Indium complexes of chlorin e6 trimethyl ester and methylpyropheophorbide a: Synthesis and photophysical characterization

Complexes of chlorin e6 trimethyl ester (H(2)Chl-e(6),), methylpyropheophorbide a (H2MePyroPheo) with indium (III) (InChl-e(6), and InMePyroPheo) were obtained from the corresponding macrocyclic ligands by complexation reaction with InIII trisacetylacetonate in acetic acid. In the case of methylpheophorbide a (H2MePheo) the complexation reaction is accompanied by side-process of exo-cyclic ring oxidation leading to inseparable mixture of InMePheo, its 13(2)-hydroxy derivative and InMePyroPheo. Spectral-luminescence and photophysical properties of H(2)Chl-e(6) and H(2)MePyroPheo and their In-III complexes were studied in DMF. Metal free chlorins have relatively long fluorescence lifetimes ((sic)(f) 5.4-7.5 ns) and moderate fluorescence and singlet oxygen quantum yields (Phi(F) ~& nbsp;0.39 and 0.29, Phi(delta & nbsp;)~& nbsp;0.47 and 0.60, for H(2)Chl-e(6) and H(2)MePyroPheo, respectively). It was revealed that insertion of the indium atom into the macrocyclic core strongly diminishes the fluorescence lifetimes ((sic)(f) 0.5-0.9 ns) and quantum yields (Phi(F) ~& nbsp;0.04-0.06), but facilitates the conversion to the triplet state leading to enhanced singlet oxygen quantum yields. Therefore, InChl-e(6) and InMePyroPheo having intense Q-band absorption in the therapeutic window (638 and 661 nm) and high values of Phi(delta) (0.84 and 0.76) can be considered as promising photosensitizers for PDT.

Automated summary

In this study, complexes of chlorin e6 trimethyl ester and methylpyropheophorbide a with indium (III) were obtained and their photophysical properties were studied. It was found that insertion of the indium atom into the macrocyclic core decreased the fluorescence lifetimes and quantum yields, but facilitated the conversion to the triplet state. Therefore, these complexes can be considered as promising photosensitizers for photodynamic therapy.