Tracking Noncovalent Interactions of π, π-Hole, and Ion in Molecular Complexes at the Single-Molecule Level

Noncovalent interactions involving aromatic rings, such as pi-stacking and pi-ion interactions, play an essential role in molecular recognition, assembly, catalysis, and electronics. However, the inherently weak and complex nature of these interactions has made it challenging to study them experimentally, especially with regard to elucidating their properties in solution. Herein, the noncovalent interactions between pi and pi-hole, pi and cation, and pi-hole and anion in molecular complexes in nonpolar solution are investigated in situ through single-molecule electrical measurements in combination with theoretical calculations. Specifically, phenyl and pentafluorobenzyl groups serve as pi and pi-hole sites, respectively, while Li+ and Cl- are employed as the cation and anion. Our findings reveal that, in comparison with homogeneous pi<middle dot><middle dot><middle dot>pi interactions, heterogeneous pi<middle dot><middle dot><middle dot>pi-hole and pi<middle dot><middle dot><middle dot>cation interactions exhibit greater binding energies, resulting in a longer binding lifetime of the molecular junctions. Meanwhile, pi<middle dot><middle dot><middle dot>Li+ and pi-hole<middle dot><middle dot><middle dot>Cl- interactions present significantly distinct binding characteristics, with the former being stronger but more flexible than the latter. Furthermore, by changing the molecular components, similar conductivity can be achieved in both molecular dimers or sandwich complexes. These results provide new insights into pi- and pi-hole-involved noncovalent interactions, offering novel strategies for precise manipulation of molecular assembly, recognition, and molecular device.