Synthesis And Properties Of 2-(2'-Hydroxyphenyl) Benzothiozole Derivatives

Organic light-emitting diodes (OLEDs) have attracted much attention due to potential application in flat-panel display and lighting. The last decades has seen great progresses in both material development and device techniques. However, the luminous efficiency and device stability are still behind what the practical applications demand. The extra low electron transporting mobility of the present n-type organic semiconductors and the consequent imbalanced transportation of the positive and negative charges in OLED have been proven to be one of the key reasons to limit the OLED efficiency and lifetime. Therefore, it is necessary to develop novel electron transporting materials with improved electron mobility.Zinc (II) 2-(2'-hydroxyphenyl)benzothiozolate (i.e. Zn(BTZ)₂) is one famous light-emitting material. Most importantly, it is a electron transporting material with comparable electron transporting ability with the well-known Alq₃. However, the lowest unoccupied molecular orbit (LUMO) level of Zn(BTZ)₂ can not match the neighbouring organic function layers and the metal cathode. Furthermore, similar to other electron transporting material, the electron mobility of Zn(BTZ)₂ is several orders of magnitude lower than the hole mobility of most organic p-type materials.In order to study and improve the electron transporting behavior, a group of 2-(2-hydroxyphenyl)benzothiozole derivatives and their zink complexes were designed and synthesized in this thesis. The electron withdrawing group such as F, CF₃ or electron-donating group such as CH₃, OCH₃ was introduced to the phenyl ring on benzothiozole frame, with the expectation that the substituent will influence the electronic state and consequently the luminous properties, frontier energy levels, and electron transporting mobility of the 2-(2'-hydroxyphenyl) benzothiozole derivatives and their Zinc (II) complexes.The target 2-(2'-hydroxyphenyl) benzothiozole compounds were synthesized through acylation of substituted aniline, protection of the hydroxyl, sulfuration by Lawson reagent, Jacobson cyclization reaction in sequence in acceptable yields. The products were purified by recrystallization and column chromatography. ¹H-NMR and MS were used to characterize the chemical structures.Finally, the excited state intramolecular proton transfer (ESIPT) in these compounds along with non-substituted 2-(2'-hydroxyphenyl)benzothiazole was studied by means of UV-Vis absorption and steady-state fluorescence in different solutions. The solvents effect study demonstrated that polar and protic solvent inhibits ESIPT process and favors the short-wavelength normal emission. While the substituent effect study revealed that the electron-donating group such as OCH₃ facilitates the ESIPT process and favors the long-wavelength tautomer emissioin. And the solvent effect will dominate to determine the spectroscopic behaviors of present ESIPT-exhibiting derivatives in comparison with the substituent effect. In addition, the competiton of intermolecular and intramolecular hydrogen bonding was studied in the dioxane-water system.The present 2-(2'-hydroxyphenyl)benzothiozole derivatives with Br , F, CF₃ and OCH₃ on the phenyl ring of the benzothiozole frame are reported for the first time.