Studies on influence of light on fluorescence of Tris-(8-hydroxyquinoline)aluminum thin films

Tris-(8-hydroxyquinoline)aluminum (Alq3) thin films, the most widely used electron transport/emissive material in the organic electroluminescent (EL) devices, have been deposited on glass substrates by thermal evaporation process. Alq3 thin films were exposed to light for various time periods under normal ambient. The fluorescence of as-prepared and light exposed Alq3 thin films and formation of luminescent quencher have been studied using fluorescence, Mass, MALDI-ToF-MS, 1H & 13C NMR, and FT-IR spectroscopy. It is observed that among the three 8-hydroxyquinoline (HQ) units in Alq3 molecule, one HQ unit is affected during the light exposure in the normal ambient. It is found that the affected resultant Alq3 molecule containing the carbonyl group acts as fluorescent quencher and the energy of excitons in the Alq3 molecule in the light exposed Alq3 thin films can be non-radiatively transferred to the neighboring fluorescent quencher, quenching the fluorescence of light exposed Alq3 thin films in the normal ambient.