Olympicene radicals as building blocks of two-dimensional anisotropic networks

I propose monoradical nanographenes without C3 symmetry as building blocks to design two-dimensional carbon crystals. As representative examples I study the honeycomb and kagome lattices, showing that by replacing the sites with olympicene radicals the band dispersion near the Fermi energy corresponds, respectively, to that of Kekule/anti-Kekule graphene and breathing kagome tight-binding models. As a consequence, finite islands of these crystals present corner states close to the Fermi energy, just like the parent models. In the case of Kekule/anti-Kekule graphene, such states are topologically protected, standing as examples of second-order topological insulators with a nonzero Z2- or Z6-Berry phase. Differently, those of the breathing kagome lattice are of trivial nature, but the ground state has been predicted to be a spin liquid in the antiferromagnetic S = 1/2 Heisenberg model. Hence, two-dimensional systems made of low-symmetric nanographenes may be convenient platforms to explore exotic physics in carbon materials.