Studies on the photoelectrochemical properties of thionine dye covalently bound to poly (acrylamidoglycolic acid)

Abstract

Thionine dye, TH⁺, covalently attached to a macromolecule, poly(acrylamidoglycolic acid) (P(AGA)), was prepared. Flash photolysis of the macromolecule-bound thionine, P(AGA)-TH⁺, in the presence of Fe(II) ions shows that the absorption spectrum of polymer-bound semithionine radical is not significantly changed from that of monomeric semithionine. The rate constant for the disproportionation reaction of polymer-bound semithionine is significantly decreased compared with that of unbound semithionine. Cyclic voltammetric studies show that the electron transfer processes occurring at the electrode are less reversible for P(AGA)-TH⁺ in homogeneous solution than for P(AGA)-TH⁺ coated onto an electrode as a thin film. For P(AGA)-TH⁺ coated onto an electrode or an electrode immersed in P(AGA)-TH⁺ in homogeneous solution, cathodic behaviour is observed at the illuminated electrode, indicating a change in the polarity of the electrode in comparison with the reaction observed at a platinum electrode with thionine and iron(II) present in homogeneous solution. Stabilization of the charge-separated thionine-iron(II) complex by the polymer network seems to be an important factor for efficient charge transfer at the electrode.