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199 results on '"Guan, Xiangguo"'

6. Luminescent ruffled iridium(iii) porphyrin complexes containing N-heterocyclic carbene ligands: structures, spectroscopies and potent antitumor activities under dark and light irradiation conditions

Author

Lam, Tsz-Lung, primary, Tong, Ka-Chung, additional, Yang, Chen, additional, Kwong, Wai-Lun, additional, Guan, Xiangguo, additional, Li, Ming-De, additional, Kar-Yan Lo, Vanessa, additional, Lai-Fung Chan, Sharon, additional, Lee Phillips, David, additional, Lok, Chun-Nam, additional, and Che, Chi-Ming, additional

Published
2019
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10. A resonance Raman spectroscopic and CASSCF investigation of the Franck-Condon region structural dynamics and conical intersections of thiophene.

Author

Wu, Xian-Fang, Zheng, Xuming, Wang, Hui-Gang, Zhao, Yan-Yin, Guan, Xiangguo, Phillips, David Lee, Chen, Xuebo, and Fang, Weihai

Subjects
THIOPHENES spectra, FRANCK-Condon principle, RAMAN spectroscopy, CYCLOHEXANE, PHOTODISSOCIATION, MOLECULAR dynamics, RESONANCE Raman effect, POTENTIAL energy surfaces
Abstract

Resonance Raman spectra were acquired for thiophene in cyclohexane solution with 239.5 and 266 nm excitation wavelengths that were in resonance with ∼240 nm first intense absorption band. The spectra indicate that the Franck-Condon region photodissociation dynamics have multidimensional character with motion mostly along the reaction coordinates of six totally symmetry modes and three nontotally symmetry modes. The appearance of the nontotally symmetry modes, the C[Single_Bond]S antisymmetry stretch +C[Single_Bond]C==C bend mode ν21(B2) at 754 cm-1 and the H7C3[Single_Bond]C4H8 twist ν9(A2) at 906 cm-1, suggests the existence of two different types of vibronic-couplings or curve-crossings among the excited states in the Franck-Condon region. The electronic transition energies, the excited state structures, and the conical intersection points 1B1/1A1 and 1B2/1A1 between 2 1A1 and 1 1B2 or 1 1B1 potential energy surfaces of thiophene were determined by using complete active space self-consistent field theory computations. These computational results were correlated with the Franck-Condon region structural dynamics of thiophene. The ring opening photodissociation reaction pathway through cleavage of one of the C[Single_Bond]S bonds and via the conical intersection point 1B1/1A1 was revealed to be the predominant ultrafast reaction channel for thiophene in the lowest singlet excited state potential energy hypersurface, while the internal conversion pathway via the conical intersection point 1B2/1A1 was found to be the minor decay channel in the lowest singlet excited state potential energy hypersurface. [ABSTRACT FROM AUTHOR]

Published
2010
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16. Stable luminescent iridium(iii) complexes with bis(N-heterocyclic carbene) ligands: photo-stability, excited state properties, visible-light-driven radical cyclization and CO2 reduction, and cellular imaging

Author

Yang, Chen, primary, Mehmood, Faisal, additional, Lam, Tsz Lung, additional, Chan, Sharon Lai-Fung, additional, Wu, Yuan, additional, Yeung, Chi-Shun, additional, Guan, Xiangguo, additional, Li, Kai, additional, Chung, Clive Yik-Sham, additional, Zhou, Cong-Ying, additional, Zou, Taotao, additional, and Che, Chi-Ming, additional

Published
2016
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21. Palladium(II) Acetylide Complexes with Pincer-Type Ligands: Photophysical Properties, Intermolecular Interactions, and Photo-cytotoxicity.

Author

Hung, Faan ‐ Fung, Wu, Shui ‐ Xing, To, Wai ‐ Pong, Kwong, Wai ‐ Lun, Guan, Xiangguo, Lu, Wei, Low, Kam ‐ Hung, and Che, Chi ‐ Ming

Subjects
PALLADIUM, ACETYLIDES, LIGANDS (Chemistry), INTERMOLECULAR interactions, DENSITY functional theory
Abstract

Two classes of cationic palladium(II) acetylide complexes containing pincer-type ligands, 2,2′:6′,2′′-terpyridine (terpy) and 2,6-bis(1-butylimidazol-2-ylidenyl)pyridine (C^N^C), were prepared and structurally characterized. Replacing terpy with the strongly σ-donating C^N^C ligand with two N-heterocyclic carbene (NHC) units results in the PdII acetylide complexes displaying phosphorescence at room temperature and stronger intermolecular interactions in the solid state. X-ray crystal structures of [Pd(terpy)(C≡CPh)]PF6 ( 1) and [Pd(C^N^C)(C≡CPh)]PF6 ( 7) reveal that the complex cations are arranged in a one-dimensional stacking structure with pair-like PdII⋅⋅⋅PdII contacts of 3.349 Å for 1 and 3.292 Å for 7. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to examine the electronic properties. Comparative studies of the [Pt(L)(C≡CPh)]+ analogs by 1H NMR spectroscopy shed insight on the intermolecular interactions of these PdII acetylide complexes. The strong Pd−Ccarbene bonds render 7 and its derivative sufficiently stable for investigation of photo-cytotoxicity under cellular conditions. [ABSTRACT FROM AUTHOR]

Published
2017
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29. Structurally robust phosphorescent [Pt(O^N^C^N)] emitters for high performance organic light-emitting devices with power efficiency up to 126 lm W−1 and external quantum efficiency over 20%

Author

Cheng, Gang, primary, Kui, Steven C. F., additional, Ang, Wai-Hung, additional, Ko, Man-Ying, additional, Chow, Pui-Keong, additional, Kwong, Chun-Lam, additional, Kwok, Chi-Chung, additional, Ma, Chensheng, additional, Guan, Xiangguo, additional, Low, Kam-Hung, additional, Su, Shi-Jian, additional, and Che, Chi-Ming, additional

Published
2014
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31. Bis(sulfonylimide)ruthenium(VI) Porphyrins: X-ray Crystal Structure and Mechanism of CH Bond Amination by Density Functional Theory Calculations

Author

Guo, Zhen, Guan, Xiangguo, Huang, Jie Sheng, Tsui, Waiman, Lin, Zhenyang, Che, Chi Ming, Guo, Zhen, Guan, Xiangguo, Huang, Jie Sheng, Tsui, Waiman, Lin, Zhenyang, and Che, Chi Ming

Abstract

The X-ray crystal structure of [Ru-VI(NMs)(2)(tmp)] (Ms=SO2- p-MeOC6H4; tmp=5,10,15,20-tetramesitylporphyrinato(2-)), a metal sulfonylimide complex that can undergo alkene aziridination and CH bond amination reactions, shows a RuN distance of 1.79(3)angstrom and Ru-N-S angle of 162.5(3)degrees. Density functional theory (DFT) calculations on the electronic structures of [Ru-VI(NMs)(2)(tmp)] and model complex [Ru-VI(NMs)(2)(por(0))] (por(0)=unsubstituted porphyrinato(2-)) using the M06L functional gave results in agreement with experimental observations. For the amination of ethylbenzene by the singlet ground state of [Ru-VI(NMs)(2)(por(0))], DFT calculations using the M06L functional revealed an effectively concerted pathway involving rate-limiting hydrogen atom abstraction without a distinct radical rebound step. The substituent effect on the amination reactivity of ethylbenzene by [Ru-VI(NX)(2)(por(0))] (X=SO2-p-YC6H4 with Y=MeO, Me, H, Cl, NO2) was examined. Electron-withdrawing Ygroups lower the energy of the LUMOs of [Ru-VI(NX)(2)(por(0))], thus facilitating their interaction with the low-lying HOMO of the ethylbenzene CH bond and hence increasing the reactivity of [Ru-VI(NX)(2)(por(0))]. DFT calculations on the amination/aziridination reactions of [Ru-VI(NSO2C6H5)(2)(por(0))] with pent-4-enal, an aldehyde substrate bearing acyl, homoallylic, and allylic CH bonds and a CC bond, revealed a lower reaction barrier for the amination of the acyl CH bond than for both the amination of the other CH bonds and aziridination of the CC bond in this substrate.

Published
2013

32. How and When Does an Unusual and Efficient Photoredox Reaction of 2-(1-Hydroxyethyl) 9,10-Anthraquinone Occur? A Combined Time-Resolved Spectroscopic and DFT Study

Author

Ma, Jiani, Su, Tao, Li, Mingde, Du, Wei, Huang, Jinqing, Guan, Xiangguo, Phillips, David Lee, Ma, Jiani, Su, Tao, Li, Mingde, Du, Wei, Huang, Jinqing, Guan, Xiangguo, and Phillips, David Lee

Abstract

The photophysics and photochemical reactions of 2-(1-hydroxyethyl) 9,10-anthroquinone (2-HEAQ) were studied using femtosecond transient absorption (fs-TA), nanosecond transient absorption (ns-TA), and nanosecond time-resolved resonance Raman (ns-TR3) spectroscopy techniques and density functional theory (DFT) calculations. In acetonitrile, 2-HEAQ underwent efficient intersystem crossing to the triplet excited state ((2-HEAQ) 3). A typical photoreduction reaction for aromatic ketones took place via production of a ketyl radical intermediate for 2-HEAQ in isopropanol. In water-containing solutions with pH values between 2 and 10, an unusual photoredox reaction reported by Wan and co-workers was detected and characterized. Observation of the protonated species in neutral and acidic aqueous solutions by fs-TA spectra indicated the carbonyl oxygen of (2-HEAQ)3 was protonated initially and acted as a precursor of the photoredox reaction. The preference of the photoredox reaction to occur under moderate acidic conditions compared to neutral condition observed using ns-TR3 spectroscopy was consistent with results from DFT calculations, which suggested protonation of the carbonyl group was the rate-determining step. Under stronger acidic conditions (pH 0), although the protonated (2-HEAQ)3 was formed, the predominant reaction was the photohydration reaction instead of the photoredox reaction. In stronger basic solutions (pH 12), (2-HEAQ)3 decayed with no obvious photochemical reactions detected by time-resolved spectroscopic experiments. Reaction mechanisms and key reactive intermediates for the unusual photoredox reaction were elucidated from time-resolved spectroscopy and DFT results. A brief discussion is given of when photoredox reactions may likely take place in the photochemistry of aromatic carbonyl-containing compounds and possible implications for using BP and AQ scaffolds for phototrigger compounds. © 2012 American Chemical Society.

Published
2012

41. Highly Enantioselective Iron-Catalyzed cis-Dihydroxylation of Alkenes with Hydrogen Peroxide Oxidant via an FeIII-OOH Reactive Intermediate.

Author

Zang, Chao, Liu, Yungen, Xu, Zhen‐Jiang, Tse, Chun‐Wai, Guan, Xiangguo, Wei, Jinhu, Huang, Jie‐Sheng, and Che, Chi‐Ming

Subjects
CATALYSTS, ENANTIOSELECTIVE catalysis, ALKENES, CHIRALITY, CHEMICAL bonds
Abstract

The development of environmentally benign catalysts for highly enantioselective asymmetric cis-dihydroxylation (AD) of alkenes with broad substrate scope remains a challenge. By employing [FeII(L)(OTf)2] (L= N, N′-dimethyl- N, N′-bis(2-methyl-8-quinolyl)-cyclohexane-1,2-diamine) as a catalyst, cis-diols in up to 99.8 % ee with 85 % isolated yield have been achieved in AD of alkenes with H2O2 as an oxidant and alkenes in a limiting amount. This '[FeII(L)(OTf)2]+H2O2' method is applicable to both ( E)-alkenes and terminal alkenes (24 examples >80 % ee, up to 1 g scale). Mechanistic studies, including 18O-labeling, UV/Vis, EPR, ESI-MS analyses, and DFT calculations lend evidence for the involvement of chiral FeIII-OOH active species in enantioselective formation of the two C−O bonds. [ABSTRACT FROM AUTHOR]

Published
2016
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44. Unraveling the Mechanism of the Photodeprotection Reaction of 8‐Bromo‐ and 8‐Chloro‐7‐hydroxyquinoline Caged Acetates

Author

Ma, Jiani, primary, Rea, Adam C., additional, An, Huiying, additional, Ma, Chensheng, additional, Guan, Xiangguo, additional, Li, Ming‐De, additional, Su, Tao, additional, Yeung, Chi Shun, additional, Harris, Kyle T., additional, Zhu, Yue, additional, Nganga, Jameil L., additional, Fedoryak, Olesya D., additional, Dore, Timothy M., additional, and Phillips, David Lee, additional

Published
2012
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45. cis-Dioxorhenium(V/VI) Complexes Supported by Neutral Tetradentate N4Ligands. Synthesis, Characterization, and Spectroscopy

Author

Ng, Vicky Yin-Ming, Tse, Chun-Wai, Guan, Xiangguo, Chang, Xiaoyong, Yang, Chen, Low, Kam-Hung, Lee, Hung Kay, Huang, Jie-Sheng, and Che, Chi-Ming

Abstract

A series of cis-dioxorhenium(V) complexes containing chiral tetradentate N4ligands, including cis-[ReV(O)2(pyxn)]+(1; pyxn = N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)cyclohexane-1,2-diamine), cis-[ReV(O)2(6-Me2pyxn)]+(cis-2), cis-[ReV(O)2(R,R-pdp)]+(3; R,R-pdp = 1,1′-bis((R,R)-2-pyridinylmethyl)-2,2′-bipyrrolidine), cis-[ReV(O)2(R,R-6-Me2pdp)]+(4), and cis-[ReV(O)2(bqcn)]+(5; bqcn = N,N′-dimethyl-N,N′-di(quinolin-8-yl)cyclohexane-1,2-diamine), were synthesized. Their structures were established by X-ray crystallography, showing Re–O distances in the range of 1.740(3)–1.769(8) Å and O–Re–O angles of 121.4(2)–124.8(4)°. Their cyclic voltammograms in MeCN (0.1 M [NBu4]PF6) display a reversible ReVI/Vcouple at E1/2= 0.39–0.49 V vs SCE. In aqueous media, three proton-coupled electron transfer reactions corresponding to ReVI/V, ReV/III, and ReIII/IIcouples were observed at pH 1. The Pourbaix diagrams of 1·OTf, 3·OTf, and 5·OTf have been examined. The electronic absorption spectra of the cis-dioxorhenium(V) complexes show three absorption bands at around 800 nm (600–1730 dm3mol–1cm–1), 580 nm (1700–5580 dm3mol–1cm–1), and 462–523 nm (3170–6000 dm3mol–1cm–1). Reaction of 1with Lewis acids (or protic acids) gave cis-[ReV(O)(OH)(pyxn)]2+(1·H+), in which the Re–O distances are lengthened to 1.788(5) Å. Complex cis-2resulted from isomerization of trans-2at elevated temperature. cis-[ReVI(O)2(pyxn)](PF6)2(1′·(PF6)2) was obtained by constant-potential electrolysis of 1·PF6in MeCN (0.1 M [NBu4]PF6) at 0.56 V vs SCE; it displays shorter Re–O distances (1.722(4), 1.726(4) Å) and a smaller O–Re–O angle (114.88(18)°) relative to 1and shows a d–d transition absorption band at 591 nm (ε = 77 dm3mol–1cm–1). With a driving force of ca. 75 kcal mol–1, 1′oxidizes hydrocarbons with weak C–H bonds (75.5–76.3 kcal mol–1) via hydrogen atom abstraction. DFT and TDDFT calculations on the electronic structures and spectroscopic properties of the cis-dioxorhenium(V/VI) complexes were performed.

Published
2017
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