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

Abstract

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.

Photorelease of Nitric Oxide (NO) in Mono- and Bimetallic Ruthenium Nitrosyl Complexes: A Photokinetic Investigation with a Two-Step Model

“…Although it seems natural to consider a route in two steps (A → B → C, eqs 3a and 3b), a first report of photokinetic behavior on these species 16 revealed the presence of apparent isosbestic points in the ultraviolet−visible (UV−vis) spectra all over the NO • release process in agreement with a simple onestep (A → C, eq 2) description of the mechanism. The present contribution is an attempt to fully elucidate this issue and to provide a complete understanding of the NO • release in bimetallic complexes.…”

Acetylacetonate Ruthenium Nitrosyls: A Gateway to Nitric Oxide Release in Water under Near-Infrared Excitation by Two-Photon Absorption

“…Different synthetic routes, summarized in Scheme , were screened from tpy ( 1a ) targeting complex [Ru II NO­(tpy)­(acac)]­(PF 6 ) 2 ( 6a , acac-RuNO ). While intermediates 2a and 3a were flawlessly prepared following reported methodologies, , the next steps proved unexpectedly difficult when compared to the synthesis of structurally related ruthenium nitrosyls of the bpy-RuNO 3+ family. , Most of these difficulties arose from the remarkably lower lability of the chlorido ligand in 3a when compared to its homologous complex [Ru II Cl­(tpy)­(bpy)]­(PF 6 ), which swiftly undergoes the needed Cl → NO 2 substitution that we found inoperative for the direct 3a → 5a conversion. The reported synthesis of 6a by T. Meyer and co-workers proposes the use of [Ru II (H 2 O)­(tpy)­(acac)]­(PF 6 ), as it bears a more labile aqua ligand.…”

“…The most successful approach implies building highly polarizable and extended π-systems featuring significant local dipoles built up by strong electron donating and withdrawing groups, represented by fluorenyl and [RuNO] 3+ submolecular fragments, respectively. The stepwise increase of the dimensionality of the complexes has allowed an enhancement of the TPA response from σ TPA = 108 GM for a dipolar mononuclear complex 25 to σ TPA = 330 GM and σ TPA = 1600 GM for quadrupolar 26 and octupolar 27 polynuclear species, respectively. These values, recorded at λ = 800 nm, represent a remarkable increase from 3 to 16 times in the TPA response, allowing NO release to be conveniently activated by NIR excitation.…”

Two-photon absorption-based delivery of nitric oxide from ruthenium nitrosyl complexes

“…A family of bimetallic RuNO species has been investigated in which the fluorenylterpyridine ligand is used as the bridge between the equivalent RuNO sub-units. 78 The resulting complexes 9–11 are shown in Fig. 13.…”