Photoacoustic spectroscopy study on intramolecular energy transfer and relaxation processes of Tb(III) complexes

The photoacoustic (PA) amplitude spectra and luminescence spectra of different Tb(III) complexes (Tb(AA)3.2H2O Na[Tb(AA)4], Tb(AA)3bpy and Tb(AA)3phen) have been measured, and the PA phase shifts of the different complexes calculated. Combined with the luminescence spectra, the PA amplitude spectra reflected the variation of the luminescence efficiency and the PA phase is directly relative to the relaxation processes. According to the variation of the luminescence efficiency and the phase shift, the intramolecular energy transfer and relaxation processes of different Tb(III) complexes were discussed.     

Photoinduced electron transfer competitive with energy transfer of the excited triplet state of [60]fullerene to ferrocene derivatives revealed by combination of transient absorption and thermal lens measurements

The quenching processes of the exited triplet state of fullerene (3C60) by ferrocene (Fc) derivatives have been observed by the transient absorption spectroscopy and thermal lens methods. Although 3C60 was efficiently quenched by Fc in the rate close to the diffusion controlled limit, the quantum yields (phi(et)) for the generation of the radical anion of C60 (C60*-) via 3C60 were quite low even in polar solvents; nevertheless, the free-energy changes (deltaG(et)) of electron transfer from Fc to 3C60 are sufficiently negative. In benzonitrile (BN), the phi(et) value for unsubstitued Fc was less than 0.1. The thermal lens method indicates that energy transfer from 3C60 to Fc takes place efficiently, suggesting that the excited triplet energy level of Fc was lower than that of 3C60. Therefore, energy transfer from 3C60 to ferrocene decreases the electron-transfer process from ferrocene to 3C60. To increase the participation of electron transfer, introduction of electron-donor substituents to Fc (phi(et) = 0.46 for decamethylferrocene in BN) and an increase in solvent polarity (phi(et) = 0.58 in BN:DMF (1:2) for decamethylferrocene) were effective.     

Synthesis, luminescence properties and energy transfer of binary and ternary rare earth complexes with aromatic acids and 1,10-phenanthroline

A series of binary and ternary rare earth (Gd, Eu, Tb) complexes with ortho hydroxyl benzoic acid, para aminobenzoic acid, nicotinic acid and 1,10-phenanthroline were synthesized. Phosphorescence spectra and lifetimes of Gd complexes were measured and the lowest triplet state energies of gadolinium binary complexes and the intramolecular energy transfer efficiencies were determined. The luminescence properties and energy transfer process of Eu3+and Tb3+ complexes were discussed.     

Strong visible up-conversion emission in Tb3+, Tm3+ and Tb3+-Tm3+ co-doped tellurite glasses sensitized by Yb3+

Up-conversion luminescence characteristics under 975 nm excitation have been investigated with Tb3+/Tm3+/Yb3+ triply doped tellurite glasses. Here, green (547 nm: (5)D(4)-->(7)F(4)) and red (660 nm: (5)D(4)-->(7)F(2)) up-conversion (UC) luminescence originating from Tb3+ is observed strongly, because of the quadratic dependences of emission intensities on the excitation power. Especially, the UC luminescence was intensified violently with the energy transfer from the Tm3+ ions involves in the Tb3+ excitation. To the Tb3+/Tm3+/Yb3+ triply doped glass system, a novel up-conversion mechanism is proposed as follows: the energy of (3)G(4) level (Tm3+) was transferred to (5)D(4) (Tb(3+)) and the 477-nm UC luminescence of Tm3+ was nearly quenched.     

Multiply doped nanostructured silicate sol-gel thin films: spatial segregation of dopants, energy transfer, and distance measurements

Physical and chemical strategies that place designed molecules in spatially separated regions of surfactant-templated mesostructured silicate thin films are used to prepare films containing rhodamine 6G (R6G), lanthanide complexes, and both simultaneously. Fluorescence and photoexcitation spectra of R6G in amorphous and structured thin films show that it is located inside the surfactant micelles of structured thin films. A silylated ligand that binds lanthanides condenses to form part of the silica framework and causes the lanthanide to localize in the silica. Luminescence and photoexcitation spectra show that energy transfer from the metal complex to R6G occurs in the films. R6G quenches Tb emission in a concentration-dependent manner. Energy transfer efficiency is calculated using the Tb luminescence lifetime, and this quantity is used to calculate the distance between Tb and R6G with the aid of Forster theory.     

Lanthanides to quantum dots resonance energy transfer in time-resolved fluoro-immunoassays and luminescence microscopy

A time-resolved fluoro-immunoassay (TR-FIA) format is presented based on resonance energy transfer from visible emitting lanthanide complexes of europium and terbium, as energy donors, to semiconductor CdSe/ZnS core/shell nanocrystals (quantum dots, QD), as energy acceptors. The spatial proximity of the donor-acceptor pairs is obtained through the biological recognition process of biotin, coated at the surface of the dots (Biot-QD), and streptavidin labeled with the lanthanide markers (Ln-strep). The energy transfer phenomenon is evident from simultaneous lanthanide emission quenching and QD emission sensitization with a 1000-fold increase of the QD luminescence decay time reaching the hundred mus regime. Delayed emission detection allows for quantification of the recognition process and demonstrated a nearly quantitative association of the biotins to streptavidin with sensitivity limits reaching 1.2 pM of QD. Spectral characterization permits calculation of the energy transfer parameters. Extremely large F?rster radii (R(0)) values were obtained for Tb (104 A) and Eu (96 A) as a result of the relevant spectral overlap of donor emission and acceptor absorption. Special attention was paid to interactions with the varying constituents of the buffer for sensitivity and transfer efficiency optimization. The energy transfer phenomenon was also monitored by time-resolved luminescence microscopy experiments. At elevated concentration (>10(-)(5) M), Tb-strep precipitated in the form of pellets with long-lived green luminescence, whereas addition of Biot-QD led to red emitting pellets, with long excited-state decay times. The Ln-QD donor-acceptor hybrids appear as highly sensitive analytical tools both for TR-FIA and time-resolved luminescence microscopy experiments.     

Characterization of the electronic excited-state energetics and solution structure of lanthanide(III) complexes with the polypyridine ligand 6,6'-bis[bis(2-pyridylmethyl)aminomethyl]-2,2'-bipyridine

Absorption, emission, and excitation spectra for solid-state and solution of Tb(III), Dy(III), and Gd(III) complexes with the polypyridine ligand 6,6'-bis[bis(2-pyridylmethyl)-aminomethyl]-2,2'-bipyridine (C36H34N8) are presented. Measurements of excited-state lifetimes and quantum yields in various solvents at room temperature and 77 K are also reported and used to characterize the excited-state energetics of this system. Special attention is given to the characterization of metal-to-ligand energy transfer efficiency and mechanisms. The measurement of circularly polarized luminescence (CPL) from the solution of the Dy(III) complex following circularly polarized excitation confirms the chiral structure of the complexes under study. No CPL is present in the luminescence from the Eu(III) or Tb(III) complex because of efficient racemization. The variation of the magnitude of the CPL as a function of temperature from an aqueous solution of DyL is used for the first time to characterize the solution equilibria between different chiral species.     

嵌段共聚物PAANa-Dendr. PE聚集体超分子结构中树枝体对铽离子发光增强的天线效应研究

本文研究了两亲嵌段共聚物PAANa-Dendr.PE组成的超分子聚集体,对Tb³⁺离子的天线效应.当PAANa-Dendr.PE聚集体存在时,Tb³⁺的发光强度明显增强.而且增强的幅度正比于树枝体的代数.因此在PAANa-Dendr.PE/Tb³⁺系统中,树枝体作为“光天线”对紫外光能的捕集,通过分子内能量传递,能量沿线性PAANa链从树枝体的三重态传递到Tb³⁺离子.从而使得Tb³⁺的发光大幅度增强.     

在硅磷酸镧中Ce^3＋离子对Tb^3＋离子的敏化

实验表明在La2O3·0.01SiO2·0.95P2O5基质中Ce^3 对Tb^3 有强的敏化作用。254nm紫外光激发下温度对Tb^3 激活的Ce^3 、Tb^3 共激活试样的发射强度的Ce^3 、Tb^3 共激活的试样Tb^3 的^5D4→^7F6:5:4跃迁的发射强度随湿度的变化。计算了Ce^3 到Tb^3 的能量传递效率。初步探讨了Ce对Tb的能量传递机理。     

β-二酮、邻菲罗啉分别与铕和铽三元配合物的合成及发光性能研究

为了寻找新的发光材料并研究β-二酮对稀土配合物发光性能的影响, 我们合成了一个新的β-二酮配体: 1-苯 基-3-(对苯乙炔苯基)-1,3-丙二酮(HPPP), 并用HPPP、邻菲罗啉(phen)分别与Eu(III)和Tb(III)反应, 合成了两个新的三元稀土配合物: Eu(PPP)3phen和Tb(PPP)3phen, 通过红外光谱、化学分析、元素分析对三元稀土配合物的组成和结构进行了表征. 研究了配合物的荧光性质, 发现β-二酮配体对配合物的发光有较大影响, 通过量子化学计算对实验结果进行了解释.     

稀土苯二甲酸配合物的发光性能和分子内能量传递(英文)

合成和表征了一系列稀土（钆，铕，铽）的邻（间）苯二甲酸配合物．通过测定了苯二甲酸配体的钆配合物的低温磷光光谱确定其相应苯二甲酸配体的最低三重态能级．同时详细讨论了配合物的发光性能，能级匹配和分子内能量传递机制．     

Luminescent lanthanide complexes of a bis-bipyridine-phosphine-oxide ligand as tools for anion detection

The Gd(3+), Tb(3+), and Eu(3+) complexes of a bis-bipyridine-phenylphosphine oxide ligand PhP(O)(bipy)(2) 1 (bipy for 6-methylene-6'-methyl-2,2'-bipyridine) have been synthesized. In acetonitrile solutions at room temperature, the Tb(3+) and Eu(3+) complexes show a metal-centered luminescence, indicative of an efficient energy transfer from the two bipy subunits to the Ln center. The photophysical properties drastically depend on the nature of the anions present in solution. In particular, addition of 2 equiv of nitrate anions to a solution containing the [Ln.1](OTf-)(3) leads to an 11-fold increase of the luminescence intensity for the Eu(3+) and a 7-fold increase for the Tb(3+) complexes. Similar effects are provided with Cl-, F-, and CH(3)COO- anions. UV-vis titration experiments were used to determine association constants for binding of, respectively, one, two, and three anions. Stepwise anion addition has also been investigated on the molecular level using quantum mechanical (QM) calculations for the Eu complexes. These calculations reproduce the experimental findings, especially if solvent molecule addition is taken into account. The X-ray crystal structure of the nitrate salt of the Tb complex, as well as QM calculation of a similar Eu complex, demonstrates the coordination of three nitrate anions in a bidentate mode and the step-by-step relegation of the bipy subunits in the second coordination sphere. These features give valuable insights into the mechanism of the overall light amplification process.     

Influence of anionic functions on the coordination and photophysical properties of lanthanide(III) complexes with tridentate bipyridines

A series of four ligands based on a 5'-methyl-2,2'-bipyridyl framework substituted in the 6 position by a carboxylic acid, a phosphonic acid, a monoethyl ester phosphonic acid, or a diethyl ester phosphonic acid are described. The pK(a) values of all ligands and their assignments are determined by a combination of UV-vis absorption spectroscopy and (1)H and (31)P NMR spectroscopy. The ability of the tridentate ligands to form complexes with trivalent lanthanide cations (Ln = La, Nd, Eu, and Lu) in buffered water solutions (Tris-HCl, pH = 7.4) is studied by UV-vis absorption spectroscopy and (1)H NMR. While the two ester ligands display a weak coordination ability toward lanthanide cations, the acid ligands form stable complexes with 1:1, 1:2, and 1:3 Ln/L ratios. A weak selectivity is observed for the middle of the lanthanide series, and the complexes of the phosphonic acid derivative are up to 2 orders of magnitude more stable than those of the carboxylic acid ligand. Photophysical properties of the free phosphonic and carboxylic acid ligands and of their complexes with La, Eu, Gd, Tb, and Lu are investigated in buffered aqueous solutions both at room temperature and 77 K. An efficient ligand-to-metal energy transfer is observed for both the Eu and Tb complexes. Despite a relatively large energy gap between the ligand-centered (3)pipi* and the Eu((5)D(0)) or Tb((5)D(4)) emitting states, the metal-centered luminescence is well sensitized with quantum yields reaching up to 45.5 and 42.2% for the Tb 1:3 complexes with carboxylic and phosphonic acid ligands, respectively.     

Rare earth hybrid materials of organically modified silica covalently bonded to a GaN matrix: multicomponent assembly and multi-color luminescence

Three kinds of rare earth hybrid materials with enhanced thermostability and photoluminescence properties have been prepared for the first time by using a functionalized GaN matrix as one of the building blocks. A number of silane coupling agents (isocyanate triethoxysilane (ICTES), 3-chloropropyl triethoxysilane (CPTES) and 3-aminopropyl triethoxysilane (APTES)) behave as the covalent linkages for modification by both hydroxylation of GaN and functionalized photoactive ligands (4-mercaptobenzoic acid (MBA), 4-hydroxybenzoic acid (HBA) and nitrobenzoyl chloride (NBC)), resulting in the precursors (MBA-ICTES-GaN, HBA-CPTES-GaN and NBC-APTES-GaN). Subsequently, multicomponent photofunctional rare earth hybrid materials with the three precursors and 1,10-phenanthroline (Phen) are assembled and characterized by their FTIR spectra, UV-vis diffuse reflectance spectra, XRD patterns, and photoluminescent behaviour (luminescence, lifetime, quantum efficiency, and energy transfer). These results reveal that the Eu(3+) hybrids with the MBA-ICTES-GaN unit have a better luminescence intensity ratio, higher quantum efficiency and longer lifetime than those with the HBA-CPTES-GaN and NBC-APTES-GaN units. Meanwhile the hybrid Phen-Tb-HBA-CPTES-GaN possesses a stronger characteristic emission of Tb(3+) ions than the other two hybrids (Phen-Tb-MBA-ICTES-GaN and Phen-Tb-NBC-APTES-GaN). Moreover, two-color-based hybrid materials are fabricated by combining different molar ratios of Eu(3+) and Tb(3+) in the same system (Phen-RE-MBA-ICTES-GaN) with emission at a wavelength of 331 nm (RE = Eu, Tb) and yellow luminescence can be achieved.     

GdAlO_3∶Tb,RE中Tb,RE的能量传递研究

采用柠檬酸盐硝酸盐燃烧法制备了GdAlO3∶Tb,RE荧光粉体.在紫外激发下(254nm),GdAlO3∶Tb发射绿色荧光(5D4→7F5,544nm),Dy共掺杂对绿色发光有增强作用,Ce共掺杂对GdAlO3∶Tb绿色发光有降低作用.激发谱和能谱研究表明:Dy能级嵌入Tb主发射能级5D4(绿色发光能级)、5D3(蓝色发光能级)能级之间,Ce能级嵌入Tb主发射能级5D4、5D3能级上方.这种能级嵌入方式,使得稀土离子之间存在声子支持的共振能量传递,但Tb→Dy→Tb能量传递使Tb绿色发射(5D4→7FJ(J=3,4,5,6))增强,蓝色发射(5D3→7FJ(J=3,4,5,6))减弱;而Ce→Tb能量传递使Tb蓝色发射增强,绿色发射减弱.     

稀土N-苯基邻氨基苯甲酸-1,10-邻菲咯啉二元、三元配合物的合成、表征及其光物理性质

合成了几种新型的稀土(钆,铕,铽)的N-苯基邻氨基苯甲酸-1,10-邻菲咯啉的二元、三元配合物.以元素分析、红外光谱和紫外光谱进行了表征,确定了组成.同时以低温磷光光谱确定了配体的三重态能级为24330cm^-1,研究了配体与稀土离子的能级匹配.详细讨论了配合物的光物理性质如发光性能和配体与稀土离子之间以及有机配体之间的分子内能量传递机制,结果发现,铽的N-苯基邻氨基苯甲酸-1,10-邻菲咯啉配合物的发光性能良好.     

Ce3+和Tb3+掺杂的稀土硼酸盐玻璃的发光性质

报道Ｃｅ＾３＋和Ｔｂ＾３＋掺杂的硼酸盐玻璃的合成及该系列玻璃的激发和发射光谱性质。在紫外光激发下,玻璃中的Ｃｅ＾３＋发射蓝紫光,Ｔｂ＾３＋发射有特征的绿光,在Ｃｅ＾３＋和Ｔｂ＾３＋共掺杂的体系中,可观察到Ｃｅ＾３＋强烈敏化Ｔｂ＾３＋发光的现象。分析表明,Ｃｅ＾３＋和Ｔｂ＾３＋之间存在辐射能量传递稿铲无辐射能量传递。     

Bimodal system (luminophore and paramagnetic contrastophore) derived from Ln(III) complexes based on a bipyridine-containing macrocyclic ligand

The synthesis of a new 15-membered polyaza-macrocyclic ligand L3H3, which is based on a 2,2'-bipyridine moiety and a diethylenetriaminetriacetic acid core, is reported. The lanthanide chelates of this octadentate ligand were programmed for bimodal probes, luminescent agents (Sm, Eu, Tb, Dy), and magnetic resonance imaging agents (Gd3+). The neutral 1:1 complexes with these Ln3+ ions were prepared and studied in aqueous solution by luminescence and NMR techniques. The main photophysical characteristics of these complexes (i.e., the absorption and luminescence spectra, the metal-centered lifetimes, and the overall luminescence yields, Phi) were measured. In addition, the role played by nonradiative pathways (vibrational energy transfer involving coordinated water molecules, involvement of ligand-to-metal charge-transfer excited states, or metal --> ligand back transfer) is discussed. The L3.Eu and L3.Tb complexes show very bright luminescence when photoexcited from the lowest-energy absorption band of the bipyridine chromophore. The luminescence quantum yields in an air-equilibrated water solution at room temperature are 0.10 and 0.21, respectively, despite the presence of one water molecule in the first coordination sphere of the metal ion. NMR data show that L3.Gd contains also one H2O molecule in the inner sphere. The proton longitudinal relaxivity, r1, of this complex is 3.4 s(-1) mM(-1) (0.47 T, 310 K) and the rotational correlation time, tau(R), is 57 ps (310 K). These values are comparable to those of the clinically used Gd-DTPA. Interestingly, the water exchange rate between the coordination site and the bulk solvent is slow (tau(M) = 3.5 micros at 310 K). The presence of water molecules in the second sphere and in rapid exchange with the solvent is discussed. Finally, it was found by luminescence and NMR experiments that these lanthanide complexes are stable versus transmetalation by several cations (especially Ca2+ and Zn2+) at physiological pH and have no interaction with blood proteins.     

Highly luminescent Eu(3+) and Tb(3+) macrocyclic complexes bearing an appended phenanthroline chromophore

A two-component ligand system (1) containing 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) as the hosting unit for the lanthanide cations and an appended asymmetrically functionalized 1,10-phenanthroline (phen) as the chromophore was synthesized. The 1:1 complexes with Eu(3+), Gd(3+), Tb(3+), and Yb(3+) have been prepared and studied in aqueous solution. For Gd.1, a relaxivity value of 2.4 mM(-1) s(-1) has been measured at 20 MHz and 25 degrees C, which indicates that there are no water molecules in the first coordination sphere of the metal ion. The analysis of high resolution (1)H NMR spectra of Yb.1 supports this view and suggests the direct involvement of the phen moiety in the coordination of the metal ion. For Eu.1 and Tb.1, the absorption and luminescence spectra, the overall luminescence efficiencies, and the metal-centered (MC) lifetimes were obtained; coordination features were also determined by comparing luminescence properties in water and deuterated water. For Eu.1 and Tb.1, the overall emission sensitization (se) process in air-equilibrated water was found to be notably effective with phi(se) = 0.21 and 0.11, respectively. A detailed study of the steps originating from light absorption at the phen unit and leading to MC sensitized emission was performed.     

Spectral and photophysical characterization of donor-pi-acceptor arylthienyl- and bithienyl-benzothiazole derivatives in solution and solid state

A comprehensive study has been made in solution at room temperature (293 K), low temperature (77 K), and in thin films (Zeonex matrixes) of the spectral and photophysical properties of six arylthienyl- and bithienyl-benzothiazole derivatives functionalized with different donor groups. Similar experiments have been carried out with two related precursors (containing the arylthienyl and aryl-bithienyl conjugated systems), and results are compared. Singlet-singlet and triplet-triplet absorption spectra, emission spectra together with lifetimes and quantum yields have been obtained, and from these data the rates for all the radiative and nonradiative processes determined, providing information on the dominant decay processes. The arylthienyl-benzothiazole derivatives show high fluorescence quantum yields (phi(F)) with negligible internal conversion (phi(IC)), whereas the bithienyl-benzothiazoles display lower but still significant phi(F) values, but now radiationless processes (phi(IC) and phi(ISC)) are competitive. A comparison with the analogous oligothiophenes is made. Singlet oxygen yields were also determined and the triplet energy transfer to (3)O2 to produce (1)O2 was found to be highly efficient with values of S(Delta)(= phi(Delta)/phi(T)) varying from 0.4 to 1.