1
|
Kim J, Woo KC, Kang M, Kim SK. Dynamic Role of the Intramolecular Hydrogen Bonding in the S 1 State Relaxation Dynamics Revealed by the Direct Measurement of the Mode-Dependent Internal Conversion Rate of 2-Chlorophenol and 2-Chlorothiophenol. J Phys Chem Lett 2023; 14:8428-8436. [PMID: 37712655 DOI: 10.1021/acs.jpclett.3c02208] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/16/2023]
Abstract
The dynamic role of the intramolecular hydrogen bond in the S1 relaxation of cis-2-chlorophenol (2-CP) or cis-2-chlorothiophenol (2-CTP) has been investigated in a state-specific manner. Whereas ultrafast internal conversion is dominant for 2-CP, the H-tunneling competes with internal conversion for 2-CTP even at the S1 origin. The S0-S1 internal conversion rate of 2-CTP could be directly measured from the S1 lifetimes of 2-CTP-d1 (Cl-C6H4-SD) as the D-tunneling is kinetically blocked, allowing distinct estimations of tunneling and internal conversion rates with increasing the energy. The internal conversion rate of 2-CTP increases by two times at the out-of-plane torsional mode excitation, suggesting that the internal conversion is facilitated at the nonplanar geometry. It then sharply increases at ∼600 cm-1, indicating that the S1/S0 conical intersection is readily accessible at the extended C-Cl bond length. The strength of the intramolecular hydrogen bond should be responsible for the distinct dynamic behaviors of 2-CP and 2-CTP.
Collapse
Affiliation(s)
- Junggil Kim
- Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea
| | - Kyung Chul Woo
- Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea
| | - Minseok Kang
- Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea
| | - Sang Kyu Kim
- Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea
| |
Collapse
|
2
|
Ashfold MNR, Kim SK. Non-Born-Oppenheimer effects in molecular photochemistry: an experimental perspective. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2022; 380:20200376. [PMID: 35341307 DOI: 10.1098/rsta.2020.0376] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Accepted: 06/28/2021] [Indexed: 06/14/2023]
Abstract
Non-adiabatic couplings between Born-Oppenheimer (BO)-derived potential energy surfaces are now recognized as pivotal in describing the non-radiative decay of electronically excited molecules following photon absorption. This opinion piece illustrates how non-BO effects provide photostability to many biomolecules when exposed to ultraviolet radiation, yet in many other cases are key to facilitating 'reactive' outcomes like isomerization and bond fission. The examples are presented in order of decreasing molecular complexity, spanning studies of organic sunscreen molecules in solution, through two families of heteroatom containing aromatic molecules and culminating with studies of isolated gas phase H2O molecules that afford some of the most detailed insights yet available into the cascade of non-adiabatic couplings that enable the evolution from photoexcited molecule to eventual products. This article is part of the theme issue 'Chemistry without the Born-Oppenheimer approximation'.
Collapse
Affiliation(s)
| | - Sang Kyu Kim
- Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea
| |
Collapse
|
3
|
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
| |
Collapse
|
4
|
Kim KK, Kim J, Woo KC, Kim SK. S 1-State Decay Dynamics of Benzenediols (Catechol, Resorcinol, and Hydroquinone) and Their 1:1 Water Clusters. J Phys Chem A 2021; 125:7655-7661. [PMID: 34432455 DOI: 10.1021/acs.jpca.1c05448] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The S1-state decaying rates of the three different benzenediols, catechol, resorcinol, and hydroquinone, and their 1:1 water clusters have been state-specifically measured using the picosecond time-resolved parent ion transients obtained by the pump (excitation) and probe (ionization) scheme. The S1 lifetime of catechol is found to be short, giving τ ∼ 5.9 ps at the zero-point level. This is ascribed to the H-atom detachment from the free OH moiety of the molecule. Consistent with a previous report (J. Phys. Chem. Lett. 2013, 4, 3819-3823), the S1 lifetime gets lengthened with low-frequency vibrational mode excitations, giving τ ∼ 9.0 ps for the 116 cm-1 band. The S1 lifetimes at the additional vibronic modes of catechol are newly measured, showing the nonnegligible mode-dependent fluctuations of the tunneling rate. When catechol is complexed with water, the S1 lifetime is enormously increased to τ ∼ 1.80 ns at the zero-point level while it shows an unusual dip at the intermolecular stretching mode excitation (τ ∼ 1.03 ns at 146 cm-1). Otherwise, it is shortened monotonically with increasing the internal energy, giving τ ∼ 0.67 ns for the 856 cm-1 band. Two different asymmetric or symmetric conformers of resorcinol give the respective S1 lifetimes of 4.5 or 6.3 ns at their zero-point levels according to the estimation from our transients taken within the temporal window of 0-2.7 ns. When resorcinol is 1:1 complexed with H2O, the S1 decaying rate is slightly accelerated for both conformers. The S1 lifetimes of trans and cis forms of hydroquinone are measured to be more or less same, giving τ ∼ 2.8 ns at the zero-point level. When H2O is complexed with hydroquinone, the S1 decaying process is facilitated for both conformers, slightly more efficiently for the cis conformer.
Collapse
Affiliation(s)
- Kuk Ki Kim
- Department of Chemistry, KAIST, Dajeon 34141, Republic of Korea
| | - Junggil Kim
- Department of Chemistry, KAIST, Dajeon 34141, Republic of Korea
| | - Kyung Chul Woo
- Department of Chemistry, KAIST, Dajeon 34141, Republic of Korea
| | - Sang Kyu Kim
- Department of Chemistry, KAIST, Dajeon 34141, Republic of Korea
| |
Collapse
|
5
|
Kim J, Woo KC, Kim SK. Femtosecond Wavepacket Dynamics Reveals the Molecular Structures in the Excited (S 1) and Cationic (D 0) States. J Phys Chem A 2021; 125:6629-6635. [PMID: 34310149 DOI: 10.1021/acs.jpca.1c04976] [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
Molecular structures in the electronically excited (S1) and cationic (D0) states of 2-fluorothioanisole (2-FTA) have been precisely refined from the real-time dynamics of the femtosecond (fs) wavepacket prepared by the coherent excitation of the Franck-Condon active out-of-plane torsional modes in the S1 ← S0 transition at 285 nm. The simulation to reproduce the experiment in terms of the beating frequencies gives the nonplanar geometry of 2-FTA in S1, where the out-of-plane dihedral angle (φ) of the S-CH3 moiety is 51° with respect to the molecular plane. The behavior of the fs wavepacket in terms of the amplitudes and phases with the change of the probe (ionization) wavelength (λprobe = 300-330 nm) provides the otherwise veiled structure of the cationic D0 state. While the 2-FTA cation adopts the planar geometry (φ = 0°) at the global minimum, it is found to have a vertical minimum at φ ≈ 135° from the perspective of the D0 ← S1 vertical transition. Ab initio calculations support the experiment quite well although the simulation using the model potentials could improve the match with the experiment, giving the new interpretation for the previously disputed photoelectron spectroscopic results.
Collapse
Affiliation(s)
- Junggil Kim
- Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea
| | - Kyung Chul Woo
- Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea
| | - Sang Kyu Kim
- Department of Chemistry, KAIST, Daejeon 34141, Republic of Korea
| |
Collapse
|
6
|
Abe K, Nakada A, Matsumoto T, Uchijyo D, Mori H, Chang HC. Functional Group-Directed Photochemical Reactions of Aromatic Alcohols, Amines, and Thiols Triggered by Excited-State Hydrogen Detachment: Additive-free Oligomerization, Disulfidation, and C(sp 2)-H Carboxylation with CO 2. J Org Chem 2021; 86:959-969. [PMID: 33211498 DOI: 10.1021/acs.joc.0c02456] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Exploring new types of photochemical reactions is of great interest in the field of synthetic chemistry. Although excited-state hydrogen detachment (ESHD) represents a promising prospective template for additive-free photochemical reactions, applications of ESHD in a synthetic context remains scarce. Herein, we demonstrate the expansion of this photochemical reaction toward oligomerization, disulfidation, and regioselective C(sp2)-H carboxylation of aromatic alcohols, thiols, and amines. In the absence of any radical initiators in tetrahydrofuran upon irradiation with UV light (λ = 280 or 300 nm) under an atmosphere of N2 or CO2, thiols and catechol afforded disulfides and oligomers, respectively, as main products. Especially, the photochemical disulfidation proceeded highly selectively with the NMR and quantum yields of up to 69 and 0.46%, respectively. In stark contrast, the photolysis of phenylenediamines and aminophenols results in photocarboxylation in the presence of CO2 (1 atm). p-Aminophenol was quantitatively carboxylated by photolysis for 17 h with a quantum yield of 0.45%. Furthermore, the photocarboxylation of phenylenediamines and aminophenols proceeds in a highly selective fashion on the aromatic C(sp2)-H bond next to a functional group, which is directed by the site-selective ESHD of the functional groups for the formation of aminyl and hydroxyl radicals.
Collapse
Affiliation(s)
- Kanae Abe
- Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan
| | - Akinobu Nakada
- Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan.,Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Takeshi Matsumoto
- Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan.,Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan
| | - Daiki Uchijyo
- Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan
| | - Hirotoshi Mori
- Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan.,Department of Theoretical and Computational Molecular Science, Institute for Molecular Science, Okazaki 444-8585, Japan
| | - Ho-Chol Chang
- Department of Applied Chemistry, Faculty of Science and Engineering, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan
| |
Collapse
|
7
|
Quentin J, MacGillivray LR. Halogen versus Hydrogen Bonding in Binary Cocrystals: Novel Conformation a Coformer with [2+2] Photoreactivity of Criss-Crossed C=C Bonds. Chemphyschem 2019; 21:154-163. [PMID: 31600417 DOI: 10.1002/cphc.201900961] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Indexed: 11/06/2022]
Abstract
A series of cocrystals involving the hydrogen- and halogen-bond donor coformers catechol (cat) and 1,2-diiodotetrafluorobenzene (1,2-di-I-tFb), respectively, is reported. Each coformer forms a cocrystal with each of the three symmetric bipyridines trans-1,2-bis(n-pyridyl)ethylene (n,n'-bpe, where: n=n'=2, 3, 4). Four novel cocrystals (cat) ⋅ (3,3'-bpe), 2(1,2-di-I-tFb) ⋅ (2,2'-bpe), 2(1,2-di-I-tFb) ⋅ (3,3'-bpe), and (1,2-di-I-tFb) ⋅ (4,4'-bpe) comprise components that assemble by either O-H⋅⋅⋅N hydrogen bonds (cat) or N⋅⋅⋅I halogen bonds (1,2-di-I-tFb). In (cat) ⋅ (3,3'-bpe), cat acts as a template to support an intermolecular [2+2] photocycloaddition of 3,3'-bpe. The reactivity occurs via a one-dimensional (1D) hydrogen-bonded tape with stacked and criss-crossed olefins that react stereoselectively and quantitatively to form rctt-tetrakis(3-pyridyl)cyclobutane (3,3'-tpcb). The reactivity of the criss-crossed olefins is facilitated by a hitherto not reported cis-gauche conformation adopted by cat. The stereochemistry of 3,3'-tpcb is confirmed in the cocrystal 2(cat) ⋅ (3,3'-tpcb).
Collapse
Affiliation(s)
- Jay Quentin
- Department of Chemistry, University of Iowa, Iowa City, IA 52242, USA
| | | |
Collapse
|
8
|
Grieco C, Hanes AT, Blancafort L, Kohler B. Effects of Intra- and Intermolecular Hydrogen Bonding on O-H Bond Photodissociation Pathways of a Catechol Derivative. J Phys Chem A 2019; 123:5356-5366. [PMID: 31242734 DOI: 10.1021/acs.jpca.9b04573] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The catechol functional motif is thought to play both a structural and photochemical role in the ubiquitous natural pigment, eumelanin. Intramolecular and intermolecular hydrogen bonding interactions lead to a variety of geometries involving the two O-H groups in catechol, but its photophysical behavior in these situations has not been comprehensively characterized. Toward this end, we monitor the UV-induced O-H bond photodissociation reaction in an exemplar catechol derivative, 4- tert-butylcatechol, possessing different intramolecular and intermolecular hydrogen bonding geometries using femtosecond transient absorption spectroscopy measurements in the UV-visible and mid-infrared regions following 265 nm photoexcitation. Three different hydrogen bonding arrangements are obtained by tuning solution complexation equilibria of the catechol with the hydrogen bond acceptor, diethyl ether (Et2O), and are verified computationally. We find that intermolecular hydrogen bonding to the free O-H group in catechol increases its first excited singlet state (S1) lifetime by 2 orders of magnitude (i.e., ∼ 16 to 1410 ps), and that O-H bond dissociation is prevented because Et2O is a poor hydrogen atom acceptor. Complexation of both O-H groups with multiple Et2O molecules further elongates the S1 lifetime to 1670 ps due to shifting of the solution equilibria that describe complex formation. Weakening of the characteristic, intramolecular hydrogen bond of the catechol derivative by intermolecular hydrogen bonding to one or more Et2O molecules does not enhance the rate of O-H bond dissociation.
Collapse
Affiliation(s)
- Christopher Grieco
- Department of Chemistry and Biochemistry , The Ohio State University , 100 West 18th Avenue , Columbus , Ohio 43210 , United States
| | - Alex T Hanes
- Department of Chemistry and Biochemistry , The Ohio State University , 100 West 18th Avenue , Columbus , Ohio 43210 , United States
| | - Lluís Blancafort
- Institut de Química Computacional i Catàlisi and Departament de Química, Facultat de Ciències , Universitat de Girona , C/M.A. Capmany 69 , 17003 Girona , Spain
| | - Bern Kohler
- Department of Chemistry and Biochemistry , The Ohio State University , 100 West 18th Avenue , Columbus , Ohio 43210 , United States
| |
Collapse
|
9
|
Zhang B. Unraveling vibrational wavepacket dynamics using femtosecond ion yield spectroscopy and photoelectron imaging. CHINESE J CHEM PHYS 2019. [DOI: 10.1063/1674-0068/cjcp1811252] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Affiliation(s)
- Bing Zhang
- State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China
| |
Collapse
|
10
|
Tuttle WD, Gardner AM, Whalley LE, Kemp DJ, Wright TG. Effects of symmetry, methyl groups and serendipity on intramolecular vibrational energy dispersal. Phys Chem Chem Phys 2019; 21:14133-14152. [DOI: 10.1039/c8cp02757a] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Intramolecular vibrational dispersal of vibrational energy is more efficient in the symmetrically-substituted p-xylene molecule than in p-fluorotoluene, p-chlorofluorobenzene or p-difluorobenzene.
Collapse
Affiliation(s)
- William D. Tuttle
- School of Chemistry, University of Nottingham, University Park
- Nottingham
- UK
| | - Adrian M. Gardner
- School of Chemistry, University of Nottingham, University Park
- Nottingham
- UK
| | - Laura E. Whalley
- School of Chemistry, University of Nottingham, University Park
- Nottingham
- UK
| | - David J. Kemp
- School of Chemistry, University of Nottingham, University Park
- Nottingham
- UK
| | - Timothy G. Wright
- School of Chemistry, University of Nottingham, University Park
- Nottingham
- UK
| |
Collapse
|
11
|
Grieco C, Kohl FR, Zhang Y, Natarajan S, Blancafort L, Kohler B. Intermolecular Hydrogen Bonding Modulates O-H Photodissociation in Molecular Aggregates of a Catechol Derivative. Photochem Photobiol 2018; 95:163-175. [PMID: 30317633 DOI: 10.1111/php.13035] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Accepted: 10/01/2018] [Indexed: 01/15/2023]
Abstract
The catechol functional group plays a major role in the chemistry of a wide variety of molecules important in biology and technology. In eumelanin, intermolecular hydrogen bonding between these functional groups is thought to contribute to UV photoprotective and radical buffering properties, but the mechanisms are poorly understood. Here, aggregates of 4-t-butylcatechol are used as model systems to study how intermolecular hydrogen bonding influences photochemical pathways that may occur in eumelanin. Ultrafast UV-visible and mid-IR transient absorption measurements are used to identify the photochemical processes of 4-t-butylcatechol monomers and their hydrogen-bonded aggregates in cyclohexane solution. Monomer photoexcitation results in hydrogen atom ejection to the solvent via homolytic O-H bond dissociation with a time constant of 12 ps, producing a neutral semiquinone radical with a lifetime greater than 1 ns. In contrast, intermolecular hydrogen bonding interactions within aggregates retard O-H bond photodissociation by over an order of magnitude in time. Excited state structural relaxation is proposed to slow O-H dissociation, allowing internal conversion to the ground state to occur in hundreds of picoseconds in competition with this channel. The semiquinone radicals formed in the aggregates exhibit spectral broadening of both their electronic and vibrational transitions.
Collapse
Affiliation(s)
- Christopher Grieco
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH
| | - Forrest R Kohl
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH
| | - Yuyuan Zhang
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH
| | - Sangeetha Natarajan
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH
| | - Lluís Blancafort
- Institut de Química Computacional i Catàlisi and Departament de Química, Facultat de Ciències, Universitat de Girona, Girona, Spain
| | - Bern Kohler
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH
| |
Collapse
|
12
|
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]
|
13
|
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]
|
14
|
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]
|
15
|
Rodrigues NDN, Staniforth M, Young JD, Peperstraete Y, Cole-Filipiak NC, Gord JR, Walsh PS, Hewett DM, Zwier TS, Stavros VG. Towards elucidating the photochemistry of the sunscreen filter ethyl ferulate using time-resolved gas-phase spectroscopy. Faraday Discuss 2018; 194:709-729. [PMID: 27711798 DOI: 10.1039/c6fd00079g] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ultrafast time-resolved ion yield (TR-IY) and velocity map imaging spectroscopies are employed to reveal the relaxation dynamics after photoexcitation in ethyl 4-hydroxy-3-methoxycinnamate (ethyl ferulate, EF), an active ingredient in commercially available sunscreens. In keeping with a bottom-up strategy, the building blocks of EF, 2-methoxy-4-vinylphenol (MVP) and 4-hydroxy-3-methoxycinnamyl alcohol (coniferyl alcohol, ConA), were also studied to assist in our understanding of the dynamics of EF as we build up in molecular complexity. In contrast to the excited state dynamics of MVP and ConA, which are described by a single time constant (>900 ps), the dynamics of EF are described by three time constants (15 ± 4 ps, 148 ± 47 ps, and >900 ps). A mechanism is proposed involving internal conversion (IC) between the initially excited S1(11ππ*) and S2(11nπ*) states followed by intramolecular vibrational redistribution (IVR) on both states, in competition with intersystem crossing onto neighbouring triplet states (15 ± 4 ps). IVR and IC within the triplet manifold then ensues (148 ± 47 ps) to populate a low-lying triplet state (>900 ps). Importantly, the fluorescence spectrum of EF at the S1 origin, along with the associated lifetime (6.9 ± 0.1 ns), suggests that population is trapped, during initial IVR, on the S1(11ππ*) state. This serves to demonstrate the complex, competing dynamics in this sunscreen filter molecule.
Collapse
Affiliation(s)
- N D N Rodrigues
- University of Warwick, Department of Chemistry, CV4 7AL, Coventry, UK.
| | - M Staniforth
- University of Warwick, Department of Chemistry, CV4 7AL, Coventry, UK.
| | - J D Young
- University of Warwick, Department of Chemistry, CV4 7AL, Coventry, UK.
| | - Y Peperstraete
- University of Warwick, Department of Chemistry, CV4 7AL, Coventry, UK. and ENS de Cachan, 61 Avenue du Président Wilson, 94230, Cachan, France
| | - N C Cole-Filipiak
- University of Warwick, Department of Chemistry, CV4 7AL, Coventry, UK.
| | - J R Gord
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, USA
| | - P S Walsh
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, USA
| | - D M Hewett
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, USA
| | - T S Zwier
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, USA
| | - V G Stavros
- University of Warwick, Department of Chemistry, CV4 7AL, Coventry, UK.
| |
Collapse
|
16
|
Ormond TK, Baraban JH, Porterfield JP, Scheer AM, Hemberger P, Troy TP, Ahmed M, Nimlos MR, Robichaud DJ, Daily JW, Ellison GB. Thermal Decompositions of the Lignin Model Compounds: Salicylaldehyde and Catechol. J Phys Chem A 2018; 122:5911-5924. [DOI: 10.1021/acs.jpca.8b03201] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Affiliation(s)
- Thomas K. Ormond
- National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, United States
| | - Joshua H. Baraban
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, United States
| | - Jessica P. Porterfield
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, United States
| | - Adam M. Scheer
- Combustion Research Facility, Sandia National Laboratory, PO Box 969, Livermore, California 94551-0969, United States
| | - Patrick Hemberger
- Laboratory for Femtochemistry and Synchrotron Radiation, Paul Scherrer Institute, CH-5234 Villigen-PSI, Switzerland
| | - Tyler P. Troy
- Chemical Sciences Division, Lawrence Berkeley National Laboratories, Berkeley, California 94720, United States
| | - Musahid Ahmed
- Chemical Sciences Division, Lawrence Berkeley National Laboratories, Berkeley, California 94720, United States
| | - Mark R. Nimlos
- National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - David J. Robichaud
- National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
| | - John W. Daily
- Center for Combustion and Environmental Research, Department of Mechanical Engineering, University of Colorado, Boulder, Colorado 80309-0427, United States
| | - G. Barney Ellison
- Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, United States
| |
Collapse
|
17
|
Baker LA, Marchetti B, Karsili TNV, Stavros VG, Ashfold MNR. Photoprotection: extending lessons learned from studying natural sunscreens to the design of artificial sunscreen constituents. Chem Soc Rev 2018; 46:3770-3791. [PMID: 28580469 DOI: 10.1039/c7cs00102a] [Citation(s) in RCA: 106] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Evolution has ensured that plants and animals have developed effective protection mechanisms against the potentially harmful effects of incident ultraviolet radiation (UVR). Tanning is one such mechanism in humans, but tanning only occurs post-exposure to UVR. Hence, there is ever growing use of commercial sunscreens to pre-empt overexposure to UVR. Key requirements for any chemical filter molecule used in such a photoprotective capacity include a large absorption cross-section in the UV-A and UV-B spectral regions and the availability of one or more mechanisms whereby the absorbed photon energy can be dissipated without loss of the molecular integrity of the chemical filter. Here we summarise recent experimental (mostly ultrafast pump-probe spectroscopy studies) and computational progress towards unravelling various excited state decay mechanisms that afford the necessary photostability in chemical filters found in nature and those used in commercial sunscreens. We also outline ways in which a better understanding of the photophysics and photochemistry of sunscreen molecules selected by nature could aid the design of new and improved commercial sunscreen formulations.
Collapse
Affiliation(s)
- Lewis A Baker
- Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK.
| | - Barbara Marchetti
- Department of Chemistry, University of Pennsylvania, Philadelphia, USA
| | | | - Vasilios G Stavros
- Department of Chemistry, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK.
| | - Michael N R Ashfold
- School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
| |
Collapse
|
18
|
Morishima F, Kusaka R, Inokuchi Y, Haino T, Ebata T. Cage effects on conformational preference and photophysics in the host-guest complex of benzenediols with 18-Crown-6. Phys Chem Chem Phys 2016; 18:8027-38. [PMID: 26924038 DOI: 10.1039/c5cp07171b] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The conformational preference and modification of photophysics of benzenediols, namely hydroquinone (HQ), resorcinol (RE) and catechol (CA), upon host-guest complex formation with 18-Crown-6 (18C6) have been investigated, under supersonically jet-cooled conditions. Laser induced fluorescence (LIF) and UV-UV hole-burning spectra indicate the presence of two conformers for HQ and RE and one conformer for CA. On the other hand, the number of isomers is reduced to one in the 18C6·HQ and 18C6·RE complexes, while the 18C6·CA complex has three stable isomers. The IR spectra of the OH stretching vibration reveal that the two OH groups are H-bonded in 18C6·CA and 18C6·RE. In 18C6·RE, RE adopts the highest energy conformation in the bare form. In 18C6·HQ, the H-bonding of one OH group affects the orientation of the other OH group. The complex formation changes the photophysics of the S1 state of the benzenediols in a different manner. In our previous work, we reported a remarkable S1 lifetime elongation in 18C6·CA complexes; the S1 lifetime of CA is elongated more than 1000 times longer (8 ps → 10.3 ns) in 18C6·CA (F. Morishima et al., J. Phys. Chem. B, 2015, 119, 2557-2565), which we called the "cage effect". In 18C6·RE, the increase of S1 lifetime is moderate: 4.0 ns (monomer) → 10.5 ns (complex). On the other hand, the S1 lifetime of HQ is shortened in 18C6·HQ: 2.6 ns (monomer) → 0.54 ns (complex). Density functional theory (DFT) calculations suggest that these behaviors are related to the S1 ((1)ππ*)-(1)πσ* energy gap, the character of the S2 state and the symmetry of benzenediol. These experimental results clearly show the potential ability of 18C6 to control the conformation and modification of the electronic structure of guest species.
Collapse
Affiliation(s)
- Fumiya Morishima
- Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
| | - Ryoji Kusaka
- Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
| | - Yoshiya Inokuchi
- Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
| | - Takeharu Haino
- Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
| | - Takayuki Ebata
- Department of Chemistry, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
| |
Collapse
|
19
|
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
| |
Collapse
|
20
|
Omidyan R, Heidari Z, Salehi M, Azimi G. Electronically Excited States of Neutral, Protonated α-Naphthol and Their Water Clusters: A Theoretical Study. J Phys Chem A 2015; 119:6650-60. [DOI: 10.1021/acs.jpca.5b02249] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Reza Omidyan
- Department of Chemistry, University of Isfahan, 81746-73441, Isfahan, Iran
| | - Zahra Heidari
- Department of Chemistry, University of Isfahan, 81746-73441, Isfahan, Iran
| | - Mohammad Salehi
- Department of Chemistry, University of Isfahan, 81746-73441, Isfahan, Iran
| | - Gholamhassan Azimi
- Department of Chemistry, University of Isfahan, 81746-73441, Isfahan, Iran
| |
Collapse
|
21
|
Weichman ML, Kim JB, Neumark DM. Slow Photoelectron Velocity-Map Imaging Spectroscopy of the ortho-Hydroxyphenoxide Anion. J Phys Chem A 2015; 119:6140-7. [PMID: 25744814 DOI: 10.1021/acs.jpca.5b00768] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report high-resolution photodetachment spectra of cryogenically cooled ortho-hydroxyphenoxide anions (o-HOC6H4O(-)) using slow photoelectron velocity-map imaging spectroscopy (cryo-SEVI). We observe transitions to the three lowest-lying electronic states of the ortho-hydroxyphenoxy radical, and resolve detailed vibrational features. Comparison to Franck-Condon simulations allows for clear assignment of vibronic structure. We find an electron affinity of 2.3292(4) eV for the neutral X̃(2)A″ ground state, improving upon the accuracy of previous experiments. We measure term energies of 1.4574(7) eV and 1.5922(48) eV for the Ã(2)A' and B̃(2)A″ excited states respectively, representing their first resolution and clear assignment. Photodetachment threshold effects are considered to explain the structure of these bands.
Collapse
Affiliation(s)
- Marissa L Weichman
- †Department of Chemistry, University of California, Berkeley, California 94720, United States
| | - Jongjin B Kim
- †Department of Chemistry, University of California, Berkeley, California 94720, United States
| | - Daniel M Neumark
- †Department of Chemistry, University of California, Berkeley, California 94720, United States.,‡Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| |
Collapse
|
22
|
Greenough SE, Horbury MD, Thompson JOF, Roberts GM, Karsili TNV, Marchetti B, Townsend D, Stavros VG. Solvent induced conformer specific photochemistry of guaiacol. Phys Chem Chem Phys 2015; 16:16187-95. [PMID: 24967653 DOI: 10.1039/c4cp02424a] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Using a combination of ultrafast solution- and gas-phase spectroscopies, together with high-level theory calculations, we demonstrate that we are able to track conformer-specific photodissociation dynamics in solution through solvent choice. We reveal this phenomenon in guaiacol (2-methoxyphenol), a key subunit of the natural biopolymer lignin. In cyclohexane, the first electronically excited (1)ππ* (S1) state in guaiacol relaxes with a time-constant of τ = 4.5 ± 0.2 ns, mediated through intersystem crossing to lower lying triplet (Tn) states and internal conversion and fluorescence back to the ground state (S0). In contrast, in methanol, a further relaxation channel is also present; the S1 state relaxes with a time-constant of τ = 2.9 ± 0.1 ns, which is now additionally mediated through coupling onto a dissociative (1)πσ* (S2) state and subsequent O-H bond fission, evidenced through the appearance of a spectral signature for the guaiacoxyl radical after ∼250 ps. With the aid of complementary calculations, we attribute this to the now absent intramolecular H-bond between OH and OMe moieties, which now favours intermolecular H-bonding to methanol, lowering the barrier to O-H dissociation and facilitating H-atom loss via tunnelling.
Collapse
Affiliation(s)
- Simon E Greenough
- Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK.
| | | | | | | | | | | | | | | |
Collapse
|
23
|
Ataelahi M, Omidyan R, Azimi G. Photophysics and photochemistry of cis- and trans-hydroquinone, catechol and their ammonia clusters: a theoretical study. Photochem Photobiol Sci 2014; 14:457-64. [PMID: 25502165 DOI: 10.1039/c4pp00356j] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Excited state hydrogen transfer in hydroquinone- and catechol-ammonia clusters has been extensively investigated by high level ab initio methods. The potential energy profiles of the title systems at different electronic states have been determined at the MP2/CC2 levels of theory. It has been predicted that double hydrogen transfer (DHT) takes place as the main consequence of photoexcited tetra-ammoniated systems. Consequently, the DHT processes lead the excited systems to the (1)πσ*-S0 conical intersections, which is responsible for the ultrafast non-radiative relaxation of UV-excited clusters to their ground states. Moreover, according to our calculated results, the single hydrogen detachment or hydrogen transfer process essentially governs the relaxation dynamics of smaller sized clustered systems (mono- and di-ammoniated).
Collapse
Affiliation(s)
- Mitra Ataelahi
- Department of Chemistry, University of Isfahan, 81746-73441 Isfahan, Iran.
| | | | | |
Collapse
|
24
|
Morishima F, Kusaka R, Inokuchi Y, Haino T, Ebata T. Anomalous Cage Effect of the Excited State Dynamics of Catechol in the 18-Crown-6–Catechol Host–Guest Complex. J Phys Chem B 2014; 119:2557-65. [DOI: 10.1021/jp508619f] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- Fumiya Morishima
- Department of Chemistry, Graduate
School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
| | - Ryoji Kusaka
- Department of Chemistry, Graduate
School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
| | - Yoshiya Inokuchi
- Department of Chemistry, Graduate
School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
| | - Takeharu Haino
- Department of Chemistry, Graduate
School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
| | - Takayuki Ebata
- Department of Chemistry, Graduate
School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
| |
Collapse
|
25
|
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.
Collapse
Affiliation(s)
- Tolga N V Karsili
- School of Chemistry, University of Bristol , Bristol BS8 1TS, United Kingdom
| | | | | | | |
Collapse
|
26
|
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.
Collapse
Affiliation(s)
- Jacob C Dean
- Department of Chemistry, Purdue University, West Lafayette, Indiana 47907-2084, USA
| | | | | | | | | |
Collapse
|
27
|
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]
|
28
|
Papaefstathiou GS, Duncan AJE, MacGillivray LR. Two act as one: unexpected dimers of catechol direct a solid-state [2+2] photodimerization in a six-component hydrogen-bonded assembly. Chem Commun (Camb) 2014; 50:15960-2. [DOI: 10.1039/c4cc07747d] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Catechol self-assembles as a dimer to function as template that directs a [2+2] photodimerization in the solid state.
Collapse
|
29
|
Woldu AS, Mai J. Computation of the bond dissociation enthalpies and free energies of hydroxylic antioxidants using the ab initio Hartree-Fock method. Redox Rep 2013; 17:252-74. [PMID: 23339861 DOI: 10.1179/1351000212y.0000000030] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022] Open
Abstract
INTRODUCTION A new method for calculating theoretical bond dissociation enthalpy (BDE) and bond dissociation free energy (BDFE) of hydroxylic antioxidants is forwarded. BDE and BDFE may be understood as activation energies accompanying the formation of transition states, which may undergo downhill homolytic dissociation. The new method does not involve the complete fission of O-H bonds. METHOD Theoretical gas phase BDE values were calculated with the ab initio unrestricted Hartree-Fock (UHF) method, as changes in enthalpy between ground singlet states (GS) and triplet dissociative states (DS). Similarly, gas phase BDFEs were estimated from the corresponding changes in Gibbs free energy. The results were then compared with reliable experimental reports. RESULTS The proposed theoretical approach of BDE and BDFE determination was tested using 10 simple phenols, 5 flavonoids, and l-ascorbic acid derivatives. The agreement between our calculated gas phase results and the adopted experimental values were generally within 0.5 kcal mol(-1), with a very few exceptions. DISCUSSION Generally, steric interactions as well as intramolecular hydrogen bonding involving the dissociating OH group should be minimized in the GS. The DS are both electronically and vibrationally exited transition states. They have one unpaired electron on the carbon atom, which bears the homolytically dissociating OH group and are second order saddle points with a fixed <C-O-H bond angel of 180°. CONCLUSION It was concluded that ab initio UHF was well suited for the estimation of gas phase BDE and BDFE. The method presented has a good potential for application across a range of hydroxylic antioxidants. Currently, work is underway to extend its application in other class of antioxidants.
Collapse
Affiliation(s)
- Ameha Seyoum Woldu
- Department of Pharmaceutical Chemistry and Pharmacognosy, School of Pharmacy, College of Health Sciences, Addis Ababa University, Addis Ababa, Ethiopia.
| | | |
Collapse
|
30
|
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]
|
31
|
Livingstone RA, Thompson JOF, Iljina M, Donaldson RJ, Sussman BJ, Paterson MJ, Townsend D. Time-resolved photoelectron imaging of excited state relaxation dynamics in phenol, catechol, resorcinol, and hydroquinone. J Chem Phys 2012; 137:184304. [DOI: 10.1063/1.4765104] [Citation(s) in RCA: 88] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|