Ruthenium Polypyridine Complexes Research Articles

Electrochemical behavior of phosphine-substituted ruthenium(II) polypyridine complexes with a single labile ligand.

A series of phosphine-substituted ruthenium polypyridine complexes, cis(P,Cl)-[Ru(trpy)(Pqn)Cl]PF6 (cis-Cl), trans(P,MeCN)-[Ru(trpy)(Pqn)(MeCN)](PF6)2 (trans-PN), cis(P,MeCN)-[Ru(trpy)(Pqn)(MeCN)](PF6)2 (cis-PN), and [Ru(trpy)(dppbz)(MeCN)](PF6)2 (PP), were synthesized and crystallographically characterized (trpy = 2,2':6',2″-terpyridine, Pqn = 8-(diphenylphosphanyl)quinoline, and dppbz = 1,2-bis(diphenylphosphanyl)benzene). In electrochemical measurements for cis-PN and PP, the reduction of cis-PN resulted in the formation of trans-PN via cis-trans isomerization and that of PP proceeded via a two-electron-transfer reaction. The mechanism of the electrochemical behaviors is discussed through consideration of five-coordinated species, [Ru(trpy)(Pqn)](n+) or [Ru(trpy)(dppbz)](n+) (n = 0-2), formed by liberation of a monodentate labile ligand.

Ruthenium Polypyridine Complexes Bearing Pyrroles and π-Extended Analogues. Synthesis, Spectroelectronic, Electrochemical, and Photovoltaic Properties

This personal account gives an overview of our research efforts dedicated to the chemistry of ruthenium polypyridine complexes, with a special focus on the effect of pyrrole substituents and their π-extended analogues. The synthesis of the complexes and their characterization will be presented, as well as their photovoltaic applications when applicable.

Anchor‐Functionalized Push‐Pull‐Substituted Bis(tridentate) Ruthenium(II) Polypyridine Chromophores: Photostability and Evaluation as Photosensitizers

AbstractStable push‐pull substituted heteroleptic bis(tridentate) ruthenium(II) polypyridine complexes with COOH or 2,2′‐bipyridine anchor groups have been prepared and characterized by 1H, 13C and 15N NMR 1D and 2D spectroscopy, infrared spectroscopy, elemental analysis, high‐resolution ESI mass spectrometry, electrochemistry, UV/Vis absorption spectroscopy, luminescence spectroscopy, and density functional calculations. The complexes feature a pronounced electronic directionality and high absorption wavelengths up to λmax = 544 nm extending to 720 nm as a result of favorable push‐pull substitutions. A remarkable photostability in the presence of water and coordinating ions (I–) was discovered for the tridentate complexes when compared with the standard ruthenium sensitizer N719 and tris(bidentate) [Ru(bpy)3](PF6)2, which are highly photolabile under the same conditions (photodissociation/photosubstitution). The complexes were studied as photosensitizers in dye‐sensitized solar cells. The incident photon‐to‐current conversion efficiency follows the absorption spectra into the NIR region. However, the high positive charge of the complexes (2+) favors the recombination of the injected electrons with I3– of the redox electrolyte, which is evidenced by high dark currents and short electron recombination lifetimes, leading to low cell performances compared with cells with the negatively charged N719 dye.

A selective, long-lived deep-red emissive ruthenium(II) polypyridine complexes for the detection of BSA

A selective, label free luminescence sensor for bovine serum albumin (BSA) is investigated using ruthenium(II) complexes over the other proteins. Interaction between BSA and ruthenium(II) complexes has been studied using absorption, emission, excited state lifetime and circular dichroism (CD) spectral techniques. The luminescence intensity of ruthenium(II) complexes (I and II), has enhanced at 602 and 613nm with a large hypsochromic shift of 18 and 5nm respectively upon addition of BSA. The mode of binding of ruthenium(II) complexes with BSA has analyzed using computational docking studies.

ChemInform Abstract: Visible‐Light‐Induced Photoredox Catalysis: An Easy Access to Green Radical Chemistry

AbstractReview: <100 refs.

Density-functional study of luminescence in polypyridine ruthenium complexes

A density-functional theory (DFT) study of five ruthenium complexes has been carried out with the goal of gaining deeper insight into factors governing luminescence lifetimes. The five compounds are [Ru(bpy)3]2+ (1), [Ru(L1)2]2+ (2), [Ru(tpy)2]2+ (3), [Ru(L1)(tpy)]2+ (4), and [Ru(L2)2]2+ (5), where bpy = 2,2′-bipyridine, tpy = 2,2′;6′,2″-terpyridine, L1 = 1,1′-[2,6-pyridinediylbis(methylene)]bis[3-methylimidazolium] hexafluorophosphate and L2 = 1,1′-[2,6-pyridinediylbis(methylene)]bis[3-methylbenziimidazolium]. Experimental work, including the synthesis and photophysical properties of 5 is also reported in the context of this study. Gas phase geometries optimized using X-ray crystallography geometries as start geometries were found to be close to the start geometries. Gas phase absorption spectra calculated using time-dependent DFT were found to be in good agreement with spectra measured in solution. A partial density of states (PDOS) analysis of the molecular orbitals shows that it is possible to recover a ligand field theory (LFT)-like picture. On the basis of this PDOS-derived LFT-like picture we propose two orbital-based luminescence indices, both motivated by the idea that luminescence quenching results from a low 3MLCT → 3MC barrier. The first luminescence index is ΔE, the difference between the eg* and lowest energy π* PDOS bands. The second luminescence index is d × π, the product of the amount of π character in the t2g band with the amount of ruthenium d character in the 1π* band. These luminescence measures are intended as qualitative rather than quantitative predictors. Low values of ΔE and high values of d × π are shown to correlate with lack of luminescence for the five compounds studied in this paper, while high values of ΔE and low values of d × π correlate well with luminescence.

Visible-Light-Induced Photoredox Catalysis: An Easy Access to Green Radical Chemistry

Photoredox catalysis by well-known ruthenium(II) polypyridine complexes and appropriate cyclometalated iridium(III) derivatives is a useful tool for redox reactions in synthetic chemistry, because these materials can effectively catalyze single-electron-transfer (SET) processes by irradiation with visible light. This provides a new strategy for efficient and selective radical reactions. We have developed several photocatalytic reactions in which organic radicals are generated by photoredox catalysis and which have remarkable merits in terms of green and sustainable chemistry. 1 Introduction 2 Photoredox Cycles of [Ru(bpy)3]2+ and Cyclometalated Iridium Complexes 3 Radical Reactions that Occur Through a Reductive Quenching Cycle 3.1 Oxyamination of Enamines 3.2 Tin-Free Giese-Type Reactions Through Oxidation of Organoborates 4 Radical Reactions Through an Oxidative Quenching Cycle 4.1 Two-Electron Transfer Process Mediated by Duroquinone: Oxidative Coupling of an Enamine with a Silyl Enol Ether 4.2 Radical Trifluoromethylation of Alkenes 5 Conclusions and Outlook

Synthesis, Characterization, and Photophysical Studies of Some Novel Ruthenium(II) Polypyridine Complexes Derived from Benzothiazolyl hydrazones

A series of five benzothiazolylhydrazone ligands 3a–3e and their seven novel Ru(II) polypyridine complexes 4a–4d, 5a, 5d, 5e of the type [Ru(N–N)2(L)]Cl2, where (N–N)2 is 2,2′-bipyridine (bpy)2 or 1,10-phenanthroline (phen)2 and (L) is ligands 3a–3e, have been synthesized and characterized by elemental analysis, IR, 1H NMR, electronic absorption, and emission spectral studies. The interpretation of the analytical data revealed that the ligands coordinate with the metal ion in a bidentate fashion through azomethine nitrogen and phenolic oxygen to form complexes. These ligands and complexes also exhibit absorption and luminescence properties.

Synthesis of a novel dinuclear ruthenium polypyridine dye for dye-sensitized solar cells application

A new dinuclear ruthenium(II) polypyridine complex has been successfully synthesized. The new compound has been characterized by spectroscopic and electrochemical methods. Its potential application as a sensitizing dye in dye-sensitized solar cells has been checked under AM 1.5 G irradiation conditions (100mWcm−2) and its performance was compared to that of a commercially available mononuclear analogous dye. The overall light-to-electricity conversion efficiency of the photovoltaic device sensitized by the new dinuclear dye has been found to be over 2.5 times lower than that sensitized by the commercial analogue, despite a much higher extinction coefficient of the former dye. The probable reasons for the lower photovoltaic activity are discussed.

Excited State Tuning of Bis(tridentate) Ruthenium(II) Polypyridine Chromophores by Push–Pull Effects and Bite Angle Optimization: A Comprehensive Experimental and Theoretical Study

The synergy of push-pull substitution and enlarged ligand bite angles has been used in functionalized heteroleptic bis(tridentate) polypyridine complexes of ruthenium(II) to shift the (1) MLCT absorption and the (3) MLCT emission to lower energy, enhance the emission quantum yield, and to prolong the (3) MLCT excited-state lifetime. In these complexes, that is, [Ru(ddpd)(EtOOC-tpy)][PF6 ]2 , [Ru(ddpd-NH2 )(EtOOC-tpy)][PF6 ]2 , [Ru(ddpd){(MeOOC)3 -tpy}][PF6 ]2 , and [Ru(ddpd-NH2 ){(EtOOC)3 -tpy}][PF6 ]2 the combination of the electron-accepting 2,2';6',2''-terpyridine (tpy) ligand equipped with one or three COOR substituents with the electron-donating N,N'-dimethyl-N,N'-dipyridin-2-ylpyridine-2,6-diamine (ddpd) ligand decorated with none or one NH2 group enforces spatially separated and orthogonal frontier orbitals with a small HOMO-LUMO gap resulting in low-energy (1) MLCT and (3) MLCT states. The extended bite angle of the ddpd ligand increases the ligand field splitting and pushes the deactivating (3) MC state to higher energy. The properties of the new isomerically pure mixed ligand complexes have been studied by using electrochemistry, UV/Vis absorption spectroscopy, static and time-resolved luminescence spectroscopy, and transient absorption spectroscopy. The experimental data were rationalized by using density functional calculations on differently charged species (charge n=0-4) and on triplet excited states ((3) MLCT and (3) MC) as well as by time-dependent density functional calculations (excited singlet states).

Water Oxidation with Mononuclear Ruthenium(II) Polypyridine Complexes Involving a Direct RuIV═O Pathway in Neutral and Alkaline Media

The catalytic water oxidation mechanism proposed for many single-site ruthenium complexes proceeds via the nucleophilic attack of a water molecule on the Ru(V)═O species. In contrast, Ru(II) complexes containing 4-t-butyl-2,6-di-1',8'-(naphthyrid-2'-yl)-pyridine (and its bisbenzo-derivative), an equatorial water, and two axial 4-picolines follow the thermodynamically more favorable "direct pathway" via [Ru(IV)═O](2+), which avoids the higher oxidation state [Ru(V)═O](3+) in neutral and basic media. Our experimental and theoretical results that focus on the pH-dependent onset catalytic potentials indicative of a PCET driven low-energy pathway for the formation of products with an O-O bond (such as [Ru(III)-OOH](2+) and [Ru(IV)-OO](2+)) at an applied potential below the Ru(V)═O/Ru(IV)═O couple clearly support such a mechanism. However, in the cases of [Ru(tpy)(bpy)(OH2)](2+) and [Ru(tpy)(bpm)(OH2)](2+), the formation of the Ru(V)═O species appears to be required before O-O bond formation. The complexes under discussion provide a unique functional model for water oxidation that proceeds by four consecutive PCET steps in neutral and alkaline media.

Rigid 5′-6-locked phenanthroline-derived nucleosides chelated to ruthenium and europium ions

We describe complexes of ruthenium and europium with rigid, 5′-6-locked 1,10-phenanthroline-containing nucleosides. Both nucleosides were synthesized from condensation of 5-amino-2′-deoxycytidine with the corresponding diketone. The ruthenium nucleoside displayed fluorescence characteristic of polypyridine ruthenium complexes with a maximum at 616nm and a quantum yield of 0.011. Binding of europium to the 1,10-phenanthroline-2,9-diacid moiety of the lanthanide binding nucleoside showed formation of a 1:1 complex with emission at 570–630nm, whose emission was enhanced by addition of two phenanthroline ligands. The lanthanide-binding nucleoside was incorporated into DNA oligonucleotides and shown to selectively bind one equivalent of europium ions.

Arylamine‐Modified Thiazoles as Donor–Acceptor Dyes: Quantum Chemical Evaluation of the Charge‐Transfer Process and Testing as Ligands in Ruthenium(II) Complexes

AbstractA series of new 4‐hydroxy‐1,3‐thiazole‐based chromophores bearing different arylamine components (triarylamines, carbazole, and phenothiazine) as electron donors and azaheterocycle components (pyridine, pyrazine and pyrimidine) as electron‐acceptor moieties have been synthesized. Elaborate quantum chemical calculations were carried out with two selected compounds to identify the natures of the HOMO/LUMO transition and of the intramolecular charge‐transfer state. The electrochemical properties were investigated: the dyes show reversible first oxidation and reduction peaks, with the former strongly dominated by the type of arylamine. The donor moieties were synthesized under Buchwald–Hartwig conditions. Several of the presented X‐ray structures provide deeper insight into the geometries of the ligands. The bidentate nature of the chromophores makes them suitable as ligands in transition metal complexes. The corresponding ruthenium(II) polypyridine complexes – Ru(dmbpy)2(L)(PF6)2 (dmbpy = 4,4′‐dimethyl‐2,2′‐bipyridine) – were successfully synthesized for seven of the ligands. The MLCT bands in these complexes are significantly broadened, resulting in improved light‐harvesting efficiencies.

Click Chemistry on a Ruthenium Polypyridine Complex. An Efficient and Versatile Synthetic Route for the Synthesis of Photoactive Modular Assemblies

In this Communication, we present the synthesis and use of [Ru(bpy)(2)(bpy-CCH)](2+), a versatile synthon for the construction of more sophisticated dyads by means of click chemistry. The resulting chromophore-acceptor or -donor complexes have been studied by flash photolysis and are shown to undergo efficient electron transfer to/from the chromophore. Additionally, the photophysical and chemical properties of the original chromophore remain intact, making it a very useful component for the preparation of visible-light-active dyads.

Synthesis of a ruthenium(II) polypyridine complex with 1,10-phenanthrolineselenazole as ligand and investigation of its G-quadruplex DNA-binding properties

A new Ru(II) complex, [Ru(bpy)2L](ClO4)2 (bpy = 2,2′-bipyridine, L = 1,10-phenanthrolineselenazole), has been synthesized and structurally characterized by elemental analysis, ESI-MS, and 1H NMR. The interaction of human telomeric oligomer 5′-AG3(T2AG3)3-3′ with the Ru(II) complex was explored by competition FRET experiment, fluorescence titration, circular dichroism spectroscopy, thermal denaturation, polymerase chain reaction stop assay, and TRAP assay. The Ru(II) complex can selectively bind to G-quadruplex DNA. The results indicated that the complex not only induces a remarkable conformational change of human telomeric DNA, but also has the ability to stabilize the G-quadruplex.

A High Molar Extinction Coefficient Bisterpyridyl Homoleptic Ru(II) Complex with trans-2-Methyl-2-butenoic Acid Functionality: Potential Dye for Dye-Sensitized Solar Cells

In our continued efforts in the synthesis of ruthenium(II) polypyridine complexes as potential dyes for use in varied applications, such as the dye-sensitized solar cells (DSSCs), this work particularly describes the synthesis, absorption spectrum, redox behavior and luminescence properties of a new homoleptic ruthenium(II) complex bearing a simple trans-2-methyl-2-butenoic acid functionality as the anchoring ligand on terpyridine moiety. The functionalized terpyridine ligand: 4′-(trans-2-methyl-2-butenoic acid)-terpyridyl (L1) was synthesized by aryl bromide substitution on terpyridine in a basic reaction condition under palladium carbide catalysis. In particular, the photophysical and redox properties of the complex formulated as: bis-4′-(trans-2-methyl-2-butenoic acid)-terpyridyl ruthenium(II) bis-hexafluorophosphate [Ru(L1)2(PF6)2] are significantly better compared to those of [Ru(tpy)2]2+ and compare well with those of the best emitters of Ru(II) polypyridine family containing tridentate ligands. Reasons for the improved photophysical and redox properties of the complex may be attributed partly to the presence of a substituted α,β-unsaturated carboxylic acid moiety leading to increase in the length of π-conjugation bond thereby enhancing the MLCT-MC (Metal-to-ligand-charge transfer-metal centred) energy gap, and to the reduced difference between the minima of the excited and ground states potential energy surfaces.

A ruthenium(ii) complex with environment-responsive dual emission and its application in the detection of cysteine/homocysteine

A ruthenium polypyridine complex [Ru(phen)(2)(IPBA)](PF(6))(2) (complex 1) (IPBA = 4-(1H-imidazo[4,5-f][1,9]phenanthroline-2-yl)benzaldehyde), which displays environment-responsive dual emissive properties, was designed and synthesized. In aprotic solvent, such as DMSO, DMF or CH(3)CN, the complex emits strong cyan light. When in protic solvent, it emits orange light. Similarly, the response of the complex to homocysteine and cysteine (Hcy/Cys) also shows obvious solvent dependence. TDDFT calculations reveal that the protonation of imidazole nitrogen in protic solution is responsible for the luminescent red shift. Hence, the complex could be used to detect Hcy/Cys in aprotic solvent, as well as in protic solvent.

New dyads using (metallo)porphyrins as ancillary ligands in polypyridine ruthenium complexes. Synthesis and electronic properties

Porphyrins bearing enaminoketones at their periphery have been used as ancillary ligands in ruthenium complexes. Free base, nickel and zinc porphyrins were successfully coordinated to Ru(bpy)(2)Cl(2) under microwave irradiation. The positive contribution of the ruthenium complex was demonstrated by the complexes' wide absorption domains that covered the 500-600 nm region where the parent porphyrins did not absorb. Electrochemical as well as computational data revealed an efficient electronic communication between the porphyrins and the ruthenium cation in the dyads.

Sevenfold enhancement on porphyrin dye efficiency by coordination of ruthenium polypyridine complexes

Sevenfold enhancement of photoconversion efficiency was achieved by incorporation of peripheral ruthenium complexes to a porphyrin dye, generating supramolecular effects capable of playing several key roles (e.g., transferring energy to, inhibiting aggregation, and accepting the hole generated in the porphyrin center after electron injection), providing new insights for the design of better DSSC photosensitizers.

Correlation of photodynamic activity and singlet oxygen quantum yields in two series of hydrophobic monocationic porphyrins

The photodynamic properties of eight hydrophobic monocationic methyl and ruthenium polypyridine complex derivatives of free-base and zinc(II) meso-triphenyl-monopyridylporphyrin series were evaluated and compared using HeLa cells as model. The cream-like polymeric nanocapsule formulations of marine atelocollagen/xanthan gum, prepared by the coacervation method, exhibited high phototoxicity but negligible cytotoxicity in the dark. Interestingly, the formulations of a given series presented similar photodynamic activities but the methylated free-base derivatives were significantly more phototoxic than the respective ruthenated photosensitizers, reflecting the higher photoinduced singlet oxygen quantum yields of those monocationic porphyrin dyes.