This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Nanographenes can be considered molecular fragments of graphene, a 2D conductive material in which carbon atoms are connected in a honeycomb pattern. Because their electronic and photophysical properties vary depending on the size and shape of the molecule, nanographenes are expected to find applications in OLEDs, organic solar cells, organic field-effect transistors and more.
For this, simple methods for synthesizing nanographenes that avoid complex multistep processes are desired. Now, a team of scientists from WPI-ITbM at Nagoya University and RIKEN has established a new two-step annulative π-extension (APEX) method that generates structurally diverse nanographenes. This research is published in the journal Angewandte Chemie International Edition.
At the molecular level, nanographenes are composed of polycyclic aromatic hydrocarbons (PAHs), networks of connected benzene rings—hexagon-shaped carbon molecules. APEX reactions provide chemists with a toolbox to connect small or large PAHs without having to prefunctionalize PAH substrates. With their new APEX method, the researchers could synthesize novel nanographenes featuring rare "defects" such as curvature, twisting and five- or seven-membered rings, rather than standard planar structures.
The two-step APEX method proceeds straightforwardly. Using a palladium catalyst and the oxidant ortho-chloranil, the researchers could selectively extend the structure of different PAHs at specific sites. They successfully generated several polyaryl intermediates.
Next, they subjected the polyaryl intermediates to an oxidative cyclization reaction. The reaction uses the oxidant dichloro-5,6-dicyano-p-benzoquinone (DDQ) and trifluoromethanesulfonic acid (TfOH) to synthesize new nanographenes with various frameworks. The frameworks consisted of 8–10 rings, including those with "cove" regions and highly fused hexagonal nanographenes.
Unexpectedly, they also synthesized a nanographene consisting of five-, six- and seven-membered rings. The researchers further analyzed the rare nanographene containing fused five-, six- and seven-membered rings with X-ray crystallography and revealed that it has a highly curved structure that deviates significantly from a planar structure. It exhibits "negative curvature," in which the two partial planes within the molecule are tilted by 34.8 degrees.
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