Fluorescence intensity traces of single dibenzoterrylene molecules in 2,3-dimethylnaphthalene crystals were studied at 270 K. It was found that these molecules are considerably more photo-stable than those of terrylene in the same crystal. Quantum-chemical calculations indicated that the creation of the reactive singlet oxygen state via the triplet state is not probable for dibenzoterrylene, in contrast to terrylene. This reaction provides the first step in typical hydrocarbon oxidation. Therefore, the lack of the triplet channel in the case of dibenzoterrylene, and its domination in the photo-oxidation of terrylene, may explain the different photo-stability of the two compounds. (C) 2010 Elsevier B.V. All rights reserved.