Rapid Capture and Storage of Solar Energy via [2+2] Photocycloaddition in α‐Cyanostilbene

Abstract Solar energy, as a vital renewable resource, plays an increasingly crucial role in the global energy system. The molecular solar thermal (MOST) energy storage technology represents an innovative solar energy storage method based on chemical reactions, with advantages such as high energy density, strong stability, and on‐demand energy release. Although significant progress has been made in the solution state, there are still relatively few reports on MOST molecular crystals that can rapidly capture and store solar energy. Herein, it is demonstrated that the donor–acceptor α‐Cyanostilbene (CS) crystals are capable of harvesting solar energy within minutes through [2+2] photocycloaddition reactions. Additionally, the polymorphic transformation and the underlying causes of the variation in their absorption spectra are investigated. At last, the energy storage capacity of the photoproducts in the crystalline and amorphous states is explored. Unfortunately, reversible energy storage and release cannot be achieved at present due to the thermal decomposition behavior of the materials. However, this study is believed to provide an interesting platform for the future development of MOST molecular crystals.