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Kim J, Woo KC, Kim KK, Kang M, Kim SK. Tunneling dynamics dictated by the multidimensional conical intersection seam in the πσ*‐mediated photochemistry of heteroaromatic molecules. B KOREAN CHEM SOC 2021. [DOI: 10.1002/bkcs.12453] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Junggil Kim
- Department of Chemistry, KAIST Daejeon Republic of Korea
| | - Kyung Chul Woo
- Department of Chemistry, KAIST Daejeon Republic of Korea
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences Nanyang Technological University Singapore Singapore
| | - Kuk Ki Kim
- Department of Chemistry, KAIST Daejeon Republic of Korea
| | - Minseok Kang
- Department of Chemistry, KAIST Daejeon Republic of Korea
| | - Sang Kyu Kim
- Department of Chemistry, KAIST Daejeon Republic of Korea
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2
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Cooper GA, Cobbin MR, Ashfold MNR. Effects of Ring Fluorination on the Ultraviolet Photodissociation Dynamics of Phenol. J Phys Chem A 2020; 124:9698-9709. [PMID: 33179506 DOI: 10.1021/acs.jpca.0c08927] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The dynamics of photoinduced O-H bond fission in five fluorinated phenols (2-fluorophenol, 3-fluorophenol, 2,6-difluorophenol, 3,4,5-trifluorophenol, and pentafluorophenol) have been investigated by H Rydberg atom photofragment translational spectroscopy following excitation at many wavelengths in the range 220 ≤ λ ≤ 275 nm. The presence of multiple fluorine substituents reduces the efficiency of O-H bond fission (by tunneling) from the first excited (11ππ*) electronic state, whereas all bar the perfluorinated species undergo O-H bond fission when excited at shorter wavelengths (to the 21ππ* state). As in bare phenol, O-H bond fission is deduced to occur by non-adiabatic coupling at conical intersections between the photoprepared "bright" ππ* states and the 11πσ* potential energy surface. In all cases, the fluorophenoxyl photoproducts are found to be formed in a range of vibrational levels, all of which include an odd number of quanta (typically one) in an out-of-plane (a″) vibrational mode; this product vibration is viewed as a legacy of the parent out-of-plane motions that promote non-adiabatic coupling to the dissociative 11πσ* potential. The radical products also show activity in in-plane vibrations involving coupled (both in- and out-of-phase) C-O and C-F wagging motions, which can be traced to the impulse between the recoiling O and H atoms and, in detail, are sensitive to the presence (or not) of an intramolecular F···H-O hydrogen bond. Upper limit values for the O-H bond dissociation energies are reported for all molecules studied apart from pentafluorophenol.
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Affiliation(s)
- Graham A Cooper
- School of Chemistry, University of Bristol, Bristol BS8 1TS, U.K
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3
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Horbury MD, Turner MAP, Peters JS, Mention M, Flourat AL, Hine NDM, Allais F, Stavros VG. Exploring the Photochemistry of an Ethyl Sinapate Dimer: An Attempt Toward a Better Ultraviolet Filter. Front Chem 2020; 8:633. [PMID: 32850651 PMCID: PMC7399488 DOI: 10.3389/fchem.2020.00633] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Accepted: 06/17/2020] [Indexed: 11/16/2022] Open
Abstract
The photochemistry and photostability of a potential ultraviolet (UV) radiation filter, dehydrodiethylsinapate, with a broad absorption in the UVA region, is explored utilizing a combination of femtosecond time-resolved spectroscopy and steady-state irradiation studies. The time-resolved measurements show that this UV filter candidate undergoes excited state relaxation after UV absorption on a timescale of ~10 picoseconds, suggesting efficient relaxation. However, steady-state irradiation measurements show degradation under prolonged UV exposure. From a photochemical standpoint, this highlights the importance of considering both the ultrafast and “ultraslow” timescales when designing new potential UV filters.
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Affiliation(s)
- Michael D Horbury
- School of Electronic and Electrical Engineering, University of Leeds, Leeds, United Kingdom
| | - Matthew A P Turner
- Department of Chemistry, University of Warwick, Coventry, United Kingdom
| | - Jack S Peters
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, Oxford, United Kingdom
| | | | | | - Nicholas D M Hine
- Department of Chemistry, University of Warwick, Coventry, United Kingdom
| | | | - Vasilios G Stavros
- Department of Chemistry, University of Warwick, Coventry, United Kingdom
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4
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Deng X, Tang Y, Song X, Liu K, Gu Z, Zhang B. Photolysis dynamics of m- and o-fluorophenol: Substitution effects on tunneling mechanism. CHEMOSPHERE 2020; 253:126747. [PMID: 32464759 DOI: 10.1016/j.chemosphere.2020.126747] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/30/2019] [Revised: 04/03/2020] [Accepted: 04/07/2020] [Indexed: 06/11/2023]
Abstract
The photolysis dynamics of m-fluorophenol (m-FPhOH) and o-fluorophenol (o-FPhOH) have been investigated with time-resolved velocity map imaging (TR-VMI) and time-resolved ion-yield (TR-IY) techniques. Following excitation to the origin of S1 (ππ∗) state of m- and o-FPhOH, H atoms elimination mediated by tunneling through the potential barrier under the S1 (ππ∗)/S2 (πσ∗) conical intersection (CI) has been observed as a Gaussian feature signal centered at a total kinetic energy release (TKER) of ∼6000 cm-1 for both molecules. The quantum tunneling mechanism has been identified as the main decay pathway of S1 state for m-FPhOH, and the tunneling lifetime of 2.1 ns has been obtained from the TR-VMI measurements of H fragments. This tunneling mechanism is further confirmed by the studies on the selective O-H deuterated species, m-FPhOD, and consolidated by our theoretical calculations. However, the photolysis dynamics is quite different for the photoexcited o-FPhOH. The much lower yield of the H atoms originating from tunneling hinders the extraction of a reliable tunneling lifetime for o-FPhOH. Our theoretical calculations exhibit a broader and higher potential barrier exists beneath the S1/S2 CI of o-FPhOH, which increase the difficulty for tunneling. Furthermore, the special existence of intramolecular hydrogen bond in o-FPhOH is probably also the key factor that affects the tunneling rate, which would restrict the O-H stretch motion.
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Affiliation(s)
- Xulan Deng
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan, 430071, China; University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Ying Tang
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan, 430071, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
| | - Xinli Song
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan, 430071, China; University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Kai Liu
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan, 430071, China; University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Zhenfei Gu
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan, 430071, China; University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Bing Zhang
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Innovation Academy for Precision Measurement Science and Technology, Chinese Academy of Sciences, Wuhan, 430071, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
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5
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Vansco MF, Marchetti B, Lester MI. Electronic spectroscopy of methyl vinyl ketone oxide: A four-carbon unsaturated Criegee intermediate from isoprene ozonolysis. J Chem Phys 2019; 149:244309. [PMID: 30599734 DOI: 10.1063/1.5064716] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Ozonolysis of isoprene, one of the most abundant volatile organic compounds in the atmosphere, proceeds through methyl vinyl ketone oxide (MVK-oxide), methacrolein oxide, and formaldehyde oxide (CH2OO) Criegee intermediates. The present study focuses on MVK-oxide, a four-carbon unsaturated carbonyl oxide intermediate, using vacuum ultraviolet photoionization at 118 nm and UV-visible induced depletion of the m/z = 86 mass channel to characterize its first π* ← π electronic transition. The electronic spectrum is broad and unstructured with its peak at 388 nm (3.2 eV). The MVK-oxide spectrum is shifted to a significantly longer wavelength than CH2OO and alkyl-substituted Criegee intermediates studied previously due to extended conjugation across the vinyl and carbonyl oxide groups. Electronic excitation results in rapid dissociation at λ ≤ 430 nm to methyl vinyl ketone and O 1D products, the latter detected by 2 + 1 resonance enhanced multiphoton ionization using velocity map imaging. Complementary electronic structure calculations (CASPT2(12,10)/AVDZ) predict two π* ← π transitions with significant oscillator strength for each of the four conformers of MVK-oxide with vertical excitation energies (and corresponding wavelengths) in the 3.1-3.6 eV (350-400 nm) and 4.5-5.5 eV (220-280 nm) regions. The computed electronic absorption profile of MVK-oxide, based on a Wigner distribution of ground state configurations and summed over the four conformers, is predicted to peak at 397 nm. UV-visible spectroscopy on the first π* ← π transition is shown by a combination of experiment and theory to provide a sensitive method for detection of the MVK-oxide Criegee intermediate that will enable further studies of its photochemistry and unimolecular and bimolecular reaction dynamics.
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Affiliation(s)
- Michael F Vansco
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
| | - Barbara Marchetti
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
| | - Marsha I Lester
- Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, USA
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6
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Excited states dissociation dynamics of indole-x-carboxaldehyde (x = 4, 5, 6, 7): Theoretical and experimental study. Chem Phys 2018. [DOI: 10.1016/j.chemphys.2018.09.019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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7
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Miyazaki M, Washio N, Fujii M. Electron-proton transfer mechanism of excited-state hydrogen transfer in phenol−(NH3) (n = 5) studied by delayed ionization detected femtosecond time-resolved NIR spectroscopy. Chem Phys 2018. [DOI: 10.1016/j.chemphys.2018.08.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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8
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Dyakov YA, Toliautas S, Trakhtenberg LI, Valkunas L. Excited state photodissociation dynamics of 2-, 3-, 4-hydroxyacetophenone: Theoretical study. Chem Phys 2018. [DOI: 10.1016/j.chemphys.2018.07.020] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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9
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Marchetti B, Karsili TNV, Ashfold MNR, Domcke W. A 'bottom up', ab initio computational approach to understanding fundamental photophysical processes in nitrogen containing heterocycles, DNA bases and base pairs. Phys Chem Chem Phys 2018; 18:20007-27. [PMID: 26980149 DOI: 10.1039/c6cp00165c] [Citation(s) in RCA: 67] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The availability of non-radiative decay mechanisms by which photoexcited molecules can revert to their ground electronic state, without experiencing potentially deleterious chemical transformation, is fundamental to molecular photostability. This Perspective Article combines results of new ab initio electronic structure calculations and prior experimental data in an effort to systematise trends in the non-radiative decay following UV excitation of selected families of heterocyclic molecules. We start with the prototypical uni- and bicyclic molecules phenol and indole, and explore the structural and photophysical consequences of incorporating progressively more nitrogen atoms within the respective ring structures en route to the DNA bases thymine, cytosine, adenine and guanine. For each of the latter, we identify low energy non-radiative decay pathways via conical intersections with the ground state potential energy surface accessed by out-of-plane ring deformations. This is followed by summary descriptions and illustrations of selected rival (electron driven H atom transfer) non-radiative excited state decay processes that demand consideration once the nucleobases are merely components in larger biomolecular systems like nucleosides, and both individual and stacked base-pairs.
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Affiliation(s)
- Barbara Marchetti
- School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
| | - Tolga N V Karsili
- School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK. and Department of Chemistry, Technische Universität München, Lichtenbergstr. 4, 85748 Garching, Germany
| | - Michael N R Ashfold
- School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
| | - Wolfgang Domcke
- Department of Chemistry, Technische Universität München, Lichtenbergstr. 4, 85748 Garching, Germany
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10
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A b initio quantum direct dynamics simulations of ultrafast photochemistry with Multiconfigurational Ehrenfest approach. Chem Phys 2017. [DOI: 10.1016/j.chemphys.2017.04.003] [Citation(s) in RCA: 79] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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11
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Schalk O, Stenrup M, Geng T, Lindh R, Thomas RD, Feifel R, Hansson T. Influence of Alkoxy Groups on the Photoinduced Dynamics of Organic Molecules Exemplified on Alkyl Vinyl Ethers. J Phys Chem A 2015; 119:11105-12. [DOI: 10.1021/acs.jpca.5b06592] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- O. Schalk
- Department
of Chemical Physics, AlbaNova University Centre, Stockholm University, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
| | | | - T. Geng
- Department
of Chemical Physics, AlbaNova University Centre, Stockholm University, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
| | | | - R. D. Thomas
- Department
of Chemical Physics, AlbaNova University Centre, Stockholm University, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
| | - R. Feifel
- Department
of Physics, University of Gothenburg, Origovägen 6B, 412 96 Gothenburg, Sweden
| | - T. Hansson
- Department
of Chemical Physics, AlbaNova University Centre, Stockholm University, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
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12
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Ruiz-Santoyo JA, Rodríguez-Matus M, Cabellos JL, Yi JT, Pratt DW, Schmitt M, Merino G, Álvarez-Valtierra L. Intramolecular structure and dynamics of mequinol and guaiacol in the gas phase: Rotationally resolved electronic spectra of their S1 states. J Chem Phys 2015; 143:094301. [DOI: 10.1063/1.4928696] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- José Arturo Ruiz-Santoyo
- División de Ciencias e Ingenierías, Universidad de Guanajuato-Campus León, León, Guanajuato 37150, Mexico
| | - Marcela Rodríguez-Matus
- División de Ciencias e Ingenierías, Universidad de Guanajuato-Campus León, León, Guanajuato 37150, Mexico
| | - José Luis Cabellos
- Departamento de Física Aplicada, Centro de Investigación y de Estudios Avanzados Unidad Mérida, Mérida, Yucatán 97310, Mexico
| | - John T. Yi
- Department of Chemistry, Winston-Salem State University, Winston-Salem, North Carolina 27110, USA
| | - David W. Pratt
- Department of Chemistry, University of Vermont, Burlington, Vermont 05405, USA
| | - Michael Schmitt
- Physikalische Chemie, Heinrich-Heine-Universität, Düsseldorf, Deutschland 40204, Germany
| | - Gabriel Merino
- Departamento de Física Aplicada, Centro de Investigación y de Estudios Avanzados Unidad Mérida, Mérida, Yucatán 97310, Mexico
| | - Leonardo Álvarez-Valtierra
- División de Ciencias e Ingenierías, Universidad de Guanajuato-Campus León, León, Guanajuato 37150, Mexico
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13
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Horbury MD, Baker LA, Quan WD, Young JD, Staniforth M, Greenough SE, Stavros VG. Bridging the Gap between the Gas Phase and Solution Phase: Solvent Specific Photochemistry in 4-tert-Butylcatechol. J Phys Chem A 2015; 119:11989-96. [DOI: 10.1021/acs.jpca.5b03621] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Michael D. Horbury
- Department of Chemistry, University of Warwick, Gibbet Hill
Road, Coventry, CV4 7AL, U.K
| | - Lewis A. Baker
- Department of Chemistry, University of Warwick, Gibbet Hill
Road, Coventry, CV4 7AL, U.K
| | - Wen-Dong Quan
- Department of Chemistry, University of Warwick, Gibbet Hill
Road, Coventry, CV4 7AL, U.K
| | - Jamie D. Young
- Department of Chemistry, University of Warwick, Gibbet Hill
Road, Coventry, CV4 7AL, U.K
| | - Michael Staniforth
- Department of Chemistry, University of Warwick, Gibbet Hill
Road, Coventry, CV4 7AL, U.K
| | - Simon E. Greenough
- Department of Chemistry, University of Warwick, Gibbet Hill
Road, Coventry, CV4 7AL, U.K
| | - Vasilios G. Stavros
- Department of Chemistry, University of Warwick, Gibbet Hill
Road, Coventry, CV4 7AL, U.K
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14
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Geiger U, Haas Y. Photochemistry of Aryl Pentazoles: para-Methoxyphenylpentazole. J Phys Chem B 2015; 119:7338-48. [DOI: 10.1021/jp5108813] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- U. Geiger
- Institute of Chemistry, The Hebrew University, Jerusalem 9190401, Israel
| | - Y. Haas
- Institute of Chemistry, The Hebrew University, Jerusalem 9190401, Israel
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15
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Karsili TNV, Marchetti B, Ashfold MNR, Domcke W. Ab initio study of potential ultrafast internal conversion routes in oxybenzone, caffeic acid, and ferulic acid: implications for sunscreens. J Phys Chem A 2014; 118:11999-2010. [PMID: 25137024 DOI: 10.1021/jp507282d] [Citation(s) in RCA: 82] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Oxybenzone (OB) and ferulic acid (FA) both find use in commercial sunscreens; caffeic acid (CA) differs from FA by virtue of an -OH group in place of a -OCH3 group on the aromatic ring. We report the results of ab initio calculations designed to explore the excited state nonradiative relaxation pathways that provide photostability to these molecules and the photoprotection they offer toward UV-A and UV-B radiation. In the case of OB, internal conversion (IC) is deduced to occur on ultrafast time scales, via a barrierless electron-driven H atom transfer pathway from the S1(1(1)nπ*) state to a conical intersection (CI) with the ground (S0) state potential energy surface (PES). The situation with respect to CA and FA is somewhat less clear-cut, with low energy CIs identified by linking excited states to the S0 state following photoexcitation and subsequent evolution along (i) a ring centered out-of-plane deformation coordinate, (ii) the E/Z isomerism coordinate and, in the case of CA, (iii) an O-H stretch coordinate. Analogy with catechol suggests that the last of these processes (if active) would lead to radical formation (and thus potential phototoxicity), encouraging a suggestion that FA might be superior to CA as a sunscreen ingredient.
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Affiliation(s)
- Tolga N V Karsili
- School of Chemistry, University of Bristol , Bristol BS8 1TS, United Kingdom
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Omidyan R, Rezaei H. Excited state deactivation pathways of neutral/protonated anisole and p-fluoroanisole: a theoretical study. Phys Chem Chem Phys 2014; 16:11679-89. [PMID: 24810549 DOI: 10.1039/c4cp00679h] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The potential energy profiles of neutral and protonated anisole and p-fluoroanisole at different electronic states have been investigated extensively by the RI-MP2 and RI-CC2 methods. The calculations reveal that the relaxation dynamics in protonated anisole and p-fluoroanisole are essentially different from those of the neutral analogues. In neutral anisole/p-fluoroanisole, the (1)πσ* state plays a vital relaxation role along the O-CH3 coordinate, yielding the CH3 radical. For both of these molecules, the calculations indicate conical intersections (CIs) between the ground and excited state potential energy (PE) curves, hindered by a small barrier, and providing non-adiabatic gates for radiation-less deactivation to the ground state. Nevertheless, for the protonated cases, besides the prefulvenic deformation of the benzene ring, it has been predicted that the lowest (1)(σ,n)π* state along the C-O-C bond angle plays an important role in photochemistry and the relaxation dynamics. The S1, S0 PE profiles of protonated anisole along with the former reaction coordinate (out-of-plane deformation) show a barrierless relaxation pathway, which can be responsible for the ultrafast deactivation of excited systems to the ground state via the low-lying S1/S0 conical intersection. Moreover, the later reaction coordinate in protonated species (C-O-C angle from 120°-180°) is consequently accompanied with the bond cleavage of C-OCH3 at the (1)(σ,n)π* state, hindered by a barrier of ∼0.51 eV, and can be responsible for the relaxation of excited systems with significant excess energy (hν≥ 5 eV). Furthermore, according to the RI-CC2 calculated results, different effects on the S1-S0 electronic transition energy of anisole and p-fluoroanisole upon protonation have been predicted. The first electronic transitions of anisole and p-fluoroanisole shift by ∼0.3 and 1.3 eV to the red respectively due to protonation.
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Affiliation(s)
- Reza Omidyan
- Department of Chemistry, University of Isfahan, 81746-73441 Isfahan, Iran.
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17
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Dean JC, Navotnaya P, Parobek AP, Clayton RM, Zwier TS. Ultraviolet spectroscopy of fundamental lignin subunits: guaiacol, 4-methylguaiacol, syringol, and 4-methylsyringol. J Chem Phys 2014; 139:144313. [PMID: 24116625 DOI: 10.1063/1.4824019] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Ultraviolet spectroscopy of the G- and S-type lignin subunits, guaiacol (G) and syringol (S), along with their para-methylated derivatives 4-methylguaiacol (4-MG) and 4-methylsyringol (4-MS), has been carried out in the cold, isolated environment of a supersonic jet. The excitation spectra and dispersed fluorescence (DFL) spectra of G and 4-MG show strong S0-S1 origins and Franck-Condon activity involving both the ring modes typical of aromatic derivatives, and the four lowest frequency out-of-plane modes (a") and lowest in-plane mode (a') involving the OH and OCH3 groups. The four low-frequency out-of-plane modes undergo extensive Duschinsky mixing between the ground and excited state. In 4-MG, combination bands involving methyl rotor levels with out-of-plane modes appeared with surprisingly high intensity, indicating a high degree of hindered rotor-vibration coupling in both S0 and S1. These mixing effects accompany the change in geometry upon π-π∗ electronic excitation going from a planar ground state to a non-planar excited state. Time-dependent density functional theory (TDDFT M05-2X∕6-311++G(d,p)) calculations predict a geometric distortion along the out-of-plane oxygen flapping coordinate, yielding a double minimum potential in S1 with a barrier to planarity of 195 cm(-1) in G. The excitation spectrum of S and 4-MS showed a much higher degree of spectral congestion and a larger geometry change evident by a shifted intensity distribution peaking ∼300 cm(-1) above the electronic origin. TDDFT calculations predict a larger geometry change in S compared with G, with the OH and H-bonded methoxy groups displaced in opposite directions above∕below the ring plane. Dispersed fluorescence from all S1 excited state levels in S∕4-MS yield only broad emission peaking far to the red of the excitation wavelength (-4500 cm(-1)). Several hypotheses regarding the source of this broad, redshifted emission were tested, but the cause remains unclear. p-Methylation was found to significantly redshift the UV absorption in both 4-MG and 4-MS, and methyl rotor transitions were assigned in both allowing for the determination of the shape and barrier heights of their respective potentials. These results provide a foundation for the discrimination of G- and S-chromophores in lignin oligomers, and demonstrate the potential for site-selective absorption.
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Affiliation(s)
- Jacob C Dean
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, USA
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18
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Roberts GM, Stavros VG. The role of πσ* states in the photochemistry of heteroaromatic biomolecules and their subunits: insights from gas-phase femtosecond spectroscopy. Chem Sci 2014. [DOI: 10.1039/c3sc53175a] [Citation(s) in RCA: 119] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
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19
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Young JD, Staniforth M, Chatterley AS, Paterson MJ, Roberts GM, Stavros VG. Relaxation dynamics of photoexcited resorcinol: internal conversion versus H atom tunnelling. Phys Chem Chem Phys 2014; 16:550-62. [DOI: 10.1039/c3cp53726a] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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20
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Karsili TNV, Wenge AM, Marchetti B, Ashfold MNR. Symmetry matters: photodissociation dynamics of symmetrically versus asymmetrically substituted phenols. Phys Chem Chem Phys 2014; 16:588-98. [DOI: 10.1039/c3cp53450b] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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21
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Karsili TNV, Wenge AM, Harris SJ, Murdock D, Harvey JN, Dixon RN, Ashfold MNR. O–H bond fission in 4-substituted phenols: S1 state predissociation viewed in a Hammett-like framework. Chem Sci 2013. [DOI: 10.1039/c3sc50296a] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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Chatterley AS, Young JD, Townsend D, Żurek JM, Paterson MJ, Roberts GM, Stavros VG. Manipulating dynamics with chemical structure: probing vibrationally-enhanced tunnelling in photoexcited catechol. Phys Chem Chem Phys 2013; 15:6879-92. [DOI: 10.1039/c3cp51108a] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Ho YC, Dyakov YA, Hsu WH, Ni CK, Sun YL, Hu WP. Photodissociation dynamics of methoxybenzoic acid at 193 nm. J Chem Phys 2012. [PMID: 23181308 DOI: 10.1063/1.4767403] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The theoretical prediction and experimental confirmation of the 1πσ* repulsive excited state along O-H bond of phenol have large impact on the interpretation of phenol and tyrosine photochemistry. In this work, we investigated the photodissociation dynamics of 2-, 3-, and 4-methoxybenzoic acid (MOBA) in a molecular beam at 193 nm using multimass ion imaging techniques. In addition, the ground state and the excited state potential energy surfaces of MOBA were investigated using ab initio calculations, and branching ratios were predicted by Rice-Ramsperger-Kassel-Marcus theory. The results show that (1) the excited state potential of 1πσ* along O-CH(3) bond remains similar to that of phenol and anisole, (2) CH(3) elimination is the major channel for three MOBA isomers, and (3) photofragment translational energy distributions show bimodal distributions, representing the dissociation on the ground state and repulsive excited state, respectively. Comparison to the study of hydroxbenzoic acid [Y. L. Yang, Y. A. Dyakov, Y. T. Lee, C. K. Ni, Y. L. Sun, and W. P. Hu, J. Chem. Phys. 134, 034314 (2011)] shows that only the intramolecular hydrogen bonding has significant effects on the excited state dynamics of phenol chromophores.
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Affiliation(s)
- Yu-Chieh Ho
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
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