Molecular solar thermal energy storage in Dewar pyrimidone beyond 1.6 MJ/kg

Storing sunlight in a compact and rechargeable form remains a central challenge for solar energy utilization. Molecular solar thermal (MOST) energy storage systems, which harness photon energy and release it as heat on demand, provide a direct approach, but have long failed to meet practical benchmarks. Inspired by the architecture of DNA, we report a pyrimidone-based MOST system that stores energy in the strained Dewar photoisomer upon excitation at 300 nm. Designed with sustainability in mind, the system operates solvent-free and remains compatible with aqueous environments while overcoming one of the field's greatest hurdles: the controlled extraction and transfer of stored heat. When catalyzed by acid, the Dewar isomer releases enough heat to boil water (~0.5 mL). These advances help point the way toward decentralized solar heat storage and off-grid energy solutions.