Photoinduced π-Bond breakage causing dynamic closing-opening shell transition of Z-type Diphenylmaleonitriles molecules.

Organic molecules with dynamic covalent-bonding characteristics have attracted much attention for their important role in constructing stimulus-responsive smart materials. However, it is difficult to realize sensitive and reversible covalent bond cleavage/formation through external stimuli in the aggregated state of molecules. Herein, a series of 2,3-diphenylmaleonitriles (DPMNs) with photoinduced π-bond cleavage properties have been designed and synthesized to construct the dynamic covalent bond materials. The cis-form 2,3-diphenylmaleonitriles (Z-DPMNs) exhibit significant photochromism in both solid and solution states under ultraviolet light and visible light. The photochromism stems from the photoinduced π-bond splitting of Z-DPMNs, resulting in a transition from the closed-shell to open-shell structure. Moreover, the twisted structure and molecular stacking of Z-DPMNs, the push-pull electron effect of substituents, and the external factors including temperature and solvent polarity have important effects on the dynamic conversion of π-bonds. Based on the sensitive and reversible optical performance transformation, Z-DPMNs can be applied as safety ink in anti-counterfeiting, information encryption and storage systems. This work not only provides an approach for constructing dynamic covalent bonds but also greatly enriches stimulus-responsive materials.