Charge transfer distance between tris(2,2′-bipyridine) ruthenium(II) redox centers incorporated in Nafion® membrane

Charge transfer between Ru(bpy) 2+ 3 (where bpy is 2,2′-bipyridine) complexes incorporated into a Nafion® membrane has been investigated using in situ spectrocyclic voltammetry and statistical calculation of the intermolecular distance between the complexes. The membrane was prepared either by a mixture casting method in which an alcoholic mixture solution of Nafion and the complex was cast to form a membrane, or by an adsorption method in which the complex was adsorbed from its aqueous solution into a precoated Nafion® membrane. It has been found that the electrochemical reactivity of the complex in a membrane prepared by the adsorption method is much higher than that prepared by the mixture casting method. The charge transfer distance between the complexes ( R 0 ) in the membrane prepared by the adsorption method was 1.6 nm (scan rate, 2 mV s −1 ; pH 5.5), when assuming a random dispersion of the complex, which is significantly longer than that (1.1 nm) in the membrane prepared by the mixture casting method. The emission lifetime of the photoexcited Ru(bpy) 2+ 3 in the membrane suggests that the complex is localized in the membrane when it is prepared by an adsorption method; such localization would make the calculated R 0 value greater than the real value. The fraction of the volume in the membrane where the complex is adsorbed was estimated as 20 ± 3%, by comparing the real local complex concentration in the membrane obtained from the R 0 value (1.1 nm) for the mixture casting system with the apparent average complex concentration.