Fully fluorinated imidodiphosphinate shells for visible- and NIR-emitting lanthanides: hitherto unexpected effects of sensitizer fluorination on lanthanide emission properties

In this paper we demonstrate that the effect of aromatic C--F substitution in ligands does not always abide by conventional wisdom for ligand design to enhance sensitisation for visible lanthanide emission, in contrast with NIR emission for which the same effect coupled with shell formation leads to unprecedented long luminescence lifetimes. We have chosen an imidodiphosphinate ligand, N-{P,P-di(pentafluorophinoyl)}-P,P-dipentafluorophenylphosphinimidic acid (HF20tpip), to form ideal fluorinated shells about all visible- and NIR-emitting lanthanides. The shell, formed by three ligands, comprises twelve fully fluorinated aryl sensitiser groups, yet no-high energy X--H vibrations that quench lanthanide emission. The synthesis, full characterisation including X-ray and NMR analysis as well as the photophysical properties of the emissive complexes [Ln(F20tpip)3], in which Ln=Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb, Y, Gd, are reported. The photophysical results contrast previous studies, in which fluorination of alkyl chains tends to lead to more emissive lanthanide complexes for both visible and NIR emission. Analysis of the fluorescence properties of the HF20tpip and [Gd(F20tpip)3] reveals that there is a low-lying state at around 715 nm that is responsible for partially quenching of the signal of the visible emitting lanthanides and we attribute it to a pi-sigma* state. However, all visible emitting lanthanides have long lifetimes and unexpectedly the [Dy(F20tpip)3] complex shows a lifetime of 0.3 ms, indicating that the elimination of high-energy vibrations from the ligand framework is particularly favourable for Dy. The NIR emitting lanthanides show strong emission signals in powder and solution with unprecedented lifetimes. The luminescence lifetimes of [Nd(F20tpip)3], [Er(F20tpip)3] and [Yb(F20tpip)3] in deuteurated acetonitrile are 44, 741 and 1111 micros. The highest value observed for the [Yb(F20tpip)3] complex is more than half the value of the Yb ion radiative lifetime.     

Stable 8-hydroxyquinolinate-based podates as efficient sensitizers of lanthanide near-infrared luminescence

New polydentate ligands (e.g., Tsox and TsoxMe) have been synthesized to take advantage of the chelating effect of bidentate 8-hydroxyquinolinate subunits connected to a N,N,N',N'-tetraaminopropyl-1,2-ethylenediamine framework and with the aim of sensitizing the NIR luminescence of Nd(III) and Yb(III) ions. Ten pK(a)'s have been determined and the interaction between the ligands and Ln(III) ions in dilute aqueous solution has been probed both by potentiometric and spectrophotometric titrations. These studies have been mostly performed with the Eu(III) ion, which is in the middle of the lanthanide series, and extended to other ions (La(III), Er(III), Lu(IIII)). Stable complexes with Ln(III) ions are formed (pLn in the range of 14-16), the four chromophoric units being coordinated to the metal center, exploiting the entropic effect generated by the anchor. The monometallic complexes [Ln(H(2)L)](3)(-) exist as the major species at physiological pH regardless of the lanthanide used. Lifetime determinations of the Nd((4)F(3/2)) and Yb((2)F(5/2)) excited levels in both H(2)O and D(2)O at buffered pH point to the absence of water molecules bound in the inner coordination sphere of the Ln(III). Photophysical properties of the free ligands and of their lanthanide complexes have been investigated in buffered aqueous solutions both at room temperature and 77 K. The low-energy triplet state makes energy transfers from the ligand to the metal ions possible; this leads to a sizable sensitization of the Nd(III)- or Yb(III)-centered luminescence ( = 0.02% and = 0.18%) for Tsox chelates. Methylation of the amide functions removes the quenching mechanism induced by the proximate N-H vibrations and increases both the lifetimes and quantum yields of the TsoxMe chelates ( = 0.04% and = 0.37%). In fact, TsoxMe yields one of the most luminescent Yb(III) compounds known in water, and this ligand appears to be suitable for the development of NIR probes for bioanalyses.     

Covalent linking of near-infrared luminescent ternary lanthanide (Er(3+), Nd(3+), Yb(3+)) complexes on functionalized mesoporous MCM-41 and SBA-15

The near-infrared (NIR) luminescent lanthanide ions, such as Er(III), Nd(III), and Yb(III), have been paid much attention for the potential use in the optical communications or laser systems. For the first time, the NIR-luminescent Ln(dbm)(3)phen complexes have been covalently bonded to the ordered mesoporous materials MCM-41 and SBA-15 via a functionalized phen group phen-Si (phen-Si = 5-(N,N-bis-3-(triethoxysilyl)propyl)ureyl-1,10-phenanthroline; dbm = dibenzoylmethanate; Ln = Er, Nd, Yb). The synthesis parameters X = 12 and Y = 6 h (X denotes Ln(dbm)(3)(H(2)O)(2)/phen-MCM-41 molar ratio or Ln(dbm)(3)(H(2)O)(2)/phen-SBA-15 molar ratio and Y is the reaction time for the ligand exchange reaction; phen-MCM-41 and phen-SBA-15 are phen-functionalized MCM-41 and SBA-15 mesoporous materials, respectively) were selected through a systematic and comparative study. The derivative materials, denoted as Ln(dbm)(3)phen-MCM-41 and Ln(dbm)(3)phen-SBA-15 (Ln = Er, Nd, Yb), were characterized by powder X-ray diffraction, nitrogen adsorption/desorption, Fourier transform infrared (FT-IR), elemental analysis, and fluorescence spectra. Upon excitation of the ligands absorption bands, all these materials show the characteristic NIR luminescence of the corresponding lanthanide ions through the intramolecular energy transfer from the ligands to the lanthanide ions. The excellent NIR-luminescent properties enable these mesoporous materials to have potential uses in optical amplifiers (operating at 1.3 or 1.5 mum), laser systems, or medical diagnostics. In addition, the Ln(dbm)(3)phen-SBA-15 materials show an overall increase in relative luminescent intensity and lifetime compared to the Ln(dbm)(3)phen-MCM-41 materials, which was explained by the comparison of the lanthanide ion content and the pore structures of the two kinds of mesoporous materials in detail.     

Assembly of hydrophobic shells and shields around lanthanides

Luminescent lanthanide complexes have been developed, based on the assembly of bulky ligands around the lanthanide ion, to provide shell-type protection of the ion from coordinated solvent molecules. Aryl-functionalised imidodiphosphinate ligands (tpip and Metpip) provide a bidentate anionic site that leads to hexa-coordinate lanthanide complexes in which the aryl groups surround the ion. There are twelve phenyl groups around the lanthanide that act as "remote" (from the binding site) sensitisers for the metal ion. It is shown that these ligands are suitable for sensitising luminescence for all the lanthanides that emit in the visible range, namely, SmIII, EuIII, TbIII, DyIII. A "builtin" shield on the ligand is designed to provide a complete block of the approach of water to the lanthanide ion. The synthesis of the ligands and their lanthanides complexes as well as detailed photophysical studies of the complexes in solution and in the solid-state are presented.     

Sensitized near-IR luminescence of Ln(III) complexes with benzothiazole derivatives

Lanthanide complexes with benzothiazole derivatives (Btz-R, R = OCH(3) and OH) and terpyridine (tpy) ligands were synthesized, and their photophysical properties were precisely investigated. The free Btz-OCH(3) ligand in toluene, excited with UV light, produced the normal emission bands around 410 nm, whereas Btz-OH produced a strong excited-state intramolecular proton transfer (ESIPT) band at 510 nm. The Ln(III) complexes (Ln = Nd, Er, and Yb) exhibited sensitized near-IR luminescence when the Btz-R ligands were excited. The sensitized luminescence quantum yields (Phi(Ln)) of the lanthanide complexes were markedly enhanced by ESIPT: for [Nd(Btz-R)(tpy)] in toluene solution, Phi(Ln) = 0.04% for Btz-OCH(3) and 0.39% for Btz-OH. The sensitized luminescence of the Er(III) complexes (Phi(Ln) = 0.002% for Btz-OCH(3) and 0.009% for Btz-OH) was less efficient than that of the Nd(III) complexes. This difference is due to the smaller energy gap between the emitting and ground levels of the Er(III) ion. The rate constants for the energy transfer from Btz-R to Ln(III) were about approximately 10(9) s(-1), as evaluated by the F?rster resonance energy transfer mechanism.     

Azulene-moiety-based ligand for the efficient sensitization of four near-infrared luminescent lanthanide cations: Nd3+, Er3+, Tm3+, and Yb3+

The ML(4) complexes formed by reaction between the bidentate azulene-based ligand diethyl 2-hydroxyazulene-1,3-dicarboxylate (HAz) and several lanthanide cations (Pr(3+), Nd(3+), Gd(3+), Ho(3+), Er(3+), Tm(3+), Yb(3+), and Lu(3+)) have been synthesized and characterized by elemental analysis, FT-IR vibrational spectroscopy and electrospray ionization mass spectroscopy. Spectrophotometric titrations have revealed that four Az(-) ligands react with one lanthanide cation to form the ML(4) complex in solution. Studies of the luminescence properties of these ML(4) complexes demonstrated that Az(-) is an efficient sensitizer for four different near-infrared emitting lanthanide cations (Nd(3+), Er(3+), Tm(3+), and Yb(3+)); the resulting complexes have high quantum yield values in CH(3)CN. The near-infrared emission arising from Tm(3+) is especially interesting for biologic imaging and bioanalytical applications since biological systems have minimal interaction with photons at this wavelength. Hydration numbers, representing the number of water molecules bound to the lanthanide cations, were obtained through luminescence lifetime measurements and indicated that no molecules of water/solvent are bound to the lanthanide cation in the ML(4) complex in solution. The four coordinated ligands protect well the central luminescent lanthanide cation against non-radiative deactivation from solvent molecules.     

Highly luminescent, triple- and quadruple-stranded, dinuclear Eu, Nd, and Sm(III) lanthanide complexes based on bis-diketonate ligands

The bis(beta-diketone) ligands 1,3-bis(3-phenyl-3-oxopropanoyl)benzene, H(2)L(1) and 1,3-bis(3-phenyl-3-oxopropanoyl) 5-ethoxy-benzene, H(2)L(2), have been prepared for the examination of dinuclear lanthanide complex formation and investigation of their properties as sensitizers for lanthanide luminescence. The ligands bear two conjugated diketonate binding sites linked by a 1,3-phenylene spacer. The ligands bind to lanthanide(III) or yttrium(III) ions to form neutral homodimetallic triple stranded complexes [M(2)L(1)(3)] where M = Eu, Nd, Sm, Y, Gd and [M(2)L(2)(3)], where M = Eu, Nd or anionic quadruple-stranded dinuclear lanthanide units, [Eu(2)L(1)(4)](2-). The crystal structure of the free ligand H(2)L(1) has been determined and shows a twisted arrangement of the two binding sites around the 1,3-phenylene spacer. The dinuclear complexes have been isolated and fully characterized. Detailed NMR investigations of the complexes confirm the formation of a single complex species, with high symmetry; the complexes show clear proton patterns with chemical shifts of a wide range due to the lanthanide paramagnetism. Addition of Pirkle's reagent to solutions of the complexes leads to splitting of the peaks, confirming the chiral nature of the complexes. Electrospray and MALDI mass spectrometry have been used to identify complex formulation and characteristic isotope patterns for the different lanthanide complexes have been obtained. The complexes have high molar absorption coefficients (around 13 x 10(4) M(-1)cm(-1)) and display strong visible (red or pink) or NIR luminescence upon irradiation at the ligand band around 350 nm, depending on the choice of the lanthanide. Emission quantum yield experiments have been performed and the luminescence signals of the dinuclear complexes have been found to be up to 11 times more intense than the luminescence signals of the mononuclear analogues. The emission quantum yields and the luminescence lifetimes are determined to be 5% and 220 micros for [Eu(2)L(1)(3)], 0.16% and 13 micros for [Sm(2)L(1)(3)], and 0.6% and 1.5 micros for [Nd(2)L(1)(3)]. The energy level of the ligand triplet state was determined from the 77 K spectrum of [Gd(2)L(1)(3)]. The bis-diketonate ligand is shown to be an efficient sensitizer, particularly for Sm and Nd. Photophysical studies of the europium complexes at room temperature and 77 K show the presence of a thermally activated deactivation pathway, which we attribute to ligand-to-metal charge transfer (LMCT). Quenching of the luminescence from this level seems to be operational for the Eu(III) complex but not for complexes of Sm(III) and Nd(III), which exhibit long lifetimes. The quadruple-stranded europium complex has been isolated and characterized as the piperidinium salt of [Eu(2)L(1)(4)](2-). Compared with the triple-stranded Eu(III) complex in the solid state, the quadruple-stranded complex displays a more intense emission signal with a distinct emission pattern indicating the higher symmetry of the quadruple-stranded complex.     

Thermal and luminescence characterization of lanthanide 2,6-naphthalenedicarboxylates series

The lanthanide 2,6-naphthalenedicarboxylates series of the formulas Ln₂(ndc)₃·nH₂O, where Ln = lanthanides from La(III) to Lu(III); ndc - C₁₀H₆(COO)₂²⁻; n = 4, 4.5 or 5 have been prepared by the precipitation method. All obtained products were examined and characterized by elemental analysis, FTIR spectroscopy, simultaneous thermal analyses TG-DSC and TG-FTIR, X-Ray diffraction patterns as well as luminescence measurements. The crystalline compounds form three isostructural groups: Ce-Sm; La and Eu-Dy; Ho-Lu. In all complexes, the ndc²⁻ ligand appears in the deprotonated form. Heating of the complexes resulted in the multi-steps decomposition process. The dehydration process leads to the formation of stable crystalline Ln₂ndc₃ compounds which further decompose to the corresponding lanthanide oxides (air atmosphere). In argon atmosphere they decompose with releasing of water, carbon oxides and naphthalene molecules. The luminescence properties of Eu(III), Nd(III), Tb(III) and Er(III) complexes were investigated. The complexes of Eu(III) and Tb(III) emitted red and green light when excited by ultraviolet light whereas Nd(III) and Er(III) display emissions in the NIR region.     

Syntheses and crystal structures of dinuclear complexes containing d-block and f-block luminophores. Sensitization of NIR luminescence from Yb(III), Nd(III), and Er(III) centers by energy transfer from Re(I)- and Pt(II)-bipyrimidine metal centers

Mononuclear complexes [Re(bpym)(CO)(3)Cl] and [Pt(bpym)(CC-C(6)H(4)CF(3))(2)] (bpym = 2,2'-bipyrimidine), in which one of the bipyrimidine sites is vacant, have been used as "complex ligands" to prepare heterodinuclear d-f complexes in which a lanthanide tris(1,3-diketonate) unit is attached to the secondary bipyrimidine site to evaluate the ability of d-block chromophores to act as antennae for causing sensitized near-infrared (NIR) luminescence from adjacent lanthanide(III) centers. The two sets of complexes so prepared are [Re(CO)(3)Cl(mu-bpym)Ln(fod)(3)] (abbreviated as Re-Ln; where Ln = Yb, Nd, Er) and [(F(3)C-C(6)H(4)-CC)(2)Pt(mu-bpym)Ln(hfac)(3)] (abbreviated as Pt-Ln; where Ln = Nd, Gd). Members of both series have been structurally characterized; the metal-metal separation across the bipyrimidine bridge is approximately 6.3 A in each case. In these complexes, the (3)MLCT (MLCT = metal to ligand charge-transfer) luminescences of the mononuclear [Re(bpym)(CO)(3)Cl] and [Pt(bpym)(CC-C(6)H(4)CF(3))(2)] complexes are quenched by energy transfer to those lanthanides (Ln = Yb, Nd, Er) that have low-lying f-f states capable of NIR luminescence; as a result, sensitized NIR luminescence is seen from the lanthanide center following excitation of the d-block unit. In the solid state, quenching of the luminescence from the d-block chromophore is complete, indicating efficient d --> f energy transfer, as a result of the short metal-metal separation across the bipyrimidine bridge. In a CH(2)Cl(2) solution, partial dissociation of the dinuclear complexes into the mononuclear units occurs, with the result that some (3)MLCT luminescence is observed from mononuclear [Re(bpym)(CO)(3)Cl] or [Pt(bpym)(CC-C(6)H(4)CF(3))(2)] present in the equilibrium mixture. Solution UV-vis and luminescence titrations, carried out by the addition of portions of Ln(fod)(3)(H(2)O)(2) or Ln(hfac)(3)(H(2)O)(2) to the d-block complex ligands, indicate that binding of the lanthanide tris(1,3-diketonate) unit at the secondary bipyrimidine site to give the d-f dinuclear complexes occurs with an association constant of ca. 10(5) M(-)(1).     

Isoquinoline-based lanthanide complexes: bright NIR optical probes and efficient MRI agents

In the objective of developing ligands that simultaneously satisfy the requirements for MRI contrast agents and near-infrared emitting optical probes that are suitable for imaging, three isoquinoline-based polyaminocarboxylate ligands, L1, L2 and L3, have been synthesized and the corresponding Gd(3+), Nd(3+) and Yb(3+) complexes investigated. The specific challenge of the present work was to create NIR emitting agents which (i) have excitation wavelengths compatible with biological applications and (ii) are able to emit a sufficient number of photons to ensure sensitive NIR detection for microscopic imaging. Here we report the first observation of a NIR signal arising from a Ln(3+) complex in aqueous solution in a microscopy setup. The lanthanide complexes have high thermodynamic stability (log K(LnL) =17.7-18.7) and good selectivity for lanthanide ions versus the endogenous cations Zn(2+), Cu(2+), and Ca(2+) thus preventing transmetalation. A variable temperature and pressure (17)O NMR study combined with nuclear magnetic relaxation dispersion measurements yielded the microscopic parameters characterizing water exchange and rotation. Bishydration of the lanthanide cation in the complexes, an important advantage to obtain high relaxivity for the Gd(3+) chelates, has been demonstrated by (17)O chemical shifts for the Gd(3+) complexes and by luminescence lifetime measurements for the Yb(3+) analogues. The water exchange on the three Gd(3+) complexes is considerably faster (k(ex)(298) = (13.9-15.4) × 10(6) s(-1)) than on commercial Gd(3+)-based contrast agents and proceeds via a dissociative mechanism, as evidenced by the large positive activation volumes for GdL1 and GdL2 (+10.3 ± 0.9 and +10.6 ± 0.9 cm(3) mol(-1), respectively). The relaxivity of GdL1 is doubled at 40 MHz and 298 K in fetal bovine serum (r(1) = 16.1 vs 8.5 mM(-1) s(-1) in HEPES buffer), due to hydrophobic interactions between the chelate and serum proteins. The isoquinoline core allows for the optimization of the optical properties of the luminescent lanthanide complexes in comparison to the pyridinic analogues and provides significant shifts of the excitation energies toward lower values which therefore become more adapted for biological applications. L2 and L3 bear two methoxy substituents on the aromatic core in ortho and para positions, respectively, that further modulate their electronic structure. The Nd(3+) and Yb(3+) complexes of the ligand L3, which incorporates the p-dimethoxyisoquinoline moiety, can be excited up to 420 nm. This wavelength is shifted over 100 nm toward lower energy in comparison to the pyridine-based analogue. The luminescence quantum yields of the Nd(3+) (0.013-0.016%) and Yb(3+) chelates (0.028-0.040%) are in the range of the best nonhydrated complexes, despite the presence of two inner sphere water molecules. More importantly, the 980 nm NIR emission band of YbL3 was detected with a good sensitivity in a proof of concept microscopy experiment at a concentration of 10 μM in fetal bovine serum. Our results demonstrate that even bishydrated NIR lanthanide complexes can emit a sufficient number of photons to ensure sensitive detection in practical applications. In particular, these ligands containing an aromatic core with coordinating pyridine nitrogen can be easily modified to tune the optical properties of the NIR luminescent lanthanide complexes while retaining good complex stability and MRI characteristics for the Gd(3+) analogues. They constitute a highly versatile platform for the development of bimodal MR and optical imaging probes based on a simple mixture of Gd(3+) and Yb(3+)/Nd(3+) complexes using an identical chelator. Given the presence of two inner sphere water molecules, important for MRI applications of the corresponding Gd(3+) analogues, this result is particularly exciting and opens wide perspectives not only for NIR imaging based on Ln(3+) ions but also for the design of combined NIR optical and MRI probes.     

含2，2＇-联嘧啶桥Ir^III-Ln^III（Ln=Nd，Yb，Er）双金属配合物的合成和光物理性质

选择具有（N^N）（N^N）位点的四齿配体2,2’-联嘧啶fbpm）作为桥联配体,利用铱配合物Ir（dfppy）2（bpm）Cl作为配体与稀土配合物Ln（TTA）3·2H2O配位,得到了Ir^III-Ln^III（Ln=Nd,Yb,Er）双金属配合物[Ir（dfppy）2（bpm）Ln（TTA）3]Cl．通过荧光滴定的方法,测定了该铱配合物与稀土离子之间的络合稳定常数．通过对铱配合物及Ir^III-Ln^III（Ln=Nd,Yb,Er）双金属配合物在可见区光谱的测定,可以观察到明显的铱配合物发光的猝灭,说明从铱中心到稀土中心发生了能量传递．同时,利用可见光选择性激发铱配合物可以获得在稀土Nd^III,Yb^III,E^III离子红外区的发光．说明了铱配合物Ir（dfppy）2（bpm）Cl作为配体可以较好地敏化稀土离子的红外发光．     

A strategy to protect and sensitize near-infrared luminescent Nd3+ and Yb3+: organic tropolonate ligands for the sensitization of Ln(3+)-doped NaYF4 nanocrystals

A strategy to sensitize and protect near-infrared (NIR) emitting Nd3+ and Yb3+ is presented. Combining protection provided by the inorganic matrix of NaYF4 nanocrystals and sensitization from tropolonate ligands capped on their surface, the lanthanide cation centered luminescence was observed through the ligand excitation. The extended lanthanide luminescence lifetimes indicate the success of this strategy.     

Near-infrared emission from novel Tris(8-hydroxyquinolinate)lanthanide(III) complexes-functionalized mesoporous SBA-15

A novel mesoporous material covalently bonded with 8-hydroxyquinoline (HQ) was synthesized (designated as Q-SBA-15). The 5-formyl-8-hydroxyquinoline grafted to (3-aminopropyl)triethoxysilane, that is, alkoxysilane modified 8-hydroxyquinoline (Q-Si), was used as one of the precursors for the preparation of the Q-SBA-15 material. On the basis of the other function of the Q-Si of coordinating to lanthanide (Ln) ions, for the first time, the LnQ 3 complexes (Ln = Er, Nd, Yb) have been covalently bonded to the SBA-15 materials. The derivative materials, denoted as LnQ 3-SBA-15, were characterized by field emission scanning electron microscopy (FE-SEM), powder X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption-desorption, and fluorescence spectra. Upon excitation at the ligands absorption bands, all of these materials show the characteristic near-infrared (NIR) luminescence of the corresponding lanthanide ions through the intramolecular energy transfer from the ligands to the lanthanide ions. The NIR luminescence of these mesoporous materials was compared with that of the corresponding pure LnQ 3 complexes and discussed in detail.     

Synthesis and luminescent properties of novel lanthanide(III) beta-diketone complexes with nitrogen p,p'-disubstituted aromatic ligands

Tris-beta-diketonate lanthanide(III) complexes (Ln = Eu, Er, Yb, Tb), of general formula [Ln(acac)3 L(m)], with chelating ligands such as 4,7-disubstituted-1,10-phenanthrolines and 4,4'-disubstituted-2,2'-bipyridines, have been synthesized and fully characterized. The inductive effects of the para-substituents on the aromatic N-donor ligands have been investigated both in the solid and in the solution states. Single-crystal X-ray structures have been determined for the diethyl 1,10-phenanthroline-4,7-dicarboxylate europium and 4,4'-dimethoxy-2,2'-bipyridine erbium derivatives, revealing a distorted square antiprismatic geometry around the lanthanide atom in both cases. The influence exerted by the p,p'-substituents with respect to the nitrogen coordinating atoms on the Ln-N bond distances is discussed comparing the geometrical parameters with those found for the crystal structures containing the fragments [Ln(III)(phen)] and [Ln(III)(bipy)] obtained from the Cambridge Structural Database. The influence exerted by the electron-attracting groups on the coordination ability of the ligands, that in some cases becomes lack of coordination of the lanthanide ions, has been also detected in solution where the loss of the ligand has been followed by UV-vis spectroscopy. Moreover, the use of relatively long alkoxy chains as substituents on the 1,10-phenanthroline ligand led to the formation of a promesogenic lanthanide complex, whose thermal behavior is encouraging for the synthesis of new lanthanide liquid-crystalline species.     

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   

Comparison of covalency in the complexes of trivalent actinide and lanthanide cations

The complexes of trivalent actinide (Am(III) and Cm(III)) and lanthanide (Nd(III) and Sm(III)) cations with bis(2,4,4-trimethylpentyl)phosphinic acid, bis(2,4,4-trimethylpentyl)monothiophosphinic acid, and bis(2,4,4-trimethylpentyl)dithiophosphinic acid in n-dodecane have been studied by visible absorption spectroscopy and X-ray absorption fine structure (XAFS) measurements in order to understand the chemical interactions responsible for the great selectivity the dithiophosphinate ligand exhibits for trivalent actinide cations in liquid-liquid extraction. Under the conditions studied, each type of ligand displays a different coordination mode with trivalent f-element cations. The phosphinate ligand coordinates as hydrogen-bonded dimers, forming M(HL2)3. Both the oxygen and the sulfur donor of the monothiophosphinate ligand can bind the cations, affording both bidentate and monodentate ligands. The dithiophosphinate ligand forms neutral bidentate complexes, ML3, with no discernible nitrate or water molecules in the inner coordination sphere. Comparison of the Cm(III), Nd(III), and Sm(III) XAFS shows that the structure and metal-donor atom bond distances are indistinguishable within experimental error for similarly sized trivalent lanthanide and actinide cations, despite the selectivity of bis(2,4,4-trimethylpentyl)dithiophosphinic acid for trivalent actinide cations over trivalent lanthanide cations.     

Synthesis and photophysical properties of Ir<Superscript>III</Superscript>-Ln<Superscript>III</Superscript> (Ln = Nd,Yb, Er) bimetallic complexes containing bipyrimidines as bridging ligands

Bipyrimidines have been chosen as (N∧N)(N∧N) bridging ligands for connecting metal centers. Ir^III-Ln^III (Ln = Nd, Yb, Er) bimetallic complexes [Ir(dfppy)₂(μ-bpm)Ln(TTA)₃]Cl were synthesized by using Ir(dfppy)₂(bpm)Cl as the ligand coordinating to lanthanide complexes Ln(TTA)₃·2H₂O. The stability constants between Ir(dfppy)₂(bpm)Cl and lanthanide ions were measured by fluorescence titration. The obvious quenching of visible emission from Ir^III complex in the Ir^III-Ln^III (Ln = Nd, Yb, Er) bimetallic complexes indicates that energy transfer occurred from Ir^III center to lanthanides. NIR emissions from Nd^III, Yb^III, and Er^III were obtained under the excitation of visible light by selective excitation of the Ir^III-based chromophore. It was proven that Ir(dfppy)₂(bpm)Cl as the ligand could effectively sensitize NIR emission from Nd^III, Yb^III, and Er^III.     

Tuning the self-assembly of lanthanide triple stranded heterobimetallic helicates by ligand design

The heterobitopic ligands L(AB4) and L(AB5) have been designed and synthesised with the ultimate aim of self-assembling dual-function lanthanide complexes containing either a magnetic and a luminescent probe or two luminescent probes emitting at different wavelengths. They react with lanthanide ions to form complexes of composition [Ln(2)(L(ABX))(3)](6+) of which three (X = 4; Ln = Pr, Nd, Sm) have been isolated and characterised by means of X-ray diffraction. The unit cells contain triple-stranded helicates in which the three ligand strands are wrapped tightly around the two lanthanide ions. In acetonitrile solution the ligands form not only homobimetallic, but also heterobimetallic complexes of composition [Ln(1)Ln(2)(L(ABX))(3)](6+) when reacted with a pair of different lanthanide ions. The yield of heterobimetallic complexes is analyzed in terms of both the difference in ionic radii of the lanthanide ions and of the inherent tendency of the ligands to form high percentages of head-head-head (HHH) helicates in which all three ligand strands are oriented in the same direction with respect to the Ln-Ln vector. The latter is very sensitive to slight modifications of the tridentate coordinating units.     

Mechanisms of sensitization of lanthanide(III)-based luminescence in transition metal/lanthanide and anthracene/lanthanide dyads

Four sets of dyads are discussed, in all of which near-infrared emitting lanthanide(III) ions such as Nd(III), Er(III) or Yb(III) are energy-acceptors which provide sensitized luminescence following energy-transfer from an antenna group. In three sets of dyads the antenna (energy-donor) group is a luminescent transition metal fragment; in the fourth the antenna is an anthracene group. A combination of photophysical studies and calculations has been used to understand the mechanisms by which energy-transfer to the lanthanide(III) ion occurs. Although definitive answers are not possible in every case due to the presence of several possible energy-transfer pathways, the relative contributions of Förster-type, Dexter-type and redox-mediated energy-transfer pathways have been analysed. Interesting results include (i) the demonstration of pure Dexter energy-transfer over 20 Å in a Ru(II)/Nd(III) dyad, and (ii) the demonstration of a redox-based mechanism for energy-transfer in anthracene/Ln(III) dyads in which the first step is photoinduced electron-transfer from the excited anthracene chromophore to a diimine ligand on the lanthanide(III) to generate a charge-separated state.     

Syntheses,structures, and electroluminescence of Ln(2)(acac-azain)(4)(mu-acac-azain)(2) [acac-azain = 1-(N-7-azaindolyl)-1,3-butanedionato,Ln = Tb(III) and Y(III)

Two new luminescent lanthanide complexes Ln(2)(acac-azain)(4)(mu-acac-azain)(2) [acac-azain = 1-(N-7-azaindolyl)-1,3-butanedionato, Ln = Tb(III), 1, Y(III), 2] have been synthesized and structurally characterized. These two dinuclear complexes are isostructural with the two lanthanide ions being bridged by two acac-azain ligands. Each of the two metal ions is further chelated by four oxygen atoms from two acac-azain ligands, resulting in a coordination number eight for each metal ion. 1 displays characteristic Tb(III) emission bands while 2 displays weak blue luminescence attributable to the ligand. Single-layer and double-layer electroluminescent devices for compound 1 were fabricated, where compound 1 doped PVK layer functions as both the emitting layer and the hole transport layer and PBD functions as an electron transport layer (in the double-layer device), demonstrating that compound 1 is a promising green emitter in electroluminescent devices.