Charge separation in photoinitiated electron transfer reactions induced by a polyelectrolyte

When uncharged molecules quench the luminescence of Ru(bpy)₃^2+* by electron transfer to the quencher, the addition of poly(vinyl sulfate) (PVS) may, through its potential field, affect the rate of quenching, enhance the net separated charge yield, and slow the back reaction of the separated photoredox products. In all such cases that we have studied the quenching rate in the presence of PVS was reduced to about 60% of the rate measured in the absence of PVS. For two neutral species, iron(III) nitrilotriacetate (FeNTA) and cobalt(III) acetylacetonate (Co(acac)₃), photoreduction of the quencher was observed, and the redox yield escaping geminate recombination was substantially increased by added PVS. In the case of FeNTA the rate of the bulk back reaction was not changed appreciably by the presence of PVS owing to the rapid neutralization of Fe(NTA)^- by protonation. For Co(acac)₃ the rate of the bulk back reaction was decreased by several orders of magnitude and the back reaction was shown to occur via the enolate form of the ligand which is released to the bulk solution.