Electrochemical Degradation of Alq3 and Hq

FIGURE 3.6. Preliminary oxidation kinetics heating chlorobenzene solutions of Hq in various conditions. Basic solutions of Hq oxidize most quickly. Similar behavior is observed for Alq3. 

The generation of a new peak not associated with either Alq3 or oxygen is indicative of the formation of a new chemical species. The mechanism of this reaction is based on the nucleophilic character of the superoxide ion toward metal ions and organic compounds.47 The neutral species shows no sensitivity to superoxide, but upon reduction, the chelate bonds are weakened enough to allow attack by the base 

The first reduction of Hq in oxygen-free solvent is observed in the cyclic voltam-mogram as a broad peak beginning at approximately — 1.7 V in DMF and ending at about —2.4 V (Fig. 3.8A).18 On the anodic wave, oxidation peaks at —1.3 V and then at —0.4 V are observed. When oxygen is present, the peak at —0.4 V can be observed as soon as the formation of superoxide occurs (Fig. 3.8C). When Hq is reduced, it simultaneously eliminates hydrogen to form oxyquinolate anions 

FIGURE 3.9. Absorbance of extracted oxidation products compared to the fluorescence of Alq3. There is significant overlap of the spectra. 

FIGURE 3.10. Resonant form of q. This anion is susceptible to oxidation at the 5-position to form quinones. 

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