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Authors: Chen, Qiang
Title: Bottom-up Syntheses of Zigzag-edged Nanographenes and Nanographene-Porphyrin Conjugates
Online publication date: 22-Apr-2021
Language: english
Abstract: In the first part of my thesis (Chapter 1), I talked about the effect of edge structures on the properties of graphene molecules (GMs) and reviewed the recent progress in the synthesis of zigzag-edged GMs. Then, I reported the synthesis of an unprecedented GM having both armchair and zigzag edges (Chapter 2), which was named as dibenzo[hi,st]ovalene (DBOV). DBOV has very intensive absorption in the long wavelength region (>600 nm) and strong red emission with high absolute fluorescence quantum yield of up to 0.79. It also showed stimulated emission in both solution and polystyrene matrix with a concentration of 1w%. Amplified spontaneous emission was also achieved for this molecule. These properties make it a promising candidate for using as active component layer in organic light-emitting diodes (OLEDs) and organic lasers. My further investigation showed the synthesis could be simplified by an ICl promoted iodobenzannulation and photochemical cyclodehydroiodination sequence (Chapter 3). This method could be applied to synthesize DBOV derivatives with different meso-substitutions in large quantities, which allows us to study the single-molecular spectroscopy and self-assembly of DBOV in 2D and 3D (Chapter 4). In addition, I also found one post-synthetic method to functionalize DBOV directly on its periphery (Chapter 5). This strategy relies on regioselective bromination of DBOV. The brominated DBOV intermediate can be used for transition-metal catalyzed coupling reactions, such as Suzuki coupling and Sonogashira coupling. These functionalized DBOV showed increased solubility in organic solvents and high fluorescence quantum yield as a result of hindered intermolecular - stacking. In addition, I also found the DBOV could be reversibly oxidized to stable radical cations and reduced back to neutral state by using strong oxidant. The functionalization method will promote the application of DBOV in other fields, for example bioimaging and materials. In the next chapter (Chapter 6), I turned to synthesize fully zigzag-edged GMs and successfully obtained circumpyrene using DBOV as starting material. The key step is to selectively fuse the two bay regions of DBOV with two C=C bonds. Spectroscopy and electrochemical studies indicate circumpyrene has high energy gap compared with the partial zigzag-edged DBOV. This could be explained by the decreased amount of -electrons in their conjugation pathway along the rim. Finally, I tried to take advantage of the zigzag edges to make new type of heteroatoms doped GMs. Taking a careful look at the geometry of zigzag edges, one could see it fits very well with the periphery of porphyrin. Here, I designed one benzo[m]tetraphene based partial zigzag-edged GM precursor and coupled it to meso-positions of porphyrin (Chapter 7). After cyclodehydrogenation, fully conjugated nanographene-porphyrin hybrids were obtained. The efficient electron communication between the GM and porphyrin parts was evidenced by the largely red-shifted UV-vis absorption of Q band of porphyrin core. In addition, the nanographene-porphyrin conjugates was found to form bilayer self-assembly at the interface of trichlorobenzene and HOPG, which will be helpful for fabricating large area thin film devices.
DDC: 500 Naturwissenschaften
500 Natural sciences and mathematics
530 Physik
530 Physics
540 Chemie
540 Chemistry and allied sciences
600 Technik
600 Technology (Applied sciences)
Institution: Johannes Gutenberg-Universität Mainz
Department: FB 09 Chemie, Pharmazie u. Geowissensch.
MaxPlanck GraduateCenter
Place: Mainz
Version: Original work
Publication type: Dissertation
License: in Copyright
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Extent: III, 283 Seiten, Illustrationen, Diagramme
Appears in collections:JGU-Publikationen

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