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Area of Science:

  • Computational Chemistry
  • Photochemistry
  • Molecular Dynamics

Background:

  • 2-(oxazol-2-yl)-3-hydroxychromone (OHC) exists in multiple low-energy conformers.
  • Conformational differences arise from OH torsion and rotation around the chromone-oxazole linkage.
  • Specific conformers (OHC-A, B, C) feature distinct intramolecular hydrogen bonding patterns (OH⋯O or OH⋯N).

Purpose of the Study:

  • Investigate the energy profiles and excited-state dynamics of proton transfer (PT) in OHC conformers.
  • Determine the influence of excited states on PT propensities and fluorescence.
  • Analyze the role of different H-bonding configurations on PT barriers and dynamics.

Main Methods:

  • Density Functional Theory (DFT) calculations at the B3LYP/cc-pVDZ level to determine ground-state energies.
  • Time-Dependent DFT (TDA-B3LYP) to compute excited-state energy profiles and PT barriers.
  • Fewest-switches surface hopping (FSSH) simulations initialized on S1 and S2 states to model excited-state dynamics.

Main Results:

  • OHC-B and OHC-C conformers have similar ground-state energies, with OHC-A slightly higher.
  • Lower PT barriers were predicted for OHC-A and OHC-B compared to OHC-C on the lowest bright excited state.
  • FSSH simulations revealed distinct intra- and inter-ring PT dynamics for different conformers, influenced by excited states.

Conclusions:

  • Excited-state dynamics significantly impact proton transfer propensities in OHC conformers.
  • The hydrogen bonding pattern and molecular conformation dictate the ease and pathway of PT.
  • Understanding these dynamics is crucial for explaining the fluorescence behavior of OHC and its PT variants.