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To examine the microenvironmental effect of DNA on the photosensitized reaction, the electron-donor-connecting porphyrin, meso-(9-phenanthryl)-tris(N-methyl-p- pyridinio)porphyrin (Phen-TMPyP), was synthesized. Phen-TMPyP can bind to oligonucleotides with two binding modes, depending on the DNA concentration. The fluorescence lifetime measurement of Phen-TMPyP shows a shorter component than that of the reference porphyrin without the phenanthryl moiety. However, the observed value is much longer than those of previously reported similar types of electron-donor-connecting porphyrins, suggesting that electron- transfer quenching by the phenanthryl moiety is not sufficient. The fluorescence quantum yield of Phen-TMPyP (5 μM) decreased with an increase in DNA concentration of up to 5 μM base pair (bp), possibly due to self-quenching through an aggregation along the DNA strand, increased with an increase in DNA concentration of more than 5 μM bp and reached a plateau. The fluorescence quantum yield of Phen-TMPyP with a sufficient concentration of DNA was larger than that of the reference porphyrin. The singlet oxygen ( 1 O2) generating activity of Phen-TMPyP was confirmed by the near- infrared emission spectrum measurement. The quantum yield of 1 O2 generation was decreased by a relatively small concentration of DNA, possibly due to the aggregation of Phen-TMPyP, and recovered with a sufficient concentration of DNA. The recovered quantum yield was rather smaller than that without DNA, indicating the quenching of 1 O 2 by DNA. These results show that a DNA strand can stabilize the photoexcited state of a photosensitizer and, in a certain case, suppresses the 1 O2 generation.

rapid communication in photoscience

Relaxation Process of the Photoexcited State and Singlet Oxygen Generating Activity of Water-soluble meso-Phenanthrylporphyrin in a DNA Microenvironment