Enhanced acidity, photophysical properties and liposome binding of perfluoroalkylated phthalocyanines lacking C-H bonds

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 pK(a) = 6. The F64Pc-2 dianion is detected already at pH 3, by singular-value decomposition analysis of electronic spectra. F64Pc-2 generates O-1(2) with quantum yields Phi(Delta) = 0.252 (in MeOH) and 0.019 in liposomes. Metallation of the Pc macrocycle to yield F64PCZn increases Phi(Delta) to 0.606 and 0.126 in MeOH and liposornes, respectively. Surprisingly, F64Pc-2 (but not F64PcH2 or F64PCZn) binds strongly to liposomes, with a binding constant K-b = 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 perfluoroalkyll pocket, is significantly enhanced by the fluorinated substituents.