Ru Polypyridyl Complexes Research Articles

Targeted Modulation of Photocatalytic Hydrogen Evolution Activity by Nickel-Substituted Rubredoxin through Functionalized Ruthenium Phototriggers.

Light-driven hydrogen evolution is a promising means of sustainable energy production to meet global energy demand. This study investigates the photocatalytic hydrogen evolution activity of nickel-substituted rubredoxin (NiRd), an artificial hydrogenase mimic, covalently attached to a ruthenium phototrigger (RuNiRd). By systematically modifying the para-substituents on Ru(II) polypyridyl complexes, we sought to optimize the intramolecular electron transfer processes within the RuNiRd system. A series of electron-donating and electron-withdrawing groups were introduced to tune the photophysical, photochemical, and electrochemical properties of the ruthenium complexes. Our findings reveal that electron-donating substituents can increase the hydrogen evolution capabilities of the artificial enzyme to a point; however, the complexes with the most electron-donating substituents suffer from short lifetimes and inefficient reductive quenching, rendering them inactive. The present work highlights the intricate balance required between driving force, lifetime, and quenching efficiency for effective light-driven catalysis, providing valuable insights into the design of artificial enzyme-photosensitizer constructs.

Tailoring Ruthenium(II) and Rhenium(I) Complexes for Turn-On Luminescent Sensing of Antimony(III)

Antimony (Sb) is currently a widespread element with key roles in telecommunication, sustainable energy, and military industries, among others. Its significant toxicity determines the need to realize sensors for water, air, and soil and the industrial process monitoring of Sb species. Unfortunately, no antimony sensors exist so far, and just laboratory analysis methods are in use. We aimed to contribute to the development of optical sensors for the metalloid by tailoring, for the first time, luminescent Ru(II) and Re(I) polypyridyl complexes to probe and quantify the presence of Sb(III). The molecular design of the complexes includes the multifunctional Sb-binding 2-(2,2′-bithien-5-yl)-1H-imidazo[4,5-f]-1,10-phenanthroline (btip) ligand that ensures the molecular binding of Sb(III) in organic media. The Ru(II)-btip complex is additionally endowed with one 2,2′-bipyrazine (bpz) or two 1,4,5,8-tetraazaphenanthrene (tap) ligands, namely [Ru(bpz)(btip)2]2+ and [Ru(tap)2(btip)]2+, that boost the excited state oxidation potential of the probe, leading to an intramolecular photoinduced electron transfer from btip to the Ru(II) core. The latter is suppressed upon interaction with Sb(III), leading to an 11-fold increase in both the luminescence intensity and lifetime of [Ru(bpz)(btip)2]2+ in the presence of ca. 50 μmol L−1 of SbCl3 in organic medium. The fluorescence intensity of [Re(CO)3(H2O)(btip)]+ also increases upon interaction with Sb(III) but to a much lesser extent due to the intraligand π*→π nature of its emission compared to the Ru(II) ligand-to-metal excited state deactivation. However, the weak π*→d emission band in the red spectral region of the former is quenched by the semimetallic element. The sensing mechanisms of the Ru(II)- and Re(I)-btip probes that allow luminescence intensity (Ru, Re), ratiometric (Ru), and lifetime measurements (Ru) are compared and discussed in this initial solution sensing study.

DFT Computational Analysis of the Mechanism of Action of Ru(II) Polypyridyl Complexes as Photoactivated Chemotherapy Agents: From Photoinduced Ligand Solvolysis to DNA Binding.

Photoactivated chemotherapy (PACT) is a form of target-oriented cancer therapy that exploits light of the proper wavelength to selectively activate the drug. Among the prodrugs used for this purpose, ruthenium-based complexes are particularly interesting, as when irradiated by light, they can release ligands by forming aquo-complexes able to bind DNA in both single and double strand fashions, causing its distortion. Using as model system a Ru(II) polypyridyl complex that has been demonstrated to be a promising photochemotherapeutic agent, all of the key aspects of the photoinduced solvolysis process and subsequent DNA interaction have been scrutinized using density functional theory (DFT) and time-dependent-DFT (TDDFT). Photoexcitation, intersystem crossing, internal conversion, mechanism by which photoinduced ligand release, and subsequent aquation steps occur have been examined. Pathways leading to the formation of both cis and trans biaquated photoproducts have been described, and the formation of the cis form of the biaquated photoproduct being the most favorable one, its reaction with a guanine base has also been reported in order to account for DNA binding.

Enantioselectively generating imidazolone dIz by the chiral DNA intercalating and “light-switching” Ru(II) polypyridyl complex via a novel flash-quench method

The 2-aminoimidazolone is a major and ubiquitous in vitro product of guanine oxidation. The flash-quench method, combining spectroscopy and product analysis, offers a novel and tunable approach to study guanine oxidation on double helical DNA. Herein we found that imidazolone dIz (2-amino-5-[(2-deoxy-β-D-erythro-pentofuranosyl)amino]-4H-imidazole-4-one) and dZ (2,2-diamino-5-[2-deoxy-β-D-erythro-pentofuranosyl)amino]-5(2H)-oxazolone) were the major oxidation products of double-strand DNA from the visible-light irradiation of the well-known DNA intercalating and light-switching Ru(OP)2dppz2+ (OP = 1,10-phenanthroline, dppz = dipyrido [3,2-a:2′,3′-c]phenazine) in the presence of a typical quencher methyl viologen (MV2+). Using ESR spin-trapping method, the radical intermediate MV•+ with typical hyperfine pattern was detected which indicated the successful formation of the corresponding Ru3+ intercalated oxidant. The formation of dIz and dZ decreased markedly with the addition of nitrotetrazolium blue chloride (NBT), a typical O2•- reactant. With a more specific and highly sensitive O2•- probe CT02-H, its ESR signal decayed rapidly in the presence of Ru(OP)2dppz2+ and MV2+, suggesting that O2•- was indeed produced. More interestingly, enantio-selective generation of oxidation products from dsDNA was observed with the two chiral forms of Ru(OP)2dppz2+. This represents the first report that the flash-quench technique with MV2+ as the quencher can oxidize dsDNA effectively to form dIz and dZ via the Ru3+/O2•- mediated mechanism. Our new findings provide a novel method to generate two radicals simultaneously, G (-H)• and O2•-, in close proximity to one another in dsDNA.

A Ru(II) Polypyridyl Complex Bearing Bathocuproine Ligand is a Potent Chemotherapeutic Agent Against Chemically Induced Skin Cancer Model

A Ru(II) Polypyridyl Complex Bearing Bathocuproine Ligand is a Potent Chemotherapeutic Agent Against Chemically Induced Skin Cancer Model

Contrasting Photosensitized Processes of Ru(II) Polypyridyl Structural Isomers Containing Linear and Hooked Intercalating Ligands Bound to Guanine-Rich DNA.

The DNA binding and cellular uptake of the lambda enantiomer of two bis-tetraazaphenanthrene (TAP) Ru(II) polypyridyl complexes containing either a linear dppn (1) or a hooked bdppz (2) benzodipyridophenazine ligand are reported, and the role of different charge-transfer states of the structural isomers in the photo-oxidation of guanine is explored. Both complexes possess characteristic metal-to-ligand charge-transfer (MLCT) bands between 400 and 500 nm and emission at ca. 630 nm in an aerated aqueous solution. Transient visible absorption (TrA) spectroscopy reveals that 400 nm excitation of 1 yields a dppn-based metal-to-ligand charge-transfer (MLCT) state, which in turn populates a dppn intraligand (3IL) state. In contrast, photoexcitation of 2 results in an MLCT state on the TAP ligand and not the intercalating bdppz ligand. Both 1 and 2 bind strongly to double-stranded guanine-rich DNA with a loss of emission. Combined TrA and time-resolved infrared (TRIR) spectroscopy confirms formation of the guanine radical cation when 2 is bound to the d(G5C5)2 duplex, which is not the case when 1 is bound to the same duplex and indicates a different mechanism of action in DNA. Utilizing the long-lived triplet excited lifetime, we show good uptake and localization of 2 in live cells as well as isolated chromosomes. The observed shortening of the excited-state lifetime of 2 when internalized in cell chromosomes is consistent with DNA binding and luminescent quenching due to guanine photo-oxidation.

Dual Photoreactive Ternary Ruthenium(II) Terpyridyl Complexes: A Comparative Study on Visible-Light-Induced Single-Step Dissociation of Bidentate Ligands and Generation of Singlet Oxygen.

The versatile and tunable ligand-exchange dynamics in ruthenium(II)-polypyridyl complexes imposed by the modulation of the steric and electronic effects of the coordinated ligands provide an unlimited scope for developing phototherapeutic agents. The photorelease of a bidentate ligand from the Ru-center is better suited for potent Ru(II)-based photocytotoxic agents with two available labile sites for cross-linking with biological targets augmented with possible phototriggered 1O2 generation. Herein, we introduced a phenyl-terpyridine (ptpy) ligand in the octahedral Ru(II) core of [Ru(ptpy)(L-L)Cl]+ to induce structural distortion for the possible photorelease of electronically distinct bidentate ligands (L-L). For a systematic study, we designed four Ru(II) polypyridyl complexes: [Ru(ptpy)(L-L)Cl](PF6), ([1]-[4]), where L-L = 1,2-bis(phenylthio)ethane (SPH) [1], N,N,N',N'-tetramethylethylenediamine (TMEN) [2], N1,N2-diphenylethane-1,2-diimine (BPEDI) [3], and bis[2-(diphenylphosphino)phenyl]ether (DPE-Phos) [4]. The detailed photochemical studies suggest a single-step dissociation of L-L from the bis-thioether (SPH) complex [1] and diamine (TMEN) complex [2], while no photosubstitution was observed for [3] and [4]. Complex [1] and [2] demonstrated a dual role, involving both photosubstitution and 1O2 generation, while [3] and [4] solely exhibited poor to moderate 1O2 production. The interplay of excited states leading to these behaviors was rationalized from the lifetimes of the 3MLCT excited states by using transient absorption spectroscopy, suggesting intricate relaxation dynamics and 1O2 generation upon excitation. Therefore, the photolabile complexes [1] and [2] could potentially act as dual photoreactive agents via the phototriggered release of L-L (PACT) and/or 1O2-mediated PDT mechanisms, while [4] primarily can be utilized as a PDT agent.

Ligand Characterization and DNA Intercalation of Ru(II) Polypyridyl Complexes: A Local Vibrational Mode Study.

We investigated in this work ruthenium-ligand bonding across the RuN framework in 12 Ru(II) polypyridyl complexes in the gas phase and solution for both singlet and triplet states, in addition to their affinity for DNA binding through π-π stacking interactions with DNA nucleobases. As a tool to assess the intrinsic strength of the ruthenium-ligand bonds, we determined local vibrational force constants via our local vibrational mode analysis software. We introduced a novel local force constant that directly accounts for the intrinsic strength of the π-π stacking interaction between DNA and the intercalated Ru(II) complex. According to our findings, [Ru(phen)2(dppz)]2+ and [Ru(phen)2(11-CN-dppz)]2+ provide an intriguing trade-off between photoinduced complex excitation and the strength of the subsequent π-π stacking interaction with DNA. [Ru(phen)2(dppz)]2+ displays a small singlet-triplet splitting and a strong π-π stacking interaction in its singlet state, suggesting a favorable photoexcitation but potentially weaker interaction with DNA in the excited state. Conversely, [Ru(phen)2(11-CN-dppz)]2+ exhibits a larger singlet-triplet splitting and a stronger π-π stacking interaction with DNA in its triplet state, indicating a less favorable photoinduced transition but a stronger interaction with DNA postexcitation. We hope our study will inspire future experimental and computational work aimed at the design of novel Ru-polypyridyl drug candidates and that our new quantitative measure of π-π stacking interactions in DNA will find a general application in the field.

Identification of mitochondrial ATP synthase as the cellular target of Ru-polypyridyl-β-carboline complexes by affinity-based protein profiling.

Ruthenium polypyridyl complexes are promising anticancer candidates, while their cellular targets have rarely been identified, which limits their clinical application. Herein, we design a series of Ru(II) polypyridyl complexes containing bioactive β-carboline derivatives as ligands for anticancer evaluation, among which Ru5 shows suitable lipophilicity, high aqueous solubility, relatively high anticancer activity and cancer cell selectivity. The subsequent utilization of a photo-clickable probe, Ru5a, serves to validate the significance of ATP synthase as a crucial target for Ru5 through photoaffinity-based protein profiling. Ru5 accumulates in mitochondria, impairs mitochondrial functions and induces mitophagy and ferroptosis. Combined analysis of mitochondrial proteomics and RNA-sequencing shows that Ru5 significantly downregulates the expression of the chloride channel protein, and influences genes related to ferroptosis and epithelial-to-mesenchymal transition. Finally, we prove that Ru5 exhibits higher anticancer efficacy than cisplatin in vivo. We firstly identify the molecular targets of ruthenium polypyridyl complexes using a photo-click proteomic method coupled with a multiomics approach, which provides an innovative strategy to elucidate the anticancer mechanisms of metallo-anticancer candidates.

SYNTHESIS, SPECTRAL STUDIES AND EVALUATION OF DNA BINDING, PHOTOCLEAVAGE, ANTICANCER ACTIVITY OF RU(II) POLYPYRIDYL COMPLEXES OF 2-(3,4,5-TRIMETHOXY-PHENYL)-H-IMIDAZOLE[4,5-F][1,10]PHENANTHROLINE

The two novel Ru(II) polypyridyl complexes of the type [Ru(NN)2L](ClO4)2.2H2O,where NN is dmp=4,4-dimethyl-1,10 ortho phenanthroline and dmb=4,4-dimethyl 2,2-bipyridine and L is Intercalator ligand, TMIP=2-(3,4,5-Trimethoxy-phenyl)-H-imidazole[4,5-f][1,10]phenanthroline were synthesized and characterized by different spectroscopic techniques. The binding ability of Ru (II) complexes with CT-DNA was investigated by Biophysical studies – UV-Visible absorption studies, Fluorescence studies (Emission & Quenching) and Viscosity studies. The binding constants of these complexes from absorption studies are 1.2x105 M-1and 8x104M-1respectively.These values are less as compared to the existing TMIP complex [Ru(phen)2TMPIP]+2, indicative of the effect of substitution over the ancillary ligand which reduce the binding capacity of metal complex to CT-DNA. The results from the viscosity studies suggest an intercalative binding mechanism. The DNA cleavage studies show that the Ru (II) complexes successfully cleaved the pBR322 DNA. Both the complexes exhibit not notable anti cancer acivity.

Insights into the anticancer photodynamic activity of Ir(III) and Ru(II) polypyridyl complexes bearing β-carboline ligands

Ir(III) and Ru(II) polypyridyl complexes are promising photosensitizers (PSs) for photodynamic therapy (PDT) due to their outstanding photophysical properties. Herein, one series of cyclometallated Ir(III) complexes and two series of Ru(II) polypyridyl derivatives bearing three different thiazolyl-β-carboline N^N′ ligands have been synthesized, aiming to evaluate the impact of the different metal fragments ([Ir(C^N)2]+ or [Ru(N^N)2]2+) and N^N’ ligands on the photophysical and biological properties. All the compounds exhibit remarkable photostability under blue-light irradiation and are emissive (605 < λem < 720 nm), with the Ru(II) derivatives displaying higher photoluminescence quantum yields and longer excited state lifetimes. The Ir PSs display pKa values between 5.9 and 7.9, whereas their Ru counterparts are less acidic (pKa > 9.3). The presence of the deprotonated form in the Ir-PSs favours the generation of reactive oxygen species (ROS) since, according to theoretical calculations, it features a low-lying ligand-centered triplet excited state (T1 = 3LC) with a long lifetime. All compounds have demonstrated anticancer activity. Ir(III) complexes 1–3 exhibit the highest cytotoxicity in dark conditions, comparable to cisplatin. Their activity is notably enhanced by blue-light irradiation, resulting in nanomolar IC50 values and phototoxicity indexes (PIs) between 70 and 201 in different cancer cell lines. The Ir(III) PSs are also activated by green (with PI between 16 and 19.2) and red light in the case of complex 3 (PI = 8.5). Their antitumor efficacy is confirmed by clonogenic assays and using spheroid models. The Ir(III) complexes rapidly enter cells, accumulating in mitochondria and lysosomes. Upon photoactivation, they generate ROS, leading to mitochondrial dysfunction and lysosomal damage and ultimately cell apoptosis. Additionally, they inhibit cancer cell migration, a crucial step in metastasis. In contrast, Ru(II) complex 6 exhibits moderate mitochondrial activity. Overall, Ir(III) complexes 1–3 show potential for selective light-controlled cancer treatment, providing an alternative mechanism to chemotherapy and the ability to inhibit lethal cancer cell dissemination.

Sensitizing TiO2 nanoparticles with Ru(II) polypyridyl complexes containing anchoring nitrile groups for applications in solar cells

In this work, five dyes-based on Ru(II) complexes with 2,2́- bipyridyl ligands substituted at the 4,4́-positions with a different number of nitrile anchoring groups and distinct −X electronic donor units were tested as TiO2 electrode sensitizers in solar cells (SCs). All dyes were PF6- salts: three complexes of formulae [Ru(4,4́-(X)2-bpy)2(Mebpy-CN)]2+ with one nitrile group and X = − CH3, –OCH, −N(CH3)2; and two of formulae [Ru(4,4′-(X)2-bpy)(Mebpy-CN)2]2+, with two nitrile units and X = –OCH3, −N(CH3)2. In all cases, bpy = 2,2′-bipyridine and Mebpy-CN = 4-methyl-2,2′-bipyridine-4′-carbonitrile. After characterizing the electrodes morphologically and optically, they were employed in DSSCs (dye-sensitized SCs) using Pt/FTO as counter-electrode (CE) and a KI/I2 in CH3CN as liquid electrolyte. Current density–voltage (J-V) and impedance spectroscopy (IS) measurements highlighted that the SC with the highest efficiency (η) is the one that contains − N(CH3)2 as donor units and two nitrile groups as anchoring entities. It could be concluded that higher electronic delocalization that occurs between the bpys substituted with strong electronic donor groups and the metal orbitals impose excellent properties to improve efficiency, which further improves if two anchoring groups are employed.

Reductive Dynamic and Static Excited State Quenching of a Homoleptic Ruthenium Complex Bearing Aldehyde Groups.

A new homoleptic Ru polypyridyl complex bearing two aldehyde groups on each bipyridine ligand, [Ru(dab)3](PF6)2, where dab is 4,4'-dicarbaldehyde-2,2'-bipyridine, was synthesized, characterized, and utilized for iodide photo-oxidation studies. In acetonitrile (CH3CN) solution, the complex displayed an intense metal-to-ligand charge transfer (MLCT) absorbance maximum at 475 nm (ε = 22,000 M-1 cm-1) and an infrared (IR) band at 1712 cm-1 assigned to the pendent aldehyde groups. Visible light excitation in air-saturated solution resulted in room temperature photoluminescence (PL) with a maximum at 675 nm, a quantum yield, ϕPL = 0.048, and an excited state lifetime, το = 440 ns, from which radiative and nonradiative relaxation rate constants were extracted, kr = 9.1 × 104 s-1 and knr = 1.8 × 106 s-1. Pulsed visible light excitation yielded transient UV-vis and IR absorption spectra consistent with an MLCT excited state; relaxation occurred with the maintenance of two isosbestic points in the visible region, and a lifetime that agreed with that measured by time-resolved PL. Cyclic voltammetry studies in a CH3CN solution with 0.1 M TBAPF6 electrolyte revealed a quasi-reversible oxidation, E°(RuIII/II) = +1.25 V vs. Fc+/0, and three sequential one-electron reductions at -1.10, -1.25, and -1.54 V vs. Fc+/0. An excited state reduction potential of E°(Ru*2+/+) = +0.89 V vs. Fc+/0 was estimated with the Rehm-Weller expression. Titration of tetrabutylammonium iodide, TBAI, into a CD3CN solution of [Ru(dab)3](PF6)2 resulted in significant shifts in the aldehyde H atom and 3,3'-biypridyl resonances that were analyzed with a 1:1 equilibrium model, from which Keq = 460 M-1 was extracted, increasing to 5800 M-1 when the solvent was changed to acetone-d6. Iodide titrations resulted in a significant quenching of the [Ru(dab)3]*2+ lifetime and quantum yield in both CH3CN and acetone solvents. In CH3CN, the quenching was mainly dynamic and well described by the Stern-Volmer model, from which a quenching rate constant, kq, of 4.5 × 1010 M-1 s-1 and an equilibrium constant, Keq, of 8.3 × 103 M-1 were obtained. In acetone, the static quenching pathway by iodide was greatly enhanced, with a Keq of 1.2 × 104 M-1 and a higher kq of 9.2 × 1010 M-1 s-1.

Untargeted metabolomics coupled with genomics in the study of sucrose and xylose metabolism in Pectobacterium betavasculorum.

Pectobacterium betavasculorum is a member of the Pectobacerium genus that inhabits a variety of niches and is found in all climates. Bacteria from the Pectobacterium genus can cause soft rot disease on various plants due to the secretion of plant cell wall degrading enzymes (PCWDEs). The species P. betavasculorum is responsible for the vascular necrosis of sugar beet and soft rot of many vegetables. It also infects sunflowers and artichokes. The main sugar present in sugar beet is sucrose while xylose is one of the main sugars in artichoke and sunflower. In our work, we applied metabolomic studies coupled with genomics to investigate the metabolism of P. betavasculorum in the presence of xylose and sucrose as the only carbon source. The ability of the strains to use various sugars as the only carbon source were confirmed by the polypyridyl complex of Ru(II) method in 96-well plates. Our studies provided information on the metabolic pathways active during the degradation of those substrates. It was observed that different metabolic pathways are upregulated in the presence of xylose in comparison to sucrose. The presence of xylose enhances extracellular metabolism of sugars and glycerol as well as stimulates EPS and IPS synthesis. In contrast, in the presence of sucrose the intensive extracellular metabolism of amines and amino acids is promoted.

Ru(II) Oligothienyl Complexes with Fluorinated Ligands: Photophysical, Electrochemical, and Photobiological Properties.

A series of Ru(II) complexes incorporating two 4,4'-bis(trifluoromethyl)-2,2'-bipyridine (4,4'-btfmb) coligands and thienyl-appended imidazo[4,5-f][1,10]phenanthroline (IP-nT) ligands was characterized and assessed for phototherapy effects toward cancer cells. The [Ru(4,4'-btfmb)2(IP-nT)]2+ scaffold has greater overall redox activity compared to Ru(II) polypyridyl complexes such as [Ru(bpy)3]2+. Ru-1T-Ru-4T have additional oxidations due to the nT group and additional reductions due to the 4,4'-btfmb ligands. Ru-2T-Ru-4T also exhibit nT-based reductions. Ru-4T exhibits two oxidations and eight reductions within the potential window of -3 to +1.5 V. The lowest-lying triplets (T1) for Ru-0T-2T are metal-to-ligand charge-transfer (3MLCT) excited states with lifetimes around 1 μs, whereas T1 for Ru-3T-4T is longer-lived (∼20-24 μs) and of significant intraligand charge-transfer (3ILCT) character. Phototoxicity toward melanoma cells (SK-MEL-28) increases with n, with Ru-4T having a visible EC50 value as low as 9 nM and PI as large as 12,000. Ru-3T and Ru-4T retain some of this activity in hypoxia, where Ru-4T has a visible EC50 as low as 35 nM and PI as high as 2900. Activity over six biological replicates is consistent and within an order of magnitude. These results demonstrate the importance of lowest-lying 3ILCT states for phototoxicity and maintaining activity in hypoxia.

Aminoquinoline-based ruthenium(II) and iridium(III) polypyridyl complexes: Investigating potential photosensitisers for cancer treatment via photodynamic therapy

Cancer is a devastating noncommunicable disease that remains one of the most pressing health challenges of the twenty-first century. Chemotherapy stands as one of the most common and effective cancer treatment methods. However, severe side effects and acquired drug resistance in many cancers have significantly diminished the efficacy of current chemotherapeutic agents. The urgent demand for novel treatment modalities has led to the development of photodynamic therapy (PDT) for the treatment of various cancer types. In this work, the synthesis of aminoquinoline-based transition metal complexes containing two PGMs (Ir(III) and Ru(II)) as potential photosensitisers is described. Mononuclear N,N-chelated Ru(II) and Ir(III) transition metal complexes were synthesized by reacting 4-aminoquinoline Schiff base ligands, which contain either a pyridyl or a quinolyl entity. The photostable Ru(II) and Ir(III) polypyridyl complexes were investigated for their potential use as PDT agents. In vitro cytotoxicity screenings conducted against a melanoma cell line (501mel) both in the absence and presence of light confirmed that all complexes demonstrated increased biological activity when exposed to visible light at 455 nm. Overall, the Ru(II) complexes are superior phototoxic agents in comparison with their Ir(III) congenors.

Unlocking the Fluorine-Free Buoy Effect: Surface-Enriched Ruthenium Polypyridine Complexes in Ionic Liquids.

Controlling the local concentration of metal complexes at the surface of ionic liquids (ILs) is a highly sought-after objective due to its pivotal implications in supported ionic liquid phase (SILP) catalysis. Equally important is to avoid per- and polyfluorinated substances due to environmental concerns. Herein, we investigate the surface enrichment of Ru polypyridyl complexes with fluorine-free alkylic side groups of varying lengths and shapes, using the hydrophilic IL [C2C1Im][OAc] as solvent. Additional charged carboxylate groups are included into the polypyridyl ligands to increase the solubility of the complex in the IL. When the ligand system is functionalized with long and hydrophobic alkyl side chains, the complex predominantly localizes at the IL/vacuum interface, as deduced from angle-resolved X-ray photoelectron spectroscopy. Conversely, in the presence of short or more bulky substituents, no surface enrichment is observed. This buoy-like behaviour with fluorine-free side groups is explored for 0.05 %mol to 1 %mol solutions. Intriguingly, surface saturation occurs at approximately 0.5 %mol, which is beneficial to the efficient operation of catalytic systems featuring high surface areas, such as SILP catalysts.

Photosensitizers Based on Bichromophoric Dyads Combining Ru(II)-Polypyridyl Complexes and Dissymmetric Perylene Monoimide Derivatives: The Nontrivial Role of Ligand Substitution.

The covalent modification of Ru(II) polypyridyl complexes (RPCs) with organic chromophores is a powerful strategy to obtain metal-based photosensitizer agents (PSs) with improved performance for application in photodynamic therapy (PDT). In this respect, perylene-imides are of particular interest due to their rich chemical-physical repertoire, and it is therefore quite surprising that their combination with RPCs has been poorly considered so far. Herein, we report on the photophysical behavior of two newly synthesized RPCs bearing a perylene monoimide appendant (PMI-Ad). Differently from the majority of RPCs-perylene-imides dyads, these chromophores are dissymmetric and are tethered to the metal centers through a single C-C bond in the 3- or 5-position of 1,10-phenanthroline (Ru-3PMI-Ad and Ru-5PMI-Ad). Both compounds show excellent singlet oxygen photosensitizing activity, with quantum yields reaching >90% in the case of Ru-3PMI-Ad. A combined spectroscopic and theoretical analysis, also involving transient absorption and luminescence lifetime measurements, demonstrates that both compounds undergo intersystem crossing on a very fast time scale (tens of picoseconds) and with high efficiency. Our results further demonstrate that the increased electron delocalization between the metal center and the PMI-Ad chromophore observed for Ru-3PMI-Ad additionally contributes to increase the singlet oxygen quantum yields by prolonging the lifetime of the triplet state.

Enhanced Photostability and Photoactivity of Ruthenium Polypyridyl-Based Photocatalysts by Covalently Anchoring Onto Reduced Graphene Oxide.

Recentstudies toward finding more efficient ruthenium metalloligands for photocatalysis applications have shown that the derivatives of the linear [Ru(dqp)2]2+ (dqp: 2,6-di(quinolin-8-yl)-pyridine) complexes hold significant promise due to their extended emission lifetime in the μs time scale while retaining comparable redox potential, extinction coefficients, and absorption profile in the visible region to [Ru(bpy)3]2+ (bpy: 2,2'-bipyridine) and [Ru(tpy)2]2+ (tpy: 2,2':6',2″-terpyridine) complexes. Nevertheless, its photostability in aqueous solution needs to be improved for its widespread use in photocatalysis. Carbon-based supports have arisen as potential solutions for improving photostability and photocatalytic activity, yet their effect greatly depends on the interaction of the metal complex with the support. Herein, we present a strategy for obtaining Ru-polypyridyl complexes covalently linked to aminated reduced graphene oxide (rGO) to generate novel materials with long-term photostability and increased photoactivity. Specifically, the hybrid Ru(dqp)@rGO system has shown excellent photostable behavior during 24 h of continual irradiation, with an enhancement of 10 and 15% of photocatalytic dye degradation in comparison with [Ru(dqp)2]2+ and Ru(tpy)@rGO, respectively, as well as remarkable recyclability. The presented strategy corroborates the potential of [Ru(dqp)2]2+ as an interesting photoactive molecule to produce more advantageous light-active materials by covalent attachment onto carbon-based supports.

Nitrile Substituents at the Conjugated Dipyridophenazine Moiety as Infrared Redox Markers in Electrochemically Reduced Heteroleptic Ru(II) Polypyridyl Complexes.

Ruthenium(II) complexes [Ru(tap)2(NN)]2+ (tap = 1,4,5,8-tetraazaphenanthrene, NN = 11-cyano-dipyrido[3,2-a:2',3'-c]phenazine (11-CN-dppz) and 11,12-dicyano-dipyrido[3,2-a:2',3'-c]phenazine (11,12-CN-dppz)) feature the C≡N groups as infrared (IR)-active redox markers. They were studied by cyclic voltammetry, UV-vis, and IR spectroelectrochemistry (SEC), and density functional theory calculations to assign the four 1e- reduction waves R1-R4 observed in dichloromethane. Generally, the NN ligands are reduced first (R1). For [Ru(tap)2(11,12-CN-dppz)]2+, R1 is sufficiently separated from R2 and delocalized over both tap ligands. Accordingly, IR SEC conducted at R1 shows a large red shift of the νs,as(C≡N) modes by -18/-28 cm-1, accompanied by a 4-fold enhancement of the νs(C≡N) intensity, comparably with reference data for free 11,12-CN-dppz. The first tap-based reduction of spin-doublet [Ru(tap)2(11,12-CN-dppz)]+ to spin-triplet [Ru(tap)2(11,12-CN-dppz)] at R2 decreased ν(C≡N) by merely -2 cm-1, while the intensity enhancement reached an overall factor of 8. Comparably, a red shift of ν(C≡N) by -27 cm-1 resulted from the 1e- reduction of [Ru(tap)2(11-CN-dppz)]2+ at R1 (poorly resolved from R2), and the intensity enhancement was roughly 3-fold. Concomitant 1e- reductions of the tap ligands (R2 and R3) caused only minor ν(C≡N) shifts of -3 cm-1 and increased the absorbance by overall factors of 6.5 and 8, respectively.