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Chi-Ming Che

Publications and source records attributed to Chi-Ming Che.

At least 91 records · Page 5Linked to original sources
PubMed2004

Light-emitting tridentate cyclometalated platinum(II) complexes containing sigma-alkynyl auxiliaries: tuning of photo- and electrophosphorescence.

The synthesis and structural, photophysical, electrochemical, and electroluminescent properties of a class of platinum(II) complexes bearing sigma-alkynyl ancillary ligands, namely [(C/N/N)Pt(C[triple bond]C]nR] [H(C/N/N) = 6-aryl-2,2'-bipyridine; n = 1-4; R = aryl, alkyl, or trimethylsilyl], have been studied. Substituents with different steric and electronic properties were introduced into the tridentate cyclometalating and arylacetylide ligands, and the pi-conjugation length of the oligoynyl moiety was homologously extended from ethynyl to octatetraynyl. The X-ray crystal structures of several derivatives confirm the Pt-(CC) ligation and reveal various intermolecular interactions, such as pi-pi, Pt...Pt, and C-H...F-C. The complexes display good thermal stability and intense phosphorescence in fluid and glassy solutions with high quantum yields and microsecond lifetimes. Their emission energies are sensitive to solvent polarity, the electronic affinities of the substituents on both the cyclometalating and arylacetylide groups, and the length of the oligoynyl ligand. By choosing appropriate cyclometalating and sigma-alkynyl ligands, the emission color of this class of platinum(II) complexes can be tuned from green-yellow to saturated red. In addition to (3)MLCT [Pt(5d) --> pi*(C/N/N)] and (3)IL(C/N/N), intriguing (3)IL(alkynyl) excited states localized on -(C[triple bond]C)(4)- and -(C[triple bond]Cpyrenyl-1) moieties that afford narrow-bandwidth emissions have been observed. Selected Pt(II) complexes were doped into the emissive region of multilayer, vapor-deposited organic light-emitting diodes. The tunable electrophosphorescence energy resembles that recorded in fluid solutions for these emitters, and the devices exhibit high luminance and efficiencies (up to 4.2 cd A(-1)).

Journal Article↗
PubMed2004

Probing the ruthenium-cumulene bonding interaction: synthesis and spectroscopic studies of vinylidene- and allenylidene-ruthenium complexes supported by tetradentate macrocyclic tertiary amine and comparisons with diphosphine analogues of ruthenium and osmium.

The synthesis and spectroscopic properties of trans-[Cl(16-TMC)Ru[double bond]C[double bond]CHR]PF(6) (16-TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, R = C(6)H(4)X-4, X = H (1), Cl (2), Me (3), OMe (4); R = CHPh(2) (5)), trans-[Cl(16-TMC)Ru[double bond]C[double bond]C[double bond]C(C(6)H(4)X-4)(2)]PF(6) (X = H (6), Cl (7), Me (8), OMe (9)), and trans-[Cl(dppm)(2)M[double bond]C[double bond]C[double bond]C(C(6)H(4)X-4)(2)]PF(6) (M = Ru, X = H (10), Cl (11), Me (12); M = Os, X = H (13), Cl (14), Me (15)) are described. The crystal structures of 1, 5, 6, and 8 show that the Ru-C(alpha) and C(alpha)-C(beta) distances of the allenylidene complexes fall between those of the vinylidene and acetylide relatives. Two reversible redox couples are observed by cyclic voltammetry for 6-9, with E(1/2) values ranging from -1.19 to -1.42 and 0.49 to 0.70 V vs Cp(2)Fe(+/0), and they are both 0.2-0.3 and 0.1-0.2 V more reducing than those for 10-12 and 13-15, respectively. The UV-vis spectra of the vinylidene complexes 1-4 are dominated by intense high-energy bands at lambda(max) < or = 310 nm (epsilon(max) > or = 10(4) dm(3) mol(-1) cm(-1)), while weak absorptions at lambda(max) > or = 400 nm (epsilon(max) < or = 10(2) dm(3) mol(-1) cm(-1)) are tentatively assigned to d-d transitions. The resonance Raman spectrum of 5 contains a nominal nu(C[double bond]C) stretch mode of the vinylidene ligand at 1629 cm(-1). The electronic absorption spectra of the allenylidene complexes 6-9 exhibit an intense absorption at lambda(max) = 479-513 nm (epsilon(max) = (2-3) x 10(4) dm(3) mol(-1) cm(-1)). Similar electronic absorption bands have been found for 10-12, but the lowest energy dipole-allowed transition is blue-shifted by 1530-1830 cm(-1) for the Os analogues 13-15. Ab initio calculations have been performed on the ground state of trans-[Cl(NH(3))(4)Ru[double bond]C[double bond]C[double bond]CPh(2)](+) at the MP2 level, and imply that the HOMO is not localized purely on the metal center or allenylidene ligand. The absorption band of 6 at lambda(max) = 479 nm has been probed by resonance Raman spectroscopy. Simulations of the absorption band and the resonance Raman intensities show that the nominal nu(C[double bond]C[double bond]C) stretch mode accounts for ca. 50% of the total vibrational reorganization energy, indicating that this absorption band is strongly coupled to the allenylidene moiety. The excited-state reorganization of the allenylidene ligand is accompanied by rearrangement of the Ru[double bond]C and Ru[bond]N (of 16-TMC) fragments, which supports the existence of bonding interaction between the metal and C[double bond]C[double bond]C unit in the electronic excited state.

Journal Article↗
PubMed2003

Polymorphic forms of a gold(I) arylacetylide complex with contrasting phosphorescent characteristics.

The spectroscopic properties and crystal structures of the gold(I) arylacetylide complexes [(R(3)P)Au(Ctbd1;CAr)] (R = Cy, Ar = 4-nitrophenyl, 1; 4-trifluoromethylphenyl, 2; pentafluorophenyl, 3; R = Ph, Ar = 4-nitrophenyl, 4) have been examined. The dipole-allowed and -forbidden transitions of 1 (4 in parentheses) at lambda(max) 340 (336) and ca. 485 (470) nm in CH(2)Cl(2) solution at 298 K are assigned to the singlet and triplet intraligand charge transfer (ILCT) transitions of the 4-nitrophenylacetylide moiety, whereas 2 (3 in parentheses) shows localized singlet and triplet acetylenic pipi transitions at lambda(max) 287 (276) and 426 nm, respectively. Two polymorphs of 1 with contrasting phosphorescent characteristics have been identified. At 298 K, the emissive form of 1, as well as 2-4, are highly phosphorescent with peak maximum at 504, 425, 521, and 495 nm, respectively; the other polymorph of 1 is nonemissive at 298 K but emission is detected at 77 K with peak maximum at 486 nm. Crystallographic studies reveal that the major differences between the emissive and nonemissive forms of 1 are the orientations of the molecular dipoles and the dihedral angles between neighboring 4-nitrophenyl moieties. Crystal 2 is isostructural to the nonemissive form of 1, but does not display polymorphism. The molecular planes of two neighboring lumophores are coplanar in the emissive form of 1, parallel in 4, and nearly perpendicular (78.6 degrees ) to each other in the nonemissive form of 1. Both the nature of the excited state and the dihedral angle between adjacent [Au(Ctbd1;CAr)] moieties determine the phosphorescent properties of these molecular crystals.

Journal Article↗
PubMed2003

A bifunctional platinum(II) complex capable of intercalation and hydrogen-bonding interactions with DNA: binding studies and cytotoxicity.

The interactions of [Pt(CNN)(4-dpt)]PF(6), (1; 4-dpt=2,4-diamino-6-(4-pyridyl)-1,3,5-triazine, HCNN=6-phenyl-2,2'-bipyridine) with double-stranded DNA, poly(dA-dT)(2), and poly(dG-dC)(2) were examined by spectroscopic, electrophoretic, and hydrodynamic methods. The spectroscopic data were analyzed with McGhee, van't Hoff, and Gibbs-Helmholtz equations. In a comparative study, [Pt(CNN)(py)]PF(6) (2; py=pyridine) was prepared and the nature of its binding towards DNA was investigated [preliminary results: ChemBioChem 2003, 4, 62-68]. For reactions with calf thymus DNA at 20 degrees C, the intrinsic binding constants for 1 and 2 are (4.6+/-0.2)x10(5) and (2.3+/-0.3)x10(4) mol(-1) dm(3), respectively. Results of DNA-binding reactions revealed that 1 and 2 preferentially bind to the AT sequence of duplex DNA. Intercalation is the preferred binding mode for 2, whereas both intercalation and minor-groove binding are observed for 1. Complex 1 is cytotoxic against a number of carcinoma cell lines, including KB-3-1, CNE-3, and HepG2, and remains potent against multidrug- or cisplatin-resistant KB-V-1 and CNE1 cell lines, for which the resistance ratios are 1.6 and 1.5, respectively. Importantly, 1 is almost an order of magnitude less toxic to the normal cell line CCD-19Lu (IC(50)=176+/-1.7 microM) and it selectively induced apoptosis leading to cancer cell death with less than 5 % detectable necrosis.

Animals↗
PubMed2003

Structural basis for vapoluminescent organoplatinum materials derived from noncovalent interactions as recognition components.

The spectroscopic properties and crystal structures of a series of platinum(II) complexes bearing functionalized sigma-alkynyl groups, namely [(tBu(2)bpy)Pt(C triple bond CAr)(2)] (tBu(2)bpy = 4,4'-bis-tert-butyl-2,2'-bipyridine, Ar = 4-pyridyl, 1; 3-pyridyl, 2; 2-pyridyl, 3; 4-ethynylpyridyl, 4; 2-thienyl, 5; pentafluorophenyl, 6) have been studied. Solid-state emissions of 1 and 6 are dependent on their crystallinity. Reversible and selective vapoluminescence was observed for 1 and 6 in the presence of chlorocarbon vapors. For solid 1, dramatic enhancement of green luminescence is observed upon sorption of CH(2)Cl(2) or CHCl(3) vapor. The excimeric orange emission for solid 6 is switched to monomeric green emission upon exposure to CH(2)Cl(2) vapor. The luminescent responses of a thin film of 1 towards various organic vapors have also been examined. In the crystallographically determined structure of 1.CH(2)Cl(2), the bis(acetylide) moiety acts as the receptor berth for a CH(2)Cl(2) molecule through concerted C-H.pi(C triple bond C) interactions, while Cl.Cl interactions connect the CH(2)Cl(2) molecules into infinite linear chains. The observed crystal lattices are arranged into scaffolds of varying porosity by weak C-H...N(py) (1.CH(2)Cl(2), 1.CH(3)CN, 4.DMF) and C-H...F-C (6, 6.CH(3)CN) interactions. The correlation between the crystal structures of 1.CH(2)Cl(2), 1.CH(3)CN, 2, 4.DMF, 5, 6, and 6.CH(3)CN and their vapoluminescence suggests that weak nonconventional hydrogen-bonding interactions preside over the reversible sensing and signalling processes.

Journal Article↗
PubMed2003

Kinetics and mechanism of the oxidation of alkylaromatic compounds by a trans-dioxoruthenium(VI) complex.

The oxidations of a series of 21 alkylaromatic compounds by trans-[Ru(VI)(L)(O)(2)](2+) (L = 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane) have been studied in CH(3)CN. Toluene is oxidized to benzaldehyde and a small amount of benzyl alcohol. 9,10-Dihydroanthracene is oxidized to anthracene and anthraquinone. Other substrates give oxygenated products. The kinetics of the reactions were monitored by UV-vis spectrophotometry, and the rate law is: -d[Ru(VI)]/dt = k(2)[Ru(VI)][ArCH(3)]. The kinetic isotope effects for the oxidation of toluene/d(8)-toluene and fluorene/d(10)-fluorene are 15 and 10.5, respectively. A plot of Delta H(++) versus Delta S(++) is linear, suggesting a common mechanism for all the substrates. In the oxidation of para-substituted toluenes, a linear correlation between log k(2) and sigma(0) values is observed, consistent with a benzyl radical intermediate. A linear correlation between Delta G(++) and Delta H(0) (the difference between the strength of the bond being broken and that being formed in a H-atom transfer step) is also found, which strongly supports a hydrogen atom transfer mechanism for the oxidation of these substrates by trans-[Ru(VI)(L)(O)(2)](2+). The slope of (0.61 +/- 0.06) is in reasonable agreement with the theoretical slope of 0.5 predicted by Marcus theory.

Journal Article↗
PubMed2003

Reactivity of dioxoosmium(VI) porphyrins toward arylhydrazine. Isolation of hydrazidoosmium and amidoosmium porphyrins.

Reactions of dioxoosmium(VI) porphyrins [Os(VI)(Por)O(2)] with excess 1,1-diphenylhydrazine in tetrahydrofuran at ca. 55 degrees C for 15 min afforded bis(hydrazido(1-))osmium(IV) porphyrins [Os(IV)(Por)(NHNPh(2))(2)] (1a, Por = TPP (meso-tetraphenylporphyrinato dianion); 1b, Por = TTP (meso-tetrakis(p-tolyl)porphyrinato dianion)), hydroxo(amido)osmium(IV) porphyrins [Os(IV)(Por)(NPh(2))(OH)] (2a, Por = TPP; 2b, Por = TTP), and bis(hydrazido(2-))osmium(VI) porphyrin [Os(VI)(Por)(NNPh(2))(2)] (3c, Por = TMP (meso-tetramesitylporphyrinato dianion)). The same reaction under harsher conditions (in refluxing tetrahydrofuran for ca. 1 h) gave a nitridoosmium(VI) porphyrin, [Os(VI)(Por)(N)(OH)] (4b, Por = TTP). Oxidation of 1a,b with bromine in dichloromethane afforded bis(hydrazido(2-)) complexes [Os(VI)(TPP)(NNPh(2))(2)] (3a) and [Os(VI)(TTP)(NNPh(2))(2)] (3b), respectively. All the new osmium porphyrins were identified by (1)H NMR, IR, and UV-vis spectroscopy and mass spectrometry; the structure of 2b was determined by X-ray crystallography (Os-NPh(2) = 1.944(6) A, Os-OH = 1.952(5) A).

Journal Article↗
PubMed2003

Metal-metal interactions in heterobimetallic d8-d10 complexes. Structures and spectroscopic investigation of [M'M' '(mu-dcpm)2(CN)2]+ (M' = Pt, Pd; M' ' = Cu, Ag, Au) and related complexes by UV-vis absorption and resonance Raman spectroscopy and ab initio calculations.

X-ray structural and spectroscopic properties of a series of heterodinuclear d(8)-d(10) metal complexes [M'M' '(mu-dcpm)(2)(CN)(2)](+) containing d(8) Pt(II), Pd(II), or Ni(II) and d(10) Au(I), Ag(I), or Cu(I) ions with a dcpm bridging ligand have been studied (dcpm = bis(dicyclohexylphosphino)methane; M' = Pt, M' ' = Au 4, Ag 5, Cu, 6; M' ' = Au, M' = Pd 7, Ni 8). X-ray crystal analyses showed that the metal...metal distances in these heteronuclear metal complexes are shorter than the sum of van der Waals radii of the M' and M' ' atoms. The UV-vis absorption spectra of 4-6 display red-shifted intense absorption bands from the absorption spectra of the mononuclear trans-[Pt(phosphine)(2)(CN)(2)] and [M' '(phosphine)(2)](+) counterparts, attributable to metal-metal interactions. The resonance Raman spectra confirmed assignments of (1)[nd(sigma)-->(n + 1)p(sigma)] electronic transitions to the absorption bands at 317 and 331 nm in 4 and 6, respectively. The results of theoretical calculations at the MP2 level reveal an attractive interaction energy curve for the skewed [trans-Pt(PH(3))(2)(CN)(2)-Au(PH(3))(2)(+)] dimer. The interaction energy of Pt(II)-Au(I) was calculated to be ca. 0.45 ev.

Journal Article↗
PubMed2003

A cyclodextrin-modified ketoester for stereoselective epoxidation of alkenes.

A beta-cyclodextrin-modified ketoester 2 was prepared by covalent attachment of a reactive ketone moiety to beta-cyclodextrin. Treatment of 2 with Oxone as terminal oxidant would produce CD-substituted dioxirane, which can effect stereoselective alkene epoxidation. The 2-mediated (S)-alpha-terpineol epoxidations proceeded to give terpineol oxides in high yields, and the stereoselectivities (i.e., cis-/trans-epoxide ratio) decreased from 2.5:1 to 1:1.2 with increasing steric bulkiness of the terpenes. This steric-dependent stereoselectivity can be understood based on different binding geometries of the 2/terpene inclusion complexes according to the (1)H NMR titration and 2D ROESY experiments. Enantioselective epoxidation of styrenes has also been achieved with 2 as catalyst (20-50 mol %) in aqueous acetonitrile solution, and up to 40% ee was obtained in 4-chlorostyrene epoxidation at 0 degrees C. Similar enantioselectivities were also obtained for the 2-mediated epoxidation of 1,2-dihydronaphthalene (37% ee), 4-chlorostyrene (36% ee), and trans-stilbene (31% ee).

Binding Sites↗
PubMed2003

Bis-intercalative dinuclear platinum(II) 6-phenyl-2,2'-bipyridine complexes exhibit enhanced DNA affinity but similar cytotoxicity compared to the mononuclear unit.

The interactions between a series of platinum complexes, including (pyridyl)(6-phenyl-2,2'-bipyridine)platinum(II) hexafluorophosphate (1), three dinuclear bis[(6-phenyl-2,2'-bipyridine)platinum(II)] complexes (2-4), and (4-aminopyridine)(4,6-diphenyl-2,2'-bipyridine)platinum(II) perchlorate (5) with DNA have been investigated. All Pt(II) complexes, except 5, were demonstrated to be DNA intercalators, based on viscosity measurements. Absorption and fluorescence titration results indicated that the addition of a phenyl ring to the 6-phenyl-2,2'-bipyridine ligand dramatically reduced the DNA binding of the Pt(II) complex 5. The dinuclear complexes 2-4 exhibited multiple binding modes of mono/bisintercalation and groove binding, as revealed by viscosity and fluorescence titration measurements. While complexes 2-4 bound to DNA with significantly enhanced affinities as compared to 1, compounds 1 and 2-4 showed similar IC(50) values against a panel of cancer cell lines. In addition, these complexes showed similar cellular uptakes. The results indicated that the cytotoxicity of these (6-phenyl-2,2'-bipyridine)platinum compounds may not be mediated through DNA binding but may involve interacting mechanisms with cellular components other than DNA.

Antineoplastic Agents↗
PubMed2003

Gold(III) porphyrins as a new class of anticancer drugs: cytotoxicity, DNA binding and induction of apoptosis in human cervix epitheloid cancer cells.

A series of gold(III) tetraarylporphyrins are stable in the presence of glutathione and exert much higher potency than cisplatin in killing human cancer cells, including the drug-resistant variants; the gold-induced cytotoxicity occurs through an apoptotic pathway according to laser confocal microscopy and flow cytometric studies.

Antineoplastic Agents↗
PubMed2003

Ruthenium porphyrin catalyzed intramolecular carbenoid C[bond]H insertion. Stereoselective synthesis of cis-disubstituted oxygen and nitrogen heterocycles.

[reaction: see text] A ruthenium porphyrin-catalyzed stereoselective intramolecular carbenoid C[bond]H insertion is described. Using [Ru(II)(TTP)(CO)] as catalyst, aryl tosylhydrazones are converted to 2,3-dihydrobenzofurans, 2,3-dihydroindoles, and beta-lactams in good yields and remarkable cis selectivity (up to 99%). Enantioselective synthesis of 2,3-dihydrobenzofurans is also achieved with [Ru(II)(D(4)-Por*)(CO)] as catalyst, and up to 96% ee is attained.

Journal Article↗
PubMed2003

3[(dx2-y2,dxy)(pz)] excited state of binuclear copper(I) phosphine complexes: effect of copper-ligand and copper-copper interactions on excited state properties and photocatalytic reductions of the 4,4'-dimethyl-2,2'-bipyridinium ion in alcohols.

A comprehensive study of the structural and spectroscopic properties of two-, three-, and four-coordinate copper(I) complexes with aliphatic phosphine ligands is presented. All complexes described in this work are characterized by X-ray crystallography. The intramolecular Cu...Cu separations in [Cu2(dcpm)2]X2, [Cu2(dcpm)2-(CH3CN)2]X2, and [Cu2(dmpm)3]-(ClO4)2 (dcpm=bis(dicyclohexylphosphino)methane; dmpm=bis(dimethylphosphino)methane; X=ClO4- and PF6-) are in the range 2.639(2)-3.021(2) A. The anion...CuI interaction is weak, as evidenced by the nearest O...Cu separation of 2.558(6) A in [Cu2(dcpm)2](ClO4)2 and the closest Cu...F separation of 2.79(1) A in [Cu2(dcpm)2](PF6)2. The absorption bands of [Cu2(dcpm)2]X2 and [Cu2(dcpm)2(CH3CN)2]X2 (X=ClO4- and PF6-) at lambda max 307-311 nm in CH2Cl2 are assigned as 1[3d sigma* --> 4p sigma] transitions; this has been confirmed by resonance Raman spectroscopy. The triplet emissions in the visible region from these complexes exhibit long lifetimes and are sensitive to the environment. The lowest emissive excited state is tentatively ascribed as 3[(dx2-y2, dxy)(pz)] in nature. For [Cu2(dcpm)2]2+ salts in CH3CN, the emissive species is postulated to be [Cu2(dcpm)2(CH3CN)n]2+ (n > or = 3). Efficient photocatalytic reduction of MV2+ (4,4'-dimethyl-2,2'-bipyridinium) to MV+ in alcoholic solutions by using [Cu2(dcpm)2](PF6)2 or [Cu2(dppm)2(CH3CN)4](ClO4)2 (dppm=bis(diphenylphosphino)methane) as a catalyst has been observed. The addition of CH3CN or use of [Cu2(dmpm)3]-(ClO4)2 as a catalyst did not allow photocatalytic reduction processes to occur.

Journal Article↗
PubMed2003

Stereoselective synthesis of functionalized pyrrolidines by ruthenium porphyrin-catalyzed decomposition of alpha-diazo esters and cascade azomethine ylide formation/1,3-dipolar cycloaddition reactions.

[reaction: see text] Ruthenium porphyrins catalyze three-component coupling reaction of alpha-diazo esters with a series of N-benzylidene imines and alkenes to form functionalized pyrrolidines in excellent diastereoselectivities. The reaction proceeds via a reactive ruthenium-carbene intermediate and its subsequent reaction with imine to generate azomethine ylide, which reacts with alkenes via 1,3-diploar cycloaddition.

Journal Article↗
PubMed2003

Structural, photophysical, and electrophosphorescent properties of platinum(II) complexes supported by tetradentate N2O2 chelates.

We present an examination of the structural and photophysical characteristics of [Pt(N(2)O(2))] complexes bearing bis(phenoxy)diimine auxiliaries (diimine=4,7-Ph(2)phen (1) and 4,4'-tBu(2)bpy (2)) that are tetradentate relatives of the quinolinolato (q) ligand. These neutral derivatives display high thermal stability (>400 degrees C in N(2)). While the crystal lattice in 1 consists of (head-to-tail)-interacting dimers, molecules of 2 are arranged into infinitely stacked planar sheets with possible pi-pi interactions but no close Pt.Pt contacts. Complexes 1 and 2 exhibit moderately intense low-energy UV/Vis absorptions around lambda=400-500 nm that undergo negative solvatochromic shifts. Both derivatives are highly luminescent in solution at 298 K with emission lifetimes in the micros range, and mixed (3)[l-->pi*(diimine)] (l=lone pair/phenoxide) and (3)[Pt(d)-->pi*(diimine)] charge-transfer states are tentatively assigned. The excited-state properties of 2 are also investigated by time-resolved absorption spectroscopy and by quenching experiments with pyridinium acceptors to estimate the excited-state redox potential. These emitters have been employed as electrophosphorescent dopants in multilayer OLEDs. Differences between the brightness, color, and overall performance of devices incorporating 1 and 2 are attributed to the influence of the diimine substituents.

Journal Article↗
PubMed2003

Solvatochromic response imposed by environmental changes in matrix/chromophore entities: luminescent cyclometalated platinum (II) complex in Nafion and silica materials.

Luminescent cyclometalated complex [Pt(L)py]+ (1) immobilised in Nafion film exhibits a solvatochromic shift in emission maximum from 530 to 650 nm upon immersion in ethanol but no effect is detected with aprotic organic solvents, whereas the emission of the [Pt(L)]+ luminophore anchored in silica materials shows a blue shift from approximately 665 to 550 nm upon exposure to pentane vapour but no shift is observed for ethanol vapour.

Journal Article↗