Bidirectional Photomodulation of Surface Tension in Langmuir Films

Abstract

Switchings ystems operating in ac ooperative manner capable of converting light energy into mechanical motion are of great interest for optical devices,d ata storage, nanoscale energy converters and molecular sensing. Herein, photoswitchable monolayers were formed at the air-water interface from either ap ure bis(thiaxanthylidene)-based photoswitchable amphiphile or from am ixture of the photoswitchable amphiphile with ac onventional lipid dipalmitoylphosphatidylcholine (DPPC). Efficient photoisomerization of the anti-folded to syn-folded geometry of the amphiphiles central core induces changes in the surface pressure in either direction, depending on the initial molecular density.A dditionally,t he switching behavior can be regulated in the presence of DPPC,w hich influences the packing of the molecules,therebycontrolling the transformation upon irradiation. Bis(thiaxanthylidene)-based photoswitchable monolayers provideapromising system to explore cooperativity and amplification of motion.

The Art of Building Small: From Molecular Switches to Motors (Nobel Lecture)

“…[35] Slight structural modification of these photo-responsive amphiphiles resulted in bidirectional optical control of surface tension in Langmuir layers. [36] Taking this design as tep further we have recently used overcrowded alkenes to achieve nanotube to vesicle to vesicle to nanotube transitions illustrating am ore complex adaptive behavior as the system is responding to light and heat in af ully reversible behavior ( Figure 3b). [37] Smallmolecule gelators are another class of fascinating structures which we studied in the context of responsive self-assembly.…”

“…Following this approach, self‐assembled multicomponent nano‐objects, that is, vesicle‐capped nanotubes and vesicles embedded in nanotubes, were obtained and the disassembly of these responsive supramolecular systems can be controlled by with light . Slight structural modification of these photo‐responsive amphiphiles resulted in bidirectional optical control of surface tension in Langmuir layers . Taking this design a step further we have recently used overcrowded alkenes to achieve nanotube to vesicle to vesicle to nanotube transitions illustrating a more complex adaptive behavior as the system is responding to light and heat in a fully reversible behavior (Figure b) .…”

Spiropyran Sulfonates for Photo- and pH-Responsive Air–Water Interfaces and Aqueous Foam

“…Such materials are capable of changing their properties like optical appearance, stability, or their structure on demand to new situations if a feedback mechanism can be established. However, prerequisites for the latter are highly responsive materials − and building blocks − such as fluid interfaces that react to an external stimulus by massive changes in their physicochemical properties. − At a fluid interface, this can be achieved by ad- and desorption of molecules and by charging and discharging of the interface which can largely change electrostatic interactions at the interface as well as by significant molecular structure changes . Such electrostatics are often used to render colloidal systems like foam or nanoparticle dispersions more stable as the long-range electrostatic disjoining forces increase when the interfaces in a colloidal system become highly charged. , In this work, we are focusing on aqueous foams as these are inherently interface-controlled systems with an established hierarchy from the molecular building blocks that are adsorbed at the air–water interface to thin foam films, bubbles, and ensembles of bubbles and finally to the macroscopically visible foam. , The latter inherits the properties of the air–water interface through structure–property relations. , Thus, aqueous foams are an ideal playground to test responsive interface-active moieties that are used to tailor also responsive foam ,,,, as a model system for soft matter materials.…”