Forward‒ and Retro‒Vapofluorochromism of Sponge‒Like Macrocycle Crystals

Achieving dynamic multicolor emission through solid-state molecular motion is of significant importance for advancing applications in organic solid-state luminescent materials. Herein, we report macrocycle crystals with unique forward‒ and retro‒vapofluorochromic behavior, which is realized by reversible amine vapor uptake and amine‒“squeeze” induced guest release. The forward‒vapofluorochromism occurs when aliphatic amines penetrate guest-free macrocycle crystals to form host‒guest complex crystals. These fluorescent properties can be reversibly toggled by exposing the amine‒loaded crystals to another amine vapor through competitive guest replacement inside the crystals. Notably, retro‒vapofluorochromism is achieved by exposing amine‒loaded crystals to α‒methylbenzylamine (MBA). Mechanistic studies show that MBA molecules do not penetrate the crystal, but rather “squeeze” the crystals to release loaded amines, driving the amine‒loaded crystals back to the guest-free phase. The demonstrated forward‒ and retro‒vapofluorochromism has already been successfully integrated into a highly secure five‒layer information encryption system.