Effects of the polyelectrolyte poly(vinyl sulfate) on the photosensitized electron-transfer reactions of tris(2,2′-bipyridine)ruthenium(II) with a dipolar zwitterionic viologen

The photosensitized electron-transfer system containing Ru(bpy)₃²⁺ as photosensitizer and N,N′-bis(4-sulfonatotolyl)-4,4′-bipyridyldiylium (BSV) as quencher was investigated in aqueous solutions containing the polyelectrolyte poly(vinyl sulfate) (PVS). This is the first system where acceleration of the forward quenching reaction together with considerable retardation of the reaction regenerating the ground-state species occurs on addition of a charged microenvironment. Both the BSV molecule, possessing a large dipole moment, and the Ru(bpy)₃²⁺ cation are concentrated in the polyelectrolyte field and steady-state emission experiments showed that the distribution of BSV in the potential field of PVS may be described by the Poisson-Boltzmann equation. The reaction betwesn BSV and Ru(bpy)₃²⁺ results in an electron transfer, yielding BSV^-· and Ru(bpy)₃³⁺ as products There is evidence for formation of an outer-sphere complex between BSV · and Ru(bpy)₃³⁺ . The yields of electron transfer were hardly affected by the presence of PVS although the rate of the reverse electron-transfer reaction was somewhat reduced. This was attributed to the distribution of charge over the BSV^-· radical anion product. The effects of pH, addition of an inert salt, and variation of coverage of the polyelectrolyte were also investigated for the system.