Supramolecular Aufbau : Folded Polymers as Building Blocks for Adaptive Organic Materials
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Aufbau: Folded Polymers as Building Blocks for Adaptive Organic Materials
Matthew J. Mio and Jeffrey S. Moore Introduction The design of inorganic and organic solids with novel structures and properties has long been the object of materials research. The classical examples of porous materials (i.e., involving reversible guest passage) are zeolites. First discovered in the mid-1700s, zeolites are hydrated, crystalline aluminosilicates that organize into stable, discrete frameworks.1 Basic structures employ tetrahedral atoms (silicon or aluminum) bridged by oxygen atoms, where each oxygen is shared between two metalloid tetrahedra. Resulting covalent lattices can be neutral or negatively charged (as a result of bridging oxides) and often employ alkali metal or alkalineearth counterions. As a consequence of this ordered structure, zeolites both benefit from and are limited by their highly geometrical nature: their rigid structures are inherently robust, yet they are difficult to process. In addition, while natural and unnatural zeolites have been characterized, harsh synthetic conditions are common to both and lead to limitations in design and processability. Even so, these impediments have not prevented constructing a myriad of architectures on zeolite host lattices.1 Strengths and weaknesses aside, zeolites demonstrate a major objective of materials chemistry: the ability to manifest macroscopic physical properties based on embedded microscopic structure.
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More recently, interest in designing architectures that lead to organic host solids has resulted in the generation of many unique systems. The promise of these materials stems from the diversity of organic molecules and the ability to organize them by harnessing the power of supramolecular chemistry. Traditional chemical synthesis involves the stepwise generation of covalent bonds via reaction to produce novel molecules. In comparison, supramolecular synthesis involves an equilibrium of noncovalent interactions (van der Waals forces, hydrogen bonds, and electrostatic forces) between the surfaces of molecular objects to produce novel supermolecules. The “reactions” of supramolecular chemistry are self-organization and self-assembly.2 These two terms are used to refer to non-atom-specific (i.e., van der Waals forces) and atom-specific (i.e., hydrogen-bonding) interactions, respectively. In this article, we detail the use of a supramolecular aufbau (buildup) design in generating novel organic materials composed of folded polymers. The system we describe illustrates how molecular-level adaptability can be expressed through supramolecular chemistry to make various structures under different conditions. The ability of supramolecular chemistry to form structures at many different size regimes may hold the key to an innovative approach to adaptive organic materials
with distinct properties. It is important to note here that supramolecular chemistry is not being proffered as a replacement for classical inorganic zeolites. On the contrary, we aim to reveal the ability
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