A series of novel cationic purpurinimides which had long wavelength absorption were designed and synthesized using purpurin-18-N-aminoimides as starting materials. They demonstrated a considerable bathochromic shift of the major absorption band in the red region of the optical spectrum (705.8-718.9nm). Newly synthesized purpurinimides were screened for their antitumor activities, and showed enhanced PDT efficiency in A549 cells as compared to purpurin-18-N-aminoimide. The results showed the novel cationic purpurinimides could be considered a promising photosensitizer in photodynamic therapy.