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.