Studies on functionalized catenanes for polymer crosslinking and guest binding

Abstract

Mechanically interlocked molecules (MIMs) are molecules in which the components are mechanically interlocked and cannot be separated without breaking at least one covalent bond. Catenane is one of the major types of MIMs, consisting of two or more mechanically interlocked macrocycles. Due to the unique structures, the components could undergo large-amplitude motions like ring rotation and elongation, and they have a higher degree of (co)conformational freedom compared with covalent molecules. Catenanes are therefore promising candidates for developing new functional materials. Reported examples on catenane applications are however rare because of the difficult synthesis. In this thesis, a scalable synthesis and the studies of applying [2]catenane in polymeric materials, molecular recognition and molecular switch are described.

In Chapter 1, an introduction on MIMs is described. Synthetic methods, properties and applications of catenanes are also discussed.

In Chapter 2, a scalable synthesis of bis(alkynyl)-[2]catenanes using Cu(I)-phenan-throline template is described. The interlocked structures were confirmed by NMR spectroscopy and MS2 experiments. The synthesized [2]catenanes were employed as crosslinkers to construct polymer networks. Mechanical properties of the gels were tested by DMA experiments, and the effects of Cu(I) ion and the size of the interlocked macrocycles on the gel mechanical properties are discussed. The storage and loss modulus are found to be independent to the size of the interlocked macrocycles in the presence of Cu(I) ions in the [2]catenane crosslinkers, which behave like rigid segment. Softness of the gels was enhanced after removal of the Cu(I) ions. The gels crosslinked by [2]catenanes with a larger size showed a greater loss modulus than that of gels crosslinked by smaller [2]catenanes, indicating that more energy is dissipated for the large-amplitude motions of the larger [2]catenane crosslinkers.

In Chapter 3, binding studies of a [2]catenane to pyridinium guests are described. It was found that the mechanical bond plays an important role in the binding when compared with non-interlocked hosts. It was also found that the binding can enhance the charge transfer from the [2]catenane host to the pyridinium guest.

In Chapter 4, photophysical properties of a [2]catenane-based molecular switch are investigated. The [2]catenane switch showed an aggregation induced emission (AIE) behavior in DMSO/H2O solvent mixture due to an intramolecular aggregation of the tetraphenylethylene moieties.