Photooxidation of Benzo[ de ]naphtho[2,1,8,7- stuv ]anthra[2,1,9,8- hijkl ]pentacene

This article describes the photooxidation of benzo de ]naphtho-2,1,8,7- stuv ]anthra2,1,9,8- hijkl ]pentacene (BNAP) synthesized by the condensation of naphthanthrone with zinc dust. When an o -dichlorobenzene solution of BNAP was irradiated with light of its maximum absorption wavelength (535 nm), the original absorption band was reduced and a new band appeared at longer wavelengths showing a peak at 606 nm. Excitation of the photobleached sample with 600 nm gave rise to fluorescence on the red side of that of BNAP by about 90 nm. The new fluorescence spectrum showed a vibrational progression of about 1,600 cm m 1 , which corresponds to the stretching of a carbonyl group. No spectral changes occurred in degassed solution. These findings suggest that BNAP reacts with singlet oxygen to form a ketone. Molecular orbital calculations revealed that the carbonyl group of the product is located at the C-18 position and that a hydroxy group is also present at the C-2 position; therefore the product is predicted as 2,18-dihydrobenzo de ]-naphtho2,1,8,7- stuv ]anthra2,1,9,8- hijkl ]pentacen-18-one.