Spectroscopic probing of the acid-base properties and photosensitization of a fluorinated phthalocyanine in organic solutions and liposomes

Hana Weitman, Smadar Schatz, Hugo E. Gottlieb, Nagao Kobayashi, Benjamin Ehrenberg

Research output: Contribution to journalArticlepeer-review

38 Citations (Scopus)

Abstract

A perfluorinated derivative of phthalocyanine was synthesized as the free base, hexadeca-(2,2,2-trifluoroethoxy) phthalocyanine (H2F48Pc), and as a zinc complex, hexadeca-(2,2,2-trifluoroethoxy)-phthalocyaninatozinc (ZnF48Pc), and their spectroscopic and photochemical properties were studied. The absorption bands are shifted bathochromically relative to simple phthalocyanines, exhibiting the longest wavelength band near 735 nm (H2F48Pc) and 705 (ZnF48Pc). The solvatochromism of both compounds was modeled by Reichardt's ET(30) parameter and Kamlet, Abboud and Taft multiparameter approach. The former, simpler, model was found to be adequate. We found that H2F48Pc undergoes unique basic and acidic titrations in organic solvents. These titration processes are accompanied by spectral changes that are explained on the basis of the chromophore's symmetry. Singular value decomposition was employed to resolve the spectra into the contributions of the species at various stages of protonation and to obtain the equilibrium constants. Nuclear magnetic resonance spectra (1H, 19F and 13C) for the free base were obtained in a tetrahydrofurand8 solution. The carbon spectrum, taken as a function of temperature, provided evidence for the presence of a tautomerization process, which switches the two internal hydrogens between the four central nitrogen atoms. As far as we know, this is the first report of the measurement of the free energy of activation for such process (ΔG† = 10.6-11.4 kcal mol-1 between 217 and 330 K) for a phthalocyanine, in solution. Like most other phthalocyanines these two compounds also act as photosensitizers and as generators of singlet molecular oxygen. The absolute quantum yields (ΦΔ) for ZnF48Pc was 0.58 ± 0.01 in benzene and 0.35 ± 0.01 in lipid vesicles. H2F48Pc had lower yields, 0.16 and 0.005, respectively. Either protonation or deprotonation of the pyrrole nitrogens in H2F48Pc low-ered the ΦΔ.

Original languageEnglish
Pages (from-to)473-481
Number of pages9
JournalPhotochemistry and Photobiology
Volume73
Issue number5
DOIs
Publication statusPublished - 2001 May

ASJC Scopus subject areas

  • Biochemistry
  • Physical and Theoretical Chemistry

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