Heteroatom-Doped [4]Triangulene: Facile Synthesis and Two-Dimensional On-Surface Self-Assemblies

Synthesis of nanographenes (NGs) with structural precision has attracted enormous interest in organic chemistry and materials science. However, their ordered two-dimensional (2D) self-assembled structures on surfaces, which are of great importance for the future nanotechnologies, remain challenging. In this work, embedding heteroatoms (oxygen-boron-oxygen) into the zigzag edges of NGs is proven as a useful strategy to afford ordered 2D self-assemblies based upon intermolecular hydrogen bonding. We have thus synthesized OBO-doped [4]triangulenes, whose planar geometry is revealed by single-crystal X-ray diffraction. Their photophysical and electrochemical properties show significant differences from those of pristine [4]triangulene. Self-assembly on metal surfaces is explored by scanning tunneling microscopy (STM) associated with the minimum spanning tree (MST) analysis. Highly ordered 2D superstructures can be demonstrated and the packing modes depend sensitively upon the substrate.