The Design, Synthesis And Property Study Of3-fold Symmetric Nanographenes

Large discotic polycyclic aromatic hydrocarbons (PAHs) or nanographenes (NGs), as subunits of nanocarbon-based materials such as graphenes, carbon nanotubes and fullerenes, have important physicochemical properties and great application potential in molecular electronic devices including the next generation of molecular computer, organic solar cells, flexible display devices, organic light-emitting diodes, organic nano wires and other fields. NGs, with well-defined structure and precise edges are also regarded as the model of graphenes, being of important theoretical value for understanding structure, properties and performance of graphenes. Innovative synthetic strategies to construct aromatic architectures of PAHs are highly desirable. However, chemical syntheses of nanographenes generally face considerable difficulties and challenges.In planning a more facile strategy that provides coronene-based NGs, we were attracted by their3-fold symmetry and thus created our synthetic concept based on a one-step covalent self-sorting assembly (CSA) strategy for construction of c-HBCs and large NGs. The total synthesis involving the CSA strategy for c-HBCs and large NGs is a concise two-step reaction sequence. Firstly, sym-tribenzylbenzene, which can be readily accessed by Suzuki coupling of1,3,5-tri(bromomethyl)benzene and3,4-dialkoxyphenyl boronic acid, is covalently self-sorting assembled with three arylaldehyde molecules into the c-HBCs and large NGs.This dissertation studies the corresponding research work revolving around a new concept named covalent self-sorting assembly as the key step to design and synthese3-fold symmetric nanographenes. This CSA chemistry could be accomplished by means of mortise-and-tenon joints, that is, three benzyl tenons automatically were mated into in three mortises that correspond to the "cove-regions" between the central ring and branched rings of an appropriate starburst dendritic aromatic molecule.At the start of the project the significance and progress of the nanographenes were reviewed and then the research ideas and research content were put forward. The details are listed as below.In the first work, we focus on developing novel routine to syntheses the intermediates of3-fold symmetric discotic nanographenes. On the one hand, sym-tribenzylbenzenes (TBBs), the intermediates of3-fold symmetric discotic nanographenes were efficient synthesized in good yields via a3-fold Suzuki coupling reaction using1,3,5-tri(bromomethyl)benzene with3,4-dialkoxyphenyl boronic acids in good to excellent yields. On the other hand, we changed synthetic route, overcame the drawback of the above reaction that is not easy to enlarge, provide the sym-tribenzylbenzenes (TBBs) starting from catechol throngh Williamson reaction, Friedel-Crafts reaction, tri-polymerization, the reduction paved the way of the intermediates of3-fold symmetric discotic nanographenes, especially for the subsequent designs and synthesis of polycyclic aromatic hydrocarbons.In the second part, we analyzed the structure of the3-fold symmetric contorted HBC using retrosynthetic analysis designed the synthesis of corresponding experiments, and probed the possible reaction route, and found a facile and efficient covalent self-sorting assemble (CSA) strategy for bottom-up synthesis of the3-fold symmetrical and highly substituted hexa-cata-hexabenzocoronenes (c-HBCs). All the reactant and the wanted c-HBCs were conformed by by NMR, MALDI-TOF. Further understanding of the structure was through the calculation of the ground state structure of representative target molecule and the X-Ray single crystal diffraction。In the third part, we attempt to use the similar reaction condition to obtain a novel sym-tribenzotetrathienocoronenes (TBTTCs) from5-methyl-2-thienaldehyde,2-thienaldehyde,3-thienaldehyde, benzo[b]thiophene-2-carbaldehyde with theTBBs, respectively.3-thienaldehyde and benzo[b]thiophene-2-carbaldehyde were indentied as the suitable reactant to provide six kinds of TBTTCs using the CSA process, which were aslo characterized by NMR, MALDI-TOF, respectively. Further understanding of the structure was through the calculation of the ground state structure of representative target molecules and the X-Ray single crystal diffraction.In the fourth part, spurred by the successful assembly of the c-HBCs, we turned to the construction of larger π-disks using our CSA concept. The application of our CSA conditions, however, with9-phenanthraldehyde, neither the one-pot synthesis nor resubmitting protocol succeeded in offering the desired product in pure form.3,6-di-tert-butyl-9-phenanthraldehyde and3,6-bis(2-methylhexan-2-yl)phenanthrene-9-carbaldehyde was chosen to avoid solubility issue using the CSA conditions HBCC was accessed successfully, respectively. All the products were studied by NMR, MALDI-TOF. Further understanding the structure was through the calculation of the ground state structure of representative target molecule and the X-Ray single crystal diffraction.In the fifth part, some properties of c-HBCs, TBTTCs, and HBCCs, such as optical properties, electrochemical properties and thermal properties, were studied by UV-Vis spectroscopy, fluorescence spectroscopy, cyclic voltammetry (CV) and thermal gravimetric analysis (TGA).Finally, the experimental results and creative point of this dissertation were summarized.Our CSA strategy makes these kinds of PAHs to be one of the most accessible large polycyclic aromatic molecules and more significantly, render the method a simple and versatile tool to be controlled in hands of chemists and materials scientists. Our CSA strategy method has significant advantages compared with the reported methods as follows:(1) The novel strcture:all the target molecules could not be prepared by the literature method;(2) Step-economy:only2steps in the total route;(3) Simple and readily available starting materials;(4) High efficiency:12or18reaction-step occurs in one-pot;(5) Mild conditions;(6) Wide scope:a diversity of c-HBCs that are functionalized both in the periphery and at the aromatic core, as well as the hetero-c-HBCs and large PAHs can be synthesized using this method;(7) All of the target molecules were revealed by NMR, MS spectrum, representative product were clearly revealed by X-ray studies. Also remarkable is that the crystal of a25ring nanographene is hitherto the largest discoid NG molecule with all-hexagonal grids to be represented by X-ray crystal structure.The as-prepared c-HBCs and related large PAHs can serve as new launching platforms for constructing even larger aromatic architectures with defined shape, size and periphery or tuning their physiochemical properties by changing the rim substituents. It will open a door for creating prosperity for this family of PAHs making the number of readily accessible possible derivatives suddenly very large. More importantly, the unique3-fold symmetrical structure and the designable and modifiable edge-functionalities of our c-HBCs permit them to serve as new launching platforms for creating larger and more complex aromatic architectures, dendrimers, starburst molecules, and starpolymers will be interesting in this family of compounds. Nanographene molecules laid the foundation of molecular devices with special physical and chemical properties, such as good solubility and thermal stability, for the organic semiconductor materials, luminescent materials, solar cells, light-emitting diodes (leds), etc. Our CSA strategy makes these kinds of PAHs to be one of the most accessible large polycyclic aromatic molecules and more significantly, render the method a simple and versatile tool to be controlled in hands of chemists and materials scientists. The versatility of our method makes these kinds of PAHs. More importantly, the unique3-fold symmetrical structure and the designable and modifiable edge-functionalities of our c-HBCs permit them to serve as new launching platforms for creating larger aromatic architectures.