Syntheses And Properties Of Dipyrido[3,2-a:2’,3’-c]Phenazine Based Donor-Acceptor Aromatic Heterocyclic Compounds

In recent years, researches on organic semiconducting materials, such as oligothiophene, porphyrin, and phthalocyanine, have received tremendous attention in the field of optoelectronic materials. These kinds of materials are believed to be promising candidates for optoelectronic devices, for instance, light-emitting diodes, dye-sensitized solar cells, and field effect transistors. Compared with inorganic semiconductor materials, organic materials are more attractive for their light weight, good flexibility, easy preparation and purification. Consequently, how to efficiently design and synthetize organic semiconducting materials has become the most improtant challenge to build high-quality electronic device.Among all kinds of organic materials, donor-acceptor (D-A) linear aromatic heterocyclic compounds have been widely used in the optoelectronic field, due to their excellent properties of conjugated molecules. Furthermore, it is easy to regulate molecular properties by adjusting the molecular structures of the donor and acceptor. The research topic of this thesis exactly aimed at the modification and improvement of molecular structures to prepare different types of molecular electronic materials via the change of different donor and acceptor groups. Simultaneously, many theoretical and experimental efforts have been made on the studies of linear conjugated compounds and complexes. Moreover, an effective strategy of molecular design via DFT calculation has been widely used in our work to simplify experimental operation.In this thesis, the aim of incorporating various D-A substituents into one molecule is tuning their electronic structures and researching the difference of their spectroscopic, electrochemical, and thermal properties. In addition, a series of transition metal complexes have been prepared to further explore their physical and chemical properties, for example, the electronic and fluorescence spectra, energy gap alterations, the limitation of solubility of compounds. The thesis consists of four sections as follows:Chapter 1:In this chapter, some optoelectronic properties of π-conjugated molecular materials are summarized, especially those about light-emitting diodes and dye-sensitized solar cells, to help the readers getting better understanding. At the same time, this chapter also presents the current research progress about DPPZ derivatives. In addition, this chapter describes the reason for choosing this topic as the main content, as well as the goals and value of this research.Chapter 2:Syntheses, characterizations, optical, electrochemical, and thermal properties of a family of linear DPPZ-based heterocyclic aromatic fluorescent compounds are described herein. Combining with theoretical calculation, a detailed comparison about the influences of different numbers of electron-donating groups (thiophene and triphenylamine) at different sites is presented in this chapter. Research suggests that the introduction of electron-donating groups at the top positions of DPPZ has stronger impacts than the bottom ones. The introduction of electron-donating groups at the top sites of DPPZ core can remarkably lower the HOMO-LUMO gaps by forming the effective intramolecular charge transfer, while the introduction of electron-donating groups at bottom positions has only neglectable impacts.Chapter 3:On the basis of the previous chapter, a family of DPPZ-based heterocyclic aromatic compounds with different electron-donating groups is described herein. Moreover, synthetic, structural, thermal and spectral comparisons have been carried out for related compounds because of their adjustable intramolecular charge transfer properties. Optical and thermal results demonstrate that the dibenzothiophen-terminated compound displays the best luminescence property with the highest fluorescence quantum yield, while the triphenylamine-terminated compound exhibits smallest band gap with the most remarkable bathochromic shift. More importantly, a series of ruthenium complexes of DPPZ derivatives has been designed and prepared successfully in this chapter. Compared with DPPZ-ligands, ruthenium complexes exhibit smaller band gap and significant reduction of fluorescence quantum yield. This kind of fluorescence quenching is commonly referred as "OFF" luminescent behavior, which can be applied in the "OFF-ON" fluorescent chemical sensor and triplet-triplet annihilation up-conversation materials.Chapter 4:In this chapter, a series of triphenylamine-terminated phenanthroline derivatives have been designed and prepared successfully. And synthetic, structural, and spectral comparisons have been carried out for related compounds to find out the impact on molecular structure, physical and chemical properties of phenanthroline derivatives, by introducing different numbers of triphenylamine electron-donating group. On this basis, in order to improve the solubility of phenanthroline derivative in biological systems, two alkoxy groups are introduced into phenanthroline ring at 5,6 positions. As a result, the solubility of phenanthroline derivative bearing two alkoxy groups has greatly increased in ethanol/water system. More importantly, in the study of fluorescence sensing property, compounds 24 and 26 both exhibit a selective fluorescent quenching effect specifically with Ag+, which can be applied in the "ON-OFF" fluorescent chemical sensor.