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A ruthenium nitrosyl complex of formula [RuII(fluorene(C6)CH2O-terpy)(bipy)(NO)]3+ (AC) in which fluorene(C6) is the 9,9-dihexylfluorene, terpy the 2,2′;6′,2′′-terpyridine, and bipy the 2,2′-bipyridine is presented with its related [RuII(MeO-terpy)(bipy)(NO)]3+ (C) and 9,9-dihexylfluorene 2-hydroxymethylfluorene (A) building blocks. The reference complex C undergoes NO release capabilities under irradiation at λ = 365 nm. The effect of the introduction of the fluorescent A antenna within the resulting AC complex is discussed both experimentally and theoretically. The importance of the encaging parameter defined as φAC·IAC, in which IAC is the quantity of light absorbed by AC and φAC the quantum yield of NO release is evidenced and found to be concentration dependent. The conditions of optimization of the antenna approach to maximize φAC·IAC are discussed. The crystal structure of [RuII(fluorene(C6)CH2O-terpy)(bipy)(NO2)](PF6), the last intermediate in the synthesis of AC is also presented. [ABSTRACT FROM AUTHOR]

Ruthenium nitrosyl (RuNO) complexes continue to attract significant research interest due to several appealing features that make these photoactivatable nitric oxide (NO˙) donors attractive for applications in photoactivated chemotherapy. Interesting examples of molecular candidates capable of delivering cytotoxic concentrations of NO˙ in aqueous media have been discussed. Nevertheless, the question of whether most of these highly polar and relatively large molecules are efficiently incorporated by cells remains largely unanswered. In this paper, we present the synthesis and the chemical, photophysical and photochemical characterization of RuNO complexes functionalized with 17α-ethinylestradiol (EE), a semisynthetic steroidal hormone intended to act as a molecular Trojan horse for the targeted delivery of RuNO complexes. The discussion is centered around two main molecular targets, one containing EE (EE-Phtpy-RuNO) and a reference compound lacking this biological recognition fragment (Phtpy-RuNO). While both complexes displayed similar optical absorption profiles and NO˙ release efficiencies in aqueous media, important differences were found regarding their cellular uptake towards dermal fibroblasts, with EE-Phtpy-RuNO gratifyingly displaying a remarkable 10-fold increase in cellular uptake when compared to Phtpy-RuNO, thus demonstrating the potential drug-targeting capabilities of this biomimetic steroidal conjugate. [ABSTRACT FROM AUTHOR]

Since the discovery of the numerous physiological roles exhibited by nitric oxide (NO), ruthenium nitrosyl (RuNO) complexes have been regarded as one of the most promising NO donors, stable, well tolerated by the body and capable of releasing NO locally and quantitatively, under light irradiation. This release can be achieved by two-photon absorption (TPA) processes, which allow the irradiation to be performed in the near infrared domain, where light has its maximum depth of penetration in biological tissues. This review provides a short introduction on the biological properties of NO, on RuNO complexes with photo-releasing capabilities, and on the origin of TPA properties in molecules. Then, the RuNO complexes with TPA capabilities are thoroughly discussed either as monometallic or polymetallic species. [ABSTRACT FROM AUTHOR]

A series of electronic and physicochemical parameters were explored to determine their effect on experimental spectroscopic and photophysical data. Through a systematic obtention of a series of meso-(o-aryl)-BODIPYs, 19F NMR spectra were analyzed and their fluorescence quantum yields in several solvents were measured. Experimental values of 19F chemical shift difference ΔδF correlate well with σ-Hammett constants, which is indicative of the inductive nature of the functional groups on the fluorine atoms. A computational DFT exploration of rotational energy barriers, electrostatic potential maps, group electronegativity, charge partitions and hardness/softness provided insight into how those traits can be directly related to the measured features. Expanded understanding of such characteristics provides design arguments and a structure–property relationship, which in a more advantageous way, would help to understand the properties of the synthesized molecules and of future attempts that are structurally related. [ABSTRACT FROM AUTHOR]

The synthesis and behavior in water of a set of various cis(Cl,Cl)-[R-tpyRuCl2(NO)](PF6) and trans(Cl,Cl)-[R-tpyRuCl2(NO)](PF6) (R = fluorenyl, phenyl, thiophenyl; tpy = 2,2′:6′,2′′-terpyridine) complexes are presented. In any case, one chlorido ligand is substituted by a hydroxo ligand and the final species arises as a single trans(NO,OH) isomer, whatever the nature of the starting cis/trans(Cl,Cl) complexes. Six X-ray crystal structures are presented for cis(Cl,Cl)-[thiophenyl-tpyRuCl2(NO)](PF6) (cis-3a), trans(Cl,Cl)-[thiophenyl-tpyRuCl2(NO)](PF6) (trans-3a), trans(NO,OH)-[phenyl-tpyRu(Cl)(OH)(NO)](PF6) (4a), trans(NO,OH)-[thiophenyl-tpyRu(Cl)(OH)(NO)](PF6) (4b), trans(NO,OEt)-[phenyl-tpyRu(Cl)(OEt)(NO)](PF6) (5a), and trans(NO,OH)-[phenyl-tpyRu(Cl)(OEt)(NO)](PF6) (5b) compounds. The different cis/trans(Cl,Cl) complexes exhibit an intense low-lying transition in the λ = 330–390 nm range, which appears to be slightly blue-shifted after Cl → OH substitution. In water, both cis/trans(Cl,Cl) isomers are converted to a single trans(NO,OH) isomer in which one chlorido- is replaced by one hydroxo-ligand, which avoids tedious separation workout. The water stable trans(NO,OH)-species all release NO with quantum yields of 0.010 to 0.075 under irradiation at 365 nm. The properties are discussed with computational analysis performed within the framework of Density Functional Theory. [ABSTRACT FROM AUTHOR]

This study focuses on the two cis/trans-(Cl,Cl)-[Ru(R-Phtpy)Cl2(NO)]+ isomers, where the R group is a NEt2 substituent on the 4′-position of the phenylterpyridine (Phtpy) moiety. The photophysical characteristic properties of the two isomers and those of one nitrosamine derivative are described. The NO release properties are evaluated and show that the cis isomer is the most efficient with a good quantum yield of NO release. The X-ray structures of three ruthenium–nitrosyl complexes and of a photoproduct are presented. [ABSTRACT FROM AUTHOR]

A series of four ruthenium(ii) complexes built from the [Ru(terpy)(bipy)(NO)]3+ core (terpy is 2,2′:6′,2′′-terpyridine and bipy is 2,2′-bipyridine) are investigated. They differ by the presence of zero, one, two, or three 4′-(4-methoxyphenyl) (MP) electron donor substituents introduced at different positions on the pyridine fragments to increase the intramolecular charge transfer capabilities towards the strongly withdrawing nitrosyl (NO) ligand. The UV-visible spectra reflect the presence and position of the MP substituents on the complexes. In the case of species containing the 4′-(MP)-terpy ligand, a low-lying transition is identified as arising from 4′-(MP)-terpy to Ru(NO) intramolecular charge transfer, which is further confirmed by TD-DFT analysis. Irradiation performed at λ = 436 nm on this isolated transition for different complexes leads to quantum yields of NO photo-release equal to 0.002 and 0.011, in a ratio of 6 (instead of 1), which allows concluding non-ambiguously that a single electron transition cannot account for the NO release mechanism. [ABSTRACT FROM AUTHOR]

Two molecules, 2,2′-(1,4-phenylenebis(ethyne-2,1-diyl))bis(4-nitroaniline) (PNA) and 2,2′-(1,4-phenylene-bis(ethyne-2,1-diyl))bis(N,N-diethyl-4-nitroaniline) (PDNA), built up from two p-nitroaniline “push–pull” nonlinear optical (NLO) chromophores slightly conjugated through a 1,4-phenylenebis(ethyne-2,1-diyl) bridge have been synthesized and fully characterized. The crystal structure of PNA reveals that the ground (off) state conformation corresponds to the centrosymmetric anti-conformer in which the molecular hyperpolarizability (β) is equal to zero. A computational investigation reveals that, once submitted to an intense electric field (E), the two p-nitroaniline subunits are gradually aligned in the direction of the field with the appearance of a metastable (on) state (β≠ 0, when E = 0), stabilized by conjugation. A loop of hysteresis is observed during the on ⇌ off cycles leading to a form of molecular bistability. The NLO response of PNA has been investigated at different field intensities by the electric-field induced second-harmonic (EFISH) technique to provide experimental evidence for this behavior. [ABSTRACT FROM AUTHOR]

We investigated the influence of the nature of the substituent on the 4′-position of terpyridine ligands and the geometry around the metal ion on the photosensitization of ruthenium nitrosyl complexes. This was achieved by synthesizing a series of [Ru(R-Phtpy)Cl2(NO)]+ complexes based on tridentate terpyridine ligands with a substituted phenyl ring on the central pyridine (R = NO2, H, Br, OMe). The properties of both cis-(Cl,Cl)[Ru(R-Phtpy)Cl2(NO)]+ and trans-(Cl,Cl)[Ru(R-Phtpy)Cl2(NO)]+ isomers are presented. The optimized geometries and UV-Vis spectra were fully computed by DFT calculations and are in agreement with the experimental data. Quantum yields of NO release were obtained by numerical modeling and parameter optimization on the time evolution of the electronic spectra during irradiation. On irradiation with visible light in MeCN both cis(Cl,Cl)- and trans(Cl,Cl)-[Ru(MeO-Phtpy)Cl2(NO)](PF6) undergo facile photorelease of NO with the concomitant formation of the photoproduct as the solvate. Unambiguous characterization of the photoproduct for R = OMe was achieved by X-ray analysis and revealed that both isomers lead to trans(Cl,Cl)-[Ru(MeO-Phtpy)Cl2(MeCN)](PF6) as the unique photoproduct. The calculation of the relaxed potential energy surface confirmed an internal rearrangement of the cis(Cl,Cl) isomer to the trans(Cl,Cl) one after NO release. [ABSTRACT FROM AUTHOR]

The 4'-(2-fluorenyl)-2,2':6',2''-terpyridine (FT) ligand and its cis(Cl,Cl)- and trans(Cl,Cl)-[RuII(FT)Cl2(NO)](PF6) complexes have been synthesized. Both isomers were separated by HPLC and fully characterized by ¹H and 13C NMR. The X-ray diffraction crystal structures were solved for FT (Pna²1 space group, a = 34.960(4), b = 5.9306(7), c = 9.5911(10) Å), and trans(Cl,Cl)-[RuII(FT)Cl2(NO)](PF6)·MeOH (P[1 with combining macron] space group, a = 10.3340(5), b = 13.0961(6), c = 13.2279(6) Å, a = 72.680(2), β = 70.488(2), γ = 67.090(2)°). Photo-release of NO• radicals occurs under irradiation at 405 nm, with a quantum yield of 0.31 and 0.10 for cis(Cl,Cl)-[RuII(FT)Cl2(NO)](PF6) and trans(Cl,Cl)-[RuII(FT)Cl2(NO)](PF6), respectively. This significant difference is likely due to the trans effect of Cl-, which favors the photo-release. UV-visible spectroscopy and cyclic voltammetry indicate the formation of ruthenium(III) species as photoproducts. A density functional theory (DFT) analysis provides a rationale for the understanding of the photo-physical properties, and allows relating the weakening of the Ru-NO bond, and finally the photo-dissociation, to HOMO → LUMO excitations. [ABSTRACT FROM AUTHOR]

Transmission of electronic information through amide bonds may be, under appropriate conditions, effectively achieved. In this work, a family of explicitly designed donor–(amide bridge)–acceptor architectures was synthesized. NMR studies and UV-vis absorption solvatochromism support that cross-conjugation leads to measurable polarization across push–pull, amide-bridged molecules. Computational analysis of structural parameters and frontier molecular orbitals shows the contribution of an additional, dienoid amide canonical structure to intramolecular electron delocalization, as the electron donor–acceptor strength of the substituents increases. Within the context of nonlinear optics and molecular materials, computational comparison between amide-bridged molecules and those containing typical linkers shows that there is a compromise between nonlinear optical response, ease of synthesis and chemical inertness, making the systems studied herein interesting alternatives for such applications. [ABSTRACT FROM AUTHOR]

The promising class of (polypyridine-ruthenium)-nitrosyl complexes capable of high yield Ru–NO/Ru–ON isomerization is targeted as a potential molecular device for the achievement of complete NLO switches in the solid state. A computational investigation conducted at the PBE0/6-31+G** DFT level for benchmark systems of general formula [R-terpyridine-RuIICl2(NO)](PF6) (R being a substituent with various donating or withdrawing capabilities) leads to the suggestion that an isomerization could produce a convincing NLO switch (large value of the βON/βOFF ratio) for R substituents of weak donating capabilities. Four new molecules were obtained in order to test the synthetic feasibility of this class of materials with R = 4′-p-bromophenyl, 4′-p-methoxyphenyl, 4′-p-diethylaminophenyl, and 4′-p-nitrophenyl. The different cis-(Cl,Cl) and trans-(Cl,Cl) isomers can be separated by HPLC, and identified by NMR and X-ray crystallographic studies. [ABSTRACT FROM AUTHOR]