Organic electroluminescent devices having derivatives of aluminium-hydroxyquinoline complex as light emitting materials

Derivatives of aluminum-hydroxyquinoline complex were synthesized and used as light emitting materials for electroluminescent devices. The absorption and photo-luminescence spectra, and also the energy levels of the derivatives were shifted from those of the mother compound by electron-withdrawing and electron-releasing groups introduced into the hydroxyquinoline ligands. Using these compounds, the relationship between the electroluminescence efficiency and the energy levels was analyzed. The results strongly suggest that part of the injected electrons and holes recombine across the interface of the stacked organic layers, the process being non-emissive. It was also observed that the current-voltage curves shift toward the lower voltages as the electron accepting energy level of the light emitting material becomes lower.