Molecular solar thermal energy storage in Dewar pyrimidone beyond 1.6 megajoules per kilogram.

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 nanometers. 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 milliliters). These advances help point the way toward decentralized solar heat storage and off-grid energy solutions.