[2.2]Paracyclophane as a Target of the Organic Solid State: Emergent Properties via Supramolecular Construction

In this account, we review the synthesis of [2.2]paracyclophanes in the organic solid state. Reactions in crystalline solids provide a means to obtain molecules with high degrees of stereocontrol that can also be unattainable in solution. We show that [2.2]paracyclophanes form in the solid state stereospecifically and in quantitative yield via intermolecular [2+2] double photodimerization reactions. The double cycloaddition that affords a paracyclophane in the solid state does not readily occur in solution. Small molecules in the form of hydrogen‐bond‐donor templates can provide access to [2.2]paracyclophanes in a solid by design. A [2.2]paracyclophane obtained using a hydrogen‐bond template is shown to exhibit attractive optical properties and has been employed as a building block of a metal‐organic framework (MOF).