Disordered Low Molecular Weight Spiropyran Exhibiting Photoregulated Adhesion Ability.

The functions of the materials composed of small molecules are highly dependent on their ordered molecular arrangements in both natural and artificial systems. Without ordered structure, small molecules hardly gain complicated functions, due to the absence of intermolecular covalent bond connection or strong network. Here, a low molecular weight spiropyran that could exhibit attractive photochromism and powerful adhesion property in disordered solid state is demonstrated. With maximum up to ∼8 MPa, the adhesion strength could be photoregulated in multiple levels, which also shows one-to-one correspondence to the specific color state. The working mechanism analysis on the photoregulated adhesion reveals that the isomer ratio of merocyanine form and the molecular packing density of spiropyran are the determining factors for the adhesion ability. The discovery of photoregulated adhesion from pure spiropyran provides a new strategy for developing functional materials by employing low molecular weight compounds.