Boosting the singlet oxygen photosensitization abilities of Zn(ii) phthalocyanines through functionalization with bulky fluorinated substituents

Abstract

In-depth, systematic photophysical studies have been performed on a series of ABAB, A₃B and A₄ ZnPcs functionalized with a varying number of bis(trifluoromethyl)phenyl units (i.e. at the B isoindoles) and other electron-withdrawing/electron-donating moieties (i.e. at the A isoindoles), to determine the influence of the susbtitution pattern on the aggregation features, fluorescence quantum yields and singlet oxygen (¹O₂) generation abilities of these molecules. As a general trend, the larger the number of bis(trifluoromethyl)phenyl units (i.e.ABAB crosswise functionalized ZnPcs), the lower the fluorescence quantum yield and the higher the ¹O₂ photosensitization. On the other hand, the electronic character of the substituents at the A isoindoles do not seem to have a clear effect on the photophysical properties of these ABAB ZnPcs. Overall, ¹O₂ quantum yields determined by the direct observation of the ¹O₂ phosphorescence are very high, with values ranging from 1 to 0.74 in THF solutions.