Chiral modified electrodes. Part 2. Marcus behaviour and high enantioselectivity in the photoelectrochemistry at a polymeric [Ru(4-methyl-4′-vinyl-2,2′-bipyridine)3]2+electrode

Abstract

Indium–tin-dioxide (ITO) and Pt electrodes can be modified with films of the photo- and redox-active polymer of [Ru(4-methyl-4′-vinyl-2,2′-bipyridine)₃]²⁺ ([Ru(vbpy)₃]²⁺). These modified electrodes show photocurrents when K₃[Co(ox)₃] is reduced in a photoelectrochemical reaction. These photocurrents are, inter alia, dependent on the potential applied to the electrode assembly. The photocurrent s. voltage plots have maxima. Changing the potential means changing the driving force of the electrode reaction and we can interpret the maximum plots by Marcus' theory for reactions in the normal and inverted region. For the investigation of a chemical reaction, electrodes with larger surfaces are necessary. In the photo-assisted reduction of K₃[Co(ox)₃] by means of a reticulated Ni-foam electrode modified by a chiral redox active polymer of [Ru(vbpy)₃]²⁺ we have found enantio-selectivity with κ=k_Λ/k_Δ of up to 12, one of the highest values of asymmetry reported for photochemical reactions. Modified electrodes, where the optically excited electron transferring species in the polymer is the chiral element, represent a new type of chiral inductor.