Stimuli-responsive supramolecular materials are of paramount importance for a broad range of applications. It is essential to impart versatility, sustainability, and scalability into these materials. Herein the authors report the design and synthesis of a new class of thermochromic supramolecular materials, which can easily be processed from water via a reversible sol-gel transition. The supramolecular materials are composed of a bis-bipyridinium acceptor, a π-electron-rich naphthalene derivative donor, and halogen counterions. Long helical nanofibers can be assembled in water, gelating at room temperature. Inked designs, thin films, and aerogels are solution-processed to exhibit thermochromic behavior based on competing π → π* and n → π* charge transfer interactions. By using different π-electron rich donors, and counterions, the authors demonstrate that both the color observed at room temperature and at high temperatures can be tailored. The results open up the door to develop novel amphiphile-based thermochromes with water processability and a large tunable color palette.

The bulk solution properties of amphiphilic formulations are derivative of their self-assembly into higher ordered supramolecular assemblies known as micelles and of their ordering at the air-water interface. Exerting control over the surface-active properties of amphiphiles and their propensity to aggregate in pure water is most often fine-tuned by covalent modification of their molecular structure. Nevertheless structural constraints which limit the performance of amphiphiles do emerge when trying to develop more sophisticated systems which undergo for example, shape-defined controlled assembly and/or respond to external stimuli. In this regard, the template-modulated assembly of the so-called "supramolecular amphiphiles" continues to make progress ordering molecules that otherwise have very little to no driving force to aggregate in a prescribed manner in aqueous solutions. Herein we describe the template-modulated micellization and ordering at the air-water interface of bipyridinium-based supramolecular amphiphiles triggered by host-guest interactions with high specificity for the neurotransmitter melatonin over its biosynthetic synthon l-tryptophan and the thermodynamic parameters governing the template-modulated micellization process. When bound to the bipyridinium units of micellized surfactant molecules, melatonin effectively serves as "molecular glue" capable of lowering the CMC by 52% as compared to untemplated solutions. Analysis of this system suggests that a hallmark of donor-acceptor template-modulated micellization in water is a strong positively correlated temperature dependence of the CMC and the absence of a U-shaped CMC-temperature curve. Our findings make a case for the incorporation of l-tryptophan-based metabolites and their classical synthetic pharmaceutical bioisosteres as potential targets/components of donor-acceptor CT-based supramolecular amphiphile systems/materials operating in water.

Reversible template-directed micellar-size and shape modulation by virtue of host-guest reversible docking of molecular templates at the micellar-solvent interface was achieved in water. By combining a π-electron deficient bipyridinium-based gemini amphiphile which is capable of binding and aligning with a π-electron rich tri(ethylene glycol)-disubstituted 1,5-diaminonaphthalene, a switchable detergent system which operates through the pH-responsive formation of bisammonium dications was realised. The binding of the 1,5-diaminonaphthalene guest to the bipyridinium-based micellar aggregate superstructure can be actuated by the addition of acid and base. Upon the addition of acid, protonation of the guest forming the dication deactivates molecular recognition with the charged head groups of the micellar aggregate by Coulombic repulsion. This process is completely reversible upon the addition of base, whereby the guest reintercalates into the superstructure -again forming donor-acceptor π-π stacks at the micellar-solvent interface amongst contiguous surfactant head groups. Synchrotron small angle X-ray scattering and dynamic laser light scattering confirm that this form of reversible directionally-templated micellisation results in an oblate spheroid-to-lamellar micelle morphological transition with a stabilising net decrease in the free energy of micellisation of 1.4 kcal mol(-1) per hydrophobic tail.

In elementary neural circuits, changes in excitability can have a strong impact in the expression of a given behavior. One example is provided by B51, a neuron with decision-making properties in the feeding neural circuit of the mollusk Aplysia. The excitability of B51 is bidirectionally modulated by external and internal stimuli in a manner that is consistent with the corresponding induced changes in feeding behavior. For example, in operant reward learning, which up-regulates feeding, B51 excitability is increased via a cAMP-dependent mechanism. Conversely, following training protocols with aversive stimuli, which down-regulate feeding, B51 excitability is decreased. In this study, we tested the hypothesis that B51 decreased excitability may be mediated by another cyclic nucleotide, cGMP. Our results revealed that iontophoretic injection of cGMP was capable of inducing both short-term (45 min) and long-term (24 h) reduction of B51 excitability. We next investigated which biochemical trigger could increase cGMP cytosolic levels. The neurotransmitter nitric oxide was found to decrease B51 excitability through the activation of the soluble guanylyl cyclase. These findings indicate that a cGMP-dependent pathway modulates B51 excitability in a manner opposite of cAMP, indicating that distinct cyclic-nucleotide pathways bidirectionally regulate the excitability of a decision-making neuron.

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On page 8604, M. A. Olson, L. Fang, and co‐workers demonstrate water‐processible thermochromic supramolecular helical fibers composed of a bis‐bipyridinium acceptor, a p‐electron rich naphthalene derivative donor, and halogen counterions. Inked designs, thin films, and aerogels fabricated from these composites exhibit reversible thermochromic behavior. The thermochromism results from competing π → π* and n → π* charge transfer interactions which are mediated by coordinating water molecules.