For all conformers 1-8, the HOMO→LUMO transition dominates the S1 state, with both 𝜋 orbitals being delocalized over both molecules. A closer inspection shed light into the binding character of the S1 state: while the latter is populated, the electronic density of the system undergoes a substantial redistribution, incorporating stronger binding contributions at the expense of other anti-or weakly bonding ones. Indeed, the isosurfaces in Figure clearly show that a nodal plane is sandwiched between the two monomers in the starting natural transition orbital (NTO), as lobes with opposite phases are directly facing each other; conversely, regions of constructive interference are featured by the final NTO, enhancing the intermolecular binding and excimer stabilization, compared to the separated constituents. Conversely, the two optimized structures in cluster 9 are characterized by an S1 state corresponding to a localized La excitation on a single monomer (see Figure ), as can be argued by the considerable oscillator strength and the absence of any significant CT contributions (see Table ). To check that this was not an artifact stemming from the well-known deficiencies of TD-DFT in dealing with the (almost dark) Lb and (bright) La transitions in PAHs, we performed single-point calculations with ADC(2).