The acid-base, spectroscopic, photophysical and liposome-binding properties of the recently synthesized free base, 29H,31H,1,4,8,11,15,18,22,25-octafluoro-2,3,9,10,16,17,23, 24-octakisperfluoro(isopropyl) phthalocyanine, F64PcH2, are reported. The perfluoroalkylation of the phthalocyanine core renders the hydrogen atoms acidic, with a pKa = 6. The F64Pc−2 dianion is detected already at pH 3, by singular-value decomposition analysis of electronic spectra. F64Pc−2 generates 1O2 with quantum yields ΦΔ = 0.252 (in MeOH) and 0.019 in liposomes. Metallation of the Pc macrocycle to yield F64PcZn increases ΦΔ to 0.606 and 0.126 in MeOH and liposomes, respectively. Surprisingly, F64Pc−2 (but not F64PcH2 or F64PcZn) binds strongly to liposomes, with a binding constant Kb = 25 (mg/mL)−1. The fully protonated F64PcH2, but not the zwitterionic F64Pc−2, might favor hydrogen bonding, thus reducing its lipophilicity. Similarly, the Lewis acidity of Zn in F64PcZn, and thus its ability to bind water within a hydrophobic perfluoroalkyl pocket, is significantly enhanced by the fluorinated substituents.
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Vol. 82 • No. 2