Synthesis, photochemistry and photosensitizing properties of metallophthalocyanines bearing spiropyrrolizidine oxindoles

Interestingly, Pc derivatives are promising photosensitizing agents for photodynamic therapy (PDT) due to their intense absorption capabilities in the visible region. Animportant aim of research into the chemistry of phthalocyanines is to enhance their solubility in various solvents. A combination of two potentially promising units (i.e. phthalocyanines and spiropyrrolizidine oxindole groups) may improve their organosolubility and biological properties. Herein, we report the synthesis and characterization of several metallophthalocyanines bearing four spiropyrrolizidine oxindole groups which enable the molecules to dissolve in number of organic solvents such as DMF, DMSO and THF. The new metallophthalocyanines (M = Zn and Ni) bearing four spiropyrrolizidine oxindoles at peripheral positions were prepared by tetramerization of corresponding phthalonitriles. The singlet oxygen generation ability of the ZnPc was quantified as singlet oxygen quantum yields (ΦΔ) and was determined in DMF using 1,3-diphenylisobenzofuran (DPBF) as a chemical quencher. A continuous decrease in DPBF absorbance at 417 nm for phthalocyanine was monitored using a UV-Vis spectrophotometer within 30 min.