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. 2016 Aug 30:6:32152.
doi: 10.1038/srep32152.

Theoretical Study of the ESIPT Process for a New Natural Product Quercetin

Yunfan Yang  1 , Jinfeng Zhao  2 , Yongqing Li  1
Affiliations

Theoretical Study of the ESIPT Process for a New Natural Product Quercetin

Yunfan Yang et al. Sci Rep. .

Abstract

The investigation of excited-state intramolecular proton transfer (ESIPT) has been carried out via the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) method for natural product quercetin in dichloromethane (DCM) solvent. For distinguishing different types of intramolecular interaction, the reduced density gradient (RDG) function also has been used. In this study, we have clearly clarified the viewpoint that two kinds of tautomeric forms (K1, K2)originated from ESIPT processconsist inthe first electronic excited state (S1). The phenomenon of hydrogen bonding interaction strengtheninghas been proved by comparing the changes of infrared (IR) vibrational spectra and bond parameters of the hydrogen bonding groups in the ground state with that in the first excited state. The frontier molecular orbitals (MOs)provided visual electron density redistribution have further verified the hydrogen bond strengthening mechanism. It should be noted that the ESIPT process of the K2 form is easier to occur than that of the K1 form via observing the potential energy profiles. Furthermore, the RDG isosurfaces has indicated that hydrogen bonding interaction of the K2 form is stronger than that of the K1 formin the S1 state, which is also the reason why the ESIPT process of the K2 form is easier to occur.

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Figures

Figure 1
Figure 1. Two expected route graphs of the ESIPT process.
Figure 2
Figure 2
Optimized geometrical configurations of the quercetin molecule: the normal form (a), The tautomeric K1 form (b), The tautomeric K2 form (c). The blue: H, the pink: C, the red: O. The dash line refers to the intramolecular hydrogen bond. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article).
Figure 3
Figure 3. Theoreticalsimulating the absorption and emissionspectrum of the quercetin molecule.
The violet vertical lines stand for the corresponding peak values in the experimental. The detail explanations of curves can be given by the legend on the top right corner.
Figure 4
Figure 4. The calculated IR vibrational spectra of thehydrogen bond groups O1-H2, O3-H4 and O5-H4 stretching absorption band in the S0 and S1 state.
The IR vibrational spectra of the normal form (a) The IR vibrational spectra of the tautomericK1 form (b) The legend can give reader the detail explanations.
Figure 5
Figure 5. The visual electron population of the frontier molecular orbitals HOMO and LUMO.
Figure 6
Figure 6
The function curves of the corresponding energy versus the O1-H2 bond length (a) The corresponding energy versus the O3-O4 bond length (b) The numerical values in the graphs stand for the potential barriers of the proton transfer process.
Figure 7
Figure 7
Scatter plot of the reduced density gradient (RDG(r)) versus Ω(r) are expressed as Function value 1 and Function value 2, respectively (a) The visual diagram of RDG isosurfaces (b) The color gradient corresponding to the diverse types of the interaction have been shown in the figure legend.
See this image and copyright information in PMC

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