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.

Automated summary

We report a dynamic organic crystal based on a Ts-extended fluorenone derivative, which exhibits anisotropic lattice expansions and reversible crystal shape deformations upon thermal stimulation. The significant and finely controllable thermomechanical change in this organic crystal promises advanced applications in diverse fields such as intelligent materials and ultrasensitive devices.