Resonance energy transfer and competing processes in donor-acceptor of sodium zinc (II)-2,9,16,23-phthalocyanine tetracarboxylate molecule.

An important issue that should be taken into consideration when applying the molecules in photodynamic therapy (PDT) of cancer is the occurrence of homo-resonance energy transfer process between them. We have determined the probability of energy transfer for sodium zinc (II)-2,9,16,23-phthalocyanine tetracarboxylate (ZnPc(COONa)4) molecules in aqueous NaOH solution. The homo-quenching effect of the molecule was also measured by calculating the diffusion controlled bimolecular rate constant of k q = 6.5 × 10(9) M(-1)s(-1), which did not show a significant competition with the rate constant of homo-resonance energy transfer process at the applied concentration of the molecules (6 μM). The Förster radius (R  0) for ZnPc(COONa)4 molecules was calculated to be 42 Å. The availability of these calculations should facilitate the potential application of ZnPc(COONa)4 molecule as an anticancer drug in PDT.