Photoswitchable Molecular Systems in Energy Storage

Photoswitchable molecular systems harness light‐induced isomerisation to convert and store solar energy as chemical potential, with the ability to release heat on demand. These systems typically comprise chromophores that undergo reversible configurational changes between low‐energy and high‐energy isomers. By absorbing photons, the molecule is driven into a metastable state that stores energy until a thermal or catalytic stimulus triggers back conversion, releasing heat. Molecular solar thermal (MOST) storage has emerged as a promising complement to conventional batteries and thermal storage, offering high energy densities, tunable lifetimes and cycle stability. Key candidates include norbornadiene–quadricyclane couples, azobenzenes and other heteroaromatic photoswitches. Advances in molecular design have focused on improving spectral match to sunlight, maximising quantum yield, extending storage lifetimes and integrating photoswitches into devices such as flow reactors, coatings or hybrid solar‐thermal panels. This approach holds global significance for decentralised heating, peak‐shaving in power grids and integration into building materials, with the potential for scalable, carbon‐neutral thermal management.

Research from Nature Portfolio

Recent studies have advanced the molecular design of photoswitch oligomers to enhance energy density and storage lifetime. By linking norbornadiene units into dimeric and trimeric architectures, researchers achieved energy densities up to 559 kJ kg⁻¹ and storage lifetimes approaching 48 days. Fine‐tuning of linker units balanced light absorption and barrier heights to optimise both harvesting efficiency and thermal stability. Another foundational contribution established robust methodology for determining photoisomerisation quantum yields in solution and solid state, accounting for competing thermal processes. A standardised protocol and accompanying software enable accurate, comparative assessment of switching efficiency, guiding molecular refinements across diverse photoswitch classes.

Photoswitchable Molecular Systems in Energy Storage publication trend

The graph below shows the total number of articles in photoswitchable molecular systems in energy storage across all publications each year (not limited to Nature Index journals).

Technical terms

Photoisomerisation: Reversible transformation between two molecular isomers induced by absorption of light.

Quantum yield: Ratio of the number of molecules undergoing photoisomerisation to the number of photons absorbed.

Energy density: Amount of chemical energy stored per unit mass of a photoswitchable molecule.

Norbornadiene–quadricyclane (NBD/QC): A molecular pair that interconverts upon irradiation and thermal or catalytic back‐conversion, used for solar thermal storage.

Molecular solar thermal (MOST) systems: Energy storage technology employing photoresponsive molecules to capture, store and release solar heat.

References

1. Molecular solar thermal energy storage in photoswitch oligomers increases energy densities and storage times. Nature Communications (2018).
2. Determining the Photoisomerization Quantum Yield of Photoswitchable Molecules in Solution and in the Solid State. Scientific Reports (2017).
3. Macroscopic heat release in a molecular solar thermal energy storage system. Energy & Environmental Science (2019).
4. Storing energy with molecular photoisomers. Joule (2021).