Heat- and Light-Directed Cycloadditions Enable a Pericyclic Cascade Reaction From a Molecular Precursor.

Stimuli-responsive materials undergo a chemical or physical change when exposed to an external signal and represent an emerging class of functional materials. For molecular solids, designing structures that respond to a given external stimulus via orthogonal reaction pathways is challenging. Molecules commonly crystallize in geometries unsuitable for an intended reaction and afford either low yields or are unreactive in solid-state chemical transformations; thus, most molecular solids only respond to one external stimulus and undergo one type of response. Here, we demonstrate the first single-component molecular solid capable of responding to heat and light through distinct chemical reaction pathways, while mechanical responses include salient or luminescent behavior. The reactant contains functionalities needed for both intramolecular and intermolecular cycloadditions, and the reaction pathway is directed via self-assembly and the applied stimulus. Moreover, an unprecedented cycloreversion-cycloaddition cascade reaction was also unlocked, and quantum mechanical calculations were further used to interrogate the mechanism of the pericyclic cascade reaction. All transformations proceed with complete regiocontrol, and sunlight affords quantitative yields for the light-triggered reaction. This work demonstrates molecular- and supramolecular-based strategies that can effectively integrate multi-stimuli-responsive behaviors into solid materials.