DESCRIPTION: (Applicant's Description) Phthalocyanines have much promise as photosensitizers for photodynamic therapy (PDT), a therapy applicable to cancer treatment. In particular, the silicon phthalocyanine Pc 4 has been shown to be highly effective both by work done in Projects 2 and 3 and Core D under the present grant, and by contract work done by others for the Drug Decision Network of NCI. This leads to the present application. The goal of one part of the work is to grow a crystal of Pc 4 which is suitable for structure determination and then to use it to determine the single-crystal X-ray structure of Pc 4. The goal of the second part of the work is to design, synthesize and characterize new photosensitizers for PDT that are highly effective or can be easily excreted. The photosensitizers to be made belong to four categories. These are: excretable Pc 4 analogues, phospholipid phthalocyanine photosensitizers, cationic aromatic amine phthalocyanine photosensitizers, and further Pc 4 and Pc 12 analogues. All of the photosensitizers contain phthalocyanine or phthalocyanine-like macrocycles. The goal of the third part of the research is to obtain basic information on the efficiency with which the new photosensitizers transduce photoenergy into the energy of chemically reactive species that can initiate photodamage. To achieve this objective, a series of photophysical and photochemical studies will be done on these compounds and on some the previously made ones. These studies will be focused mainly on members of various series of photosensitizers in which a single structural feature is changed stepwise, since it will be important to know if the changes in structure appreciably influence the photoproperties of the compounds.