Synthesis And Properties Study Of Stimuli-Resposive Organometallic Self-Assembly Systems

With the development of supramolecular chemistry, metallosupramolecular materials have become a crucial branch of chemistry and materials science. Hierarchical self-assembly is an efficient and powerful methodology to construct complicated supramolecular systems with unique functionality. The dynamic nature of coordination bonds and other non-covalent interactions endow these supramolecular systems stimuli-responsive properties. Understanding of design principle of coordination building blocks feeds back into the design of new structures with targeted functions. Based on our previous research work on coordination-driven self-assembly, we presented the construction and functionality of different stimuli-responsive coordination supramolecular systems based on supramolecular metallocycles in the dissertation.The main content of the dissertation includes the following five Chapters:In chapter one, recent developments of coordination supramolecular systems, hierarchical self-assembly of coordination supramolecular systems and stimuli-responsive coordination supramolecular systems were reviewed, and our projects in the dissertation were put forward at the end of this chapter.In the second chapter, we designed and synthesized a group of metal dendrimers with hexagonal cavities based on poly(aryl ether) dendrimers by using the coordination-driven self-assembly. Driven by CH-π, π-π interaction between periphery poly(aryl ether) dendrons, the second generation metallodendrimer was able to hierarchically self-assembled into regular vesicle-like structures. Further study indicated that due to the dynamic nature of metal-ligand bonds, the disassembly and reassembly of the obtained hexagonal metallodendrimers could be reversibly controlled by the addition and removal of bromide ions, resulting in the transition between the vesicles and micelles. Interestingly, by taking advantage of the halide-induced vesicles-micelles transition, the controlled release of fluorescence dye was successfully realized.In the third chapter, we designed and synthesized a series of cholesteryl-containing metallacycles from cholesteryl-containing dipyridine ligand and complementary accepter ligands via exo-functionalization and coordination-driven self-assembly. All these metallacycles were fully characterized by one-dimensional multinuclear (1H and 31P) and two-dimensional (1H-1H COSY,1H-1H NOESY, and DOSY) NMR spectroscopy, mass spectrometry and elemental analysis. These metallacycles were further demonstrated to undergo hierarchical self-assembly to ordered morphologies and nanostructures through Van der Waal forces and hydrogen bonding of periphery cholesteryl units. Moreover, it was found that the morphology of the metallacycle aggregates were very sensitive to solvent polarity, thus transition between various nanostructures were realized by fine-tuned variation of solvent polarity.In the fourth chapter, a new kind of ligand modified by tetra-phenylethylene (TPE) fragment was designed and synthesized, and a hexagonal metallacycle was formed by the self-assembly of this ligand. As detected by UV absorption spectra, fluorescence emission spectra measurements etc., the new TPE modified hexagonal metallacycle was aggregation-induced emission (AIE) active in many mixed solvent systemes, eg. dichloromethane/hexane, acetone/water mixed solvents. The self-assembled metallacycle’s AIE activity was better than precursor pyridine ligand under some certain conditions. This optical property could be utilized to probe the metallacycle’s aggregation process. Optical investigations indicated that the addition of heparin to the tris-TPE metallacycles solution resulted in dramatic fluorescence enhancement, which supported the aggregation between metallacycle and heparin. Moreover, as detected by SEM, TEM, and LSCM experiments, the morphology of these hierarchical aggeregates were entangled pearl-necklace networks. In particular, we observed single bead-like chains in the AFM and TEM images in very dilute solution, which provided direct, visual evidence for the aggregation of tris-TPE metallacycles and heparin. PM6 semi-empirical molecular orbital method theoretical calculation found that heparin polymer chains tend to adopt skew-crossing mode to interact with hexagonal metallacycles to form single bead-like chains and then aggregated into interconnected pearl-necklace network microstructures. More interestingly, further photopysical study revealed that this TPE-decorated metallacycle could work as a turn-on fluorescent probe for heparin detection with high sensitivity and selectivity.In the fifth chapter, we designed and synthesized a series of photochromic bisthienylethene-based metallocycles from photochromic bisthienylethene-based pyridine ligands via platinum coordination-driven self-assembly. As detected by UV spectra and multinuclear NMR (31P and 1H), the quantitative reversible conversion of opened-form to closed-form assemblies has been successfully realized by taking advantage of the photo-induced switchable property and good fatigue resistance of photochromic bisthienylethene system. Additionally, the introduction of naphthalene imide chromophore into metallocycle system endow it emission property. Photoswitchable fluoresce were successfully realized, through fluorescence resonance energy transfer (FRET) between photochromic bisthienylethene and naphthalene imide chromophore.