Binding, photophysical, and photochemical properties of tris(α,α′-diimine)ruthenium(II) complexes in polyelectrolyte solutions: Dependence on the nature of the ligands of the metal complexes and polyelectrolytes

Luminescence behaviors of seven tris(α,α′-diimine)ruthenium(II) complexes and quenching of their emission by oxygen, methylviologen (MV²⁺), and cupric ion (Cu²⁺) have been investigated in the presence of several different polyelectrolytes: poly(styrenesulfonate) (PSS), poly(vinylsulfonate) (PVS), poly(methacrylic acid) (PMA), and poly(acrylic acid) (PAA). The presence of PSS and PMA near pH 5 enhances the emission intensity and excited-state lifetimes of the metal complexes, and the effects were greater for the metal complexes with the ligands of greater hydrophobicity. On the other hand, effects of polyelectrolytes were less pronounced with PMA above pH 6, PVS, and PAA. Equilibrium dialysis studies showed that the metal complexes have much higher binding affinity to PSS than to PVS and to PMA at pH 5 than to the same polymer at pH 7. The hydrophobic and π-π interactions contribute largely to the binding. Binding of the metal complexes to PSS and PMA leads to protection of the metal complexes against quenching by oxygen and nonradiative decay processes of the excited state giving the changes observed in luminescence spectra. It was also found that the quenching by Cu²⁺ increases in PSS and PMA (pH 5) solutions, whereas the quenching by MV²⁺ increases in PSS solutions but decreases in PMA solutions near pH 5. These results indicate that interaction between the metal complexes and polyelectrolytes and the resultant changes in photophysical and photochemical properties of the metal complexes depend strongly on the hydrophobic character of the ligands of the metal complexes and the hydrophobicity and conformation of the polyelectrolytes.