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

Abstract

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 crystal 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 π-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 coefficients of 410 × 10−6 K−1 and −403 × 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 thermomechanical change in an organic crystal promises advanced applications in diverse fields, including intelligent materials and ultrasensitive devices.