A method of photodynamic therapy to treat diseased cells in an animal is generally provided. According to the method, 5-amino-2,2-dimethyl-6-[3′-(R,S)amino-4′-hydroxy-butan-1-one]-2,3-dihydro-4H-1-benzopyran-4-one or an analog thereof is administered to the animal such that the 5-amino-2,2-dimethyl-6-[3′-(R,S)amino-4′-hydroxy-butan-1-one]-2,3-dihydro-4H-1-benzopyran-4-one or an analog thereof accumulates in the diseased cells. Then, the diseased cells containing 5-amino-2,2-dimethyl-6-[3′-(R,S)amino-4′-hydroxy-butan-1-one]-2,3-dihydro-4H-1-benzopyran-4-one or an analog thereof is exposed to light energy (e.g., ultraviolet light).