Photochemical and photophysical properties of ruthenium(II) bis-bipyridine bis-nitrile complexes: Photolability

Abstract

The electrochemical and photophysical properties of two bis-nitrilo ruthenium(II) complexes formulated as [Ru(bpy)2(L)2](PF6)2, where bpy is 2,2′-bipyridine and L is AN = CH3CN and sn = NC–CH2CH2–CN, have been investigated. Electrochemical data are typical of Ru-bpy complexes with two reversible reduction peaks located near −1.3 and −1.6 V assigned to each bipyridine ligand and one RuII/RuIII oxidation wave centered at approximately +1.5 V. The sn derivative is both IR and Raman active with its coordinated CN stretch appearing at 2277 cm−1 and 2273 cm−1, respectively. The UV/Vis absorption spectrum of the sn derivative is dominated by an intense (εmax ∼ 58700 M−1 cm−1) absorption band at 287 nm assigned as a LC (π → π∗) transition. The peak observed at 418 nm (ε ∼ 10 400 M−1 cm−1) is an MLCT band while the one at 244 nm (ε ∼ 23 600 M−1 cm−1) is of LMLCT character. The AN derivative behaves similarly. Both complexes show low-temperature emission at around 537 nm with a lifetime near 10.0 μs. 1H and 13C assignments are consistent with the formulation of the complexes. The complexes undergo photosubstitution of solvent with quantum efficiencies near one. Calculated and experimental results support replacement of the nitrile ligands by solvent. Based on DFT calculations, the electron density of the HOMO lies on the metal center, the bipyridine ligands and the nitrile ligands and electron density of the LUMO resides primarily on the bipyridine ligands. The electronic spectra obtained from TDDFT calculations closely match the experimental ones.