This review demonstrates our approaches for developing functional polymer systems using dissociation processes in nonpolar media. One is the molecular design of highly swellable gels known as ...superabsorbent polymers in nonpolar organic solvents, and the other is the supramolecular design of thermo-responsive polymers. Both of them are well documented in water, but no practical molecular design for other media have ever been proposed. For designing these behaviors, the dissociation or release of the low-molecular component from macromolecular complexes should play a key role. Therefore, controlling the dissociation processes in supramolecular chemistry should be another important strategy for developing functional polymer materials.
Aggregation-induced emission (AIE) has emerged as a new class of attractive photoluminescence behavior. Understanding the precise mechanism of the AIE phenomenon will lead to the rational molecular ...design of novel molecules with AIE properties (AIEgens). In this work, we selected disubstituted derivatives of tetraphenylethene (TPE), a well-known archetypal AIEgen, as the model compounds to elucidate the AIE mechanism. As the result of photochemical experiments and quantum chemical computations, π-bond twist (π twist), including E–Z isomerization (EZI), was found to be the major factor for quenching the photoexcited state of TPE derivatives in the solution state, differently from the well-accepted propeller-like rotation of the side phenyl groups in earlier research. In photochemical experiments, the prepared TPE derivatives exhibited EZI in the solution state upon photoirradiation, and a negative correlation was observed between this isomerization and the AIE phenomenon. The theoretical computations verified the crucial role of π twist triggered by photoirradiation in the solution state, rather than intramolecular rotation. In the crystal state, π twist was efficiently suppressed by the surrounding molecules. Our results will support the realization of novel smart AIEgens that can respond to various external stimuli.
Sweet cube o' mine: Bottom‐up control of gel particles has been regarded as a great challenge. By employing internal cross‐linking of cyclodextrin metal–organic frameworks, cubic sugar gels were ...formed with sharp edges that reflect the shape of the crystals. This enabled the fabrication of shape‐ and size‐controlled polymer gels from porous crystals (see picture).
Until now, seamless fusion of metal–organic frameworks (MOFs) and covalently cross-linked polymer gels (PG) at molecular level has been extremely rare, since these two matters have been regarded as ...opposite, that is, hard versus soft. In this report, we demonstrate transformation of cubic MOF crystals to PG via inner cross-linking of the organic linkers in the void space of MOF, followed by decomposition of the metal coordination. The obtained PG behaved as a polyelectrolyte gel, indicating the high content of ionic groups inside. Metal ions were well adsorbed in the PG due to its densely packed carboxylate groups. A chimera-type hybrid material consisting of MOF and PG was obtained by partial hydrolysis of resulting cross-linked MOF. The shape of resulting PG network well reflected the crystal structure of MOF employed as a template. Our results will connect the two different network materials that have been ever studied in the two different fields to provide new soft and hard hybrid materials, and the unique copolymerization in the large void space of the MOF will open a new horizon toward “ideal network polymers” never prepared before now.
Anisotropically deforming objects have attracted considerable interest for use in molecular machines and artificial muscles. Herein, we focus on a new approach based on the crystal crosslinking of ...organic ligands in a pillared‐layer metal–organic framework (PLMOF). The approach involves the transformation from crosslinked PLMOF to polymer gels through hydrolysis of the coordination bonds between the organic ligands and metal ions, giving a network polymer that exhibits anisotropic swelling. The anisotropic monomer arrangement in the PLMOF underwent axis‐dependent crosslinking to yield anisotropically swelling gels. Therefore, the crystal crosslinking of MOFs should be a useful method for creating actuators with designable deformation properties.
Flexing MOFs: A new approach for anisotropic deforming objects is presented, which is based on the crystal crosslinking of organic ligands in a pillared‐layer metal‐organic framework (PLMOF). The anisotropic monomer arrangement in the PLMOF is responsible for the axis‐dependent crosslinking to yield anisotropically swelling gels.
The A–A/B–B step‐growth copolymerization between a monomer immobilized in the crystalline state and a monomer mobile in the solution state is demonstrated. One of the two monomers was immobilized as ...organic ligands of the metal–organic framework (MOF) and polymerized with the mobile guest monomer, resulting in the formation of linear polymers. The polymerization behavior was completely different from that of the solution polymerizations. In particular, the degrees of polymerization (DP) converged to a specific value depending on the MOF structures. The inevitable termination is caused not by imperfectness of the polymerization reaction, but by the selection of the two polymerization partners among the several adjacent immobilized monomers. This is fully supported by the Monte Carlo simulation on the basis of the polymerization mechanism. Precise immobilization of monomers in the supramolecular assemblies is a promising way for the controlled A–A/B–B step‐growth polymerization.
Two types of monomers in different environments were copolymerized in a metal–organic framework (MOF). One of the two monomers was immobilized in the MOF as an organic linker and the other is mobile in the 3D channels of the MOF. The polymerization degree converged to a specific value depending on the MOF structure. Immobilization of monomers regularly in supramolecular assemblies is a promising way for controlling step‐growth copolymerization.
The recovery of crude oil and volatile organic compounds (VOCs) spilt in the environment is an intractable problem for environmental scientists. In this paper, a new lipophilic polyelectrolyte gel as ...an absorbent for various volatile chemical compounds is demonstrated. It is prepared by radical copolymerization of an acrylate monomer with an ionic group, tetraalkylammonium tetraarylborate, octadecyl acrylate, and a crosslinker, dipropylene glycol diacrylate, in the presence of a radial initiator. Investigation of the swelling behavior for the mixtures of water or aqueous salts reveals that the gel shows similar swelling behavior to those for pure organic solvents. On the other hand, the swelling degree in THF‐water mixture is lower than that of pure THF, because THF and water are miscible to each other, and the presence of a small amount of water in THF reduces the compatibility of the gel and THF. The salting‐out effect can separate the THF‐water mixture to form a biphasic system and recover the high swelling ability of the gel. The swelling behavior in the mixture of water‐organic solvents systems provides a new insight for designing VOC and oil absorbents in various environmental conditions, especially in hydrosphere such as seas and lakes.
A new lipophilic polyelectrolyte gel is synthesized, as an absorbent for various volatile chemical compounds. Investigation of the swelling behavior for the mixtures of water or aqueous salts revealed that the gel showed similar swelling behavior to those for pure organic solvents. The systems introduced here will be useful as oil absorbents in various environmental conditions, such as hydrosphere.
In nature, swarming behavior has evolved repeatedly among motile organisms because it confers a variety of beneficial emergent properties. These include improved information gathering, protection ...from predators, and resource utilization. Some organisms, e.g., locusts, switch between solitary and swarm behavior in response to external stimuli. Aspects of swarming behavior have been demonstrated for motile supramolecular systems composed of biomolecular motors and cytoskeletal filaments, where cross-linkers induce large scale organization. The capabilities of such supramolecular systems may be further extended if the swarming behavior can be programmed and controlled. Here, we demonstrate that the swarming of DNA-functionalized microtubules (MTs) propelled by surface-adhered kinesin motors can be programmed and reversibly regulated by DNA signals. Emergent swarm behavior, such as translational and circular motion, can be selected by tuning the MT stiffness. Photoresponsive DNA containing azobenzene groups enables switching between solitary and swarm behavior in response to stimulation with visible or ultraviolet light.
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