Curved nanographene synthesized rapidly
Researchers from Nagoya University and RIKEN developed a two-step method to synthesize diverse nanographenes, including those with rare curved structures. This method uses palladium catalysts and specific oxidants.
Nanographenes, molecular fragments of graphene, are gaining attention due to their potential applications in OLEDs, organic solar cells, and organic field-effect transistors. These materials, composed of carbon atoms in a honeycomb pattern, exhibit varied electronic and photophysical properties based on their size and shape. Researchers from the Institute of Transformative Bio-Molecules (WPI-ITbM) at Nagoya University and RIKEN have developed a two-step annulative p-extension (APEX) method to synthesize structurally diverse nanographenes. This method, published in Angewandte Chemie International Edition on August 25, simplifies the synthesis process by avoiding complex multi-step procedures.
At the core of nanographenes are polycyclic aromatic hydrocarbons (PAHs), which consist of interconnected benzene rings. The APEX method allows chemists to connect PAHs without prefunctionalizing the substrates, enabling the creation of nanographenes with unique features such as curvature, twisting, and non-standard ring structures.
The APEX method involves a straightforward two-step process. Initially, a palladium catalyst and ortho-chloranil are used to extend PAH structures selectively. This step generates polyaryl intermediates, which are then subjected to oxidative cyclization using dichloro-5,6-dicyano-p-benzoquinone (DDQ) and trifluoromethanesulfonic acid (TfOH). This results in nanographenes with frameworks of 8–10 rings, including highly fused hexagonal structures and unexpected five-, six-, and seven-membered rings.
Further analysis of a nanographene with fused five-, six-, and seven-membered rings using X-ray crystallography revealed a highly curved structure with "negative curvature," where the molecule's partial planes are tilted by 34.8 degrees. This demonstrates the APEX method's efficiency in synthesizing both known and novel nonplanar nanographenes. The research team aims to expand their work to create molecular nanocarbons with diverse shapes and electronic structures in the future.
Source: Graphene Feed