Polyfluorene (PF)-based light-emitting diodes (LEDs) typically exhibit device degradation under operation with the emergence of a strong low-energy emission band (at ∼ 2.2–2.4 eV). This longer wavelength band converts the desired blue emission to blue–green or even yellow. We have studied both the photoluminescence (PL) and electroluminescence (EL) of PFs with different molecular structures and found that the low-energy emission band originates from fluorenone defects which are introduced by photo-oxidization, thermal oxidation, or during device fabrication. X-ray photo-emission spectroscopy (XPS) results show that the oxidation of PF is strongly catalyzed by the presence of calcium. The fluorenone defects generate a stronger contribution to the EL than to the PL. By utilization of a novel electron-transporting material as a buffer layer between the emissive PF and the Ca/Ag (Ba/Ag) cathode, the blue EL emission from the PF was stabilized.

Stabilized Blue Emission from Polyfluorene-Based Light-Emitting Diodes: Elimination of Fluorenone Defects

The general concepts, design criteria, and physical parameters, such as component placement and electroluminescence, that relate to the construction of OLED devices are described, followed by a discussion of the current literature detailing the use of branched and dendritic materials as the key electroluminescent elements of single- and multi-layered fabricated devices. Their configurations, efficiencies, emission intensities, and molecular structural implications are also delineated and discussed. This critical review should appeal to researchers in the synthetic, material, and physical sciences (122 references).

Dendritic macromolecules for organic light-emitting diodes

The study reported in this thesis concerns the relationship
between morphology and the properties of multicomponent
epoxy and methacrylate resins.
The thermodynamic and kinetic aspects of phase separation in
reactive, thermosetting, systems are explored and applied to
the investigation of blends of 'high performance' epoxy
resins with polyethersulphone. The mechanical properties of
the same cured blends are shown to be insensitive to
considerable variations in composition, cure and the
resulting morphology, both in the bulk-resin and in carbon
fibre-epoxy laminate forms.
Room temperature fracture and yield behaviour of highly
cross linked and rubber modified methacrylates, of rubber
modified dysfunctional epoxies, as well as of the above
mentioned epoxy/polyether sulphone blends, is investigated.
Special emphasis is placed on a comparison of the kinetics
of tensile creep between the different systems. Loss of
ductility in the highly cross linked resins is shown to
result in a very limited scope for toughness enhancement by
the usual rubber toughening methods.

Effects of phase separation in crosslinked resins containing polymeric modifiers

A series of electroactive aromatic polyamides with 4-(dimethylamino)triphenylamine [(NMe2)TPA] units in the backbone were prepared from a newly synthesized diamine monomer, 4,4′-diamino-4′′-(dimethylamino)triphenylamine, and various aromatic dicarboxylic acids via the phophorylation polyamidation reaction. These polyamides are readily soluble in many organic solvents and can be solution-cast into tough and amorphous films. They had useful levels of thermal stability associated with relatively high glass-transition temperatures (277–298 °C), 10% weight loss temperatures in excess of 500 °C, and char yields at 800 °C in nitrogen higher than 67%. The polymer films showed reversible electrochemical oxidation accompanied by strong color changes with high coloration efficiency, high contrast ratio, and rapid switching time. The optical transmittance change (Δ%T) at 640 nm between the neutral state and the fully oxidized state is up to 88%, and the coloration efficiency is as high as ca. 261 cm2/C with high opti...

High Contrast Ratio and Rapid Switching Electrochromic Polymeric Films Based on 4-(Dimethylamino)triphenylamine-Functionalized Aromatic Polyamides

Polylactic acid as a biodegradable material for all-solution-processed organic electronic devices

Novel multi-H shaped macrocyclic oligomers ((TPAF3)3 and (TPAF5)3) were designed and synthesized for use as hole-transporting emitters in blue-light-emitting diodes (LEDs). In the produced macrocyclics, three triphenylamine units are connected in series to form a macrocyclic core through the C-9's of the central fluorene units of three surrounding oligofluorenes, which, like rigid rods, stick out of the ring plane in both sides. This specific structure renders the macrocyclics better photoluminescence (PL) stabilities and lower crystallization tendencies than polyfluorenes and excellent optoelectronic properties. The macrocyclics emit deep blue fluorescence with high efficiencies both in solutions and thin films (Φ pl-film = 57% for (TPAF3)3 and 52% for (TPAF5)3). (TPAF5)3 films are stable against both electrochemical oxidation and reduction, with CV curves remaining unchanged in 10 successive potential scans. High-efficiency blue-light-emitting diodes were fabricated using the macrocyclics as the hole-tr...

Multi-H Shaped Macrocyclic Oligomers Consisting of Triphenylamine and Oligofluorene: Synthesis and Optoelectronic Properties

In this article, modified polysulfide sealants with lower compression set were prepared by a simple method of introducing the diglycidyl ether of bisphenol A resin (DGEBA epoxy resin) into sealants. The investigation on reactivity analysis and gel faction test verified that the incorporation of epoxy resin in sealants was just a blending process rather than copolyaddition with polysulfide resin. Stress–strain behavior during compression revealed that the epoxy resin could reduce the compression stress when the sealants were loaded to a certain strain, which effectively lessened crosslink breakages and benefited to compression resistance. Also the rigid phenyl structure in epoxy resin may retard incidental slide between polysulfide chains and prevent interchange reactions between disulfide linkages. The incorporation of 2 phr epoxy resin distinctly reduced compression set of polysulfide sealant from 28.3% to 11.2% after compressed 25% at 23°C for 1 day. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The effect of epoxy resin to reduce the compression set of polysulfide sealant

3D Monodisperse Oligofluorenes with Non-Conjugated Triphenylamine-Based Cores: Synthesis and Optoelectronic Properties

In this work, in situ dielectric analysis (DEA) was employed for the first time to the best of our knowledge, to monitor the curing process of polysulfide (PSF) sealant using manganese dioxide (MnO2) as the curing agent, where the gel point and ending point were determined. The obtained results were verified by rheological tests of dynamic mechanical analysis and tensile strength tests. It showed a significant difference between this curing process and those of usual thermosetting materials. The influences of the pH value of the samples and curing temperature were investigated and discussed in detail. Also, activation energies of the curing reaction of the samples with different pH values were calculated. The results proved DEA as a reliable and useful method for in situ monitoring PSF–MnO2 curing process. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Yiwu Quan

Papers

Multi-H Shaped Macrocyclic Oligomers Consisting of Triphenylamine and Oligofluorene: Synthesis and Optoelectronic Properties

The effect of epoxy resin to reduce the compression set of polysulfide sealant

3D Monodisperse Oligofluorenes with Non-Conjugated Triphenylamine-Based Cores: Synthesis and Optoelectronic Properties

The investigation on the curing process of polysulfide sealant by in situ dielectric analysis

Evaluation of thermoplastic polyolefin materials for the hard shed of composite insulators