Optical anion sensing characteristics of indium-porphyrin and lipophilic dichlorofluorescein doped polymer films Original Research Article

The anion optical sensing characteristics of polymeric membranes doped with indium-porphyrins and a lipophilic dichlorofluoscein derivative were investigated. The response mechanism is based on extraction of anions into the bulk organic film by indium-porphyrins and a simultaneous co-extraction of hydrogen ions. This results in protonation of the pH chromophore and hence a change in the optical absorbance of the polymeric film. When ordinary indium-porphyrin, indium octaethyl-porphyrin (In(OEP)) was used as ionophore, the dichlorofluorescein (DCFOE) anion acted as ligand coordinating at the indium axial position, which caused the soret band at 407 nm of indium-porphyrin complex to have very low absorption; while the DCFOE absorption spectra in the region 450–530 nm was highly distorted. Anions such as chloride, thiocyanate and salicylate increased absorption of soret band by more than two times. Anion sensors based on In(OEP)–DCFOE is fully reversible with response times of 30 s and life time of more than 1 month. When the picket fence indium-porphyrin was used as the ionophore, anions including dichlorofluorescein do not change the soret band at 407 nm significantly. A highly selective sensor for acetate anion or acetic acid can be fabricated with the indium picket fence porphyrin and DCFOE.