Excitation migration from photoexcited tris(8-hydroxyquinolino)aluminium to quinacridone in codeposited thin films

Absorption, fluorescence, and time-resolved fluorescence measurements have been carried out to demonstrate the energy transfer from photoexcited tris(8-hydroxyquinolino)aluminium (ALQ) to quinacridone (QA) in codeposited thin films. All the results indicate that the excitation energy is transferred from ALQ to QA, which distribute randomly in three dimensions in the thin films, by the Forster mechanism. From the analyses of the fluorescence decay of ALQ, the critical distance for the energy transfer between ALQ and QA molecules is determined to be 26 Angstrom. This value is in good agreement with that calculated from the fluorescence spectra of ALQ, the absorption spectra of QA, and the fluorescence quantum efficiency of ALQ. This agreement also indicates that energy migration among ALQ molecules is not an efficient process.