A metastable-state photoacid-based metal organic framework with multi-stimuli-responsive chromism

Developing multi-stimuli-responsive chromic materials has been intensively pursued as smart materials for rewritable paper, smart windows and anti-counterfeiting applications. Herein, a metastable-state photoacid, a protonated-merocyanine form of a spiropyran, was incorporated into a zirconium(IV)-based UiO-topological metal organic framework (MOF) material (form PAH-MOF) for multi-stimuli-responsive chromic materials. Photoacid on the framework of PAH-MOF adopts a stable merocyanine form. And PAH-MOF shows multi-stimuli-responsive chromism towards heating, different solvents and acids. Despite the PAH-MOF being photo-inactive in the solid state, the acidified PAH-MOF suspensions exhibit excellent visible light induced photochromism in water and ethanol. In addition, a distinct fluorescence change along with the color change is recognized, revealing a potential application in anti-counterfeiting. Our findings will help better understand the effects of MOFs on isomerization of spiropyran derivatives.