Replacing Two Chlorido Ligands by a Bipyridine Ligand in Ruthenium Nitrosyl Complexes with NO-Release Capabilities: A Comparative Study.

[Ru^II(FT)(bipy)(NO)][PF₆]₃ [FT is the electron-rich 4'-(2-fluorenyl)-2,2':6',2"-terpyridine ligand and bipy is 2,2'-bipyridine] is synthesized and characterized. It crystallizes in the triclinic P1 space group [a = 9.5362(2) Å, b = 10.3946(4) Å, c = 22.5701(8) Å, α = 94.7400(10)°, β = 94.9400(10)°, γ = 101.0680(10)]. A photochemical study is presented in comparison with that of the parents cis(Cl,Cl)-[Ru^II(FT)Cl₂(NO)][PF₆] and trans(Cl,Cl)-[Ru^II(FT)Cl₂(NO)][PF₆]. The three derivatives release nitric oxide (·NO) under irradiation at λ = 405 nm with respective quantum yields of 0.06, 0.31, and 0.10. Their two-photon absorption (TPA) cross-sections (sTPA) were investigated by the Z-scan technique on related derivatives in which two hexyl chains were introduced to improve their solubility while their spectroscopic properties remained almost unaffected. The resulting σ_TPA values of 100 GM at λ = 800 nm are in the window of transparency for human tissues, and the bipyridine-based complex exhibits a slight tendency for higher efficiency. The replacement of the [Ru^II(Cl)₂(NO)] core by [Ru^II(bipy)(NO)] provides a much simpler synthesis, and the TPA-induced ·NO-release capabilities are in the same range of magnitude. Therefore, it is envisioned that ·NO donors of greater complexity with several metal centers could be investigated in future. [ABSTRACT FROM AUTHOR]