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207 results on '"Wee, Kyung-Ryang"'

4. Efficient Molecular Array Control and Vapochromic Behavior Changes by Positional Isomer‐Dependent Molecular Building Blocks.

Author

Kim, Min‐Ji, Nam, Gwiung, Ahn, Mina, Lee, Soyoon, Son, Ho‐Jin, and Wee, Kyung‐Ryang

Subjects
STRUCTURAL isomers, INTERMOLECULAR interactions, ISOMERISM, MORPHOLOGY
Abstract

Structurally flexible organic porous molecular arrays are promising for the development of vapochromic materials with superior detection performance. Exploring the photophysical control of vapochromic materials using these molecular arrays is important for the design of new vapochromic materials. However, difficulties arise in the formation and control of organic porous molecular arrays owing to weak and less‐oriented noncovalent forces and their tendency to arrange into energetically preferred high‐density configurations. Herein, an efficient strategy is presented to control molecular arrays by manipulating the shapes of donor–acceptor–donor system‐based molecular building blocks using positional isomerism and report on the correlation between controlled molecular arrays and vapochromic behavior. Depending on their shape (Z‐shaped, quasi‐Z‐shaped, or linear shape), the building blocks formed different molecular arrays that controlled the intermolecular interactions and void volumes. This led to differences in the final microstructural morphologies. Consequently, they exhibited different vapochromic behaviors, and an in‐depth understanding of the correlation between the molecular arrays and vapochromism/vapofluorochromism is obtained. [ABSTRACT FROM AUTHOR]

Published
2024
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9. Photocatalytic Conversion of CO2to Formate/CO by an (η6-para-Cymene)Ru(II) Half-Metallocene Catalyst: Influence of Additives and TiO2Immobilization on the Catalytic Mechanism and Product Selectivity

Author

Lee, Daehan, Molani, Farzad, Choe, Min Su, Lee, Hyun Seok, Wee, Kyung-Ryang, Hwang, Seongpil, Kim, Chul Hoon, Cho, Art E., and Son, Ho-Jin

Abstract

The catalytic efficacy of the monobipyridyl (η6-para-Cymene)Ru(II) half-metallocene, [(p-Cym)Ru(bpy)Cl]+was evaluated in both mixed homogeneous (dye + catalyst) and heterogeneous hybrid systems (dye/TiO2/Catalyst) for photochemical CO2reduction. A series of homogeneous photolysis experiments revealed that the (p-Cym)Ru(II) catalyst engages in two competitive routes for CO2reduction (CO2to formate conversion via RuII-hydride vs CO2to CO conversion through a RuII–COOH intermediate). The conversion activity and product selectivity were notably impacted by the pKavalue and the concentration of the proton source added. When a more acidic TEOA additive was introduced, the half-metallocene Ru(II) catalyst leaned toward producing formate through the RuII–H mechanism, with a formate selectivity of 86%. On the other hand, in homogeneous catalysis with TFE additive, the CO2-to-formate conversion through RuII–H was less effective, yielding a more efficient CO2-to-CO conversion with a selectivity of >80% (TONformateof 140 and TONCOof 626 over 48 h). The preference between the two pathways was elucidated through an electrochemical mechanistic study, monitoring the fate of the metal-hydride intermediate. Compared to the homogeneous system, the TiO2-heterogenized (p-Cym)Ru(II) catalyst demonstrated enhanced and enduring performance, attaining TONs of 1000 for CO2-to-CO and 665 for CO2-to-formate.

Published
2024
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24. Influence of picolinate ancillary ligands on unique photophysical properties of Ir(ppz)2(LX).

Author

Kim, Daehoon, Ahn, Mina, Wee, Kyung-Ryang, and Cho, Dae Won

Abstract

Homoleptic fac-Ir(ppz)3 (ppz = phenylpyrazole) and a series of heteroleptic Ir(ppz)2(LX) complexes consisting of picolinic acid (pic), 3-hydroxypicolinic acid (picOH), and isoquinolinecarboxylic acid (iq) as ancillary ligands (LX) were synthesised to investigate the influence of the ancillary ligands on the photophysical properties of the complexes. Generally, the role of the ancillary ligand is considered insignificant compared to that of the main ligand. Ir(ppz)3 showed deep-blue emission with a vibronic structure at 77 K, whereas Ir(ppz)2(LX) showed a broad and red-shifted emission. Theoretical calculations of the molecular orbitals and energy levels were performed using density functional theory to understand the effect of the ancillary ligands on the emission changes. The 3MLCTppz state was calculated to be higher than the 3MLCTLX state. Therefore, interligand energy transfer (ILET) between the main and ancillary ligands can occur exothermically in the triplet state. The dynamics of the ILET process were monitored directly using a femtosecond time-resolved transient absorption (TA) spectroscopic technique. The 3MLCTppz state was generated upon excitation at 290 nm, and the intensity of the TA band related to the 3MLCTppz state decreased as the time delay increased. Concurrently, the TA band related to the 3MLCTLX state intensified. On the other hand, no further changes in the TA spectra were observed upon direct excitation of the 3MLCTLX state at 420 nm. In contrast with other Ir(ppz)2(LX) complexes, Ir(ppz)2(picOH) produced long-lived TA species, attributed to excited-state intramolecular proton transfer of the picOH ligand in the excited singlet state. [ABSTRACT FROM AUTHOR]

Published
2022
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27. Ultrafast excited state relaxation dynamics in a heteroleptic Ir(iii) complex, fac-Ir(ppy)2(ppz), revealed by femtosecond X-ray transient absorption spectroscopy

Author

Choi, Jungkweon, primary, Ahn, Mina, additional, Lee, Jae Hyuk, additional, Ahn, Doo-Sik, additional, Ki, Hosung, additional, Oh, Inhwan, additional, Ahn, Chi Woo, additional, Choi, Eun Hyuk, additional, Lee, Yunbeom, additional, Lee, Seonggon, additional, Kim, Jungmin, additional, Cho, Dae Won, additional, Wee, Kyung-Ryang, additional, and Ihee, Hyotcherl, additional

Published
2021
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42. Effects of intermolecular interaction on the energy distribution of valance electronic states of a carbazole-based material in amorphous thin films.

Author

Kwon, Soonnam, Wee, Kyung-Ryang, Kim, Jeong Won, Pac, Chyongjin, and Kang, Sang Ook

Subjects
*INTERMOLECULAR interactions, *SPECTRAL energy distribution, *ELECTRONICS, *AMORPHOUS substances, *CARBAZOLE, *THIN films, *ELECTRONIC structure
Abstract

Effects of intermolecular interactions on the occupied electronic structure of amorphous solid of a carbazole-based material were investigated under an assumption that the organic solid consists of randomly oriented assemblies of dimers. The electronic energy states were calculated on the ensemble of large number of random dimers, of which geometries are relaxed using semiempirical van der Waals density functional theory. Intermolecular interactions result in splitting of energy level, and further disorders occur by aggregation of randomly orientated molecules. As a result, frontier occupied energy states can be represented by a superposition of Gaussian distributions, including (i) a main distribution with full width at half maximum of 80-110 meV, depending on the methods of relaxation and (ii) shoulders separated from the center of the main distribution with a value as large as 150 meV. A possible origin for the appearance of these shoulders was ascribed to the presence of molecular assemblies consisting of more tightly bound dimers compared with the others. [ABSTRACT FROM AUTHOR]

Published
2012
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48. Control of Chemoselectivity of SET-Promoted Photoaddition Reactions of Fullerene C60with α-Trimethylsilyl Group-Containing N-Alkylglycinates Yielding Aminomethyl-1,2-dihydrofullerenes or Fulleropyrrolidines

Author

Lim, Suk Hyun, Ahn, Mina, Wee, Kyung-Ryang, Shim, Jun Ho, Choi, Jungkweon, Ahn, Doo-Sik, and Cho, Dae Won

Abstract

Knowledge about factors that govern chemoselectivity is pivotal to the design of reactions that are utilized to produce complex organic substances. In the current study, single-electron transfer (SET)-promoted photoaddition reactions of fullerene C60with both trimethylsilyl and various alkyl group-containing glycinates and ethyl N-alkyl-N-((trimethylsilyl)methyl)glycinates were explored to evaluate how the nature of N-alkyl substituents of glycinate substrates and reaction conditions govern the chemoselectivity of reaction pathways followed. The results showed that photoreactions of C60with glycinates, performed in deoxygenated conditions, produced aminomethyl-1,2-dihydrofullerenes efficiently through a pathway involving the addition of α-amino radical intermediates that are generated by sequential SET-solvent-assisted desilylation of glycinate substrates to C60. Under oxygenated conditions, photoreactions of glycinate substrates, except N-benzyl-substituted analogues, did not take place efficiently owing to quenching of 3C60* by oxygen. Interestingly, N-benzyl-substituted glycinates did react under these conditions to form fulleropyrrolidines through a pathway involving 1,3-dipolar cycloaddition of in situ formed azomethine ylides to C60. The ylide intermediates were formed by regioselective H-atom transfer from glycinates by singlet oxygen. Furthermore, methylene blue (MB)-photosensitized reactions of C60with glycinates under oxygenated conditions took place efficiently to produce fulleropyrrolidines independent of the nature of N-alkyl substituents of glycinates.

Published
2020
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49. Chromophore-Catalyst Assembly for Water Oxidation Prepared by Atomic Layer Deposition

Author

Alibabaei, Leila, Dillon, Robert J., Reilly, Caroline E., Brennaman, M. Kyle, Wee, Kyung-Ryang, Marquard, Seth L., Papanikolas, John M., and Meyer, Thomas J.

Abstract

Visible-light-driven water splitting was investigated in a dye sensitized photoelectrosynthesis cell (DSPEC) based on a photoanode with a phosphonic acid-derivatized donor−π–acceptor (D−π–A) organic chromophore, 1, and the water oxidation catalyst [Ru(bda)(4-O(CH2)3P(O3H2)2-pyr)2], 2, (pyr = pyridine; bda = 2,2′-bipyridine-6,6′-dicarboxylate). The photoanode was prepared by using a layering strategy beginning with the organic dye anchored to an FTO|core/shell electrode, atomic layer deposition (ALD) of a thin layer (<1 nm) of TiO2, and catalyst binding through phosphonate linkage to the TiO2layer. Device performance was evaluated by photocurrent measurements for core/shell photoanodes, with either SnO2or nanoITO core materials, in acetate-buffered, aqueous solutions at pH 4.6 or 5.7. The absolute magnitudes of photocurrent changes with the core material, TiO2spacer layer thickness, or pH, observed photocurrents were 2.5-fold higher in the presence of catalyst. The results of transient absorption measurements and DFT calculations show that electron injection by the photoexcited organic dye is ultrafast promoted by electronic interactions enabled by orientation of the dye’s molecular orbitals on the electrode surface. Rapid injection is followed by recombination with the oxidized dye which is 95% complete by 1.5 ns. Although chromophore decomposition limits the efficiency of the DSPEC devices toward O2production, the flexibility of the strategy presented here offers a new approach to photoanode design.

Published
2024
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