Novel families of phthalocyanine-like macrocycles—Porphyrazines with annulated strongly electron-withdrawing 1,2,5-thia/selenodiazole rings

Tetrakis(thiadiazole)porphyrazines and tetrakis(selenodiazole)porphyrazines, first described in the years 1998–2001, have later attracted the attention of different scientific groups in the world. Since the beginning and in the most recent times, a number of aspects concerning their relevance as phthalocyanine-like macrocycles, their distinct structural, electronic and UV–visible spectroscopic features, and electrochemical behavior have brought to knowledge the important role played by the externally annulated electron-withdrawing thia- and selenodiazole rings. Much has been learned about the acid–base properties of the new macrocycles, their facile electron uptake and negative charge redistribution capability within the entire macrocyclic framework. Further work has been directed to the synthesis and characterization of several low-symmetry species carrying peripherally annulated benzene or substituted benzene rings and thia- or selenodiazole rings and the structural and electronic effects caused by the progressive annulation of the heterocyclic rings in a basic phthalocyanine structure has been examined. Deselenation processes at the annulated selenodiazole rings in symmetrical and low-symmetry macrocycles and the formation of vicinal diamino functionalities have allowed diversified derivatization procedures with formation of new porphyrazine macrocycles by ring reclosure or designed external sites for exocyclic metalation in dinuclear species.