15 results on '"Jae Yoon, Shin"'
Search Results
2. First Evidence of Vibrationally Driven Bimolecular Reactions in Solution: Reactions of Br Atoms with Dimethylsulfoxide and Methanol
- Author
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Jae Yoon Shin, Michael A. Shaloski, Amanda S. Case, and F. Fleming Crim
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Bromine ,010304 chemical physics ,Chemistry ,Photodissociation ,chemistry.chemical_element ,Hydrogen atom ,010402 general chemistry ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Solvent ,symbols.namesake ,0103 physical sciences ,Atom ,Ultrafast laser spectroscopy ,Materials Chemistry ,symbols ,Molecule ,Physical and Theoretical Chemistry ,van der Waals force - Abstract
We present evidence for vibrational enhancement of the rate of bimolecular reactions of Br atoms with dimethylsulfoxide (DMSO) and methanol (CH3OH) in the condensed phase. The abstraction of a hydrogen atom from either of these solvents by a Br atom is highly endoergic: 3269 cm–1 for DMSO and 1416 or 4414 cm–1 for CH3OH, depending on the hydrogen atom abstracted. Thus, there is no thermal abstraction reaction at room temperature. Broadband electronic transient absorption shows that following photolysis of bromine precursors Br atoms form van der Waals complexes with the solvent molecules in about 5 ps and this Br•–solvent complex undergoes recombination. To explore the influence of vibrational energy on the abstraction reactions, we introduce a near-infrared (NIR) pump pulse following the photolysis pulse to excite the first overtone of the C—H (or O—H) stretch of the solvent molecules. Using single-wavelength detection, we observe a loss of the Br•–solvent complex that requires the presence of both photo...
- Published
- 2017
3. Comparative Study of Cl-Atom Reactions in Solution Using Time-Resolved Vibrational Spectroscopy
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F. Fleming Crim, Amanda S. Case, and Jae Yoon Shin
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010304 chemical physics ,Chemistry ,Infrared spectroscopy ,010402 general chemistry ,Photochemistry ,Branching (polymer chemistry) ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Reaction rate ,Solvent ,Reaction rate constant ,Excited state ,0103 physical sciences ,Materials Chemistry ,Physical and Theoretical Chemistry ,Excitation - Abstract
A Cl atom can react with 2,3-dimethylbutane (DMB), 2,3-dimethyl-2-butene (DMBE), and 2,5-dimethyl-2,4-hexadiene (DMHD) in solution via a hydrogen-abstraction reaction. The large exoergicity of the reaction between a Cl atom and alkenes (DMBE and DMHD) makes vibrational excitation of the HCl product possible, and we observe the formation of vibrationally excited HCl (v = 1) for both reactions. In CCl4, the branching fractions of HCl (v = 1), Γ (v = 1), for the Cl-atom reactions with DMBE and DMHD are 0.14 and 0.23, respectively, reflecting an increased amount of vibrational excitation in the products of the more exoergic reaction. In addition, Γ (v = 1) for both reactions is larger in the solvent CDCl3, being 0.23 and 0.40, as the less viscous solvent apparently dampens the vibrational excitation of the nascent HCl less effectively. The bimolecular reaction rates for the Cl reactions with DMB, DMBE, and DMHD in CCl4 are diffusion limited (having rate constants of 1.5 × 10(10), 3.6 × 10(10), and 17.5 × 10(10) M(-1) s(-1), respectively). In fact, the bimolecular reaction rate for Cl + DMHD exceeds a typical diffusion-limited reaction rate, implying that the attractive intermolecular forces between a Cl atom and a C═C bond increase the rate of favorable encounters. The 2-fold increase in the reaction rate of the Cl + DMBE reaction from that of the Cl + DMB reaction likely reflects the effect of the C═C bond, while both the number of C═C bonds and the molecular geometry likely play a role in the large reaction rate of the Cl + DMHD reaction.
- Published
- 2016
4. Neutral Radical and Singlet Biradical Forms of Meso-Free, -Keto, and -Diketo Hexaphyrins(1.1.1.1.1.1): Effects on Aromaticity and Photophysical Properties
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Byung Sun Lee, Atsuhiro Osuka, Min Chul Yoon, Dongho Kim, Taro Koide, Masatoshi Ishida, Jong Min Lim, Jonathan L. Sessler, and Jae Yoon Shin
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Colloid and Surface Chemistry ,Chemistry ,Excited state ,Aromaticity ,General Chemistry ,Singlet state ,Absorption (chemistry) ,Ground state ,Photochemistry ,Biochemistry ,Catalysis ,Lower energy - Abstract
We have investigated the electronic structures and photophysical properties of 5,10,20,25-tetrakis(pentafluorophenyl)-substituted hexaphyrin(1.1.1.1.1.1) (1) and its meso-keto (2) and meso-diketo derivatives (3) using various spectroscopic measurements. In conjunction with theoretical calculations, these analyses revealed fundamental structure-property relationships within this series, including unusual ground-state electronic structures with neutral, monoradical, and singlet biradical character. The meso-free species 1 is a representative 26 π-electron aromatic compound and shows characteristic spectroscopic features, including a sharp Soret band, well-defined Q-like bands, and a moderately long excited state lifetime (τ = 138 ps). In contrast, the meso-keto derivative 2 displays features characteristic of a neutral monoradical species at the ground state, including the presence of lower energy absorption bands in the NIR spectral region and a relatively short excited-state lifetime (13.9 ps). The meso-diketo 3 exhibits features similar to those of 2, specifically NIR absorptions and a short excited-state lifetime (9.7 ps). Compound 3 is thus assigned as being a ground-state singlet biradicaloid. Two photon absorption (TPA) measurements revealed comparatively large σ(2) values of 600 GM for 2 and 1600 GM for 3 with excitation at λ(ex) =1600 nm as compared to that observed for 1 (σ(2): 360 GM). The enhanced nonlinear optical properties of 2 and 3 are rationalized in terms of the open-shell electronic configuration allowing a large, field-induced fluctuation in the electron density (i.e., a large polarization). This interpretation is supported by theoretical evaluations of the static second hyperpolarizabilities (γ) and γ density analyses. Furthermore, nucleus-independent chemical shift (NICS) and harmonic oscillator model of aromaticity (HOMA) values and anisotropy of the induced current density (AICD) plots revealed a clear distinction in terms of the aromatic character of 1-3. Importantly, the open-shell radicaloid 2 and singlet biradicaloid 3 can be formally regarded as 27 π-electron nonaromatic and 26 π-electron aromatic species, respectively, constrained within a dominant 28 π-electron conjugated network. On the basis of the combined experimental and theoretical evidence, it is concluded that the meso-carbonyl groups of 2 and 3 play an important role in perturbing the macrocyclic π-conjugation of the parent hexaphyrin structure 1. In particular, they lead to the imposition of intrinsic radical and biradical character on the molecule as a whole and thus easy-to-discern modifications of the overall electronic effects.
- Published
- 2011
5. Solvent-Dependent Aromatic versus Antiaromatic Conformational Switching in meso-(Heptakis)pentafluorophenyl [32]Heptaphyrin
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Dongho Kim, Min Chul Yoon, Tomoki Yoneda, Jong Min Lim, Atsuhiro Osuka, Shohei Saito, and Jae Yoon Shin
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Absorption spectroscopy ,Chemistry ,Organic Chemistry ,Aromaticity ,General Chemistry ,Photochemistry ,Catalysis ,Crystallography ,Proton NMR ,Singlet state ,Absorption (chemistry) ,Spectroscopy ,Conformational isomerism ,Antiaromaticity - Abstract
We have investigated conformational switching dynamics of meso-heptakis(pentafluorophenyl) [32]heptaphyrin(1.1.1.1.1.1.1) in various solvents using steady-state, time-resolved, and temperature-dependent spectroscopy. Absorption and fluorescence spectra of [32]heptaphyrin are quite sensitive to solvent environments. In nonpolar toluene, the antiaromatic figure-of-eight conformation is dominant, as seen in the X-ray crystallography, based on broad and weak absorption bands without any fluorescence and moderate paratropic ring current. On the other hand, a well-resolved sharp absorption spectrum, strong fluorescence, and diatropic ring current in the 1H NMR spectrum in slightly polar THF indicate that most of [32]heptaphyrin molecules take significantly distorted Möbius conformation with aromatic character. By using transient absorption (TA) spectroscopy, the lowest singlet excited-state lifetimes have been revealed to decay biexponentially with the time constants of 5 and 65 ps for figure-of-eight and Möbius conformations, respectively. Based on these results along with vertical excitation energy calculations, we are able to assign two conformers as Hückel antiaromatic and Möbius aromatic species, respectively; it shoulf be noted that the aromaticity/antiaromaticity does not change with temperature variation. Interestingly, in moderately polar solvent, ethyl ether, we find out that these two conformational isomers coexist with a dynamic equilibrium, as revealed by excitation-wavelength-dependent TA, temperature-dependent absorption and 1H NMR spectra. Through our findings, we have demonstrated that the conformational switching dynamics between Hckel antiaromatic and Möbius aromatic conformers in [32]heptaphyrin(1.1.1.1.1.1.1) are strongly affected by solvent medium as well as temperature.
- Published
- 2011
6. Highly Pure Synthesis, Spectral Assignments, and Two-Photon Properties of Cruciform Porphyrin Pentamers Fused with Benzene Units
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Noboru Ono, Dongho Kim, Hidemitsu Uno, Hiroko Yamada, Tetsuo Okujima, Toshi Nagata, Kil Suk Kim, Kenji Kuroki, Jae Yoon Shin, and Hiroki Uoyama
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Bicyclic molecule ,Pentamer ,Organic Chemistry ,General Chemistry ,Photochemistry ,Porphyrin ,Two-photon absorption ,Catalysis ,chemistry.chemical_compound ,Crystallography ,chemistry ,Cruciform ,Molecule ,Absorption (chemistry) ,HOMO/LUMO - Abstract
Tetrameric porphyrin formation of 2-hydroxymethylpyrrole fused with porphyrins through a bicyclo[2.2.2]octadiene unit gave bicyclo[2.2.2]octadiene-fused porphyrin pentamers. Thermal conversion of the pentamers gave fully pi-conjugated cruciform porphyrin pentamers fused with benzene units in quantitative yields. UV/Vis spectra of fully pi-conjugated porphyrin pentamers showed one very strong Q absorption and were quite different from those of usual porphyrins. From TD-DFT calculations, the HOMO level is 0.49 eV higher than the HOMO-1 level. The LUMO and LUMO+1 levels are very close and are lower by more than 0.27 eV than those of other unoccupied MOs. The strong Q absorption was interpreted as two mutually orthogonal single-electron transitions (683 nm: 86 %, HOMO-->LUMO; 680 nm: 86 %, HOMO-->LUMO+1). The two-photon absorption (TPA) cross section value (sigma((2))) of the benzene-fused porphyrin pentamer was estimated to be 3900 GM at 1500 nm, which is strongly correlated with a cruciform molecular structure with multidirectional pi-conjugation pathways.
- Published
- 2010
7. Protonation-Triggered Conformational Changes to Möbius Aromatic [32]Heptaphyrins(1.1.1.1.1.1.1)
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Kil Suk Kim, Shohei Saito, Atsuhiro Osuka, Dongho Kim, Jae Yoon Shin, and Jong Min Lim
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Chemistry ,Möbius aromaticity ,Computational chemistry ,Aromaticity ,Protonation ,General Chemistry ,General Medicine ,Photochemistry ,Two-photon absorption ,Catalysis - Published
- 2008
8. 2,5-Thienylene-Bridged Triangular and Linear Porphyrin Trimers
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Jae Yoon Shin, Naoki Aratani, Shigeru Yamaguchi, Satoru Hiroto, Atsuhiro Osuka, Jianxin Song, Kil Suk Kim, Hiroshi Shinokubo, Jeyaraman Sankar, So Young Jang, Shanmugam Easwaramoorthi, and Dongho Kim
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Metalloporphyrins ,General Chemistry ,General Medicine ,Sulfides ,Cross-Linking Reagents ,Photochemistry ,Porphyrin ,Two-photon absorption ,Catalysis ,chemistry.chemical_compound ,chemistry ,Thiophene ,Dimerization - Published
- 2008
9. The photophysical properties of expanded porphyrins: relationships between aromaticity, molecular geometry and non-linear optical properties
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Kil Suk Kim, Dongho Kim, Jong Min Lim, Min Chul Yoon, Zin Seok Yoon, and Jae Yoon Shin
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Metals and Alloys ,Aromaticity ,General Chemistry ,Photochemistry ,Catalysis ,Planarity testing ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Ring size ,Nonlinear system ,chemistry.chemical_compound ,Molecular geometry ,chemistry ,Computational chemistry ,Materials Chemistry ,Ceramics and Composites ,Pyrrole - Abstract
Porphyrins, which consist of four pyrrolic subunits, are a ubiquitous class of naturally occurring compound with versatile photophysical properties. As an extension of the basic structure of the porphyrin macrocycle, there have been a multitude of approaches to synthesize expanded porphyrins with more than four pyrrole rings, leading to the modification of the macrocyclic ring size, planarity, number of pi-electrons and aromaticity. However, the relationship between the photophysical properties and the structures of expanded porphyrins has not been systematically investigated. The main purpose of this article is to describe the structure-property relationships of a variety of expanded porphyrins based on experimental and theoretical results, which include steady-state and time-resolved spectroscopic characterizations, non-linear absorption ability and nucleus-independent chemical shift calculations.
- Published
- 2008
10. Photoisomerization and relaxation dynamics of a structurally modified biomimetic photoswitch
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Riccardo Rossi Paccani, Adam D. Dunkelberger, F. Fleming Crim, Ryan D. Kieda, Stefania Fusi, Massimo Olivucci, and Jae Yoon Shin
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Rhodopsin ,Photoisomerization ,Light ,Electrons ,Pyrroline ,Photochemistry ,chemistry.chemical_compound ,Isomerism ,Biomimetics ,Molecule ,Pyrroles ,Physical and Theoretical Chemistry ,Schiff Bases ,Photoswitch ,Molecular Structure ,Chemistry ,Viscosity ,Photoelectron Spectroscopy ,Chromophore ,Photochemical Processes ,Kinetics ,Solvents ,Thermodynamics ,NAIP ,Isomerization ,Methyl group - Abstract
Recent experimental and theoretical studies on N-alkylated indanylidene pyrroline Schiff bases (NAIP) show that these compounds exhibit biomimetic photoisomerization analogous to that in the chromophore of rhodopsin. The NAIP compounds studied previously isomerize rapidly and often evolve coherently on the ground-electronic surface after reaction. We present the results of transient electronic absorption spectroscopy on dMe-OMe-NAIP, a newly synthesized NAIP analogue that differs from other NAIP compounds in the substituents on its pyrrolinium ring. Following excitation with 400 nm light, dMe-OMe-NAIP relaxes from the electronic-excited state in less than 500 fs, which is slower than in other analogues, and does not show the prominent oscillations observed in other NAIP compounds. A reduction in the amount of twisting between the rings caused by removal of the methyl group is likely responsible for the slower isomerization. Measurements in solvents of varying viscosity and structure suggest that intramolecular processes dominate the relaxation of nascent photoproducts.
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- 2012
11. Möbius antiaromatic bisphosphorus complexes of [30]hexaphyrins
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Tomohiro Higashino, Shohei Saito, Jae Yoon Shin, Takahiro Miura, Jong Min Lim, Atsuhiro Osuka, and Dongho Kim
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Chemistry ,Möbius aromaticity ,Phosphorus ,chemistry.chemical_element ,Aromaticity ,General Medicine ,General Chemistry ,Photochemistry ,Catalysis ,Antiaromaticity - Published
- 2010
12. Versatile photophysical properties of meso-aryl-substituted subporphyrins: dipolar and octupolar charge-transfer interactions
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Sung Cho, Jae Yoon Shin, Pyosang Kim, Yasuhide Inokuma, Eiji Tsurumaki, Shanmugam Easwaramoorthi, Dongho Kim, and Atsuhiro Osuka
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Photons ,Magnetic Resonance Spectroscopy ,Porphyrins ,Time Factors ,Aryl ,Organic Chemistry ,Solvatochromism ,Temperature ,General Chemistry ,Photochemistry ,Crystallography, X-Ray ,Acceptor ,Catalysis ,Absorption ,Photoexcitation ,Electron Transport ,chemistry.chemical_compound ,Spectrometry, Fluorescence ,chemistry ,Excited state ,Intramolecular force ,Moiety ,Molecule - Abstract
Donor-acceptor systems based on subporphyrins with nitro and amino substituents at meta and para positions of the meso-phenyl groups were synthesized and their photophysical properties have been systematically investigated. These molecules show two types of charge-transfer interactions, that is, from center to periphery and periphery to center depending on the peripheral substitution, in which the subporphyrin moiety plays a dual role as both donor and acceptor. Based on the solvent-polarity-dependent photophysical properties, we have shown that the fluorescence emission of para isomers originates from the solvatochromic, dipolar, symmetry-broken, and relaxed excited states, whereas the non-solvatochromic fluorescence of meta isomers is of the octupolar type with false symmetry breaking. The restricted meso-(4-aminophenyl) rotation at low temperature prevents the intramolecular charge-transfer (ICT)-forming process. The two-photon absorption (TPA) cross-section values were determined by photoexcitation at 800 nm in nonpolar toluene and polar acetonitrile solvents to see the effect of ICT on the TPA processes. The large enhancement in the TPA cross-section value of approximately 3200 GM (1 GM = 10(-50) cm(4) s photon(-1)) with donor-acceptor substitution has been attributed to the octupolar effect and ICT interactions. A correlation was found between the electron-donating/-withdrawing abilities of the peripheral groups and the TPA cross-section values, that is, p-aminophenyl > m-aminophenyl > nitrophenyl. The increased stability of octupolar ICT interactions in highly polar solvents enhances the TPA cross-section value by a factor of approximately 2 and 4, respectively, for p-amino- and m-nitrophenyl-substituted subporphyrins. On the other hand, the stabilization of the symmetry-broken, dipolar ICT state gives rise to a negligible impact on the TPA processes.
- Published
- 2009
13. Conformational changes of meso-aryl substituted expanded porphyrins upon protonation: effects on photophysical properties and aromaticity
- Author
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Jae Yoon Shin, Kil Suk Kim, Zin Seok Yoon, Atsuhiro Osuka, Dongho Kim, Satoru Hiroto, Jong Min Lim, Soji Shimizu, Min Chul Yoon, and Hiroshi Shinokubo
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Chemistry ,Aryl ,Aromaticity ,Protonation ,Photochemistry ,Two-photon absorption ,Planarity testing ,Surfaces, Coatings and Films ,Crystallography ,symbols.namesake ,chemistry.chemical_compound ,Stokes shift ,Materials Chemistry ,symbols ,Physical and Theoretical Chemistry ,Triplet state ,Pyrrole - Abstract
meso-Hexakis(pentafluorophenyl) [30]heptaphyrin(1.1.1.1.1.1.0) and meso-hexakis(pentafluorophenyl) [38]nonaphyrin(1.1.0.1.1.0.1.1.0) have been investigated with a particular focus on their photophysical properties affected by protonation with acids using steady-state and time-resolved spectroscopic measurements along with femtosecond Z-scan method. It was found that the smaller Stokes shift and longer excited singlet/triplet state lifetimes of protonated [30]heptaphyrin and [38]nonaphyrin compared to their distorted neutral counterparts are strongly associated with the rigid and planar molecular structures. Much larger two photon absorption cross-section values of protonated [30]heptaphyrin and [38]nonaphyrin (6300 and 6040 GM) than those of their neutral forms (1350 and 1300 GM) also reflect the enhanced rigidity and planarity as well as aromaticity. In parallel with this, the nucleus-independent chemical shift (NICS) values of protonated forms exhibit large negative values, -14.3 and -11.5 ppm for [30]heptaphyrin and [38]nonaphyrin, respectively, at central positions. Thus we have demonstrated the structure-property relationships between molecular planarity, photophysical properties, and aromaticity of expanded porphyrins upon protonation based on our experimental and theoretical investigations. This study also promises a possibility of structural control of expanded porphyrins through protonation in which the molecular flexibilities of expanded porphyrins lead to distorted structures especially as the number of pyrrole rings increases.
- Published
- 2009
14. A Stable Non-Kekulé Singlet Biradicaloid from meso-Free 5,10,20,25-Tetrakis(Pentafluorophenyl)-Substituted [26]Hexaphyrin(1.1.1.1.1.1)
- Author
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Atsuhiro Osuka, Ko Furukawa, Taro Koide, Hiroshi Shinokubo, Kil Suk Kim, Dongho Kim, and Jae Yoon Shin
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Delocalized electron ,Colloid and Surface Chemistry ,Unpaired electron ,Chemistry ,General Chemistry ,Singlet state ,Photochemistry ,Biochemistry ,Catalysis ,Electronic states - Abstract
A meso,meso-diketohexaphyrin was isolated and characterized as a chemically stable non-Kekulé singlet biradicaloid. Two unpaired electrons are seemingly delocalized on two tripyrrolic units separated by C=O bonds. These results underscore the potential of expanded porphyrins to achieve unique electronic states.
- Published
- 2010
15. Cruciform Porphyrin Pentamers
- Author
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K. S. Kim, Tetsuo Okujima, Kenji Kuroki, Hiroko Yamada, D. Kim, N. Ono, Jae Yoon Shin, Hidemitsu Uno, Toshi Nagata, and Hiroki Uoyama
- Subjects
chemistry.chemical_compound ,Cruciform ,Chemistry ,Retro-Diels–Alder reaction ,Photochemistry ,Two-photon absorption ,Porphyrin - Published
- 2010
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