Synthesis And Characterization Of Benzothiazole-based Organic Optoelectronic Materials

Benzothiadiazole, a type of important molecular core in the application of Organic Electronics,its excellent electron-accepting ability make it not only always used as core unit for emission colorstunning in organic light-emitting diodes (OLEDs), but also interact with donor group as an acceptorto quality proper HOMO and LUMO energies for application in organic photovoltaic(OPV).Therefore, we connected this unit with itself in different position, and investigated the basicmechanism of electroluminescence and photoluminescence based on the synthetic compound. In themeanwhile, considering two crucial factors in OPV, we connected this unit with large size aromaticring to synthetic the new large flat compound for application in OPV.Firstly, for organic electroluminescent, we designed and synthesized two types of isomers basedon thiophene and Benzothiadiazole, and their homologous molecular structure, similarelectroluminescence and different photoluminescence provide a good platform for deep explorationinto the relationship between PL and EL. Whether in solution or film, these compounds have achievedcontinuous luminescence accompanied by the single emission peak. The fluorescent OLED device of2T shows a low turn-on voltage at2.45V with the maximum luminance of1825cd/m2and low red-shift of EL (26nm), while3T has a highly red-shifted EL up to53nm, which was supposed to beintrinsically resulted from the largely reorganized molecular structures at charged states triggered bythe external electronic field during the OLED operation. These findings based on systematic analysisof mechanisms, theoretical calculations and experimental results may provide a valuable perspectiveon the relationship between PL and EL, particularly play an instructive role in the design of OLEDmaterials.Secondly, the most important factors to improve device performance are improving the mobilityand absorption ability for OPV materials, and based on these two points, we kept trying to combinethe benzothiadiazole with strong electron withdrawing ability and large aromatic ring structure highmobility combined and finally synthesized a new large flat structural unit. The small molecule whichwas prepared by this unit and coupled reaction, and based on this compound, the energies of molecularfrontier orbitals decrease with increasing number of fluorine atoms, but remain constant energy gap;introducing the strong electron donating group can broaden the absorption spectrum. Meanwhile, the core without bromine atoms showed very strong crystal properties in an atomic force microscope,which has potential applications in molecular self-assembly. Applying these compounds in OPVdevices can exhibit prospects in terms of conversion solar energy to electrical energy.Finally, we prepared six polymer donor materials by making large flat structural unit and twotypes of OPV obvious structural unit polymerize. We initially found that large flat structural cansimultaneously connect with donor and acceptor units and can successfully adjust the band gap toabout1.5eV, and especially when connecting with acceptor DPP, the band gap can be adjusted to1.37eV; the absorption spectrum show this polymer can fully absorb sunlight, which means the sixmaterials have been applied in the device. For materials which were polymerized with BDT units, westudied the influences of just changing the molecular chain and the kind of alkyl chain on its overallperformance, but results turned out it had little help for improving performances. After optimizationof device, the final performances are Voc=0.78V，Jsc=10.07mA/cm2，FF=0.411，PCE=3.22%.