Non‐uniform Photoinduced Unfolding of Supramolecular Polymers Leading to Topological Block Nanofibers

Abstract

Synthesis of one‐dimensional nanofibers with distinct topological (higher‐order structural) domains in the same main chain is one of the challenging topics in modern supramolecular polymer chemistry. Non‐uniform structural transformation of supramolecular polymer chains by external stimuli may enable preparation of such nanofibers. To demonstrate feasibility of this post‐polymerization strategy, we prepared a photoresponsive helically folded supramolecular polymers from a barbiturate monomer containing an azobenzene‐embedded rigid π‐conjugated scaffold. In contrast to previous helically folded supramolecular polymers composed of a more flexible azobenzene monomer, UV‐light induced unfolding of the newly prepared helically folded supramolecular polymers occurred nonuniformly, affording topological block copolymers consisting of folded and unfolded domains. The formation of such blocky copolymers indicates that the photoinduced unfolding of the helically folded structures initiates from relatively flexible parts such as termini or defects. Spontaneous refolding of the unfolded domains was observed after visible‐light irradiation followed by aging to restore fully folded structures.

Nanoengineering of Curved Supramolecular Polymers: Toward Single-Chain Mesoscale Materials

“…As an improved photoresponsive monomer design to afford SP helicoid , we have synthesized 11 in which the azobenzene unit was embedded in a relatively rigid π-conjugated scaffold (Figure 6a). 45 This rigid monomer indeed afforded SP helicoid in pure MCH by 1 K min −1 cooling (Figure 6b). In addition, SP helicoid of 11 was found to be robust compared to that of 7 as it exhibited resistance to photoinduced unfolding at ambient temperature.…”

“…As an improved photoresponsive monomer design to afford SP helicoid , we have synthesized 11 in which the azobenzene unit was embedded in a relatively rigid π-conjugated scaffold (Figure a) . This rigid monomer indeed afforded SP helicoid in pure MCH by 1 K min –1 cooling (Figure b).…”

“…AFM images showing (b and c) unfolding of SP helicoid of 11 into SP random upon exposure to UV irradiation, (e and f) phototriggered ring-opening of SP toroid of 7 leading to extended SPs through reorganization, (h and i) vis- and UV-light-induced unfolding–refolding between SP helicoid and SP random of 9 , and (j) transformation of SP helicoid of 9 close into SP ribbon upon heating followed by cooling. Reproduced with permission from refs , , and . Copyright 2021 and 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim and 2021 American Chemical Society.…”

Acylhydrazone-based supramolecular assemblies undergoing a converse sol-to-gel transition on trans → cis photoisomerization

“…Photoisomerization is a process that reversibly converts one isomer into another with a clean and remote light source, which has been applied in a broad range of systems, including photoactuators, sustained drug release systems, information storage, photochromic materials, and photogated devices. [1][2][3][4][5][6][7][8][9] Photoisomeric supramolecular assemblies, as an elegant combination of reversible photoisomers and dynamic noncovalent interactions, possess various intriguing properties, such as degradability, shape memory, and phase transition. [10][11][12][13][14] Generally, photoisomerization from a relatively planar isomer to a distorted one gives rise to the disassembly of supramolecular systems, which is ascribed to the steric hindrance of the nonplanar isomers failing to orderly stack with each other (Fig.…”

Three-level hierarchical self-assembly of azobenzene conjugated phenylalanines into superhelical nanostructures with light-switchable helicity

“…Among these, light has attracted particular attention owing to the advantages of its convenient, noninvasive, instantaneous and precise control. 14 a , b Light-responsive moieties, including spiropyran, 15 azobenzene, 16 diarylethene, 17 and stilbene, 18 have been utilized to achieve the switching of self-assembled structures. However, in many cases, although changes in molecular conformation can result in changes in chiral signals, such as circular dichroism (CD), it is difficult to cause an obvious change in morphologies.…”