Singlet oxygen generating activity of an electron donor connecting porphyrin photosensitizer can be controlled by DNA.

To control the activity of singlet oxygen ((1)O2) generation by photosensitizer through interaction with DNA, the electron- donor-connecting water-soluble porphyrin, meso-(9-anthryl)tris(N-methyl-p-pyridinio)porphyrin (AnTMPyP), was designed and synthesized. Molecular orbital calculation speculated that the photoexcited state of AnTMPyP can be deactivated via intramolecular electron transfer from the anthracene moiety to the porphyrin moiety, forming a charge-transfer (CT) state. The electrostatic interaction between the cationic porphyrin and anionic DNA predicts a rise in the CT state energy, leading to the inhibition of the electron transfer quenching. AnTMPyP showed almost no fluorescence in an aqueous solution, and the fluorescence lifetime was very short (<0.04 ns). Furthermore, this porphyrin did not demonstrate (1)O2 generating activity under photoirradiation. The fluorescence intensity and lifetime of AnTMPyP were markedly increased in the presence of DNA. The photosensitized (1)O2 generation by this porphyrin was also enhanced through interaction with DNA. The estimated quantum yield of (1)O2 generation by AnTMPyP interacting with DNA without guanine sequence was 0.22. The molecular design to control the photosensitized (1)O2 generation is possible based on the regulation of electron transition and steric hindrance of photosensitizing molecule.