Thiophene Sulfone Single Crystal as a Reversible Thermoelastic Linear Actuator with an Extended Stroke and Second-Harmonic Generation Switching

Dynamic organic crystals are becoming recognized as some of the fastest materials for converting light or heat to mechanical work. The degree of deformation and the response time of any actuating material are often exclusive of each other; however, both factors influence the material's overall performance limits. Unlike polymers, whose disordered structures are not conducive to rapid energy transfer, cooperative phase transitions in dynamic molecular crystals that are amenable to rapid and concerted martensitic-like structure switching could help circumvent that limitation. Here, we report that single crystals of a dibenzothiophene sulfone derivative exhibit extraordinarily large, rapid, and reversible elongation when they undergo a thermally induced phase transition. The value for the linear stroke of ∼15% along the long crystal axis with retention of macroscopic integrity of this material is remarkable and capitalizes on an anisotropic lattice switching with relative changes of 14.8% and -9.5% along its crystallographic a and c axes, respectively, resulting in a visible macroscopic elongation of the crystal. The transitioning crystals deliver forces ranging from 0.19 to 15 μN and a work density of ∼7 × 10-3 J m-3. The phase transformation is accompanied by a change in symmetry between centrosymmetric and noncentrosymmetric space groups and a significant change in both the fluorescence and the second-order nonlinear optical (NLO) response. The combination of these properties makes this material a favorable choice for low-power, precise, and small-scale NLO actuation applications.