Fast photochromism in solid: Microenvironment in metal-organic frameworks promotes the isomerization of donor-acceptor Stenhouse adducts

The isomerization of photoresponsive molecules in the solid state is always restricted due to the intermolecular stacking. In this work, we fabricated solid powdery materials with fast and efficient photochromism by embedding donor-acceptor Stenhouse adducts (DASAs) into the nanocages of metal-organic frameworks (MOFs). Visible light irradiation (530 nm, 40 mW/cm2) induces linear-to-cyclic isomerization of DASAs in ~7.7 s with a 100% conversion efficiency, which is with the same order of magnitudes as that in solution. Meanwhile, the isomerization of loaded DASAs is fully reversible after repeated treating by visible light and heat. The microenvironment in the nanocages of MOFs is able to promote the isomerization to either linear or cyclic DASAs, which was unfold by density functional theory calculations. All in all, the solid powdery materials are further applied as additives to realize photochromism of bulk materials, which show reversible color change under visible light and heat.