Electron transfer reactions of osmium(II) complexes with phenols and phenolic acids

• The geometry of [Os(II) (NN)3]2+ are distorted octahedral.
• The MLCT excited state of the [Os(II) (NN)3]2+ are quenched by sterically hindered phenols.
• The binding constant studies show that the ground state interaction was present in the system.
• Luminescent quenching constants also confirmed the static quenching of [Os(II) (NN)3]2+ by sterically hindered phenols.
• The electron transfer rate is in accordance with Rehm-Weller equation.

Three [Os(NN)3]2+ complexes (NN = polypyridine) with ligands of varying hydrophobicity were synthesized and characterized by NMR spectral techniques. The geometry of the molecules are optimized by DFT calculations. The interaction between [Os(NN)3]2+ complexes and phenolate ion in ground state is confirmed by absorption spectral study and the binding constant values are in the range of 3–740 M−1. The photoinduced electron transfer reaction of these [Os(NN)3]2+ complexes with phenols and phenolic acids at pH 12.5 leads to the formation of phenoxyl radical confirmed through transient absorption spectral study. Binding constants and electron transfer rate constants within the [Os(NN)3]2+–phenolate ion adduct account for the change for the overall quenching constant with the change of structure of reactants.

Optimized structures of (a) [Os(bpy)3]2+, (b) [Os(dmbpy)3]2+ and (c) [Os(phen)3]2+.Figure optionsDownload as PowerPoint slide