Red-colored and solvent-free membranes based on the picket fence cobaltporphyrin (CoP) complexed with two or three kinds of polymer-ligands were prepared, and their visible absorbance responses to oxygen partial pressure were studied. The four CoP complexes with copolymers of 4- and 1-vinylimidazole and 4- and 2-vinylpyridine as a polymer-ligand were characterized by different oxygen affinity: In this order of the copolymers, the oxygen affinity of CoP was decreased by a factor of 10. The membrane composed of the three CoP complexes displayed a selective and continuous response in the visible absorbance ascribed to the oxygen-adduct formation over a wide range of oxygen partial pressure, i.e., 0.01-76 cmHg at atmospheric total pressure. On the other hand, the membrane composed of the two complexes with strong and weak affinity responded in a stepwise manner to oxygen partial pressure. The CoP complexed with and fixed in the polymer-ligands could form an oxygen adduct rapidly and reversibly just as the CoP complex did in a solution. The oxygen response rate of the membrane was shortened inversely with the square root of its thickness. The operational lifetime was longer than 1 month, which was much prolonged for the CoP complexed with the fluoroalkyl methacrylate copolymers: The latter also displayed a selective and reversible oxygen response in water.
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