Redox Properties of Metalloporphyrin Excited States, Lifetimes, and Related Properties of a Series of Para-Substituted Tetraphenylporphine Carbonyl Complexes of Ruthenium(II)

Article abstract of DOI:10.1021/ja00391a013

Excited-state and redox properties of Ru(p-XTPP)(CO), X = MeO, Me, H, F, Cl, H, and Br, have been defined.Emission bands were centered at 730 +/- 3 nm and excited-state lifetimes were in the range of 30 +/- 10 μs.Two one-electron oxidations in CH2Cl2 ranged from 0.74 to 0.86 V for the first step and from 1.18 to 1.27 V for the second one.A one-electron reduction process in (CH3)2SO ranged from -1.35 to -1,24 V.Excited-state lifetimes and redox potentials exhibit a weak dependence on the Hammet ?_p function.In general, redox potentials increase as the electron-withdraving power of the substituents increases, whereas excited-state lifetimes decrease.The first oxidation step (0.74-0.86 V) and the reduction step are, respectively, assigned to ?-electron removal or acceptance by porphyrin ring.The second oxidation is assigned to removal of an electrone from the ruthenium(II) center.The excited state is shown to be T(?-?*) state of porphyrin ring and to exhibit photoredox behavior involving both oxidative and reductive quenching.Redox product separation occured in flash photolysis quenching experiments and back-reactions took place at near-diffusion-controlled rates.The redox potential of the Ru(TPP)(CO)^+/* couple was estimated from emission and redox data to be -0.57 +/- 0.03 V; it was determined from oxidative quenching studies to be -0.56 +/- 0.10 V.Comparison to the excited-state properties of Ru(bpy)3²⁺ is made, and the utility of porphyrin complexes as potential solar energy storage catalysts is examined.