Synthesis And Photophysical Study Of2-(2’-hydroxyphenyl)Benzothiazole (HBT) Derivatives

The excited-state proton transfer (ESIPT) is one of the most fundamental and important reactions in chemical reactions. It has extracted intensive research attentions due to its special optical characteristics and the application in optoelectronic materials, such as large Stokes shift, two peak emission and no self-absorption. HBT derivatives are typical of ESIPT based molecules. Therefore, HBT derivatives have become a focus topic in science.In recent years, as the extensive research of HBT derivatives in photophysics and theory, the theoretical models related to structure have been well established. However, there still have some problems which have greatly limited the application of its special ESIPT process in photoelectric material. For example, the concentration quenching leads to low fluorescent quantum yield due to the keto emission of HBT derivatives and the two peak emission fails to cover the whole visible spectrum. In allusion to the problems mentioned above, in this paper, we synthesize a group of HBT derivatives from simple starting material and method by the chemical modification of HBT, namely HBT-1, HBT-2, HBT-3, HBT-4. HBT-5, HBT-6, HBT-7, and HBT-8. The intermediates and products were purified by recrystallization and column chromatography and characterized by MS, MALDI-TOF-MS and1HNMR. The electroluminescence (EL) properties of these products are still in progress.The photophysical properties of the synthetic HBT derivatives were investigated by means of UV-Vis absorption and steady state photoluminescence (PL) spectra in different solvents. Our results indicate HBT-1and HBT-2exhibit typical aggregation-induced enhanced emission (AIEE), which can be characterized by the enhancement of the fluorescence emission from the solid films to the solutions. Similar to HBT derivatives, HBT-2, HBT-3, HBT-5, HBT-6, and HBT-7show both typical two peak emission and new emission band from phenolate anion in ethanol solutions. This is in contrary to most small molecules that barely show tri-fluorescence merit. For HBT-5, ESIPT induce and takes place prior to ESCT in non-proton organic solvent, which can result in great influence on the keto emission by the changes of solvent polarity. Meanwhile, we can realize the white light emission by adjusting the ratio between enol emission and keto emission in different proportions of acetonitrile and ethanol solutions. All these preliminary data suggest that these compounds have potential application in the field of fluorescent probe, optical storage and OLEDs.