Synthesis and luminescence properties of lanthanide complexes with a new tripodal ligand featuring N‐thenylsalicylamide arms

To explore the relationship between the structure of the ligands and the luminescent properties of the lanthanide complexes, luminescent lanthanide complexes of a new tripodal ligand, featuring N‐thenylsalicylamide arms, were synthesized and characterized by elemental analysis, IR and TGA measurements. Photophysical properties of the complexes were studied by means of UV ? visible absorption and steady‐state luminescence spectroscopy. The results of UV ? vis spectra indicate that metal binding does not disturb the electronic structure of the ligand. Excited‐state luminescence lifetimes and quantum yields of the complexes were determined. The photoluminescence analysis suggested that there is an efficient ligand ? Ln(III) energy transfer for the Tb(III) complex, and the ligand is an efficient 'antenna' for Tb(III). From a more general perspective, the results demonstrated the potential application of the lanthanide complex as luminescent materials in material chemistry. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and luminescence properties of lanthanide complexes with a new tripodal ligands featuring salicylamide arms

A series of luminescent lanthanide complexes with a new tripodal ligand featuring salicylamide arms, 2,2′,2″‐nitrilotris(2‐furfurylaminoformylphenoxy)triethylamine (L), were synthesized and characterized by elemental analysis, IR and molar conductivity measurements. Photophysical properties of the complexes were studied by means of UV–vis absorption and steady‐state luminescence spectroscopy. Excited‐state luminescence lifetimes and quantum yield of the complexes were determined. Luminescence studies demonstrated that the tripodal ligand featuring salicylamide arms exhibits a good antennae effect with respect to the Tb(III) and Dy(III) ion due to efficient intersystem crossing and ligand to metal energy transfer. From a more general perspective, this work offers interesting perspectives for the development of efficient luminescent stains and enlarges the arsenal for developing novel luminescent lanthanide complexes of salicylamide derivatives. Copyright © 2009 John Wiley & Sons, Ltd.     

UV light‐tunable fluorescent inks and polymer hydrogel films based on carbon nanodots and lanthanide for enhancing anti‐counterfeiting

Novel water‐soluble green fluorescent carbon nanodots (CNs) using methacrylic acid and m‐phenylenediamine as precursors were first synthesized using a one‐pot hydrothermal method. Red fluorescent lanthanide complexes were prepared using lanthanide ion Eu³⁺ and pyridine‐2,6‐dicarboxylic acid. The optical properties of CNs were characterized using ultraviolet visible (UV) spectra and fluorescence spectra, microscopic morphology was characterized using transmission electron microscopy (TEM) and dynamic light scattering (DLS), and the elemental composition was characterized using Fourier transform‐infrared spectroscopy (FT‐IR) and X‐ray photoelectron spectra (XPS). The fluorescence spectra of the lanthanide complexes were also measured. A simple strategy was developed to prepare UV light‐tunable fluorescent inks and polymer hydrogels films based on CNs and lanthanide complexes. The fluorescent inks and polymer hydrogels films could be repeatedly switched between green and red fluorescence. The change of color depended on luminescence of the CNs and the lanthanide complexes under 254 and 365 nm UV light, respectively. The UV light‐tunable fluorescent inks and polymer hydrogels films could enhance its anti‐counterfeiting function for data and information.     

Visible‐near‐infrared luminescent lanthanide ternary complexes based on beta‐diketonate using visible‐light excitation

We used the synthesized dinaphthylmethane (Hdnm) ligand whose absorption extends to the visible‐light wavelength, to prepare a family of ternary lanthanide complexes, named as [Ln(dnm)₃phen] (Ln = Sm, Nd, Yb, Er, Tm, Pr). The properties of these complexes were investigated by Fourier transform infrared (FT‐IR) spectroscopy, diffuse reflectance (DR) spectroscopy, thermogravimetric analyses, and excitation and emission spectroscopy. Generally, excitation with visible light is much more advantageous than UV excitation. Importantly, upon excitation with visible light (401–460 nm), the complexes show characteristic visible (Sm³⁺) as well as near‐infrared (Sm³⁺, Nd³⁺, Yb³⁺, Er³⁺, Tm³⁺, Pr³⁺) luminescence of the corresponding lanthanide ions, attributed to the energy transfer from the ligands to the lanthanide ions, an antenna effect. Now, using these near‐infrared luminescent lanthanide complexes, the luminescent spectral region from 800 to 1650 nm, can be covered completely, which is of particular interest for biomedical imaging applications, laser systems, and optical amplification applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Characterization of tetrakis(thiadiazole)porphyrazine metal complexes by magnetic circular dichroism and magnetic circularly polarized luminescence

The magnetic circular dichroism (MCD) spectra of metal complexes of tetrakis(thiadiazole)porphyrazines ([TTDPzM] with M = 2H^I, Zn^II, Mg^II(H₂O), and Cd^II) have been recorded in dimethyl formamide solution. Together with the UV–Vis spectra, the MCD spectra provide useful information about the structure and electronic properties of the complexes. The experimental UV–Vis and MCD spectra compare pretty well with DFT calculations of two sorts, based either on the sum-over-states (SOS) approach or on the complex polarization propagator approach. They further corroborate the findings and interpretation of MCD spectra of porphyrazines based on the model of Michl for peripheral molecular orbitals. Magnetic circularly polarized luminescence (MCPL) spectra, quite uncommon in the literature, have been recorded for [TTDPzM] (M = 2H^I, Zn^II, Mg^II(H₂O)).     

Electronic absorption and MCD spectra for octacyanometallate complexes M(CN)8, M=Mo(IV), W(IV), n=4 and Mo(V), W(V), n=3

Electronic absorption and 8.0 T magnetic circular dichroism (MCD) spectra are reported for M(CN)₈ ⁴⁻, M=Mo(IV) and W(IV), in aqueous solution and M(CN)₈ ³⁻, M=Mo(V) and W(V), in acetonitrile solutions. In addition some absorption and MCD spectra are reported for the M(CN)₈ ³⁻ ions embedded in thin poly methyl methacrylate (PMMA) plastic films at temperatures from 295 to 10 K. The temperature dependence of the MCD spectra confirms the presence of C terms. The solution and PMMA spectra for the both Mo and W complexes in either the IV or V oxidation states are remarkably similar to each other for the same oxidation state and are interpreted within a D_2d structural framework for the isotropic environment. The weak bands below 3.0 μm⁻¹ (1 μm⁻¹=10⁴ cm⁻¹) for the M(IV) complexes are assigned as metal-localized ligand field (LF) transitions. LF transitions are also suggested for weaker unresolved absorption between 3.0 and 3.6 μm⁻¹ for the M(V) ions. The intense bands above 3.6 μm⁻¹ for M(IV) and 4.6 μm⁻¹ for M(V) complexes are interpreted as metal to ligand charge transfer (MLCT) from the metal b₁(x²−y²) HOMO to CN⁻-based π * orbitals. The prominent intense bands observed below 4.5 μm⁻¹for the M(V) complexes are assigned as ligand to metal charge transfer (LMCT) from occupied non-bonding or weakly π bonding CN⁻ orbitals to the half-filled b₁(x²−y²) HOMO.     

Synthesis,characterization and luminescent properties of lanthanide complexes with an unsymmetrical tripodal ligand

Solid complexes of lanthanide nitrates with an novel unsymmetrical tripodal ligand, butyl‐N,N‐bis[(2′‐benzylaminofomyl)phenoxyl)ethyl]‐amine ( L ) have been synthesized and characterized by elemental analysis, infrared spectra and molar conductivity measurements. At the same time, the luminescent properties of the Sm(III), Eu(III), Tb(III) and Dy(III) nitrate complexes in solid state were also investigated. Under the excitation of UV light, these complexes exhibited characteristic emission of central metal ions. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis,characterization and luminescent properties of europium complexes with 2,4,6‐tris‐(2‐pyridyl)‐s‐triazine as highly efficient sensitizers

Using 2,4,6‐tris‐(2‐pyridyl)‐s‐triazine (TPTZ) as a neutral ligand, and p‐hydroxybenzoic acid, terephthalic acid and nitrate as anion ligands, five novel europium complexes have been synthesized. These complexes were characterized using elemental analysis, rare earth coordination titrations, UV/vis absorption spectroscopy and infrared spectroscopy. Luminescence spectra, luminescence lifetime and quantum efficiency were investigated and the mechanism discussed in depth. The results show that the complexes have excellent emission intensities, long emission lifetimes and high quantum efficiencies. The superior luminescent properties of the complexes may be because the triplet energy level of the ligands matches well with the lowest excitation state energy level of Eu³⁺. Moreover, changing the ratio of the ligands and metal ions leads to different luminescent properties. Among the complexes, Eu₂(TPTZ)₂(C₈H₄O₄)(NO₃)₄(C₂H₅OH)·H₂O shows the strongest luminescence intensity, longest emission lifetime and highest quantum efficiency. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis and characterization of pure and Li+ activated Alq3 complexes for green and blue organic light emitting diodes and display devices

Pure and Li⁺‐doped Alq₃ complexes were synthesized by simple precipitation method at room temperature, maintaining the stoichiometric ratio. These complexes were characterized by X‐ray diffraction, ultraviolet‐visible absorption and Fourier transform infrared and photoluminescence (PL) spectra. X‐ray diffraction analysis reveals the crystalline nature of the synthesized complexes, while Fourier transform infrared spectroscopy confirm the molecular structure, the completion of quinoline ring formation and presence of quinoline structure in the metal complex. Ultraviolet‐visible and PL spectra revealed that Li⁺ activated Alq₃ complexes exhibit the highest intensity in comparison to pure Alq₃ phosphor. Thus, Li⁺ enhances PL emission intensity when doped into Alq₃ phosphor. The excitation spectra lie in the range of 383–456 nm. All the synthesized complexes other than Liq give green emission, while Liq gives blue emission with enhanced intensity. Thus, he synthesized phosphors are the best suitable candidates for green‐ and blue‐emitting organic light emitting diode, PL liquid‐crystal display and solid‐state lighting applications. Copyright © 2013 John Wiley & Sons, Ltd.     

A study of the K+-site mutant of ascorbate peroxidase: mutations of protein residues on the proximal side of the heme cause changes in iron ligation on the distal side

A series of ferric and ferrous derivatives of wild-type ascorbate peroxidase (APX) and of an engineered K⁺-site mutant of APX that has had its potassium cation binding site removed have been examined by electronic absorption and magnetic circular dichroism (MCD) spectroscopy at 4??°C. Wild-type ferric APX has spectroscopic properties that are very similar to those of ferric cytochrome c peroxidase (CCP) and likely exists primarily as a five-coordinate high-spin heme ligated on the proximal side by a histidine at pH 7. There is also evidence for minority contributions from six-coordinate high- and low-spin species (histidine-water, histidine-hydroxide, and bis-histidine). The K⁺-site mutant of APX varies considerably in the electronic absorption and MCD spectra in both the ferric and ferrous states when compared with spectra of the wild-type APX. The electronic absorption and MCD spectra of the engineered K⁺-site APX mutant are essentially identical to those of cytochrome b ₅, a known bis-imidazole (histidine) ligated heme system. It therefore appears that the K⁺-site mutant of APX has undergone a conformational change to yield a bis-histidine coordination structure in both the ferric and ferrous oxidation states at neutral pH. This conformational change is the result of mutagenesis of the protein to remove the K⁺-binding site which is located ～8?Å from the peroxide binding pocket. Thus, mutations of protein residues on the proximal side of the heme cause changes in iron ligation on the distal side.     

Novel Na+ doped Alq3 hybrid materials for organic light‐emitting diode (OLED) devices and flat panel displays

Pure and Na⁺‐doped Alq₃ complexes were synthesized by a simple precipitation method at room temperature, maintaining a stoichiometric ratio. These complexes were characterized by X‐ray diffraction, Fourier transform infrared (FTIR), UV/Vis absorption and photoluminescence (PL) spectra. The X‐ray diffractogram exhibits well‐resolved peaks, revealing the crystalline nature of the synthesized complexes, FTIR confirms the molecular structure and the completion of quinoline ring formation in the metal complex. UV/Vis absorption and PL spectra of sodium‐doped Alq₃ complexes exhibit high emission intensity in comparison with Alq₃ phosphor, proving that when doped in Alq₃, Na⁺ enhances PL emission intensity. The excitation spectra of the synthesized complexes lie in the range 242–457 nm when weak shoulders are also considered. Because the sharp excitation peak falls in the blue region of visible radiation, the complexes can be employed for blue chip excitation. The emission wavelength of all the synthesized complexes lies in the bluish green/green region ranging between 485 and 531 nm. The intensity of the emission wavelength was found to be elevated when Na⁺ is doped into Alq₃. Because both the excitation and emission wavelengths fall in the visible region of electromagnetic radiation, these phosphors can also be employed to improve the power conversion efficiency of photovoltaic cells by using the solar spectral conversion principle. Thus, the synthesized phosphors can be used as bluish green/green light‐emitting phosphors for organic light‐emitting diodes, flat panel displays, solid‐state lighting technology – a step towards the desire to reduce energy consumption and generate pollution free light. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and luminescence properties of polymer–rare earth complexes containing salicylaldehyde‐type bidentate Schiff base ligand

Using molecular design and polymer reactions, two types of bidentate Schiff base ligands, salicylaldehyde–aniline (SAN) and salicylaldehyde–cyclohexylamine (SCA), were synchronously synthesized and bonded onto the side chain of polysulfone (PSF), giving two bidentate Schiff base ligand‐functionalized PSFs, PSF–SAN and PSF–SCA, referred to as macromolecular ligands. Following coordination reactions between the macromolecular ligands and Eu(III) and Tb(III) ions (the reaction occurred between the bonded ligands SAN or SCA and the lanthanide ion), two series of luminescent polymer–rare earth complexes, PSF–SAN–Eu(III) and PSF–SCA–Tb(III), were obtained. The two macromolecular ligands were fully characterized by Fourier transform infrared (FTIR), ¹H NMR and UV absorption spectroscopy, and the prepared complexes were also characterized by FTIR, UV absorption spectroscopy and thermo‐gravity analysis. On this basis, the photoluminescence properties of these complexes and the relationships between their structure and luminescence were investigated in depth. The results show that the bonded bidentate Schiff base ligands, SAN and SCA, can effectively sensitize the fluorescence emission of Eu(III) and Tb(III) ions, respectively. PSF–SAN–Eu(III) series complexes, namely the binary complex PSF–(SAN)₃–Eu(III) and the ternary complex PSF–(SAN)₃–Eu(III)–(Phen)₁ (Phen is the small‐molecule ligand 1,10‐phenanthroline), produce strong red luminescence, suggesting that the triplet state energy level of SAN is lower and well matched with the resonant energy level of the Eu(III) ion. By contrast, PSF–SAN–Eu(III) series complexes, namely the binary complex PSF–(SCA)₃–Tb(III) and the ternary complex PSF–(SCA)₃–Tb(III)–(Phen)₁, display strong green luminescence, suggesting that the triplet state energy level of SCA is higher and is well matched with the resonant energy level of Tb(III).     

Chiroptical Spectra of Tetrakis (+)‐3‐Heptafluorobutylrylcamphorate Ln(III) Complexes with an Encapsulated Alkali Metal Ion: Solution Structures as Revealed by Chiroptical Spectra

The preparation of tetrakis((+)‐hfbc) lanthanide(III) complexes with an encapsulated alkali metal and ammonium ions M[Ln((+)‐hfbc)₄] (hereafter abbreviated as M‐Ln : (+)‐hfbc, (+)‐heptafluorobutyrylcamphorate; M, ammonium or benzyl ammonium ions as well as alkali metal ions) was reported and discussed. The electronic circular dichroism (CD) spectra in the intraligand π?π* transition of M–Ln were examined in view of the solvent effect. Here, the concentration, alkali metal, and ammonium ion dependences are compared with the solid CD, ⁵D₀ ← ⁷F₀(Eu(III)) excitation spectra, circularly polarized luminescence, and vibrational circular dichroism. It has been revealed that the dodecahedral eight coordinate DD‐8‐M‐Ln complexes in crystals are equilibrated between the diastereoselectively formed square antiprism eight coordinate SAPR‐8‐M‐Ln and [Ln((+)‐hfbc)₃] in EtOH and CH₃CN solutions or between the SAPR‐8‐M‐Ln and DD‐D_2d(mmmm)‐8‐M‐Ln complexes in CHCl₃ solution. The observed CD couplets are found to reflect the exciton CD couplets which are useful to determine the four‐bladed SAPR‐(llll) absolute configuration around the lanthanide(III) ion. Chirality 24:1055–1062, 2012. © 2012 Wiley Periodicals, Inc.     

Lanthanide Circularly Polarized Luminescence: Bases and Applications

Lanthanide (III) luminescence is very characteristic: it is characterized by narrow emission bands, large Stokes shift, and a long excited state lifetime. Moreover, chiral lanthanide complexes can emit strongly circularly polarized light in a way that is almost precluded to purely organic molecules. Thanks to the sensitivity and specificity of the Ln circularly polarized luminescence (CPL) signal, CPL‐active complexes are therefore employed as bioanalytical tools and other uses can be envisaged in many other fields. Here we present a brief overview of the most recently developed CPL‐active lanthanide complexes and a selected few examples of their applications. We briefly discuss the main mechanisms that can rationalize the observed outstanding CPL properties of these systems, and some practical suggestions on how to measure and report data. Chirality 27:1–13, 2015. © 2014 Wiley Periodicals, Inc.     

A ligand field model for MCD spectra of biological cupric complexes.

A ligand field calculation of magnetic circular dichroism (MCD) spectra is described that provides new insights into the information contained in electronic spectra of copper sites in metalloenzymes and synthetic analogs. The ligand field model uses metal-centered p- and f-orbitals to model sigma, pi LMCT mixing mechanism for intensity, allowing the basic features of optical absorption, MCD, and electron paramagnetic resonance spectra to be simultaneously computed from a single set of parameters and the crystallographically determined ligand coordinates. We have used the model to predict changes in spectra resulting from the transformation of electronic wavefunctions under systematic variation in geometry in pentacoordinate ML5 complexes. The effectiveness of the calculation is demonstrated for two synthetic copper model compounds and a galactose oxidase enzyme complex representing limiting coordination geometries. This analysis permits immediate recognition of characteristic patterns of MCD intensity and correlation with geometry. A complementarity principle between MCD and CD spectra of transition metal complexes is discussed.     

Lanthanide Tris(β‐diketonates) as Useful Probes for Chirality Determination of Biological Amino Alcohols in Vibrational Circular Dichroism: Ligand to Ligand Chirality Transfer in Lanthanide Coordination Sphere

A series of lanthanide tris(β‐diketonates) functioned as useful chirality probes in the vibrational circular dichroism (VCD) characterization of biological amino alcohols. Various chiral amino alcohols induced intense VCD signals upon ternary complexation with racemic lanthanide tris(β‐diketonates). The VCD signals observed around 1500 cm^?1 (β‐diketonate IR absorption region) correlated well with the stereochemistry and enantiomeric purity of the targeted amino alcohol, while the corresponding monoalcohol, monoamine, and diol substrates induced very weak VCD signals. The high‐coordination number and dynamic property of the lanthanide complex offer an effective chirality VCD probing of biological substrates. Chirality 26:293–299, 2014. © 2014 Wiley Periodicals, Inc.     

Synthesis,photoluminescence properties and theoretical insights on 1,3‐diphenyl‐5‐(9‐anthryl)‐2‐pyrazoline and ‐1H‐pyrazole

1,3‐Diphenyl‐5‐(9‐anthryl)‐2‐pyrazoline and 1,3‐diphenyl‐5‐(9‐anthryl)‐1H‐pyrazole with an anthryl chromophore were synthesized and characterized using ¹H NMR, ¹³C NMR, FT‐IR, mass spectrometry and elemental analysis. Their optical properties were characterized by UV–vis absorption and fluorescence spectroscopy. It was observed that the absorption and fluorescence spectra of the two compounds showed a red shift with respect to that of anthracene. Pyrazole exhibited high fluorescent quantum yields (Φ_f = 0.90 in toluene) while pyrazoline showed nearly no fluorescence in solution. The significant fluorescence divergence of the two similar compounds was investigated theoretically through density functional theory (DFT) calculations. The energetically lowest‐lying state S₁ in the pyrazoline exhibited both characteristics of locally excited and electron‐transfer states that resulted in the fluorescence quenching of anthryl chromophore whereas the S₁ state in the pyrazole corresponded to an optically allowed state that led to high fluorescence quantum yields in solutions. Copyright © 2012 John Wiley & Sons, Ltd.     

Photoluminescent properties of novel design heteroleptic Zn(II) complexes

Three novel heteroleptic Zn(II) complexes containing 8‐hydroxy quinoline and various pyrazolone‐based derivatives were synthesized and their structures confirmed by ¹H–nuclear magnetic resonance, mass spectrometry, Fourier transform infra‐red spectroscopy, UV–vis analysis and element analysis. All three complexes showed good photoluminescence properties in the solid state and in solution in the maximum emission range from 475 to 490 nm with a quantum yield of 0.45 to 0.51. Absorption spectra revealed that the complexes possessed a maximum absorption range of 272–281 nm with a band gap of 2.59–2.68 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital of all the complexes were determine by cyclic voltammetry. All complexes displayed high thermal stability. These characteristics were assessed to find suitability for an alternative cheap light emitter for organic light‐emitting diodes.     

The synthesis and characterization of nucleotide complexes involving an asymmetric metal

The synthesis of cobalt and chromium complexes of H₄ATP and H₄GTP in which the metal is asymmetric are reported. These compounds were characterized by visible spectroscopy, fast atom bombardment mass spectroscopy (FAB MS), and ³¹P NMR. The mass spectral data allow identification of the complexes to be made from ions in the molecular weight region. The effect of an asymmetric metal greatly alters the appearance of the ³¹P NMR spectra in comparison to complexes which do not have this feature. Complexes of uridine diphosphoglucose, UDPG, are also reported. The effect of an asymmetric metal ion on the chromatographic and spectral properties of the complexes are discussed.     

Magnetic circular dichroism and spin equilibrium of methemoglobin and its subunits

The intensity of the Soret magnetic circular dichroism (MCD) spectra of various complexes of methemoglobin subunits (α⁺ and β⁺) as well as methemoglobin (metHb A) was correlated well with the spin states of ferric heme. Upon the subunit association, spin state transition toward higher spin was observed only in high spin derivatives and the changes in spin state were due to mainly those of β⁺ chains. The effect of an allostric effector, inositol hexaphosphate (IHP), on the MCD spectra of metHb A derivatives was observed much significantly for high spin forms than low spin ones.