In conclusion, although the transition metal azahemiporphycenes studies have proved nonemissive, they vary widely in terms of their ability to sensitize singlet oxygen. Thus, Pd[Me-AHP] was found to exhibit a singlet oxygen quantum yield of 84%, while the corresponding value for Pt[Me-AHP] is 11%. In contrast, Mn[Me-AHP] does not sensitize singlet oxygen at all.