular solar thermal fuel (STF) harnesses solar energy from solar radiation and stores it as chemical energy. The stored energy is released as heat in the presence of suitable stimuli. Recently, azobenzene and its several derivatives are largely 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 the stability of the STF material in single molecular level. In addition, the intermolecular interactions between the azo-molecules in an STF material play an important role in altering the energy storage efficiency of the system. Therefore, a precise arrangement of photochromic compounds is highly essential, which can be achieved by adjusting the chemical structure of the photoswitches, anchoring the photoswitches with 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 intermolecular interactions between the photoswitches can be exploited to achieve highly efficient STF materials. The major intermolecular interactions controlling factors such as structural design of the photochromes, and templating technologies are addressed in detail. The throughout idea to tune the intermolecular interactions in STF material will provide rational guidance and facilitate future development of efficient STF materials for large-scale applications in renewable energy sources.