Switching Hydrogen Bonding to π-Stacking: The Thiophenol Dimer and Trimer

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Supramolecular Chemistry

Background:

• Understanding intermolecular forces is crucial for molecular self-assembly.
• Thiophenol's aggregation behavior is influenced by π-stacking and hydrogen bonding.
• Sulfur-containing compounds exhibit unique interaction potentials.

Purpose of the Study:

• To investigate the interplay between π-stacking and hydrogen bonding in thiophenol self-aggregation.
• To characterize the structures and dynamics of thiophenol dimers and trimers.
• To elucidate the role of sulfur-centered hydrogen bonds in molecular assembly.

Main Methods:

• Jet-cooled broadband rotational spectroscopy was employed.
• Analysis of spectral data to determine molecular structures and dynamics.
• Comparison of experimental results with theoretical predictions.

Main Results:

• Two distinct isomers of the thiophenol dimer were identified.
• Dispersion-driven π-stacked structures were observed, stabilized by S-H···S hydrogen bonds.
• Evidence of large-amplitude internal motion, specifically a concerted ring inversion, was found in the dimer global minimum.
• A symmetric top structure was assigned for the thiophenol trimer.
• The torsional barrier for the dimer inversion was determined to be 250.3 cm⁻¹.

Conclusions:

• The study highlights the balance between π-stacking and hydrogen bonding in thiophenol aggregation.
• Sulfur hydrogen bonds play a significant role in stabilizing the observed structures.
• Substituent effects can modulate π-stacking geometries in similar systems.