Macroscopic motion of supramolecular assemblies actuated by photoisomerization of azobenzene derivatives

Abstract

Submillimetre size self-assemblies composed of oleate and azobenzene derivatives show forceful motions such as screwtype coiling-recoiling motion by photoirradiation.In the past half century, many molecular-level machines which 10 change their molecular structure upon exposure to stimuli have been reported. 1 Nowadays, studies on macroscopic thermal motion of soft matters received attentions from the viewpoint of biomimetics. 2,3 Next key step for soft matters is to create a material whose macroscopic motion is controlled by external 15 stimuli. 4 One of the strategies is to create soft materials consisting of subunits sensitive to external inputs, for instance, the photoinduced bending of polymer films consisted of azobenzene derivatives. 5,6 Another strategy is to create soft materials in which macroscopic motions of molecular assemblies 20 are actuated by small amount of molecular machines. 7 To date, there are few reports describing macroscopic mechanical behaviour based on the latter strategy. 8 Here, we report reversible and spatially controlled macroscopic motion of oleate assembles which have submillimetre length. 25Mixtures of oleic acid (1H) and oleate (1 -) ( Fig. 1) are capable of self-assembly in aqueous solution. The morphology of the mixture depends on pH and ionic strength (I). [9][10][11] In I = 0.1 pH 8-10 aqueous media, oleates form vesicles (Fig. 2a). Between pH 7 and 8, they form several complex aggregates called "blocks" that 30 exhibit an inverted hexagonal phase 12 (Fig. 2b). In the transition region, helical and straight multilayer assemblies are coexisted with vesicles and blocks. 11 It is considered that the shape of assembly depends on the ratio of 1H and 1 -in each assembly. According to the microscopic observations of shape and 35 dynamics described in Ref. 11, the helical assemblies are sufficiently flexible to change their macroscopic helical pitch and curvature, but are also elastic because of the highly-ordered stacking structure of oleate molecules in the assembly. As demonstrated in Fig. 3, the helical assemblies exhibit a highly 40 elastic response to mechanical stress. We assumed that this softness and elasticity of the self-assembly is suitable to the spatially moving material in which motion of molecular machine should be propagated.Azobenzene derivatives 2-5 ( Fig. 1) display reversible 2-5 by addition of 70 mM KH 2 PO 4 -K 2 HPO 4 buffer solution (1.0 mL) and sonication for 20 min. A 125 µL aliquot of each suspension containing one of 2-5 was placed in a sealed microscope slide and incubated for 1 day at 25°C. All 60 azobenzene derivatives dissolved into oleate assemblies. The pH range required for formation of helical assemblies was slightly lowered by the addition of 2-5. 14 Helical assemblies were formed when pH 7.3 buffer solution was used as the dispersing medium (the pH of the dispersion was approximately 7.5); pH 65 values of buffer solution higher than 7.3 resulted in vesicle formation, and pH values lower than 7.3 led to the formation of

Structure and growth behavior of centimeter-sized helical oleate assemblies formed with assistance of medium-length carboxylic acids

“…Their spontaneous winding-rewinding dynamics are probably induced by intrinsic fluctuations of the helical assembly, 20 and their rotation-rerotation motions are actuated by photoisomerization of an azobenzene derivative loaded as a minor component in the helical assembly. 33 Here, we have described the growth dynamics of a centimeter-length helical assembly from a terminal scaffold in the presence of additional carboxylates. To date, only millimeter-and centimeter-length self-assemblies, such as fibers and microtubes composed of amphiphilic molecules, have been reported.…”

“…[27][28][29][30][31][32] Namely, an ONa paste is hydrated by contact with aqueous buffered solution to grow tubular assemblies from the interface between the paste and the aqueous solution. We previously described another method, 20,33 in which ONa is dispersed in an aqueous buffered solution by ultrasonication. Then, the dispersed colloidal oleates gather together to form macroscopic tubular, cylindrical, or helical assemblies, with micelles and vesicles in the bulk solution.…”

“…Assembly shapes included helical assemblies (length = 10-1000 μm), giant vesicles (radius < 100 μm), and block-style aggregates 33 (radius < 10 μm). …”

Stimulus-responsive hydrogels: Theory, modern advances, and applications

“…The azobenzene systems also bring reversibility to their stacking, shifting from trans to cis forms and back in response to 360 and 440 nm light, respectively. The wavelength of light that these systems respond to can be altered by manipulation of the end groups attached to the benzene rings [300]. …”

Dissipative and Autonomous Square‐Wave Self‐Oscillation of a Macroscopic Hybrid Self‐Assembly under Continuous Light Irradiation

“…The assembly flips repeatedly in an autonomous manner under continuous blue-light irradiation, as shown in Figure 1 and Movies S1-S3 in the Supporting Information (SI). Mechanical self-oscillation is established by successively alternating photoisomerization processes and multi-stable phase transitions.Azobenzenes have frequently been employed in the creation of photomechanically working objects [3][4][5] 11] and patterned dynamics. [12,13] Azobenzene is isomerized from the trans to cis form by ultraviolet (UV) irradiation.…”