Photoisomerization-Induced Melting and Spontaneous Crystallization in Acicular Star-Shaped Microcrystals

In recent years, significant advancements have occurred in the development of smart materials, particularly in creating molecular crystals that can convert light energy into mechanical work. In this study, we focus on the synthesis, characterization, and photomechanical behavior of a new molecule, bis(2,2,2-trifluoroethyl) (E)-2-(3-(anthracen-9-yl)allylidene)malonate (trans-ATF), which is capable of forming acicular star-shaped microcrystals resembling sea Urchins. These crystals are formed via the seeded growth method from aqueous surfactant solution. When these microcrystals are exposed to visible light while suspended in an aqueous medium, they undergo a process in which the tips of these microcrystals temporarily become liquid and move inward towards the center. This transformation is initiated by the photoisomerization of trans-ATF to cis-ATF when absorbing visible light. After this phase, the melted crystals quickly return to their solid state in less than a minute while maintaining a balance between the two different photoisomers of the ATF molecule. In the presence of suspended silica microspheres, the star-shaped trans-ATF microcrystals undergo a similar melting process induced by visible light. During this process, the melted branches capture and pull these suspended silica microspheres towards the center of the molten crystal structure. This leads to the silica microspheres becoming enclosed within the molten crystal, which then solidifies again