Correlation between the efficiency of singlet oxygen generation and the luminescence parameters of photosensitizers

The quantum yield of interconversion to triplet states for free-base 2,3,7,8,12,13,17,18-octaethylporphyrin and 5,10,15,20-tetraphenylporphyrin, as well as of metallocomplexes with Mg(II), Zn(II), Pd(II), and Pt(II) ions, have been defined based on the data on the efficiency of photosensitized singlet oxygen generation. The quantum yields of singlet oxygen generation were measured for above mentioned compounds in different solvents. The maximum values of quantum yields of singlet oxygen generation are take place for compounds with heavy ions of Pd(II) and Pt(II) that due to intensification of internal heavy atom effect on intersystem crossing. The high quantum yields of singlet oxygen generation for case of free-base porphyrins indicate strong spin–orbit coupling in the absence of the internal heavy atom effect for these compounds. The specific features of the internal heavy atom effect on the triplet state deactivation rates for some porphyrins with Pd(II) and Pt(II) ions at room temperature and at 77 K were estimated.