Sensitized luminescence of Eu and Tb macrocyclic complexes bearing benzophenone antennae

Sensitized luminescence behavior of lanthanide (Ln=Eu³⁺, Tb³⁺) macrocyclic cyclen (1,4,7,10-tetraazacyclododecane) complexes bearing one or four benzophenone (BP) moieties as antenna (LnL1 and LnL4) has been studied in water. Despite higher molar extinction coefficient of EuL4 owing to four antennae, it shows only one-thirtieth the luminescence intensity of EuL1. Energy level of triplet excited-state of BP antenna (E_T) is only a few kJ mol⁻¹ higher than that of ⁵D₂ excited-state of Eu³⁺, thus promoting a back energy transfer (BET) from ⁵D₂ of Eu³⁺ to ground-state BP antennae. On EuL4 bearing four antennae, BET occurs more rapidly than that on EuL1, thus exhibiting much weaker luminescence. For Tb complexes, the energy gap between E_T of BP antenna and ⁵D₄ excited state of Tb³⁺ is large enough (>13 kJ mol⁻¹), such that practically no BET occurs. The luminescence intensity of TbL4 is, however, lower (two-third) than that of TbL1. Time-resolved luminescence measurement reveals that hydration number of Tb³⁺ within TbL4 is twice that within TbL1. This is because the structural distortion of ligands on TbL4, caused by an intramolecular dipole-dipole interaction among the BP antennae, allows coordination of higher number of H₂O molecules to Tb³⁺, thus leading to a strong Tb luminescence quenching via O-H oscillators.     

Eu(III) and Tb(III) luminescent lanthanide systems derived from DTPA-bisamide and DTTA-based ligands incorporating bipyridine antenna

Four new polycarboxylate ligands H₃Lⁿ have been synthesized by the attachment of two or one 2,2′-bipyridine subunits onto a diethylenetriamine pentacarboxylic acid (DTPA-bisamide derivatives: H₃L¹, H₃L²) or a diethylenetriamine tricarboxylic acid (DTTA derivatives: H₃L³, H₃L⁴) core. The neutral Eu^III and Tb^III complexes of these chelates have been prepared and studied from their UV-vis and luminescence data. The main photophysical characteristics of these complexes, i.e. the absorption and luminescence spectra, the metal-centred lifetimes and the overall luminescence yields (Φ) were measured in buffered aqueous solutions. In addition the role played by non-radiative paths (vibrational energy transfer involving coordinated water molecules, involvement of ligand-to-metal charge-transfer excited states, or metal→ligand back-transfer) was investigated. In all complexes, we found that the bidentate bipyridine chromophore is not coordinated to the lanthanide ion, allowing one (LnL¹, LnL²) or two (LnL³, LnL⁴) water molecules to penetrate the first coordination sphere of the metal. Although the bipyridine chromophore behaves as remote (from the binding site) light-harvesting unit for the lanthanide ion in these systems, a sizeable sensitization of the Eu- and Tb-centred luminescence can be effective (LnL², LnL³, Φ=16-19% in aerated D₂O solutions). Our photophysical investigations show that overall non-radiative deactivation is not dependant of thermally activated non-radiative channels but the efficiency of the ligand→Ln intramolecular energy transfer has to be taken into account to explain the obtained results.     

Luminescence and crystal-field fitting of two optical isomeric complexes of europium

FT-IR and Raman vibrational spectra and electronic emission spectra have been recorded for enantiomers of europium complexes with DBM: dibenzoylmethanate 1,2, and TTFA: 2-thenoyltrifluoroacetonate 3,4, employing the chiral ligands L_SS(+)- and L_RR(-)-4,5-pinene bipyridine. Contrary to the previously published X-ray data, where geometrical differences were stated to occur for particular enantiomers, the vibrational (and the emission) spectra of the individual optical isomers of a complex are not distinguishable. Using excitation into the Eu³⁺⁵D₂ multiplet term, the emission intensity is weak from ⁵D₁, whereas a complex structure is observed for the ⁵D₀→⁷F_J transitions. Features in the vibronic sidebands exhibit similar derived vibrational energies to those observed in the Raman spectra. Fittings of 25 4f⁶ crystal-field energy levels of 2 and 4 have been attempted with some approximations concerning the local Eu³⁺ environments. The ⁵D₀ emission lifetimes are monoexponential and are 0.5 (1,2) and 0.9 ms (3,4) at room temperature.     

Synthesis,structures and near-infrared luminescence properties of Ho and Yb coordination complexes

Four Ln³⁺ coordination complexes with the formulas [Ln(p-toluylate)₂(Ac)(H₂O)]_n (Ln=Ho 1, Yb 2) and {[Ln₂(OOCCH₂CH₂COO)₃(H₂O)₄]·6H₂O}_n (Ln=Ho 3, Yb 4) were synthesized hydrothermally. Their structures were determined by single-crystal X-ray diffraction. Complexes 1 and 2 are isomorphic and form infinite 2D network structures comprising p-toluylate and acetate (Ac^–) moieties. Complexes 3 and 4 are also isomorphic and possess infinite 2D structures in which succinate acts as bridging ligands that are connected to a 3D hydrogen bonding network by O–H…O hydrogen bonds. Solid-state IR and UV-Vis-NIR spectra, excitation and emission spectra were determined for the four complexes at room temperature. Complexes 1 and 2 exhibit characteristic NIR emission bands of Ln³⁺ ions but these are shifted and split relative to the theoretical positions. This is also evident for their UV-Vis-NIR spectra. The influence of ligands on enhancing the NIR luminescence of Ln³⁺ ions in complexes is discussed.     

Photophysical properties of a series of high luminescent europium complexes with fluorinated ligands

A series of high luminescent europium complexes have been synthesized, such as Eu(TFNB)₃phen (1), Eu(PFNP)₃phen (2), Eu(HFNH)₃phen (3) and Eu(PFND)₃phen (4), which have β-diketone ligands containing fluorinated alkyl chains with different lengths and conjugated naphthyl groups, i.e., 4,4,4-trifluoro-1-(2-naphthyl)butane-1,3-dione (TFNB); 4,4,5,5,5-pentafluoro-1-(2-naphthyl)pentane-1,3-dione (PFNP); 4,4,5,5,6,6,6-heptafluoro-1-(2-naphthyl)hexane-1,3-dione (HFNH) and 4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-pentadecafluoro-1-(2-naphthyl)decane-1,3-dione (PFND). And 10-phenanthroline (phen) is coordinated as the neutral second ligand in 1-4. The crystal structures of 1 and 2 have been studied, which are typical and similar to that of 3. The results of TGA-DTA suggest that these Eu complexes have good thermal stabilities. By means of absorption and (time resolved) emission spectroscopy including determination of luminescence quantum yields, energy transfer dynamics and so on, the following results have been obtained: first, these Eu complexes show characteristic pure red color photoluminescence emission with high quantum efficiencies from the central Eu³⁺ ions through the excitation of the ligands; secondly, photophysical properties of 1, 2, 3 and 4, especially the lifetimes of excited states ⁵D₀ of Eu³⁺ ions and quantum efficiencies are influenced by the different lengths of fluorinated alkyl chains, though the singlets (S₁) and triplets (T₁) of the fluorinated ligands are almost the same.     

Structural and luminescence studies of trivalent europium complexes with pentaethylene glycol and 18-crown-6 ligands in the presence of picrate anion

Two new isostructural complexes of europium picrate (Eu-Pic) with pentaethylene glycol (EO5) and 18-crown-6 (18C6) ligands formed complexes of molecular formula [Eu(Pic)₂(18C6)]⁺(Pic)⁻I and [Eu(Pic)₂(EO5)]⁺(Pic)⁻II have been isolated and characterised. Compound I showed 10-coordination number through six oxygen atoms from the 18C6 ligand and two bidentate picrate anions. Meanwhile, compound II exhibited 9-coordination number via six oxygen atoms from EO5 ligand, two oxygen atoms from a bidentate and one oxygen atom from monodentate picrate anions. Photoluminescence (PL) spectra of the solid-state europium complexes display sharp lines which are assigned to ⁵D₀→⁷F_0-4 and ⁵D₁→⁷F_1,2,4 transitions. No emission of polyether ligands is observed, indicating that the energy transfer from the polyether ligands to the Eu³⁺ ion is quite efficient. The PL spectra of [Eu(Pic)₂(OH₂)₆]⁺(Pic)⁻·6H₂O III, [Eu(NO₃)₃(OH₂)₃]·(18C6) IV, [Eu(NO₃)₃·6H₂O] V and Eu₂O₃VI are also observed. Compounds I-IV exhibited high Ω₂ intensity parameter values, namely 16.93, 10.23, 17.10 and 12.35 (in units of 10⁻²⁰ cm²), respectively. These relatively high values reflect the hypersensitive behaviour of the ⁵D₀→⁷F₂ transition and indicate that the Eu³⁺ ion is located in a highly polarisable chemical environment.     

Syntheses, structures and photophysical properties of heteronuclear Zn-Ln coordination complexes

Four heteronuclear Zn-Ln coordination complexes, [Nd₂Zn₂(p-toluylate)₁₀(phen)₂] (1), [Ln₂Zn₂(p-toluylate)₁₀(phen)₂]·2(HAc)_1/2 (Ln=Tb 2, Ho 3) and [PrZn₂(p-toluylate)₅(Ac)₂(phen)₂] (4) (phen=1, 10-phenanthroline), are synthesized by the hydrothermal method and their structures are measured by single-crystal X-ray diffraction. The IR and UV-vis-NIR absorption spectra and the emission spectra in the visible and near-infrared (NIR) regions of the four complexes are determined at room temperature. In the NIR region (or in the visible region), the complexes show the characteristic emission bands of Ln³⁺ ions, which may be attributed to sensitization from the ligands (the ligand directly-coordinated to Ln³⁺ ions and d-block) to Ln³⁺ ions after forming the Zn-Ln complexes. It is reported for the first time in this paper that the Zn-Pr complex 4 can exhibit the broad emission band in the NIR region. In addition, the shift, split or broadness of the ff emission bands in the NIR region of complexes 1, 3 and 4 are discussed.     

Three green luminescent cadmium complexes containing 8-aminoquinoline ligands: Syntheses, crystal structures, emission spectra and DFT calculations

Three complexes, Cd(8-aminoql)₂×₂ (8-aminoql=8-aminoquinoline; X⁻=ClO₄⁻, SCN⁻, 1 and 2, respectively) and Cd(8-aminoql)(N₃)₂ (3), were synthesized and structurally characterized. For each complex, the Cd²⁺ ion exhibits distorted octahedral coordination geometry. Two 8-aminoquinoline molecules and two counter-anions are coordinated to the Cd²⁺ center to form a mononuclear species with two trans-ClO₄⁻ anions for 1, while two SCN⁻ anions adopt a cis-configuration for 2. The intermolecular H-bonding interactions between the -NH₂ groups and the O atom (1) and the S atom (2) result in the formation of a 2-D layered structure. In the crystal of 3, the N₃⁻ anions bridging the neighboring Cd(8-aminoql)²⁺ units form a 1-D coordination polymer. The three complexes emit green luminescence. The emission bands possess a broad asymmetric feature, which can be assigned to L′LCT transitions based on DFT and TDDFT calculations.     

An asymmetric imidazole derivative as potential fluorescent chemosensor for Fe in aqueous solution

A novel conjugated molecule, L, based on 2,4,5-triphenylimidazole and 6-phenyl-2,2′-bipyridine (HC^∧N^∧N) was synthesized in two steps. The molecule can recognize Fe³⁺ in aqueous solution (THF/H₂O, 1/1, v/v) by the appearance of new emission bands at 416 and 442 nm, which can be attributed to the emission of the newly formed L-Fe³⁺ complex. The binding constant of the complex was calculated to be (6.6±0.39)×10³ M⁻¹, and its formation was also confirmed by the appearance of isosbestic points at 312 and 381 nm in the UV-visible spectral titration experiment. While other transition and rare-earth metal ions, such as Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Pb²⁺, Eu³⁺ and Nd³⁺, can only cause some decrease of L's fluorescence, alkali and alkaline earth metal ions, such as Li⁺, Na⁺, K⁺, Mg²⁺ and Ca²⁺, almost have no effect on L's fluorescence. The fluorescence of L can be recovered by the addition of EDTA to the L-Fe³⁺ system just due to EDTA's stronger chelating ability than that of L.     

High light electroluminescence of novel Cu(I) complexes

Three novel Cu(I) complexes, [CuDPEphos(NN)]BF₄, where NN=1-(4-5′-phenyl-1,3,4-oxadiazolylbenzyl)-2-pyridinylbenzoimidazole (OXD-Pybm; L1) (1), 1-(4-carbazolylbutyl)-2-pyridinylbenzimidazole (Carl-Pybm; L2) (2), and 1-H-2-pyridinylbenzimidazole (HPybm; L3) (3), were synthesized. The photoluminescent (PL) properties of 1-3 and the electroluminescent (EL) properties of complexes 1 and 2 were systematically studied. The maximum brightness of 2-based devices was 8669 cd/m², which should be the best among the reported Cu(I) complexes-based devices.     

The effect of codopants on spectral-kinetic characteristics of luminescence of scintillation glasses doped with terbium ions

The effect of Ce³⁺ and Pr³⁺ ions on spectral-kinetic characteristics of luminescence of lithium–phosphate–borate glasses is studied. It is shown that terbium ion luminescence caused by transitions from ⁵D₃ and ⁵D₄ multiplets to the ground 7FJ term is detected in samples containing Tb³⁺/Ce³⁺ and Tb³⁺/Pr³⁺. It has been found that an increase in the concentration of cerium ions from 0.2 to 1 wt % leads to an increase in the intensity of main luminescence bands of terbium ions. In Tb³⁺/Pr³⁺ glasses, a decrease in the relative light yield is observed with an increase in the concentration of Pr³⁺ ions. Processes of energy transfer between Tb³⁺/Ce³⁺ and Tb³⁺/Pr³⁺ ions are discussed.     

Photosensitized luminescence of thermostable polynuclear Eu(III) complexes

Tetranuclear europium(III) complexes, [Eu₄(μ-O)(L₁)₁₀] (L₁=2-hydroxy-4-octyloxybenzophenone,1) and [Eu₄(μ-O)(L₂)₁₀] (L₂=2-hydroxy-4-dodecyloxybenzophenone,2) were synthesized by the reaction of lanthanide nitrates with L₁ or L₂ in the presence of triethylamine in methanol. The photosensitized emission bands of the both Eu(III) complexes in THF-d₈ were observed around 579, 590, 615, 653, and 699 nm by the excitation of the ligands at 380 nm, whereas the emission from the mononuclear complex 3 containing ethanol molecules was almost quenched. The emission efficiencies were determined to be 3.1±0.1% for 1 and 3.9±0.1% for 2, respectively. The differential scanning calorimetry (DSC) measurements demonstrated that the decomposition points of 1 and 2 were 309 °C and 320 °C, respectively, indicating high thermostability of these complexes compared to the mononuclear Eu(III) complex 3 (250 °C). New strategy for designing stable rare earth compounds giving strong emission would be emphasized by introducing polynuclear complexes. Polynuclear complexes should open a wide range of molecular design for photosensitized luminescence and thermal stability.     

Spectral-luminescent properties of Eu<Superscript>3+</Superscript> ions in inorganic D<Subscript>2</Subscript>O and POCl<Subscript>3</Subscript>-SnCl<Subscript>4</Subscript> solvents

Absorption and luminescence spectra of Eu³⁺ ions in D₂O and POCl₃-SnCl₄ inorganic solvents were measured. Oscillator strengths and spontaneous radiation transition probabilities for the most intense electron transitions in Eu³⁺ were calculated. Judd-Ofelt parameters, the radiative lifetime of the ⁵ D ₀ metastable level of Eu³⁺ in D₂O-Eu³⁺ and POCl₃-SnCl₄-Eu³⁺ solutions, and matrix elements for radiative transitions from the ⁵ D ₀ level were determined. The luminescence lifetime of the ⁵ D ₀ level of Eu³⁺ in these solutions was measured. The photoluminescence quantum yield for transitions from the ⁵ D ₀ level of Eu³⁺ in ⁵ D ₀ and POCl₃-SnCl₄-Eu³⁺ solutions was found to be 0.32 and 0.88, respectively.     

Intramolecular Energy Transfer and Co-luminescence Effect in Rare Earth Ions (La, Y, Gd and Tb) Doped with Eu3+ β-diketone Complexes

In this paper, Eu³⁺ β-diketone Complexes with the two ligands 1-(2-naphthoyl)-3, 3, 3-trifluoroacetonate (TFNB) and 2’2-bipyridine (bpy) have been synthesized. Furthermore, we reported a systematical study of the co-fluorescence effect of Eu(TFNB)₃bpy doped with inert rare earth ions (La³⁺, Gd³⁺ and Y³⁺) and luminescence ion Tb³⁺. The co-luminescence effect can be found by studying the luminescence spectra of the doped complexes, which means that the existence of the other rare earth ions (La³⁺, Y³⁺, Gd³⁺ and Tb³⁺) can enhance the luminescence intensity of the central Eu³⁺, which may be due to the intramolecular energy transfer between rare earth ions and Eu³⁺. The efficient intramolecular energy transfer in all the complexes mainly occurs between the ligand TFNB and the central Eu³⁺. Full characterization and detail studies of luminescence properties of all these synthesized materials were investigated in relation to co-fluorescence effect between the central Eu³⁺ and other inert ions. Further investigation into the luminescence properties of all the complexes show that the characteristic luminescence of the corresponding Eu³⁺ through the intramolecular energy transfers from the ligand to the central Eu³⁺. Meantime, the differences in luminescence intensity of the ⁵D₀→⁷F₂ transition, in the ⁵D₀ lifetimes and in the ⁵D₀ luminescence quantum efficiency among all the synthesized materials confirm that the doped complex Eu_0.5Tb_0.5(TFNB)₃bpy exhibits higher ⁵D₀ luminescence quantum efficiency and longer lifetime than the pure Eu(TFNB)₃bpy complex and other materials.     

Optical oxygen sensing materials based on trinuclear starburst ruthenium(II) complexes assembled in mesoporous silica

The preparation and oxygen sensing properties of optical materials based on two trinuclear starburst ruthenium(II) complexes: [Ru₃(bpy)₆(TMMB)]⁶⁺ (1) and [Ru₃(phen)₆(TMMB)]⁶⁺ (2) (bpy=2,2′-bpyridine, phen=1,10-phenathroline, TMMB=1,3,5-tris[2-(2′-pyridyl)benzimidazoyl]methylbenzene) assembled in two mesoporous silicate (MS) are described in this paper. The luminescence of Ru complexes/silicate assemble materials can be quenched by molecular oxygen with good sensitivity (I₀/I₁>5 for 2/MS and I₀/I₁>3 for 1/MS), indicating that trinuclear starburst Ru(II) complexes/MS systems are sensitive to oxygen molecules.     

Fluoreszenzlebensdauern und Mehrphononenprozesse in wasserhaltigen Salzen von Eu3+ und Tb3+

The lifetimes of the fluorescent levels⁵ D ₀ and⁵ D ₁ of Eu³⁺ and⁵ D ₄ of Tb³⁺ were measured in the hydrated ethylsulfate, bromate, chloride, nitrate, and sulfate at 4.2°K, 77°K and 300°K. In the case of the ethylsulfate and chloride, the lifetimes were also measured in deuterated crystals and in crystals diluted with diamagnetic Yttrium. The results show that the lifetimes of the fluorescent levels are determined by spontaneous radiationless energy transfer from the rare earth ion to the optical vibrational modes of the water of crystallisation. Assuming a Coulomb interaction between the ion and the surrounding water molecules, the probability for the radiationless transition⁵ D ₁→⁵ D ₀ of the Eu³⁺-ion in the ethylsulfate was calculated in the low temperature limit. The agreement between the theoretical and experimental value is satisfactory. For the probabilities of radiationless desactivation of the fluorescent levels⁵ D ₀ of Eu³⁺ and⁵ D ₄ of Tb³⁺, the empirical form of a product [1] of two factors, one depending only on the rare earth ion and the other only on the lattice, was derived theoretically. Both fluorescent levels are desactivated by a 5-phonon process with the stretching vibrations of the surrounding water molecules.     

Hydrothermal synthesis,characterization, and luminescence of Ca<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>:RE (RE = Eu<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript>, Dy<Superscript>3+</Superscript>) nanofibers

Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers were synthesized by the hydrothermal reaction method. The structural refinement was conducted on the base of the X-ray powder diffraction (XRD) measurements. The surface properties of the Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers were investigated by the measurements such as the scanning electron microscope (SEM), transmission electron microscope (TEM), and the energy dispersive spectrum (EDS). The nanofiber has a diameter of about 100 nm and a length of several micrometers. The luminescence properties such as photoluminescence excitation (PLE) and emission spectra (PL), decay lifetime, color coordinates, and the absolute internal quantum efficiency (QE) were reported. Ca₂B₂O₅:Eu³⁺ nanofibers show the red luminescence with CIE coordinates of (x = 0.41, y = 0.51) and the luminescence lifetime of 0.63 ms. The luminescence of Ca₂B₂O₅:Tb³⁺ nanofibers is green color (x = 0.29, y = 0.53) with the lifetime of 2.13 ms. However, Dy³⁺-doped Ca₂B₂O₅ nanofibers present a single-phase white-color phosphor with the fluorescence decay of 3.05 ms. Upon near-UV excitation, the absolute quantum efficiency is measured to be 65, 35, and 37 % for Eu³⁺-, Tb³⁺-, Dy³⁺-doped Ca₂B₂O₅ nanofibers, respectively. It is suggested that Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers could be an efficient phosphor for lighting and display.     

TOWARDS DEEP AND SIMPLE UNDERSTANDING OF THE TRANSCENDENTAL EIGENPROBLEM OF STRUCTURAL VIBRATIONS

When using exact methods for undamped free vibration problems the generalized linear eigenvalue problem (K−ω²M) D=0 of approximate methods, e.g., finite elements, is replaced by the transcendental eigenvalue problem K (ω) D=0. Here ω is the circular frequency; D is the displacement amplitude vector; M and K are the mass and static stiffness matrices; and K (ω) is the dynamic stiffness matrix, with coefficients which include trigonometric and hyperbolic functions involving ω and mass because elements (for example, bars or beams) are analyzed exactly by solving their governing differential equations. The natural frequencies of this transcendental eigenvalue problem are generally found by the Wittrick-Williams algorithm which gives the number of natural frequencies below ω_t, a trial value of ω, as ∑J_m+s{K (ω_t)} wheres {} denotes the readily computed sign count property of K (ω) and the summation is over the clamped-clamped natural frequencies of all elements of the structure. Understanding the alternative solution forms of the transcendental eigenvalue problem is important both to accelerate convergence to natural frequencies, e.g., by plotting ∣K (ω)∣, and to improve the mode calculations, which lack the complete reliability of natural frequencies obtained by using the Wittrick-Williams algorithm. The three solution forms are: ∣K (ω)∣=0; D=0 with ∣K (ω)∣→∞; and ∣K (ω)∣≠0 with D≠0. The literature covers the first two forms thoroughly but the third form has been almost totally ignored. Therefore, it is now examined thoroughly, principally by analytical studies of simple bar structures and also by confirmatory numerical results for a rigidly jointed plane frame. Although structures are unlikely to have exactly the properties giving this form, it needs to be understood, particularly because ill-conditioning can occur for structures approximating those for which it occurs.     

Nonlinear optical absorption and fluorescence of phosphine-substituted bithiophenes in the violet-blue spectral region

The nonlinear optical absorptions of two 5,5′-bis(diphenylphosphino)-2,2′-bithiophene derivatives, Ph₂(X)P(C₄H₂S)₂P(X)Ph₂ (X = O, 1; S, 2), have been investigated by direct transmission measurement with both picosecond and nanosecond laser pulses from 420 nm to 480 nm. Saturated dichloromethane solutions of 1 and 2 exhibit strong nonlinear optical absorptions in this violet-blue spectral region with that of 2 being stronger at all wavelengths. In the picosecond regime, at 420 nm, the transmittance rapidly falls to 50% when the incident fluence is 0.22 J/cm² for 1 and 0.11 J/cm² for 2. Two-photon absorption appears to be the primary mechanism for this nonlinear absorption. The two-photon absorption coefficients β for 1 (2.1 cm/GW) and 2 (4.4 cm/GM) were obtained by fitting the measurement of transmittance as the function of incident beam intensity at 420 nm. These β values are comparable with some of the best results obtained for organic materials in the green, red and infrared spectral region. Both compounds also show fluorescence with an emission peak at 390 nm for 1 and 400 nm for 2. The fluorescence of 1 is considerably stronger than is that of 2. The combination of the wide band gap and strong fluorescence emission of 1 makes it a promising candidate as a host material for blue organic light emitting diodes.     

A naphthyridine based macrocyclic “switching on” fluorescent receptor for cadmium

A new macrocyclic receptor 1 having [1,8]-naphthyridine fluorophore is designed and synthesized for selective fluorescence sensing of Cd²⁺. Receptor 1 selectively responds to Cd²⁺ over other tested metal ions via a large enhancement of emission intensity due to the cation-induced CHEF (chelation enhanced fluorescence) effect. Receptor 1 although exhibits some affinity towards Zn²⁺, it selectively binds Cd²⁺ over Zn²⁺. Binding and selectivity were examined by ¹H-NMR, fluorescence, UV-vis, mass and IR-spectroscopic techniques.