The effect of electron donating and withdrawing groups on the morphology and optical properties of Alq₃

By adding electron donating (EDG) and withdrawing groups (EWG) to the Tris-(8-hydroxyquinoline) aluminum (Alq₃) molecule, the emission color can be tuned. In this study the effect of EDG and EWG on the morphology and optical properties of Alq₃ were investigated. Alq₃ powders was synthesized with an EDG (-CH₃) substituted at positions 5 and 7 ((5,7-dimethyl-8-hydroxyquinoline) aluminum) and EWG (-Cl) at position 5 ((5-chloro-8-hydroxyquinoline) aluminum). A broad absorption band at ~380 nm was observed for Alq₃. The bands of the substituted samples were red-shifted. The un-substituted Alq₃ showed a high intensity emission peak at 500 nm. The -Cl and -CH₃ samples showed a red-shift of 33 and 56 nm respectively. The morphology of the samples was studied using a scanning electron microscope. The photo degradation of the samples was also investigated and the dimethyl sample shows the least degradation to the UV irradiation over the 24 h of continuous irradiation.