Large and long-term photon energy storage in diazetidines <i>via</i> [2+2] photocycloaddition

Abstract

We report a series of <i>p</i>-functionalized phenylbenzoxazoles that offer remarkable energy storage, exceeding 300 J g^-1, for the first time among intermolecular cycloaddition-based molecular solar thermal energy storage systems. The [2 + 2] photocycloaddition of phenylbenzoxazoles generates diazetidine cycloadducts that store energy for up to 23 years in the solid state and release energy upon triggered cycloreversion. The solid-state phase transition contributes to increasing overall energy storage densities, and the dearomative cycloaddition process is revealed to be critical for maximizing the intrinsic energy storage capacities. The solvent-assisted cycloreversion is also used to accelerate the energy release from the emerging molecular scaffold.