Synthesis, structural characterization, photophysical, electrochemical, and anion-sensing studies of luminescent homo- and heteroleptic ruthenium(II) and osmium(II) complexes based on terpyridyl-imidazole ligand

A series of hetero- and homoleptic tridentate ruthenium(II) and osmium(II) complexes of compositions [(tpy-PhCH(3))Ru(tpy-HImzphen)](ClO(4))(2) (1), [(H(2)pbbzim)Ru(tpy-HImzphen)](ClO(4))(2) (2), and [M(tpy-HImzphen)(2)](ClO(4))(2) [M = Ru(II) (3) and Os(II) (4)], where tpy-PhCH(3) = 4'-(4-methylphenyl)-2,2':6',2"-terpyridine, H(2)pbbzim = 2,6-bis(benzimidazole-2-yl)pyridine and tpy-HImzphen = 2-(4-[2,2':6',2"]terpyridine-4'-yl-phenyl)-1H-phenanthro[9,10-d]imidazole, have been synthesized and characterized by using standard analytical and spectroscopic techniques. X-ray crystal structures of three complexes 2, 3, and 4 have been determined. The absorption spectra, redox behavior, and luminescence properties of the complexes have been thoroughly investigated. All of the complexes display moderately strong luminescence at room temperature with lifetimes in the range of 10-55 ns. The effect of solvents on the absorption and emission spectral behavior of the complexes has also been studied in detail. The anion sensing properties of all the complexes have been studied in solution using absorption, emission, and (1)H NMR spectral studies and by cyclic voltammetric (CV) measurements. It has been observed that the complexes 1, 3, and 4 act as sensors for F(-)only, whereas 2 acts as sensor for F(-), AcO(-), and to some extent for H(2)PO(4)(-). It is evident that in the presence of excess of anions deprotonation of the imidazole N-H fragment(s) occurs in all cases, an event which is signaled by the development of vivid colors visible with the naked eye. The receptor-anion binding/equilibrium constants have been evaluated.     

Synthesis, photophysical, photochemical, and redox properties of nitrospiropyrans substituted with Ru or Os tris(bipyridine) complexes

Photochromic nitrospiropyrans substituted with 2,2'-bipyridine (bpy), [Ru(bpy)3]2+, and [Os(bpy)3]2+ groups were synthesized, and their photophysical, photochemical, and redox properties investigated. Substitution of the spiropyran with the metal complex moiety results in strongly decreased efficiency of the ring-opening process as a result of energy transfer from the excited spiropyran to the metal center. The lowest excited triplet state of the spiropyran in its open merocyanine form is lower in energy than the excited triplet MLCT level of the [Ru(bpy)3]2+ moiety but higher in energy than for [Os(bpy)3]2+, resulting in energy transfer from the excited ruthenium center to the spiropyran but inversely in the osmium case. The open merocyanine form reduces and oxidizes electrochemically more easily than the closed nitrospiropyran. Like photoexcitation, electrochemical activation also causes opening of the spiropyran ring by first reducing the closed form and subsequently reoxidizing the corresponding radical anion in two well-resolved anodic steps. Interestingly, the substitution of the spiropyran with a Ru or Os metal center does not affect the efficiency of this electrochemically induced ring-opening process, different from the photochemical path.     

Preparation and structural characterization of Os(II) and Ru(II) complexes,MCl2(vdpp)2 [M = Os or Ru,vdpp = 1,1-bis(diphenylphosphino)ethene]

A reaction between Os₂(O₂CCH₃)₄Cl₂ and vdpp [vdpp = 1,1-bis(diphenylphosphino) ethene] was investigated. When the reactants, in the presence of LiCl, were heated in toluene OsCl₂(vdpp)₂,1, was formed. In a similar reaction Ru₂(O₂CCH₃)₄Cl with vdpp afforded RuCl₂(vdpp)₂,2. The molecular structures of1 and2 were elucidated using X-ray crystallography. Single crystals of1 and2 grown from dichloromethanehexane crystallize in the space group P2₁/c with these cell dimensions: a = 11.046(2)Å, b = 18.168(3)Å, c = 12.678(3)Å, β = 110.24(2)° and V = 2387(2)ų for1 and a = 11.055(1)Å, b = 18.199(3)Å, c = 12.693(2)Å, β = 110.16(1)°, V = 2392(1)ų for2. The molecules of1 and2 are isostructural. Metal atoms reside on inversion centers relating the two halves of the molecules. The complexes are six-coordinate with two four-membered chelate rings and trans chlorine atoms. For RuCl₂(vdpp)₂ the PMP angle in the chelate ring is 73.13(2)° and the PCP angle in the chelate ring is 98.6(1)°. These values are 72.74(3)° and 97.9(2)°, respectively, for OsCl₂(vdpp)₂. There is a disordered dichloromethane solvent molecule present in the lattice and there are no unusual intermolecular contacts.     

Aryl-diamide bridged binuclear ruthenium (II) tris(bipyridine) complexes: Synthesis, photophysical, electrochemical and electrochemiluminescence properties

Several new symmetrical aromatic hydrocarbon bridged bipyridine ligands and their binuclear Ru (II) complexes have been designed, synthesized and characterized on the basis of ¹H NMR, MS and HRMS. Their absorption and emission properties, electrochemical behaviors and electrochemical luminescence were investigated. All ruthenium complexes show characteristic MLCT absorption and similar redox potential. Among the three complexes reported, 4c has the best electrochemical luminescence property.     

Synthesis, structural characterization and anion-sensing studies of metal(II) complexes based on 3,3',4,4'-oxydiphthalate and N-donor ligands

Using a multicarboxylate ligand, 3,3',4,4'-oxydiphthalic acid (H(4)ODPA), and N-donor ligands, five metal(II)-ODPA complexes formulated as Cu(4)(ODPA)(2)(L1)(4)(H(2)O)(10)·2H(2)O (L1 = 4-(2-(pyridin-4-yl)vinyl)pyridine) (1), Co(H(2)ODPA) (L1)(H(2)O) (2), Zn(2)(ODPA)(2)(H(2)PIP)(2)·H(2)O (PIP = 1,3-bis(4-piperidinyl)propane) (3), Mn(2)(ODPA)(phen)(H(2)O)(2) (phen = phenanthroline) (4) and Cu(2)(H(2)ODPA)(2)(phen)(4)·H(2)O (5) have been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction. Complex 1 shows a three dimensional (3D) framework with an unprecedented (4.6(4).8)(2)(4(2).6(4)) topology generated by the polycatenation of 2D layers. Complex 2 exhibits a uninodal 4-connected 3D architecture with 6(5)8-cds topology. Complex 3 shows a uninodal 2D layer with 4(4)-sql topology. Complex 4 has a binodal (4,6)-connected non-interpenetrated 3D architecture with (3.4(3).5.6)(3(2).4(3).5(4).6(4).7(2)) topology. Complex 5 is a mononuclear Cu(II) complex. Complexes 1 and 5 can irreversibly and reversibly detect SCN(-), Cl(-), Br(-) and I(-) in water, respectively. Complexes 2-4 are not feasible candidates for colorimetric detection of anions in aqueous solution. The metal(II) species and the structure of the metal complex play important roles in the colorimetric detection.     

Supramolecular metal-polypyridyl and Ru(II) porphyrin complexes: photophysical, electron paramagnetic resonance, and electrochemical studies

A series of mixed-metal supramolecular porphyrin arrays in which the geometry of the central metal-polypyridyl moiety defines the spatial arrangement of two or more Ru(II)-porphyrin units through axial coordination have been prepared by employing self-assembly based protocols, and their photophysical and electrochemical properties have been studied. The electrochemical properties of the constituent parts of these arrays depend only on their own chemical environment, regardless of the nuclearity and the overall charge of the compound; in this way species with predetermined redox patterns can be obtained via the synthetic control of the self-assembly process. Interestingly, several of these arrays are luminescent both at room and at low temperatures, and in many cases core-to-periphery or periphery-to-core intramolecular energy transfer processes take place according to the nature of the central metal template.     

Synthesis, characterization, electrochemical and photophysical properties of elbow-shaped trinuclear Ru(II) complexes, building blocks for novel supramolecular constructions

Three trinuclear elbow-shaped Ru(II) complexes based on the non symmetrical bridging PHEHAT ligand (PHEHAT = 1,10-phenanthrolino[5,6-b]-1,4,5,8,9,12-hexaazatriphenylene) have been prepared and characterized by NMR, electrochemistry, absorption and emission spectroscopy. It is shown that the dichloro trinuclear complex 1 should behave as an excellent precursor for the synthesis of larger species. Indeed, it reacts easily with 1,10-phenanthroline (phen) and 1,4,5,8-tetraazaphenanthrene (TAP) and leads to the trinuclear compounds 2 and 3, respectively. The electrochemical and emission studies indicate that for 2 and 3, there is an intramolecular energy transfer from the center to the periphery of the elbow-shaped trinuclear complex, whereas for complex 1 the energy transfer takes place in the other direction.     

Synthesis,characterization, and photophysical studies of new bichromophoric ruthenium(II) complexes

The photophysical properties of a series of prepared ruthenium tris(bipyridine) complexes, covalently linked to aromatic species, of type [Ru(bpy)(2)-(4-methyl-4'-(arylaminocarbonyl)-2,2'-bipyridine)](2+) ([Ru(bpy)(2)(mbpy-L)](2+), where bpy = 2,2'-bipyridine; mbpy = 4-methyl-4'-carbonyl-2,2'-bipyridine; and L = 2-aminonaphthyl (naph), 9-aminoanthryl (anth), 1-aminopyrenyl (pyr), or 9-aminoacridinyl (acrd)) were studied by electronic absorption spectroscopy and steady state and time resolved luminescence spectroscopies. The absorption spectra of the MLCT electronic transition of the complexes are similar, which is in agreement with a practically constant redox potential of Ru(III/II) close to 1.28 V versus Ag/AgCl. However, the luminescence spectra of the new complexes are red shifted compared to Ru(bpy)(3)(2+), and this effect is ascribed to solvation and inductive effects of the amide group which enhance the symmetry breakdown among the three bipyridyl ligands. The energy stabilization of the (3)MLCT state is in the range 2.1-8.4 kJ/mol. The triplet-triplet energy transfer between the Ru complex and the aromatic species linked by an amide spacer is a slow process with rate constants of 2.6 x 10(4), 3.6 x 10(4), and 4.9 x 10(4) s(-)(1) for anthracene, acridine, and pyrene as acceptors in methanol, respectively. The energy transfer rate constant increases with decreasing polarity of the solvent. In dichloromethane, the rate constants for anthracene, acridine, and pyrene acceptors are 2.6 x 10(5), 1.5 x 10(5), and 2.9 x 10(5) s(-)(1), respectively. The low efficiency of energy transfer is due to the small difference in triplet energy between donor and acceptor species, weak electronic coupling, and unfavorable Franck-Condon factors, despite the short separation distance between donor and acceptor species in an amide bridge.     

Synthesis,structural characterization,and photophysical studies of hexanuclear gold(I) chalcogenido complexes

A hexanuclear gold(I) selenido cluster and its sulfido counterpart, [Au₆{μ‐Ph₂PN(CH₂‐o‐Py)PPh₂}₃(μ₃‐E)₂](ClO₄)₂ (E = S, Se), with bridging bis(diphenylphosphino)amine ligands were synthesized and characterized. The X‐ray crystal structure of the selenido cluster was determined, with the gold core possessing a distorted heterocubane structure. Intramolecular aurophilic interactions with short Au(I)?Au(I) contacts of around 3.09–3.13 Å were observed. The complexes were found to emit strongly in the solid state with orange to red emission colors. Their electronic absorption and emission properties were also investigated.     

Synthesis,photophysical, electrochemical,and ion-binding properties of Ru(II) polypyridyl complexes containing benzo-15-crown-5

Two polypyridyl ligands, 5-(4′-ethynylbenzo-15-crown-5)-2,2′-bipyridine (L¹) and 3-bromo-8-(4′-ethynylbenzo-15-crown-5)-1,10-phenanthroline (L²), and their Ru(II) complexes [(bpy)₂RuL](PF₆)₂ have been prepared and characterized. Both complexes exhibit metal-to-ligand charge transfer absorption at around 452 nm and emission at around 640 nm in MeCN solution. Electrochemical studies of the complexes reveal a Ru(II)-centered oxidation at around 1.31 V and three ligand-centered reductions. The binding ability of the complexes with Na⁺ has been investigated by UV/Vis absorption, emission, and electrochemical titrations. Addition of Na⁺ to MeCN solutions of both complexes results in a progressive enhancement of the emission, a red-shift of the UV/Vis absorption, and a progressive cathodic shift of the Ru(II)-centered E _1/2 couple. The stability constants for the 1:1 stoichiometry adducts of the complexes with Na⁺ have been obtained from the UV/Vis absorption titrations.     

Physical, photophysical and structural properties of ruthenium(II) complexes containing a tetradentate bipyridine ligand

The focus of this report is the synthesis and properties of two new analogues of ruthenium(ii) tris-bipyridine, a monomer and dimer. The complexes contain the ligand 6,6'-(ethan-1,2-diyl)bis-2,2'-bipyridine (O-bpy) which contains two bipyridine units bridged in the 6,6' positions by an ethylene bridge. Crystal structures of the two complexes formulated as [Ru(bpy)(O-bpy)](PF6)2 and [(Ru(bpy)2)2(O-bpy)](PF6)4 reveal structures of lower symmetry than D3 which affects the electronic properties of the complexes as substantiated by density functional theory (DFT) and time dependent density functional theory (TDDFT) calculations. The HOMO lies largely on the ruthenium center; the LUMO spreads its electron density over the bipyridine units, but not equally in the mixed O-bpy-bpy complexes. Calculated Vis/UV spectra using TDDFT methods agree with experimental spectra. The lowest lying triplet excited state for [Ru(bpy)(O-bpy)](PF6)2 is 3MC resulting in a low emission quantum yield and a large chloride ion photosubstitution quantum yield.     

Synthesis, characterization, and pH-induced luminescence switching of two trinuclear Ru(II) polypyridyl complexes containing imidazole

Two tripodal ligands H₃L¹ and H₃L² containing imidazole rings have been prepared by the reaction of 1,10-phenanthroline-5,6-dione with 1,3,5-tris[(4-formylphenoxy)methyl]benzene and 1,3,5-tris[(2-formylphenoxy)methyl]benzene, respectively. Trinuclear Ru(II) complexes [(bpy)₆Ru₃H₃L^1?C2](PF₆)₆ (bpy=2,2??-bipyridine) have been obtained by the condensation of Ru(bpy)₂Cl₂?·?2H₂O with ligands H₃L¹ and H₃L², respectively. The pH effects on the UV?CVis absorption and emission spectra of both complexes have been studied, and ground- and excited-state ionization constants of both complexes have been derived. The photophysical properties of both complexes are strongly dependent on the solution pH. They act as pH-induced switchable luminescence sensors through protonation and deprotonation of the imidazole groups, with a maximum on?Coff ratio of 6 in buffer solution at room temperature.     

Synthesis,characterization, electrochemical and photophysical properties of bimetallic complexes of rhenium(I) and osmium(II)

Monometallic and bimetallic diimine complexes of rhenium(I) and osmium(II), [(CO)₃(bpy)Re(4,4′-bpy)](PF₆) I, [(CO)₃(bpy)Re(4,4′-bpy)Re(bpy)(CO)₃](PF₆)₂II, [Cl(bpy)₂Os(4,4′-bpy)](PF₆) III and [Cl(bpy)₂Os(4,4′-bpy)Os(bpy)₂Cl](PF₆)₂IV, and a new heterobimetallic complex of rhenium(I) and osmium(II) [(CO)₃(bpy)Re(4,4′-bpy)Os(bpy)Cl](PF₆)₂V (bpy = 2,2′-bipyridine; 4,4′-bpy = 4,4′-bipyridine) have been synthesized and characterized by various spectral techniques. The photophysical properties of all the complexes have been studied and a comparison is made between the heterobimetallic and corresponding monometallic and homobimetallic complexes. Emission and transient absorption spectral studies reveal that excited state energy transfer from the rhenium(I) chromophore (∗Re) to osmium(II) takes place. The energy transfer rate constant is found to be 8.7 × 10⁷ s⁻¹.     

Six-membered ring chelate complexes of Ru(II): structural and photophysical effects

The structural and photophysical properties of Ru(II)-polypyridyl complexes with five- and six-membered chelate rings were studied for two bis-tridentate and two tris-bidentate complexes. The photophysical effect of introducing a six-membered chelate ring is most pronounced for the tridentate complex, leading to a room-temperature excited-state lifetime of 810 ns, a substantial increase from 180 ns for the five-membered chelate ring model complex. Contrasting this, the effect is the opposite in tris-bidentate complexes, in which the lifetime decreases from 430 ns to around 1 ns in going from a five-membered to six-membered chelate ring. All of the complexes were studied spectroscopically at both 80 K and ambient temperatures, and the temperature dependence of the excited-state lifetime was investigated for both of the bis-tridentate complexes. The main reason for the long excited-state lifetime in the six-membered chelate ring bis-tridentate complex was found to be a strong retardation of the activated decay via metal-centered states, largely due to an increased ligand field splitting due to the complex having a more-octahedral geometry.     

New star-shaped trinuclear Ru(II) polypyridine complexes of imidazo[4,5-f][1,10]phenanthroline derivatives: syntheses, characterization, photophysical and electrochemical properties

A series of new star-shaped trinuclear Ru(II) complexes of imidazo[4,5-f][1,10]phenanthroline derivatives, [{Ru(bpy)(2)}(3){μ-mes(1,4-phO-Izphen)(3)}](ClO(4))(6)·4H(2)O (6), [{Ru(phen)(2)}(3){μ-mes(1,4-phO-Izphen)(3)}](ClO(4))(6)·3H(2)O (7), [{Ru(bpy)(2)}(3){μ-mes(1,2-phO-Izphen)(3)}](ClO(4))(6)·4H(2)O (8), and [{Ru(phen)(2)}(3){μ-mes(1,2-phO-Izphen)(3)}](ClO(4))(6)·3H(2)O (9) [mes(1,4-phO-Izphen)(3) (4) = 2,4,6-tri methyl-1,3,5-tris(4-oxymethyl-1-yl(1H-imidazo-2-yl-[4,5-f][1,10]phenanthroline)phenyl)benzene and (mes(1,2-phO-Izphen)(3) (5) = 2,4,6-trimethyl-1,3,5-tris(2-oxymethyl-1-yl(1H-imidazo-2-yl[4,5-f][1,10]phenanthroline)phenyl)benzene] have been synthesized and characterized. Their photophysical and electrochemical properties have also been studied. The core molecule, 1,3,5-tris(bromomethyl)-2,4,6-trimethylbenzene (1) and the trialdehyde intermediate, 2,4,6-trimethyl-1,3,5-tris(4-oxymethyl-1-formylphenyl)benzene (2) are characterized by single crystal X-ray diffraction: triclinic, P1[combining macron]. The complexes 6-9 exhibit Ru(II) metal centered emission at 618, 601, 615, and 605 nm, respectively, in fluid solution at room temperature. The emission profile and emission maxima are similar and independent of the excitation wavelength for each complex. The complexes 6-9 undergo metal centered oxidation and the E(1/2) values for the Ru(II)/Ru(III) redox couples are 1.33, 1.34, 1.35, and 1.35 V versus Ag/Ag(+), respectively, which are cathodically shifted with respect to that of the mononuclear complex [Ru(bpy)(2)(PIP)](2+) (PIP = 2-phenylimidazo[4,5-f][1,10]phenanthroline). The study demonstrates the versatility of the highly symmetric trinucleating imidazo[4,5-f][1,10]phenanthroline-based core ligands 4 and 5 in forming trinuclear Ru(II) complexes.     

Luminescent bis-tridentate ruthenium(II) and osmium(II) complexes based on terpyridyl-imidazole ligand: synthesis, structural characterization, photophysical, electrochemical, and solvent dependence studies

Homo- and heteroleptic bis-tridentate ruthenium(II) and osmium(II) complexes of compositions [(tpy-PhCH(3))Ru(tpy-HImzPh(3))](ClO(4))(2) (1), [(H(2)pbbzim)Ru(tpy-HImzPh(3))] (ClO(4))(2) (2) and [M(tpy-HImzPh(3))(2)](ClO(4))(2) [M = Ru(II) (3) and Os(II) (4)], where tpy-PhCH(3) = p-methylphenyl terpyridine, H(2)pbbzim = 2,6-bis(benzimidazole-2-yl)pyridine and tpy-HImzPh(3) = 4'-[4-(4,5-diphenyl-1H-imidazol-2-yl)-phenyl]-[2,2':6',2']terpyridine, have been synthesized and characterized by using standard analytical and spectroscopic techniques. These compounds were designed to increase the room temperature excited-state lifetimes of bisterpyridine-type ruthenium(II) and osmium(II) complexes. The X-ray crystal structures of two homoleptic complexes 3 and 4 have been determined and show that both the compounds crystallized in orthorhombic form with space group Fddd. The photophysical and redox properties of the complexes have been thoroughly investigated. All the complexes display moderately strong luminescence at room temperature with lifetimes in the range of 6-35 ns. The complexes are found to undergo one reversible oxidation in the positive potential window (0 to +1.6 V) and one irreversible and two successive quasi-reversible reductions in the negative potential window (0 to -2.0 V). The influence of solvents on the photophysical properties of the complexes has also been investigated in detail.     

Synthesis,characterization, and electrochemical studies of Co(II,III) dithiocarbamate complexes

Cobalt(II) complexes of N-methyl phenyl, 1-phenylpiperazyl, and morpholinyl dithiocarbamates have been synthesized and characterized by UV–Visible, FTIR, ¹H-, ¹³C-NMR, and mass spectrometry. The spectroscopic data indicated that two ligands coordinated in bidentate chelating to the metal ion to form four-coordinate cobalt(II) complexes (1–3), which was confirmed by mass analysis (TOF MS ES⁺) of the complexes with m/z [M]⁺ = 450.98, 382.94, and 382.94 for 1, 2, and 3, respectively. Single crystal analysis of 2A and 3A show centrosymmetric mononuclear cobalt(III) bonded to three dithiocarbamate ligands forming a distorted octahedral geometry, indicating the cobalt(II) undergoes aerial oxidation to cobalt(III) during recrystallization. In addition, 2A crystallized with one solvated molecule of toluene. The redox behaviors of the complexes were studied by cyclic and square wave voltammetry in dichloromethane; the result revealed a metal centered redox process consisting of a one-electron quasi-reversible process assigned to Co(III)/Co(IV) oxidation and a corresponding Co(IV)/Co(III) reduction. Randles–Sevcik plots (anodic peak current versus the square root of the scan rate (I_p,a versus ν^1/2)) for the redox couples revealed diffusion-controlled behavior.     

Photophysical, electrochemical and anion sensing properties of Ru(II) bipyridine complexes with 2,2'-biimidazole-like ligand

A new anion sensor [Ru(bpy)(2)(DMBbimH(2))](PF(6))(2) (3) (bpy is 2, 2'-bipyridine and DMBbimH(2) is 7,7'-dimethyl-2,2'-bibenzimidazole) has been developed. Its photophysical, electrochemical and anion sensing properties are compared with two previously investigated systems, [Ru(bpy)(2)(BiimH(2))](PF(6))(2) (1) and [Ru(bpy)(2)(BbimH(2))](PF(6))(2) (2) (BiimH(2) is 2,2'-biimidazole and BbimH(2) is 2,2'-bibenzimidazole). The high acidity of the N-H fragments in these complexes make them easy to be deprotonated by strong basic anions such as F(-) and OAc(-), and they form N-H···X hydrogen bonds with weak basic anions like Cl(-), Br(-), I(-), NO(3)(-), and HSO(4)(-). Complex 3 displays strong hydrogen bonding with these 5 weak basic anions, with binding constants between 17,000 and 21,000, which are larger than those observed in complex 1, with binding constants between 3300 and 5700, and in complex 2, which shows no hydrogen bonding toward Cl(-), Br(-), I(-), and NO(3)(-), and forms considerable hydrogen bonds with HSO(4)(-) with a binding constant of 11,209. These hydrogen bonding behaviours give different NMR, emission and electrochemical responses. The different anion binding affinity of these complexes may be mainly attributed to their different pK(a1) values, 7.2 for 1, 5.7 for 2, and 6.2 for 3. The additional methyl groups at the 7 and 7' positions of complex 3 may also play an important role in the enhancement of anion binding strength.     

Star-shaped electrochemiluminescent metallodendrimers with central polypyridyl Ru(II) complexes: Synthesis and their photophysical and electrochemical properties

Several dendritic bridging ligands were designed and synthesized to develop more sensitive and efficient electrochemiluminescent (ECL) polynuclear Ru(II) complexes. Various types of novel two-armed, four-armed and six-armed tris(bipyridyl)ruthenium core dendrimers were synthesized by coordinating dendritic polybipyridyl ligands with Ru(II) complexes, and the effect of the ligand and the dendritic network on the ECL characteristics were studied. Their electrochemical redox potentials, UV, photoluminescence (PL), and relative ECL intensities were also investigated in detail. The synthesized metallodendrimers exhibited strong metal-to-ligand charge transfer (MLCT) absorption at 428-451 nm and emission at 591-601 nm. Most of the newly synthesized metallodendrimers showed enhanced ECL intensities compared to the reference complex, [Ru(o-phen)₃](PF₆)₂. In particular, the ECL intensities of the six-armed heptanuclear ruthenium complexes were almost four times greater than that of [Ru(o-phen)₃]²⁺. These metallodendrimers could be utilized as efficient ECL materials and light emitting devices.     

Synthesis, characterization, DNA binding and cleavage studies of chiral Ru(II) salen complexes

Interaction of chiral Ru(II) salen complexes (S)-1 and (R)-1 with Calf Thymus DNA (CT-DNA) was studied by absorption spectroscopy, competitive binding study, viscosity measurements, CD measurements, thermal denaturation study and cleavage studies by agarose gel electrophoresis. The DNA binding affinity of (S)-1 (6.25 × 10³ M⁻¹) was found to be greater than (R)-1 (3.0 × 10³ M⁻¹). The antimicrobial studies of these complexes on five different gram (+)/(−) bacteria and three different fungal organisms showed selective inhibition of the growth of gram (+) bacteria and were not affective against gram (−) and fungal organisms. Further, the (S)-1 enantiomer inhibited the growth of organisms to a greater extent as compared to (R)-1 enantiomer.