Production of singlet molecular oxygen from the oxygen quenching of the lowest excited singlet state of aromatic molecules in n-hexane solution

The quantum yield of sensitized photoperoxidation of 2,5-dimethylfuran in oxygen-saturated n-hexane solution has been measured. The sensitizers used were 9-methylanthracene, 9-phenylanthracene, 9,10-dimethylanthracene, 9,10-diphenylanthracene, perylene, pyrene, 1,6-diphenylhexatriene, and rubrene, and the sensitized oxidation quantum yields were found to be 0.97, 1.09, 1.14, 1.20, 1.27, 0.79, 1.02, and 1.20, respectively. The experimental results indicate that singlet molecular oxygen can be produced directly from the oxygen quenching of the lowest excited singlet state of many aromatic molecules, i.e., the process S/sub 1/ + /sup 3/O/sub 2/ ..-->.. T/sub 1/ + /sup 1/O/sub 2/ is not negligible when compared to S/sub 1/ + /sup 3/O/sub 2/ ..-->.. T/sub 1/ + /sup 3/O/sub 2/. This shows that the former process must also be taken into consideration in the general treatment of oxygen quenching of the fluorescence from aromatic molecules.