Ultrafast Vibrational Relaxation Dynamics of C=O and C=C Stretching Modes of Ethyl Acetoacetate in Deuterated Water and Cyclohexane

Abstract

As a prototype of both β-diketone and α,β-enone compounds, ethyl acetoacetate (EAC) has been known to exist in multiple structures in solutions. In this paper, femtosecond infrared pump-probe spectroscopy was used to examine the vibrational relaxation processes of the C＝O and C＝C stretching modes, appeared in the region of 6 μm wavelength (1600～ 1800 cm -1 in frequency), of the EAC tautomers in deuterated water (D 2 O) and cyclohexane. Steady-state infrared spectroscopy and quantum chemistry computations were used to understand the characteristics of these vibrational bands and their line shapes. The results showed that in water EAC exists in the keto form, while in cyclohexane it exists in both keto and enol forms, and perhaps in two possible keto forms. As a result of structural rigidity, the steady-state infrared absorption peak is narrow for the enol form, suggesting mainly homogenous broadening; while those of the keto form exhibit the feature of both homogenous and heterogeneous broadenings. The apparent infrared line shapes of the keto and enol forms were somewhat different even in the same solvent. Population dynamics and anisotropy dynamics of the C＝O and C＝C stretching mode were obtained and examined by transient infrared pump-probe measurement. In D 2 O, the vibrational energy relaxation rate of the C＝O modes was found to be faster than that in cyclohexane, which can be attributed to the formation hydrogen bond between EAC and solvent molecules. The vibrational relaxation process of the enol form was found to be different from that of the keto form, which can be contributed to Fermi resonance interaction between the C＝O stretching mode and the COH bending mode. With the aid of the quantum chemistry calculations, it is concluded that there exists a fast vibrational population equilibrium process between the C＝O and C＝C stretching modes and the COH in-plane bending mode via Fermi resonance. Anisotropy experiments showed a fast orientation dynamics for EAC in cyclohexane than in water, reflecting different solvations. Further, quantum beating was observed in the anisotropy dynamics due to the coherence between the ssand as-modes, especially for the keto form, suggesting a coherent excitation between the related vibrational modes.

A Ln(iii)-3-hydroxypyridine pH responsive probe optimized by DFT

“…This mechanism is possible due to the relatively low reduction potential of Eu(III) and has been observed for a number of coordinating phenoxides in the literature. 16,[31][32][33] LMCT-band energies of Eu(III) are strongly affected by ligand electronegativity 30,32,[48][49][50][51] and the formation of the LMCT state is evidence for a signicant change in the electron donating ability of the oxygen of the hydroxypyridyl ring upon deprotonation of the pyridyl nitrogen, consistent with direct deprotonation of a coordinating phenol.…”

Ultrafast vibrational and structural dynamics of dimeric cyclopentadienyliron dicarbonyl examined by infrared spectroscopy

“…Postnumerical Fourier transform along the t-axis yielded the frequency domain 2D IR spectra, with a digital resolution of 1 cm À1 along both frequency axes. The projection of a 2D IR spectrum on detection frequency (o t ), in direct comparison with an IR pump-probe signal that was collected using k 3 (pump) and an attenuated k 1 (probe) under magic-angle polarization (54.71) conditions, 41,[56][57][58] was used to phase the 2D IR spectra. The coherence time usually scans over 2.5 ps at a step of 5 fs for a given T. A series of T-dependent 2D IR spectra were collected.…”

Intermolecular Hydrogen Bonding Structural Dynamics in Ethylene Glycol by Femtosecond Nonlinear Infrared Spectroscopy

“…瞬态红外光谱是研究振动弛豫动力学、 结构动 力学和振动能量传递的有效手段. 20,29,33,34 在本工作 中, 我们以飞秒泵浦-探测红外光谱为研究手段, 结 合稳态红外光谱测量和量子化学计算, 在波长为 3 μm 的中红外区域内, 利用-OH 伸缩振动为分子结 构探针, 研究了极性溶剂(乙腈、 丙酮、 四氢呋喃和二 甲基亚砜)条件下乙二醇分子间氢键超快动力学, 并 探讨了溶剂性质对氢键动力学的影响. Probing frequencies for the ν1→2 signals are: (a) 3337 cm -1 , (b) 3247 cm -1 , (c) 3204 cm -1 , (d) 3167 cm -1 .…”