Topological Defects Induced High-Spin Quartet State in Truxene-Based Molecular Graphenoids

Topological defects in graphene materials introduce exotic properties with both fundamental importance and technological implications, absent in their defect-free counterparts. Although individual topological defects have been widely studied, collective magnetic behaviors originating from well-organized multiple topological defects remain a great challenge. Here, we examined the collective magnetic properties originating from three pentagon topological defects in truxene-based molecular graphenoids using scanning tunneling microscopy (STM) and non-contact atomic force microscopy. Unpaired p electrons were introduced into the aromatic topology of truxene molecular graphenoids one by one by dissociating hydrogen atoms at the pentagon defects via atom manipulation. STM measurements, together with density functional theory calculations, suggested that the unpaired electrons were ferromagnetically coupled, forming a collective highspin quartet state of S = 3/2. Our work demonstrates that collective spin ordering could be realized through engineering regular patterned topological defects in molecular graphenoids, providing a new platform for designing one-dimensional ferromagnetic spin chains and two-dimensional ferromagnetic networks. [GRAPHICS] .