MOLECULAR DESIGN OF LIGHT EMITTING POLYMERS

Fluorene-based alternating and statistical copolymers were synthesized by employing reaction methods of Wittig,Heck and Suzuki.The copolymers were classified into three groups with the photoluminescence(PL)emission maxima at420,475 and 500 nm,respectively.Statistical copolymers with two chromophores having PL emission maxima at 420 and475 nm emitted light with the emission maximum at 475 nm on photoexcitation at 365 nm and improved the quantumefficiency by the energy transfer.However,the intramolecular energy transfer was inefficient compared to the intermolecularenergy transfer when the two chromophores were apart from each other in the range of the Forster critical distance.Fluorene-pyridinedivinylene alternating copolymer was synthesized by the Wittig reaction and found to have physical,electronic andelectrochemical properties of the individual units intact.The double-layered light emitting diode(LED)with the statisticalcopolymer as an emitting layer and the pyridine-containing copolymer as an electron transporting-hole blocking layer,whichwere sandwiched between ITO and Al,displayed a quantum efficiency of 0.1%.

Polymer light-emitting devices using poly(ethylene oxide) as an electron injecting layer

The performance of polymer light emitting devices(PLEDs)based on polyvinyl carbazole(PVK)is improved by introducing a nanoscale interfacial thin layer,made of poly(ethylene oxide)(PEO),between the calcium cathode and the PVK emissive layer.It is believed that the PEO layer plays a key role in enhancing the device performance.In comparison to the device with Ca/Al as the cathode,the performance of the PLED with PEO/Ca/Al cathode,including the driving voltage,luminance efficiency is significantly improved.These improvements are attributed to the introduction of a thin layer of PEO that can lower the interfacial barrier and facilitate electron injection.

Alkali metal salts doped pluronic block polymers as electron injection/transport layers for high performance polymer light-emitting diodes

A series of alkali metal salts doped pluronic block copolymer F127 were used as electron injection/transport layers (ETLs) for polymer light-emitting diodes with poly[2-(4-(3′,7′-dimethyloctyloxy)-phenyl)-p-phenylenevinylene] (P-PPV) as the emission layer. It was found that the electron transport capability of F127 can be effectively enhanced by doping with alkali metal salts. By using Li2CO3 (15%) doped F127 as ETL, the resulting device exhibited improved performance with a maximum luminous efficiency (LE) of 13.59 cd/A and a maximum brightness of 5529 cd/m2, while the device with undoped F127 as ETL only showed a maximum LE of 8.78 cd/A and a maximum brightness of 2952 cd/m2. The effects of the doping concentration, cations and anions of the alkali metal salts on the performance of the resulting devices were investigated. It was found that most of the alkali metal salt dopants can dramatically enhance the electron transport capability of F127 ETL and the performance of the resulting devices was greatly improved.

SYNTHESIS AND CHARACTERIZATION OF FULLY SOLUBLE POLYPHENYLENEVINYLENE

Fully soluble poly[2-methoxy-5-(2'-ethylhexyl)-oxy)-p-phenylenevinylene] (MEH-PPV) was synthesized by the addition of molecular weight modifiers (chain stopper, Free radical scavengers) to a polymerization system containing monomer, catalyst and a solvent. These PPV products synthesized in this work were characterized by IR, NMR, UV-visible spectroscopy and GPC. Results show that the M-w of polyphenylvinylene (PPV) can be controlled by the addition of chain stopper (benzyl bromide) and radical inhibitor (2,6-di-tert-butyl-4-methyl phenol). The polymerization mechanism in the presence of these additives was also discussed. A dual mechanism involving carbene for PPV polymerization was proposed.

Packing Adjustment Towards High Mobility Luminescent Conjugated Polymers

Next generation display and lighting technology calls for thinner,cheaper and more-flexible unit devices.Polymer light emitting transistor(PLET),which integrates logic function of organic field effect transistor(OFET),luminescence function of organic light emitting diode(OLED),and potential mechanical properties,is believed to be the raising star in this field.However,great challenges remain in developing the core materials of PLETs,which simultaneously require the integration of high ambipolar mobility and strong solid-state luminescence properties.Herein,high mobility luminescent thienopyrroledione-benzodiathiadiazole-fluorene-based conjugated polymer was chosen as polymer backbone,and polymers TBT-1 and TBT-2(TBT=thienopyrroledione-benzodiathiadiazole-thienopyrrole-dione)with red luminescence were obtained by direct arylation polymerization(DArP).By introducing linear alkyl side chains,the packing orientation is changed from face-on in TBT-1 thin film to edge-on in TBT-2 thin film,which is beneficial for improving the field effect performance.The average hole and electron mobility of TBT-2 are 1.1×10^(-2)and 2.0×10^(-3)cm^(2)·V^(-1)·s^(-1),respectively.This work provides new design strategy for high mobility luminescent conjugated polymers,which can be used in PLETs.