“…A similar effect is observed when the frontier π -MOs of naphthalocyanine (9) and anthracocyanine (10) are compared to those of Pc (8), but it is smaller in magnitude since the additional rings lie further from the inner perimeter where the largest MO coefficients are anticipated for the frontier π -MOs derived from the HOMO and LUMO of the parent perimeter ( Figure 3). Benzo substitution has a destabilizing effect on the energy of the a MO because there is an antibonding interaction at the point of attachment of the C 4 H 4 bridges that are added upon fused-ring-expansion and there are also nodal planes on the 4 aza-nitrogens and hence a smaller stabilization effect due to the electronegativity (1), and its analogues fused-ring-expanded at the pyrrole β -carbons with benzene (2), 2,3-naphthalene (3), anthracene (4), phenanthrene (5), and phenanthroline (6) moieties, and the corresponding tetraazaporphyrins (7-12), β , β -tetrapyrazino-substituted tetraazaporphyrin (13), and its analogues fused-ring-expanded with benzene (14), 2,3-naphthalene (15), phenanthrene (16), and phenanthroline (17) moieties, and the corresponding β , β -tetrabenzopyrazino-substituted structures (18)(19)(20)(21)(22). Bolder black lines are used to highlight the 4 frontier π -MOs that are associated with Michl's perimeter model.…”