New ruthenium sensitizers containing styryl and antenna fragments

Amphiphilic ligands 4′-((4-(5-pyridin-4-yloxy)pentyloxy)styryl)-4-methyl-2,2′-bipyridine (L1), 4,4′-bis((E)-4-(5-(pyridin-4-yloxy)pentyloxy)styryl)-2,2′-bipyridine (L2), 4′-(4-(5-(4′-cyano-4-biphenoxy)pentyloxy)styryl)-4-methyl-2,2′-bipyridine (L3), and 4′-(4-(5-(zinc tetrakis-5,10,15-tritolyl-20-(4-hydroxyphenyl)porphyrin)pentyloxy)styryl)-4-methyl-2,2′-bipyridine (L4) and their heteroleptic ruthenium(II) complexes of the types [Ru(L1)(L)(NCS)₂] (D20), [Ru(L2)(L)(NCS)₂] (D21), [Ru(L3)(L)(NCS)₂] (D22), and [Ru(L4)(L)(NCS)₂] (D23) (where L = 4,4′-bis(carboxylic acid)-2,2′-bipyridine) have been synthesized, as photosensitizers for nanocrystalline dye-sensitized solar cells. All complexes D20-D23 exhibit a broad MLCT band around 520-530 nm in DMF and an emission band around 740-790 nm in DMF. We have studied photovoltaic performances based on the newly synthesized dyes. Under standard AM 1.5 sunlight, the dye D20 gave a short-circuit photocurrent density of 13.31 mA/cm², an open-circuit voltage of 0.64 V, and a fill factor of 0.68, corresponding to an overall conversion efficiency of 5.81%.     

Synthesis, characterization, photophysics and intramolecular energy transfer process in bimetallic rhenium(I)-ruthenium(II) complexes

Two new heterobimetallic complexes of rhenium(I) and ruthenium(II) [(CO)₃(NN)Re(4,4′-bpy)Ru(NN)₂Cl](PF₆)₂ and already known monometallic complexes [Cl(NN)₂Ru(4,4′-bpy)](PF₆) and [(CO)₃(NN)Re(4,4′-bpy)](PF₆) and bimetallic complexes [Cl(NN)₂Ru(4,4′-bpy)Ru(NN)₂Cl](PF₆)₂, [(CO)₃(NN)Re(4,4′-bpy)Re(NN)(CO)₃](PF₆)₂ (NN = 2,2′-bipyridine, 1,10-phenanthroline; 4,4′-bpy = 4,4′-bipyridine) are synthesized and characterized by spectral techniques. The photophysical properties of all the complexes are studied. It is found that attachment of rhenium(I) altered the photophysical characteristics of ruthenium(II). Excited state energy transfer from the rhenium(I) chromophore to the ruthenium(II) is observed upon excitation at 355 nm.     

Ruthenium(II) mixed-ligand complexes containing 2-(6-methyl-3-chromonyl)imidazo[4,5-f][1,10]-phenanthroline: Synthesis, DNA-binding and photocleavage studies

Two novel Ru(II) complexes [Ru(bpy)₂(MCMIP)]²⁺ (1) and [Ru(phen)₂(MCMIP)]²⁺ (2) (bpy = 2,2′-bipyridine; phen = 1,10-phenanthroline; MCMIP = 2-(6-methyl-3-chromonyl)imidazo[4,5-f][1,10]-phenanthroline) have been synthesized and characterized by elemental analysis, mass spectra and ¹H NMR. The DNA-binding properties of the complexes were investigated by absorption, emission, melting temperature and viscosity measurements. Experimental results indicate that the two complexes can intercalate into DNA base pairs. Upon irradiation at 365 nm, two Ru(II) complexes were found to promote the cleavage of plasmid pBR 322 DNA from supercoiled form I to nicked form II, and the mechanisms for DNA cleavage by the complexes were also investigated.     

Preparation and photophysical studies of copper(I) and ruthenium(II) complexes of 4,4′-bis(3,5-dimethoxyphenyl)-6,6′-dimethyl-2,2′-bipyridine

We report the synthesis of a new ligand, 4,4′-bis(3,5-dimethoxyphenyl)-6,6′-dimethyl-2,2′-bipyridine, optimised for binding to copper(I) and with pendant functionality that can eventually be developed into metallodendritic structures. The synthesis and photophysical properties of complexes with copper(I) and ruthenium(II) are reported. The solid state structure of the complex [Cu(1)₂][PF₆] · MeCN (1 = 4,4′-bis(3,5-dimethoxyphenyl)-6,6′-dimethyl-2,2′-bipyridine) is also described.     

pH- and DNA-induced dual molecular light switches based on a novel ruthenium(II) complex

A novel Ru(II) complex, [Ru(bpy)₂(btppz)]Cl₂, where bpy = 2,2′-bipyridine and btppz = benzo[h]tripyrido[3,2-a:2′,3′-c:2″,3″-j]phenazine, has been synthesized and characterized. The pH effects on UV-visible (UV-vis) absorption and emission spectra of the complex have been studied and ground- and excited-state ionization constants of the complex have been derived. The calf thymus DNA (ct-DNA) binding properties of the complex were investigated with UV-vis absorption and luminescence spectrophotometric titrations, steady-state emission quenching by [Fe(CN)₆]⁴⁻, DNA competitive binding with ethidium bromide, DNA melting experiments, reverse salt titrations and viscosity measurements. The complex was demonstrated to act as dual molecular switches: pH-induced “on-off” emission switch with an on-off intensity ratio of ∼54 which is favorably compared with those reported for structurally analogous Ru(II) complexes, and a DNA molecular light switch with a luminescence enhancement factor of 22 as it intercalatively bound to the DNA.     

Energy transfer pathways in pyridylporphyrin Re(I) adducts

Dimeric and pentameric adducts between a meso-4′ pyridylporphyrin core and either one or four rhenium(I) bipyridine tricarbonyl units, fac-[Re(CO)₃(bipy)(4′MPyP)][CF₃SO₃] and fac-[{Re(CO)₃(bipy)}₄(4′TPyP)][CF₃SO₃]₄(4′MPyP = 4′-monopyridylporphyrin, 4′TPyP = 4′-tetrapyridylporphyrin), respectively, were synthesized and their photophysical behaviors were investigated by emission and absorption time resolved experiments. The adducts exhibit distinctive supramolecular features, different from those of the molecular components. Upon excitation of the core, the typical porphyrin fluorescence is quenched. This effect is attributed to enhanced intersystem crossing in the porphyrin unit, owing to the heavy atom effect provided by the attached rhenium unit(s). Following excitation of rhenium fragments the typical rhenium MLCT emission is not observed while partial sensitization of the porphyrin fluorescence occurs, indicating that fast intercomponent energy and/or electron transfer processes take place in competition with the intersystem crossing in the rhenium unit.     

DNA- and RNA-binding and enhanced DNA-photocleavage properties of a ferrocenyl-containing ruthenium(II) complex

The interaction of [Ru(bpy)₂(fip)](PF₆)₂ {bpy = 2,2′-bipyridine, fip = 2-ferrocenyl-1H-imidazo[4,5-f][1,10]-phenanthroline} with calf thymus DNA and yeast tRNA was investigated comparatively by UV-visible absorption and luminescence spectrophotometric titrations, steady-state emission quenching by [Fe(CN)₆]^4 −, ethidium bromide competition experiment, DNA thermal denaturation, viscosity measurements and salt effect studies. The results suggest that the complex binds to the DNA more strongly than to the RNA. The density functional theory calculations were also carried out in order to better understand the nucleic acid binding properties. Agarose gel electrophoresis showed that the complex exhibited enhanced DNA-photocleavage capacity on pUC 18 plasmid DNA under irradiation at 360 nm as compared with a ferrocenyl-free analogous complex.     

Artificial photosynthesis based on dye-sensitized nanocrystalline TiO2 solar cells

A new series of amphiphilic heteroleptic ruthenium(II) sensitizers [Ru(H₂dcbpy)(dhbpy)(NCS)₂] (C1), [Ru(H₂dcbpy)(bccbpy)(NCS)₂] (C2), [Ru(H₂dcbpy)(mpubpy)(NCS)₂] (C3), [Ru(H₂dcbpy)(bhcbpy)(NCS)₂] (C4) have been synthesized and fully characterized by UV-Vis, emission, NMR and cyclic voltammetric studies (where dhbpy = 4,4′-dihexyl-2,2′-bipyridine, bccbpy = 4,4′-bis(cholesteroxycarbonyl)-2,2′-bipyridine, mpubpy = 4-methyl-4′-perfluoro-1H,1H,2H,2H,3H,3H-undecyl-2,2′-bipyridine, bhcbpy = 4,4′-Bis(hexylcarboxamido)-2,2′-bipyridine). The amphiphilic amide heteroleptic ruthenium(II) sensitizers, self-assembled on TiO₂ surface from ethanol solution, reveal efficient sensitization in the visible window range yielding ≈80% incident photon-to-current efficiencies (IPCE). Under standard AM 1.5 sunlight, the C4 sensitizer gave 15 mA/cm² short circuit photocurrent density, 0.66 fill factor and an open circuit voltage of 0.75 V, corresponding to an overall conversion efficiency of 7.4%.     

Synthesis and properties of red emitter Ru(II) complexes based on 6,6′-disubstituted-4,4′-bipyrimidine

Heteroleptic complexes [Ru(bpy)₂(R₂bpm)]²⁺, where bpy = 2,2′-bipyridine and R₂bpm = 6,6′-diaryl-4,4′-bipyrimidine, have been synthesized and characterized, together with the homoleptic complex [Ru(R₂bpm)₃]²⁺, in which R₂bpm = 6,6′-diphenyl-4,4′-bipyrimidine. The substituent aryl on the bipyrimidine has significant effects on the properties of these complexes as compared to the parent [Ru(bpy)₂(bpm)]²⁺ complex. The complexes exhibit Ru-to-bpm charge transfer (CT) absorptions centered at about 540 nm and Ru-to-bpy CT absorptions centered at about 435 nm. The assignment of the low energy absorptions is supported by the relative ease of the reduction of the new complexes as compared to [Ru(bpy)₃]²⁺. The new complexes exhibit a relatively intense emission at room temperature, with lifetimes in the 10-50 ns range, with the homoleptic species exhibiting the higher-energy (maximum at 724 nm) and the longest-lived (τ = 48 ns) emission among the complexes. Luminescence lifetimes and quantum yields are governed by the energy gap law, indicating that direct deactivation to the ground state is the dominant relaxation pathway for 1-6, while thermally activated processes are inefficient.     

Selective recognition of homocysteine and cysteine based on new ruthenium(II) complexes

A series of the new ruthenium(II) complexes with different number of aldehyde groups have been synthesized and characterized for the simple and selective sensing of homocysteine (Hcy) and cysteine (Cys). The reaction of these ruthenium(II) complexes with Hcy and Cys afforded thiazinane or thiazolidine derivatives which resulted in the obvious changes in the UV-visible spectra and strong enhancement of the luminescence intensity of the system. The luminescence enhancement of [Ru(dmb)₂(L2)]²⁺ (dmb: 4,4′-dimethyl-2,2′-bipyridine) showed a good linearity in the concentration of 4.2-350 μM and 6-385 μM with the detection limits of 0.3 μM and 1 μM for Hcy and Cys, respectively. The absorption and emission bands from metal-to-ligand charge transfer transition in the visible region and the large Stokes shift of the ruthenium(II) complex chromophore made it suitable for biological applications.     

Solution luminescence from chloro(2,2′:6′,2″-terpyridine)platinum(II) chloride in micelles

Previously characterized as being non-luminescent in room-temperature fluid solution, the coordination compound chloro(2,2′:6′,2″-terpyridine)platinum(II) chloride can display two types of luminescence in certain microenvironments. In aqueous solutions of anionic and neutral surfactants having concentrations near or above their critical micelle concentration, [Pt(terpy)Cl]Cl (10-50 μM) displays broad emission centered at ∼610 nm that is characterized as metal-to-ligand charge transfer phosphorescence (³MLCT). In high concentration (10-100 mM) solutions having no surfactant, [Pt(terpy)Cl]Cl aggregates form. Excitation in the 470-540 nm region results in a long-wavelength emission centered at ∼720 nm that is characterized as metal-metal-to-ligand charge transfer phosphorescence (³MMLCT). This emission can also be detected in lower concentration solutions (10-50 μM) with surfactant concentration below its critical micelle concentration. Enhancement of ³MLCT luminescence is also found for the related phenylacetylide complex cation [Pt(terpy)(CCPh)]⁺ in micelles of the anionic surfactant sodium dodecyl sulfate.     

Synthesis, photoluminescence and electrochemiluminescence of ruthenium(II) polypyridyl complexes based on bipyridine derivatives with carbazole moieties

Six complexes (1-6) with the type of [Ru(bpy)₂L]X₂ (1-3: L = L1-L3, X = Cl⁻; 4-6: L = L1-L3, X = PF₆⁻) were synthesized based on 2,2′-bipyridine and three 2,2′-bipyridine derivatives L1, L2 and L3 (L1 = 5,5′-dibromo-2,2′-bipyridine, L2 = 5-bromo-5′-carbazolyl-2,2′-bipyridine, L3 = 5,5′-dicarbazolyl-2,2′-bipyridine). The complexes 1-6 were characterized by ¹H NMR, MS(ESI) and IR spectra, along with the X-ray crystal structure analysis for 1, 5 and 6. Their photophysical properties and electrochemiluminescence (ECL) properties were investigated in detail. In the UV-Vis absorption spectra, all complexes 1-6 show strong intraligand (π → π^∗) transitions and metal-ligand charge transfer (MLCT, dπ (Ru) → π^∗) bands. Upon the excitation wavelengths at ∼508 nm, all complexes 1-6 exhibit typical MLCT emission of ruthenium(II) polypyridyl complexes. The introduction of carbazole moieties improves the MLCT absorption and emission intensity. The ruthenium(II) complexes 1-6 exhibit good electrochemiluminescence (ECL) properties in [Ru(bpy)₂L]²⁺/tri-n-propylamine (TPrA) acetonitrile solution and the complexes with PF₆⁻ showed higher ECL emission intensity than that of the complexes with Cl⁻ based on the same ligands.     

Hydrothermal synthesis and crystal structure of one-dimensional organic/inorganic hybrid material: [Mo4O12(2,2′-bpy)3]n

A new polyoxomolybdenum compound [Mo₄O₁₂(2,2′-bpy)₃]_n (1) (2,2′-bpy = 2,2′-bipyridine) has been hydrothermally synthesized and characterized by elemental analysis, IR spectroscopy, TG analysis, and single crystal X-ray diffraction. The solid state structure is a 1D chain with a repeat unit of three corner-sharing {MoO₄N₂} octahedra and one {MoO₄} tetrahedron.     

X-ray structure and magnetic properties of dinuclear and polymer iron(II) complexes

Five new octahedral iron(II) complexes [FeL2(4-dpa)]_n(EtOH) (1), [FeL2(bipy)]_n(DMF) (2), [FeL1(bpee)]_n (3), [Fe₂L3(1-meim)₄](1-meim)₄ (4) and [FeL1(DMAP)₂] (5), with L1 and L2 being tetradentate coordinating Schiff base like ligands (L1 = (E,E)-[{diethyl-2,2′-[1,2-phenylenebis(iminomethylidyne)]bis[3-oxobutanato](2-)-N,N′,O³,O³′}, L2 = (3,3′)-[{1,2-phenylenebis(iminomethylidyne)]bis(2,4-pentane-dionato)(2-)-N,N′,O²,O²′}) and L3 being a octadentate dinucleating coordinating Schiff base like ligand ({tetraethyl-(E,E,E,E)-2,2′,2′′,2′′′-[1,2,4,5-phenylentetra(iminomethylidine)]tetra[3-oxobutanoato](2-)-N,N′,N′′,N′′′,O³,O³′,O³′′,O³′′′}); 4-dpa = di(4-picolyl)-amine, bipy = 4,4′-bipyridine, bpee = trans-1,2-bis(4-pyridyl)ethylene, 1-meim = 1-methylimidazole and DMAP = 4-dimethylaminopyridine, have been synthesized and characterised using X-ray structure analysis and T-dependent susceptibility measurements. Both methods indicate that all iron(II) centres are in the paramagnetic high-spin state over the whole temperature range investigated. The O-Fe-O angle, the so called bit of the equatorial ligand, is with an average of 111° in the region typical for high-spin iron(II) complexes of this ligand type. In the case of compound 1 an infinite two-dimensional hydrogen bond network can be found, for the compounds 2-4 no hydrogen bond interactions are observed between the complex molecules. A comparison of the curve progression obtained from the magnetic measurements of the mononuclear complex 5 and the polymeric complexes 1-3 leads to the conclusion that no magnetic interactions are mediated over the bridging axial ligands. For the dinuclear complex 4 weak antiferromagnetic interactions between the two iron centres are found.     

Luminescent probes for indole-binding proteins derived from ruthenium(II) polypyridine complexes

We report here the synthesis, characterisation, electrochemical, photophysical and protein-binding properties of four luminescent ruthenium(II) polypyridine indole complexes [Ru(bpy)₂(L1)](PF₆)₂ (1), [Ru(bpy)₂(L2)](PF₆)₂ (2), [Ru(L1)₃](PF₆)₂ (1a), and [Ru(L2)₃](PF₆)₂ (2a) (bpy = 2,2′-bipyridine; L1 = 4-(N-(2-indol-3-ylethyl)amido)-4′-methyl-2,2′-bipyridine; L2 = 4-(N-(6-N-(2-indol-3-ylethyl)hexanamidyl)amido)-4′-methyl-2,2′-bipyridine). Their indole-free counterparts, [Ru(bpy)₂(L3)](PF₆)₂ (3) and [Ru(L3)₃](PF₆)₂ (3a) (L3 = 4-(N-(ethyl)amido)-4′-methyl-2,2′-bipyridine), have also been synthesised for comparison purposes. Cyclic voltammetric studies revealed ruthenium-based oxidation at ca. +1.3 V versus SCE and diimine-based reductions at ca. −1.20 to −2.28 V. The indole moieties of complexes 1, 2, 1a and 2a displayed an irreversible wave at ca. +1.1 V versus SCE. All the ruthenium(II) complexes exhibited intense and long-lived orange-red triplet metal-to-ligand charge-transfer ³MLCT (dπ(Ru) → π*(L1-L3)) luminescence upon visible-light irradiation in fluid solutions at 298 K and in alcohol glass at 77 K. The binding of the indole-containing complexes to bovine serum album (BSA) has been studied by quenching experiments and emission titrations.     

Preparation and properties of ruthenium (II) complexes of 2,2′:6′,2″-terpyridines substituted at the 4′-position with heterocyclic groups

Four ligands whose general formula is R-terpy with terpy = 2,2′:6′,2″ terpyridine bearing at the 4′-position a substituent R = 2-furyl, 2-pyrrolyl, 2-thienyl and 5-2,2′bithienyl were synthesised. The absorption spectra and the electrochemical behaviour of the corresponding homoleptic Ru(II) complexes were investigated and compared to those of the parent complex [Ru(terpy)]²⁺. Due to the donor effect of the grafted heterocyclic groups, the absorption and emission maxima are red-shifted and the energy levels of the HOMO Π(t_2g) metal orbitals are slightly higher. The incorporation of these heterocyclic moieties extends the electronic delocalisation over the corresponding ligands, leading to higher emission quantum yields. Cyclic voltammetric studies of pyrrolyl-, thienyl- and bithienyl-functionalised complexes show that an electroactive layer can be deposited on the electrode. Preliminary results point out that an electrodeposited film could be used as a photocathode in an aqueous electrolyte.     

Synthesis and characterization of β-diketonato ruthenium(II) complexes with two 4-bromo or protected 4-ethynyl-2,2′-bipyridine ligands

Two new mononuclear mixed-ligand ruthenium(II) complexes with acetylacetonate ion (2,4-pentanedionate, acac) and functionalized bipyridine (bpy) in position 4, [Ru(bpyBr)₂(acac)](PF₆) (2; bpyBr = 4-Bromo-2,2′-bipyridine, acac = 2,4-pentanedionate ion) and [Ru(bpyOH)₂(acac)](PF₆) (3; bpyOH = 4-[2-methyl-3-butyn-2-ol]-2,2′-bipyridine) were prepared as candidates for building blocks. The ¹H NMR, ¹³C NMR, UV-Vis, electrochemistry and FAB mass spectral data of these complexes are presented.     

DNA-binding and photocleavage studies of mixed polypyridyl ruthenium(II) complexes with calf thymus DNA

New mixed polypyridyl {NMIP = 2′-(2″-nitro-3″,4″-methylenedioxyphenyl)imidazo-[4′,5′-f][1,10]-phenanthroline, dmb = 4,4′-dimethyl-2,2′-bipyridine, bpy = 2,2′-bipyridine} ruthenium(II) complexes [Ru(dmb)₂(NMIP)]²⁺ (1) and [Ru(bpy)₂(NMIP)]²⁺ (2) have been synthesized and characterized. The binding of these complexes to calf thymus DNA (CT-DNA) has been investigated with spectroscopic methods, viscosity and electrophoresis measurements. The experimental results indicate that both complexes could bind to DNA via partial intercalation from the minor/major groove. In addition, both complexes have been found to promote the single-stranded cleavage of plasmid pBR 322 DNA upon irradiation. Under comparable experimental conditions compared with [Ru(phen)₂(NMIP)]²⁺, during the course of the dialysis at intervals of time, the CD signals of both complexes started from none, increased to the maximum magnitude, then no longer changed, and the activity of effective DNA cleavage dependence upon concentration degree lies in the following order: [Ru(phen)₂NMIP]²⁺ > complex 2 > complex 1.     

pH effects on optical and DNA binding properties of a thiophene-containing ruthenium(II) complex

A new ruthenium(II) complex, [Ru(bpy)₂(Htip)]Cl₂ {where bpy = 2,2′-bipyridine and Htip = 2-(thiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline}, has been synthesized and characterized by ¹H NMR spectroscopy, elemental analysis, and mass spectrometry. The pH effects on UV-Vis absorption and emission spectra of the complex have been studied, and the ground- and excited-state acidity ionization constant values have been derived. The calf thymus (ct) DNA binding properties of the complex have been investigated with UV-Vis absorption and luminescence titrations, steady-state emission quenching by [Fe(CN)₆]⁴⁻, DNA competitive binding with ethidium bromide, DNA melting experiments, and viscosity measurements. The molecular structures and electronic properties of [Ru(bpy)₂(Htip)]²⁺ and deprotonated form [Ru(bpy)₂(tip)]⁺ have also been investigated by means of density functional theory calculations in an effort to understand the DNA binding properties. The results suggest that the complex undergo three-step successive protonation/deprotonation reactions with one of which occurring over physiological pH region, and act as a ct-DNA intercalator with an intrinsic DNA binding constant value on 10⁵ M⁻¹ order of magnitude that is insensitive to pH.     

Synthesis, structure, spectroscopic, magnetic and electrochemical studies of Ni phen-dione complex

The first crystal structure of Ni^II phen-dione complex is reported. This compound is [Ni(bpy)₂(phen-dione)](PF₆)₂ (bpy = 2,2′-bipyridine and phen-dione = 1,10-phenanthroline-5,6-dione). The complex has been characterized by elemental analysis, IR and electronic absorption spectroscopy and cyclic voltammetry. The electrochemical behavior and electronic spectrum of [Ni(bpy)₂(phen-dione)](OAc)₂ has also been studied in buffered solutions at pH between 1 and 8. ORTEP drawing of [Ni(bpy)₂(phen-dione)](PF₆)₂ · 2CH₃CN shows that the coordination geometry around the Ni^II is a distorted octahedron, with bite angles of 78.1-78.8° for all three bidentate ligands and the two pyridyl rings of the bpy ligands are nearly co-planar, as are the two pyridyl rings of phen-dione.