Synthesis, X-ray crystal structure and photophysics of butterfly shape orange and red emanating polynuclear complexes of tris(dibenzoylmethanato)Ln(III) (Ln = Sm/Eu) and exo-bidentate 4,4'-bipyridine.

Reaction of two equivalents of [Ln(dbm)3(H2O)] (Ln = Sm/Eu/Gd) with one equivalent of 4,4'-bipyridine (4,4'-bpy) led to the formation of rare polynuclear complexes of the type [Ln(dbm)3(4,4'-bpy)]n (dbm is the anion of 1,3-diphenyl-1,3-propanedione) instead of symmetrically bridged dinuclear complexes. The structure of the complexes has been established by the single crystal X-ray diffraction (SC-XRD) method and shows that the coordination sphere is composed of a LnO6N2 core (octacoordinated). Shape analysis further revealed that the geometry around Ln(III) is distorted square anti-prismatic with SHAPE value 0.738 and 25.719 for [Sm(dbm)3(4,4'-bpy)]n and [Eu(dbm)3(4,4'-bpy)]n, respectively. Photoluminescence (PL) properties of [Sm(dbm)3(4,4'-bpy)]n and [Eu(dbm)3(4,4'-bpy)]n are discussed in the solid-state and PMMA hybrid film (w/w 6%). By employing theoretical modelling in conjunction with the experimental PL data and crystal structure and an energy transfer (ET) mechanism for the sensitized PL of [Eu(dbm)3(4,4'-bpy)]n is proposed and discussed in detail. Finally, the role of each ligand in sensitized PL of [Eu(dbm)3(4,4'-bpy)]n is calculated and discussed by the chemical partitions of the radiative decay.Graphical abstract.

Heteroleptic samarium complexes with high quantum yields for temperature sensing applications.

Two new crystallographically characterized samarium complexes, [Sm(fod)3(L1)] (1) and [Sm(fod)3(L2)] (2) {L1 = 4,7-diphenyl-1,10-phenanthroline (bath), L2 = 2,2':6',2''-terpyridine and fod = anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione (Hfod)}, were synthesized and thoroughly characterized. Single-crystal (SC) analysis shows that complex 1 is an eight-coordinate structure with a distorted square antiprism geometry (D4d), whereas complex 2 possesses a nine-coordinate structure with distorted muffin geometry (Cs). The NMR results are in line with SC-XRD analysis, which further validate that the complexes remain intact in solutions. The photophysical characteristics of the complexes were studied in both visible and near infra-red (NIR) regions. The PLQY values of the present complexes were found to be higher than those reported in the literature except for a tetrakis Sm complex. This result indicates that both the ligands act as effective antennas for the present systems. A comparison of PLQY and emission lifetime values within the present complexes (in solid state) reveals that energy transfer from terpy to Sm3+ is more effective than that from the bath ligand. Various color parameters of the complexes were calculated, and the determined CCT values suggest that the complexes may be used as warm light sources. The determined band gap values for the complexes are in the range of those for semiconductors, which suggest the application of present systems in the field of optoelectronics. The curve between the emission intensity and temperature for complex 1 shows a perfect linearity (χ2 = 0.99), which suggests that this complex can have potential application as a temperature sensor in the range 60-350 K.

Theoretical Modeling (Sparkle RM1 and PM7) and Crystal Structures of the Luminescent Dinuclear Sm(III) and Eu(III) Complexes of 6,6,7,7,8,8,8- Heptafluoro-2,2-dimethyl-3,5-octanedione and 2,3-Bis(2-pyridyl)pyrazine: Determination of Individual Spectroscopic Parameters for Two Unique Eu3+ Sites.

Heteroleptic homo dinuclear complexes [Sm(fod)3(µ-bpp)Sm(fod)3] and [Eu(fod)3(µ-bpp)Eu(fod)3] and their diamagnetic analogue [Lu(fod)3(µ-bpp)Lu(fod)3] (fod is the anion of 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione (Hfod) and bpp is 2,3-bis(2-pyridyl)pyrazine) are synthesized and thoroughly characterized. The lanthanum gave a 1:1 adduct of La(fod)3 and bpp with the molecular formula of [La(fod)3bpp]. The 1H NMR and 1H-1H COSY spectra of the complexes were used to assign the proton resonances. In the case of paramagnetic Sm3+ and Eu3+ complexes, the methine (of the fod moiety) and the bpp resonances are shifted in the opposite direction and the paramagnetic shifts are dipolar in nature, which decrease with increasing distance of the proton from the metal ion. The single-crystal X-ray analyses reveal that the complexes (Sm3+ and Eu3+) are dinuclear and crystallize in the triclinic P1 space group. Each metal in a given complex is eight coordinate by coordinating with six oxygen atoms of three fod moieties and two nitrogen atoms of the bpp. Of the two metal centers, in a given complex, one has a distorted square antiprism arrangement and the other acquires a distorted dodecahedron geometry. The Sparkle RM1 and PM7 optimized structures of the complexes are also presented and compared with the crystal structure. Theoretically observed bond distances are in excellent agreement with the experimental values, and the RMS deviations for the optimized structures are 2.878, 2.217, 2.564, and 2.675 Å. The photophysical properties of Sm3+ and Eu3+ complexes are investigated in different solvents, solid, and PMMA-doped thin hybrid films. The spectroscopic parameters (the Judd-Ofelt intensity parameters, radiative parameters, and intrinsic quantum yield) of each Eu3+ sites are calculated using the overlap polyhedra method. The theoretically obtained parameters are close to the experimental results. The lifetime of the excited state is 38.74 µs for Sm3+ and 713.62 µs for the Eu3+ complex in the solid state.

Optical Properties of New Terbium(III) Ternary Complexes Containing Anionic 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione and Neutral Sensitizers in Solution, Solid and PMMA Thin Films: Intra and Interphase Colour Tuning.

Four new terbium(III) ternary complexes, [Tb(fod)3 (indazole)] (1), [Tb(fod)3 (tptz)] (2), [Tb(fod)3 (impy)] (3) and [Tb(fod)3 (tppo)2 ] (4) with 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, (Hfod) and N and O donors are synthesized and structurally characterized. The photoluminescence of the complexes are studied in solid, chloroform solution and thin PMMA hybrid films (PMMA is a poly(methyl methacrylate)). The ligand-based emission is dominant in solution of 3 and 4. The effect of ancillary ligands on the photoluminescence of terbium(III) ion is investigated. The mechanism of energy transfer is discussed and correlates the luminescence of acceptor terbium ion with the triplet state energy level of donor ligands. Among the four complexes studied, the luminescence from 1 is most intense followed by 2, 4 and 3. The Commission International de I'Eclairage (CIE) color coordinates of these complexes are calculated and presented. The complexes 3 and 4 show intraphase color tuning when excited under different UV wavelengths. The emission color of [Tb(fod)3 (tppo)2 ] (4) changes from pure blue to turquoise green via almost pure white under 360, 328 and 280 nm UV excitation wavelengths respectively. The [Tb(fod)3 (impy)] (3) show similar results. The complex [Tb(fod)3 (tptz)] (2) displays interphase color tuning from yellow (solution) to turquoise green (solid) and fascinatingly incorporation of complex in PMMA polymer generates white light under same excitation wavelength (360 nm).

Red, orange-red and near-infrared light emitting ternary lanthanide tris ß-diketonate complexes with distorted C4v geometrical structures.

This paper presents three crystallographically and solution NMR (one- and two-dimensional) characterised ternary Ln(iii) complexes, and their photo-physical and opto-electronic properties in the visible and NIR regions. The single crystal X-ray diffraction analysis indicates that the complexes are nona-coordinate with a chemical composition of [Ln(hfaa)3(Hind)3] (hfaa = anion of hexafluoroacetylacetone, Hind = indazole and Ln = Pr, Nd and Sm). The Ln ions, in the complexes, are coordinated to six O-atoms of three hfaa and three N-atoms of three monodentate Hind ligands, making the coordination polyhedra LnO6N3 with distorted monocapped square antiprismatic geometries, low symmetry structures that promote radiative transitions, suggesting efficient energy transfer from the organic ligands to the metal ion. The NMR analysis confirms the nona-coordinate structures and shows the isostructurality of the complexes in solution. The excitation of the complexes at 310 nm led to the characteristic of both visible and near infrared luminescence of the Pr, Nd and Sm complexes. The samarium complex displayed very strong orange-red luminescence. In contrast to the solution, the PMMA doped samples of the complexes showed an enhancement in the emission lifetime and the quantum yield. A triple layered NIR-emitting OLED, fabricated using the Nd-complex as an emitting layer, showed good optical and electrical performances.

Efficient Layers of Emitting Ternary Lanthanide Complexes for Fabricating Red, Green, and Yellow OLEDs.

A series of novel nona- and octacoordinate highly volatile and luminescent complexes, [Eu(hfaa)3(indazole)3] and [Ln(hfaa)3(indazole)2] (Ln = Tb, Dy, and Lu), were synthesized using a monoanionic bidentate hexafluoroacetylacetone (hfaa(-)) and a neutral monodentate indazole ligand. The X-ray diffraction analyses of their single-crystals indicate that the complexes are mononuclear. The Eu complex is nonacoordinate and has a distorted monocapped square antiprismatic structure whereas the terbium and dysprosium complexes are octacoordinate and possess a trigonal bicapped prism geometry. The indazole units are involved in π-π stacking interaction and N-H···F hydrogen bonding with the fluorine atoms of hfaa(-). The photophysical studies of indazole and the complexes show that the triplet states are at the appropriate positions and make ligand-to-metal energy transfer process efficient. A strong protective shield is provided by the coordination of three hfaa(-) moieties (which have low frequency C-F vibrational oscillators), and two/three ancillary indazole ligands around these metal ions ascribe higher quantum yields and longer radiative life times (ΦEu = 69% ± 10, 989 ± 1 µs, ΦTb = 33% ± 10, 546 ± 1 µs, and ΦDy = 2.5% ± 10, 13.6 ± 1 µs) to these novel compounds. The emission from europium, terbium, and dysprosium are, respectively, red, green, and yellow. Finally, these compounds were used, as emitting layers, to fabricate electroluminescent devices of their respective colors. The best devices are found with the following structure: ITO/CuPc (15 nm)/[Eu complex]:CBP or [Tb complex]:CBP or [Dy complex]:CBP (80 nm)/BCP (25 nm)/AlQ (30 nm)/LiF (1 nm)/Al (100 nm), which indicates an improved EL performance for the Eu device over the Eu devices reported in the literature. The ligand, indazole, is a good sensitizer for trivalent europium, terbium, and dysprosium ions. It together with hfaa(-) plays an important role in fabricating OLEDs, especially, processed at low temperature.

The correlation between f-f absorption and sensitized visible light emission of luminescent Pr(III) complexes: role of solvents and ancillary ligands on sensitivity.

The electronic absorption, excitation and sensitized visible light emission studies of three praseodymium (III) complexes: [Pr(fod)(3)(bpy)], [Pr(fod)(3)(phen)] and [Pr(fod)(3)(bpm)](n) (fod = anion of 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione; bpy=2,2'-bipyridyl, phen=1,10-phenanthroline, bpm=2,2'-bipyrimidine) in a series of non-aqueous solvents is presented. The f-f absorption transitions of Pr(III) are environment sensitive which is reflected by the change in the intensity (oscillator strength) and band shape (stark splitting) upon change in the solvent and/or the ligands. The sensitization of intense Pr(III) emission, in the visible region, of the complexes in solution upon excitation into the ligand centered π→π* absorption band is remarkable. The planar phen has pronounced impact and increases considerably the emission intensity of Pr(III) luminescence than the flexible bpy while bpm has been found least effective in promoting the emission intensity. The intensity of the f-f absorption and sensitized emission are correlated with the nature of the solvents. The donor solvent pyridine enhances the emission intensity of the [Pr(fod)(3)(phen)] drastically and of [Pr(fod)(3)(bpy)] marginally while the luminescent intensity of [Pr(fod)(3)(bpm)](n) is decreased. The combined photophysical studies demonstrate that entry of the solvent molecule(s) to inner coordination sphere (complex-solvent interaction) is governed by the structure and basicity of the ancillary heterocyclic ligand attached to the Pr(III) complex. The strong donor DMSO transforms the three complexes into a similar species, [Ln(fod)(3)(DMSO)(2)], which results in similar electronic absorption and emission properties of the complexes in this solvent. The results demonstrate that highly luminescent praseodymium chelates can be designed with ligands containing suitable energy levels and their emission properties can be further modulated through suitable ancillary ligands and donor solvents, thus opening perspectives for applications in electroluminescent devices and luminescent probes.

Hypersensitivity in the luminescence and 4f-4f absorption properties of mono- and dinuclear EuIII and ErIII complexes based on fluorinated ß-diketone and diimine/ bis-diimine ligands.

The results of our investigation on the sensitized luminescence properties of three Eu(III) ß-diketonate complexes of the form [Eu(2)(fod)(6)(µ-bpm)], [Eu(fod)(3)(phen)] and [Eu(fod)(3)(bpy)] and 4f-4f absorption properties of their Er(III) analogues ( fod = anion of 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione, bpm = 2,2'-bipyrimidine, phen = 1,10-phenanthroline and bpy = 2,2'-bipyridyl) in a series of non-aqueous solvents are presented. The Eu(III) complexes are highly luminescent and their luminescence properties (intensity and band shape) are sensitive to the changes in the inner coordination sphere of the Eu(III) ion. The luminescence intensity of the mononuclear complexes in pyridine is drastically decreased. The coordination structure of the complexes in pyridine is transformed into a more symmetrical one which results into a slow radiative rate of the emission from the complexes. The ancillary ligands, phen and bpy are found better co-sensitizers as compared to the bpm to sensitize Eu(III)-luminescence. The 4f-4f absorption properties (oscillator strength and band shape) of the Er(III) complexes demonstrate that (4)G(11/2) ← (4)I(11/2) and (2)H(11/2) ← (4)I(15/2) hypersensitive transitions of Er(III) are very sensitive in some coordinating solvents which reflects complex-solvent interaction in solution. The hypersensitive transitions of [Er(fod)(3)(phen)] remain unaffected in any of the solvents and this complex retains its bulk composition in solution. The erbium complexes as well as the Er(fod)(3) chelate are invaded by DMSO. This solvent enters the inner coordination sphere by replacing heterocyclic ligand and the complexes acquire similar structure [Er(fod)(3)(DMSO)(2)] in this solvent. The results reveal that the luminescence and absorption properties of lanthanide complexes in solution can be controlled by tuning the coordination structure through ancillary ligands and donor solvents. This work shall prove useful in designing new biological applications with such probes.