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.     

Calix[4]arene derivative functionalized lanthanide (Eu, Tb) SBA-15 mesoporous hybrids with covalent bonds: assembly, characterization and photoluminescence

Three kinds of novel macrocylic calix[4]arene derivatives functionalized SBA-15 type of mesoporous hybrids (Calix-S15, Calix-NO(2)-S15 and Calix-NH(2)-S15) are synthesized by co-condensation of tetraethoxysilane (TEOS) and modified organic ligand (Calix-Si, Calix-NO(2)-Si and Calix-NH(2)-Si) in the presence of Pluronic P123 surfactant as a template. The structural preservation of these three parent materials is confirmed by FTIR spectra, (29)Si MAS NMR spectra, XRD pattern, and N(2) adsorption-desorption measurements. The ternary mesoporous luminescent hybrids containing Ln(3+) (Eu(3+), Tb(3+)) complexes covalently attached to the functionalized ordered mesoporous SBA-15, which are designated as Ln(Calix-S15)phen, Ln(Calix-NO(2)-S15)phen and Ln(Calix-NH(2)-S15)phen, are obtained by introducing lanthanide ions and 1,10-phenanroline into the corresponding parent material via covalent bond assembling methods. XRD pattern, TEM and N(2) adsorption-desorption measurements are employed to characterize the mesostrcture of the resulting lanthanide mesoporous hybrids. The photoluminescent behavior (luminescence, lifetime, quantum efficiency, and energy transfer) for these chemically bonded mesoporous hybrids is studied in detail. Also, their quantum efficiencies are determined, which indicates that the different mesoporous hybrid material systems derived from different functionalized calix[4]arene derivative bridges present different luminescence behavior.     

Lanthanide (Eu3+, Tb3+) Centered Mesoporous Hybrids with 1,3‐Diphenyl‐1,3‐Propanepione Covalently Linking SBA‐15 (SBA‐16) and Poly(methylacrylic acid)

1,3‐Diphenyl‐1,3‐propanepione (DBM)‐functionalized SBA‐15 and SBA‐16 mesoporous hybrid materials (DBM‐SBA‐15 and DBM‐SBA‐16) are synthesized by co‐condensation of modified 1,3‐diphenyl‐1,3‐propanepione (DBM‐Si) and tetraethoxysilane (TEOS) in the presence of Pluronic P123 and Pluronic F127 as a template, respectively. The as‐synthesized mesoporous hybrid material DBM‐SBA‐15 and DBM‐SBA‐16 are used as the first precursor, and the second precursor poly(methylacrylic acid) (PMAA) is synthesized through the addition polymerization reaction of the monomer methacrylic acid. These precursors then coordinate to lanthanide ions simultaneously, and the final mesoporous polymeric hybrid materials Ln(DBM‐SBA‐15)₃PMAA and Ln(DBM‐SBA‐16)₃PMAA (Ln=Eu, Tb) are obtained by a sol‐gel process. For comparison, binary lanthanide SBA‐15 and SBA‐16 mesoporous hybrid materials (denoted as Ln(DBM‐SBA‐15)₃ and Ln(DBM‐SBA‐16)₃) are also synthesized. The luminescence properties of these resulting materials are characterized in detail, and the results reveal that ternary lanthanide mesoporous polymeric hybrid materials present stronger luminescence intensities, longer lifetimes, and higher luminescence quantum efficiencies than the binary lanthanide mesoporous hybrid materials. This indicates that the introduction of the organic polymer chain is a benefit for the luminescence properties of the overall hybrid system. In addition, the SBA‐15 mesoporous hybrids show an overall increase in luminescence lifetime and quantum efficiency compared with SBA‐16 mesoporous hybrids, indicating that SBA‐15 is a better host material for the lanthanide complex than mesoporous silica SBA‐16.     

Lanthanide-centered organic-inorganic hybrids through a functionalized aza-crown ether bridge: coordination bonding assembly, microstructure and multicolor luminescence

This work focuses on the synthesis of a series of chemically bonded lanthanide/inorganic/organic hybrid materials (CE-15-Si-Ln, CE-16-Si-Ln, CE-18-Si-Ln) containing a novel aza-crown ether organic component. The materials show red emission (Ln = Eu), green emission (Ln = Tb) and near-infrared (NIR) luminescence (Ln = Nd). Three functional molecular precursors (denoted as CE-15-Si, CE-16-Si, CE-18-Si) have been synthesized with two or three N-substituted pendant arms containing chelating groups which can not only fulfill the high coordination numbers of Ln(3+) ions but also form an inorganic Si-O-Si network with tetraethoxysilane (TEOS). The resulting amorphous materials exhibit regular uniform microstructures for the organic and the inorganic components which are covalently linked through Si-O bonds via a self-assembly process. These hybrids present strong luminescent intensities in red, green and NIR ranges by embedding selected Ln(3+) ions into the hybrid system, which may lead to potential applications in organic electroluminescence displays, light emitting devices, functional membranes or chemical/biomedical sensors.     

Near-infrared luminescent hybrid materials doped with lanthanide (Ln) complexes (Ln = Nd, Yb) and their possible laser application

The crystal structures of ternary Ln(DBM)(3)phen complexes (DBM = dibenzoylmethane, phen = 1,10-phenanthroline, and Ln = Nd, Yb) and their in situ syntheses via the sol-gel process are reported. The properties of the Ln(DBM)(3)phen complexes and their corresponding Ln(3+)/DBM/phen-co-doped luminescent hybrid gels obtained via an in situ method (Ln-D-P gel) have been studied. The results reveal that the lanthanide complexes are successfully in situ synthesized in the corresponding Ln-D-P gels. Both Ln(DBM)(3)phen complexes and Ln-D-P gels display sensitized near-infrared (NIR) luminescence upon excitation at the maximum absorption of the ligands, which contributes to the efficient energy transfer from the ligands to the Ln(3+) ions (Ln = Nd, Yb), an antenna effect. The radiative properties of the Nd(3+) ion in a Nd-D-P gel are discussed using Judd-Ofelt analysis, which indicates that the (4)F(3/2) --> (4)I(11/2) transition of the Nd(3+) ion in the Nd-D-P gel can be considered as a possible laser transition.     

Long-lived near-infrared luminescent lanthanide complexes of imidodiphosphinate "shell" ligands

Near-infrared emitting complexes of Nd(III), Er(III), and Yb(III) based on hexacoordinate lanthanide ions with an aryl functionalized imidodiphosphinate ligand, tpip, have been synthesized and fully characterized. Three tpip ligands form a shell around the lanthanide with the ligand coordinating via the two oxygens leading to neutral complexes, Ln(tpip)3. In the X-ray crystal structures of Er(III) and Nd(III) complexes there is evidence of CH-pi interactions between the phenyl groups. Photophysical investigations of solution samples of the complexes demonstrate that all complexes exhibit relatively long luminescence lifetimes in nondeuteurated solvents. Luminescence studies of powder samples have also been recorded for examination of the properties of NIR complexes in the solid state for potential material applications. The results underline the effective shielding of the lanthanide by the twelve phenyl groups of the tpip ligands and the reduction of high-energy vibrations in close proximity to the lanthanide, both features important in the design of NIR emitting lanthanide complexes.     

Luminescence tuning of imidazole-based lanthanide(III) complexes [Ln = Sm, Eu, Gd, Tb, Dy

To tune the lanthanide luminescence in related molecular structures, we synthesized and characterized a series of lanthanide complexes with imidazole-based ligands: two tripodal ligands, tris{[2-{(1-methylimidazol-2-yl)methylidene}amino]ethyl}amine (Me(3)L), and tris{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(3)L), and the dipodal ligand bis{[2-{(imidazol-4-yl)methylidene}amino]ethyl}amine (H(2)L). The general formulas are [Ln(Me(3)L)(H(2)O)(2)](NO(3))(3)·3H(2)O (Ln = 3+ lanthanide ion: Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)), [Ln(H(3)L)(NO(3))](NO(3))(2)·MeOH (Ln(3+) = Sm (6), Eu (7), Gd (8), Tb (9), and Dy (10)), and [Ln(H(2)L)(NO(3))(2)(MeOH)](NO(3))·MeOH (Ln(3+) = Sm (11), Eu (12), Gd (13), Tb (14), and Dy (15)). Each lanthanide ion is 9-coordinate in the complexes with the Me(3)L and H(3)L ligands and 10-coordinate in the complexes with the H(2)L ligand, in which counter anion and solvent molecules are also coordinated. The complexes show a screw arrangement of ligands around the lanthanide ions, and their enantiomorphs form racemate crystals. Luminescence studies have been carried out on the solid and solution-state samples. The triplet energy levels of Me(3)L, H(3)L, and H(2)L are 21?000, 22?700, and 23?000 cm(-1), respectively, which were determined from the phosphorescence spectra of their Gd(3+) complexes. The Me(3)L ligand is an effective sensitizer for Sm(3+) and Eu(3+) ions. Efficient luminescence of Sm(3+), Eu(3+), Tb(3+), and Dy(3+) ions was observed in complexes with the H(3)L and H(2)L ligands. Ligand modification by changing imidazole groups alters their triplet energy, and results in different sensitizing ability towards lanthanide ions.     

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).     

Mesoporous hybrids containing Eu complexes covalently bonded to SBA-15 functionalized: Assembly, characterization and photoluminescence

A novel series of luminescent mesoporous organic-inorganic hybrid materials has been prepared by linking Eu³⁺ complexes to the functionalized ordered mesoporous SBA-15 which was synthesis by a co-condensation process of 1,3-diphenyl-1,3-propanepione (DBM) modified by the coupling agent 3-(triethoxysilyl)-propyl isocyanate (TEPIC), tetraethoxysilane (TEOS), Pluronic P123 surfactant as a template. It was demonstrated that the efficient intramolecular energy transfer in the mesoporous material Eu(DBMSi-SBA-15)₃phen mainly occurred between the modified DBM (named as DBM-Si) and the central Eu³⁺ ion. So the Eu(DBMSi-SBA-15)₃phen showed characteristic emission of Eu³⁺ ion under UV irradiation with higher luminescence quantum efficiency. Moreover, the mesoporous hybrid materials exhibited excellent thermal stability as the lanthanide complex was covalently bonded to the mesoporous matrix.     

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.     

近红外发光稀土配合物及杂化材料研究进展

稀土因其特殊的物理和化学性质,在信息技术、能源技术、生物技术等高科技领域及国防建设等方面都起着非常重要的作用,中国作为稀土大国,十分重视对稀土材料的研究和开发。稀土离子近红外发光(750～1700 nm)在激光和光纤通讯、医学诊断、免疫分析等热门领域的潜在应用,受到了科研人员的极大关注。稀土离子本身发光极弱,通过分子内传能有机配体可以敏化稀土离子发光,但稀土配合物常受外界干扰,其稳定性较差,若将其与凝胶、介孔材料、离子液体等无机基质复合,得到具有良好光、热稳定性和化学稳定性的有机/无机杂化材料。总结了近些年来近红外发光稀土配合物及近红外发光稀土杂化材料的研究进展,并对其发展前景进行了展望。     

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.     

Structural and photophysical properties of coordination networks combining [Ru(bipy)(CN)4]2- anions and lanthanide(III) cations: rates of photoinduced Ru-to-lanthanide energy transfer and sensitized near-infrared luminescence

Co-crystallization of K2[Ru(bipy)(CN)4] with lanthanide(III) salts (Ln = Pr, Nd, Gd, Er, Yb) from aqueous solution affords coordination oligomers and networks in which the [Ru(bipy)(CN)4]2- unit is connected to the lanthanide cation via Ru-CN-Ln bridges. The complexes fall into two structural types: [{Ru(bipy)(CN)4}2{Ln(H2O)m}{K(H2O)n}] x xH2O (Ln = Pr, Er, Yb; m = 7, 6, 6, respectively), in which two [Ru(bipy)(CN)4]2- units are connected to a single lanthanide ion by single cyanide bridges to give discrete trinuclear fragments, and [{Ru(bipy)(CN)4}3{Ln(H2O)4}2] x xH2O (Ln = Nd, Gd), which contain two-dimensional sheets of interconnected, cyanide-bridged Ru2Ln2 squares. In the Ru-Gd system, the [Ru(bipy)(CN)4]2- unit shows the characteristic intense (3)metal-to-ligand charge transfer luminescence at 580 nm with tau = 550 ns; with the other lanthanides, the intensity and lifetime of this luminescence are diminished because of a Ru --> Ln photoinduced energy transfer to low-lying emissive states of the lanthanide ions, resulting in sensitized near-infrared luminescence in every case. From the degree of quenching of the Ru-based emission, Ru --> Ln energy-transfer rates can be estimated, which are in the order Yb (k(EnT) approximately 3 x 10(6) sec(-1), the slowest energy transfer) < Er < Pr < Nd (k(EnT) approximately 2 x 10(8) sec(-1), the fastest energy transfer). This order may be rationalized on the basis of the availability of excited f-f levels on the lanthanide ions at energies that overlap with the Ru-based emission spectrum. In every case, the lifetime of the lanthanide-based luminescence is short (tens/hundreds of nanoseconds, instead of the more usual microseconds), even when the water ligands on the lanthanide ions are replaced by D2O to eliminate the quenching effects of OH oscillators; we tentatively ascribe this quenching effect to the cyanide ligands.     

Structural and near-IR photophysical studies on ternary lanthanide complexes containing poly(pyrazolyl)borate and 1,3-diketonate ligands

The ligands tris[3-(2-pyridyl)pyrazol-1-yl]hydroborate (L1, potentially hexadentate) and bis[3-(2-pyridyl)pyrazol-1-yl]dihydroborate (L2, potentially tetradentate) have been used to prepare ternary lanthanide complexes in which the remaining ligands are dibenzoylmethane anions (dbm). [Eu(L1)(dbm)2] is eight-coordinate, with L1 acting only as a tetradentate chelate (with one potentially bidentate arm pendant) and two bidentate dbm ligands. [Nd(L1)(dbm)2] was also prepared but on recrystallization some of it rearranged to [Nd(L1)2][Nd(dbm)4], which contains a twelve-coordinate [Nd(L1)2]+ cation (two interleaved hexadentate podand ligands) and the eight-coordinate anion [Nd(dbm)4]- which, uniquely amongst eight-coordinate complexes having four diketonate ligands, has a square prismatic structure with near-perfect O8 cubic coordination. Formation of this sterically unfavourable geometry is assumed to arise from favourable packing with the pseudo-spherical cation. The isostructural series of complexes [Ln(L2)(dbm)2](Ln = Pr, Nd, Eu, Gd, Tb, Er, Yb) was also prepared and all members structurally characterised; again the metal ions are eight-coordinate, from one tetradentate ligand L2 and two bidentate dbm ligands. Photophysical studies on the complexes with Ln = Pr, Nd, Er, and Yb were carried out; all show the near-IR luminescence characteristic of these metal ions, with longer lifetimes in CD3OD than in CH3OH. For [Yb(L2)(dbm)2], two species with different luminescence lifetimes were observed in CH3OH solution, corresponding to species with zero or one coordinated solvent molecules, in slow exchange on the luminescence timescale. For [Nd(L2)(dbm)2] a single average solvation number of 0.7 was observed in MeOH. For [Pr(L2)(dbm)2] a range of emission lines in the visible and NIR regions was detected; time-resolved measurements show a particularly high susceptibility to quenching by solvent CH and OH oscillators.     

Synthesis, characterization, and luminescence properties of the ternary europium complex covalently bonded to mesoporous SBA-15

A novel mesoporous SBA-15 type of hybrid material (phen-SBA-15) covalently bonded with 1,10-phenanthroline (phen) ligand was synthesized by co-condensation of tetraethoxysilane (TEOS) and the chelate ligand 5-[N,N-bis-3-(triethoxysilyl)propyl]ureyl-1,10-phenanthroline (phen-Si) in the presence of Pluronic P123 surfactant as a template. The preservation of the chelate ligand structure during the hydrothermal synthesis and the surfactant extraction process was confirmed by Fourier transform infrared (FTIR) and (29)Si MAS NMR spectroscopies. SBA-15 consisting of the highly luminescent ternary complex Eu(TTA)(3)phen (TTA = 2-thenoyltrifluoroacetone) covalently bonded to a silica-based network, which was designated as Eu(TTA)(3)phen-SBA-15, was obtained by introducing the Eu(TTA)(3).2H(2)O complex into the hybrid materials via a ligand exchange reaction. XRD, TEM, and N(2) adsorption measurements were employed to characterize the mesostructure of Eu(TTA)(3)phen-SBA-15. For comparison, SBA-15 doped with Eu(TTA)(3).2H(2)O and Eu(TTA)(3)phen complexes and SBA-15 covalently bonded with a binary europium complex with phen ligand were also synthesized, and were named SBA-15/Eu(TTA)(3), SBA-15/Eu(TTA)(3)phen, and Eu-phen-SBA-15, respectively. The detailed luminescence studies on all the materials showed that, compared with the doping sample SBA-15/Eu(TTA)(3)phen and binary europium complex functionalized sample Eu-phen-SBA-15, the Eu(TTA)(3)phen-SBA-15 mesoporous hybrid material exhibited higher luminescence intensity and emission quantum efficiency. Thermogravimetric analysis on Eu(TTA)(3)phen-SBA-15 demonstrated that the thermal stability of the lanthanide complex was evidently improved as it was covalently bonded to the mesoporous SBA-15 matrix.     

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.     

Highly luminescent bis-diketone lanthanide complexes with triple-stranded dinuclear structure

A new bis-β-diketone, 3,3'-bis(4,4,4-trifluoro-1,3-dioxobutyl)biphenyl (BTB), has been designed and prepared for the synthesis of a series of dinuclear lanthanide complexes [Ln(2)(BTB)(3)(C(2)H(5)OH)(2)(H(2)O)(2)] [Ln = Eu (1), Gd (2)], [Ln(2)(BTB)(3)(DME)(2)] [Ln = Nd (3), Yb (4); DME = ethylene glycol dimethyl ether] and [Eu(2)(BTB)(3)(L)(2)] [L = 2,2-bipydine (5); 1,10-phenanthroline (6); 4,7-diphenyl-1,10-phenanthroline (7)]. Complexes 1-7 have been characterized by various spectroscopic techniques and their photophysical properties are investigated. X-ray crystallographical analysis reveals that complexes 1, 3 and 4 adopt triple-stranded dinuclear structures which are formed by three bis-bidentate ligands with two lanthanide ions. The complexes 1 and 3-7 display strong visible red or NIR luminescence upon irradiation at ligand band around 372 nm, depending on the choice of the lanthanide. The solid-state photoluminescence quantum yields and the lifetimes of Eu(3+) complexes are determined and described.     

Preparation of hybrid mesoporous silica luminescent nanoparticles with lanthanide(III) complexes and their exhibition of white emission

We chose dipicolinic acid as a tridentate chelating unit featuring ONO donors to react with lanthanide(III) ions to yield tight and protective N(3)O(6) environments around the lanthanide(III) ions. We immobilized the lanthanide(III)-dipicolinic acid complexes on colloidal mesoporous silica with diameter smaller than 100 nm by a covalent bond grafting technique and obtained nearly monodisperse luminescent Eu-dpa-Si and Tb-dpa-Si functionalized hybrid mesoporous silica nanomaterials. These hybrid nanomaterials were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, nitrogen adsorption-desorption, and photoluminescence spectroscopic techniques. The hybrid mesoporous silica nanoparticles exhibit intense emission lines upon UV-light irradiation, owing to the effective intramolecular energy transfer from the chromophore to the central lanthanide Eu(3+) and Tb(3+) ions. Furthermore, the functionalized nanomaterials can be turned to white light materials after annealing at high temperature.     

Highly Efficient Visible‐to‐NIR Luminescence of Lanthanide(III) Complexes with Zwitterionic Ligands Bearing Charge‐Transfer Character: Beyond Triplet Sensitization

Two zwitterionic‐type ligands featuring π–π* and intraligand charge‐transfer (ILCT) excited states, namely 1,1′‐(2,3,5,6‐tetramethyl‐1,4‐phenylene)bis(methylene)dipyridinium‐4‐olate (TMPBPO) and 1‐dodecylpyridin‐4(1 H)‐one (DOPO), have been prepared and applied to the assembly of lanthanide coordination complexes in an effort to understand the ligand‐direction effect on the structure of the Ln complexes and the ligand sensitization effect on the luminescence of the Ln complexes. Due to the wide‐band triplet states plus additional ILCT excitation states extending into lower energy levels, broadly and strongly sensitized photoluminescence of f→f transitions from various Ln³⁺ ions were observed to cover the visible to near‐infrared (NIR) regions. Among which, the Pr, Sm, Dy, and Tm complexes simultaneously display both strong visible and NIR emissions. Based on the isostructural feature of the Ln complexes, color tuning and single‐component white light was achieved by preparation of solid solutions of the ternary systems Gd‐Eu‐Tb (for TMPBPO) and La‐Eu‐Tb and La‐Dy‐Sm (for DOPO). Moreover, the visible and NIR luminescence lifetimes of the Ln complexes with the TMPBPO ligand were investigated from 77 to 298 K, revealing a strong temperature dependence of the Tm³⁺ (³H₄) and Yb³⁺ (²F_5/2) decay dynamics, which has not been explored before for their coordination complexes.     

镧系稀土四元配合物Ln(NO_3)_2(phen)_2(CH_3COCHCOCH_3)的合成及晶体结构表征

以乙酰丙酮(Hacac)、邻菲咯啉(phen)、硝酸根为配体,8-羟基喹啉为酸度调节剂合成出一个系列的镧系轻稀土四元配合物Ln(NO3)2(phen)2(CH3COCHCOCH3)(Ln=La,Ce,Pr,Nd,Sm)。配合物的结构与性质由元素分析,IR,1HNMR和TGA等表征。单晶Ce(NO3)2(phen)2(CH3COCHCOCH3)·H2O结构经由X射线衍射仪分析表明,晶体属单斜晶系,空间群P21/n,晶胞参数为a=1.11017(8)nm,b=0.98401(7)nm,c=1.34453(10)nm,β=102.0530(10)°,V=1.43641(18)nm3,Dc=1.715g·cm-3,Z=2,F(000)=742。配合物呈单核结构,中心离子Ce髥配位数为10。