Date of Award
Doctor of Philosophy (PhD)
Chemistry & Biochemistry
The objectives of the work described in this thesis are the design and synthesis of shapepersistent phenylene vinylene macrocycles (PVMs) and covalent organic polyhedrons (COPs) using dynamic covalent chemistry (DCvC); and the study of their applications in host-guest chemistry, light harvesting, gas adsorption and separation. DCvC has achieved tremendous progress during the past decade, and its application in constructing complex molecular architectures has attracted increasing attention. Conventional design and preparation of purely organic covalent architectures through irreversible bond formation usually requires multi-step synthesis and is very time consuming and low-yielding. DCvC exhibits a significant advantage: the reversible nature of the bond formation in DCvC (“self-correction”-enabled) allows the most thermodynamically stable product to be produced predominantly in one step from readily accessible precursors.
DCvC has been applied in constructing macrocyclic compounds for decades. Moore and coworkers have applied alkyne metathesis in constructing shape-persistent arylene ethynylene macrocycles. Such macrocyclic compounds showed interesting stacking properties for solid-state engineering.
Shape-persistent COPs with well-defined intrinsic cavities have been a research focus due to their unique structure features such as customizable geometry and isolated cavities. Moreover, constructed only through robust covalent bonds, the COPs usually have much higher chemical and thermal stability than their supramolecular analogues.
Further study beyond COPs involves incorporating COPs into frameworks to construct COFs. In this case, we can have individual well-defined built-in COPs in the frameworks, which are expected to be highly porous and be great candidate materials for gas adsorption, molecular separation, catalysis, chemical sensing and drug delivery. Currently, there are still some limiting factors that impede the COP synthesis through DCvC, and the most critical issue is that the dynamic covalent bonds formed are usually labile and cannot survive harsh conditions. Our research goals are to develop novel DCvC methods utilizing more robust dynamic covalent bonds, and to construct shape-persistent molecular cages using such DCvC methods.
In Chapter 1, an overview is given of the current (state-of-art) development and applications of covalent organic cage molecules. The advantages of the DCvC approach will be highlighted.
In Chapter 2 the synthesis and aggregation study of shape-persistent phenylene vinylene macrocycles (PVMs) are described. With substitution groups varied, the PVMs exhibit very different aggregation behaviors, which help us to understand the structure-property relationship of this class of compounds.
In Chapter 3, a porphyrin-based molecular prism is described, which is the first shapepersistent organic molecular cage prepared via alkyne metathesis. More interestingly, the cage compound is able to selectively bind C70 over C60, (KC70/KC60>1000), thus showing great potential for fullerene separation applications.
In Chapter 4, the formation of a ternary nanohybrid system consisting of the porphyrinbased molecular prism, fullerenes, and single-walled carbon nanotubes (SWCNTs) is described. A prototype device fabricated from this nanohybrid material gave decent photoconversion efficiency.
In Chapter 5, the synthesis of a porphyrin-based macrocycle is detailed. Unlike the 4-arm molecular cage reported in Chapter 4, this 2-arm macrocycle shows a highly adaptive cavity size and gives highest binding affinity for the larger fullerenes, i.e. C84.
Chapter 6 focuses on perspectives and recommended future work based on current research progress. The construction of organic cage frameworks (OCFs) from covalent polyhedron molecules was pursued. Given the large intrinsic cavities of the molecular polyhedrons, the designed OCFs are anticipated to have large cavities and be highly porous. Moreover, since the COPs have shown very strong binding affinity for fullerenes, the designed OCFs can be used for capturing as well as separating fullerenes.
Zhang, Chenxi, "Design, Synthesis, and Structure-Property Relationship Study of Shape-Persistent Phenylene Vinylene Macrocycles and Porphyrin-based Molecular Cages through Dynamic Covalent Chemistry" (2014). Chemistry & Biochemistry Graduate Theses & Dissertations. 113.