Bimetallic Ruthenium Nitrosyl Complexes with Enhanced Two-Photon Absorption Properties for Nitric Oxide Delivery

One monometallic and three bimetallic ruthenium nitrosyl (RuNO) complexes are presented and fully characterized in reference to a parent monometallic complex of formula [FTRu(bpy)(NO)](3+), where FT is a fluorenyl-substituted terpyridine ligand, and bpy the 2,2'-bipyridine. These new complexes are built with the new ligands FFT, TFT, TFFT, and TF-CC-TF (where an alkyne C C group is inserted between two fluorenes). The crystal structures of the bis-RuNO 2 and bis-RuNO complexes built from the TFT ligand are presented. The evolution of the spectroscopic features (intensities and energies) along the series, at one-photon absorption (OPA) correlates well with the TD-DFT computations. A spectacular effect is observed at two-photon absorption (TPA) with a large enhancement of the molecular cross-section (sigma(TPA)), in the bimetallic species. In the best case, sigma(TPA), is equal to 1523 +/- 98 GM at 700 nm, in the therapeutic window of transparency of biological tissues. All compounds are capable of releasing NO center dot under irradiation, which leads to promising applications in TPA-based drug delivery.