Solid-state white light-emitting electrochemical cells using iridium-based cationic transition metal complexes

White electroluminescent (EL) emission from single-layered solid-state light-emitting electrochemical cells (LECs) based on host-guest cationic iridium complexes has been successfully demonstrated. The devices show white EL spectra (Commission Internationale de l'Eclairage coordinates ranging from (x, y) = (0.45, 0.40) to (0.35, 0.39) at 2.9-3.3 V with high color rendering indices up to 80. Peak external quantum efficiency and peak power efficiency of the white LEC reach 4% and 7.8 lm/W, respectively. These results suggest that white LECs based on host-guest cationic transition metal complexes may be a promising alternative for solid-state lighting technologies.     

Bioimaging agents based on redox-active transition metal complexes

Detecting the fluctuation and distribution of various bioactive species in biological systems is of great importance in determining diseases at their early stages. Metal complex-based probes have attracted considerable attention in bioimaging applications owing to their unique advantages, such as high luminescence, good photostability, large Stokes shifts, low toxicity, and good biocompatibility. In this review, we summarized the development of redox-active transition metal complex-based probes in recent five years with the metal ions of iron, manganese, and copper, which play essential roles in life and can avoid the introduction of exogenous metals into biological systems. The designing principles that afford these complexes with optical or magnetic resonance (MR) imaging properties are elucidated. The applications of the complexes for bioimaging applications of different bioactive species are demonstrated. The current challenges and potential future directions of these probes for applications in biological systems are also discussed.

This review summarizes transition metal complexes as bioimaging agents in optical and magnetic resonance imaging.     

Tetraimine macrocyclic transition metal complexes as building blocks for molecular devices

The synthetic strategy initiated by Busch and further developed in recent years resulted in an impressive variety of new azamacrocyclic ligand superstructures. In this contribution, we have reviewed papers containing general synthetic strategies, structural and electronic properties and results of electrochemical studies for a long series of neutral and charged macrocyclic tetraimine complexes of transition metals leading to a new type of homo- and heteronuclear[2]catenanes as examples of switchable molecular machines. The whole series consists of neutral and charged mono-, bis- and trismacrocycles and appropriate reference neutral molecules and many of their derivatives. The bismacrocyclic moieties are constructed from simpler tetraazamacrocyclic fragments. When two of them are linked through polymethylene chains, they form face-to-face biscyclidenes—rectangular box-like moieties. They can host some small guest molecules (water, π-electron-donating compounds) and are stabilized by hydrogen bonds with solvent molecules or a shell of neighboring counterions. Neutral thiol derivatives are used as recognition sites of monolayers self-assembled on electrode surfaces to be employed in devices based on donor–acceptor interactions.Our catenanes consist of bismacrocyclic transition metal complexes linked by aliphatic chains and interlocked with a substituted crown ether. We have proved that under external stimuli – electrochemical pulses – the heteronuclear catenane exhibits controlled intramolecular relocation of the crown ether between two positions. The relocation is possible due to π?π interactions between the aromatic fragments of the crown ether and the transition metal (Ni, Cu) coordinating macrocyclic rings.Our model tetraimine complexes of transition metals can also be used to solve the problem of controlling directional relative movement of molecular fragments present in complex supramolecules. On the way to this aim we have synthesized trismacrocyclic derivatives which are now appropriately modified to serve as components of complex catenanes.     

Thin-film solid-state electroluminescent devices based on tris(2,2'-bipyridine)ruthenium(II) complexes

The behavior of light-emitting electrochemical cells (LEC) based on solid films ( approximately 100 nm) of tris(2,2'-bipyridine)ruthenium(II) between an ITO anode and a Ga-In cathode was investigated. The response times were strongly influenced by the nature of the counterion: small anions (BF(4)(-) and ClO(4)(-)) led to relatively fast transients, while large anions (PF(6)(-), AsF(6)(-)) produced a slow time-response. From comparative experiments of cells prepared and tested in a glovebox to those in ambient, mobility of the anions in these films appears to be related to the presence of traces of water from atmospheric moisture. An electrochemical model is proposed to describe the behavior of these LECs. The simulation results agreed well with experimental transients of current and light emission as a function of time and show that the charge injection is asymmetric at the two electrodes. At a small bias, electrons are the major carriers, while for a larger bias the conduction becomes bipolar.     

A new class of electroluminescent metal complexes based on quinoline ligands containing the sulfanylamino group

The synthesis and properties of a new class of electroluminescent metal complexes based on quinoline ligands containing the sulfanylamino group in position 8 are described. These complexes contain C-N-M-N chains in the chelate cycles instead of the traditionally used C-O-M-N chains.     

New electroluminescent materials based on chelate zinc complexes

Three new chelate zinc complexes with azomethine groups characterized by luminescence in the visible spectral region were synthesized: bis(N-(2-oxybenzylidene)cyclohexylamine)zinc, bis(N-(2-oxybenzylidene)-4-tert-butylaniline)zinc, and N,N′-bis(oxybenzylidene)-1,2-phenylenediaminezinc. Their spectral properties were studied. Based on these complexes, we prepared electroluminescence devices giving an intense emission in the blue, green, and red spectral regions.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2056–2059, October, 2004.     

Divalent transition metal complexes

4-(4-ethoxy-phenylhydrazono)-1-phenyl-3-methyl-1H-pyrazolin-5(4H)-one (5a) (H-EMPhP) as ligand and its Cu(II), Co(II) and Ni(II) complexes 4(a-c) were synthesized and characterized by their thermal and spectral properties. The azocoupling product (H-EMPhP), able of azo-hydrazone tautomerism 5(a-d), act as a bidentate ligand involving in coordination the azogroup nitrogen of its common anion (7) and the oxygen atom that is bound to the pyrazole ring of the mentioned anion (7).     

Studies on transition metal murexide complexes

Iron, cobalt, nickel, copper, zinc, cadmium and mercury murexide complexes have been prepared and characterized. The thermal properties of these complexes are studied deeply by DTA technique where their thermal peaks are explained. The multi-stages thermal decomposition mechanism is proposed. The thermodynamic parameters of the decomposition steps are calculated. The entropy change values for all complexes are of the same magnitude and all transition states of the thermal reactions are more ordered than the reactants. The thermal reactions proceed in complicated mechanisms. The fractions appeared in the calculated orders of the thermal reactions confirmed that these reactions proceeded via complex mechanisms.     

Ab initio study of phosphorescent emitters based on rare-earth complexes with organic ligands for organic electroluminescent devices

An ab initio approach is developed for calculation of low-lying excited states in Ln(3+) complexes with organic ligands. The energies of the ground and excited states are calculated using the XMCQDPT2/CASSCF approximation; the 4f electrons of the Ln(3+) ion are included in the core, and the effects of the core electrons are described by scalar quasirelativistic 4f-in-core pseudopotentials. The geometries of the complexes in the ground and triplet excited states are fully optimized at the CASSCF level, and the resulting excited states have been found to be localized on one of the ligands. The efficiency of ligand-to-lanthanide energy transfer is assessed based on the relative energies of the triplet excited states localized on the organic ligands with respect to the receiving and emitting levels of the Ln(3+) ion. It is shown that ligand relaxation in the excited state should be properly taken into account in order to adequately describe energy transfer in the complexes. It is demonstrated that the efficiency of antenna ligands for lanthanide complexes used as phosphorescent emitters in organic light-emitting devices can be reasonably predicted using the procedure suggested in this work. Hence, the best antenna ligands can be selected in silico based on theoretical calculations of ligand-localized excited energy levels.     

Stability of thin-film solid-state electroluminescent devices based on tris(2,2'-bipyridine)ruthenium(II) complexes

The factors affecting the operating life of the light-emitting electrochemical cells (LECs) based on films of tris(2,2'-bipyridine)ruthenium(II) both in sandwich (using an ITO anode and a Ga:Sn cathode) and planar (using interdigitated electrode arrays (IDAs)) configurations were investigated. Stability of these devices is greatly improved when they are produced and operated under drybox conditions. The proposed mechanism of the LEC degradation involves formation of a quencher in a small fraction of tris(2,2'-bipyridine)ruthenium(II) film adjacent to the cathode, where light generation occurs, as follows from the observed electroluminescence profile in the LECs constructed on IDAs, showing that the charge injection in such devices is highly asymmetric, favoring hole injection. Bis(2,2'-bipyridine)diaquoruthenium(II) is presumed to be the quencher responsible for the device degradation. A microscopic study of photo- and electroluminescence profiles of planar light-emitting electrochemical cells was shown as a useful approach for studies of charge carrier injection into organic films.     

Polyoxometalate tri-supported transition metal complexes containing mixed-valent transition metal ions

Three compounds, [AsMo₈V₆O₄₂][Cu(2,2?-bpy)₂]₂[Cu(2,2?-bpy)]·4H₂O (1), [PMo₈V₆O₄₂][Cu(2,2?-bpy)₂]₂[Cu(2,2?-bpy)]·3H₂O (2) and [PMo₈V₆O₄₂][Cu(2,2?-bpy)₂]₂[Cu(2,2?-bpy)]·3.5H₂O (3), have been synthesized under hydrothermal conditions and characterized by IR, UV–vis, XRD, TG, elemental analysis, and X-ray diffraction analysis. Single-crystal X-ray structure analysis reveals that 1 and 2 are isostructural and isomorphous, whereas 2 and 3 are polymorphs. Polymorphs of 1 have not been synthesized yet. The mixed-valent transition metal ion in 1–3 has been further confirmed by TG analyses. Catalytic properties of 1 and 2 have also been studied.     

邻菲啰啉钌(Ⅱ)配合物的结构及电致发光性能的研究

合成了三-(1,10-邻菲啰啉)钌发光配合物Ru(phen)3(PF6)2(phen=1,10-邻菲啰啉),得到了其单晶结构.单晶结构分析结果表明,Ru(phen)3(PF6)2具有层状结构特征,阳离子[Ru(phen)3]2+和阴离子PF-6分别构成了正电荷层和负电荷层,正、负电荷层交替排列形成了晶体结构.分别以Ru(phen)3Cl2和Ru(phen)3(PF6)2制备了单层结构的电化学发光器件(LECs),器件结构为[ITO/Ru(Ⅱ)-配合物(100 nm)/Al(200 nm)].结果显示:以Ru(phen)3(PF6)2为发光层的器件显示的最高效率和亮度分别为0.24 cd/A和1 829 cd/m2,而以Ru(phen)3Cl2为发光层的器件显示的最高效率和亮度分别为0.18 cd/A和350 cd/m2,表明Ru(phen)3(PF6)2比Ru(phen)3Cl2具有更优异的电致发光性能.     

Bridging vinylalkylidene transition metal complexes

Vinylalkylidene transition metal complexes have been extensively used as ‘multitalent tools’ in organic synthesis, covering a broad field of applications. The vinylalkylidene ligands can be monodentate; alternatively they can adopt a bridging coordination mode in complexes with two adjacent metal atoms. As for other unsaturated organic ligands which can bond in both mono- and di-nuclear modes, the bridging coordination can give rise to new and different chemical properties from those found when the ligand is bound to a single metal centre. Likewise, the synthetic routes to bridging vinylalkylidene complexes offer a broader range of possibilities compared to those used to make mononuclear vinylalkylidenes. In spite of the fact that bridging vinylalkylidene complexes have been known for about 40 years, their synthetic potential as C₃ activated fragments has so far been under-exploited. Comparison with other C₃ bridged ligands (allenyls and allyls) indicates that vinylalkylidene ligands are reactive and versatile species. This review article gives an overview of the chemistry of bridging vinylalkylidene complexes to focus attention on their potential as synthetic tools.     

Fluorenone hydrazine-S-benzyldithiocarbazate transition metal complexes

Summary New Cu^II, Co^II, Ni^II, Cd^II, Zn^II, Hg^II, Pd^II and UO ₂ ^II complexes of the Schiff base ligand (FBz) formed by condensation of fluorenone withS-benzyldithiocarbazate have been prepared and characterized by elemental analysis, magnetic and spectroscopic measurements. The Cu(FBz)₂(Cl)₂ complex is paramagnetic. The Ni(FBz-H)₂ complex is diamagnetic, four-coordinate and square planar. The Co^II ion is oxidized in the presence of the Schiff base with the concomitant formation of Co^III complex of empirical formulae Co(FBz)Cl₃OH₂. The ligand was tested as a corrosion inhibitor for copper. Inhibition efficiency was calculated and the limiting concentration of FBz to give maximum efficiency was 10^–3 mol dm^–3 at 25°C. The polarographic reduction of FBz was investigated in Britton-Robinson buffer solutions of pH 3–10. The polarograms at dme indicated that the depolarizer is reduced through two two-electron irreversible diffusion-controlled waves. The mechanistic pathway of the electrode reaction is commensurate with this result.     

New vic-dioxime transition metal complexes

New vic-dioxime ligands and their Cu^II, Co^III, Ni^II and VO^IV complexes have been prepared and characterized by elemental analyses, i.r. and u.v. spectra, magnetic moments and molar conductance data. The Co^III complexes are diamagnetic. The ¹H- and ¹³C-n.m.r. and g.c./m.s. spectra of the vic-dioxime ligands and their Co^III complexes were recorded. The compounds are all non-electrolytes.     

分子尺度电致发光器件

近年来,有机单分子电致发光研究在材料和器件方面取得了突破,是分子电子学新兴的研究方向之一。本文综述了扫描隧道显微镜法、纳米间隙电极法等测量单分子尺度电致发光的研究进展。根据电致发光谱图,可以确定分子器件的发光类型,并得到单个分子的指纹信息。     

Bimacrocyclic NHC transition metal complexes

The preparation of seven concave NHC metal complexes derived from bimacrocyclic imidazolinium salt 1 is reported. The silver complex 2, obtained in 86% yield by reacting 1 with silver(I) oxide, was used to give copper complex 3, rhodium complex 5 and iridium complex 6 by transmetalation in good yields. Palladium complex 4 was obtained by reaction of the azolium salt 1 with palladium dichloride in 3-chloropyridine. The rhodium and iridium dicarbonyl complexes 7 and 8 were prepared via ligand exchange from the COD complexes 5 and 6. Silver complex 2, copper complex 3 and palladium complex 4 were characterized by single-crystal X-ray analysis. Silver complex 2 and copper complex 3 were tested in the cyclopropanation of styrene and indene with EDA (ethyl diazoacetate), where good results were obtained with 3, while low conversion and catalyst decomposition was observed with 2.     

Molecular orbital calculations on transition metal complexes

INDO SCF MO calculations are reported for the complexes (C₅H₅)M(C₇H₇) (M = Ti, V and Cr), and for the corresponding V and Cr cations. The results correctly predict¹ A ₁ ground states for the V⁺ and the neutral Ti and Cr species, and for the neutral V and Cr⁺ complexes confirm the² A ₁ ground levels. The formally metald-levels followed theH ^core sequencee ₂<a ₁<e ₁, and the most important interactions were those between the metale ₂ level and the ligand C₇H₇ -orbitals, and between the metale ₁ level and the ligand C₅H₅ -orbitals. Calculations also satisfactorily reproduced other experimental quantities, and the results indicate that thee ₂ ligand interaction becomes more important, and thee ₁ ligand interaction less important, with increasing size of the ligand ring.     

Investigation of thin-layer chromatography properties of some transition metal complexes based on ditiocarbamates

Sodium diethyldithiocarbamate (DEDTC) and ammonium pyrolidinedithiocarbamate (PyDTC) are prepared as their Co or Cu (M) complexes [M(DEDTC)(2) and M(PyDTC)(2), respectively]. The complexes are prepared by reactions of DEDTC and PyDTC with metal (II) nitrates, and they are examined for chromatographic properties using thin-layer chromatography systems. These complexes and their mixtures are spotted on the activated and non-activated 250-microm thick thin layers of commercial silica gel (Si-60GF(254)). Pure toluene and a toluene-cyclohexane mixture (3:1, v/v) are used as mobile phases for running the complexes. These chromatographic systems are successfully used for the qualitative analysis of the corresponding metal cations and the separation of components in both M(DEDTC)(2) and M(PyDTC)(2) complex mixtures. In addition, non-activated layers are more successful than activated layers. This study may be useful in understanding the effects of stationary and mobile phase properties, retention mechanisms, and the effects of the nature of metal and ligand type on the chromatographic behavior and parameters [e.g., retention factors, theoretical plate numbers, and resolution] of the complexes.     

Design of molecular switches based on transition metal bis(dicarbollide) complexes

The paper presents a review of the state of the art and prospects for the development of rotary molecular switches based on transition metal bis(dicarbollide) complexes.