From Photoinduced Supramolecular Polymerization to Responsive Organogels
2021
Xu, Fan | Pfeifer, Lukas | Crespi, Stefano | Leung, Franco King-Chi | Stuart, Marc C. A. | Wezenberg, Sander J. | Feringa, Ben L.
Controlling supramolecular polymerization by external stimuli holds great potential toward the development of responsive soft materials and manipulating self-assembly at the nanoscale. Photochemical switching offers the prospect of regulating the structure and properties of systems in a noninvasive and reversible manner with spatial and temporal control. In addition, this approach will enhance our understanding of supramolecular polymerization mechanisms; however, the control of molecular assembly by light remains challenging. Here we present photoresponsive stiff-stilbene-based bis-urea monomers whose trans isomers readily form supramolecular polymers in a wide range of organic solvents, enabling fast light-triggered depolymerization–polymerization and reversible gel formation. Due to the stability of the cis isomers and the high photostationary states (PSS) of the cis–trans isomerization, precise control over supramolecular polymerization and in situ gelation could be achieved with short response times. A detailed study on the temperature-dependent and photoinduced supramolecular polymerization in organic solvents revealed a kinetically controlled nucleation–elongation mechanism. By application of a Volta phase plate to enhance the phase-contrast method in cryo-EM, unprecedented for nonaqueous solutions, uniform nanofibers were observed in organic solvents.
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