Organic crystal-based flexible smart materials

Although the famous brittle characteristics of molecular crystals are unfavorable when they are used as flexible smart materials (FSMs), an increasing number of organic crystal-based FSMs have been reported recently. This breaks the perception of their stiff and brittle properties and promises a bright future for basic research and practical applications. Crystalline smart materials present considerable advantages over polymer materials under certain circumstances, rendering them potential candidates for certain applications, such as rapidly responsive actuators, ON/OFF switching, and microrobots. In this review, we summarize the recent developments in the field of organic crystal-based FSMs, including the derivatives of azobenzene, diarylethene, anthracene, and olefin. These organic crystal-based FSMs can bend, curl, twist, deform, or respond otherwise to external stimuli, such as heat or light. The detailed mechanisms of their smart behaviors are discussed with their potential applications in exciting intelligent fields. We believe this review could provide guidelines toward future fabrication and developments for novel organic crystal-based FSMs and their advanced smart applications.