Photoluminescence and electrogenerated chemiluminescence of a bis(bipyridyl)ruthenium(II)-porphyrin complex

The photoluminescence (PL) and electrogenerated chemiluminescence (ECL) of [H₂(MPy3,4DMPP)Ru(bpy)₂Cl](PF₆), where H₂MPy3,4DMPP = meso-tris-3,4-dimethoxyphenyl-mono-(4-pyridyl)porphyrin and bpy = 2,2′-bipyridine, are reported in acetonitrile. The compound has a complex absorbance spectrum with bands characteristic of both the porphyrin and ruthenium moieties. PL emission maxim are observed at 655 nm when excited at the maximum absorption intensity corresponding to the porphyrin Soret π → π^∗ band, and around 600 nm when excited at wavelengths corresponding to Ru(dπ)-bpy (π^∗) MLCT transition. The photoluminescence efficiency (?_em) of the 655 nm emission is 0.039 and that of the free porphyrin is 0.69 compared to at 0.042.[H₂(MPy3,4DMPP)Ru(bpy)₂Cl](PF₆) displays complex electrochemical behavior, with one electrochemically reversible Ru^II-Ru^III oxidation and two quasi-reversible waves at more cathodic potentials corresponding to the porphyrin moiety. Oxidative ECL was generated using the coreactant tri-n-propylamine (TPrA). ECL efficiencies (?_ecl) were 0.14 for [H₂(MPy3,4DMPP)Ru(bpy)₂Cl]⁺ and 0.099 for H₂MPy3,4DMPP using as the standard (?_ecl = 1). ECL intensity was linear with respect to concentration from 1 to 0.001 μM.The ECL intensity peaks at potentials corresponding to oxidation both the ruthenium and porphyrin moieties as well as TPrA, indicating that multiple pathways for formation of the excited state are possible. However, an ECL spectrum shows a band similar in energy and shape to that of the Soret emission (655 nm for the PL and 656 nm for the ECL, respectively), indicating the same excited state is formed in each experiment.