Porphyrazines, or tetraazaporphyrins, are tetrapyrrole macrocycles similar to porphyrins and . Pioneered by Patrick Linstead as an extension of his work on phthalocyanines,Cook, A. H.; Linstead, R. P., "Phthalocyanines. XI. The preparation of octaphenylporphyrazines from diphenylmaleinitrile." J. Chem. Soc. 1937, 929-933. DOI: 10.1039/JR9370000929 porphyrazines differ from porphyrins in that they contain -meso nitrogen atoms, rather than carbon atoms, and differ from phthalocyanines in that their β-pyrrole positions are open for substitution. An extension of the aromatic core of porphyrazines, by adding pyrazine groups, can allow the formation of another class of analogs, called tetrapyrazinoporphyrazines. These differences confer physical properties that are distinct from both porphyrins and phthalocyanines.Ghosh, A.; Fitzgerald, J.; Gassman, P.G.; Almof, J. Inorg. Chem., 1994, 33, 6057-6060. DOI: 10.1021/ic00104a014
Porphyrazines exhibit fluorescence from the first excited singlet state (S1 → S0)Shushkevich, I.K.; Pershukevich, P.P.; Stupak, A.P.; Solov'ev, K.N.; Journal of Applied Spectroscopy, 2005, 72, 767-770. at visible and NIR wavelengths which is typical of tetrapyrrole macrocycles. Dual-emission from organic fluorophores is not common but, as observed in phthalocyanines,Chahraoui, D., Valat, P., and Kossanyi, J., Fluorescence of Phthalocyanines: Emission from an Upper Excited State. Res. Chem. Intermed., 1992, 17, 219-232.Kaneko, Y., Nishimura, Y., Takane, N., Arai, T., Sakuragi, H., Kobayashi, N., Matsunaga, D., Pac, C., and Tokumaru, K., Violet emission observed from phthalocyanines. J. Photochem. Photobiol. A, 1997, 106, 177-183. violet emission from an upper excited state (S2 → S0) is observed in porphyrazines.Lee, S., White, A.J.P., Williams, D.J., Barrett, A.G.M., and Hoffman, B.M. Synthesis of Near-IR Absorbing/Emitting Porphyrazine Derivatives with Tunable Solubility. J. Org. Chem., 2001, 66, 461-465.Lee, S.; Stackow, R.; Foote, C.S.; Barrett, A.G.M.; Hoffman, B.M.; Tuning the Singlet Oxygen Quantum Yield of Near-IR-absorbing Porphyrazines. Photochem. Photobio., 2003, 77, 18-21.Trivedi, E.R., Vesper, B.J., Weitman, H., Ehrenberg, B., Barrett, A.G.M., Radosevich, J.A., and Hoffman, B.M., Chiral bis-Acetal Porphyrazines as Near-infrared Optical Agents for Detection and Treatment of Cancer. Photochem. Photobio., 2010, 86, 410-417.
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