A joint research team including Chief Scientist Kenichiro Itami at the RIKEN Pioneering Research Institute and Associate Professor Hideto Ito at the Graduate School of Science, Nagoya University, succeeded in developing a new method for synthesizing diverse and complex nanographenes from polycyclic aromatic hydrocarbons (PAHs) in fewer steps. The findings were published in the online edition of Angewandte Chemie International Edition.
Provided by RIKEN
The joint research team established a two-step annulative π-extension (two-step APEX) method that directly connects naphthalene skeletons of various structures to unsubstituted PAHs using palladium catalysts, followed by oxidative ring closure.
In conventional APEX methods, applicable π-extending reagents were limited, imposing constraints on the structural diversity of synthesizable nanographenes. In the new method, sterically crowded aromatic ring sites can also be introduced, enabling the synthesis of planar and curved nanographenes in which 8 to 10 rings are fused. Particularly, for nanographenes in which five-membered, six-membered, and seven-membered rings are fused consecutively, single-crystal X-ray structure analysis revealed that they possess curved structures that deviate significantly from planarity, exhibiting negative curvature in which two subplanes within the molecule are tilted by 34.8 degrees.
In the crystal, the molecules were stacked in columns while rotating by 180 degrees, forming weak π-π interactions between molecules. This curved nanographene showed broad absorption from 440 to 570 nanometers (nm) and exhibited orange luminescence with a maximum at 576 nm.
Successfully expanding the structural space of nanographenes that was difficult to access using conventional methods provides a new synthetic platform for exploring unknown optical and electronic functions arising from their structures.
Journal Information
Publication: Angewandte Chemie International Edition
Title: Diversity-Oriented Two-Step Annulative π-Extension Enables Access to Structurally Complex Nanographenes
DOI: 10.1002/anie.2205198
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