The S-1-S-0 fluorescence of tetrasulfonated aluminum phthalocyanine (AlPcS43-) is quenched by azaferrocene (AF) by both dynamic and static quenching, the last being due to the complexation of two molecules of AF by the phthalocyanine (presumably to its axial sites). Fluorescence quenching studies revealed that some other nitrogen ligands can cooperate with AF, giving nonfluorescent, mixed hexacoordinate adducts. This leads to "cooperative" static quenching observed for imidazole and 4-aminopyridine.