Noemí Rubio

A comparison between the photophysical and photosensitising properties of tetraphenyl porphycenes and porphyrins

The photophysical properties of 2,7,12,17-tetraphenylporphycene (TPPo) and its palladium(II) (PdTPPo) and copper(II) (CuTPPo) complexes as well as comparisons with those of their porphyrin counterparts are reported. All porphycenes absorb in the red part of the spectrum, but only TPPo shows fluorescence (ΦF = 0.15). This compound presents good quantum yields of triplet (ΦT = 0.33) and singlet oxygen (ΦΔ = 0.23) formation. In the case of PdTPPo, fluorescence is inhibited by the internal heavy-atom effect and the triplet and singlet oxygen quantum yields are enhanced (ΦT = ΦΔ = 0.78). The presence of the paramagnetic ion Cu(II) in CuTPPo further enhances the non-radiative transitions leading to an internal conversion quantum yield Φic = 0.65 and to a triplet quantum yield ΦT = 0.35. With a triplet lifetime of 700 ns, CuTPPo is nevertheless able to sensitise singlet oxygen with a quantum yield that strongly depends on the oxygen concentration in the environment. These photophysical properties, together with their ability to kill several cancer cell lines, place these sensitisers in a good position to be used in photodynamic therapy (PDT).

Asymmetric porphycenes: synthesis and photophysical properties of 9-substituted 2,7,12,17-tetraphenylporphycenes

The effects of 9-substitution on the photophysical properties of tetraphenylporphycenes (TPPo) have been examined using an electron acceptor, an electron donor, and an electroneutral substituent as model compounds. Introduction of the acetoxy group enhances the fluorescence ability of the compound, with only a small reduction in the singlet oxygen quantum yield. The optical and photophysical properties of a nitro-porphycene are reported for the first time. The compound is emerald green, contrasting with the typical blue color of porphycenes. While this compound is much less fluorescent than unsubstituted TPPo, its singlet oxygen quantum yield is only slightly lower, almost identical to that of the 9-acetoxy compound (9-AcOTPPo). Finally, the electron-donor amino group is found to induce the greatest changes in the porphycene photophysics, decreasing strongly its fluorescence and singlet oxygen quantum yields. With the exception of such electron donors, introduction of substituents at the 9 (meso) position of tetraphenylporphycenes is not detrimental to their photophysics and photosensitizing ability and thus can be exploited for targeted photodynamic therapy purposes.

Ground- and excited-state interactions of 2,7,12,17-tetraphenylporphycene with model target biomolecules for type-I photodynamic therapy

Biosubstrate-sensitizer binding is one of the factors that enhances the type-I mechanism over the type-II in the whole photodynamic process. 2,7,12,17-Tetraphenylporphycene (TPPo), a second-generation photosensitizer, is a hydrophobic compound with good photophysical properties for photodynamic therapy applications that has proved its ability for the photoinactivation of different cell lines. Nevertheless, little is known about its mechanism of action. This paper focuses on the study of the interaction/binding of TPPo with different model biomolecules that may favor the type-I mechanism in the overall photodynamic process, including nucleosides, proteins, and phospholipids. Compared with more hydrophilic photosensitizers, it is concluded that TPPo is more likely to undergo type-II (singlet oxygen) than type-I (electron transfer) photodynamic processes in biological environments.