Magnesium Azaphthalocyanines: An Emerging Family of Excellent Red-Emitting Fluorophores

• Published in: Inorganic chemistry Vol. 51; no. 7; pp. 4215 - 4223
• Main Authors: Zimcik, Petr, Novakova, Veronika, Kopecky, Kamil, Miletin, Miroslav, Uslu Kobak, Rabia Zeynep, Svandrlikova, Eva, Váchová, Lenka, Lang, Kamil
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 02.04.2012
• Subjects: Fluorescence; Fluorescent Dyes - chemical synthesis; Furans - chemistry; Indoles - chemical synthesis; Magnesium - chemistry; Molecular Structure; Quantum Theory; Singlet Oxygen; Spectrometry, Fluorescence; Water - chemistry; Zinc - chemistry
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic2027016

Magnesium(II), zinc(II), and metal-free phthalocyanines (Pcs) and azaphthalocyanines (AzaPcs) containing alkylsulfanyl, aryloxy, and dialkylamino peripheral substituents have been synthesized. The complexation of magnesium(II) by metal-free Pcs and AzaPcs has been studied in detail to determine the optimal reaction conditions necessary to ensure a complete conversion. Photophysical and photochemical measurements in tetrahydrofuran showed that magnesium(II) AzaPcs with aryloxy and alkylsulfanyl substituents have excellent fluorescent properties (ΦF up to 0.73) and that the corresponding zinc(II) Pcs are efficient singlet oxygen producers (ΦΔ up to 0.68). The presence of dialkylamino substituents causes intramolecular charge transfer within the molecule that competes with fluorescence and singlet oxygen formation. Alkylsulfanyl MgAzaPc and ZnAzaPc were the most photostable compounds among the series of studied derivatives. In addition, high molar absorption coefficients (ε ∼ 300 000 M–1 cm–1), absorption (λmax ∼ 650 nm), and emission (λem ∼ 660 nm, high ΦF) in the red region suggest that these molecules are potential fluorescent probes that are superior to the commercial red cyanine dye Cy5. MgAzaPc, when incorporated into lipidic bilayers of liposomes, maintains excellent fluorescence properties (ΦF = 0.64). Water-soluble MgAzaPc with quaternary ammonium peripheral substituents retained a high fluorescence quantum yield even in water (ΦF = 0.25). The described properties show that magnesium(II) AzaPcs are excellent red-emitting fluorophores with potential applications as fluorescent probes in sensing or in vitro imaging applications.