Kang Mun Lee

Phosphorescence Color Tuning of Cyclometalated Iridium Complexes by o-Carborane Substitution

Heteroleptic (C(^)N)(2)Ir(acac) (C(^)N = 4-CBppy (1); 5-CBppy (2), 4-fppy (4) CB = ortho-methylcarborane; ppy = 2-phenylpyridinato-C(2),N, 4-fppy = 2-(4-fluorophenyl)pyridinato-C(2),N, acac = acetylacetonate) complexes were prepared and characterized. While 1 exhibits a phosphorescence band centered at 531 nm, which is red-shifted compared to that of unsubstituted (ppy)(2)Ir(acac) (3) (λ(em) = 516 nm), the emission spectrum of 2 shows a blue-shifted band at 503 nm. Comparison with the emission band for the 4-fluoro-substituted 4 (λ(em) = 493 nm) indicates a substantial bathochromic shift in 1. Electrochemical and theoretical studies suggest that while carborane substitution on the 4-position of the phenyl ring lowers the (3)MLCT energy by a large contribution to lowest unoccupied molecular orbital (LUMO) delocalization, which in turn assigns the lowest triplet state of 1 as [d(π)(Ir)→π*(C(^)N)] (3)MLCT in character, the substitution on the 5-position raises the (3)MLCT energy by the effective stabilization of the highest occupied molecular orbital (HOMO) level because of the strong inductive effect of carborane. An electroluminescent device incorporating 1 as an emitter displayed overall good performance in terms of external quantum efficiency (6.6%) and power efficiency (10.7 lm/W) with green phosphorescence.

Heteroleptic tris-cyclometalated iridium(III) complexes supported by an o-carboranyl-pyridine ligand

Heteroleptic tris-cyclometalated Ir(III) complexes supported by the o-carboranyl-pyridine (CBpy) as a novel C^N chelating ligand were synthesized and characterized. While the CBpy ligand contributes to the electronic stabilization of complexes, their photophysical properties are dominated by 2-arylpyridine ligands.

Selective and competitive cysteine chemosensing: resettable fluorescent “turn on” aqueous detection via Cu2+ displacement and salicylaldimine hydrolysis

A novel rechargeable meso-aryl Bodipy-based Cys sensing ensemble has been developed (“turn on,” ΦF = <0.05 → 0.72, limit of detection = 6.0 × 10−6 M) with exceptional selectivity over homocysteine, N-acetylcysteine, glutathione (GSH) and methionine.

Ortho-carborane-functionalized luminescent polyethylene: potential chemodosimeter for the sensing of nucleophilic anions.

Closo-1,2-C2B10H12, so called ortho-carborane, is a wellknown icosahedral boron-cluster compound that possesses unique properties, such as a highly polarizable s-aromatic character, an electron-withdrawing nature, a high B content, and a high thermal and chemical stability. Owing to these interesting properties, compounds derived from orthocarborane have received a great deal of attention as promising materials in a wide range of applications, such as catalysis, hybrid materials, optoelectronic materials, doping agents in conducting polymers, potentiometric sensors, and boron-neutron-capture therapy (BNCT) . Whilst a number of studies on the design and synthesis of ortho-carborane-based compounds have focused on small molecular systems, polymers bearing carborane moieties are recently attracting great interest because the incorporation of carborane moieties into a polymer backbone could lead to the modulation of the electronic and optical properties of the polymer. Although the majority of polymeric carboranes developed so far have been utilized in main-chain, conjugate polymers, the development of side-chain polymers has rarely been reported; this scarcity is in spite of various advantages of this type of polymer including the ability to control the polymer architecture in terms of molecular weight, functionality, and the degree of incorporation that may lead to intriguing properties. In this regard, polyolefins with pendant ortho-carboranemoieties can be considered as a novel class of such sidechain carboranyl polymers. As single-site catalytic systems based on Group 4 organometallic complexes have been an effective and straightforward method for the preparation of functionalized polyolefins, it could be anticipated that the catalytic (co)polymerization of a-olefins bearing electron-deficient, bulky carborane groups may lead to the production of carboranyl polymers with well-defined structures. To this end, the copolymerization of ethylene with w-orthocarboranyl-a-olefin as a co-monomer using a [Me2SiACHTUNGTRENNUNG(h5C5Me4) ACHTUNGTRENNUNG(h1-N-tBu)TiCl2] (CGC)/methylaluminoxane (MAO) catalytic system was explored to develop a carboranefunctionalized polyethylene. In particular, it was found that the resulting polymer displayed not only photoluminescence under UV irradiation but also luminescence quenching in the presence of nucleophilic anions, thus revealing potential chemodosimetric sensing properties. Herein, the synthesis, characterization, and luminescent properties of polyethylene with side-chain ortho-methyl-carboranes are described. The ortho-carborane-substituted a-olefin, 1-methyl-2-(oct7-en-1-yl)-closo-1,2-carborane (1) was employed as a co-monomer. Carborane 1 was prepared from the reaction of 8bromo-1-octene in the presence of a catalytic amount of lithium iodide and the lithium salt generated in situ from 1-methyl-ortho-carborane and nBuLi in good yield after purification (70 %). The identity of 1 was confirmed by multinuclear NMR spectroscopy and mass spectroscopy. Whilst the H and C NMR spectra showed the expected resonances corresponding to the methyl and the octenyl substituents at the 1and 2-carbon positions of ortho-carborane, respectively, the B NMR signals detected in the region of d 4~ 10 ppm in a 1:1:2:2:4 ratio confirmed the presence of a closo-carborane cage. The copolymerization reactions of ethylene and 1 were achieved at different co-monomer concentrations using a CGC/MAO catalytic system at 75 8C under atmospheric ethylene pressure (Scheme 1). [a] Dr. M. H. Park, K. M. Lee, Prof. Dr. Y. Do Department of Chemistry KAIST Daejeon 305–701 (Republic of Korea) Fax: (+82) 42-350-2810 E-mail : ykdo@kaist.ac.kr [b] T. Kim, Prof. Dr. M. H. Lee Department of Chemistry and Energy Harvest-Storage Research Center University of Ulsan Ulsan 680–749 (Republic of Korea) Fax: (+82) 52-259-2348 E-mail : lmh74@ulsan.ac.kr Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201100012.

New class of scorpionate: tris(tetrazolyl)-iron complex and its different coordination modes for alkali metal ions.

We report formation of a new metallascorpionate ligand, [FeL3](3-) (IPtz), containing a Fe core and three 5-(2-hydroxyphenyl)-1H-tetrazole (LH2) ligands. It features two different binding sites, oxygen and nitrogen triangles, which consist of three oxygen or nitrogen donors from tetrazole. The binding affinities of the complex for three alkali metal ions were studied using UV spectrophotometry titrations. All three alkali metal ions show high affinities and binding constants (>3 × 10(6) M(-1)), based on the 1:1 binding isotherms to IPtz. The coordination modes of the alkali metals and IPtz in the solid were studied using X-ray crystallography; two different electron-donor sites show different coordination numbers for Li(+), Na(+), and K(+) ions. The oxygen triangles have the κ(2) coordination mode with Li(+) and κ(3) coordination mode with Na(+) and K(+) ions, whereas the nitrogen triangles show κ(3) coordination with K(+) only. The different binding affinities of IPtz in the solid were manipulated using multiple metal precursors. A Fe-K-Zn trimetallic complex was constructed by assembly of an IPtz ligand, K, and Zn precursors and characterized using X-ray crystallography. Oxygen donors are coordinated with the K ion via the κ(3) coordination mode, and nitrogen donors are coordinated with Zn metal by κ(3) coordination. The solid-state structure was confirmed to be a honeycomb coordination polymer with a one-dimensional infinite metallic array, i.e., -(K-K-Fe-Zn-Fe-K)n-.

Synthesis and photophysical properties of phenanthroimidazole–triarylborane dyads: intriguing ‘turn-on’ sensing mediated by fluoride anions

Phenanthroimidazole-based triarylborane compounds with an N-phenyl (1Ph, 2Ph) or N-biphenyl (1BP, 2BP) bridge were synthesized and characterized. All four compounds exhibit a dual emission pattern in their photoluminescence (PL) spectra, which can be separated into high- (λem = ca. 380 nm in THF) and low-energy (λem = ca. 480 nm) emissions. While the high-energy emission remains largely unchanged in different organic solvents, the low-energy emission exhibits clear signs of positive solvatochromism. The results of the photophysical analysis and theoretical calculations suggest that the high-energy emission corresponds to a π–π* transition band arising from the phenanthroimidazole, whereas the low-energy emission originates from an intramolecular charge transfer (ICT) transition between phenanthroimidazole and the triarylborane moiety. UV-vis titration experiments examining the association of 1Ph, 2Ph, 1BP, and 2BP with fluoride demonstrate that these compounds associate with a 1:1 binding stoichiometry in THF and binding constants (Ka) that are estimated to be around 1.0–3.0 × 104 M−1. These compounds show a ratiometrically increased fluorescence response in PL titration experiments upon binding of fluoride to the borane moiety, thereby giving rise to a ‘turn-on’ chemosensor for detection of fluoride anions. The ‘turn-on’ properties can be judged as a result of the reinforcement of π–π* transition on phenanthroimidazole and the restriction of ICT transition to triarylborane.

Synthesis and Dual-Emission Feature of Salen-Al/Triarylborane Dyads

Novel salen-Al/triarylborane dyad complexes were prepared and characterized with their corresponding mononuclear compounds. The UV-vis and photoluminescence experiments for dyads exhibited photoinduced energy transfer from borane to the salen-Al moiety in an intramolecular manner. Theoretical calculation and fluoride titration results further supported these intramolecular energy-transfer features.

Meso-thienyl and furyl rotor effects in BF2-chelated dipyrrin dyes: solution spectroscopic studies and X-ray structural packing analysis of isomer and congener effects

Well-defined discrete fluorescent molecular systems with very subtle steric/electronic differences are interesting when considering solid-state packing and solution substituent effects. Herein, we report the synthesis and characterization of four 4,4-difluoro-1,3,5,7-tetramethyl-8-(C4H3 X)-4-bora-3a,4a-diaza-s-indacene complexes (X = O, S). Various NMR spectroscopic experiments were used to assign all relevant atoms (CD2Cl2): 19F, 11B, 1H, 13C, 13C–H undecoupled, 1H–1H COSY, 1H–1H NOESY, 1H–13C HSQC, and 1H–13C HMBC NMR spectroscopy. UV-Vis and fluorescence studies were undertaken for all compounds. Chemical shift differences were found between isomers and congeners; for congeners, aromatic δ differences were attributed to electron-poor character. Also, compounds 1–4 were studied crystallographically. In the solid state, internal dihedral planes and intermolecular packing patterns can be compared.

Supramolecular Pt(II) and Ru(II) Trigonal Prismatic Cages Constructed with a Tris(pyridyl)borane Donor

We report a novel example of supramolecular cages containing a Lewis acidic trigonal boron center. Self-assembly of the tris(pyridyl)borane donor 1 with diruthenium (2) or platinum (3), as an electron acceptor, furnished boron-containing trigonal prismatic supramolecular cages 5 and 6, which were characterized by 1H NMR and electrospray ionization time-of-flight mass spectroscopy and X-ray crystallography. The molecular structure of cage 5 was confirmed as a trigonal prismatic cage with an inner dimension of about 400 Å3. The fluoride binding properties of borane ligand 1 and Pt cage 6 were studied. UV/vis absorption titration studies demonstrated that the boron center of cage 6 undergoes strong binding interaction with the fluoride ion, with an estimated binding constant of 1.3 × 1010 M-2 in acetone based on the 1:2 binding isotherm. The binding was also confirmed by 1H NMR titration. Photoluminescence titration studies showed that cage 6 emitted borane-centered fluorescence (τ = 2.21 ns), which was gradually quenched upon addition of fluoride. When excess fluoride was added to a solution of 6, however, dissociation of the pyridyl ligand from the Pt(II) center was observed.

Dimeric alumatranes as catalysts for trimethylsilylcyanation reaction

The solid-state structures of dimeric alumatranes with three five-membered rings chelated by [(OCMe2CH2)nN(CH2CH2O)3−n]3− (n = 1, L1; n = 2, L2; n = 3, L3), which vary by the number of CMe2 groups adjacent to the OH functionality [1 (L1H3), 2 (L2H3), and 3 (L3H3)], were determined by single-crystal X-ray diffraction. The X-ray structures revealed that the aluminum geometries were slightly distorted trigonal bipyramids. The obtained aluminum complexes are the first structurally characterized dimeric alumatranes with tricyclic five-membered rings. Quite unexpectedly, the sterically bulky side arms with dimethyl substituents were always located in the bridging sites, as determined by density functional theory calculations. Their solution-state structures were analyzed by 1H, 13C, and 27Al NMR techniques, and their gas-phase structures were determined by mass spectrometry. Unlike Al(OCH2CH2)3N, complexes 1–3 were all dimeric in the solid state, solution phase, and gas phase. In addition, they were found to promote the reaction of aryl, heteroaryl, and alkyl aldehydes with trimethylsilylcyanide to provide the corresponding products in excellent yields under mild conditions of room temperature, a short reaction time of 1 h, and a very low catalyst loading of 0.5 mol%.