Ana de Bettencourt-Dias

A Water-Soluble Pybox Derivative and Its Highly Luminescent Lanthanide Ion Complexes

A new water-soluble Pybox ligand, 1, has been synthesized and found to crystallize in the monoclinic P2(1)/n space group with unit cell parameters a = 6.0936(1) Å, b = 20.5265(4) Å, c = 12.0548(2) Å, and β = 90.614(1)°. In the crystal, a water molecule is bound through hydrogen-bonding interactions to the nitrogen atoms of the oxazoline rings. This ligand was used to complex a variety of lanthanide ions, opening up new avenues for luminescence and catalysis in aqueous environment. These complexes are highly luminescent in aqueous solutions, in acetonitrile, and in the solid state. Aqueous quantum yields are high at 30.4% for Eu(III), 26.4% for Tb(III), 0.32% for Yb(III), and 0.11% for Nd(III). Er(III) did not luminesce in water, but an emission efficiency of 0.20% could be measured in D(2)O. Aqueous emission lifetimes were also determined for the visible emitting lanthanide ions and are 1.61 ms for Eu(III) and 1.78 ms for Tb(III). Comparing emission lifetimes in deuterated and nondeuterated water indicates that no water molecules are coordinated to the metal ion. Speciation studies show that three species form successively in solution and the log β values are 5.3, 9.6, and 13.8 for Eu(III) and 5.3, 9.2, and 12.7 for Tb(III) for 1:1, 2:1, and 3:1 ligand to metal ratios, respectively.

Uranyl sensitization of samarium(III) luminescence in a two-dimensional coordination polymer.

Heterometallic carboxyphosphonates UO(2)(2+)/Ln(3+) have been prepared from the hydrothermal reaction of uranyl nitrate, lanthanide nitrate (Ln = Sm, Tb, Er, Yb), and phosphonoacetic acid (H(3)PPA). Compound 1, (UO(2))(2)(PPA)(HPPA)(2)Sm(H(2)O)·2H(2)O (1) adopts a two-dimensional structure in which the UO(2)(2+) metal ions bind exclusively to the phosphonate moiety, whereas the Ln(3+) ions are coordinated by both phosphonate and carboxylate functionalities. Luminescence studies of 1 show very bright visible and near-IR samarium(III)-centered emission upon direct excitation of the uranyl moiety. The Sm(3+) emissive state exhibits a double-exponential decay with lifetimes of 67.2 ± 6.5 and 9.0 ± 1.3 μs as measured at 594 nm, after excitation at both 365 and 420 nm. No emission is observed in the region typical of the uranyl cation, indicating that all energy is either transferred to the Sm(3+) center or lost to nonradiative processes. Herein we report the synthesis, crystal structure, and luminescent behavior of 1, as well as those of the isostructural terbium, erbium, and ytterbium analogues.

Lanthanide-based emitting materials in light-emitting diodes

Since the description of efficient electroluminescence from aluminium tris(hydroxyquinoline) in the mid 1980s, interest in new complexes and polymers with luminescence properties as emitting layers in light-emitting diodes has steadily increased. Recently, Ln(III) ion complexes have gained in importance for this type of application. Here we review some of the seminal work in the area, along with new developments in the field. The photophysical characterization of complexes of lanthanide ions both in solution and in the solid state allows the determination of which of the complexes might be successfully utilized as emitting layers in light-emitting diodes for display applications. However, the architecture of the device is also of major importance, to allow for good charge transport and recombination and thus obtain pure colors and high emission quantum efficiency.

Para-Derivatized Pybox Ligands As Sensitizers in Highly Luminescent Ln(III) Complexes

New complexes of pyridine-bis(oxazoline) derivatized with -H, -OMe, and -Br at the para position of the pyridine ring with Eu(III) and Tb(III) have been isolated. These are highly luminescent in the solid state, regardless of the ligand-to-metal ratio. Several of the metal complexes were isolated and characterized by single crystal X-ray diffraction, showing the rich diversity of structures that can be obtained with this family of ligands. [Eu(PyboxOMe)(3)](NO(3))(3)·3CH(2)Cl(2), 1, crystallizes in the monoclinic space group P2(1)/n and has the cell parameters a = 14.3699(10) Å, b = 13.4059(9) Å, c = 25.8766(18) Å, β = 95.367(1)°, and V = 4963.1(6) Å(3). The isostructural [Tb(PyboxOMe)(3)](NO(3))(3)·3CH(2)Cl(2), 2, crystallizes with the parameters a = 14.4845(16) Å, b = 13.2998(15) Å, c = 25.890(3) Å, β = 94.918(2)°, and V = 4969.1(10) Å(3). 3, a 1:1 complex with the formula [Eu(PyboxBr)(NO(3))(3)(H(2)O)], crystallizes in the monoclinic P2(1)/c space group with a = 11.649(2) Å, b = 8.3914(17) Å, c = 20.320(4) Å, β = 100.25(3)°, and V = 1954.5(7) Å(3). 4, a product of the reaction of PyboxBr with Tb(NO(3))(3), is [Tb(PyboxBr)(2)(η(2)-NO(3))(η(1)-NO(3)](2)[Tb(NO(3))(5)]·5H(2)O. It crystallizes in the monoclinic space group P2(1) with a = 15.612(3) Å, b = 14.330(3) Å, c = 16.271(3) Å, β = 92.58(3)°, and V = 3636.5(13) Å(3). [Tb(Pybox)(3)](CF(3)SO(3))(3)·3CH(2)CN, 5, crystallizes in the triclinic space group P1̅ with a = 12.3478(2) Å, b = 15.0017(2) Å, c = 16.1476(4) Å, α = 100.252(1)°, β = 100.943(1)°, γ = 113.049(1)°, and V = 2594.80(8) Å(3). Finally, compound 6, [Tb(Pybox)(2)(NO(3))(H(2)O)](NO(3))(2)·CH(3)OH, crystallizes in the triclinic P1̅ space group with a = 9.7791(2) Å, b = 10.1722(2) Å, c = 15.3368(3) Å, α = 83.753(1)°, β = 78.307(1)°, γ = 85.630(1)°, and V = 1482.33(5) Å(3). In solution, the existence of 3:1, 2:1, and 1:1 species can be observed through absorption and luminescence speciation measurements as well as NMR spectroscopy. The stability constants in acetonitrile, as an average obtained from absorption and emission titrations, are log β(11) = 5.4, log β(12) = 8.8, and log β(13) = 12.8 with Eu(III) and log β(11) = 4.5, log β(12) = 8.4, and log β(13) = 11.7 for the Tb(III) species with PyboxOMe. Pybox displayed stability constants log β(11) = 3.6, log β(12) = 9.1, and log β(13) = 12.0 with Eu(III) and log β(11) = 3.7, log β(12) = 9.3, and log β(13) = 12.2 for the Tb(III) species. Finally, PyboxBr yielded log β(11) = 7.1, log β(12) = 12.2, and log β(13) = 15.5 for the Eu(III) species and log β(11) = 6.2, log β(12) = 11.0, and log β(13) = 15.4 with Tb(III). Photophysical characterization was performed in all cases on solutions with 3:1 ligand-to-metal ion stoichiometry and allowed determination of quantum yields and lifetimes of emission for PyboxOMe of 23.5 ± 1.6% and 1.54 ± 0.04 ms for Eu(III) and 21.4 ± 3.6% and 1.88 ± 0.04 ms for Tb(III). For Pybox these values were 25.6 ± 1.1% and 1.49 ± 0.04 ms for Eu(III) and 23.2 ± 2.1% and 0.44 ± 0.01 ms for Tb(III) and for PyboxBr they were 35.8 ± 1.6% and 1.46 ± 0.03 ms for Eu(III) and 23.3 ± 1.3% and a double lifetime of 0.79 ± 0.05/0.07 ± 0.01 ms for Tb(III). A linear relationship between the triplet level energies and the Hammett σ constants was found. Lifetime measurements in methanol as well as the NMR data in both methanol and acetonitrile indicate that all complexes are stable in the 3:1 stoichiometry in solution and that there is no solvent coordination to the metal ion.

Pyrenes, Peropyrenes, and Teropyrenes: Synthesis, Structures, and Photophysical Properties

The design of a relatively simple and efficient method to extend the π-conjugation of readily available aromatics in one-dimension is of significant value. In this paper, pyrenes, peropyrenes, and teropyrenes were synthesized through a double or quadruple benzannulation reaction of alkynes promoted by Brønsted acid. This novel method does not involve cyclodehydrogenation (oxidative aryl-aryl coupling) to arrive at the newly incorporated large arene moieties. All of the target compounds were synthesized in moderate to good yields and were fully characterized with the structures unambiguously confirmed by X-ray crystallography. As expected, photophysical characterization clearly shows increasing red-shifts as a function of extended conjugation within the fused ring systems.

Estimating the Donor–Acceptor Distance To Tune the Emission Efficiency of Luminescent Lanthanide Compounds

The influence of the donor-acceptor distance RL on the photophysical properties, including the emission quantum yield, of two europium complexes with the same coordination number, and thus similar microsymmetries, was investigated by spectroscopic and computational methods. K3[Eu(dipicCbz)3] was synthesized using the new ligand dipicCbz and its photophysical properties compared to Cs3[Eu(dipic)3]. We found that a 50% increase in RL from 4.1 to 6.5 Å results in a substantial decrease in the emission efficiency from 24 to 1.8%.

ZnS Nanoparticles Sensitize Luminescence of Capping-Ligand-Bound Lanthanide Ions

2,6-Bis(diethylamide)-4-oxo(3-thiopropane)pyridine (BDP) and 2,6-bis(methyl ester)-4-oxo(3-thiopropane)pyridine (BMP) were synthesized. These compounds chelated LnIII ions and sensitized their emission. The 3:1 complexes of BDP displayed efficiencies of 18% and 12% for EuIII and TbIII, respectively. The analogous complexes of BMP had efficiencies of 23% and 18% for EuIII and TbIII, respectively. Both BDP and BMP were used to cap ZnS nanoparticles (NPs) in a one-pot synthesis, and then LnIII ions were added, resulting in systems with metal ions at the surface of the capped NPs. Photoexcitation of the EuIII and TbIII systems through NPs capped with these two ligands, with the carboxylato derivative of BMP [dicarboxylato-4-oxo(3-thiopropane)pyridine] and the nonchromophore 3-mercaptopropionate, resulted in sensitized LnIII-centered emission. The EuIII-containing systems displayed higher efficiencies in the range 0.04-0.23% than the corresponding TbIII-containing systems with efficiencies in the range 0.01-0.15%. The NPs capped with BDP were the exception; in this case, efficiencies of 0.36% and 0.79% for EuIII and TbIII, respectively, were observed.

Cadmium- and zinc-alloyed Cu–In–S nanocrystals and their optical properties

Cadmium (Cd)- and zinc (Zn)-alloyed copper–indium–sulfide (Cu–In–S or CIS) nanocrystals (NCs) several nanometers in diameter were prepared using thermal decomposition methods, and the effects of Cd and Zn on optical properties, including the tuning of NC photoluminescence (PL) wavelength and quantum yield (QY), were investigated. It was found that incorporation of Cd into CIS enhances the peak QY of NCs whereas Zn alloying diminishes the peak. In contrast with Zn alloying, Cd alloying does not result in a pronounced luminescence blue shift. The further PL decay study suggests that Cd alloying reduces surface or intrinsic defects whereas alloying with Zn increases the overall number of defects.

Mn doped AIZS/ZnS nanocrystals: Synthesis and optical properties

In this work, Mn doped AIZS/ZnS (Mn:AIZS/ZnS) nanocrystals (NCs) have been synthesized in an approach using heat-up and drop-wise addition of precursors. On the basis of the characterization of these doped NCs on their optical properties and materials, it is found that: (1) as more Mn atoms are doped into NCs, the doped NCs present photoluminescence (PL) red-shift and quantum yield quenching; (2) the doped NCs possess a short PL lifetime in tens of microseconds and a long PL lifetime in hundreds of microseconds, and the short lived PL is more dominant than the long lived one; and (3) the doped NCs present a reversible PL thermal quenching in a range from room temperature to 170°C. Possible PL mechanisms of these NCs were discussed by analyzing their time-resolved PL spectra and thermal stability.

Synthesis, Ligation and Solvent Extraction Properties of NCMPO-decorated Pyridine and Pyridine N-oxide Platforms

Stepwise syntheses of 2-{[2-(diphenylphosphoryl)acetamido]methyl}pyridine 1-oxide, 2-[Ph2P(O)CH2C(O)N(H)CH2]C5H4NO (6), 2-{[2-(diphenylphosphoryl)acetamido]methyl}-6-[(diphenylphosphoryl)methyl]pyridine 1-oxide, 2-[Ph2P(O)CH2C(O)N(H)CH2]-6-[Ph2P(O)CH2]C5H3NO (7) and 2,6-bis{[2-(diphenylphosphoryl)acetamido]methyl}pyridine 1-oxide, 2,6-[Ph2P(O)CH2C(O)N(H)CH2]2C5H3NO (8), are reported along with spectroscopic characterization data and single crystal X-ray diffraction structure determination for 6·2H2O, 7 and 2,6-[Ph2P(O)CH2C(O)N(H)CH2]2C5H3N·MeOH 18·MeOH, the pyridine precursor of 8. Molecular mechanics computations indicate that 6, 7 and 8 should experience minimal steric hindrance to donor group reorganization that would permit tridentate, tetradentate and pentadentate docking structures for the respective ligands on lanthanide cations. However, crystal structure determination for the lanthanide complexes, {[Yb(6)(NO3)3]·(MeOH)}n, {[Lu(6)(NO3)3]·(MeOH)}n, [Er(6)2(H2O)2](NO3)3·(H2O)4}n, {[La(13)(NO3)3(MeOH)]·(MeOH)}n, {[Eu(7)(NO3)2(EtOAc)0.5(H2O)0.5](NO3)}2·MeOH and [Dy3(7)4(NO3)4(H2O)2](NO3)5·(MeOH)5·(H2O)2 reveal solid-state structures with mixed chelating/bridging ligand : Ln(III) interactions that employ lower than the maximal denticity. The binding of 6 and 7 with Eu(III) in the solid state and in MeOH solutions is also accessed by emission spectroscopy. The acid dependence for solvent extractions with 6 and 7 in 1,2-dichloroethane for Eu(III) and Am(III) in nitric acid solutions is described and compared with the behavior of n-octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (OPhDiBCMPO, 1b) and 2-[(diphenyl)phosphinoylmethyl]pyridine N-oxide (DPhNOPO, 4a).