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 crystals, 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.