Synthesis, Photophysical Properties, and Toxicity of o-Xylene-Bridged Porphyrin Dimers

In this work, a number of new porphyrin dimers coupled with spacers based on alpha,alpha'-dibromo-o-xylene were synthesized and characterized by H-1, C-13 NMR, H-1-H-1 COSY NMR, UV-vis-spectroscopy, and MALDI-TOF mass spectrometry. The initial A3B-type hydroxy-substituted porphyrins form dimer structures with high yields of 80-85%, while the use of amino-substituted porphyrins as starting compounds leads to the heterocyclization and formation of N-heterocycle fused porphyrins. For porphyrin dimers, photophysical properties and quantum yields of singlet oxygen were investigated. The peripheral alkoxy-substituents increase fluorescence quantum yield in comparison with the unsubstituted compounds. Also, it was found that dimers are characterized by lower singlet oxygen quantum yields compared to the corresponding monomers. Model aggregation experiments in micellar systems demonstrate stabilization of the photoactive monomolecular form of all the porphyrins, using nonionic surfactant Triton X-100. Cytotoxicity of received dimers shows high inhibition against HEK293T cells in the absence of light.