Optical materials are needed for various applications that emit light. Highly emissive dyes are expected to be widespread in materials creation but they display emission quenching in the solid state. Flood, Laursen, and colleagues discovered the first universal solution to this 150-year-old problem. They report a class of fluorescent materials and the design rules that allow cationic dyes to be plugged into an ionic lattice to reinstate their bright emission.
Supramolecular polymers have enabled far-reaching fundamental science and the development of diverse macromolecular technologies owing to the reversible and noncovalent chemical connectivities that define their properties. Despite the unabated development of these materials using highly tailorable recognition elements, anion-based polymers remain rare as a result of the weak interactions they mediate. Here, we use design rules inspired by cation-driven polymers to demonstrate a new noncovalent link based on receptor-stabilized anion−anion interactions that enables the efficient linear polymerization of simple difunctional phosphonates. The linear main chain connectivity and molecular topology were confirmed by single crystal X-ray diffraction, which demonstrates the rare 2:2 stoichiometry between the anionic phosphonate end groups and a pair of π-stacked cyanostar macrocycles. The stability of these links enables rapid polymerization of difunctional phosphonates employing different aliphatic linkers (C 6 H 12 , C 8 H 16 , C 10 H 20 , C 12 H 24 ). Diphosphonates with greater chain flexibility (C 12 H 24 ) enable greater polymerization with an average degree of polymerization of nine emerging at 10 mM. Viscosity measurements show a transition from oligomers to polymers at the critical polymerization concentration of 5 mM. In a rare correlation, NMR spectroscopy shows a coincident molecular signature of the polymerization at 5 mM. These polymers are highly concentration dependent, reversibly polymerize with acid and base, and respond to competitive anions. They display the design simplicity of metallo-supramolecular polymers with transfer of the strong 2:2 recognition chemistry to macromolecules. The simplicity and understanding of this new class of supramolecular polymer is anticipated to open opportunities in tailoring anion-based functional materials.
Sequence-controlled
supramolecular polymers offer new design paradigms
for generating stimuli-responsive macromolecules with enhanced functionalities.
The dynamic character of supramolecular links present challenges to
sequence definition in extended supramolecular macromolecules, and
design principles remain nascent. Here, we demonstrate the first example
of using stoichiometry-control to specify the monomer sequence in
a linear supramolecular polymer by synthesizing both a homopolymer
and an alternating copolymer from the same glycol-substituted cyanostar
macrocycle and phenylene-linked diphosphate monomers. A 2:1 stoichiometry
between macrocycle and diphosphate produces a supramolecular homopolymer
of general formula (A)n comprised of repeating
units of cyanostar-stabilized phosphate–phosphate dimers. Using
a 1:1 stoichiometry, an alternating (AB)n structure
is produced with half the phosphate dimers now stabilized by the additional
counter cations that emerge hierarchically after forming the stronger
cyanostar-stabilized phosphate dimers. These new polymer materials
and binding motifs are sufficient to bear normal and shear stress
to promote significant and tunable adhesive properties. The homopolymer
(A)n, consisting of cyanostar-stabilized anti-electrostatic linkages, shows adhesion strength comparable
to commercial superglue formulations based on polycyanoacrylate but
is thermally reversible. Unexpectedly, and despite including traditional
ionic linkages, the alternating copolymer (AB)n shows weaker adhesion strength more similar to commercial white
glue based on poly(vinyl acetate). Thus, the adhesion properties can
be tuned over a wide range by simply controlling the stoichiometric
ratio of monomers. This study offers new insight into supramolecular
polymers composed of custom-designed anion and receptor monomers and
demonstrates the utility of emerging functional materials based on
anion–anion linkages.
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