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. 2025 Mar 20;30(6):1381.
doi: 10.3390/molecules30061381.

Unveiling the ESIPT Luminescence Mechanism of 4'-N,N-Diethylamino-3-Hydroxyflavone in Ionic Liquid: A Computational Study

Jin Yang  1 , Qi Li  1 , Meilin Guo  1 , Lu Yan  1 , Lixia Zhu  1 , Jing Zhao  1 , Guangxiong Hu  1 , Hang Yin  1 , Ying Shi  1
Affiliations

Unveiling the ESIPT Luminescence Mechanism of 4'-N,N-Diethylamino-3-Hydroxyflavone in Ionic Liquid: A Computational Study

Jin Yang et al. Molecules. .

Abstract

Excited state intramolecular proton transfer (ESIPT) within molecules in solvents plays important roles in photo-chemistry and photo-biology. Herein, the influence of 1-ethyl-3-methyl-imidazolium bis (trifluoromethylsulfonyl) imide ([EMIm][NTf2]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIm][PF6]) on the ESIPT of 4'-N,N-diethylamino-3-hydroxyflavone (DEAHF) was explored. The density functional theory and time-dependent density functional theory methodologies were used. The calculated fluorescence spectrum reveals that the fluorescence peaks of DEAHF in [EMIm][NTf2] and [BMIm][PF6] originate from the emission of N* and T* forms. The structure's optimization, infrared spectra, non-covalent interactions and the scanning of potential energy curves collectively demonstrate that the ESIPT of DEAHF likely happen more in [EMIm][NTf2] than in [BMIm][PF6]. The solvation effects in [BMIm][PF6] exhibit greater prominence compared to those in [EMIm][NTf2], as evidenced by the free energy curve. The alterations in dipole moment indicate a substantial solvation relaxation during the ESIPT processes. Our aforementioned research offers backing for the advancement of novel fluorescent probes.

Keywords: DFT/TDDFT; ESIPT; dual phosphorescence; ionic liquid; solvation effect.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Molecular structures of (a) DEAHF of N forms, (b) DEAHF of T forms, (c) [EMIm][NTf2] and (d) [BMIm][PF6].
Figure 2
Figure 2
Calculated IR spectra of DEAHF molecule in its N form in S0 and S1 states in [EMIm][NTf2] (a) and [BMIm][PF6] (b). Black line represents S0 state, and red line represents S1 state.
Figure 2
Figure 2
Calculated IR spectra of DEAHF molecule in its N form in S0 and S1 states in [EMIm][NTf2] (a) and [BMIm][PF6] (b). Black line represents S0 state, and red line represents S1 state.
Figure 3
Figure 3
RDG scatter plots of DEAHF molecules in (a) [EMIm][NTf2] and (b) [BMIm][PF6].
Figure 4
Figure 4
Potential energy curves of DEAHF in (a) [EMIm][NTf2] and (b) [BMIm][PF6] along with O1-H1 bond length in S0 and S1 states.
Figure 5
Figure 5
Relative energy as a function of the distance of O1-H1. The different lines represent the free energy in gas. [EMIm][NTf2] and [BMIm][PF6] correspond to the S0 and S1 states, respectively.
Figure 6
Figure 6
The changes in dipole moment along the distance of O1-H1. The different lines represent the dipole moment in gas, and [EMIm][NTf2] and [BMIm][PF6] correspond to the S0 state and the S1 state, respectively.
See this image and copyright information in PMC

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