Control of photoreactivity in organic solids through large synthons

Controlling photoreactivity in organic solids has attracted significant interest from chemists and material scientists for a long time. Although the pioneering works in this field date back to the 1970s when Schmidt formulated the topochemical principle based on cinnamic acid derivatives, the advent of the subject of crystal engineering allowed scientists to tune photoreactivity in a supramolecular way using hydrogen bonding and other non-covalent interactions. The design of organic solids became easier with the formulation of the concept of supramolecular synthons. However, over the years it has transpired that small synthons, despite capturing necessary chemical and geometric details, are often insufficient to provide sufficient control in many design strategies. In this context, the idea of large synthons was coined. Large synthons, in the present context, represent modular synthons often involving composite interactions which contain sufficient chemical and geometrical information for a targeted design and provide sufficient structural insulation that makes the strategy robust and general. These modular large synthons are often considered a starting point in Long Range Synthon Aufbau Module (LSAM)-based design strategies. Despite their potential in crystal design, robust large synthons are often difficult to implement in design strategies as they are generally formed by the combined effects of weak interactions and may lack in recurrence. This talk will focus on how a robust large synthon can be helpful, especially in the context of bi-component crystal design, based on benzilic acid and stilbazole derivatives. Benzilic acid, a well-known molecule in the context of Benzil-Benzilic acid rearrangement, also contains intriguing supramolecular features that help in large synthon formation. The key focus of the talk will address: (i) crystal design with diverse photoresponses, (ii) tuning photoreactivity/photoresponses in the respective solids through a large synthon approach, and (iii) the role of modularity of such large synthons in crystal design.