Molecular dynamics of excited state intramolecular proton transfer: 3-hydroxyflavone in solution

Journal Article · Mon May 21 00:00:00 EDT 2012 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.4707736· OSTI ID:22047212

Bellucci, Michael A; Coker, David F ^[1]

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1. Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215 (United States)

The ultrafast enol-keto photoisomerization in the lowest singlet excited state of 3-hydroxyflavone is investigated using classical molecular dynamics in conjunction with empirical valence bond (EVB) potentials for the description of intramolecular interactions, and a molecular mechanics and variable partial charge model, dependent on transferring proton position, for the description of solute-solvent interactions. A parallel multi-level genetic program was used to accurately fit the EVB potential energy surfaces to high level ab initio data. We have studied the excited state intramolecular proton transfer (ESIPT) reaction in three different solvent environments: methylcyclohexane, acetonitrile, and methanol. The effects of the environment on the proton transfer time and the underlying mechanisms responsible for the varied time scales of the ESIPT reaction rates are analyzed. We find that simulations with our EVB potential energy surfaces accurately reproduce experimentally determined reaction rates, fluorescence spectra, and vibrational frequency spectra in all three solvents. Furthermore, we find that the ultrafast ESIPT process results from a combination of ballistic transfer, and intramolecular vibrational redistribution, which leads to the excitation of a set of low frequency promoting vibrational modes. From this set of promoting modes, we find that an O-O in plane bend and a C-H out of plane bend are present in all three solvents, indicating that they are fundamental to the ultrafast proton transfer. Analysis of the slow proton transfer trajectories reveals a solvent mediated proton transfer mechanism, which is diffusion limited.

• OSTI ID: 22047212
• Journal Information: Journal of Chemical Physics, Vol. 136, Issue 19; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
74 ATOMIC AND MOLECULAR PHYSICS
ACETONITRILE
FLUORESCENCE
FLUORESCENCE SPECTROSCOPY
INTERACTIONS
ISOMERIZATION
METHANOL
MOLECULAR DYNAMICS METHOD
PHOTOCHEMISTRY
POTENTIAL ENERGY
PROTONS
REACTION KINETICS
SIMULATION
SOLUTIONS
SOLVENTS
SURFACES
VIBRATIONAL STATES