The Excitation Spectra of Singlet Oxygen and Photoluminescence of Methyl Pheophorbide-a

Abstract

The correlation between the photoluminescence intensity of a dye-sensitizer (methyl pheophorbide-a, MPP-a) and the efficiency of the singlet oxygen ( 1 𝑂2) generation is studied. The excitation spectrum of 1 𝑂2 emission at 1270 nm has one strong band at 403 nm that coincides with the Soret band of MPP-a and only a weak peak at 667 nm, which practically coincides with the strongest band of the MPP-a excitation spectrum. Therefore, the choice of an excitation wavelength for the efficient 1 𝑂2 generation should be based on direct measurements of the excitation spectra of the sensitized 1 𝑂2 emission. K e y w o r d s: singlet oxygen, photodynamic therapy, photosensitization, dye sensitizer, methyl pheophorbide-a.

Wavelength dependence of the efficiency of singlet oxygen generation upon photoexcitation of photosensitizers

“…The experimental data allows to conclude that the efficiency of singlet oxygen generation in the case of Pd-TPP photosensitizer is significantly higher for excitation in the Soret band (λexc.= 417 nm) than for excitation in the visible region of the spectrum -Q band (λexc.=562 nm). Previously, the similar behavior of excitation spectra of singlet oxygen luminescence measured in spectral range of absorption of photosensitizer were reported in [3,4] for other porphyrin derivatives, but the origin of this effect was not well explained.…”