The aim of this project is to measure the fluorescence quantum yields, fluorescence lifetime, triplet quantum yields an triplet lifetime for fifteen photosensitizers, and correlate these measurements with the comparative in vitro photoinactivation efficiency of these fifteen photosensitizers on PTK2 kangaroo rat epithelial kidney cells. The fifteen photosensitizers are: phthalocyanine (PC), its di and tetrasulfonate (PcDs, PcTs) derivatives, zinc metallated complex of Pc, PcDs, and PcTs; chloroaluminum phthalocyanine and its tetrasulfonate (CIAIPc, CIAIPcTs); naphthalocyanine (Npc), its zinc metallated complex (ZnNPc); methyl pheophorbide a (Mppb); mono-L-aspartyl chlorin e6 (MACE); tin etiopurpurine (SnEt); hematoporphyrin-IX (Hp), and Photofrin (Pll), a concentrated form of HpD. Photophysical measurements will take place in phosphate buffered saline (PBS) where possible, or in PBS-Cremophor for the chlorin derivatives. Photosensitizers will be introduced to PTK2 cells for twenty-four hours, exposed to light at the appropriate wavelength from a Nd-YAG laser, and the photokill efficiency of each complex assessed utilizing the trypan blue test for cell viability. This experiment seeks to provide a model for predicting the photokill efficiency of photosensitizers based on their photophysical properties.