Cocrystals and Templates to Control Solid-State [2+2] Photodimerizations

In this chapter, we present historical and current developments on the use of the process of cocrystallization as an effective tool in solid-state synthesis. In particular, we provide an account on uses of cocrystallizations using small-molecule templates to direct intermolecular [2+2] photodimerizations. While geometric criteria for a [2+2] photodimerization to proceed in the solid state have been known since the late 1960s, effects of crystal packing have largely prevented chemists from designing solids with olefins that routinely undergo the reaction. The historical significance of the photoreaction makes the cycloaddition an excellent system to develop cocrystallization strategies involving templates. The emergence of templates as a means to control reactivity in the solid state can be traced to the field of supramolecular chemistry and a concurrent growth of crystal engineering.