Texaphyrin metal complexes having improved functionalization including the addition of electron donating groups to positions 12, 15, 18 and/or 21 and/or the addition of electron withdrawing groups to positions 15 or 18 of the macrocycle. Electron donating groups at positions 12, 15, 18 and/or 21 contribute electrons to the aromatic .pi. system of the macrocycle which stabilizes the metal complex to demetallation and the imine bonds to hydrolysis, these texaphyrin metal complexes having enhanced stability are useful for localization, magnetic resonance imaging, radiosensitization, radiation therapy, fluorescence imaging, photodynamic tumor therapy and applications requiring singlet oxygen production for cytotoxicity. Electron withdrawing groups at positions 15 or 18 render the macrocycle more readily reduced, i.e. the redox potential is lower and the macrocycle more readily gains an electron to form a radical. Such texaphyrins having a low redox potential are useful for radiosensitization applications.