Photoresponsive supramolecular copolymers from diarylethene–perylene bisimide hydrogen bonded complexes

Substituent alkyl-chain-dependent supramolecular chirality, tunable chiroptical property, and dye adsorption in azobenzene-glutamide-amphiphile based hydrogel

Controlling the supramolecular chirality of a self-assembly system by molecular structure design and external stimuli in aqueous solution is significant but challenging. Here, we design and synthesize several glutamide-azobenzene-based amphiphiles with different length alkyl chains. The amphiphiles can form self-assemblies in aqueous solution and show CD signals. As the number of the alkyl chain of amphiphiles increases, the CD signals of the assemblies can be enhanced. However, the long alkyl chains conversely restrict the isomerization of the azobenzene and the corresponding chiroptical property. Moreover, the alkyl length can determine the nanostructure of the assemblies and exert critical influence on the dye adsorption efficiency. This work exhibits some insights into the tunable chiroptical property of the self-assembly by delicate molecular design and external stimuli, and emphasizes the molecular structure can determine the corresponding application.

Diarylethene-Powered Light-Induced Folding of Supramolecular Polymers

Helical folding of randomly coiled linear polymers is an essential organization process not only for biological polypeptides but also for synthetic functional polymers. Realization of this dynamic process in supramolecular polymers (SPs) is, however, a formidable challenge because of their inherent lability of main chains upon changing an external environment that can drive the folding process (e.g., solvent, concentration, and temperature). We herein report a photoinduced reversible folding/unfolding of rosette-based SPs driven by photoisomerization of a diarylethene (DAE). Temperature-controlled supramolecular polymerization of a barbiturate-functionalized DAE (open isomer) in nonpolar solvent results in the formation of intrinsically curved, but randomly coiled, SPs due to the presence of defects. Irradiation of the randomly coiled SPs with UV light causes efficient ring-closure reaction of the DAE moieties, which induces helical folding of the randomly coiled structures into helicoidal ones, as evidenced by atomic force microscopy and small-angle X-ray scattering. The helical folding is driven by internal structure ordering of the SP fiber that repairs the defects and interloop interaction occurring only for the resulting helicoidal structure. In contrast, direct supramolecular polymerization of the ring-closed DAE monomers by temperature control affords linearly extended ribbon-like SPs lacking intrinsic curvature that are thermodynamically less stable compared to the helicoidal SPs. The finding represents an important concept applicable to other SP systems; that is, postpolymerization (photo)reaction of preorganized kinetic structures can lead to more thermodynamically stable structures that are inaccessible directly through temperature-controlled protocols.

Future of Supramolecular Copolymers Unveiled by Reflecting on Covalent Copolymerization

Supramolecular copolymers are an emerging class of materials, and in the last years their potential has been demonstrated on a broad scale. Implementing noncovalent polymers with multiple components can bring together useful features such as dynamicity and new functionalities. However, mastering and tuning the microstructure of these systems is still an open challenge. In this Perspective, we aim to trace the general principles of supramolecular copolymerization by analyzing them through the lens of the well-established field of covalent copolymerization. Our goal is to delineate guidelines to classify and analyze supramolecular copolymers in order to create a fruitful platform to design and investigate new multicomponent systems.