1,2,5-chalcogenadiazole-annulated tripyrazinoporphyrazines: Synthesis, spectral characteristics, and influence of the heavy atom effect on their photophysical properties

A series of low-symmetry ZnII, MgII, and metal-free porphyrazine derivatives with one 1,2,5-chalcogenadiazole ring (with S, Se or Te) and three pyrazines bearing tert-butylsulfanyls were synthesized. The absorption maxima of ZnII complexes lay at 660, 674, and 707 nm for S, Se, and Te, respectively, indicating increasing contribution of the 1,2,5-chalcogenadiazole rings to the π-electronic system. Photophysical studies revealed that introduction of Se as a chalcogen and ZnII as a central metal causes an increase in the singlet oxygen quantum yield, reaching a value of 0.81, whereas the combination of S and MgII gives only 0.39. This takes place on the account of the fluorescence quantum yields that differ significantly from 0.072 (ZnII+Se) to 0.51 (MgII+S). These results demonstrated the two-dimensional heavy atom effect combining the role of the chalcogen (first dimension) as well as the central metal (second dimension). Attempts to prepare oxygen-containing isologues led to the formation of an unexpected side product.