The present invention provides a photodynamic therapy to a patient having at least one tumor comprising the steps of: administering a compound of formula 6 (wherein R1 and R2 are defined as the above) in a pharmaceutically acceptable carrier to the patient waiting for a sufficient time to allow the administered compound to be taken up by a target tissue having the at least one tumor and irradiating a region of the patient containing the target tissue, wherein growth of the tumor is inhibited.