Optical anion sensing characteristics of indiumporphyrin and lipophilic dichlorofluorescein doped polymer films

The anion optical sensing characteristics of polymeric membranes doped with indiumporphyrins 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 407nm of indium-porphyrin complex to have very low absorption; while the DCFOE absorption spectra in the region 450-530nm 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 30s and life time of more than 1 month. When the picket fence indiumporphyrin was used as the ionophore, anions including dichlorofluorescein do not change the soret band at 407nm significantly. A highly selective sensor for acetate anion or acetic acid can be fabricated with the indium picket fence porphyrin and DCFOE.