Theoretical examination of picosecond phenol migration dynamics in phenylacetylene solution

- Phenol dissolved in phenylacetylene hydrogen may hydrogen bond to either the triple bond or aromatic ring of phenylacetylene.
- These two hydrogen bonds have vibrational frequencies that are distinguishable in an IR spectrum.
- 2D vibrational echo spectroscopy has been used to find the timescale of the migration between these sites.
- We use first principles calculations and molecular dynamics to simulate this behavior.
- We find that both inter- and intra-molecular migration pathways occur.

The time-dependent dynamics of phenol dissolved in liquid phenylacetylene is theoretically investigated through first-principles calculations and molecular dynamics. By modeling the hydroxyl functional group with a Morse potential, the bond becomes site-sensitive, vibrating at distinct frequencies when bound at the phenylacetylene triple bond and aromatic ring. This can be exploited to simulate 2D-IR echo spectra using Fourier analysis. The resulting dynamics yields a phenol migration time between the two primary binding sites on phenylacetylene of 3-5 ps in excellent agreement with experiment. Furthermore, this study finds that the mechanism for this migration is strongly influenced by an indirect pathway, in contrast to prior experimental interpretation. The dynamics is found to be primarily dictated by van der Waals forces instead of hydrogen bonding forces, a conclusion that is supported by first principles calculations.