STUDIES ON THE PHOTOELECTROCHEMICAL PROPERTIES OF THIONINE DYE COVALENTLY BOUND TO POLY(ACRYLAMIDOGLYCOLIC ACID)

Thionine dye, TH+, covalently attached to a macromolecule, poly(acryla midoglycolic acid) (P(AGA)), was prepared. Flash photolysis of the mac romolecule-bound thionine, P(AGA)-TH+, in the presence of Fe(II) ions shows that the absorption spectrum of polymer-bound semithionine radic al is not significantly changed from that of monomeric semithionine. T he 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 trans fer processes occurring at the electrode are less reversible for P(AGA )-TH+ in homogeneous solution than for P(AGA)TH+ coated onto an electr ode as a thin film. For P(AGA)-TH+ coated onto an electrode or an elec trode immersed in P(AGA)-TH+ in homogeneous solution, cathodic behavio ur is observed at the illuminated electrode, indicating a change in th e polarity of the electrode in comparison with the reaction observed a t a platinum electrode with thionine and iron(II) present in homogeneo us solution. Stabilization of the charge-separated thionine-iron(II) c omplex by the polymer network seems to be an important factor for effi cient charge transfer at the electrode.