Jae Buem Oh

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.

Novel extended π-conjugated Zn(II)-porphyrin derivatives bearing pendant triphenylamine moiety for dye-sensitized solar cell: synthesis and characterization

We have designed and synthesized novel Zn(II)-porphyrin derivatives for dye-sensitized solar cells. The derivatives incorporate the electron-donating group of a pendant triphenylamine into cyano-substituted ([TPA]Zn-Por-CN1) or non-substituted stilbene moiety ([TPA]Zn-Por1) in the 5,10,15-meso-position and carboxylic acid group in the 20-meso-position in a porphyrin derivative. Their chemical structures were characterized by 1H NMR, FT-IR, UV-vis absorption, EI-mass, and MALDI-TOF mass spectroscopies. Their electrochemical properties were studied by cyclic voltammetry measurement. These Zn(II)-porphyrin derivatives have been used to fabricate dye-sensitized solar cells based on I-/I2 liquid electrolytes as dye sensitizers and their device performances were evaluated by comparing with that of a standard Ru(II) complex dye. [TPA]Zn-Por-CN1 showed higher power conversion efficiency than that of [TPA]Zn-Por1, due to a broader absorption band around 435 nm. Short-circuit photocurrent density (Jsc), open-circuit voltage (Voc), fill factor (FF), and power conversion efficiency (η) of DSSC for [TPA]Zn-Por-CN1 were evaluated to be Jsc = 6.3 mA.cm-2, Voc = 0.737 V, FF = 0.683, and η = 3.1%, respectively.

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

LANTHANIDE(III)-CORED SUPRAMOLECULAR COMPLEXES WITH LIGHT-HARVESTING DENDRITIC ARRAYS FOR ADVANCED PHOTONICS APPLICATIONS

We have designed and developed novel lanthanide(III)-cored supramolecular systems with light-harvesting dendritic arrays for advanced photonics applications such as planar waveguide amplifiers, plastic lasers, and light-emitting diodes. The supramolecular ligands, such as naphthalenes and metalloporphyrins, were specially designed and synthesized in order to provide enough coordination sites to form stable lanthanide(III)-chelated complexes. The energy levels of the supramolecular ligands were tailored to maintain the effective energy transfer process from supramolecular ligands to lanthanide(III) ions for getting a higher optical amplification gain. Also, efficient energy transfer pathways for the sensitization of lanthanide ions by supramolecular ligands were investigated, for the first time to the best our knowledge. Furthermore, to enhance the optophysical properties of novel supramolecular systems, aryl ether-functionalized dendrons as photon antennas have been incorporated into lanthanide-cored supramolecular systems, yielding novel lanthanide-cored dendritic materials with efficient site-isolation effect.

THERMALLY STABLE PERFLUORINATED POLYIMIDES WITH PENDANT PERFLUORINATED AROMATIC UNIT FOR PHOTONIC APPLICATIONS

We have designed and synthesized novel thermally stable perfluorinated polyimides with pendant perfluorinated aromatic unit for photonic applications. At first, we developed a new synthetic route to a perfluorinated aromatic diamine by protecting-deprotecting as well as by nucleophilic bromine displacement reactions, affording a new diamine with a pendant perfluorinated aromatic unit. Its chemical structure was identified by 1H-, 19F- and 13C-NMR spectroscopies as well as mass spectrometry. Novel fluorinated polyimides were prepared by condensation polymerization of the present fluorinated diamine with various dianhydrides. The resultant polyimides are thermally stable over 400°C. The refractive index and birefringence of the resultant polyimides are 1.5844 ~ 1.5040 and 0.01 ~ 0.03 at 633 nm, respectively.