The 1-Naphthol Dimer and Its Surprising Preference for π-π Stacking over Hydrogen Bonding

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Computational Chemistry

Background:

• Understanding the structure of molecular dimers is crucial for predicting their physical and chemical properties.
• Previous studies on the 1-naphthol dimer yielded conflicting structural assignments, highlighting challenges in characterizing non-covalent interactions.
• Dispersion-bound systems, like the 1-naphthol dimer, present unique complexities in energetic and structural evaluations.

Purpose of the Study:

• To experimentally determine the most abundant structural configuration of the 1-naphthol dimer.
• To resolve discrepancies between previous spectroscopic studies on the 1-naphthol dimer's structure.
• To provide an accurate structural model for larger, dispersion-bound molecular systems.

Main Methods:

• Chirped-pulse Fourier transform microwave spectroscopy was employed for experimental identification of the 1-naphthol dimer.
• UV-IR dip double resonance spectroscopy data from a previous study was re-evaluated.
• Improved theoretical analysis was utilized to reconcile experimental findings and computational models.

Main Results:

• The most abundant 1-naphthol dimer was experimentally identified with a V-shaped, partially overlapping π-π stacked structure.
• This structure lacks canonical hydrogen bonds between the 1-naphthol subunits.
• The newly determined structure is consistent with previously obtained UV-IR spectroscopic data, resolving prior contradictions.

Conclusions:

• The V-shaped, non-hydrogen-bonded structure represents the most stable configuration of the 1-naphthol dimer.
• This study clarifies the structural ambiguity surrounding the 1-naphthol dimer.
• The findings offer insights into the accurate evaluation of energetics and structures for complex, larger dispersion-bound molecular systems.