Structure and Bonding in π‑Stacked Perylenes: The Impact of Charge on Pancake Bonding

Perylene (PER) is
a prototype of polycyclic aromatic
hydrocarbons
(PAHs), which play a pivotal role in various functional and electronic
materials due to favorable molecule-to-molecule overlaps, which enhance
electronic transport. This study provides guidelines regarding the
impact of molecular charge on pancake bonding, a form of strong π-stacking
interaction. Pancake bonding significantly boosts interaction energies
within the monopositive dimer ([(C20H12)2]•+ or PER2+), crucial
for stabilizing aggregation and crystal formation. We discovered energetically
feasible sliding and rotation pathways within the [(C20H12)2]•+ dimer, connecting
different configurations found in the Cambridge Structural Database
(CSD). The dimer’s charge profoundly influences the pancake
bond order (PBO) and the strength and structural preferences of pancake
bonding. The most stable configuration is found in the monocationic
state (PER2+), featuring a pancake bond order
of 1/2 with one-electron multicenter bonding (1e/mc) with similar
characteristics for charge −1. Increasing the total charge
of the dimer to +2 or −2 leads to an unstable local minimum.
Diverse distribution of pancake bonding types present in crystal structures
is interpreted with modeling based on dimer computations with varying
charges.