Investigation On The Synthesis And Photophysical Properties Of Highly Solid-state Emissive Molecules And Bridge-nitrogen Containing Heteroacenes

Compared with conventional inorganic optoelectronics materials, organic optoelectronics materials have attracted substantial interests and investigation in recent years, due to their advantages, such as light-weight, low-cost, simple-process, flexibility and reel-to-reel coating applied in large area, higher luminous efficiency and wider choice of luminous color. They can be widely utilized in the field of organic light-emitting diodes (OLEDs), organic photovoltaic cells (OPVs), organic field effect transistor (OFETs), organic solid-state lasers and organic fluorescent sensors.In these organic photoelectric devices, the organic emissive materials are usually used in the forms of aggregate or thin solid films. As we known, most of the emissive materials are highly emissive in dilute solution, but severe fluorescence quenching in the solid state as the result of intermolecular interactions, thus greatly affecting the properties of materials and efficiency of devices. Therefore the rational design of such highly emissive organic materials in solid state is still a challenging and interesting issue. The front two parts of this dissertation are about the design and synthesises of the novel highly emissive organic π-conjugated molecules in solid state through promoting the intramolecular charge transfer and suppressing the intermolecular interaction.In these organic photoelectric materials, the polyacene and heteroacenes have attracted extensive attention and research due to its unique property of linear π-electron delocalized. Recently, extensive efforts have brought significant progress in the development of high performance optoelectronic devices based on these polyacenes and heteroacenes, especially to development the high performance organic field-effect transistors (OFETs). Recently, mostly of the research is mainly focused on the polyacene and sulfur-containing heteroacenes, while only a few reports is about nitrogen-containing heteroacenes, and even rarely reported on the nitrogen-bridge-containing heteroacenes. So the latter two parts of this dissertation are about the synthesises of a series of pyrazolo[1,5-a]pyridine derivatives with nitrile group substituted at the pyridine ring and further to obtain nitrogen-bridge-containing heteroacenes.The first part of this dissertation, we have designed and synthesized a new class of organoboron compounds containing a boryl and an amino group as acceptor and donor at the o,o’-positions of biphenyls. The distance between the boryl group and the amino group is much shorter than those of the through-space CT emitting organoboron compounds reported so far. We also synthesized two reference compounds with only the amino group or both the boryl and the amino group at the p-position of biphenyls. We find that the biphenyl derivative with o,o’-substituent not only have longer emission wavelength and large Stokes shift, but also have high fluorescence quantum efficiency (ΦF=0.86) in solid state. In addition, binding of the fluoride ions results in the remarkable blue shift and color change of the fluorescence, enabling colorimetric and ratiometric fluoride ion sensing.The second part, one symmetrical and two unsymmetrical dimesityboryl-substituted2,1,3-benzothiadiazole (BTD) derivatives have been prepared through Pd(0)-catalyzed Suzuki-Miyaura coupling reaction. These compounds are characterized by X-ray crystallography, UV-vis and fluorescence spectroscopy in solution and in solid state, DFT calculations, thermogravimetric analysis (TGA) and titration of fluoride ion. All these compounds display intense fluorescence not only in solution but also in the solid state due to steric bulkiness of the boryl group, which is effective to suppress the intermolecular interaction in the solid state. In addition, the symmetrical boryl-substituted BTD displays prompt fluorescence responses to fluoride ions with high sensitivity through the complexation of the boron center with fluoride, demonstrating its potential utility as fluorescent sensor for fluoride ions.The third part, we have developed the novel JWang’s tandem reaction to synthesize several pyrazolo[1,5-a]pyridine derivatives with nitrile group substituted at the pyridine ring by condensing the4-bromobut-2-enenitrile with pyrazole-aldehydes in mild conditions. The obtained novel compounds are particularly interesting molecules and can be further modified on the nitrile group to construct potential biological activity molecular.The fourth part, we try to synthesize bridged-nitrogen five-cyclic heteroacenes from benzene-1,2,4,5-tetraamine. However, it is difficult to purify and separate the intermediate product due to the poor solubility. Thus we used4,7-dibromo-2,1,3-benzothiadiazole as a starting material to synthesize4,7-diphenyl-pyrido[1,2-a]benzimidazole derivatives. In addition, the4,7-dibromo-2,1,3-benzothiadiazole goes by nitration, coupling and reduction to give the corresponding diamine or tetraamine derivative, and the reaction conditions of next cyclization reaction is on exploring.