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Solubilization of Hydrophobic Zinc Phthalocyanine Derivatives-Spectral and Photophysicochemical Consequences

Abimbola Ogunsipe and Uduak Aletan

Methods of solubilizing some hitherto insoluble zinc phthalocyanine derivatives (unsubstituted zinc phtalocyanine, ZnPc, zinc tetra-t-butylphenoxyphthalocyanine, ZnTBPc, zinc tetranitophthalocyanine, ZnTNPc and zinc naphthalocyanine, ZnNPc) are presented. The spectral and photophysico-chemical changes accompanying the solubilization are also discussed. The identified methods are (i) ring sulphonation and (ii) cyclodextrin encapsulation. The cyclodextrins employed were hydroxypropyl-γ- cyclodextrin and unsubstituted β-cyclodextrin. The formation of the inclusion complexes was confirmed by proton nuclear magnetic resonance spectroscopy and X-ray powder diffraction patterns. Job’s plots were employed to confirm the stoichiometry of the inclusion complexes and showed 2:1 and 4:1 (cyclodextrin:phthalocyanine) inclusion behaviour. Sulphonation of the complexes was attended by spectral red-shifting, while cyclodextrin inclusion brought about no noticeable spectral shifts. The solubilized complexes gave higher singlet oxygen quantum yields than their insoluble counterparts, but are less susceptible to photodegradation as depicted in the former’s lower photodegradation quantum yield values. Sulphonation of ZnPc resulted in increase in triplet state and singlet oxygen yields. Fluorescence quantum yield values were hardly affected by cyclodextrin encapsulation, while the sulphonated derivatives are less fluorescent.