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Bis-sulfone- and bis-sulfoxide-spirobifluorenes are a promising class of high-triplet-energy electron-acceptor hosts for blue phosphorescent light-emitting devices. The molecular design and synthetic route are simple and facilitate tailoring of the solubilities of the host materials without lowering the high-energy triplet state. The syntheses and characterization (including single-crystal structures) of four electron-accepting hosts are reported; the trend in their reduction potentials is consistent with the electron-withdrawing nature of the sulfone or sulfoxide substituents. Emission maxima of 421–432 nm overlap with the MLCT absorption of the sky-blue emitter bis(4,6-difluorophenyl-pyridinato)(picolinato)iridium(III) (FIrpic), allowing effective energy transfer from the acceptor hosts to FIrpic. Theoretical calculations show that the introduction of sulfone groups leads to better electron acceptors compared to analogous phosphine oxide functionalized hosts and, at the same time, preserves the energy of the lowest-lying triplet above that of the FIrpic emitter. The new hosts have been tested in phosphorescent light-emitting electrochemical cells (LECs). Large effects of the various solubilizing moieties on the device performance are observed and discussed.

We report on charge- and ion-transport ionic hosts made from an imidazolium-cation-modified aryl-1,2,4-triazole, phosphineoxide-carbazole, and phosphineoxide. The hosts are white solids that have short-wavelength absorption cut-off at 28,200 cm(-1)) and that exhibit oxidation at (-2.75) V against ferrocene with a wide redox gap of >3.9 V. (C) 2014 Elsevier B.V. All rights reserved.

The luminescent transition metal complexes [Re(CO)(3)Cl(bppz)] and [Pt(CC-C(6)H(4)CF(3))(2)(bppz)] [bppz = 2,3-bis(2-pyridyl)pyrazine], in which one of the diimine binding sites of the potentially bridging ligand bppz is vacant, have been used as 'complex ligands' to make heterodinuclear d-f complexes by attachment of a {Ln(dik)(3)} fragment (dik = a 1,3-diketonate) at the vacant site. When Ln = Pr, Nd, Er or Yb the lanthanide centre has low-energy f-f excited states capable of accepting energy from the (3)MLCT excited state of the Pt(II) or Re(I) centre, quenching the (3)MLCT luminescence and affording sensitised lanthanide(III)-based luminescence in the near-IR region. UV/Vis and luminescence spectroscopic titrations allowed measurement of (i) the association constants for binding of the {Ln(dik)(3)} fragment at the vacant diimine site of [Re(CO)(3)Cl(bppz)] or [Pt(CC-C(6)H(4)CF(3))(2)(bppz)], and (ii) the degree of quenching of the (3)MLCT luminescence according to the nature of the Ln(III) centre. In all cases Nd(III) was found to be the most effective of the series at quenching the (3)MLCT luminescence of the d-block component because the high density of f-f excited states of the appropriate energy make it a particularly effective energy-acceptor.

Reaction of the potentially bis-bidentate bridging ligand 3,6-bis(2-pyridyl)tetrazine (BPTZ) with various lanthanide complexes [Ln(tta)3(H2O)2] [Htta = thenoyl(trifluoro) acetone; Ln = La, Nd, Gd, Er, Yb] in aqueous ethanol afforded the mononuclear complexes [Ln(tta)3(BPTZ)] (Ln = La, Nd) or the dinuclear complexes [{Ln(tta)3}2(μ-BPTZ)] (Ln = Gd, Er, Yb) in which one or two, respectively, lanthanide tris-diketonate {Ln(tta)3} units are bound to the N,N-bidentate compartments of BPTZ. Crystal structures of the dinuclear complexes [{Yb(tta)3}2(μ-BPTZ)] ·CH2Cl2 and [{Gd(tta)3} 2(μ-BPTZ)]·2CH2Cl2 show that the metal centres have an approximately square-antiprismatic eight-coordinate geometry; there are close contacts above and below the plane of the BPTZ bridging ligand between peripheral trifluoromethyl groups from a tta ligand associated with each metal centre. It is not apparent why the larger lanthanides La and Nd only give a mononuclear complex whereas the smaller lanthanides Gd, Er and Yb give the dinuclear complex in each case. UV/Vis spectroscopic titrations of a solution of BPTZ in CH2Cl2 with increasing amounts of [Ln(tta)3(H2O)2] (Ln = La and Yb) show very similar behaviour, with stepwise binding constants K1 and K2 for association of the two {Ln(tta)3} units of ca. 106 M-1 and 105 M-1; allowing for the expected statistical factor of 4 there is an additional reduction in the value of K2 compared to K1 which may be associated with a steric interaction between the two {Ln(tta)3} units when the dinuclear complex forms. Steady-state and time-resolved luminescence studies on the complexes with Yb, Nd and Er, both in the solid state and CH 2Cl2 solution, show that near-IR luminescence on the microsecond timescale can be sensitised by irradiation either at 337 nm into the tta-based transition, or at 520 nm into the low-energy BPTZ-centred transition. © The Royal Society of Chemistry 2003.

International audience; Homoleptic mononuclear nine-coordinate lanthanum(III) and europium(III) tris-complexes [Ln(N(wedge)N(wedge)O)3].nH2O with two tridentate N-benzylbenzimidazole pyridine-2-carboxylates exhibit a rare C3-symmetry of the lanthanide coordination polyhedron in the solid state, as confirmed by luminescence spectroscopy and by X-ray crystallography (the three N(wedge)N(wedge)O ligands are arranged "up-up-up" around the lanthanide ion). The symmetry, however, is changed to the more common C1 upon dissolution of the complexes in dichloromethane, as revealed by luminescence spectroscopy (the three ligands are likely to be arranged "up-up-down"). The new europium complexes emit efficient ligand-sensitized metal-centered luminescence with excited-state lifetimes of 1.56-2.18 ms and quantum yields of 25-41% in the solid and in solution. The change of the symmetry from (a higher) C3 to (a lower) C1 alters the luminescence spectrum, shortens the radiative lifetime, and increases the luminescence efficiency of the europium complexes.

EZ-C acknowledges the University of St Andrews for financial support. We report four cationic iridium(III) complexes [Ir(C^N)2(dtBubpy)](PF6) that have sulfurpentafluoride-modified 1-phenylpyrazole and 2-phenylpyridine cyclometalating (C^N) ligands (dtBubpy = 4,4'-di-tert-butyl-2,2'-bipyridyl). Three of the complexes were characterized by single-crystal X-ray structure analysis. In cyclic voltammetry, the complexes undergo reversible oxidation of iridium(III) and irreversible reduction of the SF5 group. They emit bright green phosphorescence in acetonitrile solution and in thin films at room temperature, with emission maxima between 482–519 nm and photoluminescence quantum yields of up to 79%. The electron-withdrawing sulfur pentafluoride group on the cyclometalating ligands increases the oxidation potential and the redox gap and blue-shifts the phosphorescence of the iridium complexes more than do the commonly-employed fluoro and trifluoromethyl groups. The irreversible reduction of the SF5 group may be a problem in organic electronics; for example, the complexes do not exhibit electroluminescence in light-emitting electrochemical cells (LEECs). Nevertheless, the complexes exhibit green to yellow-green electroluminescence in doped multilayer organic light-emitting diodes (OLEDs) with emission maxima ranging from 501–520 nm and with an external quantum efficiency (EQE) of up to 1.7% in solution-processed devices. Postprint

We report on seven new anionic benzimidazole-pyridine carboxylate and tetrazolate tridentate (NNO)-N-boolean AND-O-boolean AND and (NNN)-N-boolean AND-N-boolean AND ligands that are modified with chromophore (phenyl, biphenyl, naphthyl) and solubilizing groups. The ligands are UV chromophores with the lowest-energy absorption maxima at 312-335 nm and with the molar absorption coefficients of (20-25) x 10(3) M-1 cm(-1) in DMSO solution. The ligands form neutral complexes with trivalent lanthanides and sensitize the red luminescence of europium. The triplet state energies of the deprotonated ligands, which were measured from the phosphorescence spectra of their lanthanum complexes at 77 K, are in the range of (18.8-21.1) x 10(3) cm(-1). We also describe synthesis of non-symmetric pyridines that are 2,6- and 2,4,6-substituted with hydroxymethyl, carboxaldehyde, and carbonitrile groups. (C) 2014 Elsevier B.V. All rights reserved.