Molecular Solar Thermal Energy Storage: Anthracene Systems and Beyond

Licentiate thesis, 2024

The increasing global demand for energy has led scientists to explore alternative sources to fossil fuels. Several works have been done on renewable energy harvesting methods, such as hydropower, geothermal, solar, wind, and marine energies. Among these sources, significant progress has been made in harnessing solar energy over the past few decades; the main challenge lies in effectively storing it. One method of storing solar energy is the use of organic photoswitches, which store solar energy in the form of chemical bonds and release it when needed; this approach is known as molecular solar thermal energy storage (MOST). When photoswitches absorb solar energy, they convert to a metastable photoisomer through a process called photoisomerization. The stored energy can then be released as heat when triggered by heat, light, or catalyst.

In this thesis, two types of anthracene systems, namely anthracene derivatives and linked anthracene systems, along with the Norbornadiene-Quadricylane system, were evaluated as potential MOST candidates. A series of anthracene derivatives with varying substituents and substitution positions were synthesized and characterized to study the structure-property relations. A comparison of physical, photophysical, and energy storage properties of mono and di-substitution is presented along with alkylated anthracene variants. Additionally, detailed characterization and comparison of aryl-linked anthracenes with various substituents are also studied, with the aim of eliminating the concentration dependence of the photoisomerization quantum yield.

Furthermore, a series of benzothiadiazole-substituted NBDs were examined, aiming to improve the solar spectral match of NBDs. The study revealed that these systems have a significant redshift and better solar spectral match compared to previously reported NBDs. This work highlights the complexity of optimizing all parameters for an efficient MOST system within a single molecule.