Mechanochemical Improvement of Norbornadiene-Based Molecular Solar-Thermal Systems Performance

Molecular solar-thermal systems (MOST) offer a promising alternative to store and release solar energy compared to more conventional solar cells. Especially, the norbornadiene-based system was found to be, until now, the most efficient organic-based MOST offering, when opportunely substituted, several promising candidates that could lead to commercial use. Nevertheless, all carried out experimental attempts largely lack a proper design, hence finding difficulties in improving selected MOST properties. Here, a novel theoretical approach is described and applied to the norbornadiene-quadricyclane system, with the goal to study the effect of applied mechanical external forces, which can be traduced into a steric substitution effect. Especially we found that, while the absorption energy cannot be almost modified, the stored energy can be increased by ca. 70 kJ/mol and, at the same time, a consistent increase (ca. 10 kJ/mol) of the quadricyclane activation energy can be obtained. Moreover, we show that optimal complex forces, resulting from a combination of different contributions, could be suitably converted into substitution patterns and allow further improvements of the MOST properties.