Hwan Kyu Kim

Lanthanide-cored supramolecular systems with highly efficient light-harvesting dendritic arrays towards tomorrow’s information technology

We have developed novel lanthanide-cored supramolecular systems with highly efficient light-harvesting dendritic arrays for integrated planar waveguide-typed amplifiers. Er3+ ions were encapsulated by the supramolecular ligands, such as porphyrins and macrobicyclics. The supramolecular ligands have been designed and synthesized to provide enough coordination sites for the formation of stable Er(III)-chelated complexes. For getting a higher optical amplification gain, also, the energy levels of the supramolecular ligands were tailored to maintain the effective energy transfer process from supramolecular ligands to erbium(III) ions. Furthermore, to maximize the light-harvesting effect, new aryl ether-functionalized dendrons as photon antennas have been incorporated into lanthanide-cored supramolecular systems. In this paper, molecular design, synthesis and luminescent properties of novel lanthanidecored integrated supramolecular systems with highly efficient light-harvesting dendritic arrays will be discussed.

Second-order NLO polyamideimides based on functionalized stilbene derivatives: direct polycondensation and characterization

Abstract Polyamideimides having nonlinear optical (NLO)-active chromophores were synthesized by direct polycondensation of 4-[N,N′-bis(2-aminoethyl)amino]-4′-nitrostilbene (DANS-diamine) with oxy-bis[N-(4-phenylene)trimellitic imide] (BCI), N-(3-carboxyphenyl)-trimellitimide (BTI) and trimellitic anhydride chloride (TMAC). The direct polycondensation of NLO polyamideimides without a curing step may ameliorate the optical property of NLO polymers by reducing the optical propagation loss. The resulting polymers were highly soluble in aprotic polar solvents such as DMF, DMAc, NMP, etc. The NLO polyamideimides exhibited the inherent viscosity range of 0.14–0.33 dl g−1. Molecular structural characterization for the resulting polymers was achieved by 1H n.m.r., FTi.r. and u.v.-visible spectroscopies. The glass transition temperature for the resulting NLO polyamideimides was in the range 142–224°C and they showed thermal stability up to 260°C. The polymer solutions could be spin coated onto indium—tin-oxide (ITO) glass or quartz disc substrates to form optical quality thin films. The electro-optic coefficients (r33) at the wavelength of 1.3 μm, measured by a simple reflection method, for polymer thin films poled around the glass transition temperature were in the range 1.9–7.4 pm V−1.

Synthesis and optical properties of novel side chain NLO organic/inorganic polymers via sol-gel process

SummaryNovel side chain NLO organic/inorganic polymers were developed by sol-gel process of dye-contained triethoxysilane with tetraethoxysilane. A NLO moiety based on 4-[N, N-bis(2-hydroxyethyl)amino]-4′-nitrostilbene (diol-DANS) was covalently bounded to the triethoxysilane derivative. The sol-gel derived NLO polymers were analyzed by analytic techniques, including FT-IR, TGA, solid state 29Si-NMR, SEM, etc. The incorporation of the DANS dye into silicon oxide networks induces high dimensional stability of dipole alignment and the easy film fabrication. They exhibited a significant improvement in the thermal stability at high temperatures exceeding 270°C. The electro-optic coefficient at 1.3 μm is 4.3 pm/V for the copolymer containing 50 wt % of the dye-contained triethoxysilane system poled with corona discharge and is shown excellent long-term stability with 80% of initial value even after 3 hrs at 150°C.

Synthesis and electroluminescence properties of novel silicon-based copolymers containing oxadiazole and fluorene units for PLED

Abstract Novel silicon-based copolymers containing an electron-deficient oxadiazole unit and a fluorine unit have been successfully synthesized through the Heck reaction. They are soluble in common organic solvents such as THF, CHCl3, etc. Their UV–visible absorption spectra exhibit a strong maximum band at the range of 355–381 nm in thin film. Upon a photoexcitation of 350 nm, their photoluminescence spectra show a strong maximum band around 455–475 nm in thin film. The multi-layered light-emitting diodes (LEDs) of Al(200 nm)/Ca(50 nm)/EL polymer(80 nm)/PEDOT(50 nm)/ITO were fabricated. J–V curves show the turn-on voltage in the range of 4.4–7 V. These LEDs emit the white emissive color, due to the combination of a blue electroluminescent (EL) color and a red EL color arising from the formation of a certain charge complex.

Synthesis and luminescent properties of novel silicon-based poly(p-phenylene) related polymers containing oxadiazole units for PLED

Two silicon-based alternating copolymers, namely SiHMOXD-1 and SiHMOXD-2, functionalized with an electron-deficient oxadiazole units, have been successfully synthesized through Heck reaction for blue light-emitting materials. The chemical structure and purity of these polymers have been characterized by FT-IR, H-NMR and C-NMR, gel permeation chromatography, 11 3 UV–Vis, photoluminescence (PL) and excitation spectroscopies, etc. The SiHMOXD-1 exhibits one strong UV absorption band at 356 nm. With an excitation wavelength of 366 nm, its PL spectrum shows a strong band at 425 nm in the blue region. The SiHMOXD-2 shows one strong UV absorption band at 342 nm. With an excitation wavelength of 352 nm, its PL spectra gives two strong bands at 425 and 456 nm in the blue region. 2002 Elsevier Science B.V. All rights reserved.

Synthesis and Luminescent Properties of Lanthanide-Cored Supramolecular Complexes Based on Porphyrins for Optical Amplification

Abstract We have investigated the development of lanthanide-cored supramolecular complexes containing porphyrins to circumvent the solubility problem and maximize the optical amplification properties. Their chemical structures were identified by FT-IR, 1H-NMR, UV-Vis absorption and emission spectroscopies. FB-Por 1 and 2 show a very intense UV-visible absorption band at 419 nm, which is attributed to the Soret band. In addition, the relatively weak bands at 516, 551, 591 and 647 nm are assigned to the Q bands. Upon a photoexcitation wavelength with 430 nm, the PL spectra of FB-Por 1 and 2 exhibit a strong band at 653 nm and a weak peak at 715 nm. Zn-Por 1 and 2 show a very intense band at 420 nm for B-band π∽π* transitions. In addition, the weak bands at 547 and 585 nm were assigned to the Q bands. With an excitation wavelength of 430 nm, the PL spectra of Zn-Por 1 and 2 show a moderate band at 596 nm and a strong band at 646 nm.

Molecular Design and Photophysical Criteria for Lanthanide Emission Enhancement in Erbium(III)-Cored Complexes Based on Dendritic Ligands for Information Technology

Recently, luminescent lanthanide complexes have considerable interest because of their academic interests and potential utility in a wide variety of photonic applications, such as planar waveguide amplifiers, plastic lasers, lightemitting diodes, and luminescent probes. The 4f electrons in lanthanide (Ln) ions are slightly perturbed by the effects of lattice phonons and static strain fields in the coordination environment of ions, since the f-electrons are shielded by the outer 5s and 5p electrons. It leads to the sharp spectral line-like emission bands. Also, the forbidden 4f -4f n electronic transitions renders the low absorption and emission cross-section of lanthanide ions, while luminescent lifetime is relatively long. To overcome these shortcomings, recently, luminescent ligands are being used to excite Ln ions via an energy transfer from the luminescent ligands to the Ln ions. In most cases, the luminescent Ln ions are usually coordinated to the organic luminescent ligands, acting as sensitizers or antenna chromophores, which efficiently absorb and transfer light to excite Ln ions via energy transfer process. This sensitization process is much more effective than the direct excitation of Ln ions, since the absorption coefficients of organic chromophores are many orders of magnitude larger than the intrinsically low molar absorption coefficients (typically 1-10 M cm) of Ln ions. Recently, several research groups have focused on developing the efficient artificial light-harvesting (LH) lanthanide complexes, in which the use of dendrimers for light harvesting systems has been widely demonstrated. The encapsulation of luminescent Ln ions into a luminescent dendrimer can lead to a system capable of shielding central Ln ion from nonradiative environment and efficiently transferring excited energy from the peripheral chromophores to the focal point of the dendrimer. For example, Frechet et al. have reported the site isolation and antenna effects on luminescent properties of spherical lanthanide(III)-cored dendrimer complexes. Although its spectral overlap integral (J) between the emission band of peripheral antenna and the absorption band of Ln ions was not satisfactorily large to obtain the effective energy transfer, the Frechet arylether typed dendrons were widely used as light-harvesting antenna. Moreover, very recently, to enhance the near-infrared (NIR) emission intensity and maintain the effective energy transfer process, our research efforts have been focused on developing stable and inert Er(III)-encapsulated complexes with artificial light-harvesting systems using dendritic luminescent ligands based on metalloporphyrins, naphthalenes, and anthracenes bearing the Frechet aryl-ether dendrons, namely, (Er3+-[Gn-Pt-Por]3(terpy), Er 3+-[Gn-Naph]3(terpy) and Er3+-[Gn-An]3(terpy)). We observed that the NIR emission intensity of the lanthanide complexes was dramatically enhanced with increasing the generation number (n) of the Frechet aryl-ether dendrons, due to the site-isolation and light-harvesting effects. Two possible energy transfer (ET) pathways for the sensitized emission in luminescent Ln(III) complexes have been suggested, as schematically illustrated in Scheme I. It is well-believed that in general only energy transfer from the

Temperature effect on photoluminescent properties of red light-emitting materials based on Ru(II)-chelated complexes

Abstract A new class of silicon-based copolymers containing Ru(II)-chelated complexes for new red light-emitting materials was developed by well-known Heck reaction between distyrylsilane monomer and the difunctionalized metal-chelated complexes. Ru(II)-chelated copolymers I and II showed one strong band approximately 265–289 nm for ligand units, one strong absorption band approximately 386–392 nm for π-conjugated backbones, and a broad shoulder metal-to-ligand charge transfer band approximately 460–465 nm. Ru(II)-chelated polymers exhibited a negligibly broad band approximately 495–500 nm in the greenish blue region and one/or two strong bands in the red region at room temperature. The photoluminescent (PL) properties of all materials as a function of temperatures were also investigated. With a photoexcitation wavelength of 325 nm at various temperatures, their PL intensity approximately 673–675 nm increased gradually with decreasing temperature, due to the restraint of the thermal relaxation decay.

Synthesis and Luminescent Properties of Novel Silicon-based Electroluminescent Copolymers with Ruthenium(II)-Chelated Complexes

Abstract A new class of silicon-based alternating copolymers having Ruthenium(II)-chelated complexes was synthesized to use as electroluminescent materials by Heck reaction between organosilicon divinyl monomers and Ru(II)-chelated monomers. The incorporation of organosilicon units with the aromatic or aliphatic groups on the silicon atoms into ®-conjugated systems improved their processability and interrupted the ®-conjugation length. The maximum absorption wavelength (λmax) of a non-chelated polymer (SiHMPhen) containing a phenanthroline (Phen) unit exhibited one strong bands at 305 nm for Phen units and a moderate peak around 350 nm for π-conjugated backbones. With an excitation wavelength of 360 nm, the PL spectrum of SiHMPhen exhibits a strong band at 420 nm in the blue region. Ru(II)-chelated copolymers showed strong absorption bands around 386–392 nm. Upon a photoexcitation with 400 nm, their PL spectra show a strong band at 430 nm in the blue region. The Ru(II)-chelated copolymers were thermally stable up to 300°C in air.

Synthesis and Luminescent Properties of Hyperbranched Poly(P-Phenylene)s by Molecular Architecture Engineering

Abstract Hyperbranched poly(p-phenylene)s, as a new family of electroluminescent materials, were synthesized by both Suzuki reaction and a nickel-catalyzed Grignard coupling reaction. P48 and P410 showed the UV absorption band at the longer wavelength than P38 and P310, even though they have the same number of consecutive phenyl groups. Photoluminescent (PL) spectra of P48 and P410 showed a blue emission at 490–496 nm, while P38 and P310 thin films showed a maximum PL peak around 420–440 nm in the deep blue region.