The growing global urgency for sustainable and efficient energy solutions has driven extensive research into renewable energy technologies. Molecular solar thermal (MOST) systems present a promising approach to both capture and store solar energy. MOST systems utilise molecular photoswitches that absorb sunlight and undergo reversible isomerisation to a higher energy metastable state, storing the captured energy in the strained chemical bonds of the photoisomer. The stored energy can then be released as heat and on demand upon triggering the back-conversion to the parent isomer. Despite several photoswitches being proposed and studied as MOST candidates, the search for the ideal switch that fulfils all the criteria for an efficient MOST system—a high energy storage density (> 0.3 MJ·kg−1), absorption that overlaps with the solar spectrum, extended thermal half-lives and high photoisomerisation quantum yields—is ongoing. In this chapter, we provide a comprehensive review of emerging photoswitchable molecular systems as MOST candidates, with a focus on their switching mechanisms, i.e. solid-state switching, and photochemical properties while also describing how these parameters influence the key performance metrics. We assess a wide range of photoswitches, including recently developed candidates together with well-established systems that, whilst extensively studied in other contexts, are now being reconsidered for their relevance to MOST. In addition, we critically assess the limitations and challenges associated with each class of photoswitch, highlighting the specific characteristics that require further optimisation for successful MOST implementation. Overall, this chapter aims to shed light on the evolving landscape of photoswitchable molecules that are shaping the next generation of MOST energy storage systems.