The key ingredient for a negative singlet-triplet gap is a molecular edge with alternating electron-donor (D) and electron-acceptor (A) groups. In 3T-b, where the rim is made of 18 carbon atoms, the central borazine unit plays a fundamental role creating an alternating pattern of electron poor and electron rich sites on the rim, thus leading to a negative ST gap. Accordingly, upon gradually breaking the bonds that connect the central BN 3 unit to the edge, one recovers a cyclic polyene structure, losing the ST inversion (see Fig. ).