Engineering Triangulene Building Blocks with Tunable Magnetic Exchange Coupling for All-Carbon-Based Molecular Spintronics

Nanographenes are prospective candidates for spintronic materials that feature spin-polarization at zigzag edges. Triangulenes possess a distinct rule of large total spins analogous to transition metal elements and may be regarded as artificial atoms. In this work, we explore design principles using triangulene building blocks to construct nanographene fragments with various shapes and sizes including simple dimeric systems, rhombenes, double-arrow systems, and superzethrenes. Empirical rules for each system relating their sizes and the most stable high spin states are derived, which correspond to the ferromagnetic arrangement of their constituent triangulene units. Coupling mechanisms constituting effective triangulene units are proposed for each system rationalized by Clar sextet Lewis structures. We find that both the spin multiplicities and exchange energies within 10⁰-l0² meV can be modulated by the connection scheme and the bridge geometry. Our results provide numerical references and valuable empirical rules of molecular design models for future all-carbon-based spintronics.