Sythesis, Characterization And Properties Of Tris(8-hydroxyquinoline)(Alq₃) Derivatives With Electron Pushing And Drawing Substituents

A novel tris-(8-hydroxyquinoline)aluminum derivative with pushing-drawing substitutes, tris-(4-methyl-6-fluorine-8-hydroxyquinoline)aluminum(4Me6FAlq₃) was designed and synthesized in this paper. PL spectrum could be changed by introducing strong electron-accepting group of fluorine atom at 6-position and electron-donating group of methyl at 4-position at ring of quinoline. The route for synthesis with five steps was optimized, and the chemical structure and purity were fully characterized by FTIR, ¹H NMR, MS and elementary analysis.The impact of different substitutes on optical character of 4Me6FAlq₃ was studied. Its absorption and photoluminescence spectra was investigated both in solutions and in thin films. Compared to the unsubstituted Alq₃ and 6FAlq₃, it was found that the absorption and photoluminescence spectra of 4Me6FAlq₃ were blue-shifted by introducing the electron-pushing-drawing substitutes. The photoluminescence quantum yield of 4Me6FAlq₃ was high up to 2.94 (in case of Alq₃: 1). It could be explained that electron cloud distribution on the whole molecule was changed due to the fluorine atom at 6-position and the methyl group at 4-position.The energy band of 4Me6FAlq₃ was studied by cyclic voltammetry measurement, which tested the LUMO and HOMO energy levels as -2.82 eV and -6.18 eV, respectively. Band-gap of this derivative was wider than that of Alq₃,indicating the good results of tuning optical properties.The thermal stability and aggregate of of 4Me6FAlq₃ was studied. It was foundthat the thermal decomposition temperature was 356℃, a little bit lower than that of Alq₃(369℃) and 6FAlq₃(363℃). Its glass transition temperature was 162℃, and its maximum weight loss peak was located at 419℃. It was obvious that the thermal stability of 4Me6FAlq₃ was very good. Powder XRD results showed that 4Me6FAlq₃ was in a non-crystal structure, very favorable for OLED fabrication.