Investigation of cobalt porphyrin doped polymer membrane films for the optical sensing of imidazole and its derivatives

A cobalt(II) porphyrin was successfully incorporated into polymer membranes for the optical sensing of imidazole and its derivatives. This research has led to a better understanding of the behavior of Co(II) porphyrin in solution and in polymeric membranes. In aprotic dichloromethane (DCM), the Co(II) tetraphenylporphyrin (CoTPP) and Co(II) octaethylporphyrin (CoOEP) show a sensitive response to imidazole due to the strong ligation of the N-3 on the imidazole ring to the Co(II) center, which induces an absorbance change to the Soret band. However, when doped in polymeric films, only the CoTPP exhibits moderate sensitivity towards aqueous imidazole, histamine and histidine. This weakened coordination ability of CoTPP towards imidazole in the polymer films may be due to the coordination of the plasticizer, the impurities from the THF and polymer matrix at the Co(II) center. The selectivity of the polymer films towards imidazole over common anions is high. Lifetime of the cobalt(II) porphyrin incorporated polymer film was relatively short.