A threshold for charge transfer in aromatic interactions? A quantitative study of pi-stacking interactions

Area of Science:

• Organic Chemistry
• Supramolecular Chemistry
• Physical Chemistry

Background:

• Understanding non-covalent interactions between aromatic systems is crucial in chemistry and materials science.
• Triptycene derivatives offer unique conformational control for studying such interactions.

Purpose of the Study:

• To quantitatively investigate attractive interactions between substituted arenes in a parallel displaced configuration.
• To explore the influence of electronic substituents on aromatic interaction strength.

Main Methods:

• Utilized triptycene-derived molecular conformational reporters to precisely control and measure arene arrangements.
• Observed charge-transfer bands to detect and quantify interactions, particularly between electron donors and acceptors.
• Analyzed substituent effects on interaction free energies using quantitative structure-property relationships.

Main Results:

• Attractive interactions were observed between substituted arenes in the parallel displaced configuration.
• Charge-transfer bands indicated significant interactions when strong donors and acceptors were involved.
• Substituent effects showed opposing trends for electron-deficient versus mildly perturbed arenes.
• The free energy of interaction did not linearly correlate with substituents in Hammett plots for strong donor-acceptor systems.

Conclusions:

• Electrostatic models alone are insufficient to explain the nonlinear relationship between free energy and substituents in these aromatic interactions.
• The study highlights the complex interplay of electronic and steric factors governing arene-arene interactions.