Multi-stimuli Responsive System Research Articles

Redox-Driven In Situ Helix Reversal of Graphene-Based Hydrogels.

Controlling the handedness of dynamic helical nanostructures of supramolecular assemblies by external stimuli is of great fundamental significance with appealing morphology-dependent applications. Significantly, access to in situ chirality transformation of dynamic multistimuli-responsive systems can provide channels for real-time monitoring of the transfer processes in biological systems. However, efforts to achieve helix inversion in an all-gel-state and to comprehend the phenomena at a molecular scale are scarce. Herein, we introduce an example of supramolecular hydrogel in which graphene oxide (GO) incorporation leads to opposite helicity of the l-phenylalanine derivative (LPFEG) upon UV irradiation. The gelator modulates different degrees of packing that are responsible for the initial construction of right-handed nanofibers in GO surfaces and for the change in helix to preferred left-handedness in RGO surfaces caused by GO reduction. Specifically, LPFEG shows a mixture of right- and left-handed nanofibers with an appropriate exposure to UV light. A thermal-reversible transformation of chirality is also discovered in the supramolecular assemblies, allowing a dynamic and invertible flip of helicity upon heating and cooling. The morphology transformation makes the hybrid an ideal candidate for application in a precisely controlled drug delivery process. It can unexpectedly serve as a photosensitizer and a carrier for enantioselective absorption of specific chiral drugs enantiomer (l-dopa and S-naproxen sodium) and also exhibit on-demand drug release due to the helix reversal induced by light irradiation. Our results illustrate how the surface reactivity can direct the helical organization of adsorbed fibers, which in turn provide control over enantioselective absorption of chiral drug enantiomers, further giving rise to on-demand drug release due to handedness inversion upon UV irradiation.

Dynamic multistimuli-responsive reversible chiral transformation in supramolecular helices

The design of new chiral chromophores that allow tunable assembly of higher order helical structures by using natural stimuli offers promising avenue in understanding various biological processes. In particular, access to dynamic multistimuli-responsive systems can provide real-time monitoring of chiral transformation in chemical and biological systems. We report on the synthesis of naphthalenediimide appended L-glutamate (NDI-L-Glu) that self-assembles into chiral supramolecular structures under physiological conditions. Specifically, NDI-L-Glu shows a mixture of left- and right-handed helices under physiological conditions, and any deviation from the ambient biochemical environment has a remarkable influence on the chirality of these structures. For instance, acidic environments shift the helicity to left-handedness while the alkaline conditions reversed the helical structures to right-handedness, thereby mimicking the molecular virulence mechanism of tobacco mosaic virus (TMV). The chirality of these supramolecular assemblies can also be controllably tuned by using temperature as an external stimulus, allowing reversible flip of helicity.

Smart foams based on dual stimuli-responsive surfactant

Smart foams were fabricated by using a novel switchable surfactant, AZO-B4, which contains tertiary amine and azobenzene groups corresponding to CO2/N2 and photo stimuli. The foamability and foam stability of AZO-B4 is similar as cetyltrimethylammonium bromide (CTAB). On the one hand, the foam is reversible response to CO2/N2. On the other hand, the foam can be reversible triggered by UV irradiation. All the foaming/defoaming can be performed at room temperature. The multi-stimuli responsive systems can fine wide application in industries where stabilization and destabilization of foams are both desired.

Hierarchical Assembly of Amphiphilic POSS-Cyclodextrin Molecules and Azobenzene End-Capped Polymers

Stimuli-responsive polymers have been widely studied because of their potential use in nanocarriers and nanocontainers. In this study, a smart multistimuli responsive system was prepared through a light controlled supramolecular assembly. Mono cyclodextrin substituted isobutyl polyhedral oligomeric silsesquioxane (mCPOSS), an amphiphilic molecule, was synthesized by copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC), while azobenzene end-capped poly(ethylene glycol)-b-poly(2-(dimethylamino)ethyl methacrylate) copolymer (PEG-b-PDMAEMA-azo, PPA), a biocompatible pH/temperature-responsive macromolecule, was synthesized by atom transfer radical polymerization and CuAAC. The self-assembly process of PPA and mCPOSS in aqueous solution was as followed: first, mCPOSS self-assembled into a nanosphere in aqueous solution because of its amphipathic property; then, the trans-azo end groups of the PPA interacted with the cyclodextrin cavities on the nanosphere, and complex micelles were formed by the supramolecula...

Multi-stimuli responsive foams combining particles and self-assembling fatty acids

Foams that respond to external stimuli are a new type of highly functional soft matter and an emerging research subject in the field of materials and colloid science. Herein, we report a new way to control foam stability using light irradiation. This unconventional approach involves a combination of the thermal response of a fatty acid and the ability of carbon black to convert light stimulus to heat. This simple system features both high foamability and high foam stability, but can easily be destroyed by light. Upon exposure to UV or solar illumination, the carbon black particles absorb light causing an increase in temperature inside the foam lamella. This results in a transition of the fatty acid assemblies from tubes, which stabilize the foam films, to micelles, leading to rapid foam destabilization. The foam destabilization rate under UV irradiation was correlated to foam liquid fraction, fatty acid concentration, as well as carbon black concentration. Our approach for the formulation of photo-thermo-responsive foams could be easily generalized and extended to magnetic particles, giving rise to the first foams exhibiting thermo-photo-magneto-tuneable stability. Such multi-stimuli responsive systems can find applications in diverse industries requiring highly stable systems which can be destroyed on-demand.

Multistimuli Two-Color Luminescence Switching via Different Slip-Stacking of Highly Fluorescent Molecular Sheets

Color tuning and switching of the solid-state luminescence of organic materials are attractive subjects for both the fundamental research and practical applications such as optical recording. We report herein cyanostilbene-based highly luminescent molecular sheets which exhibit two-color fluorescence switching in response to pressure, temperature, and solvent vapor. The origin for the multistimuli luminescence switching is the two-directional shear-sliding capability of molecular sheets, which are formed via intermolecular multiple C-H···N and C-H···O hydrogen bonds. The resulting two distinctive crystal phases are promoted by different modes of local dipole coupling, which cause a substantial alternation of π-π overlap. These changes can be directly correlated with the subsequent intermolecular excitonic and excimeric coupling in both phases, as demonstrated by an in-depth theory-assisted spectroscopic and structural study. Finally, we have prepared a first device demonstrator for rewritable fluorescent optical recording media which showed multistimuli luminescence tuning with fast response. Our multistimuli responsive system is unique in terms of the slip-stacking of molecular sheets and thus provides a novel concept of rewritable fluorescent optical recording media.