Description

The purpose of this chapter is the brief review of the fundamental study of porphyrin “theranostics” by DNA. Porphyrins have been studied as photosensitizer for photodynamic cancer therapy. The activity control of fluorescence emission and photosensitized singlet oxygen generation by porphyrins using the interaction with DNA is the initial step in achieving theranostics. To control these photochemical activities, several types of electron donor‒connecting porphyrins were designed and synthesized. The theoretical calculations speculated that the photoexcited state of these porphyrins can be deactivated via intramolecular electron transfer, forming a charge‒transfer state. The electrostatic interaction between the cationic porphyrin and DNA predicts a rise in the energy of the charge‒transfer state, leading to the inhibition of electron transfer quenching. Pyrene‒ and anthracene‒connecting porphyrins showed almost no fluorescence in an aqueous solution. Furthermore, these porphyrins could not photosensitize singlet oxygen generation. These porphyrins bind to a DNA groove through an electrostatic interaction, resulting in the increase of fluorescence intensity. The photosensitized singlet oxygen‒generation activity of DNA‒binding porphyrins could also be confirmed. On the other hand, several other porphyrins could not demonstrate the activity control properties. To realize effective activity control, a driving force of more than 0.3 eV is required for the porphyrins.

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