Self-healing gold mirrors and filters at liquid-liquid interfaces.

The optical and morphological properties of lustrous metal self-healing liquid-like nanofilms were systematically studied for different applications (e.g., optical mirrors or filters). These nanofilms were formed by a one-step self-assembly methodology of gold nanoparticles (AuNPs) at immiscible water-oil interfaces, previously reported by our group. We investigated a host of experimental variables and herein report their influence on the optical properties of nanofilms: AuNP mean diameter, interfacial AuNP surface coverage, nature of the organic solvent, and nature of the lipophilic organic molecule that caps the AuNPs in the interfacial nanofilm. To probe the interfacial gold nanofilms we used in situ (UV-vis-NIR spectroscopy and optical microscopy) as well as ex situ (SEM and TEM of interfacial gold nanofilms transferred to silicon substrates) techniques. The interfacial AuNP surface coverage strongly influenced the morphology of the interfacial nanofilms, and in turn their maximum reflectance and absorbance. We observed three distinct morphological regimes; (i) smooth 2D monolayers of "floating islands" of AuNPs at low surface coverages, (ii) a mixed 2D/3D regime with the beginnings of 3D nanostructures consisting of small piles of adsorbed AuNPs even under sub-full-monolayer conditions and, finally, (iii) a 3D regime characterised by the 2D full-monolayer being covered in significant piles of adsorbed AuNPs. A maximal value of reflectance reached 58% in comparison with a solid gold mirror, when 38 nm mean diameter AuNPs were used at a water-nitrobenzene interface. Meanwhile, interfacial gold nanofilms prepared with 12 nm mean diameter AuNPs exhibited the highest extinction intensities at ca. 690 nm and absorbance around 90% of the incident light, making them an attractive candidate for filtering applications. Furthermore, the interparticle spacing, and resulting interparticle plasmon coupling derived optical properties, varied significantly on replacing tetrathiafulvalene with neocuproine as the AuNP capping ligand in the nanofilm. These interfacial nanofilms formed with neocuproine and 38 nm mean diameter AuNPs, at monolayer surface coverages and above, were black due to aggregation and broadband absorbance.

Conductive gold nanoparticle mirrors at liquid/liquid interfaces.

Gold nanoparticle (Au NP) mirrors, which exhibit both high reflectance and electrical conductance, were self-assembled at a [heptane + 1,2-dichloroethane]/water liquid/liquid interface. The highest reflectance, as observed experimentally and confirmed by finite difference time domain calculations, occurred for Au NP films consisting of 60 nm diameter NPs and approximate monolayer surface coverage. Scanning electrochemical microscopy approach curves over the interfacial metallic NP films revealed a transition from an insulating to a conducting electrical material on reaching a surface coverage at least equivalent to the formation of a single monolayer. Reflectance and conductance transitions were interpreted as critical junctures corresponding to a surface coverage that exceeded the percolation threshold of the Au NP films at the [heptane + 1,2-dichloroethane]/water interface.

Sensitized near-IR luminescence of lanthanide complexes based on push-pull diketone derivatives.

Lanthanide complexes with two push-pull diketone derivatives as sensitizers have been developed as synthons for near-infrared emitting materials. The ligand substituents consist of a carbazole moiety with hole-transport properties and an aromatic or heteroaromatic unit. According to quantitative NMR analysis and complementary HPLC experiments, the diketones are predominantly in their enolic form in polar solvents such as THF and MeCN at room temperature. The preferred cis-enol form contributes strongly to the binding of lanthanide ions (Ln = Nd, Gd, Er). The resulting tris(diketonate) ternary complexes with terpyridine (Ln = Nd, Er) display sizeable near-IR emission with long luminescence lifetimes.

2,2'-Bipyrimidine as efficient sensitizer of the solid-state luminescence of lanthanide and uranyl ions from visible to near-infrared.

Treatment of Ln(NO(3))(3)nH(2)O with 1 or 2 equiv 2,2'-bipyrimidine (BPM) in dry THF readily afforded the monometallic complexes [Ln(NO(3))(3)(bpm)(2)] (Ln=Eu, Gd, Dy, Tm) or [Ln(NO(3))(3)(bpm)(2)]THF (Ln=Eu, Tb, Er, Yb) after recrystallization from MeOH or THF, respectively. Reactions with nitrate salts of the larger lanthanide ions (Ln=Ce, Nd, Sm) yielded one of two distinct monometallic complexes, depending on the recrystallization solvent: [Ln(NO(3))(3)(bpm)(2)]THF (Ln=Nd, Sm) from THF, or [Ln(NO(3))(3)(bpm)(MeOH)(2)]MeOH (Ln=Ce, Nd, Sm) from MeOH. Treatment of UO(2)(NO(3))(2)6H(2)O with 1 equiv BPM in THF afforded the monoadduct [UO(2)(NO(3))(2)(bpm)] after recrystallization from MeOH. The complexes were characterized by their crystal structure. Solid-state luminescence measurements on these monometallic complexes showed that BPM is an efficient sensitizer of the luminescence of both the lanthanide and the uranyl ions emitting visible light, as well as of the Yb(III) ion emitting in the near-IR. For Tb, Dy, Eu, and Yb complexes, energy transfer was quite efficient, resulting in quantum yields of 80.0, 5.1, 70.0, and 0.8 %, respectively. All these complexes in the solid state were stable in air.

Homo- and heterodinuclear helicates of lanthanide(III), zinc(II) and aluminium(III) based on 8-hydroxyquinoline ligands.

Homonuclear helicates with rare-earth-metal(III) ions or heteronuclear derivatives with rare-earth-metal and aluminium or zinc centres are obtained in alkali-metal-templated self-assembly processes from isobutenylidene-bridged homoditopic bis(2-carbamido-8-hydroxyquinoline)-derived ligands 1-H(2) and 2-H(2) or heteroditopic (8-hydroxyquinoline)(2-carbamido-8-hydroxyquinoline)-derived ligands 3-H(2) and 4-H(2). Diamagnetic coordination compounds possess a high stability in organic solvents such as CDCl(3), [D(4)]MeOH or [D(6)]DMSO and can be well characterised by (1)H NMR spectroscopy by using methylene protons and the protons of the vinylic units of the ligand as stereochemical or symmetry probes, respectively. Some of the homonuclear complexes could be crystallised and were characterised by using X-ray diffraction studies. The complexes adopt a triple-stranded helical structure with a central templating cation encapsulated in their interior. An unusual orientation of the double bond of one spacer towards this cation is observed. The homo- and heterodinuclear helicates with ytterbium(III), neodymium(III) or erbium(III) of ligands 2 and 4 were of special interest owing to their near-infrared (NIR) emitting properties, which were investigated depending on the lanthanide and on the encapsulated alkali-metal cation.

Surprisingly bright near-infrared luminescence and short radiative lifetimes of ytterbium in hetero-binuclear Yb-Na chelates.

New heterobinuclear lanthanide complexes with benzoxazole-substituted 8-hydroxyquinolines, [Ln(ligand)(2)(mu-ligand)(2)Na] (Ln: Yb, Lu), have been prepared and their structure established by X-ray crystallography, (1)H NMR spectroscopy, and photophysical studies. The complexes display efficient ligand-sensitized near-infrared luminescence of ytterbium at 925-1075 nm with lifetimes and quantum yields as high as 22 micros and 3.7%, in the solid state, and 20 micros and 2.6% in CH(2)Cl(2) solution, respectively. These quantum yields are the highest reported to date for ytterbium complexes with organic ligands containing C-H bonds. A long-wavelength and intense intraligand charge-transfer transition (lambda(max) = 446-456 nm; epsilon approximately 1.2 x 10(4) M(-1) cm(-1)) allows for the excitation of infrared luminescence with visible light up to 600 nm. Remarkable features of these complexes include (i) quantitative ligand-to-Yb(III) energy transfer resulting in high overall efficiency of the ytterbium luminescence, (ii) unusually short radiative lifetime of the Yb(III) ion, 706-745 micros for solutions in CH(2)Cl(2), calculated from the f-f absorption spectra, and 513-635 micros estimated for solid state samples from quantum yield and lifetime data, and (iii) the unexpected large influence of second-sphere composition on the radiative lifetime of ytterbium.

Highly luminescent homoleptic europium chelates.

The need for efficient and photostable lanthanide luminescent materials is dramatically increasing, in particular with respect to their growing application in lighting devices and biosciences. To this end, we have developed a facile synthesis of benzimidazole-substituted pyridine-2-carboxylic acids that efficiently sensitize europium luminescence in homoleptic neutral nine-coordinate complexes with overall quantum yields of 56-61% and lifetimes of 2.1-2.6 ms in the solid state at ambient conditions. The complexes reported here are potential synthons for the design of a variety of luminescent materials.

Benzothiazole- and benzoxazole-substituted pyridine-2-carboxylates as efficient sensitizers of europium luminescence.

A facile synthesis of benzothiazole- and benzoxazole-substituted pyridine-2-carboxylic acids has been developed. These ligands form mononuclear nine-coordinate complexes [Ln(kappa(3)-ligand)(2)(kappa(1)-ligand)(H(2)O)(2)] with light and heavy trivalent lanthanides, as established from the X-ray analysis of 11 complexes. A crystal structure of a minor product, the anhydrous nine-coordinate complex [Eu(kappa(3)-L)(3)], has also been determined. Photophysical studies of gadolinium chelates indicate that the triplet states of the new ligands are located at 20400-21400 cm(-1). The ligands are good sensitizers of the europium luminescence with ligand-to-metal energy transfer efficiency in the range 60-100%. The overall quantum yields of the europium emission are substantial, 12-14% in the solid state, and increase to 29-39% upon replacement of two metal-coordinated water molecules with dimethylsulfoxide in solution. The luminescence of near-infrared emitting lanthanides is also sensitized, but quantum yields are much smaller, reaching 0.17% for neodymium and 1.25% for ytterbium in DMSO, while energy transfer efficiencies for these two ions are below 50%.

Structural, spectroscopic, and thermodynamic consequences of anti-chelate effect in nine-coordinate lanthanide podates.

The connection of three tridentate 2,6-bis(1-ethyl-benzimidazol-2-yl)pyridine binding units to an extended sulfur-containing tripodal anchor in the ligand L9 yields nine-coordinate podates [Ln(L9)](3+) upon reaction with trivalent lanthanides, Ln(III). Structural analysis of [Eu(L9)](ClO(4))(3) in the solid state with the help of the bond valence method shows that the peripheral ethyl groups are responsible for a specific distortion of the triple-helical structure, which allows a closer approach of the nitrogen donors toward the central metal, while minimizing interstrand repulsion. The consequences of this distortion on the Eu(III) luminescent probe are investigated by high-resolution emission spectroscopy, while paramagnetic NMR data collected in acetonitrile demonstrate that [Ln(L9)](3+) adopts a single relaxed C(3)-symmetrical structure along the complete lanthanide series. The persistence of the triple-helical structure in solution is obtained at the cost of severe constraints in the helically wrapped organic tripod, which strongly disfavor intramolecular cyclization processes. The resulting antichelate effect can be exploited for the selective preparation of polynuclear complexes with tripodal ligands.

Intrinsic quantum yields and radiative lifetimes of lanthanide tris(dipicolinates).

The efficiency with which the surroundings of trivalent lanthanide ions sensitize their luminescence (eta(sens)) is a key parameter in the design of highly emitting molecular edifices and materials. Evaluation of eta(sens) requires the measurement of the overall and intrinsic quantum yields obtained upon ligand and metal excitation, respectively. We describe a modified integration sphere enabling absolute determination of these quantities on small amounts of solid samples or solutions (60 muL). The sphere is tested for linear response of emitted versus absorbed light intensities with increasing concentration of Cs(3)[Ln(dpa)(3)] solutions (Ln = Eu, Tb). The overall (Q = 29 +/- 2%) and intrinsic (Q = 41 +/- 2%) quantum yields obtained for Eu allow the direct calculation of eta(sens) (71 +/- 6%) while the radiative lifetime (tau(rad) = 4.1 +/- 0.3 ms) is calculated from Q and the observed lifetime. The intrinsic quantum yield matches the value extracted from emission parameters using the simplified equation proposed by Werts et al. but, on the other hand, the theoretical estimate using spontaneous transition probabilities calculated from Judd-Ofelt (JO) parameters is off by -25% (3.15 ms). In the case of Cs(3)[Tb(dpa)(3)], the molar absorption coefficient of the (5)D(4)<--(7)F(6) transition is too small to measure Q for the solution but this quantity could be determined for the microcrystalline sample (72 +/- 5%, tau(rad) = 1.9 +/- 0.1 ms). In this case, the JO theoretical estimate leads to a much too short tau(rad) value. The large difference in eta(sens) for microcrystalline samples of Eu (85%) and Tb (42%) tris(dipicolinates) is attributed to back energy transfer in the latter compound consecutive to a sizeable overlap between the (5)D(4)-->(7)F(6) emission and the absorption spectrum of the dipicolinate triplet, this overlap being smaller in the case of the solution. The overall quantum yield of Na(3)[Yb(dpa)(3)] in aqueous solution is very low (0.015 +/- 0.002%) due to both poor sensitization efficiency (8%) and small intrinsic quantum yield (Q = 0.178 +/- 0.003%; tau(rad) = 1.31 +/- 0.02 ms). For evaluating intrinsic quantum yields of Yb in aqueous solutions of coordination compounds from lifetimes, a value of 1.2-1.3 ms is recommended.

Modulating the near-infrared luminescence of neodymium and ytterbium complexes with tridentate ligands based on benzoxazole-substituted 8-hydroxyquinolines.

An improved synthesis of 2-(2'-benzothiazole)- and 2-(2'-benzoxazole)-8-hydroxyquinoline ligands that combine a tridentate N,N,O-chelating unit for metal binding and extended chromophore for light harvesting is developed. The 2-(2'-benzoxazole)-8-hydroxyquinoline ligands form mononuclear nine-coordinate complexes with neodymium, [Nd(kappa(3)-ligand)(3)], and an eight-coordinate complex with ytterbium, [Yb(kappa(3)-ligand)(2) x (kappa(1)-ligand) x H(2)O], as verified by crystallographic characterization of five complexes with four different ligands. The chemical stability of the complexes increases when the ligand contains 5,7-dihalo-8-hydroxyquinoline versus an 8-hydroxyquinoline group. The complexes feature a ligand-centered visible absorption band with a maximum at 508-527 nm and an intensity of (7.5-9.6) x 10(3) M(-1) x cm(-1). Upon excitation with UV and visible light within ligand absorption transitions, the complexes display characteristic lanthanide luminescence in the near-infrared at 850-1450 nm with quantum yields and lifetimes in the solid state at room temperature as high as 0.33% and 1.88 micros, respectively. The lanthanide luminescence in the complexes is enhanced upon halogenation of the 5,7-positions in the 8-hydroxyquinoline group and upon the addition of electron-donating substituents to the benzoxazole ring. Facile modification of chromophore units in 2-(2'-benzoxazole)-8-hydroxyquinoline ligands provides means for controlling the luminescence properties of their lanthanide complexes.

Luminescent bimetallic lanthanide bioprobes for cellular imaging with excitation in the visible-light range.

A series of homoditopic ligands H(2)L(CX) (X=4-6) has been designed to self-assemble with lanthanide ions (Ln(III)), resulting in neutral bimetallic helicates of overall composition [Ln(2)(L(CX))(3)] with the aim of testing the influence of substituents on the photophysical properties, particularly the excitation wavelength. The complex species are thermodynamically stable in water (log beta(23) in the range 26-28 at pH 7.4) and display a metal-ion environment with pseudo-D(3) symmetry and devoid of coordinated water molecules. The emission of Eu(III), Tb(III), and Yb(III) is sensitised to various extents, depending on the properties of the ligand donor levels. The best helicate is [Eu(2)(L(C5))(3)] with excitation maxima at 350 and 365 nm and a quantum yield of 9 %. The viability of cervix cancer HeLa cells is unaffected when incubated with up to 500 mum of the chelate during 24 h. The helicate permeates into the cells by endocytosis and locates into lysosomes, which co-localise with the endoplasmatic reticulum, as demonstrated by counterstaining experiments. The relatively long excitation wavelength allows easy recording of bright luminescent images on a confocal microscope (lambda(exc)=405 nm). The new lanthanide bioprobe remains undissociated in the cell medium, and is amenable to facile derivatisation. Examination of data for seven Eu(III) and Tb(III) bimetallic helicates point to shortcomings in the phenomenological rules of thumb between the energy gap DeltaE((3)pipi*-(5)D(J)) and the sensitisation efficiency of the ligands.

Near-infrared luminescence of nine-coordinate neodymium complexes with benzimidazole-substituted 8-hydroxyquinolines.

A new class of benzimidazole-substituted 8-hydroxyquinoline ligands has been prepared that contain a monoanionic tridentate N,N,O-coordinating unit. These ligands form charge-neutral lanthanide complexes of the type [Ln(L-R) 3]. nH 2O or [Ln 2(L2) 3]. nH 2O ( n = 1-3) with early lanthanides from La (III) to Gd (III) inclusive. Crystallographic characterization was carried out for 11 complexes with 6 different ligands. In all of these structures, the lanthanide ion was found to be nine-coordinated by three ligands arranged in an "up-up-down" fashion around the metal center. The coordination environment can be described as a tricapped trigonal prism, with N atoms of quinoline rings occupying capping positions. Upon deprotonation of the ligand and complex formation, a new absorption band appears in the visible range of the spectrum with a maximum in the range of 466-483 nm and molar absorption coefficient of (7.2 - 18) x 10 (3) M (-1) cm (-1). Its origin is likely to be an intraligand phenolate-to-pyridyl charge transfer transition centered on the 8-hydroxyquinolate chromophore. Upon excitation in ligand absorption bands, new Nd (III) complexes display characteristic metal-centered luminescence in the near-infrared region from 850 to 1450 nm with quantum yields and lifetimes in solid state at room temperature as high as 0.34% and 1.2 mus, respectively.

Structural and luminescent properties of micro- and nanosized particles of lanthanide terephthalate coordination polymers.

Reaction in water between rare earth ions (Ln = Y, La-Tm, except Pm) and the sodium salt of terephthalic acid leads to a family of lanthanide-based coordination polymers of general formula [Ln2(C8H4O4)3(H2O)4] n with Ln = La-Tm or Y. The isostructurality of the compounds with the previously reported Tb-containing polymer is ascertained on the basis of their X-ray powder diffraction diagrams. The coordination water molecules can be reversibly removed without destroying the crystal structure for compounds involving one of the lighter lanthanide ions (La-Eu). For compounds involving one of the heavier lanthanide ions (Tb-Tm) or yttrium, a structural change occurs during the drying process. X-ray diffraction data show this new anhydrous phase corresponding to the linking of pairs of Er(III) ions through mu-carboxylate bridges. Porosity profiles calculated for the anhydrous phases of Tb(III) and Er(III) show the presence of channels with very small sections. The luminescent properties of all the compounds have been recorded and the two most luminescent polymers, namely, the europium- and the terbium-containing ones, have been studied in more detail. Tb(III)-containing compounds display large quantum yields, up to 43%. Polyvinylpyrrolidone nanoparticles doped with [Ln2(C8H4O4)3(H2O)4] n (Ln = Eu, Tb, Er) have also been synthesized and characterized. The encapsulation of the coordination polymers results in somewhat reduced luminescence intensities and lifetime, but the nanoparticles can be dispersed in water and remain unchanged in this medium for more than 20 h.

Role of the ancillary ligand N,N-dimethylaminoethanol in the sensitization of Eu(III) and Tb(III) luminescence in dimeric beta-diketonates.

Two types of dimeric complexes [Ln2(hfa)6(mu2-O(CH2)2NHMe2)2] and [Ln(thd)2(mu2,eta2-O(CH2)2NMe2)]2 (Ln = YIII, EuIII, GdIII, TbIII, TmIII, LuIII; hfa- = hexafluoroacetylacetonato, thd- = dipivaloylmethanato) are obtained by reacting [Ln(hfa)3(H2O)2] and [Ln(thd)3], respectively, with N,N-dimethylaminoethanol in toluene and are fully characterized. X-ray single crystal analysis performed for the TbIII compounds confirms their dimeric structure. The coordination mode of N,N-dimethylaminoethanol depends on the nature of the beta-diketonate. In [Tb2(hfa)6(mu2-O(CH2)2NHMe2)2], eight-coordinate TbIII ions adopt distorted square antiprismatic coordination environments and are O-bridged by two zwitterionic N,N-dimethylaminoethanol ligands with a Tb1...Tb2 separation of 3.684(1) A. In [Tb(thd)2(mu2,eta2-O(CH2)2NMe2)]2, the N,N-dimethylaminoethanol acts as chelating-bridging O,N-donor anion and the TbIII ions are seven-coordinate; the Tb1...Tb1A separation amounts to 3.735(2) A within centrosymmetric dimers. The dimeric complexes are thermally stable up to 180 degrees C, as shown by thermogravimetric analysis, and their volatility is sufficient for quantitative sublimation under reduced pressure. The EuIII and TbIII dimers display metal-centered luminescence, particularly [Eu2(hfa)6(O(CH2)2NHMe2)2] (quantum yield Q(L)Ln = 58%) and [Tb(thd)2(O(CH2)2NMe2)]2 (32%). Consideration of energy migration paths within the dimers, based on the study of both pure and EuIII- or TbIII-doped (0.01-0.1 mol %) LuIII analogues, leads to the conclusion that both the beta-diketone and N,N-dimethylaminoethanol ligands contribute significantly to the sensitization process of the EuIII luminescence. The ancillary ligand increases considerably the luminescence of [Eu2(hfa)6(O(CH2)2NHMe2)2], compared to [Ln(hfa)3(H2O)2], through the formation of intra-ligand states while it is detrimental to TbIII luminescence in both beta-diketonates. Thin films of the most luminescent compound [Eu2(hfa)6(O(CH2)2NHMe2)2] obtained by vacuum sublimation display photophysical properties analogous to those of the solid-state sample, thus opening perspectives for applications in electroluminescent devices.

Linear polynuclear helicates as a link between discrete supramolecular complexes and programmed infinite polymetallic chains.

The contribution of the solvation energies to the assembly of polynuclear helicates reduces the free energy of intermetallic repulsion, DeltaE(MM), in condensed phase to such an extent that stable D(3)-symmetrical tetranuclear lanthanide-containing triple-stranded helicates [Ln(4)(L4)(3)](12+) are quantitatively produced at millimolar concentrations, despite the twelve positive charge borne by these complexes. A detailed modelling of the formation constants using statistical factors, adapted to self-assembly processes involving intra- and intermolecular connections, provides a set of five microscopic parameters, which can be successfully used for rationalizing the stepwise generation of linear bi-, tri- and tetranuclear analogues. Photophysical studies of [Eu(4)(L4)(3)](12+) confirm the existence of two different binding sites producing differentiated metal-centred emission at low temperature, which transforms into single site luminescence at room temperature because of intramolecular energy funelling processes.

Rational tuning of melting entropies for designing luminescent lanthanide-containing thermotropic liquid crystals at room temperature.

The connection of twelve peripheral and divergent dodecyloxy chains to a central tridentate aromatic binding unit provides the dodecacatenar ligand L11, for which room-temperature mesomorphism is detected. An enthalpically unbalanced large melting entropy (DeltaSmL11=226 J mol(-1) K(-1)) results from the programmed microsegregation induced in the crystalline phase, a phenomenon which is maintained in the associated lanthanide complexes [Ln(L11)(NO3)3] and [Ln(L11)(CF3CO2)3]2. Low-temperature melting processes (-43

Enhancement of near-IR emission by bromine substitution in lanthanide complexes with 2-carboxamide-8-hydroxyquinoline.

Three novel 2-carboxamide-8-hydroxyquinoline derivatives wrap helically around trivalent lanthanide ions to form monometallic 3 : 1 complexes possessing strong NIR emission.

Encapsulation of labile trivalent lanthanides into a homobimetallic chromium(III)-containing triple-stranded helicate. Synthesis, characterization, and divergent intramolecular energy transfers.

The segmental bidentate-tridentate-bidentate ligand L2 reacts with M(II) (M = Cr, Zn) and Ln(III) (Ln = La, Eu, Gd, Tb, Lu) to give the heterotrimetallic triple-stranded helicates [MLnM(L2)3]7+. For M = Zn(II), the isolated complexes [ZnLnZn(L2)3](CF3SO3)7 (Ln = Eu, Tb) display only lanthanide-centred luminescence arising from the pseudo-tricapped trigonal prismatic LnN9 coordination site. For M = Cr(II), rapid air oxidation provides Cr(III) and leads to the isolation of inert [CrLnCr(L2)3](CF3SO3)9 (Ln = Eu, Tb) complexes, in which divergent intramolecular Ln --> Cr energy transfers can be evidenced. Taking [ZnEuZn(L2)3]7+ as a luminescent standard for Eu-centred emission, a quantitative treatment of the energy migration processes indicates that the rate constant characterizing the Eu --> Cr energy transfer is more efficient in the trimetallic system, than in the analogous simple bimetallic edifice. Particular attention is focused on potential control of directional energy transfer processes in Cr-Ln pairs.