Iron(II) Complexes of 2,6-Di[4-(ethylcarboxy)pyrazol-1-yl]pyridine with Reversible Guest-Modulated Spin-Crossover Behavior

Three solvatomorphs of the iron(II) complex of 2,6-di[4-(ethylcarboxy)pyrazol-1-yl]pyridine (bpCOOEt₂p) of formulas [Fe(bpCOOEt₂p)₂](ClO₄)₂·1.5MeNO₂ (1), [Fe(bpCOOEt₂p)₂](ClO₄)₂·MeNO₂ (2), and [Fe(bpCOOEt₂p)₂](ClO₄)₂·2MeNO₂ (3) have been prepared and characterized. They show interesting spin-crossover (SCO) properties ranging from partial to complete thermal spin transitions and a light-induced excited spin-state trapping (LIESST) effect. In solvatomorph 2, a robust structure is formed with channels that enable the entrance or removal of solvent molecules by vapor diffusion without losing the crystallinity. Thus, solvent-exchanged samples [Fe(bpCOOEt₂p)₂](ClO₄)₂·MeNO₂ (2·MeNO ₂ ), [Fe(bpCOOEt₂p)₂](ClO₄)₂·MeCN (2·MeCN), [Fe(bpCOOEt₂p)₂](ClO₄)₂·0.5Me₂CO (2·Me ₂ CO), and [Fe(bpCOOEt₂p)₂](ClO₄)₂·MeCOOH (2·MeCOOH) were prepared by vapor diffusion of the solvents in a crystal of the compound previously heated to 400 K in a single-crystal to single-crystal (SCSC) fashion. Interestingly, this causes a change of spin state with a stabilization of the low-spin state in 2·Me ₂ CO and the high-spin state in 2·MeCN. Therefore, the SCO properties of 2 can be tuned in a reversible way by exposure to different solvents.

Redox and guest tunable spin-crossover properties in a polymeric polyoxometalate

A bifunctionalized polyoxometalate (POM), [V6O19(C16H15N6O)2]2-, which contains a redox active hexavanadate moiety covalently linked to two tridentate 2,6-bis(pyrazol-1-yl)pyridine (1-bpp) ligands, has been prepared and characterized. Reaction of this hybrid molecule with Fe(ii) or Zn(ii) ions produces crystalline neutral 1D networks of formula Fe[V6O19(C16H15N6O)2]·solv (2) and Zn[V6O19(C16H15N6O)2]·solv (3) (solv = solvent molecules). Magnetic properties of 2 show an abrupt spin-crossover (SCO) with the temperature, which can be induced by light irradiation at 10 K (Light-Induced Excited Spin-State Trapping, LIESST effect). Interestingly, this porous and flexible structure enables reversible exchange of solvents in 2, which allows tuning the temperature of the thermal SCO. In 2 and 3, the hexavanadate unit can be reduced by electrochemical or chemical means in a reversible way. Chemical reduction and reoxidation by a postsynthetic method is accompanied by the insertion in the structure of the reductant and oxidant molecules (cobaltocene and tribromide, respectively), which provokes drastic changes in the spin state of Fe(ii). This leads to an elegant switching multifunctional material in which SCO properties of the Fe(ii) complexes coexist with the redox properties of the POM and can be tuned by a variety of stimuli such as temperature, light, solvent exchange or electron transfer. During the reduction process, 3 undergoes a single-crystal-to-single-crystal one-electron reduction, which confirms the presence of cobaltocenium cations by single crystal X-ray diffraction.

Strain Switching in van der Waals Heterostructures Triggered by a Spin-Crossover Metal-Organic Framework

Van der Waals heterostructures (vdWHs) provide the possibility of engineering new materials with emergent functionalities that are not accessible in another way. These heterostructures are formed by assembling layers of different materials used as building blocks. Beyond inorganic 2D crystals, layered molecular materials remain still rather unexplored, with only few examples regarding their isolation as atomically thin layers. Here, the family of van der Waals heterostructures is enlarged by introducing a molecular building block able to produce strain: the so-called spin-crossover (SCO). In these metal-organic materials, a spin transition can be induced by applying external stimuli like light, temperature, pressure, or an electric field. In particular, smart vdWHs are prepared in which the electronic and optical properties of the 2D material (graphene and WSe₂ ) are clearly switched by the strain concomitant to the spin transition. These molecular/inorganic vdWHs represent the deterministic incorporation of bistable molecular layers with other 2D crystals of interest in the emergent fields of straintronics and band engineering in low-dimensional materials.

Reversible tuning of luminescence and magnetism in a structurally flexible erbium–anilato MOF

By combining 3,6-N-ditriazolyl-2,5-dihydroxy-1,4-benzoquinone (H₂trz₂An) with NIR-emitting Er^III ions, two different 3D neutral polymorphic frameworks (1a and 1b), differing in the number of uncoordinated water molecules, formulated as [Er₂(trz₂An)₃(H₂O)₄]_n·xH₂O (x = 10, a; x = 7, b), have been obtained. The structure of 1a shows layers with (6,3) topology forming six-membered rings with distorted hexagonal cavities along the bc plane. These 2D layers are interconnected through the N4 atoms of the two pendant arms of the trz₂An linkers, leading to a 3D framework, where neighboring layers are eclipsed along the a axis, with hexagonal channels filled with water molecules. In 1b, layers with (6,3) topology in the [101] plane are present, each Er^III ion being connected to three other Er^III ions through bis-bidentate trz₂An linkers, forming rectangular six-membered cavities. 1a and 1b are multifunctional materials showing coexistence of NIR emission and field-induced slow relaxation of the magnetization. Remarkably, 1a is a flexible MOF, showing a reversible structural phase transition involving shrinkage/expansion from a distorted hexagonal 2D framework to a distorted 3,6-brickwall rectangular 3D structure in [Er₂(trz₂An)₃(H₂O)₂]_n·2H₂O (1a_des). This transition is triggered by a dehydration/hydration process under mild conditions (vacuum/heating to 360 K). The partially dehydrated compound shows a sizeable change in the emission properties and an improvement of the magnetic blocking temperature with respect to the hydrated compound, mainly related to the loss of one water coordination molecule. Theoretical calculations support the experimental findings, indicating that the slight improvement observed in the magnetic properties has its origin in the change of the ligand field around the Er^III ion due to the loss of a water molecule.

Tuning of luminescent and SIM properties is herein reported, in a novel flexible 3D anilato-based Er^III-MOF, displaying reversible shrinkage/expansion from a distorted hexagonal to a 3,6-brickwall rectangular structure.

The effect of tether groups on the spin states of iron(II)/bis[2,6-di(pyrazol-1-yl)pyridine] complexes

The synthesis of six 2,6-di(pyrazol-1-yl)pyridine derivatives bearing dithiolane or carboxylic acid tether groups is described: [2,6-di(pyrazol-1-yl)pyrid-4-yl]methyl (R)-lipoate (L1), 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxamido]ethyl (R)-lipoate (L2), 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxy]ethyl (R)-lipoate (L3), N-([2,6-di(pyrazol-1-yl)pyrid-4-ylsulfanyl]-2-aminoethyl (R)-lipoamide (L4), 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxamido]acetic acid (L5) and 2-[(2,6-di(pyrazol-1-yl)pyridine)-4-carboxamido]propionic acid (L6). The iron(ii) perchlorate complexes of all the new ligands exhibit gradual thermal spin-crossover (SCO) in the solid state above room temperature, except L4 whose complex remains predominantly high-spin. Crystalline [Fe(L6)2][ClO4]2·2MeCN contains three unique cation sites which alternate within hydrogen-bonded chains, and undergo gradual SCO at different temperatures upon warming. The SCO midpoint temperature (T1/2) of the complexes in CD3CN solution ranges between 208-274 K, depending on the functional group linking the tether groups to the pyridyl ring. This could be useful for predicting how these complexes might behave when deposited on gold or silica surfaces.

Insertion of single-ion magnets based on mononuclear Co(II) complexes into ferromagnetic oxalate-based networks

The 1 : 2 and 1 : 1 Co(ii) complexes of the L ligand (L = 6-(3,5-diamino-2,4,6-triazinyl)2,2'-bipyridine) with formulas [CoII(L)2](ClO4)2·0.5MeCN·Et2O (1) and [CoII(L)(CH3CN)2(H2O)](ClO4)2·MeCN (2) have been prepared. The structural and magnetic characterization of the two compounds shows that they contain octahedral high-spin Co(ii) and present a field-induced slow relaxation of the magnetization. 1 has been inserted into a bimetallic oxalate-based network leading to a novel achiral 3D compound of formula [CoII(L)2][MnIICrIII(ox)3]2·(solvate) (3) exhibiting ferromagnetic ordering below 4.6 K. EPR measurements suggest a weak magnetic coupling between the two sublattices.

Hexakis-adducts of [60]fullerene as molecular scaffolds of polynuclear spin-crossover molecules

A family of hexakis-substituted [60]fullerene adducts endowed with the well-known tridentate 2,6-bis(pyrazol-1-yl)pyridine (bpp) ligand for spin-crossover (SCO) systems has been designed and synthesized. It has been experimentally and theoretically demonstrated that these molecular scaffolds are able to form polynuclear SCO complexes in solution. UV-vis and fluorescence spectroscopy studies have allowed monitoring of the formation of up to six Fe(ii)–bpp SCO complexes. In addition, DFT calculations have been performed to model the different complexation environments and simulate their electronic properties. The complexes retain SCO properties in the solid state exhibiting both thermal- and photoinduced spin transitions, as confirmed by temperature-dependent magnetic susceptibility and Raman spectroscopy measurements. The synthesis of these complexes demonstrates that [60]fullerene hexakis-adducts are excellent and versatile platforms to develop polynuclear SCO systems in which a fullerene core is surrounded by a SCO molecular shell.

Polynuclear spin-crossover molecules showing both thermal and photoinduced spin transitions have been prepared using a [60]fullerene hexakis-adduct endowed with Fe(ii) complexes of tridentate 2,6-bis(pyrazol-1-yl)pyridine (bpp) ligand.

Ground-State Spin Blockade in a Single-Molecule Junction

It is known that the quantum mechanical ground state of a nanoscale junction has a significant impact on its electrical transport properties. This becomes particularly important in transistors consisting of a single molecule. Because of strong electron-electron interactions and the possibility of accessing ground states with high spins, these systems are eligible hosts of a current-blockade phenomenon called a ground-state spin blockade. This effect arises from the inability of a charge carrier to account for the spin difference required to enter the junction, as that process would violate the spin selection rules. Here, we present a direct experimental demonstration of a ground-state spin blockade in a high-spin single-molecule transistor. The measured transport characteristics of this device exhibit a complete suppression of resonant transport due to a ground-state spin difference of 3/2 between subsequent charge states. Strikingly, the blockade can be reversibly lifted by driving the system through a magnetic ground-state transition in one charge state, using the tunability offered by both magnetic and electric fields.

Spin-crossover iron(ii) complex showing thermal hysteresis around room temperature with symmetry breaking and an unusually high T(LIESST) of 120 K

The Fe(ii) complex of 4′,4′′ carboxylic acid disubstituted dipyrazolylpyridine shows spin-crossover around room temperature and the LIESST effect with T(LIESST) of 120 K.

Unravelling the spin-state of solvated [Fe(bpp)2]2+ spin-crossover complexes: structure-function relationship

This paper reports firstly the syntheses, crystal structures, and thermal and magnetic properties of spin crossover salts of formulae [Fe(bpp)₂]₃[Cr(CN)₆]₂·13H₂O (1) and [Fe(bpp)₂][N(CN)₂]₂·H₂O (2) (bpp = 2,6-bis(pyrazol-3-yl)pyridine) exhibiting hydrogen-bonded networks of low-spin [Fe(bpp)₂]²⁺ complexes and [Cr(CN)₆]^3- or [N(CN)₂]^- anions, with solvent molecules located in the voids. Desolvation of 1 is accompanied by a complete low-spin (LS) to a high-spin (HS) transformation that becomes reversible after rehydration by exposing the sample to the humidity of air. The influence of the lattice water on the magnetic properties of spin-crossover [Fe(bpp)₂]X₂ complex salts has been documented. In most cases, it stabilises the LS state over the HS one. In other cases, it is rather the contrary. The second part of this paper is devoted to unravelling the reasons why the lattice solvent stabilises one form over the other through magneto-structural correlations of [Fe(bpp)₂]²⁺ salts bearing anions with different charge/size ratios (X^n-). The [Fe(bpp)₂]²⁺ stacking explaining these two different behaviours is correlated here with the composition of the second coordination sphere of the Fe centers and the ability of these anions to form hydrogen bonds and/or π-π stacking interactions between them or the bpp ligand.

Iron(ii) complexes of tris(2-pyridylmethyl)amine (TPMA) and neutral bidentate ligands showing thermal- and photo-induced spin crossover

Three new mononuclear Fe(ii) complexes have been prepared and characterized by the combination of tetradentate tris(2-pyridylmethyl)amine (TPMA) with three neutral bidentate ligands, such as ethylenediamine (en), 1,2-diaminopropane (pn) and 2-picolylamine (2-pic), in compounds [FeII(TPMA)(en)](ClO4)2 (1), [FeII(TPMA)(2-pic)](ClO4)2 (2) and [FeII(TPMA)(pn)](ClO4)2 (3). Structural and magnetic characterization demonstrates that the three compounds present a complete SCO behavior. The absence of strong intermolecular interactions and solvent molecules leads to reversible and gradual spin transitions. The different ligands allow tuning T1/2 from 130 K (2) to 325 K (3). The compound with the lowest T1/2 (2) shows the LIESST effect with a TLIESST of 43 K. Interestingly, the use of these relatively small bidentate ligands leads to the crystallization in non-centrosymmetric space groups in contrast with previous studies using other bidentate ligands.

Spin-crossover compounds based on iron(ii) complexes of 2,6-bis(pyrazol-1-yl)pyridine (bpp) functionalized with carboxylic acid and ethyl carboxylic acid

New salts of the iron(ii) bppCOOH and bppCOOEt spin crossover complexes have been studied.

Photomagnetic properties of an Fe(ii) spin-crossover complex of 6-(3,5-diamino-2,4,6-triazinyl)-2,2′-bipyridine and its insertion into 2D and 3D bimetallic oxalate-based networks

The Fe(ii) complex of 6-diaminotriazyl-2,2′-bipyridine shows the LIESST effect and has been used as a countercation of two oxalate-based ferromagnets.

Spin-crossover complex encapsulation within a magnetic metal–organic framework

We report the solid-state incorporation of a mononuclear iron(iii) spin-crossover (SCO) complex within the pores of a magnetic metal–organic framework (MOF).

Graphene related magnetic materials: micromechanical exfoliation of 2D layered magnets based on bimetallic anilate complexes with inserted [FeIII(acac2-trien)]+ and [FeIII(sal2-trien)]+ molecules

The syntheses, structures and magnetic properties of the coordination compounds of formula [FeIII(acac2-trien)][MnIICrIII(Cl2 An)3]·(CH3CN)2 (1), [FeIII(acac2-trien)][MnIICrIII(Br2An)3]·(CH3CN)2 (2) and [GaIII(acac2-trien)][MnIICrIII(Br2An)3]·(CH3CN)2 (3) are reported. They exhibit a 2D anionic network formed by Mn(ii) and Cr(iii) ions linked through anilate ligands, while the [FeIII(acac2-trien)]+ or [GaIII(acac2-trien)]+ charge-compensating cations are placed inside the hexagonal channels of the 2D network, instead of being inserted in the interlamellar spacing. Thus, these crystals are formed by hybrid layers assembled through van der Waals interactions. The magnetic properties indicate that these compounds behave as magnets exhibiting a long-range ferrimagnetic ordering at ca. 11 K, while the inserted Fe(iii) cations remain in the high-spin state. As for graphene, these layered materials can be exfoliated in atomically-thin layers with heights down to 2 nm by using the well-known Scotch tape method. Hence, this micromechanical procedure provides a suitable way to isolate ultrathin layers of this kind of graphene related magnetic materials. Interestingly, this method can also be successfully used to exfoliate the 2D anilate-based compound [FeIII(sal2-trien)][MnIICrIII(Cl2An)3]·solv (4), which exhibits the typical alternated cation/anion layered structure. This result shows that the micromechanical exfoliation method, which has been extensively used for exfoliating van der Waals layered solids, can also be useful for exfoliating layered coordination compounds, even when they are formed by ionic components.

Electrochromic polyoxometalate material as a sensor of bacterial activity

Lactobacillus fermentum, a healthy bacterium of human microbiota, acts as an electron donor for the electrochromic polyoxometalate [P₂Mo^VI₁₈O₆₂]⁶⁻. This reaction affords a means of evaluating the activity of the bacterium.

White light-emitting electrochemical cells based on the Langmuir-Blodgett technique

Light-emitting electrochemical cells (LECs) showing a white emission have been prepared with Langmuir-Blodgett (LB) films of the metallosurfactant bis[2-(2,4-difluorophenyl)pyridine][2-(1-hexadecyl-1H-1,2,3-triazol-4-yl)pyridine]iridium(III) chloride (1), which work with an air-stable Al electrode. They were prepared by depositing a LB film of 1 on top of a layer of poly(N,N'-diphenyl-N,N'-bis(4-hexylphenyl)-[1,1'-biphenyl]-4,4'-diamine (pTPD) spin-coated on indium tin oxide (ITO). The white color of the electroluminescence of the device contrasts with the blue color of the photoluminescence of 1 in solution and within the LB films. Furthermore, the crystal structure of 1 is reported together with the preparation and characterization of the Langmuir monolayers (π-A compression isotherms and Brewster angle microscopy (BAM)) and LB films of 1 (IR, UV-vis and emission spectroscopy, X-ray photoelectron spectroscopy (XPS), specular X-ray reflectivity (SXR), and atomic force microscopy (AFM)).

A spin-crossover complex based on a 2,6-bis(pyrazol-1-yl)pyridine (1-bpp) ligand functionalized with a carboxylate group

[Fe(bppCOOH)₂](ClO₄)₂ shows an abrupt spin transition (T_1/2 = 380 K, T_LIESST = 60 K) due to a hydrogen-bonded linear network of complexes.

Tuning the nuclearity of iron(iii) polynuclear clusters by using tetradentate Schiff-base ligands

Three novel octanuclear, hexanuclear and tetranuclear complexes of high-spin Fe(iii) ions were obtained by the reaction of the N,N′-bis-(1R-imidazol-4-ylmethylene)-ethane-1,2-diamine ligand (R = H, CH₃) and its derivatives with Fe(ClO₄)₃·6H₂O and KSCN.

A family of layered chiral porous magnets exhibiting tunable ordering temperatures

A simple change of the substituents in the bridging ligand allows tuning of the ordering temperatures, Tc, in the new family of layered chiral magnets A[M(II)M(III)(X2An)3]·G (A = [(H3O)(phz)3](+) (phz = phenazine) or NBu4(+); X2An(2-) = C6O4X2(2-) = 2,5-dihydroxy-1,4-benzoquinone derivative dianion, with M(III) = Cr, Fe; M(II) = Mn, Fe, Co, etc.; X = Cl, Br, I, H; G = water or acetone). Depending on the nature of X, an increase in Tc from ca. 5.5 to 6.3, 8.2, and 11.0 K (for X = Cl, Br, I, and H, respectively) is observed in the MnCr derivative. Furthermore, the presence of the chiral cation [(H3O)(phz)3](+), formed by the association of a hydronium ion with three phenazine molecules, leads to a chiral structure where the Δ-[(H3O)(phz)3](+) cations are always located below the Δ-[Cr(Cl2An)3](3-) centers, leading to a very unusual localization of both kinds of metals (Cr and Mn) and to an eclipsed disposition of the layers. This eclipsed disposition generates hexagonal channels with a void volume of ca. 20% where guest molecules (acetone and water) can be reversibly absorbed. Here we present the structural and magnetic characterization of this new family of anilato-based molecular magnets.

Patterning of magnetic bimetallic coordination nanoparticles of Prussian blue derivatives by the Langmuir-Blodgett technique

We report a novel method to prepare patterns of nanoparticles over large areas of the substrate. This method is based on the adsorption of the negatively charged nanoparticles dispersed in an aqueous subphase onto a monolayer of the phospholipid dipalmitoyl-l-α-phosphatidylcholine (DPPC) at the air-water interface. It has been used to prepare patterns of nanoparticles of Prussian blue analogues (PBA) of different size (K(0.25)Ni[Fe(CN)(6)](0.75) (NiFe), K(0.25)Ni[Cr(CN)(6)](0.75) (NiCr), K(0.25)Ni[Co(CN)(6)](0.75) (NiCo), Cs(0.4)Co[Cr(CN)(6)](0.8) (CsCoCr), and Cs(0.4)Co[Fe(CN)(6)](0.9) (CsCoFe)). The behavior of DPPC monolayer at the air-water interface in the presence of the subphase of PBA nanoparticles has been studied by the compression isotherms and Brewster angle microscopy (BAM) images. Atomic force microscopy (AFM) of the transferred films on mica substrates shows that patterns of the nanoparticles are observed for a 10(-4) M concentration of the subphase, based on the nanoparticle precursors, at surface pressures between 1 and 6 mN/m and transfer velocities from 10 to 80 mm/min. Vertical, horizontal, or tilted fringes of the nanoparticles with respect to the transfer direction can be obtained depending on the transfer velocity and surface pressure.

Multifunctionality in hybrid magnetic materials based on bimetallic oxalate complexes

This tutorial review illustrates the design of multifunctional oxalate-based magnetic materials through the combination of the intrinsic magnetism of the metal-organic framework and the additional properties introduced by several organic/inorganic functional cations.

Structural and magnetic characterization of Pd nanoparticles encapsulated in apoferritin

Pd nanoparticles exhibiting permanent magnetism at room temperature have been prepared within the apoferritin cavity. Pd nanoparticles in air and under an inert atmosphere were synthesized to study the influence of the aerobic and anaerobic conditions in the final magnetic properties. The surface of nanoparticles as well as the type of crystalline phase could determine the magnetic properties. X-ray powder diffraction, including Debye-function analysis, transmission electronic microscopy, and magnetization measurements have been used for characterizing the nanoparticles.

Dual-emitting Langmuir-Blodgett film-based organic light-emitting diodes

Langmuir-Blodgett (LB) films containing alternating layers of the metallosurfactants bis(4,4'-tridecyl-2,2'-bipyridine)-(4,4'-dicarboxy-2,2'-bipyridine) ruthenium(II)-bis(chloride) (1) and bis[2-(2,4-difluorophenyl)pyridine](4,4'-dinonadecyl-2,2'-bipyridine)iridium(III) chloride (2) have been prepared. Langmuir monolayers at the air-water interface of 1 and 2 with different anions in the subphase have been characterized by pi-A compression isotherms and Brewster angle microscopy (BAM). The transferred LB films have been characterized by IR, UV-vis and emission spectroscopy, and atomic force microscopy (AFM). Electroluminescent devices formed by LB films containing alternating layers of these two molecules show dual emission by simple mixing of the two emitters in a single LB film, and by preparing two stacked configurations, in which a LB layer of the ruthenium complexes is deposited on top of a LB layer of the iridium complexes and the inverse situation. The color of the electroluminescence can be tuned by changing the thickness of each LB layer. Due to efficient hole blocking of a layer of the iridium complexes when deposited on top of the layer of ruthenium complexes, in that configuration the green emission of the iridium complexes is suppressed. In the opposite case, excitons are generated in both layers although most likely preferentially in the layer of the iridium complexes.

Dual-emissive photoluminescent Langmuir-Blodgett films of decatungstoeuropate and an amphiphilic iridium complex

Langmuir monolayers and Langmuir-Blodgett (LB) films of the decatungstoeuropate [Eu(W(5)O(18))(2)](9-) (EuW(10)) and the amphiphilic Ir complex 1 have been successfully fabricated by using the adsorption properties of the EuW(10) polyanion dissolved in the aqueous subphase onto a positively charged 1 monolayer at the air-water interface. The compression isotherms and Brewster angle microscopy (BAM) of monolayers of 1 on pure water (1 monolayer) and on a subphase containing 10(-6) M EuW(10) and 10(-3) M NaCl (1/EuW(10) monolayer) have been studied. Infrared and UV-vis spectroscopy of the transferred LB films indicate that EuW(10) and 1 molecules are incorporated within these LB films. X-ray reflectivity (SXR) and atomic force microscopy (AFM) experiments indicate that LB films of 1 present a heterogeneous morphology while 1/EuW(10) films show a flatter and more homogeneous surface as well as a layered structure with a periodicity of 4.1 nm. Mixed monolayers of 1 and DODA (dimethyldioctadecylammonium bromide) have been prepared with EuW(10) polyanions in the subphase to control the concentration of 1 and EuW(10) polyanions within the LB films. AFM and SXR experiments with the transferred LB films show that the dilution of 1 with DODA improves the layered structure. The luminescence of 1 is partially quenched by EuW(10) in the 1/EuW(10) LB films, while emission from EuW(10) is not detected. On the other hand, emission from both entities is preserved in the LB films prepared from mixed DODA/1 monolayers, in which the red and yellow emissions arise independently from EuW(10) and 1, respectively. The different DODA:1 ratios lead to changes in the emission color. Therefore, they constitute a promising color-tunable luminescent material.

Molecular ionic junction for enhanced electronic charge transfer

We present the first evidence of charge injection improvement in an organic electroluminescent device provided by a single ionic molecular layer. A hole-dominated, hybrid organic-inorganic light-emitting device is used as a probe to verify the effectiveness of the ionic compound monolayer on modifying the metal oxide cathode. The rearrangement of ions under an applied bias induces a strong field at the electrode-organic interface resulting in an enhancement of the electron injection into the organic semiconductor. A strong decrease in turn-on voltage for electroluminescence is observed for the device containing the ionic molecular monolayer.