Membranes of the picket fence cobalt porphyrin complexed with poly(vinylimidazole and -pyridine)s: Selective optical response to oxygen

Red-colored and solvent-free membranes based on the picket fence cobaltporp hyrin (CoP) complexed with two or three kinds of polymer-ligands were prepa red, 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 diffe rent 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 oxy gen 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. Th e 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. Th e oxygen response rate of the membrane was shortened inversely with the squ are root of its thickness. The operational lifetime was longer than 1 month , which was much prolonged for the CoP complexed with the fluoroalkyl metha crylate copolymers: The latter also displayed a selective and reversible ox ygen response in water.