Microscopic visualization and mechanism investigation of the crystal jumping behavior of a cyclic chalcone derivative

Dynamic molecular crystals have attracted considerable attention as smart materials for promising applications in high-technology areas. The dynamic behaviors of bending, twisting, and rotation in response to external stimuli have been widely investigated, while jumping crystals have rarely been reported. Here, a highly luminescent cyclic chalcone crystal with remarkable photo-induced jumping behavior is designed. The donor-acceptor character, five-membered cyclic structure and steric hindrance of the diphenylamino group synergistically contribute to the formation of tightly connected "molecular pairs" in a crystal, a pre-organized structure for cycloaddition. The crystal structure analyses show that the photo-induced [2+2] cycloaddition reaction leads to large molecular shrinkage and lattice distortion, thus prompting the crystal to jump and crack violently. Notably, the crystal's self-waveguide emission makes visualization of the microscopic dynamic process easy for the first time. Besides, the monomer reactant can recover from the dimer product when melted or dissolved. The special jumping behavior combined with reversible cycloaddition and ring opening reactions endow the crystal with great potential as a multi-responsive smart material.