Synthesis And Properties Of Fluoro (8 - Hydroxyquinoline) Aluminum

Five substituted aluminum tris(8-hydroxyquinoline) (Alq₃) derivatives were synthesized by brief Skraup reaction: tris-(n-fluoro-8-hydroxyquinoline) aluminum (nFAlq₃, n=5, 6, 7 and 6,7), The chemical structure and purity were fully characterized by ¹H NMR, MS and elementary analysis.The absorption and photoluminescence spectra of these substituted Alq₃ derivatives were investigated both in solutions and in thin films. It was found that the absorption and photoluminescence spectra could be tailored by changing the substituted position of the fluorine atoms. Compared to the unsubstituted Alq₃, the absorption and emission peaks of 5FAlq₃ in solution were red-shifted, and the quantum efficiency declined greatly; while the absorption and emission peaks of 6FAlq3 were blue-shifted, and the quantum efficiency increased greatly; 7FAlq3 was on the other hand kept similar to Alq₃. The quantum efficiency of these Alq₃ derivatives was changed by using different organic solvents. The absorption and photoluminescence spectra in thin films were similar to those in solutions with a few nanometers red-shift due to the intermolecular interaction.The energy band structure of these Alq₃ derivatives were determined by cyclic voltammetry measurements. Their electron cloud distribution were also calculated by quantum simulation. It was found that the electron cloud distribution of Alq₃ compound was greatly changed by introducing the fluorine atom at different position. The F group at C-5 position took part in the forming of the HOMO of Alq₃ through conjugation effect, giving rise to the higher HOMO level of 5FAlq3. It might enhance the coupling interaction between the metal Al and ligands, and provide additional paths for non-radioactive decay. The photoluminescence quantum yield of 5FAlq3 thus declined greatly. The light-sound exchange experiment confirmed the existence of the non-radiation energy loss in these fluorinated Alq₃ derivatives, which varied with the different position of fluorination.The surface morphology of fluorinated Alq3 derivatives in thin film was investigated by SEM and AFM images, which indicated amorphous form to all of the Alq3 derivatives, even at elevated temperatures. The XRD results also revealed that the thin films were non-crystalline. The results suggest that fluorination has no effect on the morphology of Alq3 derivatives, which is good to electroluminescence.The preliminary OLED properties of these fluorinated Alq3 derivatives were investigated, which were not satisfied and need to be optimized. However, the results confirmed that introducing the fluorine atoms at different positions indeed could tune the optical properties of Alq3 compound.