H-bonding-assisted energy retention in bicyclic diene photoswitches for rechargeable solar thermal batteries: CASSCF, CASPT2, and DLPNO-CCSD(T) insights

Molecular solar thermal (MOST) systems have the potential to harness and store a vast amount of solar energy, making them promising for renewable energy solutions. However, the integration of solar absorption, high energy storage density, and long thermal half-life into a single photochromic couple remains a contemporary challenge, hindering their practical deployment. In this work, we present a rational design strategy to enhance key properties of a bridged bicyclic diene (BBD)-based photoswitch through elongation of the unsaturated bridge and strategic functionalization. The introduced substituents promote synergistic non-covalent interactions, particularly intramolecular hydrogen bonding and reinforce push-pull electronic effects, collectively enabling pronounced bathochromic shifts in absorption without compromising energy storage capacity and duration. Comprehensive electronic structure analyses carried out using the CASSCF, CASPT2, and DLPNO-CCSD(T) methods ensure the robustness of the findings. This study provides valuable design principles for next-generation MOST systems by leveraging the cooperative effects of non-covalent interactions and electronic modulation through functionalization.