Fluorenone-Containing Polyfluorenes and Oligofluorenes: Photophysics, Origin of the Green Emission and Efficient Green Electroluminescence (original) (raw)
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Chemistry of …, 2007
2,7-Bis(3,4,5-trimethoxyphenylethenyl)fluorenone (OFOPV) and a segmented oligomer analogue linking OFOPV units with polymethylene flexible spacerssalt-poly(2,6-dimethoxylphenylene-4-vinylene-[9fluorenone-2-yl-7-vinylene]3,5-dimethoxyphenylene-4-[1,6-hexanedioxyl]) (pFOPV)swere synthesized and their luminescence properties studied. Solution-phase photoluminescence (PL) of OFOPV and pFOPV shows concentration-dependent relative intensities of a fine-structured higher energy band and a featureless lower energy band, consistent with solution excimer formation. Neat film PL and electroluminescence (EL) spectra using 100% OFOPV and pFOPV emitter layers show red emission bands (λ max ∼ 610 nm). Solid film PL spectra of OFOPV diluted in PMMA or Zeonex are significantly blue-shifted relative to the neat film spectra. PL and EL spectra of 2,7-bis(3,4,5-trimethoxyphenylethenyl)-9,9-diethylfluorene (OFPV) blended with <1% by weight of OFOPV gives significant green region (g-band) emission in addition to the normal blue emission of OFPV. Monomeric OFOPV produced by adventitious oxidation is therefore identified as giving g-band emission in thermally stressed OFPV-based OLEDs, due to intermolecular energy transfer from OFPV excitons to lower energy OFOPV. The red emission in neat solid-phase OFOPV and pFOPV appear to arise from fluorenone-type excimers that do not play a direct role in g-band emission in this case. (12) Gurge, R. M.; Hickl, M.; Krause, G.; Lahti, P. M.; Hu, B.; Yang
Synthesis and luminescence properties of three novel polyfluorene copolymers
Polymer, 2003
We report on the synthesis and characterization (including structural, optical, electrochemical and electroluminescence properties) of three alternating F-alt-X copolymers, where F is 9,9-bis(2 0-ethylhexyl)fluorene unit and the X comonomer varies from a phenylene, to a thiophene and to a thiophene-S,S-dioxide unit. Among these X comonomers, the phenylene group is at the origin of a blue-emitting copolymer with unitary luminescence efficiency in solution, while thiophene-S,S-dioxide promotes the highest electron affinity. These copolymers are also used in the fabrication of light-emitting diodes.
Materials
Using palladium-catalyzed Suzuki polycondensation, we synthesized new light-emitting fluorene copolymers containing the dicyano derivatives of stilbene and phenanthrene and characterized them by gel permeation chromatography, UV-vis absorption spectroscopy, spectrofluorimetry, and cyclic voltammetry. The photoluminescence spectra of the synthesized polymers show significant energy transfer from the fluorene segments to the dicyanostilbene and 9,10-dicyanophenanthrene units, which is in agreement with the data of theoretical calculations. OLEDs based on these polymers were fabricated with an ITO/PEDOT-PSS (35 nm)/p-TPD (30 nm)/PVK (5 nm)/light emitting layer (70–75 nm)/PF-PO (20 nm)/LiF (1 nm)/Al (80 nm) configuration. Examination of their electroluminescence revealed that copolymers of fluorene with dicyanostilbene show yellow-green luminescence, while polymers with 9,10-dicyanophenanthrene have a greenish-blue emission. The 9,10-dicyanophenanthrene units have a more rigid structure...
Synthetic Metals, 2000
A copolymer derived from fluorene has been synthesised using a fluorene monomer functionalised with poly ethylene oxide Ž. Ž. Ž. PEO-like segments as comonomer in a poly dihexylfluorene main chain. Efficient blue-green polymer light-emitting diodes LEDs based on this material and working under ambient atmosphere are reported. When using ITO as anode and aluminium as cathode, operating voltage at around 25 V are required to obtain emission intensity of 1 mW cm y2. By decreasing the film thickness from 250 to 110 nm and using calcium instead of aluminium, the corresponding operating voltage can be reduced by approximately 50% without Ž. significant loss of luminescence efficiency. Light-emitting electrochemical cells LECs are also demonstrated, leading to threshold Ž. operating voltages close to the electrochemical gap of poly fluorene .
Efficient light emitting diodes from polyfluorene copolymer blends
Synthetic Metals, 2005
Highly efficient light emitting diodes were obtained by blending blue-emitting poly [(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(N,N -diphenyl)-N,N-di(p-butyl-oxyphenyl)-1,4-diaminobenzene] (I) with green-emitting poly[(9,9-dioctyl-2,7-divinylene-fluorenylene)-alt-co-{2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene}] (II). Only green emission was obtained from the films of polymer blends and from corresponding double-layer LEDs, indicating an almost complete Förster energy transfer from I to II. These devices show enhanced external quantum efficiency, higher brightness and lower turn on voltages. Luminance and efficiency of 2.6 × 10 4 cd/m 2 and 2.55%, respectively, were obtained.
Blue light-emitting diodes based on novel polyfluorene copolymers
Journal of Luminescence, 2007
This study presents the synthesis and characterisation of a series of fluorene-based conjugated copolymers, together with the preparation and characterisation of the corresponding light-emitting devices. The polymers consist of alkoxyphenyl-substituted fluorene units together with different amounts of a hole-transporting triphenylamine-substituted fluorene unit: 0%, 10%, 25% and 50%. All polymers (P0, P1, P2, and P3) show high photoluminescence efficiency (Z PL) and light emission (both PL and EL) in the blue spectral region. Electrochemical studies show improved hole injection as the ratio of the triphenylamine-substituted segment is increased. The electroluminescence quantum efficiencies (EQEs) of the devices increase six times going from P0 to P1. Compared with P1, polymers P2 and P3 show lower efficiencies in devices. These findings indicate the presence of an optimal polymer composition, where balance between the charge-carrier mobilities has been reached.
Optical and electroluminescent properties of polyfluorene copolymers and their blends
Polymer, 2005
We have synthesized and characterized a new green Ir(III) complex, Ir(mpp) 3 , with the ligand 3-methyl-2-phenylpyridine (Hmpp) and fabricated phosphorescent light emitting devices with the complex as a triplet emissive dopant in PVK. The PL and EL spectra of the PVK film doped with the complex confirm an efficient energy transfer from carbazole excimer to Ir complex. The device showed a maximum external quantum efficiency of 4.5% for 2% Ir(mpp) 3 doping concentrations, and a peak luminance of 25,000 cd/m 2 . The device demonstrates the effect brought in by the finetuning of the ligand, 2-phenylpyridine in the form of the methyl substitution in the pyridine ring.
Chemistry of …, 2005
A novel conjugated polyfluorene/poly(p-phenylenevinylene) copolymer containing the pendant bis(4alkoxyphenyl) groups in the C-9 position of every alternating fluorene unit has been synthesized and well structurally characterized. The photoluminescence spectrum of this polymer exhibits strong concentration and excitation wavelength dependence in solution. The excited triplet-state maximum of polymer occurs in the region of 460-540 nm with a lifetime of 65.8 µs. This copolymer displays a minor positive nonlinear absorption at the focus of the laser irradiation, suggesting possible reverse saturable absorption. The stable electroluminescent spectrum of the polymer light-emitting diode device based on this copolymer (device configuration, indium-tin oxide/Au/copolymer/LiF/Al) was obtained with a peak wavelength of 515 nm. The bright-green emission observed over the whole active area of the copolymer closely resembles the photoluminescence of the most concentrated solution (0.5 M) used. This suggests that chain stacking in the solid state is responsible for the observed green electroluminescence.