Tetrakis(thiadiazole)porphyrazines. 8. Singlet oxygen production, fluorescence response and liposomal incorporation of tetrakis(thiadiazole) porphyrazine macrocycles [TTDPzM] (M = MgII(H2 O), ZnII, AlIIICl, GaIIICl, CdII, CuII, 2HI)

The photoactivity for the generation of singlet oxygen, 1O 2, the key cytotoxic agent in the anticancer treatment known as photodynamic therapy (PDT), and the fluorescence response of the highly electron-deficient tetrakis(thiadiazole)porphyrazines of formula [TTDPzM] (M = Mg II(H 2O), Zn II, Al IIICl, Ga IIICl, Cd II, Cu II, 2H I) were examined (c ≅ 10 -5 M) in dimethylformamide (DMF) and/or in DMF preacidified with HCl (DMF/HCl; [HCl] = 1-4 × 10 -4 M). The singlet oxygen quantum yield (Φ Δ) of all the compounds was determined by using a widely employed procedure based on the selective oxidation of the 1,3-diphenylisobenzofuran (DPBF), modified in part as reported. The list of the Φ Δ values indicates excellent photosensitizing properties for the series of compounds carrying "closed shell" metal ions, with values measured in DMF/HCl respectful of the "heavy atom effect" for the first four lighter centers, increasing in the order Mg II < Al III < Zn II < Ga III. Data of Φ Δ concerning the unmetalated species [TTDPzH 2], present in solution in the form of the corresponding anion [TTDPz] 2-, and the Cd II and Cu II complexes are also presented and discussed. Extensive discussion is also developed on the fluorescence quantum yield values Φ F, with data on the Mg II and Al III compounds in DMF/HCl (0.44 and 0.53, respectively) indicative of promising perspectives for applications in fluorescence imaging techniques. The Φ F data of the studied porphyrazine series, Φ F Pz, correlate linearly with those of the homologous phthalocyaninato complexes, Φ F Pc, suggesting a closely similar behaviour between the two classes of compounds. The incorporation of [TTDPzZn] into liposomes was successfully achieved following the detergent depletion method (DDM) from a mixed micellar solution by means of gel-filtration. Retention of [TTDPzZn] (∼40%) in its photoactive monomeric form into liposomes is proved by absorption and fluorescence spectra, this proposing the Zn II complex as a promising candidate for use in PDT. © 2012 The Royal Society of Chemistry.