Design, Synthesis And Properties Of Benzothiadiazole-based Small Red-emitting Molecule Materials

Compared with their polymer counterparts, small molecular organic compounds present the potential of a better reproducibility of synthesis and purification. On the other hand, with respect to vacuum deposition, solution-processing technology can possibly afford low-cost, large-area and flexible OLED displays. Thus, Solution-processable molecular semiconductor materials have received increasing attention.The thesis begins with a brief introduction of the general principle of OLED. The current development of organic molecular red light-emitting fluorescence materials was discussed. Then we designed and synthesized a series of soluble red light-emitting materials. The optical, thermal and electrochemical properties of the compounds are investigated. The detailed results of research were described as follows:(1) A series of light-emitting small molecule compounds S1-S5and H1-H5, which were based on2,1,3-benzothiadiazole with different thiophene units as the core and end-capped with9-(4-phenyl)-9H-carbazole and9-(4-vinylphenyl)-9H-carbazole, were synthesized by Suzuki-coupling or Heck-coupling reactions. Research results showed that these small molecules possess good solubility, broad absorption and relatively high thermal stability. UV-vis absorption spectra showed that the absorbance spectral range of molecules were broaden effectively and the band gap were reduced by modulating the conjugated chain and changing the substitute position of alkyl chains.(2) Two solution-processible star-shaped light-emitting small molecules P1and P2consisting of electron-accepting unit (triphenylamine or9-(4-phenyl)-9H-carbazole) and electron-donating unit (2,1,3-benzothiadiazole with thiophene units) were synthesized. For the molecule design of electroluminescent materials, non-symmetrical molecule structure may prevent the formation of molecular aggregation state thus increasing luminescent efficiency. The star-shaped configuration improved the balance of hole injection and avoided intermolecular aggregation or excimer formation. UV-vis absorption spectra and Cyclic voltammetry investigation displayed that both small molecules possess broad absorption range and low band gap properties. TGA and DSC reveal that their decomposition temperatures (Tg) are higher.