In this work, phthalonitrile (3) and zinc(II) phthalocyanine (4) were prepared. To determine the photodynamic therapy potential of compound 4, singlet oxygen quantum yield, DNA binding and cleavage, and topoisomerase I inhibition experiments were performed. The singlet oxygen quantum yield value of compound 4 was found higher than that of the standard unsubstituted zinc(II) phthalocyanine compound (Std-ZnPc). The binding experiments showed that compound 4 interacted with ct-DNA strongly via nonintercalation mode. pBR322 plasmid DNA cleavage activity of the compound was investigated using agarose gel electrophoresis. The results showed that the compound 4 had important DNA cleavage activity. The E. coli DNA topoisomerase I inhibition effects of compound 4 were investigated using agarose gel electrophoresis. Compound 4 had an E. coli topoisomerase I inhibitory effect at increasing concentrations. The results showed that compound 4 has photosensitizer potential in photodynamic therapy.