The photoquenching reaction of [Pt2(pop)4]4− (pop2− = pyrophosphite(2−)) with [Mo(CN)8]4− was studied in 0.01 M HCl or HClO4 in the presence of various added electrolytes (0.49 M) (LiCl, NaCl, KCl, CsCl, NH4Cl, (C2H5)4NCl, and NaClO4) at 25 °C. The quenching rate constants (kq) differ by nearly 1 order of magnitude from 1.17 × 107 (LiCl) to 9.90 X 107 M−1 s−1 (CsCl). The phosphorescence lifetime (τ0) in the absence of the quencher is practically constant (8.3–8.6 μs) regardless of the type of electrolyte added, kq, shows a linear correlation with the reciprocal of the cation Stokes radii except for the case of (C2H5)4N+. The cation effect was interpreted by considering a precursor ion triplet among two negatively charged reactants and a foreign cation. The role of the cation is to reduce the Coulombic barrier of the two reactants in order to form an encounter complex.
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