In silico design of dihydroazulene/vinylheptafulvene photoswitches for solar-energy storage guided by an all-around performance descriptor

The possibility to use the reversible cycling of molecular photoswitches between isomeric forms as a means to store and release solar energy has stimulated the development of candidate systems based on several different core structures, such as the dihydroazulene/vinylheptafulvene (DHA/VHF) couple. However, a major challenge in these efforts is to simultaneously realize many of the performance criteria required of the switches for such applications. Here, we take on this challenge by first introducing an all-around performance descriptor that combines three key criteria (related to energy density, storage time and light-absorption characteristics), and by then using density functional theory (DFT) methods to calculate its values for 52 newly designed DHA/VHF switches. Through this approach, we are able to identify several switches with excellent overall properties that contain a structural motif absent in all DHA/VHF compounds considered for solar-energy storage in the existing literature. For some of these switches, we also provide retrosynthetic analyses for their preparation and perform DFT calculations to demonstrate that they form the energy-storing VHF isomer through a facile DHA  VHF photoisomerization reaction. All in all, we conclude that these switches show great promise for further development towards applications in solar-energy storage.