Newly synthesized zinc phthalocyanine bearing sixteen quaternized imidazolyl moieties on the periphery displays high water-solubility, lack of aggregation and high singlet oxygen quantum yield in water (Φ_Δ > 0.33). The in vitro tests indicated excellent anticancer photodynamic activity (EC₅₀ = 36.7 nM) and low dark toxicity to non-cancerous cells (TC₅₀ = 395 μM).