Tris-(8-hydroxyquinoline) aluminum (Alq(3)) 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. Alq(3) thin films were exposed to light for various time periods under normal ambient. The fluorescence of as-prepared and light exposed Alq(3) thin films and formation of luminescent quencher have been studied using fluorescence, Mass, MALDI-ToF-MS, H-1 & C-13 NMR, and FT-IR spectroscopy. It is observed that among the three 8-hydroxyquinoline (HQ) units in Alq(3) molecule, one HQ unit is affected during the light exposure in the normal ambient. It is found that the affected resultant Alq(3) molecule containing the carbonyl group acts as fluorescent quencher and the energy of excitons in the Alq(3) molecule in the light exposed Alq(3) thin films can be non-radiatively transferred to the neighboring fluorescent quencher, quenching the fluorescence of light exposed Alq(3) thin films in the normal ambient. (C) 2009 Elsevier B.V. All rights reserved.