Water-soluble bis(imidazolylporphyrin) self-assemblies with large two-photon absorption cross sections as potential agents for photodynamic therapy

Two water-soluble porphyrin self-assemblies consisting of bisacetylene- and monoacetylene-linked conjugated bis(imidazolyiporphyrin) have been synthesized. Two-photon absorption (2PA) cross section values in water were determined as 7500 GM for bisacetylene- and 7900 GM for monoacetylene-linked bisporphyrin by femtosecond open-aperture Z-scan measurement. These values were almost the same as those for the similar structure reported previously in CHCl3. Therefore, the structure is suggested to be similar in CHCl3 and aqueous solutions. Both compounds were found to efficiently generate sin-let oxygen upon one-photon irradiation in a manner similar to protoporphyrin, as demonstrated by the time-resolved luminescence measurement at the characteristic band of 1270 nm. Photocytotoxicities for HeLa cancer cells were examined and found to be as high as those of hematoporphyrin, demonstrating that these newly prepared compounds are potential candidates as 2PA-photodynamic therapy agents.