Acetylacetone in hydrogen solids: IR signatures of the enol and keto tautomers and UV induced tautomerization

Lozada‐Garcia, Rolando Rafael; Čeponkus, Justinas; Chin, W.; Chevalier, Michèle; Crépin, C.

doi:10.1016/j.cplett.2011.01.055

Cited by 37 publications

(56 citation statements)

References 28 publications

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“…This is in contrast to the cryogenic matrices experiments where AA in parahydrogen solids upon continuous irradiation at 248 nm forms the keto form, though in a very small amount compared to the formation of the NCE form. 43 Hence, for all three pump wavelengths the formation of the NCE form through rotamerization as suggested above, takes place predominantly within the first nanoseconds. The percentage of photoproduct formation of AA in dioxane has been derived for the three different excitation wavelengths and was found to be 27, 29, and 28% upon excitation at 248, 265, and 285 nm, respectively (see Table 1).…”

Section: ■ Results and Discussionmentioning

confidence: 65%

Ultrafast UV-Induced Photoisomerization of Intramolecularly H-Bonded Symmetric β-Diketones

et al. 2014

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In photoinduced molecular reaction dynamics, the effects of electronic charge redistribution can lead to multiple pathways that are determined by the nature of the initial structures involved and the environment the molecule of interest is studied in. The β-diketones are a common example of this complexity. They show keto−enol tautomerism that is almost totally shifted toward the enolic form. However, compared to the gas phase, the photochemistry proceeds completely differently by virtue of the solvent environment for these compounds, which are used in commercial sunscreen agents due to a high absorption in the ultraviolet (UV) and fast deactivation processes. We disclose these dynamics by investigating three symmetrical β-diketones in various solvents. To observe these effects on an ultrafast time scale directly in the UV spectral region where the relevant electronic transitions take place, we have developed and employed femtosecond transient absorption with detection capability in the deep UV. Our studies confirm that electronic excitation of the chelated enol form does not lead to any ultrafast photochemistry other than proton transfer followed by rotamerization. The formation of the nonchelated conformers takes place on a picosecond time scale through a dark state, whereas the recovery to the stable chelated enol form is a comparably slow process. ■ INTRODUCTIONDerivatives of β-diketones are of great importance in diverse research fields by virtue of several remarkable chemical features that lead to a variety of applications. 1 For example, they are widely employed as chelating agents due to their binding affinity for transition metals, 1 or they are even contained in commercial sunscreen products 2−4 owing to the fast deactivation processes after ultraviolet (UV) irradiation. The most prominent property of β-diketones is their keto−enol tautomerism that is shifted almost totally toward the enolic form. 5−7 With structural similarities to relevant biomolecules and photochromic substances on the one hand, and the molecules' own versatility in combination with their structural simplicity on the other hand, small β-diketones are prototypical candidates for a systematic study of the photoinduced processes and the subsequent deactivation channels upon which the wide applicability of β-diketones is based.C o m p o u n d s l i k e β -d i k e t o n e s o f t y p e R−C(O)−CH 2 −C(O)−R, where R = H, CH 3 , have drawn continuous attention from chemists and physicists of different research areas because of the pronounced keto−enol tautomerism that is observable (and exploitable) in the gas 5,8 and the liquid phase 6,9 and even in isolated cryogenic matrices. 7,10 The reason for the stabilization of the enolic form is an intramolecular H-bond, coupled with a π-electronic delocalization over the O−C−C−C−O pseudocycle (see Scheme 1). The two simplest and smallest structures exhibiting the central six membered ring closed by the intramolecular Hbond in the chelated enol (CE) form are the compounds malonaldehyde (M...

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Section: ■ Results and Discussionmentioning

confidence: 65%

Ultrafast UV-Induced Photoisomerization of Intramolecularly H-Bonded Symmetric β-Diketones

et al. 2014

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“…1) so only a small amount of the β-diketone form (keto) is present in the gas phase. 8,[18][19][20] Theoretically, eight stable enolic isomers are found: the chelated enol form -depicted in Fig. 17 Many experimental and theoretical works support the Cs symmetry.…”

Section: Introductionmentioning

confidence: 95%

“…For many years, this compound has served as prototype in the investigations of three important physico-chemical processes: intramolecular proton transfer, 1-4 keto-enolic tautomerism [5][6][7][8] and photo-induced isomerization. For many years, this compound has served as prototype in the investigations of three important physico-chemical processes: intramolecular proton transfer, 1-4 keto-enolic tautomerism [5][6][7][8] and photo-induced isomerization.…”

Section: Introductionmentioning

confidence: 99%

Double deuterated acetylacetone in neon matrices: infrared spectroscopy, photoreactivity and the tunneling process

Gutiérrez-Quintanilla

Chevalier

Crépin

2016

Phys. Chem. Chem. Phys.

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The effect of deuteration of acetylacetone (C5O2H8) is explored by means of IR spectroscopy of its single and double deuterated isotopologues trapped in neon matrices. The whole vibrational spectra of chelated enols are very sensitive to the H-D exchange of the hydrogen atom involved in the internal hydrogen bond. UV excitation of double deuterated acetylacetone isolated in neon matrices induces the formation of four open enol isomers which can be divided into two groups of two conformers, depending on their formation kinetics. Within each group, one conformer is more stable than the other: slow conformer interconversion due to a tunneling process is observed in the dark at low temperature. Moreover, IR laser irradiation at the OD stretching overtone frequency is used to induce interconversion either from the most stable to the less stable conformer or the opposite, depending on the excitation wavelength. The interconversion process is of great help to assign conformers which are definitively identified by comparison between experimental and calculated IR spectra. Kinetic constants of the tunneling process at play are theoretically estimated and agree perfectly with experiments, including previous experiments with the totally hydrogenated acetylacetone [Lozada García et al., Phys. Chem. Chem. Phys., 2012, 14, 3450].

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“…29 In addition, they can be produced in the atmospheric oxidation of volatile organic compounds and their degradation can be initiated by photolysis. 30 As the simplest symmetric E-diketone, acetylacetone has been a subject of numerous theoretical [31][32][33][34][35][36][37][38] and experimental studies, 31,[39][40][41][42][43][44][45] which mainly focused on its structures in the ground state, the intramolecular proton transfer, and the Theory and Computation 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 5 keto-enol tautomerism in the gas phase, 31-36,46-49 various solvents, 35 the isolated matrices, 31,49 and nano-confinement environments. 37 Although AcAc is a prototype of E-diketones, it exists mainly as the enolic form …”

Section: Introductionmentioning

confidence: 99%

Multiple-State Nonadiabatic Dynamics Simulation of Photoisomerization of Acetylacetone with the Direct ab Initio QTMF Approach

Xie

Cui

Fang

2017

J. Chem. Theory Comput.

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In the present work, the quantum trajectory mean-field (QTMF) approach is numerically implemented by ab initio calculation at the level of the complete active space self-consistent field, which is used to simulate photoisomerization of acetylacetone at ∼265 nm. The simulated results shed light on the possible nonadiabatic pathways from the S state and mechanism of the photoisomerization. The in-plane proton transfer and the subsequent S → S transition through the E-S/S-1 intersection region is the predominant route to the S state. Meanwhile, rotational isomerization occurs in the S state, which is followed by internal conversion to the S state in the vicinity of the E-S/S-2 conical intersection. As a minor pathway, the direct S → S → S transition can take place via the E-S/S/S three-state intersection region. The rotamerization in the S state was determined to be the key step for formation of nonchelated enolic isomers. The final formation yield is predicted to be 0.57 within the simulated period. The time constant for the S proton transfer was experimentally inferred to be ∼70.0 fs in the gas phase and ∼50.0 fs in dioxane, acetonitrile, and n-hexane, which is well-reproduced by the present QTMF simulation. The S lifetime of 2.11 ps simulated here is in excellent agreement with the experimentally inferred values of 2.12, 2.13, and 2.25 ps in n-hexane, acetonitrile, and dioxane, respectively. The present study provides clear evidence that a direct ab initio QTMF approach is a reliable tool for simulating multiple-state nonadiabatic dynamics processes.

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Acetylacetone in hydrogen solids: IR signatures of the enol and keto tautomers and UV induced tautomerization

Cited by 37 publications

References 28 publications

Ultrafast UV-Induced Photoisomerization of Intramolecularly H-Bonded Symmetric β-Diketones

Ultrafast UV-Induced Photoisomerization of Intramolecularly H-Bonded Symmetric β-Diketones

Double deuterated acetylacetone in neon matrices: infrared spectroscopy, photoreactivity and the tunneling process

Multiple-State Nonadiabatic Dynamics Simulation of Photoisomerization of Acetylacetone with the Direct ab Initio QTMF Approach

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