Perfluoroalkylated anthracene endoperoxide: Synthesis, characterization, crystal structure analysis, and computational insights

Aromatic endoperoxides serve as important intermediate species toward generating singlet state oxygen, which is key to photodynamic therapy applications. Gaining insights for fine-tuning endoperoxide stability and degree of oxygen-oxygen bond activation is of fundamental and practical interest for the chemical and medicinal communities. We report here that 9,10-bisperfluorooctyl-anthracene, upon exposing to light and air, is almost quantitatively converted to 9,10-bisperfluorooctyl-anthracene endoperoxide (compound 1) at room temperature. H-1 NMR spectra and the X-ray crystal structure revealed that the resulting compound 1 is stable at room temperature without further decomposition. The crystal structure analysis showed that the compound 1 is stabilized by F center dot center dot center dot O intramolecular interactions along with F center dot center dot center dot F, F center dot center dot center dot H and F center dot center dot center dot C intermolecular interactions. DFT calculations further indicate that the degree of oxygen-oxygen bond activation in anthracene endoperoxides, reflected as changes of O-O, C-O bond distances, may not solely depend on the electronic effect of substituents at the 9,10- positions. This uncertainty warrants further investigation both experimentally and computationally.