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)3²⁺), and a quencher, methyl viologen (MV²⁺), within a carrageenan hydrogel matrix at an electrode surface is described. Ru(bpy)3²⁺ 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)3²⁺, MV²⁺, and triethanolamine and resulted in a maximum value of 12 μA/cm² after the hydrogel was cured with a solution containing 5 mM Ru(bpy)3²⁺ 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)3²⁺. The quenching rate constant of Ru(bpy)3²⁺* by MV²⁺ in the hydrogel was 4.2 X 10⁸ M^-1 s^-1. The photocurrent action spectrum was consistent with Ru(bpy)3²⁺ acting as the photochromophore. Offsetting the potential of the hydrogel electrode verified the role of the MV^2+/+ redox couple as the source of the current. © 1991, American Chemical Society. All rights reserved.

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Author Alvin L. Crumbliss Chemistry