Trans-scale crystal dynamics for controlling kinetic responses in organic molecular systems.

The origin and control of material dynamics are fundamental to understanding functional systems from molecular assemblies to engineered devices. The ability to actively control and directly visualize rapid chemical and structural changes in a single crystal remains a major challenge in solid-state chemistry, limiting our understanding of dynamic functions in molecular materials. Here, we report an anthracene-based molecular crystal platform that enables dual physical control of solid-state [4 + 4] photocycloaddition through temperature and light. Chemically engineered 1,8-bis(pentafluorophenyl)anthracene single crystals construct photoactive face-to-face π-stacks, allowing the reaction to be induced by visible-light irradiation. The crystals exhibit thermally switchable on/off reaction states controlled by the accumulation of lattice strain accelerated by heating. Furthermore, we observe the reaction and dynamics under various light sources, including UV, white LED, laser, and sunlight, demonstrating dual controllability by heat and light. Importantly, weak light irradiation with an LED enables direct observation of intermediate states in the single crystal, revealing a correlation between lattice strain and photoconversion rate. On these bases, we identify that the reaction kinetics depend on the light propagation direction and the relative orientation of the molecular transition dipole moment, providing a new parameter for directional photodynamic control. This trans-scale approach, integrating chemical molecular packing design, photo-thermal science, and anisotropic parameters, establishes a general strategy for tunable and observable crystal dynamics.