THE PHOTOPHYSICAL PROPERTIES OF A RUTHENIUM-SUBSTITUTED PHTHALOCYANINE

Laser flash photolysis, pulse radiolysis and time-resolved near-IR luminescence were used to study the photoproperties of a novel water-soluble metallophthalocyanine with no peripheral substitution. The phthalocyanine induces a significant reduction in tumour size or complete tumour eradication by photodynamic therapy (PDT). Yet, although this phthalocyanine sensitizes the production of singlet oxygen with a quantum yield of 0.3 in methanol, the quantum yield of singlet oxygen production in air-saturated D2O is less than 0.01 (the detection limit of our equipment). This is explained in terms of the combined effect of the triplet state lifetime of the phthalocyanine (1.2 mu s in nitrogen-saturated methanol and 0.65 mu s in nitrogen-saturated water) and the near tenfold reduction in the oxygen concentration from methanol to water. Therefore we propose that, in aqueous solution, a non-singlet-oxygen-mediated mechanism, probably electron transfer, prevails and leads to the observed PDT effect.