Bipyridyl Ligands Research Articles

Excited-State Relaxation of Ruthenium Polypyridyl Compounds Relevant to Dye-Sensitized Solar Cells

Remarkably little is known about metal-to-ligand charge transfer (MLCT) excited-state relaxation pathways for the ruthenium polypyridyl compounds commonly utilized in dye-sensitized solar cells. Herein, we report variable-temperature photoluminescence studies of compounds of the general type cis-Ru(LL)2(X)2, where LL is a bipyridyl ligand and X is CN(-) or NCS(-), and contrast them with the well-known Ru(bpy)3(2+) and Os(bpy)3(2+), where bpy is 2,2'-bipyridine, to identify relaxation pathways. In fluid acetonitrile and propylene carbonate solutions, excited-state relaxation was found to obey a first-order kinetic model. An Arrhenius analysis revealed internal conversion to two different states, assigned to an upper MLCT excited state and a ligand field excited state. Relaxation through the upper MLCT excited state typically displayed pre-exponential factors of 10(7)-10(8) s(-1) with activation energies of 400-900 cm(-1), while relaxation rates through ligand field states occurred with 10(14)-10(15) s(-1) and activation energies of 4000-5000 cm(-1). Nonradiative decay through LF states was sensitive to the ligand identity, but in a manner that was not fully consistent with the spectrochemical series. Excited-state relaxation of cis-Ru(dcbH2)2(NCS)2, where dcbH2 is 4,4'-(CO2H)2-2,2'-bipyridine, sometimes termed N3, anchored to mesoporous TiO2 or ZrO2 thin films immersed in CH3CN occurred through the upper MLCT excited state with activational parameters in surprisingly good agreement with those abstracted from data measured in fluid solution. An important finding from these studies is that the population of dissociative ligand field excited states is unlikely to lead to unwanted photochemistry of dye-sensitized solar cells based on cis-Ru(LL)2(NCS)2-type compounds at room temperature.

Clathrochelate-based bipyridyl ligands of nanoscale dimensions: easy-to-access building blocks for supramolecular chemistry

Boronic acid-capped clathrochelates were used to build rigid, linear bipyridyl ligands with adjustable lengths between 1.5 and 5.4 nm. The syntheses can be accomplished in one or two steps from simple starting materials. The potential of these ligands as building blocks for metallasupramolecular chemistry is unveiled through the preparation of a discrete metallamacrocyclic structure and a heterometallic coordination polymer.

Biomimetic model for [FeFe]-hydrogenase: asymmetrically disubstituted diiron complex with a redox-active 2,2′-bipyridyl ligand

[FeFe]-hydrogenases feature a unique active site in which the primary catalytic unit is directly coordinated via a bridging cysteine thiolate to a secondary, redox active [4Fe4S] unit. The goal of this study was to evaluate the impact of a bidentate, redox non-innocent ligand on the electrocatalytic properties of the (μ-S(CH(2))(3)S)Fe(2)(CO)(4)L(2) family of [FeFe]-hydrogenase models as a proxy for the iron-sulfur cluster. Reaction of the redox non-innocent ligand 2,2'-bipyridyl (bpy) with (μ-S(CH(2))(3)S)Fe(2)(CO)(6) leads to substitution of two carbonyls to form the asymmetric complex (μ-S(CH(2))(3)S)Fe(2)(CO)(4)(κ(2)-bpy) which was structurally characterized by single crystal X-ray crystallography. This complex can be protonated by HBF(4)·OEt(2) to form a bridging hydride. Furthermore, electrochemical investigation shows that, at slow scan rates, the complex undergoes a two electron reduction at -2.06 V vs. Fc(+)/Fc that likely involves reduction of both the bpy ligand and the metal. Electrocatalytic reduction of protons is observed in the presence of three distinct acids of varying strengths: HBF(4)·OEt(2), AcOH, and p-TsOH. The catalytic mechanism depends on the strength of the acid.

High-performance pure blue phosphorescent OLED using a novel bis-heteroleptic iridium(iii) complex with fluorinated bipyridyl ligands

A novel pure blue phosphorescent emitter FK306 with fluorinated bipyridyl ligands was developed. The Ip level was determined to be 6.3 eV by photoelectron yield spectroscopy (PYS) in the solid state. The photophysical properties of a FK306/mCP film were evaluated. An 11 wt% doped film showed a peak photoluminescence at 454 nm and a high photoluminescent quantum yield (ηPL) of 78 ± 1%. A transient PL decay curve exhibited almost single-exponential decay (98%) with the phosphorescence lifetime (τp) of 1.51 μs at room temperature. A blue OLED with a structure of [ITO (130 nm)/TAPC (40 nm)/FK306 11–20 wt% doped mCP (10 nm)/B3PyPB (50 nm)/LiF (0.5 nm)/Al (100 nm)] was fabricated and evaluated. A high power efficiency of over 30 lm W−1 and an external quantum efficiency of over 17% were observed. The CIE chromaticity diagram (x, y) was evaluated to be (0.16, 0.25), clearly indicating blue emission. These are the first decent performances using a blue emitter with bipyridyl ligands so far.

Tris(2,2′-bipyridine-κ2N,N′)cobalt(II) bis(hexafluoridophosphate)

In the title compound, [Co(C10H8N2)3](PF6)2, the CoII atom is coordinated by the six N atoms of three 2,2′-bipyridyl ligands and adopts a highly distorted octa­hedral geometry. The crystal used was a merohedral twin, the refined ratio of twin components being 0.820 (1):0.180 (1). The crystal structure features weak C—H⋯F inter­actions, forming a three-dimensional network.

A Homologous Series of First-Row Transition-Metal Complexes of 2,2′-Bipyridine and their Ligand Radical Derivatives: Trends in Structure, Magnetism, and Bonding

The organometallic first-row transition-metal complexes [M(2,2'-bipy)(mes)2] (M = Cr (1), Mn (2), Co (4), Ni (5); 2,2'-bipy = 2,2'-bipyridine; mes = 2,4,6-Me3C6H2) were reacted with potassium and a suitable alkali-metal sequestering agent to yield salts of the anionic species [M(2,2'-bipy)(mes)2](-). The neutral parent compounds and their corresponding anionic congeners were characterized by single-crystal X-ray diffraction in [Cr(2,2'-bipy)(mes)2]·1.5C6H6, [Mn(2,2'-bipy)(mes)2], [Co(2,2'-bipy)(mes)2]·THF, [Ni(2,2'-bipy)(mes)2], [K(dibenzo-18-crown-6)·THF][Cr(2,2'-bipy)(mes)2]·2THF, [K(18-crown-6)][Mn(2,2'-bipy)(mes)2]·2THF, [K(18-crown-6)][Mn(2,2'-bipy)(mes)2]·0.67py·0.67tol, [K(2,2,2-crypt)][Co(2,2'-bipy)(mes)2], and [K(2,2,2-crypt)][Ni(2,2'-bipy)(mes)2]. These species, along with the previously reported neutral and anionic iron complexes [Fe(2,2'-bipy)(mes)2](0/-) (3/3(-)), form a homologous series of compounds which allow for an in-depth study of the interactions between metals and ligands. Single-crystal X-ray diffraction data, DFT calculations, and various spectroscopic and magnetic measurements indicate that the anionic complexes (1(-)-5(-)) can be best formulated as M(II) complexes of the 2,2'-bipyridyl radical anion. These findings complement recent studies which indicate that bond metric data from single-crystal X-ray diffraction may be employed as an important diagnostic tool in determining the oxidation states of bipyridyl ligands in transition-metal complexes.

A one-dimensional heterometallic coordination polymer with a three-dimensional supramolecular framework: poly[μ2-aqua-diaqua(2,2′-bipyridyl)(μ5-2-sulfonatobutanedioato)copper(II)sodium(I)

The title compound, [CuNa(C(4)H(3)O(7)S)(C(10)H(8)N(2))(H(2)O)(3)](n), consists of one Cu(II) cation, one Na(I) cation, one 2-sulfonatobutanedioate trianion (SSC(3-)), one 2,2'-bipyridyl (bpy) ligand and three coordinated water molecules as the building unit. The coordination of the Cu(II) cation is composed of two pyridyl N atoms, one water O atom and two carboxylate O atoms in a distorted square-pyramidal coordination geometry with an axial elongation. The Na(I) cation is six-coordinated by three water molecules and three carboxylate O atoms from three SSC(3-) ligands in a distorted octahedral geometry. Two SSC(3-) ligands link two Cu(II) cations to form a Cu(2)(SSC)(2)(bpy)(2) macrocyclic unit lying across an inversion centre, which is further linked by Na(I) cations via Na-O bonds to give a one-dimensional chain. Interchain hydrogen bonds link these chains to form a two-dimensional layer, which is further extended into a three-dimensional supramolecular framework through π-π stacking interactions. The thermal stability of the title compound has also been investigated.

Novel MnII coordination compounds constructed from benzoate and various bipyridyl ligands: Magnetic property and catalytic activity

Three new MnII-benzoates coordination polymers containing various bipyridyl ligands (3,3′-dipicoylamine (3), 3-methylisoquinoline (4), and 4,4′-dithiopyridine (5)) and a [Mn6(O2CPh)10(μ4-OH)2(CH3OH)3(H2O)]·1.5(C4H4N2) cluster (1) have prepared and their structures were determined. The bipyridyl ligands can act as bridging ligands to produce 1-D or 2-D polymeric compounds. The pyrazine produced a Mn6 cluster molecule, and 3-methylisoquinoline did a benzoate-bridged 1-D MnII compound. The Mn6 cluster (1) and 1-D MnII compounds (3) and (4) show antiferromagnetic property. The compounds 1, 3, and 4 have catalyzed efficiently the transesterification of a variety of esters, while 5 has displayed a very slow conversion. The thermal stabilities of these complexes were also examined.

Bis(2,2′-bipyridyl-κ2 N,N′)dichloridorhodium(III) perchlorate

The asymmetric unit of the title compound, [RhCl2(C10H8N2)2]ClO4, consists of one unit of the cationic complex [RhCl2(bipy)2]+ and one uncoordinated perchlorate anion. The RhIII atom is coordinated by four N atoms from two bipyridyl ligands and two Cl atoms, forming a distorted octa­hedral environment. The Cl ligands are cis. Two intramolecular C—H⋯Cl hydrogen bonds occur in the cationic complex . In the crystal, mol­ecules are linked together by a hydrogen-bond network involving the H atoms of bipyridyl rings and perchlorate anions. An O atom of the perchlorate anion is disordered over two sites, with an occupancy-factor ratio of 0.78 (3):0.22 (3).

Synthesis and properties of iridium polymer complexes based on novel bipyridyl ligands

A novel monomer, viz., bipyridyl-containing dicarboxylic acid, was synthesized from 6-pyridyl-3,4-pyridine dicarboxylic acid anhydride and 5-aminoisophthalic acid. Novel polymer macroligands, viz., copolyamides containing 5, 15, 30, and 45% of the bipyridyl side groups, were obtained based on this monomer by low-temperature polycondensation. Metal polymer complexes (MPC) with different Ir(ppy)2 content were synthesized by the reaction of the polymer ligand with the binuclear complex [Ir(ppy)2Cl]2 (ppy is 2-phenylpyridine) and their properties were studied.

PH Control of Intramolecular Energy Transfer and Oxygen Quenching in Ru(II) Complexes Having Coupled Electronic Excited States

This work illustrates the control of excited state energy transfer processes via variation of pH in transition metal complexes. In these systems a Ru(II) complex having two carboxylated bipyridyl ligands is covalently linked to pyrene via one of two different pyrene derivitized bipyridyl ligands. The energy of the Ru to carboxy-bipyridine (3)MLCT state is pH dependent while the pyrene triplet energy remains unchanged with solution acidity. At pH 0 the (3)MLCT state is the lowest energy state, and as the pH is raised and the carboxy-bipyridyl ligands are successively deprotonated, the energy of the (3)MLCT state rises above that of the pyrene triplet, resulting in a significant increase in the lifetime of the observed emission. Detailed analysis of ultrafast and microsecond time-resolved excited state decays result in a description of excited state decay that involves initial equilibration of the (3)MLCT and pyrene triplet states followed by relaxation to the ground state. The lifetime of excited state decay is defined by the position of the equilibrium, going from 2 μs at pH 0 to >10 μs at higher pH as the equilibrium favors the pyrene triplet. In addition, quenching of the excited state by dissolved oxygen exhibits a pH dependence that parallels that of the excited state lifetime. The results illustrate the utility of exploiting excited state equilibria of this type in the development of highly effective luminescent oxygen sensors.

Catena-Poly[[[tetraaquacopper(II)]-μ-4,4′-bipyridyl-κ2N:N′] tetrafluoridosuccinate tetrahydrate

In the title compound, {[Cu(C10H8N2)(H2O)4](C4F4O4)·4H2O}n, the CuII atom adopts an elongated octa­hedral geometry because of the Jahn–Teller effect. Both cation and anion have crystallographic twofold rotation symmetry with the twofold axes passing through the Cu and N atoms and through the midpoint of the central C—C bond. The 4,4′-bipyridyl ligand links the CuII atoms into a linear chain along the b axis. O—H⋯O hydrogen-bonding inter­actions between the cationic chains and the tetra­fluorido­succinate anions and the free water mol­ecules generate a three-dimensional supra­molecular network.

Electroluminescence from two new ruthenium(II) complexes as phosphorescent dopant: Positive effect of swallow-tail bipyridyl ligand

Two new orange-red emitting ruthenium complexes, [Ru(bpy)2(4,4′-bis(3-ethylheptyl)-2,2′-bipyridine)](PF6)2 and [Ru(bpy)2(4-dihexylmethyl-4′-heptyl-2,2′-bipyridine)](PF6)2 with branched alkyl side groups on the bipyridyl ligand have been synthesized and used as dopants in an organic light emitting device. The device that contains the complex containing the 4-dihexylmethyl-4′-heptyl-2,2′-bipyridine ligand 1.0 wt.% doped polymer blends of poly(vinylcarbazole) and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol as the emitting layer reached to a luminous efficiency of 7 cd/A, and a maximum brightness of 3824 cd/m2 with an electroluminescence spectral peak at 600 nm and Commission Internationale de L’Eclairage chromaticity coordinates of (0.57, 0.39). The swallow-tail alkyl substituent in this complex played a significant role in lowering the tendency to aggregate and presenting a better electroluminescence efficiency than that of the complex derived from the 4,4′-bis(3-ethylheptyl)-2,2′-bipyridine) ligand in a device.

(Carbonato-κ(2)O,O')bis-(5,5'-dimethyl-2,2'-bipyridyl-κ(2)N,N')cobalt(III) bromide trihydrate.

In the title complex, [Co(CO3)(C12H12N2)2]Br·3H2O, the CoIII cation has a distorted octa­hedral coordination environment. It is chelated by four N atoms of two different 5,5′-dimethyl-2,2′-bipyridyl (dmbpy) ligands in axial and equatorial positions, and by two O atoms of a carbonate anion completing the equatorial positions. Although the water mol­ecules are disordered and their H atoms were not located, there are typical O⋯O distances between 2.8 and 3.0 Å, indicating O—H⋯O hydrogen bonding. The crystal packing is consolidated by C—H⋯O and C—H⋯Br hydrogen bonds, as well as π–π stacking inter­actions between adjacent pyridine rings of the dmbpy ligands, with centroid–centroid distances of 3.694 (3) and 3.7053 (3) Å.

Improving spectral response of monocrystalline silicon photovoltaic modules using high efficient luminescent down‐shifting Eu3+ complexes

ABSTRACTOne way to improve the spectral response of solar cells in the ultraviolet (UV) region is to convert high energy photons into lower energy ones via luminescent down‐shifting (LDS) technique. Eu3+ complexes are excellent LDS species because of their high luminescence quantum efficiency and large Stokes‐shift. In this paper, we aim to optimize the LDS property of Eu3+ complexes for monocrystalline silicon (c‐Si) photovoltaic (PV) modules by chemical modification of the UV absorbing antenna ligands. Our results show that the LDS performances of Eu3+ complexes are strongly dependent on their absorption and emission properties. By carefully modifying the absorption and emission features, the LDS performances of Eu3+ complexes can be significantly improved. The spectroscopic features of the Eu3+ complex with a bispinene‐containing bipyridyl ligand match well with the requirement of ideal LDS species for the c‐Si PV module. Simple coating of polyvinyl acetate film doped with this complex onto the surface of c‐Si PV module leads to increase of the external quantum efficiency in the UV region and enhancement of the PV module efficiency η (from 16.05% to 16.37%). Copyright © 2012 John Wiley & Sons, Ltd.

Synthesis, structure, photophysics and electrochemiluminescence of Re(i) tricarbonyl complexes with cationic 2,2-bipyridyl ligands

Two water soluble Re(I) tricarbonyl diimine complexes containing cationic 2,2'-bipyridyl ligands [Re(L1)(CO)(3)(AN)](2+) (1) and [Re(L2)(CO)(3)(AN)](3+) (2) (L1 and L2: a cationic 2,2'-bipyridyl ligand, AN: acetonitrile) were synthesized and characterized. Their photophysical, electrochemical and electrochemiluminescent properties were investigated. The crystal structures of the two complexes have also been determined. Electrochemiluminescence (ECL) of the two complexes 1 and 2 have been studied in aqueous buffer solution in the presence of co-reactant tri-n-propylamine (TPrA) or 2-(dibutylamino)ethanol (DBAE) at a Au working electrode. The ECL behavior of the complexes was also studied in the presence of several surfactants such as Triton X-100 and Zonyl FSN. The ECL signals of the rhenium(I) complex were enhanced about 190-fold and 70-fold at a Au electrode in the presence of Triton X-100 for the [Re(L1)(CO)(3)(AN)](2+)/TPrA and [Re(L1)(CO)(3)(AN)](2+)/DBAE systems, respectively.

Bifunctional 3D Cu-MOFs containing glutarates and bipyridyl ligands: selective CO2 sorption and heterogeneous catalysis

We report bifunctional three-dimensional (3D) Cu-MOFs with high selectivity of CO(2) over N(2) and H(2) as well as high catalytic activity for transesterification of esters. The Cu-MOFs containing Cu(2) dinuclear units connected by glutarates and bipyridyl ligands are formulated as [{Cu(2)(Glu)(2)(μ-bpa)}·(CH(3)CN)](n) (1) and [{Cu(2)(Glu)(2)(μ-bpp)}·(C(3)H(6)O)](n) (2) (Glu = glutarate, bpa = 1,2-bis(4-pyridyl)ethane, bpp = 1,3-bis(4-pyridyl)propane). These two new bifunctional 3D Cu-MOFs possess very similar pore shape with different pore dimensions. Their gas sorption behaviors were investigated by using CO(2), N(2) and H(2) at suitable temperatures. Both MOFs exhibited good CO(2) selectivity over N(2) and H(2). MOF 1 having a smaller pore dimension exhibited much higher CO(2) adsorption enthalpy than MOF 2 having a larger pore dimension. However, MOF 2 exhibited more enhanced CO(2) uptake ability than MOF 1. A subtle variation of pore dimension indeed influenced the CO(2) uptake ability somewhat significantly especially at higher temperatures such as 273 K and 298 K. Heterogeneous catalytic activities of the MOFs were also investigated in detail. Only MOF 1 appeared to be an efficient, mild, and easily recyclable heterogeneous catalyst for the transesterification of esters and constitutes a promising class of heterogeneous catalysts that allowed reuse without a significant loss of activity through twenty runs with ester.

Flexible dye-sensitized ZnO quantum dots solar cells

ZnO QDs were successfully synthesized by using a simple synthetic route. The synthesized ZnO QDs have different shapes with highly crystalline nature and their size was found to be ca. 3–5 nm. At the same time, a series of modified N719 dyes were obtained via ion-exchange reactions and characterized by FTIR and HRMS measurements. When the modified N719 dyes were used as a sensitizer for ZnO QDs-based flexible solar cells, the photovoltaic properties were enhanced significantly. A highest efficiency of 2.94% was achieved; this might be attributed to the fact that the aggregate of Zn2+/dye on the surface of ZnO QDs can be suppressed efficiently owing to a less carboxylated (COOH) bipyridyl ligand in the modified N719 dye, inhibiting the formation of chelation between ZnO QDs and dye.

Copper(i) complexes with bipyridyl and phosphine ligands: a systematic study

Phosphorescent copper(I) complexes carrying 2,2'-bipyridyl derivatives and phosphine ligands have been prepared and fully characterised. The role of the bipyridyl as well as the phosphine ligands in defining the optical, as well as the chemical properties of the complexes, are discussed. The light emission of these complexes is investigated as a function of the molecular geometry: rigid complexes with restricted freedom to rearrange in the excited state are found to show a quantum yield of phosphorescence one order of magnitude higher than those complexes with no steric constraint. The complexes have been extruded in a polymer matrix as a proof of principle of their processability.

Selective complexation and extraction of Ag(i) and Zn(ii) versus Pb(ii) by polymer beads modified by attachment of a bipyridyl–calixarene-based chelate

The selective extraction of silver(I) and zinc(II) species from ternary mixtures involving lead(II) as the main component was performed using a Wang benzaldehyde resin supported calixarene–bipyridyl ligand. The extraction efficiency and selectivity was evaluated and quantified by complexation experiments using ionic liquid chromatography. Silver and zinc were extracted while lead stayed in solution. The selective recovery of these ions was realized by a treatment of the loaded resin with EDTA for zinc, followed by nitric acid for silver.