Photoactivated cycloaddition can store solar energy for decades in strained molecules

A new class of molecular ‘photoswitch’ – stable in the solid state – can store solar energy upon excitation with visible light. This overcomes some critical challenges of conventional energy storage structures, such as thermal stability and optical sensitivity beyond the UV spectrum – both attractive properties towards scale-up and commercialisation.

‘Our compounds store solar energy in highly strained chemical bonds,’ explains lead author Grace Han from Brandeis University in the US. ‘The absorption of light triggers a chemical change. An external stimulus sparks the reverse reaction, liberating the stored energy, usually as heat.’ These strained systems, stable for several decades, release the energy on demand, upon thermal activation or UV irradiation. They can store up to 51J/g, which is enough energy to heat up 1g of water over 10 degrees.