Three naphthalimide (NI) derivatives (NIN, NIP, and NIO) as photosensitizers for the G-selective oxidation were synthesized, and the mechanism of the photosensitized one-electron oxidation of DNA by the NI derivatives was studied. NIN possessing a cationic side chain exhibited strong association with the olizodeoxynucleotides (ODNs) due to an electrostatic interaction between the phosphate groups of ODN and the cationic group of NIN, while no association was observed for NIP possessing an anionic side chain due to electrostatic repulsion among the phosphate groups. The DNA-binding properties of NIO with a neutral side chain were intermediate between those of NIN and NIP. The effects of the electrostatic interaction and repulsion between the NI derivatives and ODN and stacked G bases on the photosensitized one-electron oxidation of ODN were studied by the nanosecond transient absorption measurement and HPLC analysis. The yield of the NI derivatives in the triplet excited state ((NI)-N-3*) observed immediately after a 355-nm laser flash decreased with an increase in the binding constants, and almost no transient absorption was observed when NIN was used as a photosensitizer. This result indicates that rapid charge separation occurs between the NI in the singlet excited state ((1)Nl*) and the adjacent nucleobase, followed by a rapid charge recombination between the NI radical anion and the adjacent nucleobase radical cation when NIN is bound to ODN. Therefore, the sequence dependence of the one-electron oxidation of ODN was investigated using NIP, which does not bind to ODN. By monitoring the one-electron reduced form of NIP (NIP.-) produced by the electron transfer from ODN to (NIP)-N-3*, we found that the charge-separation efficiency increased with the sequence of sequential G's, such as GG and GGG, because of the oxidation potential of G decreased by the stacking effect of G's. To clarify the relationship between the formation of the transient intermediates observed during the LFP and actual amount of ODN oxidative damage, we performed the quantitative analysis of the ODN oxidative lesion caused by the NI derivatives using HPLC. With respect to the sequence of ODN, larger amounts of G consumed by the photosensitized one-electron oxidation were observed with ODN possessing multiple G, GG, and GGG compared to a single G. In contrast to the LFP experiments, a similar amount of oxidative damage was observed for three synthetic NI derivatives, indicating that the association of the NI derivatives to ODN apparently has no effect on the one-electron oxidative process. This might be due to the O-2 involved in the one-electron oxidation process. These results are discussed in the context of the concentration of 02 in the solution.