Photoresponsive Supramolecular Polymers: From Light-Controlled Small Molecules to Smart Materials.

Photoresponsive supramolecular polymers are well-organized assemblies based on highly oriented and reversible noncovalent interactions containing photosensitive molecules as (co-)monomers. They have attracted increasing interest in smart materials and dynamic systems with precisely controllable functions, such as light-driven soft actuators, photoresponsive fluorescent anticounterfeiting and light-triggered electronic devices. The present review discusses light-activated molecules used in photoresponsive supramolecular polymers with their main photo-induced changes, e.g., geometry, dipole moment, and chirality. Based on these distinct changes, supramolecular polymers formed by light-activated molecules exhibit photoresponsive disassembly and reassembly. As a consequence, photo-induced supramolecular polymerization, "depolymerization," and regulation of the lengths and topologies are observed. Moreover, the light-controlled functions of supramolecular polymers, such as actuation, emission, and chirality transfer along length scales, are highlighted. Furthermore, a perspective on challenges and future opportunities is presented. Besides the challenge of moving from harmful UV light to visible/near IR light avoiding fatigue, and enabling biomedical applications, future opportunities include light-controlled supramolecular actuators with helical motion, light-modulated information transmission, optically recyclable materials, and multi-stimuli-responsive supramolecular systems.