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.
Halogen bonds involving an aromatic moiety as an acceptor, otherwise known as R-X…π interactions, have increasingly been recognized as being important in materials and in protein-ligand complexes. These types of interactions have been the subject of many recent investigations, but little is known about the ways in which the strengths of R-X…π interactions vary as a function of the relative geometries of the interacting pairs. Here we use the accurate CCSD(T) and SAPT2+3δMP2 methods to investigate the potential energy landscapes for systems of HBr, HCCBr, and NCBr complexed with benzene. It is found that only the separation between the complexed molecules have a strong effect on interaction strength while other geometric parameters, such as tilting and shifting R-Br…π donor relative to the benzene plane, affect these interactions only mildly. Importantly, it is found that the C6v (T-shaped) configuration is not the global minimum for any of the dimers investigated.
Rigorous investigations
of the organobase-catalyzed ring-opening
polymerizations (ROPs) of a series of five-membered cyclic carbonate
monomers derived from glucose revealed that competing transcarbonylation
reactions scrambled the regiochemistries of the polycarbonate backbones.
Regioirregular poly(2,3-α-
d
-glucose carbonate) backbone
connectivities were afforded by 1,5,7-triazabicyclo[4.4.0]dec-5-ene
(TBD)-catalyzed ROPs of three monomers having different cyclic acetal
protecting groups through the 4- and 6-positions. Small molecule studies
conducted upon isolated unimers and dimers indicated a preference
for Cx–O2 vs Cx–O3 bond cleavage from tetrahedral intermediates
along the pathways of addition–elimination mechanisms when
the reactions were performed at room temperature. Furthermore, treatment
of isolated 3-unimer or 2-unimer, having the carbonate linkage in
the 3- or 2-position as obtained from either Cx–O2 or Cx–O3
bond cleavage, respectively, gave the same 74:26 (3-unimer:2-unimer)
ratio, confirming the occurrence of transcarbonylation reactions with
a preference for 3-unimer vs. 2-unimer formation in the presence of
organobase catalyst at room temperature. In contrast, unimer preparation
at −78 °C favored Cx–O3 bond cleavage to afford
a majority of 2-unimer, presumably due to a lack of transcarbonylation
side reactions. Computational studies supported the experimental findings,
enhancing fundamental understanding of the regiochemistry resulting
from the ring-opening and subsequent transcarbonylation reactions
during ROP of glucose carbonates. These findings are expected to guide
the development of advanced carbohydrate-derived polymer materials
by an initial monomer design via side chain acetal protecting groups,
with the ability to evolve the properties further through later-stage
structural metamorphosis.
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.
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