Chiral supramolecular polymer
In recent years, supramolecular polymers have attracted great attention due to their unique structural characteristics and application value. In the preparation of traditional high-molecular polymers, first, monomer molecules need to undergo a certain polymerization reaction to connect the monomer units to each other in the form of covalent bonds. In supramolecular polymers, the monomer units are connected by non-covalent bonds such as hydrogen bonding, aromatic accumulation, donor-acceptor action, solvophobic action, and metal coordination action. Due to the existence of these non-covalent bonds, the polymerization and degradation of supramolecular polymers can occur reversibly, thus giving them the characteristics of low temperature processing, self-healing, and response to environmental stimuli. It is a "smart material". However, due to the weak bond characteristics of non-covalent bonds, it is still a huge challenge to construct supramolecular polymers with high stability and high molecular weight.
Researchers from the Laboratory of Physical Organic Chemistry and the State Key Laboratory of Life Organic Chemistry of the Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences have collaborated with researchers from Peking University to simulate the principle of self-assembly in nature to construct diverse biological macromolecules such as DNA, using supramolecular A multivalent strategy is used to construct a class of highly stable chiral supramolecular polymers. Its construction is first through the introduction of DDA-AAD (D-hydrogen bond donor, A-hydrogen bond acceptor) type multiple hydrogen bond building blocks with the introduction of porphyrin units at the end. It is formed by intermolecular hydrogen bond hexamerization in low-polarity solvents Disc-shaped structure, this hydrogen-bond-stabilized disc-shaped structure is further formed by the six zinc porphyrin units extending around its periphery and the pyridine in the chiral ligand R-2 (or S-2) through N-Zn coordination The highly stable layered chiral supramolecular polymer, the stereoselectivity of its assembly process comes from the induction of the chiral center in R-2 (or S-2).
The research also shows that there is a process of self-correction and conversion from kinetic control to thermodynamic control during the formation of the supramolecular polymer. The driving force of the system comes from the two non-covalent interactions of hydrogen bonding and metal coordination. Although the strength of a single non-covalent interaction is not great, when multiple non-covalent interactions (a basic There are eighteen hydrogen bonds and six metal coordination functions in the unit) When the synergy is added, a strong binding capacity can be produced, which not only realizes the preparation of highly stable supramolecular polymers, but also ensures the use of assembly motifs. The inherent chiral center induces the effectiveness of stereoselectivity at the polymer level. This strategy demonstrates the great potential of using the multivalence of supramolecular chemistry for multi-level ordered assembly.
In addition, since porphyrin is a large π conjugated system with very excellent photoelectric properties, the higher degree of polymerization of the resulting supramolecular polymer also means that there are thousands of porphyrin units in a single polymer chain in a specific In an orderly arrangement in a chiral environment, such polymers may have some applications as light-absorbing antennas or in other optoelectronic devices.
The work was published in the Journal of the American Chemical Society (J. Am. Chem. Soc. 2011, 133, 11124-11127) in the form of a communication.
The research work was supported by the National Natural Science Foundation of China, the Ministry of Science and Technology and the Shanghai Municipal Science and Technology Commission.
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