From Photoinduced Supramolecular Polymerization to Responsive Organogels

Abstract

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 <i>trans</i> 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 <i>cis</i> isomers and the high photostationary states (PSS) of the <i>cis</i>-<i>trans</i> isomerization, precise control over supramolecular polymerization and <i>in situ</i> 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.