The tub-shaped 8 π-electron cyclooctatetraene (COT) provides a very interesting building unit for the design of novel π-expanded COT-based molecular carbon frameworks. The fusion of additional aromatic rings to the COT core enables the preparation of new carbon-rich polycyclic aromatic hydrocarbons (PAHs) with negative curvatures. While the chemical reduction behavior of the parent COT is well studied, the new curved π-expanded COT-based nanocarbons provide unique scaffolds for investigation of their electron acceptor abilities. The enlarged π-surface of such PAHs coupled with their highly contorted carbon frameworks open new potential applications as advanced electron and alkali metal storage materials. In this work, we report our recent studies of a series of π-expanded COT-based carbon frameworks. We have found that in contrast to COT that serves as a two-electron acceptor, larger COT-based PAHs can accept multiple electrons in the stepwise chemical reduction reactions with alkali metals. The resulting products have been isolated as single crystalline materials and fully characterized with X-ray crystallographic and spectroscopic tools. This revealed unique structural rearrangement pathways for the central 8-membered ring accompanied by exceptional alkali metal binding patterns that are framework- and charge-dependent. Importantly, the multi-electron uptake and structural rearrangement were found to be reversible, thus contributing to the potential use of such PAHs as stimuli-response materials.

Alkali metal Induced multi-electron reduction of COT-based carbon frameworks

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