Intersystem crossing yields in anthanthrene and perylene from photosensitised peroxidation

The quantum yields of anthanthrene and perylene sensitised photoperoxidation of 9, 10-dimethyianthracene and 9,10-dimethyl-1, 2-benzanthracene have been measured as a function of dissolved oxygen concentration in benzene solution. An analysis of the data in terms of the O-2(1)Delta g intermediate provides intersystern crossing yields for anthanthrene (0.23 +/- 0.04) and perylene (0.06 +/- 0.06); together with the respective quantum yields of fluorescence of 0.73 +/- 0.05 and 0.89 +/- 0.05. these indicate that intenal conversion does not contribute significantly to the overall relaxation of the lowest excited singlet states of these molecules.