Practical syntheses of N-hexylcarbazol-2-yl- and -3-yl-boronic acids, their cross-coupled products and a derived tris-cyclometalated (pyridin-2-yl)carbazole iridium(III) complex

The syntheses of N-hcxylcarbazol-2-yl- and -3-yl-boronic acids (1 and 2) are described on a ca. 7 g scale, starting from commercially available 2,5-dibromonitrobenzene (4) and carbazole (11), respectively. Compounds I and 2 underwent efficient palladium-catalyzed cross-coupling reactions under Suzuki-Miyaura conditions to yield products 17, 18 and 20. Compound 18 reacted with IrCl3 to give the tris-cyclometalated (pyridin-2-yl)carbazole iridium(III) complex 21, the X-ray crystal structure of which is reported

White polymeric light-emitting diode based on a fluorene polymer/Ir complex blend system

Efficient white-polymeric light-emitting diodes (PLED) were fabricated as a single active layer containing blue-emitting poly(9,9-bis(2-ethylhexyl)fluorene-2,7-diyl) endcapped with bis(4-methylphenyl)phenylamine; (PF2/6am4), and yellow-orange-emitting iridium [tri-fluorenyl] pyridine complex [Ir(Fl(3)Py)(3)]. The fluorene-like ligands in the blended device prevent phase segregation and also enhance energy transfer from the polymer host to the guest due to efficient overlap of wave function (Dexter process) and host singlet emission and guest absorption bands (Forster process) which reduces the loading level required to produce white emission. The two emitted colors complement each other and doping levels of 2%-3% produce white emission. Above a certain current density, depending on the doping level, the device Commission Internationale de L'Eclairage (CIE) coordinates become bias independent and a stabilized white emission can be obtained. A white-emitting PLED (coordinates 0.348, 0.367) of peak external quantum efficiency of 2.8%, and luminance of 16000 cd/m(2) at applied voltage of 5 V (i.e., 4.57 cd/A) was obtained. (C) 2005 American Institute of Physics

Oligo(fluorenyl) pyridine ligands and their tris-cyclometalated iridium(III) complexes: synthesis, photophysical properties and electrophosphorescent devices

The new extended tri- and penta-fluorenylpyridine ligands Fl(3)Py 2 and Fl(5)Py 3 and their tris-cyclometalated iridium(III) complexes Ir[Fl(3)Py](3) 5 and Ir[Fl(5)Py](3) 6 have been synthesised and their properties compared with the known iridium( III) complex Ir[Fl(1)Py](3) 4. The lowest energy (emissive) excited states of the complexes 4-6 are dominated by ligand centred (LC) (3)pi ->pi* triplet states, as observed for their uncomplexed ligands 1-3. The emission maximum of complex 4 is similar to 546 nm with a triplet lifetime of 2.8 mu s. For complexes 5 and 6 the emission maxima are both similar to 566 nm with triplet lifetimes of 7.4 mu s and 7.8 mu s, respectively. Devices made from poly(9,9'-spirobifluorene) (PSF) as the host and doped with complexes 4-6 show good stability; the EL spectra are unchanged after repeated operation over several days. Devices containing complexes 5 and 6 exhibit higher external quantum efficiency (EQE) values. Turn-on voltages of similar to 3 V, giving an EQE of 2.8% at a current density of 30 mA cm(-2), with a power efficiency of 4.3 lm W-1 and electroluminescence (EL) intensity of 25 000 cd m(-2) at 550 mA cm(-2) were observed for ITO/PEDOT : PSS/PSF : 6/Ca/Al devices

Bridged diiridium complexes for electrophosphorescent OLEDs : synthesis, X-ray crystal structures, photophysics, and devices.

Results are presented which challenge the accepted view that dinuclear transition metal–ligand complexes are unsuitable for organic light-emitting device (OLED) applications due to their low luminescence quantum efficiencies. We establish for the first time that halo- and pseudo-halo-bridged diiridium(III) species are viable electrophosphorescent dopants in OLEDs. New cyclometalated chloro- and isocyanate-bridged diiridium(III) complexes, viz. tetrakis[9,9-dihexyl-2-(pyridin-2-yl)fluorene-C2,N′]-bis(μ-chloro)diiridium(III) [Ir(flpy)2Cl]2 (complex 3) and tetrakis[9,9-dihexyl-2-(pyridin-2-yl)fluorene-C2,N′]-bis(μ-isocyanate)diiridim(III) [Ir(flpy)2NCO]2 (complex 4) were obtained in high yield from the 9,9-dihexyl-2-(pyridin-2-yl)fluorene (flpyH) ligand 1. The X-ray crystal structures are described for 3 and the monomeric complex Ir(flpy)2NCO(DMSO) (5) which was obtained from 4. The solution-state photophysical properties of complexes 3 and 4 are characterised by emission from mixed 3π–π*/3MLCT states at [similar]545–550 nm. Complex 4 displays a solution-state photoluminescence quantum yield which is five times that of the dichloro-bridged analogue 3. This is ascribed to an increase in the ligand-LUMO/metal eg gap which reduces the probability of non-radiative decay processes. Spin-coated organic light emitting devices (OLEDs) made from the host polymer poly(9,9-bis-2-ethylhexylfluorene-2,7-diyl) (PF2/6) end-capped with bis-(4-methylphenyl)phenylamine (PF2/6am4) doped with 12.5 wt% of the complexes 3 and 4 show good stability: turn-on voltages are low (<4 V) with maximum EL intensities of [similar]1300 and 13 000 cd m−2, and peak external quantum efficiencies (EQE) of 0.1 and 0.8%, at ca. 400 and 60 mA cm−2, respectively

Intramolecular charge transfer assisted by conformational changes in the excited state of fluorene-dibenzothiophene-S,S-dioxide co-oligomers

The strong solvatochromism observed for two fluorene-dibenzothiophene-S,S-dioxide oligomers in polar solvents has been investigated using steady-state and time-resolved fluorescence techniques. A low-energy absorption band, attributed to a charge-transfer (CT) state, is identified by its red shift with increasing solvent polarity. In nonpolar solvents, the emission of these conjugated luminescent oligomers shows narrow and well-resolved features, suggesting that the emission comes from a local excited state (LE), by analogy to their conjugated fluorene-based polymer counterparts. However, in polar solvents, only a featureless broad emission is observed at longer wavelengths (CT emission). A linear correlation between the energy maximum of the fluorescence emission and the solvent orientation polarizability factor Δf (Lippert−Mataga equation) is observed through a large range of solvents. In ethanol, below 230 K, the emission spectra of both oligomers show dual fluorescence (LE-like and CT) with the observation of a red-edge excitation effect. The stabilization of the CT emissive state by solvent polarity is accompanied/followed by structural changes to adapt the molecular structure to the new electronic density distribution. In ethanol, above 220 K, the solvent reorganization occurs on a faster time scale (less than 10 ps at 290 K), and the structural relaxation of the molecule (CTunrelaxed → CTRelaxed) can be followed independently. The magnitude of the forward rate constant, k1(20 °C) ≈ 20 × 109 s-1, and the reaction energy barrier, Ea ≈ 3.9 kcal mol-1, close to the energy barrier for viscous flow in ethanol (3.54 kcal mol-1), show that large-amplitude molecular motions are present in the stabilization of the CT state