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 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. [Display omitted] •A thermomechanically responsive organic single crystal is created•The process of crystal shape deformation can be precisely controlled•Dynamic regulation of weak intermolecular interactions plays a key role in deformation•Significant thermal expansion is the result of molecular collective reorientation Here, Shi et al. demonstrate controllable shape deformation of an organic crystal by virtue of its giant anisotropic thermal expansion. The fluorenone derivative crystal’s molecular configuration exhibits changes with temperature, facilitating continuous shape deformation and enabling practical applications such as precisely controlled microswitching in electric circuits.