The magnetic couplings in all of these dimers are primarily determined by the kinetic exchange, resulting in an AFM interaction and anti-parallel spin alignment, as demonstrated earlier. However, the dihedral angle between the monomers can subtly modify the overlap of SOMOs as well as the balance between the kinetic and potential exchange. Although the monomers are planar, the directly connected dimers are distorted as free molecules. For example, TRI-TRI and TRI(N)-TRI(N) have dihedral angles of 37º and 38º in the free state due to the steric hindrance between neighboring H atoms (Figure ). Controlling the dihedral angle between the monomers is another means to further regulate the magnetic interactions, as it can be planarized by surface deposition, but also fine-tuned by steric control units (SCUs). Our findings, as depicted in Figure , demonstrate that a decrease in the dihedral angle φ results in an increase in the J value of TRI-TRI, which becomes the largest in coplanar configuration. Specifically, planar TRI-TRI has a value of J = -16 meV, twice as large as for the free dimer (J = -7.7 meV). This is attributed to the enhanced overlap integral of the SOMO by 28% between the building units (Table ). This J value in the planar configuration corresponds to the on-surface structure, and is consistent with the experimental singlet-triplet gap of 14 meV for TRI-TRI on an Au(111) surface. Other directly-linked dimers also enhance their magnetic couplings in their planar configurations, as shown in Table and Figures S18-21 for TOT-TOT, TAM-TAM, TRI(B)-TRI(B) and PLY-PLY. The largest J value of -165 meV, 37 meV higher than in the distorted configuration, is possessed by the planar TAM-TAM. This increase is, again, attributed to the promoted conjugation and correspondingly stronger overlap of SOMOs in the planar structure: the overlap integral raises from 0.448 to 0.526, and the electronic coupling from 0.56 to 0.62 eV (Table ). The magnetic behavior of the TRI(N)-TRI(N) is particularly interesting, as we have observed that the sign of the magnetic coupling can be changed by varying the dihedral angle. Specifically, both FM and AFM interactions have been observed, depending on the value of φ. For angles between 30º and ~70º, the AFM interaction dominates and J < 0, whereas, for other angles, we predict FM interaction with J > 0.