Triangulene series: from precursor design towards on-surface synthesis and characterization.

Abstract

Triangulene and its higher homologs are a class of zigzag-edged triangular graphene molecules (ZTGMs) with high-spin ground states. These open-shell molecules are predicted to host ferromagnetically coupled edge states with net spins scaling with the molecular size, which are considered as the promising candidates for future molecular spintronics applications. Unfortunately, the synthesis of unsubstituted [n]triangulene series and the direct observation of their edge states have been a long-standing challenge due to the molecules high chemical reactivity towards oxygen. However, recent advances in the rational design of elegant organic precursors allows for the on-surface synthesis and characterization of three types of unsubstituted [n]triangulene series, namely [3]-, [4]- and [5]triangulene. In this review, we will highlight the key aspects of this rapidly-developing field ranging from the principles of precursor design to synthetic strategies and characterization of the fundamental properties of a homologous series of triangulene molecules synthesized on the surface. We will also discuss the challenges and future directions in this field.