The on-site Coulomb repulsion, U, also influences the overall magnetic interaction, especially for dimers with weak coupling (Figure ). It is primarily determined by the elementary monomer, as systems sharing the same building units have similar U (Table ). For instance, the U values of the TRI-series of molecules is around 2 eV, whereas that of the TRI(N)-series is approximately 1 eV, as the TRI monomer has two unpaired electrons, compared to only one spin in the TRI(N) monomer. Consequently, searching for non-Kekulé building blocks with unpaired πelectrons, such as Clar's goblet and other triangulene systems, offers great promise for achieving metal-free spin-dimers and polymers with strong electron correlation. It is worth mentioning that, unlike the typical Hubbard model and inorganic metal complexes where the spins are fully localized on a single site, in metal-free systems, SOMOs are delocalized, and therefore, the U value is also affected by the conjugation, particularly for those with a large SOMO overlap and strong electronic coupling. This dispersive spin site is observed, for example, in TOT-TOT, yielding a small U value of 0.09 eV (Figure and Table ).