Can Dispersion Forces Govern Aromatic Stacking in an Organic Solvent?

Area of Science:

• Physical Chemistry
• Supramolecular Chemistry
• Computational Chemistry

Background:

• Aromatic stacking is crucial in molecular recognition and materials science.
• Experimental validation of dominant forces in aromatic stacking in solution is limited.
• Understanding these forces is key to designing functional organic molecules.

Purpose of the Study:

• To experimentally investigate the size-dependence of aromatic stacking interactions in organic solvents.
• To determine the primary energetic contributions governing these interactions.
• To correlate experimental findings with theoretical calculations.

Main Methods:

• Studied size-dependence of aromatic stacking using phenyl-phenyl and anthracene-pyrene systems in organic solution.
• Measured interaction energies and correlated them with theoretical calculations.
• Employed symmetry-adapted perturbation theory (SAPT) to analyze energy components (dispersion, induction, exchange, electrostatics, solvation).

Main Results:

• Observed a significant variation (approx. 7.5 kJ/mol) in interaction energy with increasing aromatic system size.
• Found a strong correlation between experimental data and SAPT-derived dispersion energies.
• Demonstrated poor correlation with induction, exchange, electrostatic, and solvation energy components.
• Showed high correlation between experimental data, SAPT-dispersion energies, and changes in solvent accessible area upon complexation.

Conclusions:

• Experimental results strongly support the dominance of van der Waals dispersion forces in aromatic stacking within organic solutions.
• The size-dependence of these interactions is consistent with dispersion forces being the primary driver.
• Dispersion forces remain dominant even when competing with polarizable solvents.