Dynamically manipulating the handedness of supramolecular chirality and chiroptical properties is a challenging task, which is important in the fabrication of responsive and smart functional materials. Here we report the dynamic evolution of supramolecular chirality inversion and the inversion of corresponding circularly polarized luminescence via the multiple-constituent coassemblies driven by hydrogen bonds. Cyanostilbene-conjugated amino acids were employed as building units, self-assembling into nanoarchitectures with 21 column chirality. After being incorporated into a binary coassembly with melamine and its derivative, 21 column chirality was transformed into helical chirality with macroscopic nanohelices. Such structural evolution enabled chirality inversion accompanied by inversion of circularly polarized luminescence. Isomerization triggered by photo irradiation appended responsiveness to morphology, supramolecular chirality as well as chiroptical properties, and inversion of circularly polarized luminescence was further achieved specifically. This work illustrating the dynamic chirality evolution and responsiveness provides an alternative perspective for the design and fabrication of smart chiroptical materials.

Dynamic evolution of supramolecular chirality manipulated by H-bonded coassembly and photoisomerism

We synthesize and characterize a triblock polymer with asymmetric tetramethoxyazobenzene (TMAB) and β-cyclodextrin functionalization, taking advantage of the well-characterized azobenzene derivative-cyclodextrin inclusion complex to promote photoresponsive, self-contained folding of the polymer in an aqueous system. We use 1H NMR to show the reversibility of (E)-to-(Z) and (Z)-to-(E) TMAB photoisomerization, and evaluate the thermal stability of (Z)-TMAB and the comparatively rapid acid-catalyzed thermal (Z)-to-(E) isomerization. Important for its potential use as a functional material, we show the photoisomerization cyclability of the polymeric TMAB chromophore and calculate isomerization quantum yields by extinction spectroscopy. To verify self-inclusion of the polymeric TMAB and cyclodextrin, we use two-dimensional 1H NOESY NMR data to show proximity of TMAB and cyclodextrin in the (E)-state only; however, (Z)-TMAB is not locally correlated with cyclodextrin. Finally, the observed decrease in photoisomerization quantum yield for the dual-functionalized polymer compared to the isolated chromophore in an aqueous solution confirms TMAB and β-cyclodextrin not only are in proximity to one another, but also form the inclusion complex.

Dual-Stimuli Responsive Single-Chain Polymer Folding via Intrachain Complexation of Tetramethoxyazobenzene and β-Cyclodextrin.

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Photoswitchable assembly of long-lived azobenzenes in water using visible light.

β-cyclodextrin (βCyD) derivatives equipped with aromatic appendages at the secondary face exhibit tailorable self-assembling capabilities. The aromatic modules can participate in inclusion phenomena and/or aromatic–aromatic interactions. Supramolecular species can thus form that, at their turn, can engage in further co-assembling with third components in a highly regulated manner; the design of nonviral gene delivery systems is an illustrative example. Endowing such systems with stimuli responsiveness while keeping diastereomeric purity and a low synthetic effort is a highly wanted advancement. Here, we show that an azobenzene moiety can be “clicked” to a single secondary O-2 position of βCyD affording 1,2,3-triazole-linked βCyD-azobenzene derivatives that undergo reversible light-controlled self-organization into dimers where the monomer components face their secondary rims. Their photoswitching and supramolecular properties have been thoroughly characterized by UV–vis absorption, induced circular dichroism, nuclear magnetic resonance, and computational techniques. As model processes, the formation of inclusion complexes between a water-soluble triazolylazobenzene derivative and βCyD as well as the assembly of native βCyD/βCyD-azobenzene derivative heterodimers have been investigated in parallel. The stability of the host–guest supramolecules has been challenged against the competitor guest adamantylamine and the decrease of the medium polarity using methanol–water mixtures. The collective data support that the E-configured βCyD-azobenzene derivatives, in aqueous solution, form dimers stabilized by the interplay of aromatic–aromatic and aromatic-βCyD cavity interactions after partial reciprocal inclusion. Photoswitching to the Z-isomer disrupts the dimers into monomeric species, offering opportunity for the spatiotemporal control of the organizational status by light.

https://pubs.acs.org/doi/pdf/10.1021/acs.joc.3c00564

Reversible Light-Induced Dimerization of Secondary Face Azobenzene-Functionalized β-Cyclodextrin Derivatives

Patterns formed under external stresses are often critical for ensuring functionality of soft materials. We focus on dynamic control of pattern formation and restructuring in hydrogels with host-guest interactions. We extend three-dimensional gel Lattice Spring Model to capture the dynamics of photo-responsive hydrogels with pendant azobenzene moieties immersed in the  cyclodextrin (  -CD) solution. While trans -azobenzene moieties are accommodated by the  -CD cavities forming inclusion complexes resulting in hydrogel swelling, an exposure to UV irradiation induces trans -to- cis photoisomerization leading to decomplexation and matrix deswelling. We demonstrate swelling-induced patterns in confined samples upon adding the  -CD solution in the dark. Further, we show that spatiotemporal variations in UV irradiation effectively control patterns formed and hysteresis loops. We introduce soft confinements via illuminating specific regions of unconstrained samples with UV light. Our results indicate that features of patterns and hysteresis in systems’ response to external conditions can be regulated via well-defined illumination patterns. experimental We buckling of thin hydrogel films under rigid confinement upon immersion of the hydrogel with long edges into the  -CD solution. Further, we utilize variations in light irradiation conditions to control pattern formation in thin hydrogel films under rigid and soft confinements and to control hysteresis in hydrogel response to changes in external environments. The soft is introduced via illuminating specific regions of the thin samples with UV light; this patterned illumination introduces localized regions with higher rigidity. While significant progress been made in understanding swelling-induced pattern formation in various hydrogels , herein formation and hysteresis loops are modeled in the hydrogels with host-guest interactions. Our results show that an onset of buckling and specific features of patterns along with in systems’ response to external conditions can be effectively controlled in networks with host-guest interactions via well-defined illumination patterns.

Journal Pre-proof Photocontrol of pattern formation and hysteresis loops in polymer gels with host-guest interactions

Hydrophilic host-guest complexes, consisting of water-soluble azobenzene and α-, β-, or γ-cyclodextrins, have been proposed as a model to study supramolecular photoresponsive systems in aqueous environments through a full spectrometric approach combined with a simulation and data fitting methodology. Various essential and complementary spectroscopic techniques have been used: circular dichroism to determine whether the complex is formed or not, NMR for the stoichiometry elucidation, and UV-visible spectrophotometry to obtain the association equilibrium constant of each complex and the quantum yield for each photochemical process. A step-by-step fitting procedure is presented, which enables the determination of all thermodynamic and photokinetic parameters. A sequential methodology is applied to dissipate all uncertainties on the variability of the results and to develop a relevant and reliable protocol applicable to other types of complexes. The proposed procedure has thus been shown to be very robust and largely applicable to other photoresponsive host-guest systems.

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Jorge Royes

Papers

Quantitative Kinetic Modeling in Photoresponsive Supramolecular Chemistry: The Case of Water-Soluble Azobenzene/Cyclodextrin Complexes