Eu(III) and Tb(III) luminescence sensitized by thiophenyl-derivatized nitrobenzoato antennas

Thiophenyl-derivatized nitrobenzoic acid ligands have been evaluated as possible sensitizers of Eu(III) and Tb(III) luminescence. The resulting solution and solid-state species were isolated and characterized by luminescence spectroscopy and X-ray crystallography. The Eu(III) complex with 2-nitro-3-thiophen-3-yl-benzoic acid, 1, crystallizes in the monoclinic space group C2/c with a = 28.569(3) A, b = 17.7726(18) A, c = 17.7073(18) A, beta= 126.849(2) degrees, and V = 7194.6(13) A3. The Tb(III) complex with this ligand, 2, is isostructural, and its cell parameters are a = 29.755(6) A, b = 18.123(4) A, c = 19.519(4) A, beta= 130.35(3) degrees, and V = 8021(3) A3. Eu(III) crystallizes with 3-nitro-2-thiophen-3-yl-benzoic acid as a triclinic complex, 3, in the space group P1 with a = 11.045(2) A, b = 12.547(3) A, c = 15.500(3) A, alpha = 109.06(3)degrees, beta = 94.79(3) degrees, gamma = 107.72(3) degrees. and V = 1893.5(7) A3. With the ligand 5-nitro-2-thiophen-3-yl-benzoic acid, Eu(III) yields another molecular compound, 4, triclinic P1, with a = 10.649(2) A, b = 14.009(3) A, c = 15.205(3) A, alpha= 112.15(3) degrees, beta = 100.25(3) degrees, gamma = 106.96(3) degrees, and V = 1900.5(7) A3. All compounds dissolve in water and methanol, and the methanolic solutions are luminescent. The solution species have a metal ion-to-ligand ratio of 1:1. The quantum yields have been determined to be in the range of 0.9-3.1% for Eu(III) and 4.7-9.8% for Tb(III). The highest values of these correspond to the most intense luminescence reported for Ln(III) solutions with this type of sensitizer. The lifetimes of luminescence are in the range of 248.3-338.9 micros for Eu(III) and 208.6-724.9 micros for Tb(III). The stability constants are in the range of log 11 = 2.73-4.30 for Eu(III) and 3.34-4.18 for Tb(III) and, along with the energy migration pathways, are responsible for the reported efficiency of sensitization.     

Synthesis, characterization of the luminescent lanthanide complexes with (Z)-4-(4-methoxyphenoxy)-4-oxobut-2-enoic acid

(Z)-4-(4-Methoxyphenoxy)-4-oxobut-2-enoic acid and its solid rare earth complexes LnL3.2H2O (Ln=La, Eu, Tb) were synthesized and characterized by means of MS, elemental analysis, FTIR, 13C NMR and TG-DTA. The IR and 13C NMR results show that the carboxylic groups in the complexes coordinated to the rare earth ions in the form of a bidentate ligand, but the ester carboxylic groups have not taken part in the coordination. The luminescence spectra of Eu(III) and Tb(III) complexes in solid state were also studied. The strong luminescence emitting peaks at 616nm for Eu(III) and 547nm for Tb(III) can be observed, which could be attributed to the ligand has an enhanced effect to the luminescence intensity of the Eu and Tb.     

Lanthanide(III) Complexes of 4,10‐Bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H6do2a2p) in Solution and in the Solid State: Structural Studies Along the Series

Complexes of 4,10‐bis(phosphonomethyl)‐1,4,7,10‐tetraazacyclododecane‐1,7‐diacetic acid (trans‐H₆do2a2p, H₆ L ) with transition metal and lanthanide(III) ions were investigated. The stability constant values of the divalent and trivalent metal‐ion complexes are between the corresponding values of H₄dota and H₈dotp complexes, as a consequence of the ligand basicity. The solid‐state structures of the ligand and of nine lanthanide(III) complexes were determined by X‐ray diffraction. All the complexes are present as twisted‐square‐antiprismatic isomers and their structures can be divided into two series. The first one involves nona‐coordinated complexes of the large lanthanide(III) ions (Ce, Nd, Sm) with a coordinated water molecule. In the series of Sm, Eu, Tb, Dy, Er, Yb, the complexes are octa‐coordinated only by the ligand donor atoms and their coordination cages are more irregular. The formation kinetics and the acid‐assisted dissociation of several Ln^III–H₆ L complexes were investigated at different temperatures and compared with analogous data for complexes of other dota‐like ligands. The [Ce( L )(H₂O)]^3? complex is the most kinetically inert among complexes of the investigated lanthanide(III) ions (Ce, Eu, Gd, Yb). Among mixed phosphonate–acetate dota analogues, kinetic inertness of the cerium(III) complexes is increased with a higher number of phosphonate arms in the ligand, whereas the opposite is true for europium(III) complexes. According to the ¹H NMR spectroscopic pseudo‐contact shifts for the Ce–Eu and Tb–Yb series, the solution structures of the complexes reflect the structures of the [Ce(H L )(H₂O)]^2? and [Yb(H L )]^2? anions, respectively, found in the solid state. However, these solution NMR spectroscopic studies showed that there is no unambiguous relation between ³¹P/¹H lanthanide‐induced shift (LIS) values and coordination of water in the complexes; the values rather express a relative position of the central ions between the N₄ and O₄ planes.     

Visible and near-infrared intense luminescence from water-soluble lanthanide [Tb(III), Eu(III), Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), Er(III)] complexes

The synthesis of a new ligand (1) containing a single phenanthroline (phen) chromophore and a flexibly connected diethylenetriamine tetracarboxylic acid unit (DTTA) as a lanthanide (Ln) coordination site is reported [1 is 4-[(9-methyl-1,10-phenantrol-2-yl)methyl]-1,4,7-triazaheptane-1,1,7,7-tetraacetic acid]. From 1, an extended series of water-soluble Ln.1 complexes was obtained, where Ln is Eu(III), Tb(III), Gd(III), Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), and Er(III). The stoichiometry for the association was found 1:1, with an association constant K(A) > or = 10(7) s(-1) as determined by employing luminescence spectroscopy. The luminescence and photophysical properties of the series of lanthanide complexes were investigated in both H2O and D2O solutions. High efficiencies for the sensitized emission, phi(se), in air-equilibrated water were observed for the Ln.1 complexes of Eu(III) and Tb(III) in the visible region (phi(se) = 0.24 and 0.15, respectively) and of Sm(III), Dy(III), Pr(III), Ho(III), Yb(III), Nd(III), and Er(III) in the vis and/or near-infrared region [phi(se) = 2.5 x 10(-3), 5 x 10(-4), 3 x 10(-5), 2 x 10(-5), 2 x 10(-4), 4 x 10(-5), and (in D2O) 4 x 10(-5), respectively]. For Eu.1 and Tb.1, luminescence data for water and deuterated water allowed us to estimate that no solvent molecules (q) are bound to the ion centers (q = 0). Luminescence quenching by oxygen was investigated in selected cases.     

Synthesis,characterization and luminescence properties of Eu(III) and Tb(III) complexes with novel pyrazole derivatives and 1,10-phenanthroline

Two novel pyrazole-derived ligands, 3-chloro-6-(3,5-dimethyl-1H-pyrazol-1-yl)picolinic acid (CDPA) and 3-chloro-6-(3,5-dimethyl-1H-pyrazol-1-yl)-N-phenylpicolinamide (CDPP) were prepared by 3,6-dichloropicolinic acid (DCPA). Their complexes with terbium(III) and europium(III) were synthesized. The complexes were characterized by elemental analysis, infrared spectra, ¹H NMR and TG–DTG. Furthermore, the above complexes using 1,10-phenanthroline as a secondary ligand were also synthesized and characterized. The luminescence properties of these complexes in solid state were investigated. The results suggested that Tb(III) complexes exhibit more efficient luminescence than Eu(III) complexes and the fluorescence of the complexes with 1,10-phenanthroline as a secondary ligand was prominently stronger than that of complexes without this ligand., and the three ligand (DCPA), (CDPP) and (CDPA) are excellent sensitizers to Eu(III) and Tb(III) ion.     

Highly Luminescent and Thermally Stable Lanthanide Coordination Polymers Designed from 4-(Dipyridin-2-yl)aminobenzoate: Efficient Energy Transfer from Tb(3+) to Eu(3+) in a Mixed Lanthanide Coordination Compound

Herein, a new aromatic carboxylate ligand, namely, 4-(dipyridin-2-yl)aminobenzoic acid (HL), has been designed and employed for the construction of a series of lanthanide complexes (Eu(3+) = 1, Tb(3+) = 2, and Gd(3+) = 3). Complexes of 1 and 2 were structurally authenticated by single-crystal X-ray diffraction and were found to exist as infinite 1D coordination polymers with the general formulas {[Eu(L)(3)(H(2)O)(2)]}(n) (1) and {[Tb(L)(3)(H(2)O)].(H(2)O)}(n) (2). Both compounds crystallize in monoclinic space group C2/c. The photophysical properties demonstrated that the developed 4-(dipyridin-2-yl)aminobenzoate ligand is well suited for the sensitization of Tb(3+) emission (Φ(overall) = 64%) thanks to the favorable position of the triplet state ((3)ππ*) of the ligand [the energy difference between the triplet state of the ligand and the excited state of Tb(3+) (ΔE) = (3)ππ* - (5)D(4) = 3197 cm(-1)], as investigated in the Gd(3+) complex. On the other hand, the corresponding Eu(3+) complex shows weak luminescence efficiency (Φ(overall) = 7%) due to poor matching of the triplet state of the ligand with that of the emissive excited states of the metal ion (ΔE = (3)ππ* - (5)D(0) = 6447 cm(-1)). Furthermore, in the present work, a mixed lanthanide system featuring Eu(3+) and Tb(3+) ions with the general formula {[Eu(0.5)Tb(0.5)(L)(3)(H(2)O)(2)]}(n) (4) was also synthesized, and the luminescent properties were evaluated and compared with those of the analogous single-lanthanide-ion systems (1 and 2). The lifetime measurements for 4 strongly support the premise that efficient energy transfer occurs between Tb(3+) and Eu(3+) in a mixed lanthanide system (η = 86%).     

Probing Effect of Solvation on Photoexcited Quadrupolar Donor-Acceptor-Donor Molecule via Ultrafast Raman Spectroscopy

The symmetric and quadrupolar donor-acceptordonor (D-A-D) molecules usually exhibit excitedstate charge redistribution process from delocalized intramolecular charge transfer (ICT) state to localized ICT state. Direct observation of such charge redistribution process in real-time has been intensively studied via various ultrafast time-resolved spectroscopies. Femtosecond stimulated Raman spectroscopy (FSRS) is one of the powerful methods which can be used to determine the excited state dynamics by tracking vibrational mode evolution of the specific chemical bonds within molecules. Herein, a molecule, 4, 4′-(buta-1, 3-diyne-1, 4-diyl)bis(N, N-bis(4-methoxyphenyl)aniline), that consists of two central adjacent alkyne (-C≡C-) groups as electron-acceptors and two separated, symmetric N, N-bis(4-methoxyphenyl)aniline at both branches as electron-donors, is chosen to investigate the excited-state photophysical properties. It is shown that the solvation induced excited-state charge redistribution in polar solvents can be probed by using femtosecond stimulated Raman spectroscopy. The results provide a fundamental understanding of photoexcitation induced charge delocalization/localization properties of the symmetric quadrupolar molecules with adjacent vibrational markers located at central position.

     

Short Radiative Lifetime and Non-Triplet Sensitization in Near-Infrared-Luminescent Yb(III) Complex with Tripodal Schiff Base

We prepared Ln(III) (Ln=Eu, Gd, and Yb) complexes with a tripodal Schiff base, tris[2-(5-methylsalicylideneimino)ethyl]amine (H₃L) and studied their photophysical properties. Upon ligand excitation, YbL showed Yb(III)-centered luminescence in the near-infrared region. While the overall quantum yield (0.60(1)%) of YbL in acetonitrile was moderate among the reported values for Yb(III) complexes, its radiative lifetime (0.33(2) ms) was significantly shorter than those reported previously. We propose that the ligand-to-metal charge-transfer (LMCT) state mediated the sensitization in YbL. The emission and excitation spectra of EuL indicated the participation of the LMCT state in the sensitization. The radiative lifetime (0.84(7) ms) for EuL in the solid state was rather short compared to those of reported Eu(III) complexes. Our results show that the Yb(III) complex with the Schiff base ligand has two features: the short radiative lifetime and the non-triplet sensitization path.     

Synthesis, characterizations and luminescent properties of three novel aryl amide type ligands and their lanthanide complexes

Three new aryl amide type ligands, N-(phenyl)-2-(quinolin-8-yloxy)acetamide (L(1)), N-(benzyl)-2-(quinolin-8-yloxy)acetamide (L(2)) and N-(naphthalene-1-yl)-2-(quinolin-8-yloxy)acetamide (L(3)) were synthesized. With these ligands, three series of lanthanide(III) complexes were prepared: [Ln(L(1))(2)(NO(3))(2)]NO(3), [Ln(L(2))(2)(NO(3))(2)(H(2)O)(2)]NO(3).H(2)O and [Ln(L(3))(2)(NO(3))(2)(H(2)O)(2)]NO(3).H(2)O (Ln=La, Sm, Eu, Gd). The complexes were characterized by the elemental analyses, molar conductivity, (1)H NMR spectra, IR spectra and TG-DTA. The fluorescence properties of complexes in the solid state and the triplet state energies of the ligands were studied in detail, respectively. It was found that the Eu(III) complexes have bright red fluorescence in solid state. The energies of excited triplet state for the three ligands are 20325 cm(-1) (L(3)), 21053 cm(-1) (L(2)) and 22831 cm(-1) (L(1)), respectively. All the three ligands sensitize Eu(III) strongly and the order of the emission intensity for the Eu(III) complexes with the three ligands is L(3)>L(2)>L(1). It can be explained by the relative energy gap between the lowest triplet energy level of the ligand (T) and (5)D(1) of Eu(III). This means that the triplet energy level of the ligand is the chief factor, which dominates Eu(III) complexes luminescence.     

Synthesis, characterization and luminescence property of N,N'-di(pyridine N-oxide-2-yl)pyridine-2,6-dicarboxamide and corresponding lanthanide (III) complexes

A new ligand, N,N'-di(pyridine N-oxide-2-yl)pyridine-2,6-dicarboxamide (LH2) and its several lanthanide (III) complexes (La, Eu, Gd, Tb, Y) were synthesized and characterized in detail based on elemental analysis, conductivity measurements, IR, 1H NMR, MS (FAB) and UV spectra and TG-DTA studies. The results indicated that the composition of these binary complexes is [Ln(LH2)(NO3)2.H2O]NO3.nH2O (n=0-1); while the ligand has a good planar structure with strong hydrogen bonds. The fluorescence spectra exhibits that the Tb (III) complex and the Eu (III) complex display characteristic metal-centered fluorescence in solid state while ligand fluorescence is completely quenched. However, the Tb (III) complex displays more effective luminescence than the Eu (III) complex, which is attributed to especial effectivity in transferring energy from the lowest triplet energy level of the ligands (T) onto the excited state (5D4) of Tb (III) than that (5D1) of Eu (III).     

Simultaneous spectrophotometric determination of atrazine and cyanazine by chemometric methods

Three novel ligands containing pyridine-2,6-dicarboxylic acid unit, trans-4 -(4'-methoxystyryl) pyridine-2,6-dicarboxylic acid, trans-4-(4'-(dimethylamino)styryl)pyridine-2,6-dicarboxylic acid, and trans-4-(4'-(diphenylamino)styryl)pyridine-2,6-dicarboxylic acid were synthesized and their complexes with Eu(III), Tb(III) ions were successfully prepared. The ligands and the corresponding metal complexes were characterized by means of MS, elemental analysis, IR, (1)H NMR and TG-DTA. The luminescence spectra of Eu(III) and Tb(III) complexes in solid state were studied. The strong luminescence emitting peaks at 615 nm for Eu(III) and 545 nm for Tb(III) can be observed. The applications in cell imaging of the europium and terbium complexes were investigated.     

Direct excitation luminescence spectroscopy of Eu(III) complexes of 1,4,7-tris(carbamoylmethyl)-1,4,7,10- tetraazacyclododecane derivatives and kinetic studies of their catalytic cleavage of an RNA analog

The macrocycles 1,4,7-tris(carbamoylmethyl)-1,4,7,10-tetrazacyclododecane (1), 1,4,7-tris[(N-ethyl)carbamoylmethyl]-1,4,7,10-tetraazacyclododecane (2), 1,4,7-tris[(N,N-diethyl)carbamoylmethyl]-1,4,7,10-tetraazacyclododecane (3) and their Eu(III) complexes are prepared. Studies using direct Eu(III) excitation luminescence spectroscopy show that all three Eu(III) complexes exhibit only one predominant isomer with two bound waters under neutral to mildly basic conditions (Eu(X)(H(2)O)(2) for X = 1-3). There are no detectable ligand ionizations over the pH range 5.0-8.0 for Eu(3), 5.0-8.5 for Eu(2) or 5.0-9.5 for Eu(1). The three Eu(III) complexes show a linear dependence of second-order rate constants for the cleavage of 4-nitrophenyl-2-hydroxyethylphosphate (HpPNP) on pH in the range 6.5-8.0 for Eu(3), 7.0-8.5 for Eu(2) and 7.0-9.0 for Eu(1). This pH-rate profile is consistent with the Eu(III) complex-substrate complex being converted to the active form by loss of a proton and with Eu(III) water pK(a) values that are higher than 8.0 for Eu(3), 8.5 for Eu(2) and 9.0 for Eu(1). Inhibition studies show that Eu() binds strongly to the dianionic ligand methylphosphate (K(d) = 0.28 mM), and more weakly to diethylphosphate (K(d) = 7.5 mM), consistent with a catalytic role of the Eu(III) complexes in stabilizing the developing negative charge on the phosphorane transition state.     

Synthesis,characterization and cytotoxic/cytostatic activity of Sm(III) and Gd(III) complexes

New Sm(III) and Gd(III) complexes of deprotonated 4-hydroxy-3[1-(4-nitrophenyl)-3-oxobutyl]-2H-1-benzopyran-2-one (Acenocoumarol) were synthesized and characterized using FT-IR, FT-Raman, NMR spectra, and elemental analyses. The vibrational study gave evidence for the coordination of ligand to lanthanide ions. The ligand and its lanthanide(III) complexes were tested for their cytotoxic/cytostatic activity against two tumor cell lines and peritoneal mouse macrophages. The Sm(III) and Gd(III) complexes exhibit good activity against melanoma B16 and fibrosarcoma L929 and are stronger inhibitors of tumor cell proliferation than the ligand. Besides their cytotoxicity to tumor cells, Acenocoumarol and its gadolinium(III) and samarium(III) complexes modulate NO generation in activated macrophages.     

A heterobimetallic ruthenium-gadolinium complex as a potential agent for bimodal imaging

Trinuclear heterobimetallic Ln(III)-Ru(II) complexes (Ln = Eu, Gd) based on a 1,10-phenanthroline ligand bearing a diethylenetriaminepentaacetic acid (DTPA) core have been synthesized and fully characterized by a range of experimental techniques. The (17)O NMR and proton nuclear magnetic relaxation dispersion (NMRD) measurements of Gd(III)-Ru(II) show that, in comparison to the parent Gd-DTPA, this complex exhibits improved relaxivity, which is the result of an increase of the rotational correlation time. Relaxometry and ultrafiltration experiments indicate that the 1,10-phenanthroline ligand has a high affinity for noncovalent binding to human serum albumin, which results in a high relaxivity r(1) of 14.3 s(-1) mM(-1) at 20 MHz and 37 °C. Furthermore, the Ln(III)-Ru(II) complexes (Ln = Eu, Gd) show an intense light absorption in the visible spectral region due to metal-to-ligand charge transfer (MLCT) transitions. Upon excitation into the MLCT band at 440 nm, the complexes exhibit a bright-red luminescence centered at 610 nm, with a quantum yield of 4.7%. The luminescence lifetime equals 540 ns and is therefore long enough to exceed the fluorescent background. Monometallic lanthanide complexes have also been synthesized, and the Eu(III) analogue shows a characteristic red luminescence with a quantum yield of 0.8%. Taking into account the relaxometric and luminescent properties, the developed Gd(III)-Ru(II) complex can be considered as a potential in vitro bimodal imaging agent.     

Complexation of lanthanides, actinides and transition metal cations with a 6-(1,2,4-triazin-3-yl)-2,2':6',2'-terpyridine ligand: implications for actinide(III)/lanthanide(III) partitioning

The quadridentate N-heterocyclic ligand 6-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2'?:?6',2'-terpyridine (CyMe(4)-hemi-BTBP) has been synthesized and its interactions with Am(III), U(VI), Ln(III) and some transition metal cations have been evaluated by X-ray crystallographic analysis, Am(III)/Eu(III) solvent extraction experiments, UV absorption spectrophotometry, NMR studies and ESI-MS. Structures of 1:1 complexes with Eu(III), Ce(III) and the linear uranyl (UO(2)(2+)) ion were obtained by X-ray crystallographic analysis, and they showed similar coordination behavior to related BTBP complexes. In methanol, the stability constants of the Ln(III) complexes are slightly lower than those of the analogous quadridentate bis-triazine BTBP ligands, while the stability constant for the Yb(III) complex is higher. (1)H NMR titrations and ESI-MS with lanthanide nitrates showed that the ligand forms only 1:1 complexes with Eu(III), Ce(III) and Yb(III), while both 1:1 and 1:2 complexes were formed with La(III) and Y(III) in acetonitrile. A mixture of isomeric chiral 2:2 helical complexes was formed with Cu(I), with a slight preference (1.4:1) for a single directional isomer. In contrast, a 1:1 complex was observed with the larger Ag(I) ion. The ligand was unable to extract Am(III) or Eu(III) from nitric acid solutions into 1-octanol, except in the presence of a synergist at low acidity. The results show that the presence of two outer 1,2,4-triazine rings is required for the efficient extraction and separation of An(III) from Ln(III) by quadridentate N-donor ligands.     

Supramolecular coordination chemistry in aqueous solution: lanthanide ion-induced triple helix formation

The self-assembly of dinuclear triple helical lanthanide ion complexes (helicates), in aqueous solution, is investigated utilizing laser-induced, lanthanide luminescence spectroscopy. A series of dinuclear lanthanide (III) helicates (Ln(III)) based on 2,6-pyridinedicarboxylic acid (dipicolinic acid, dpa) coordinating units was synthesized by linking two dpa moieties using the organic diamines (1R,2R)-diaminocyclohexane (chxn-R,R) and 4,4'-diaminodiphenylmethane (dpm). Luminescence excitation spectroscopy of the Eu3+ 7F0-->5D0 transition shows the apparent cooperative formation of neutral triple helical complexes in aqueous solution, with a [Eu2L3] stoichiometry. Eu3+ excitation peak wavelengths and excited-state lifetimes correspond to those of the [Eu(dpa)3]3- model complex. CD studies of the Nd(III) helicate Nd2(dpa-chxn-R,R)3 reveal optical activity of the f-f transitions, indicating that the chiral linking group induces a stable chirality at the metal ion center. Molecular mechanics calculations using CHARMm suggest that the delta delta configuration at the Nd3+ ion centers is induced by the chxn-R,R linker. Stability constants were determined for both ligands with Eu3+, yielding identical results: log K = 31.6 +/- 0.2 (K in units of M-4). Metal-metal distances calculated from Eu3+-->Nd3+ energy-transfer experiments show that the complexes have metal-metal distances close to those calculated by molecular modeling. The fine structure in the Tb3+ emission bands is consistent with the approximate D3 symmetry as anticipated for helicates.     

Calix[4]azacrowns as novel molecular scaffolds for the generation of visible and near-infrared lanthanide luminescence

Two calix[4]azacrowns, capped with two aminopolyamide bridges, were used as ligands for the complexation of lanthanide ions [Eu(III), Tb(III), Nd(III), Er(III), La(III)]. The formation of 1:2 and 1:1 complexes was observed, and stability constants, determined by UV absorption and fluorescence spectroscopy, were found to be generally on the order of log beta(11) approximately 5-6 and log beta(12) approximately 10. The structural changes of the ligands upon La(III) complexation were probed by 1H NMR spectroscopy. The two ligands were observed to have opposite fluorescence behaviors, namely, fluorescence enhancement (via blocking of photoinduced electron transfer from amine groups) or quenching (via lanthanide-chromophore interactions) upon metal ion complexation. Long-lived lanthanide luminescence was sensitized by excitation in the pi,pi band of the aromatic moieties of the ligands. The direct involvement of the antenna triplet state was demonstrated via quenching of the ligand phosphorescence by Tb(III). Generally, Eu(III) luminescence was weak (Phi(lum) 相似文献   

Self-assembly of highly luminescent lanthanide complexes promoted by pyridine-tetrazolate ligands

Two tridentate pyridine-tetrazolate ligands (H(2)pytz and H(2)pytzc), analogues of the well-known dipicolinate (H(2)dpa) ligand, have been synthesized in a straightforward manner and used for lanthanide(III) coordination. The structures of the resulting tris-ligand complexes were determined in solution ((1)H-NMR), where they remain undissociated, as well as in the solid state (X-ray diffraction). The solubility of these anionic complexes can be easily tuned by changing the countercation. The bis-tetrazolate-pyridine ligand H(2)pytz sensitizes very efficiently both the visible and near-IR emission of the lanthanides, with unusually high luminescence quantum yields in solid state (61% and 65% for Eu and Tb, respectively, and 0.21% for Nd) and in water (63% for Tb and 18% for Eu). Furthermore, the absorption window of the complexes is significantly extended towards the visible region up to 330 nm. The results show that the bis-tetrazolate-pyridine ligand provides a very attractive alternative to the classic dipicolinate ligand.     

Sensitized luminescence in dinuclear lanthanide(III) complexes of bridging 8-hydroxyquinoline derivatives with different electronic properties

Three new dinuclear lanthanide(III) complexes {Eu(hfac)(3)(H(2)O)}(2)(μ-HPhMq)(2) (2) and {Ln(hfac)(3)(H(2)O)}(2)(μ-HMe(2)NC(6)H(4)Mq)(2) (Ln = Eu, 3; Nd, 4) with 8-hydroxylquinoline derivatives in μ-phenol mode were synthesized and characterized, where hfac(-) = hexafluoroacetylacetonate, HPhMq = 2-methyl-5-phenylquinolin-8-ol, and HMe(2)C(6)H(4)Mq = 5-(4-(dimethylamino)phenyl)-2-methylquinolin-8-ol. Compared with that (400 nm) for {Eu(hfac)(3)}(2)(μ-HMq)(2) (1, HMq = 2-methy-8-hydroxylquinoline), the excitation wavelength for sensitized lanthanide luminescence is extended to ca. 420 nm for 2, and 500 nm for 4 by introducing a phenyl or 4-(dimethylamino)phenyl to 8-hydroxylquinoline. These dinuclear lanthanide(III) complexes exhibit distinctly fluoride-induced lanthanide(III) emission enhancement in both intensity and lifetime due to replacing coordination water molecules or formation of strong O-H···F hydrogen bonds with coordinated H(2)O and μ-phenol, thus suppressing significantly the non-radiative O-H oscillators.     

Lanthanide complexes of chiral 3 + 3 macrocycles derived from (1R,2R)-1,2-diaminocyclohexane and 2,6-diformyl-4-methylphenol

The enantiopure amine macrocycle H(3)L, as well as the parent macrocyclic Schiff base H(3)L1, the 3 + 3 condensation product of (1R,2R)-1,2-diaminocyclohexane and 2,6-diformyl-4-methylphenol, are able to form mononuclear complexes with lanthanide(III) ions. The lanthanide(III) complexes of H(3)L have been studied in solution using NMR spectroscopy and electrospray mass spectrometry. The NMR spectra indicate the presence of complexes of low C(1) and C(2) symmetry. The (1)H and (13)C NMR signals of the Lu(III) complex obtained from H(3)L have been assigned on the basis of COSY, TOCSY, NOESY, ROESY and HMQC spectra. The NMR data reveal unsymmetrical binding of lanthanide(III) ion and the presence of a dynamic process corresponding to rotation of Lu(III) within the macrocycle. The [Ln(H(4)L)(NO(3))(2)](NO(3))(2)(Ln = Sm(III), Eu(III), Dy(III), Yb(III) and Lu(III)) complexes of the cationic ligand H(4)L(+) have been isolated in pure form. The X-ray analysis of the [Eu(H(4)L)(NO(3))(2)](NO(3))(2) complex confirms the coordination mode of the macrocycle determined on the basis of NMR results. In this complex the europium(III) ion is bound to three phenolate oxygen atoms and two amine nitrogen atoms of the monoprotonated macrocycle H(4)L(+), as well as to two axial bidendate nitrate anions. In the presence of a base, mononuclear La(III), Ce(III) and Pr(III) complexes of the deprotonated form of the ligand L(3-) can be obtained. When 2 equivalents of Pr(III) are used in this synthesis Na(3)[Pr(2)L(NO(3))(2)(OH)(2)](2)NO(3).5H(2)O is obtained. The NMR, ES MS and an X-ray crystal model of this complex show coordination of two Pr(III) ions by the macrocycle L. The X-ray crystal structure of the free macrocycle H(3)L1 has also been determined. In contrast to macrocyclic amine H(3)L, the Schiff base H(3)L1 adopts a cone-type conformation resembling calixarenes.