Mapping the Energy Landscape of Polycyclic Aromatic Hydrocarbon π-π Stacking Using a High-Precision Torsional Balance Based on the 13,14-Diphenyl-6,7-dihydrodibenzo[b,j][4,7]Phenanthroline Scaffold.

π-π stacking interactions are central to supramolecular assembly, material properties, and biomolecular organization. However, their intrinsically weak nature and sensitivity to geometric variation make them difficult to quantify experimentally. Here, we introduce a new molecular torsional balance based on a 13,14-diphenyl-6,7-dihydrodibenzo[b,j][4,7]phenanthroline (DHDBPT) scaffold that simultaneously achieves rotational restriction and conformational flexibility. This feature enables quantitative measurements of π-π interactions across multiple stacking geometries. Fluorine substituents are installed as a reliable probe for rotamer equilibria through integration of 19F NMR signals. Eighteen homodimeric and four heterodimeric torsional balances were synthesized and studied. Across the series of homo-stacked and hetero-stacked PAH dimers, the measured stabilizations range from 0.3 to over 2.0 kcal mol-1 and correlate strongly with interfacial π-surface overlap. These results demonstrate that dispersion dominates PAH stacking even in solution, while contributions from other interactions are secondary. The DHDBPT torsional balance offers an energetic resolution of ∼0.2 kcal mol-1 and structural resolution on the Å scale. It provides a general platform for interrogating weak noncovalent interactions with high precision.