Visible light activated dendrimers for solar thermal energy storage and release below 0 °C

Abstract

Molecular solar thermal (MOST) fuels offer a closed-cycle and renewable energy storage strategy that can harvest photons within the chemical conformations and release heat on demand through reversible isomerization of molecular photoswitches. However, most reports rely on the ultraviolet (UV) light storage at room temperature, which significantly restricts the application of MOST fuels. Here, we present a novel fluorochloroazobenzene-containing dendrimer that can not only efficiently store photon energy and release heat in the visible light range but also exhibit excellent application potential below 0 °C. These excellent properties are attributed to the neighbouring halogen atoms modulating the intramolecular interactions of NN groups and the favourable chain mobility of the dendrimer at low temperature. The energy density of the dendrimer fuel after harvesting green light (520 nm) can reach 0.046 MJ kg⁻¹ (19.0 kJ mol⁻¹) accompanied by a storage half-life of up to approximately 20.6 days. Moreover, blue light-triggered heat release from the MOST film in low-temperature environments (−2 °C) can increase the temperature by 3.7 °C, exhibiting significant de-icing effects. Our work provides a fascinating avenue to fabricate visible light activated MOST fuels and unlocks the possibility of developing natural sunlight storage.