Improvement of azobenzene photothermal energy storage density via grafting onto g-C3N4 and introducing hydrogen bonding

Abstract

This paper proposes a molecular model of covalent grafting of azobenzene derivatives with graphite-like carbon nitride based on hydrogen bond regulation to improve the azobenzene photothermal energy storage density. The enthalpy of isomerization (ΔH) of azobenzene molecular cis-trans isomers is calculated using density functional theory, and the magnitude of ΔH is used to evaluate the photothermal storage performance of the azobenzene graphite-like carbon nitride model. The results showed that the molecular ΔH value increased by 0.105–0.243 eV after the azobenzene derivatives were covalently grafted to the graphitic carbon nitride template. In addition, when the donator group replaced the active benzene ring ortho-site of azobenzene, its value was 0.069–0.295 eV higher than that of the electron-withdrawing groups. Moreover, intramolecular hydrogen bonds can stabilize cis-trans isomers and increase the energy of azobenzene. Compared with unsubstituted azobenzene, the energy of azobenzene ΔH containing one intramolecular hydrogen bond increased by 0.295 eV, while the energy of azobenzene ΔH containing multiple intramolecular hydrogen bonds increased by 0.775 eV.