Finally, we discuss the mechanism behind the enhanced force generation. The superior performance of compound 3 can be attributed to its structural features: the large dihedral angle (51.58°) between the salicyl and phenyl planes enables efficient photoisomerization, while the nitro group enhances photoresponsivity. The molecular layers stacked along the thickness direction facilitate anisotropic thermal expansion . When exposed to light, compound 3 exhibits both enol-keto photoisomerization and thermal effects. In thin crystals, photoisomerization causes bending away from the light source, while thermal expansion dominates in thick crystals . The maximum force generation observed during top illumination suggests significant thermal expansion in the thickness direction. The crystal's negative thermal expansion coefficient along the length direction near room temperature likely contributes to the overall mechanical response. The force generation increased with crystal size in regions of sufficient light intensity (Supplementary Figure ).