Comparison of photophysicochemical properties of hexaphenoxycyclotriphosphazenyl-substituted metal-free, mono- and bis-lutetium phthalocyanines

The aim of this study is to compare the photophysicochemical properties of hexaphenoxycyclotriphosphazenyl-substituted metal-free (1), mono-(phthalocyaninato) lutetium(III) (2) [LuIII(AcO)(Pc)] (Pc = phthalocyaninato, AcO = acetate) and bis-(phthalocyaninato) lutetium(III) (3) [LuIIIPc2]. The synthesis and characterization (using the elemental analysis, mass spectrometry, IR, 1H, and 31P NMR and UV–vis spectroscopy) of new compounds (2, 3) are described in this study. The electronic absorption and fluorescence spectral properties of compounds 1–3 are investigated. Photophysical (fluorescence quantum yields and lifetimes) and photochemical (singlet oxygen and photodegradation quantum yields) measurements are also studied on hexaphenoxycyclotriphosphazenyl-appended metal-free, mono- and bis-lutetium phthalocyanines in dimethylsulfoxide (DMSO). Photophysical and photochemical properties of phthalocyanines are very useful for photodynamic therapy (PDT) applications. Singlet oxygen quantum yields (ΦΔ) give an indication of the potential of the complexes as photosensitizers in PDT applications. Hexaphenoxycyclotriphosphazenyl-substituted mono-(phthalocyaninato) lutetium(III) complex (2) gave good singlet oxygen quantum yield (0.66) in DMSO. Thus, this complex shows potential as Type II photosensitizer for PDT of cancer.