From Photoinduced Supramolecular Polymerization to Responsive Organogels

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.