The excellent performance of Pd[Me-AHP] could be rationalized via transient absorption spectroscopy, which revealed substantial population of the triplet state, while such populations were found to be much lower and essentially zero for Pt and Mn, respectively. By virtue of their strong absorption in the red and high singlet oxygen-sensitizing ability, palladium azahemiporphycenes appear to exhibit considerable promise as a new class of triplet photosensitizers for photodynamic therapy.