Unexpected Charge Effects Strengthen π-Stacking Pancake Bonding

Phenalenyls (PLYs) are important synthons in many functional and electronic materials, which often display favorable molecule-to-molecule overlap for electron or hole transport. They also serve as a prototype for pi-stacking pancake bonding based on two-electron multicenter bonding (2e/mc). Unexpected near-doubling of the binding energy is obtained for the positively charged PLY2+ dimer with an effect similar to that seen for the positively charged olympicenyl (OPY) radical dimer. This charge effect is reversed for the perfluorinated (PF) dimers, and the negatively charged perfluorinated (PF) dimers PF-PLY2- and PF-OPY2- become strongly bound. Long-range interactions reflect these differences. Also surprising is that in this case the pancake bonding corresponds to single-electron (1e/mc) or a threeelectron (3e/mc) multicenter bonding in contrast to the 2e/mc bonding that occurs for the neutral radical dimers. The strong preference for a large intermolecular overlap is maintained in these charged dimers. Importantly, the preference for pi-bonding in the charged dimers compared to sigma-bonding is strongly enhanced relative to the neutral PLY dimers.

Automated summary

Phenalenyls (PLYs) are important synthons in functional and electronic materials, with favorable molecule-to-molecule overlap for electron or hole transport. The unexpected effects of charge on binding energy in PLY dimers and the preference for pi-bonding over sigma-bonding in charged dimers are noteworthy. Long-range interactions and multicenter bonding play important roles in these charged dimers.