ELECTROCHEMISTRY AND PHOTOCURRENTS OF THE TRIS(BIPYRIDINE)RUTHENIUM(II) AND METHYL VIOLOGEN CATIONS IMMOBILIZED IN CARRAGEENAN HYDROGEL

A procedure for immobilization of both a photochromophore, tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)3(2+)), and a quencher, methyl viologen (MV2+), within a carrageenan hydrogel matrix at an electrode surface is described. Ru(bpy)3(2+) and MV2+ exhibited diffusion coefficients that ranged from 10(-7) to 10(-6) cm2/s in the hydrogel, which represents an improvement over other immobilization matrices. Photolysis of the resulting hydrogel surface modified electrodes gave rise to a significant photocurrent which depended on the concentrations of Ru(bpy)3(2+), MV2+, and triethanolamine and resulted in a maximum value of 12-mu-A/cm2 after the hydrogel was cured with a solution containing 5 mM Ru(bpy)3(2+) and 50 mM MV2+. The photocurrent was the result of reoxidation of MV+ at the electrode surface following reduction of MV2+ by photoexcited Ru(bpy)3(2+). The quenching rate constant of Ru(bpy)3(2+*) by MV2+ in the hydrogel was 4.2 x 10(8) M-1 s-1. The photocurrent action spectrum was consistent with Ru(bpy)3(2+) acting as the photochromophore. Offsetting the potential of the hydrogel electrode verified the role of the MV2+/+ redox couple as the source of the current.