Efficient synthetic route to anhydrous mononuclear tris(8-quinolinolato)lanthanoid complexes for organic light-emitting devices

Quantitative Sensitization Efficiencies in NIR-Emissive Homoleptic Ln(III) Complexes Using 2-(5-Methylpyridin-2-yl)-8-hydroxyquinoline

A series of isostructural lanthanide complexes [Ln(MPQ)₃] (Ln = Nd, Gd, Er, Yb, Lu) using a monoanionic tridentate methylpyridyl-substituted 8-hydroxyquinoline ligand (MPHQ = 2-(5-methylpyridin-2-yl)-8-hydroxyquinoline) have been prepared and characterized using elemental analysis (CHN), single-crystal X-ray diffraction (XRD), and ¹H NMR spectroscopy. This ligand forms homoleptic charge-neutral lanthanide complexes with three coordinated ligands arranged in an "up-up-down" fashion around the metal center. The photophysical properties of the Nd, Er, and Yb complexes were investigated using absorption and emission spectroscopy, with the latter species displaying efficient sensitization in the Near Infra-Red (NIR) region and a photoluminescence quantum yield (PLQY) as high as 1.0% in CH₂Cl₂ solution. The intersystem crossing and energy-transfer processes involved in the antenna effect were further investigated using transient absorption techniques, which revealed essentially quantitative sensitization efficiencies for the NIR-emitting cations.

Construction of lanthanide single-molecule magnets with the “magnetic motif” [Dy(MQ)4]−

[Dy₂(MQ)₄(NO₃)₃]⁺ is SMM-silent (SMM = single-molecule magnet) owing to the unfavourable magnetic interactions. Introducing an additional “magnetic motif” [Dy(MQ)₄]⁻ to diminish such interactions gave a trinuclear [Dy₃(MQ)₈(NO₃)], which behaves as an SMM.

Phenalenyl-based mononuclear dysprosium complexes

The phenalenyl-based dysprosium complexes [Dy(PLN)2(HPLN)Cl(EtOH)] (1), [Dy(PLN)3(HPLN)]·[Dy(PLN)3(EtOH)]·2EtOH (2) and [Dy(PLN)3(H2O)2]·H2O (3), HPLN being 9-hydroxy-1H-phenalen-1-one, have been synthesized. All compounds were fully characterized by means of single crystal X-ray analysis, paramagnetic (1)H NMR, MALDI-TOF mass spectrometry, UV-vis spectrophotometry and magnetic measurements. Both static (dc) and dynamic (ac) magnetic properties of these complexes have been investigated, showing slow relaxation of magnetization, indicative of single molecule magnet (SMM) behavior. Attempts to synthesize sublimable phenalenyl-based dysprosium complexes have been made by implementing a synthetic strategy under anhydrous conditions. The sublimed species were characterized and their thermal stability was confirmed. This opens up the possibility to deposit phenalenyl-based lanthanides complexes by sublimation onto surfaces, an important prerequisite for ongoing studies in molecular spintronics.

Surprisingly bright near-infrared luminescence and short radiative lifetimes of ytterbium in hetero-binuclear Yb-Na chelates

New heterobinuclear lanthanide complexes with benzoxazole-substituted 8-hydroxyquinolines, [Ln(ligand)(2)(mu-ligand)(2)Na] (Ln: Yb, Lu), have been prepared and their structure established by X-ray crystallography, (1)H NMR spectroscopy, and photophysical studies. The complexes display efficient ligand-sensitized near-infrared luminescence of ytterbium at 925-1075 nm with lifetimes and quantum yields as high as 22 micros and 3.7%, in the solid state, and 20 micros and 2.6% in CH(2)Cl(2) solution, respectively. These quantum yields are the highest reported to date for ytterbium complexes with organic ligands containing C-H bonds. A long-wavelength and intense intraligand charge-transfer transition (lambda(max) = 446-456 nm; epsilon approximately 1.2 x 10(4) M(-1) cm(-1)) allows for the excitation of infrared luminescence with visible light up to 600 nm. Remarkable features of these complexes include (i) quantitative ligand-to-Yb(III) energy transfer resulting in high overall efficiency of the ytterbium luminescence, (ii) unusually short radiative lifetime of the Yb(III) ion, 706-745 micros for solutions in CH(2)Cl(2), calculated from the f-f absorption spectra, and 513-635 micros estimated for solid state samples from quantum yield and lifetime data, and (iii) the unexpected large influence of second-sphere composition on the radiative lifetime of ytterbium.

Bis(μ-2-methyl-quinolin-1-ium-8-olato-κO:O')bis-[(2-methyl-quinolin-1-ium-8-olato-κO)tris-(nitrato-κO,O')lanthanum(III)]

The two independent N-heterocycles in the centrosymmetric title compound, [La₂(C₁₀H₉NO)₄(NO₃)₆], exist in the zwitterionic form. One of these binds to one metal center, whereas the other bridges two metal centers. The La atom is chelated by three nitrate groups and is surrounded by nine O atoms in a coordination environment based on a distorted monocapped square-anti­prism. The dinuclear structure is further stabilized by intra­molecular N—H⋯O(nitrate) hydrogen bonds.

Effective and efficient photoluminescence of salicylate-ligating terbium(iii) clusters stabilized by multiple phenyl–phenyl interactions

A luminescent nonanuclear terbium(III) hydroxo cluster, Tb(9)(Hesa)(16)(mu-OH)(10)(NO(3)) (Hesa: hexyl salicylate), stabilized by unique two-way phenyl ring interactions, pi-pi stackings (d = 3.482-3.599 A) and C-H-pi interactions (d = 2.75-3.03 A) between adjacent pairs of salicylates, was structurally characterized based on X-ray analysis, and the favourable absorption change and efficient photoluminescent characteristic were rationalized as being due to J-type pi-pi stackings, which are dramatically enhanced by hexyl groups in hexyl salicylate ligands.