Mechanical Motion and Modulation of Thermal‐Actuation Properties in a Robust Organic Molecular Crystal Actuator

Abstract Dynamic molecular crystals are thought to be an emerging functional material with enormous tunability in physicochemical properties. Here, a smart crystal, 6‐Chloronicotinic acid (6‐CNA), is reported, responding to heat stimulus by bending, splitting‐to‐self‐healing, and jumping, induced thermally by a reversible single‐crystal‐to‐single‐crystal phase transition. This phase transition proceeds by a well‐organized migration of the habit plane, which is reproducible after more than twenty phase transition cycles. The temperature function introduced externally can realize a reversible migration of the habit plane and also act as a jump switch. A comprehensive analysis of the microscopic observations demonstrates that the heterogeneity of phase transition and the homogeneity of self‐driven orientations account for the splitting‐to‐self‐healing. Utilization of the reversible phase transition of 6‐CNA single crystal can generate a pushing force that is > 10⁴ times the gravitational force of the crystal, thus making 6‐CNA an actuator to drive the reversible movement of a glass plate. Both forms of these crystal materials are mechanically compliant in two dimensions and can be twisted in terms of requirement. This excellent actuation performance, reversibility of the phase transition, and soft nature make it a prospective candidate for robust single‐crystal actuators.