Spectroscopic insights on imidazole substituted phthalocyanine photosensitizers: Fluorescence properties, triplet state and singlet oxygen generation

摘要

Imidazole substituted metal phthalocyanine (Pc) complexes were synthesized. UV-vis absorption, steady state and time-resolved fluorescence, as well as laser flash photolysis were used to measure the photophysical and photosensitizing properties. All the imidazoleCphthalocyanine conjugates show high Φ_T (quantum yield of excited triplet formation), high Φ_? (singlet oxygen formation yield, >0.50) and good fluorescence properties (quantum yield Φ_f > 0.20 and lifetime τ_f > 3.0 ns). Compared to the unsubstituted Pc, both α- and β-imidazole substitutions result in the remarkable decrease in Φ_f and τ_f, but the a-substitution is stronger. The imidazole substitution, on the other hand, causes the increase of Φ_T, τ_T, and Φ_? values. Magnesium phthalocyanine (MgPc) is more susceptible to the substitution than zinc phthalocyanine (ZnPc). The mechanism responsible for the result is suggested based on the involvement of intramolecular photoinduced electron transfer. The high Φ_? and appropriate fluorescence properties make the Pcs good candidate for PDT photosensitizers.