Controllable shape deformation of an organic single crystal actuated by anisotropic thermal expansion

Organic crystals demonstrating large thermal expansion effects are rarely reported. In particular, it is a challenge to effectively translate the expansion or contraction of crystal lattices to macroscopic crys-tal shape deformations, which are useful for the construction of high-precision microscale actuators and soft robotics. Here, we report a dynamic organic crystal based on a Ts-extended fluorenone derivative, 4-DTpFO, which, upon thermal stimulation, exhibits anisotropic lattice expansions along with a fully reversible crystal shape deformation. A molecular configuration change results in expansion with positive and negative thermal expansion coeffi-cients of 410 x 10-6 K-1 and -403 x 10-6 K-1, respectively, in the temperature range of 350-440 K, before a second-order phase transition occurs. The applicability is demonstrated in a thermal microswitch. Such a significant but finely controllable thermome-chanical change in an organic crystal promises advanced applica-tions in diverse fields, including intelligent materials and ultrasensi-tive devices.