Self‐Assembly of Photoresponsive Molecular Amphiphiles in Aqueous Media

Abstract

Amphiphilic molecules, comprising hydrophobic and hydrophilic moieties and the intrinsic propensity to self‐assemble in aqueous environment, sustain a fascinating spectrum of structures and functions ranging from biological membranes to ordinary soap. Facing the challenge to design responsive, adaptive, and out‐of‐equilibrium systems in water, the incorporation of photoresponsive motifs in amphiphilic molecular structures offers ample opportunity to design supramolecular systems that enables functional responses in water in a non‐invasive way using light. Here, we discuss the design of photoresponsive molecular amphiphiles, their self‐assembled structures in aqueous media and at air–water interfaces, and various approaches to arrive at adaptive and dynamic functions in isotropic and anisotropic systems, including motion at the air–water interface, foam formation, reversible nanoscale assembly, and artificial muscle function. Controlling the delicate interplay of structural design, self‐assembling conditions and external stimuli, these responsive amphiphiles open several avenues towards application such as soft adaptive materials, controlled delivery or soft actuators, bridging a gap between artificial and natural dynamic systems.

Molecular photoswitches in aqueous environments

“…3,[12][13][14][15] While photocages are photolabile protecting groups that are cleaved upon irradiation and hence, can only be activated once, 13,16,17 photoswitches can be reversibly interconverted between different (functional) isomers. 3,18 This reversible nature makes them interesting candidates for a wide range of applications, including those that take place in water, where they act as photoresponsive amphiphiles, [19][20][21][22][23][24][25][26][27] hydrogel constituents, 28,29 probes for chemical biology, [30][31][32] or bioactive agents in photopharmacology. 6,7,30,33 Molecular photoswitches are typically organic molecules bearing extended aromatic systems to make them responsive to (visible) light.…”

“…Naturally, the applications and examples discussed in this review are coming from these fields. Consequently, photoswitches which are designed to be intentionally amphiphilic or lipophilic to form (supramolecular) (self-) assemblies, nano-, and microstructures in aqueous environment, 21,[42][43][44][45] or (hydro)gels, [46][47][48][49][50][51] do not face the same obstacles as the ones intended to be fully water-soluble and hence, lie outside the scope of this review and we refer the reader to our recent overview. 21 parameters that affect it and are used to predict it, as well as methods to determine the aqueous solubility of a compound of interest.…”

Self‐Sustained Marangoni Flows Driven by Chemical Reactions**

“…Light has also been investigated as an external stimulus to remotely control these interfacial flows. While it has been used directly to locally heat an interface, [32] recent works have shown its potential when combined with photo-switchable surfactants [33][34][35][36][37] for the manipulation of μm-range objects. In that case, light intensity and surfactant concentration were used to regulate the flow velocity.…”

Self-sustained Marangoni Flows Driven by Chemical Reactions

“…Light has also been investigated as an external stimulus to remotely control these interfacial flows. While it has been used directly to locally heat an interface 31 , recent works have shown its potential when combined with photo-switchable surfactants 32,33 for the manipulation of μmrange objects. In that case, light intensity and surfactant concentration were used to regulate the flow velocity [34][35][36] .…”