Hyun-Nam Cho

Blue light emitting polymers

Abstract Polymer light emitting diodes have a good chance to become the main display system in the near future since diodes have many advantages concerning preparation and operation over other display systems. This review focuses on blue light emitting polymers introduced in the literature during the last 10 years. The characteristics of the photoluminescence and electroluminescence of these polymers is reviewed. Synthesis methods for blue light emitting polymers with conjugations in the polymer backbone are also described.

Control of band gaps of conjugated polymers by copolymerization

Abstract Dihexylfluorenes have been coupled with a chemical unit such as vinylene, phenylene, vinylenephenylene or vinylenealkoxyphenylene to preserve conjugation in the alternating copolymers by employing the reactions of Heck, Suzuki and Wittig. All the copolymers display good photoluminescence (PL) and the PL spectra are broad to show vibronic structures as well as emission of the interchain excitons or excimers, except PDHFPP which shows a sharp PL spectrum. The broad spectra become sharp on dilution in chloroform to 10−5 mol l−1 due to a diminishing effect of the interchain excitons or excimers. The electronic state of polydihexylfluorene with the PL emission peak at 420 nm is changed to a lower-energy state when a vinylene or vinylene-para-phenylene unit is coupled to the alkylfluorene unit. The decrease in the energy state is pronounced when the two alkoxy units are attached to the phenylene unit to show the PL emission peak at 510 nm. However, no change in the electronic energy state is observed when a phenylene, vinylene-meta-phenylene or glycol-capped vinylenephenylene unit is coupled with the dialkylfluorene unit.

Synthesis of new class of processable electroluminescent poly(terephthalylidene) derivatives with ether and sulfide linkage

Abstract A new series of the processable poly(terephthalylidene) derivatives containing single atom linkage were prepared by condensation reactions between bis(4-formylphenyl)ether or sulfide and 2,5-bis(hexyloxyl)-1,4-xylene bis (triphenyl phosphonium chloride), respectively. The resulting polymers were soluble in common organic solvents and could be spun-cast on glass plate coated with ITO electrode obtaining highly transparent homogeneous thin films. Chemical structures of the polymer were confirmed by IR, UV-visible, 1 H and 13 C NMR spectra. We observed successfully the electroluminescence spectra and maximum peaks at 525xa0nm and 505xa0nm from the devices made by the synthesized polymers. The present polymers have the strong absorption band at around 395xa0nm and 383xa0nm, which are due to the π – π ∗ transition of the conjugated segments of corresponding polymers. I–V curve showing typical rectifying diode characteristics. EL spectrum of the polymer was very similar to the PL spectrum indicating that the origins of the light emission in both cases are the same.

Improved efficiency of polymer LEDs using electron transporting layer

We report the use of fluorene based copolymers containing quinoline (POF66, P1F66) and pyridine(PFPV) units as electron transporting polymers for multi-layered LEDs. Double-layer device structure combining P1F66 as electron-transporting layer with the emissive MEH-PPV showed a maximum quantum efficiency of 0.03%, which is 30 fold increased compared with ITO/MEHPPV/Al single-layer device. The ETL with the electron deficient moiety improved the LED performance by the characteristics of electron transporting as well as hole blocking between emissive layer and metal cathode.

Third-Order Optical Nonlinearity of Poly(1,6-Heptadiyne) Derivatives Containing Mesogenic Moiety

Abstract Poly (1,6-heptadiyne) derivatives with side group liquid crystalline mesogens were prepared by the metathesis polymerization with transition metal catalyst. It was found that the MoCl5-based catalyst systems were very effective for the polymerization of 1,6-heptadiyne monomers with various mesogenic groups. Polymerization of these monomers gave to the conjugated polyenes that contain cyclic recurring unit in the polymer backbone. Resulting polymers with electron donating mesogenic groups exhibited good solubility in common organic solvents and were easily spin coatable on fused silica substrate. Copolymerization of the mesogen-containing monomers with diethyl dipropargyl malonate (DEDPM) was also attempted to improve their physical properties. The third-order nonlinear optical susceptibility, x (3), was evaluated by the optical third-harmonic generation measurement. The near-resonant x (3) value was found to be in the range of 1.75 ∼ 8.22 × 10−11 esu at the fundamental wavelength of 1.907 μm.

Synthesis and characterization of new side chain liquid crystalline polymers based on poly(dipropargylamine) main chain

SummaryA new thermotropic side-chain liquid crystalline polymers based on poly (dipropargylamine) backbone were prepared by metathesis polymerization with transition metal catalysts. It was found that the MoCl5-EtAlCl2 catalyst system were very effective for the cyclopolymerization of presently investigated monomers. Resulting polymers were soluble in common organic solvents such as THF, chloroform, etc. The number-average molecular weight (n

Synthesis and properties of a new side chain liquid crystalline polymer by methathesis polymerization

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Synthesis and properties of poly(dipropargyl-16-crown-5)

n) values of the polymers were in the range of 6.49x103–11.6x103, relative to polystyrene standard by GPC.Thermal properties of the monomers and the polymers synthesized were examined by differential scanning calorimetry (DSC) and cross-polarized optical microscopy. Both monomer and polymer displayed enantiotropic liquid crystallinity showing the reversible phase transition.