Researchers synthesize curved, defect-rich nanographene in two steps

Researchers at Nagoya University and RIKEN have developed a new two-step annulative π-extension (APEX) method that grants access to a far broader range of structurally diverse nanographenes than previous approaches allow – including a rare, non-planar structure built from fused five-, six-, and seven-membered rings.

Nanographenes – molecular fragments of graphene built from polycyclic aromatic hydrocarbons (PAHs) – are of interest for OLEDs, organic solar cells, and organic field-effect transistors, since their electronic and photophysical properties can be tuned through size and shape. APEX reactions, which build fused aromatic frameworks directly onto unfunctionalized PAHs via C-H functionalization, have made such molecules more accessible, but the structural diversity achievable has been limited by the small number of complex, predesigned reagents available for one-step approaches. The team’s method splits the process in two. First, a palladium catalyst paired with the oxidant ortho-chloranil selectively arylates PAHs at specific sites using a broad range of naphthalene-based aryltrimethylsilanes – including sterically congested variants that are difficult to introduce through conventional cross-coupling – to build structurally complex polyarylene intermediates. Second, an oxidative cyclodehydrogenation (Scholl reaction), driven by DDQ and triflic acid, closes these intermediates into nanographenes containing 8 to 10 fused rings, spanning both planar and warped frameworks.

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