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 (σ TPA ), in the bimetallic species. In the best case, σ 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 * under irradiation, which leads to promising applications in TPA-based drug delivery.

We report herein a molecular engineering strategy based on the design of a multipolar ruthenium-nitrosyl (Ru-NO) complex with a three-branched architecture. The three ruthenium-nitrosyl units are introducted at the periphery of a highly -delocalized truxene core bearing three terpyridine ligands. The two-photon absorption capabilities of the complex were investigated by the Z-scan technics. The strong electronic coupling among the individual arms gives rise to a very strong two-absorption response ( 800nm ~ 1600 GM), which corresponds to a 16 times enhancement of the capability of a single arm reference, promoting thereby an efficient light-driven NO release process in aqueous medium.

Using the compound [RuII(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) as a reference, two new compounds are presented in which carbon‐carbon double and triple bonds are inserted between the fluorenyl substituent and the terpyridine to provide an extended conjugation path. The electronic properties of the three complexes are compared experimentally by UV‐visible spectroscopy and computationally by means of the density functional theory. All of them exhibit a capability for NO release under irradiation on their low‐energy transition located in the 400–500 nm range, with a quantum yield around 0.01. Their two‐photon absorption (TPA) cross sections are investigated by the Z‐scan technique at λ=800 nm. While the reference compound exhibits a cross‐section equal to 108 GM, the introduction of double and triple bonds leads to increased cross‐sections equal to 131 GM and 150 GM, respectively. These values are discussed in reference to the two‐level model in use for “push‐pull” dipolar TPA chromophores.