Structure and NIR luminescence of lanthanide(III) complexes with an organic tridentate ligand

Some lanthanide (Ln) complexes (Ln = Er, Nd, Yb) with an organic ligand, 6-diphenylamine carbonyl 2-pyridine carboxylic acid (HDPAP), have been synthesized. The crystal structure and near infrared luminescence of these complexes (Er-DPAP, Nd-DPAP and Yb-DPAP) have been investigated. The results showed that the lanthanide complexes have electroneutral structures and the near infrared (NIR) emission exhibits characteristic narrow emission of the lanthanide ions. The energy transfer mechanisms in the lanthanide complexes were discussed.     

Synthesis and photoluminescence properties of asymmetrical europium(III) complexes involving carbazole, phenanthroline and bathophenanthroline units

Three novel europium complexes, Eu(CCHPD)₃Phen = Tris[1-(9H-carbazol-9-yl)-3-[(6-(9H- carbazol-9-yl)hexoxy)-phenyl]-1,3-dione](1,10-phenanthroline) europium(III), Eu(CCHPD)₃Bath = Tris[1-(9H-carbazol-9-yl)-3-[(6-(9H-carbazol-9-yl)hexoxy)-phenyl]-1,3-dione](bathophenanthroline) europium(III) and Eu(CPD)₃Phen = Tris[1-(9H-carbazol-9-yl)-3-phenylpropane]-1,3-dione](1,10-phenanthroline) europium(III), have been synthesized and characterized (Scheme 1). Involved ligands consist of different chelating and non-chelating units: appended carbazole (Br-Carb), phenanthroline (Phen), bathophenanthroline (Bath) and 1-(9H-carbazol-9-yl)-3-phenylpropane]-1,3-dione (CPD). The luminescence properties show that the carbazole moiety is a better sensitizer for the metal centred (MC) emitting states relative to Phen and Bath. Moreover, its charge-transporting properties make such complexes appealing for their application in electroluminescent devices.     

The multichromophore approach: A case of temperature controlled switching between single and dual emission in Ru(II) polypyridyl complexes

A new series of ruthenium(II) complexes, based on 4′-(9-anthryl)-2,2′:6′,2″-terpyridine (an-tpy), have been synthesized from the Ru(III) precursor (an-tpy)RuCl₃ (4). These new Ru(II) complexes, [(an-tpy)Ru(tpy-pm-R)] (R = H, 3a; Cl, 3b; phenyl, 3c; p-bromophenyl, 3d), have extended π-conjugation through the 5′-substituted pyrimidyl group, and have been characterized by analytical and spectroscopic methods, and X-ray single crystal structure determination for 3b and 3d. Luminescence lifetime measurements have shown that the anthryl chromophore greatly increases room temperature (r.t.) excited-state lifetime, even though it is not directly connected to the ligand involved in the metal-to-ligand charge transfer (³MLCT) emitting state. This result demonstrates that an equilibrium is established between the anthryl triplet state (³an) and the ³MLCT state even though the two chromophores are physically separated by more than one nanometer. At low temperature in rigid matrix, such equilibrium does not take place and emission arises from both ³an and ³MLCT excited states. The temperature dependence of the excited-state equilibration induces a temperature switch from single (room temperature) to dual (77 K) emission behavior.     

Synthesis and characterization of a novel photoluminescent three-dimensional metal-organic framework

A novel metal-organic framework containing one-dimensional channels of formula [Zn₃(Aco)₂(H₂O)₆]_n (H₃Aco = aconitic acid) has been synthesized and characterized by FT-IR spectroscopy, thermogravimetric analysis (TG), X-ray analysis, and solid state photoluminescence spectra. X-ray crystallographic studies reveal that there are two kinds of crystallographically independent Zn atoms in the title complex. The most interesting feature of the structure is an unprecedented 3D MOF containing infinite Zn(1) linear chains and heterochiral Zn(2) single-stranded helices. The linear chains and helices happen to be perpendicular to each other. Photoluminescence properties of the title compound have been examined in the solid state at room temperature.     

Synthesis and bioluminescence of difluoroluciferin

A new synthesis route to firefly luciferin analogs was developed via the synthesis of 5′,7′-difluoroluciferin. As a luciferase substrate, it produces maximal bioluminescence at a much lower pH than is optimal for native luciferin, and at lower pH it gives much more of the red-shifted emission that is characteristic of the phenolate. These features are attributed to the enhanced acidity of the o,o-difluorophenol.     

Ketimine synthesis in the coordination sphere of thallium (I)

[AuTl(C₆F₅)₂(en)] (en = ethylenediamine) reacts with cyclic ketones as cyclopentanone (Cy⁵O), cyclohexanone (Cy⁶O) or cycloheptanone (Cy⁷O) in 1:1 or 1:2 molar ratio leading to products of stoichiometry [AuTl(C₆F₅)₂{Cy^xN(CH₂)₂NH₂}] (x = 5 1, 6 2 or 7 3), or [AuTl(C₆F₅)₂{Cy^xN(CH₂)₂NCy^x}] (x = 5 4, 6 5 or 7 6). Addition of ethylenediamine to the ketimine complexes in chloroform regenerates [AuTl(C₆F₅)₂(en)], the starting material, and the free ketimines, as their NMR and mass spectra evidenced. The ketimine complexes display luminescence in solid state at room temperature and at 77 K at higher wavelengths than the diamine starting product (505 nm). The excited states responsible for this behaviour are assigned to orbitals due to the gold-thallium interactions.     

Self-assembly of 3-D 4d-4f coordination frameworks based on pyridine-3,5-dicarboxylic acid: Syntheses, crystal structures and luminescence

The hydrothermal reactions of H₂PDC, AgNO₃ with Eu₂O₃ or Tb(NO₃)₃·6H₂O gave rise to two novel three-dimensional 4d-4f heterometallic metal-organic coordination polymers, AgEu(PDC)₂ (1) and AgTb(PDC)₂ (2) (H₂PDC = pyridine-3,5-dicarboxylic acid), and characterized by elemental analysis, IR, thermal analysis and single-crystal X-ray diffraction. Complexes 1 and 2 crystallize in the monoclinic system, P2/c space group; the structure determination reveal that both of them are isostructural and feature an unusual three-dimensional heterometallic network structure in which infinite lanthanide-carboxylate chains are linked by [Ag(PDC)₂]³⁻ metalloligands to form a mixed-metal coordination network. Moreover, the luminescent properties of two complexes have also been investigated at room temperature.     

Synthesis, structures, and luminescence properties of mixed ligand Cd(II) and Zn(II) coordination compounds mediated by 1,2-bis(4-pyridyl)ethane

Interaction of cadmium(II) or zinc(II) acetate with 1,2-bis(4-pyridyl)ethane (bpe) in the presence of dioxime(1,2-cyclohexanedionedioxime = NioxH₂ or diphenylglyoxime = dpgH₂) resulted in three complexes with the compositions [Cd₂(CH₃COO)₄(NioxH₂)₂(bpe)(H₂O)₂] (1), [Cd(CH₃COO)₂(bpe)(H₂O)]_n (2) and [Zn(CH₃COO)₂(NioxH₂)(bpe)(H₂O)]_n (3), which were characterized by single-crystal X-ray diffraction, elemental analysis, IR, and luminescence spectroscopy. Dioxime-containing binuclear molecule 1 and 1D linear polymer 3 possess moderate luminescence properties, while the dioxime-free 1D polymer 2 demonstrates strong blue luminescence.     

Heteroleptic κ(N,C)-2-phenylpyridine platinum complexes: The use of bis(pyrazolyl)borates as ancillary ligands

Luminescent platinum(II) bis(pyrazolyl)borate complexes bearing orthometalated phenylpyridines (based on 2-phenylpyridine, 3-hexyloxy-2-phenylpyridine and (4-(pyridine-2-yl)-phenyl)methanol) and bis(pyrazolyl)borate ligands (employed as potassium dihydridobis(pyrazolyl)borate and potassium dihydridobis(3,5-dimethylpyrazolyl)borate) have been synthesized and characterized. By reaction of K₂PtCl₄ with phenylpyridine ligands a precursor has been obtained which was further converted to the corresponding heteroleptic complexes. All platinum(II) bis(pyrazolyl)borate complexes have been investigated by nuclear magnetic resonance, Fourier transform infrared spectroscopy, thermal analysis and UV-Vis absorption spectroscopy. Luminescence as well as lifetime measurements in solution and in the solid state have been performed to establish a qualitative relationship between structure and luminescence properties. The absorption and emission properties of these complexes are governed by the nature of the orthometalating ligand with emission maxima ranging from 488 to 551 nm. Emission spectra at room temperature show well-resolved vibronic fine structures and a strong spin-orbit coupling. For the compounds under investigation the mixing of the excited states leads to apparent lifetimes in the microsecond regime (5.7-8.6 μs), rendering these materials phosphorescent.     

Effects of bis(salicylidene)trimethylenediamine and 2,2′-bipyridyl on luminescence and extraction of tris(pivaloyltrifluoroacetonato)Eu(III)

The UV, excitation and luminescence spectra of EuA₃B to be the extracted species as well as the extraction of Eu(III) with pivaloyltrifluoroacetone, HA, and/or Lewis bases, B (2,2′-bipyridyl, bpy, and bis(salicylidene)trimethylenediamine, H₂saltn) into CHCl₃ were measured. The results are summarized: the stability constants of EuA₃bpy and EuA₃H₂saltn complexes are 5.85 ± 0.05 and 2.95 ± 0.06 as , respectively. The present results suggest that because of intramolecular hydrogen bonding, the stability and luminescence of the H₂saltn complex including the quantum yield are smaller than those of the bpy complex. The weaker luminescence is also concerned with the fact that the less stable complexes easily dissociate in solvents to diminish the essential concentration.