Bottom-Up: Can Supramolecular Tools Deliver Responsiveness from Molecular Motors to Macroscopic Materials?

Summary Motion is omnipresent, as is obvious from the artificial machines in the macro-world and the biomolecular motors in living systems, controlling dynamic behavior along many length scales. With the emergence of molecular machines in the past decades, a major step has been made toward responsive materials and dynamic molecular systems. Photochemical rotary molecular motors hold a unique position, as embedding nanoscale motors in macroscopic materials enables light-driven responsive and adaptive properties. Although the synthesis and engineering of discrete molecular motors in the solution phase are well understood, the design and construction of motorized smart materials that operate at the supramolecular and macroscopic levels provide several fundamental challenges. This Review highlights emerging methodologies that take advantage of the supramolecular toolbox for the bottom-up assembly of responsive materials. Illustrative examples include muscle-like actuators, motor-based metal-organic frameworks, and motorized liquid crystal films and droplets. Emphasis is on how the light-responsive behavior and motion of rotary molecular motors can be communicated, delivered, and amplified to result in a specific dynamic output ranging from the nanoscale and molecular level all the way to the macroscopic scale and materials level. Furthermore, general guidelines for the supramolecular amplification of molecular motion and challenges and perspectives for the development of future motorized smart materials are presented.