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.

Mechanistic Insight into Supramolecular Polymerization in Water Tunable by Molecular Geometry

“…3,[8][9][10][11] The mechanism of solute-solute interactions in these assemblies is well-established, 1,2,4 whereas the solute-solvent interplay attracted the interest of supramolecular chemists more recently. [12][13][14] Water is a unique medium for self-assembly in Nature, and many exquisite assemblies, [15][16][17][18][19][20][21][22][23][24] low-molecular-weight gels, [25][26][27][28][29] and supramolecular polymers [30][31][32][33][34][35][36] have been developed in aqueous media focusing on various applications, such as biomolecular materials 37,38 and soft actuators. [39][40][41] However, detailed insight into supramolecular polymerization in water is far from being as well understood as it is in organic solvents.…”

Spiropyran/Merocyanine Amphiphile in Various Solvents: A Joint Experimental–Theoretical Approach to Photophysical Properties and Self-Assembly

“…Light as a contactless stimulus offers multiple advantages such as tunable optical wavelength and intensities as well as high temporal and spatial control. Several classes of photoresponsive amphiphilic molecules are distinguished: intrinsic light-switches, photoresponsive molecular amphiphiles (a photoresponsive unit is chemically included into a classical surfactant “head-tail” structure), and photoresponsive supramolecular amphiphiles (a photoresponsive component is introduced via noncovalent interactions) [ 1 ]. The self-organized ensembles of photoresponsive amphiphiles manipulated by light fundamentally enable new pathways towards aqueous bio-compatible materials, that can change certain properties in a predictable manner or can provide best performance when operation circumstances change [ 2 ].…”

Structure–Performance Relationships for Tail Substituted Zwitterionic Betaine–Azobenzene Surfactants

“…Azobenzene-containing surfactants (azo-surfactants) are usually used as an additive in multicomponent formulations to elicit a photoresponse from systems as a whole. , The use of azo-surfactants as the sole surfactant in micellar self-assemblies is less common, and studies on their structure–behavior relationships in this area are less comprehensive, although some discussion of the electronic properties of such materials and how this relates to their use in supramolecular (assembled) systems has been recently made in the literature. , Rational design of new azo-surfactants requires an understanding of the role that incorporated structural motifs will play in the properties of both trans and cis isomers. Previous studies utilizing neutral azo-surfactants have shown that even small changes in the size and polarity of the head group or linker (Figure ) can facilitate large changes in the solubility and aggregate morphology of azo-surfactants. ,, …”

“…23,27 The use of azo-surfactants as the sole surfactant in micellar self- assemblies is less common, and studies on their structure− behavior relationships in this area are less comprehensive, although some discussion of the electronic properties of such materials and how this relates to their use in supramolecular (assembled) systems has been recently made in the literature. 28,29 Rational design of new azo-surfactants requires an understanding of the role that incorporated structural motifs will play in the properties of both trans and cis isomers.…”