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 imidazole–phthalocyanine conjugates show high Φ T (quantum yield of excited triplet formation), high Φ Δ (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 α-substitution is stronger. The imidazole substitution, on the other hand, causes the increase of Φ T , τ T , and Φ Δ 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 Δ and appropriate fluorescence properties make the Pcs good candidate for PDT photosensitizers.