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

Abstract

[Ru II (FT)(bipy)(NO)][PF 6 ] 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 P 1 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)Cl 2 (NO)][PF 6 ] and trans (Cl,Cl)‐[Ru II (FT)Cl 2 (NO)][PF 6 ]. 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 ( σ TPA ) 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.