Journal
JOURNAL OF LUMINESCENCE
Volume 172, Issue -, Pages 29-33Publisher
ELSEVIER
DOI: 10.1016/j.jlumin.2015.11.026
Keywords
Time-dependent density functional theory; Excited-state intramolecular proton transfer; Frontier molecular orbitals; Hydrogen bond; Potential energy curves
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Time-dependent density functional theory (TD-DFT) method at B3LYP/6-31G(d,p) theoretical level was employed to investigate the excited-state intramolecular proton transfer (ESIPT) reaction of 6-amino-2-(2'-hydroxyphenyl)benzoxazole in dichloromethane and methanol solvents. Upon photo-excitation, the intramolecular hydrogen bond between the hydroxyl and neighboring N atom is significantly strengthened, which provides a driving force in facilitates the ESIPT reaction. The calculated steady-state absorption and fluorescence spectra agree well with the experimental results. Especially, after the photo excitation from HOMO (pi) to LUMO (pi*), the rearrangement of electronic density distribution of frontier molecular orbitals (MOs) is a very important positive factor for the ESIPT process. The potential energy curves confirm that, after photo-excitation, the EXIPT reaction occurs with the H atom of the hydroxyl group remove to the neighboring N atom. By contrast, the potential barrier of the 6A-HBO-MeOH complex in the S-1 state falls ca. 3.57 kcal/mol, lower than the isolated 6A-HBO. It is likely that the ESIPT reaction occurs more easily for the 6A HBO-MeOH complex due to the influence of the intermolecular hydrogen bonding. (C) 2015 Elsevier B.V. All rights reserved.
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