Pure red-light emitting europium based complexes as efficient UV light converters: synthesis, crystal structure and photoluminescence properties.

This paper reports three new crystallographically characterized europium complexes with composition as follows: [Eu(fod)3(L1)] (1), [Eu(fod)3(L2)] (2) and [Eu(fod)3(L3)] (3) {L1 = benzimidazole (bzi), L2 = 4,7-diphenyl-1,10-phenanthroline (bath), L3 = 2-(2-pyridyl) benzimidazole (py-im) and fod = anion of 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione (Hfod)}. The single crystal (SC) XRD analysis shows that complex 1 is seven-coordinated while complexes 2 and 3 are eight-coordinated with the geometrical structures of a mono-capped octahedron and a trigonal dodecahedron, respectively. The NMR spectra of the complexes validate the SC-XRD results in solution. The complexes are stable in solution as no dissociation of any ligand was observed in the NMR spectra of the complexes. The photophysical properties of the complexes in solution, solid state, and PMMA thin films were studied. The hypersensitive transition 5D0 → 7F2 dominates the emission spectra in all phases, showing the highly asymmetric environment around the Eu(III) ion. The bath ligand is found to be the best sensitizer of the Eu ion and hence complex 2 shows the strongest luminescence properties with the highest absolute quantum yield among the three complexes. The CIE coordinate analysis shows that pure red-luminescence is emitted by the Eu complexes in the solid state since the coordinates found in this phase are closer to the standard NTSC 1987 values. The optical band gaps were determined for the complexes and the observed values suggest that the complexes can have possible applications in the field of semiconductor materials.

Phase controlled colour tuning of samarium and europium complexes and excellent photostability of their PVA encapsulated materials. Structural elucidation, photophysical parameters and the energy transfer mechanism in the Eu(3+) complex by Sparkle/PM3 calculations.

Luminescent [Sm(acac)3(pyz)2] (1) and [Eu(acac)3(pyz)2] (2) complexes (acac is the anion of acetylacetone and pyz is pyrazine) have been synthesized and thoroughly characterized by microanalyses, TGA, DTA, IR, ESI-MS(+) and NMR spectroscopy. The photophysical properties of these complexes have been investigated. The Sparkle/PM3 model was utilized for predicting the ground-state geometry of (2). The Judd-Ofelt intensity parameters, radiative parameters, intramolecular energy transfer rates and quantum efficiency are calculated and discussed. The intramolecular energy transfer rates predict that the major energy transfer (96%) is from the ligand triplet state to the levels (5)D1 (74.53%) and (5)D0 (21.87%) of the Eu(3+) ion, in the complex. Complexes (1) and (2) were analysed for colour tuning properties and these show varying colours upon changing phases. This property would possibly allow the use of these complexes as 'colour indicators'. The photoluminescence and photostability of the thin hybrid films of both complexes (1) and (2) in polyvinyl alcohol (PVA) are investigated and discussed. The hybrid films of (1) and (2) are quite robust due to their higher photostability. An important feature of complex (2) is that the excitation window extends close to the visible range (393 nm). The lasing property of the Eu(3+) complex in various phases is also presented.

Sensitization of visible and NIR emitting lanthanide(III) ions in noncentrosymmetric complexes of hexafluoroacetylacetone and unsubstituted monodentate pyrazole.

A series of highly volatile eight-coordinate air and moisture stable lanthanide complexes of the type [Ln(hfaa)3(L)2] (Ln = Pr (1), Nd (2), Eu (3), Gd (4), Tb (5), Dy (6), Ho (7), Er (8), Tm (9), and Yb (10); hfaa = anion of hexafluoroacetylacetone and L = pyrazole) have been synthesized and characterized by elemental analysis, IR, ESI-MS(+), and NMR studies. Single-crystal X-ray structures have been determined for the Eu(III) and Dy(III) complexes. These complexes crystallize in the monoclinic space group P2(1)/c. The lanthanide ion in each of these complexes is eight-coordinate with six oxygen atoms from three hfaa and two N-atoms from two pyrazole units, forming a coordination polyhedron best describable as a distorted square antiprism. The NMR spectra reveal that both the pyrazole units remain attached to the metal in solution and the ß-diketonate and pyrazole protons are shifted in opposite directions in the case of paramagnetic complexes. The lanthanide-induced chemical shifts are dipolar in nature. The hypersensitive transitions of Nd(III), Ho(III), and Er(III) are sensitive to the environment (solvent), which is reflected by the oscillator strength and band shape of these transitions. The band shape due to the hypersensitive transition of Nd(III) in noncoordinating chloroform and dichloromethane is similar to those of the typical eight-coordinate Nd(III) ß-diketonate complexes. The quantum yield and lifetime of Pr(III), Eu(III), Tb(III), Dy(III), and Tm(III) in visible and Pr(III), Nd(III), Dy(III), Ho(III), Er(III) Tm(III), and Yb(III) in the NIR region are sizable. The environment around these metal ions is asymmetric, which leads to increased radiative rates and luminescence efficiencies. The quantum yield of the complexes reveal that ligand-to-metal energy transfer follows the order Eu(III) > Tb(III) ≫ Pr(III) > Dy(III) > Tm(III). Both ligands (hfaa and pyrazole) are good sensitizers for all the visible and NIR emitters effectively, except for Tb(III), Dy(III), and Tm(III), where pyrazole gave a negative effect (e.g., energy back-transfer) that is due to poor intramolecular energy transfer match. The good luminescent properties make these NIR-luminescent complexes to have potential application in optical communication, telecommunications, and fluoroimmunoassays.

Aortic dissection in a case of Turner's syndrome.

A case report is presented of an aortic dissection in a patient with Turner's syndrome that went undiagnosed. A thorough discussion of this fatal condition in this group of patients is included.

Optical absorption spectroscopic studies on holmium(III) complexes with beta-diketone and heterocyclic amines: the environment effect on 4f-4f hypersensitive transitions.

The optical absorption spectra of [Ho(acac)(3)(H(2)O)(2)].H(2)O, [Ho(acac)(3)phen] and [Ho(acac)(3)bpy] (where acac is the anion of acetylacetone; phen is 1,10-phenanthroline and bpy is 2,2'-bipyridyl) complexes in the visible region, in a series of non-aqueous solvents (methanol, ethanol, isopropanol, chloroform, acetonitrile and pyridine.) have been analyzed. The largest intensity variation was observed in the (5)G(6)<--(5)I(8) (centered at 450 nm), and (5)G(5), (3)H(5), (3)H(6)<--(5)I(8) (centered at 360 nm) transition regions. The band shape and oscillator strength of the hypersensitive transitions display pronounced changes as compared to Ho(3+) aqua-ion. The band shapes of the hypersensitive transitions show remarkable changes on passing from aqueous solution to various non-aqueous solutions which is the result of change in the environment about the Ho(III) ion in the various solutions and suggests coordination of solvent molecule(s), in some cases. The results clearly show that among the solvents studied pyridine is the most effective in promoting the 4f-4f spectral intensity. It has been inferred from this study that 2,2'-bipyridyl is a stronger ligand for heavier lanthanides. A comparative account of hypersensitivity in the present complexes with those of other adducts of Ho(beta-diketoenolate)(3) with heterocyclic amines is discussed. The TGA analyses showed that the phen complex is thermally more stable over its bpy analogue.

Nuclear magnetic resonance and optical absorption spectroscopic studies on paramagnetic praseodymium(III) complexes with beta-diketone and heterocyclic amines.

The optical absorption spectra of [Pr(acac)(3)(H(2)O)(2)].H(2)O, [Pr(acac)(3)phen.H(2)O] and [Pr(acac)(3)bpy] (where acac is the anion of acetylacetone, phen is 1,10-phenanthroline and bpy is 2,2'-bipyridyl) have been analyzed in the visible region in a series of non-aqueous solvents (methanol, ethanol, isopropanol, chloroform, acetonitrile and pyridine). The complexes display four non-hypersensitive 4f-4f transitions ((3)P(2), (3)P(1)+(1)I(6), (3)P(0) and (1)D(2)) from the (3)H(4) ground state. The band shape of the transitions shows remarkable changes upon dissolving in different solvents. Distinctively different band shapes have been observed for phen and bpy complexes. The phen is more effective in producing changes and the splitting of the bands is more pronounced in phen complex since it is a stronger ligand and leads to stronger Pr-N(phen) bond. The splitting of the bands is indicative of partaking of f-orbitals in bonding. The NMR signals of heterocyclic amines have been shifted to high fields while the resonances due to acetylacetone moiety have moved to low fields which is the consequence of change in geometry of the complexes upon coordination of the heterocyclic amines and reflects the importance of geometric factor (3cos(2)theta-1) in changing sign of the shift and to a good approximation the shifts arise predominantly from the dipolar mechanism. The phen complexes have narrower line width than bpy complexes. The line broadening in the case of bpy complexes is suggestive of exchange between inter-converting forms. The bpy possesses some degree of rotational freedom about C(6)-C(6') bond and the two pyridine rings undergo scissoring motion with respect to each other.

Optical absorption and NMR spectroscopic studies on paramagnetic neodymium(III) complexes with beta-diketone and heterocyclic amines. The environment effect on 4f-4f hypersensitive transitions.

The optical absorption spectra of [Nd(acac)3(H2O)2].H2O, [Nd(acac)3bpy] and [Nd(acac)3phen(H2O)2] (where acac=acetylacetone, bpy=2,2'-bipyridyl and phen=1,10-phenanthroline) complexes in the visible region, in a series of non-aqueous solvents (methanol, ethanol, isopropanol, chloroform, acetonitrile, pyridine, nitrobenzene and dimethylsulphoxide) have been analyzed. The transition 4G(5/2)<--4I(9/2) (Nd-VI) located near the middle of the visible region (17,500 cm(-1)) is hypersensitive. Its behavior is in sharp contrast to many other typically weak and consistently unvaried, normal 4f-4f transitions. The oscillator strength of this transition for the chelate as well as its adducts with phen and bpy in any of the solvent employed is larger than the oscillator strength of Nd3+ aqua-ion. It is most intense in pyridine for all the complexes studied and, therefore, pyridine is the most effective in promoting f-f spectral intensity. The band shape and oscillator strength of the hypersensitive transitions display pronounced changes as compared to Nd3+ aqua-ion. The band shapes of the hypersensitive transitions show remarkable changes on passing from aqueous solution to various non-aqueous solutions, which is the result of change in the environment about the Nd(III) ion in the various solutions and suggests change in the environment about the Nd(III) ion in the various solutions and suggests coordination of solvent molecule(s), in some cases. A comparative account of hypersensitivity in the present complexes with those of other adducts of Nd(beta-diketoenolate)3 with heterocyclic amines is discussed. The NMR signals of heterocyclic amines have been shifted to high fields while the resonances due to acetylacetone moiety have moved to low fields. The paramagnetic shift in the complexes is dipolar in nature.

4f-4f absorption spectra and hypersensitivity in nine-coordinate Ho(III) and Er(III) complexes in different environments.

The effect of change in the environment upon 4f-4f absorption spectra of nine-coordinate Ho(III) and Er(III) complexes with thiocyanate and 2,2'-bipyridyl in methanol, DMSO, DMF and pyridine have been investigated. The oscillator strength for hypersensitive and non-hypersensitive transitions have been calculated and variation in the intensity and band shape with respect to solvent type is rationalized in terms of solvent structure and coordinating properties. A comparison with 1,10-phenanthroline complexes is investigated and has been found that phen has a larger impact on the transition intensities for these ions. Pyridine has been found most effective in promoting 4f-4f intensity. The results indicate that it is important to consider both the static and dynamic coupling mechanism while analysing the oscillator strength of hypersensitive transition.

Optical absorption and NMR spectroscopic studies on paramagnetic trivalent lanthanide complexes with 2,2'-bipyridine.; The solvent effect on 4f-4f hypersensitive transitions.

The optical absorption and NMR studies of trivalent lanthanide chloride complexes with 2,2'-bipyridine (bpy) are presented and discussed. The NMR spectra of paramagnetic complexes exhibit lower as well as higher field shifts of bpy resonances that reflect change in geometry and reveals importance of the factor (3 cos2 theta - 1 ) in changing sign of the shift. The paramagnetic shifts recorded have been analyzed and the intramolecular shift ratios suggest that the paramagnetic shift is predominantly dipolar in origin. Electronic spectral studies of the Pr, Nd, Ho, Er and Dy complexes in different solvents (viz. methanol, pyridine, DMSO and DMF), which differ with respect to donor atoms, reveal that the chemical environment around the lanthanide ion has great impact on f-f transitions and any change in the environment results in modifications of the spectra. The oscillator strength for the hypersensitive and non-hypersensitive transitions have been determined and changes in the oscillator strength and band shape with respect to solvent type is rationalized in terms of ligand (solvent) structure and coordination properties.

4f-4f absorption spectra of nine-coordinate Pr (III) and Nd (III) complexes in different environments.

Absorption spectroscopic studies on the mixed-ligand complexes of Pr (III) and Nd (III) with 2,2'-bipyridyl and thiocyanate in pyridine, DMSO, DMF and methanol are presented. The oscillator strengths for the hypersensitive and non-hypersensitive transitions have been calculated and variation in the oscillator strength and band shapes with respect to solvent type is rationalized in terms of solvent structures and coordinating properties. A comparison is made with 1,10-phenanthroline complexes and has been shown that bpy is a weaker ligand than phen for these ions. Pyridine has been found most effective in promoting 4f-4f intensity and the increase in the oscillator strength in this solvent is due to dynamic ligand polarization mechanism.

4f-4f hypersensitivity in the absorption spectra and NMR studies on paramagnetic lanthanide chloride complexes with 1,10-phenanthroline in non-aqueous solutions.

The optical absorption and NMR studies of trivalent lanthanide chloride complexes with 1,10-phenanthroline (phen) are presented and discussed. The 1H NMR spectra of the complexes of La, Pr, Nd, Eu and Yb have been studied in methanol-d(4). The resonances of phen in the NMR spectra of the paramagnetic complexes have been shifted to lower as well as higher fields, which is a manifestation of dipolar interaction. The H (2) protons of the heterocyclic amine display broad resonances. The degree of broadening in Pr, Nd, and Yb complexes follows the order Pr < Nd < Yb. The inter- and intra-molecular shift ratios show that the paramagnetic shift is predominantly due to dipolar interaction. The electronic spectra of Pr, Nd, Ho and Er complexes have been investigated in methanol, pyridine, DMSO and DMF, which reveal that the hypersensitive transitions exhibit larger variation in oscillator strength values and band shapes. The change in the coordination geometry of the complexes and relative basicity of ligand are found responsible for oscillator strength and band shape variation. The interelectronic repulsion and covalency parameters show covalent nature of bonding between the metal and the ligand.