Azole-Based Diarylethenes Containing Benzoheteroarene π-Linkers for Solar Thermal Energy Storage: Influence of Aromaticity and Noncovalent Interactions

Diarylethene photoswitches featuring azole-based diaryl units combined with benzoheteroarene π-linkers have gained significant research interest in recent years due to their potential to achieve higher photocyclization efficiencies compared to conventional dithienylethene switches. In this work, we investigate the suitability of these photoswitches for molecular solar thermal energy storage (MOST) applications through computational modeling of their electrocyclization and cycloreversion reactions. Our calculations demonstrate that it is possible to achieve simultaneously both large energy-storage densities (0.29-0.35 MJ kg-1) and prolonged energy-storage times (half-lives of up to 124 days) under ambient conditions in dithiazolyl and dioxazolyl switches containing six distinct benzoheteroarene π-linkers. Furthermore, isomerization stabilization energy calculations and noncovalent interaction analysis reveal that the variations in energy-storage densities and times between the azole-based and dithienylethene switches stem from differences in aromaticities of the diaryl core and π-linker, as well as changes in noncovalent interactions. Notably, we demonstrate that the relative populations of photoreactive anti-parallel and non-photoreactive parallel conformers of the ring-open form of these switches are governed by weak intramolecular C···C interactions between the two aryl rings. These findings highlight the importance of optimizing such interactions to enhance energy-storage efficiencies in MOST systems.