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

Responsiveness to external stimuli not only widely exists in biological systems, but also is identified as the key to constructing smart materials. Photochemical-driven rotary molecular motors are a family of synthetic small molecules that show unidirectional rotation at the nanoscale upon light irradiation. Being able to control motion at the molecular and nanoscale brings up the fundamental question of how to make the next leap forward to build dynamic molecular systems and responsive materials. The synthesis and fundamental properties of these discrete molecular motors have been well investigated in the solution phase. However, the control of dynamic function at the scale of macroscopic materials is still in its infancy. Supramolecular self-assembly can provide a solution to realize responsive systems and soft actuators. Based on the spectacular developments in supramolecular chemistry, a series of molecular toolboxes are exploited that proved to be highly versatile and reliable in elaborating well-organized assemblies from discrete molecular building blocks. This Review highlights the recent progress of responsive macroscopic materials based on supramolecular assemblies of molecular motors. Molecular design strategies are systematically discussed. In particular, several supramolecular approaches are highlighted to deliver and amplify the responsive behavior of molecular motors across length scales to the macroscopic level. Finally, critical challenges and unexplored opportunities of supramolecular motorized materials are proposed, outlining a blueprint of future research directions and promising applications.