For all dimer conformers, the xyz coordinates were transformed into displacement coordinates, as described in the Methods section (Section 2) and Supporting Information (Section S1). All transformed coordinates are available in the SI. Two groups of monomers in our study can be considered homologous. Phen and BzQuin are homologues, with the only difference being the substitution of N for CH at one position on the ring system. Similarly, DBF, DBT, DBTO, Fluor, and MeCarb can all be considered homologues of each other, with the ring system being mostly identical, and only the apical position of the 5-membered ring, and groups pendant to it, varying. Since the monomers are homologous, it is possible for them to form homologous dimers, where the only difference between dimers is in the substituted portions of the monomers. In practice, substitutions such as N for CH or N-Me for C=O cause small distortions both within the monomers and in their relative displacement and rotation, but these are generally small enough that the conformers are recognizably homologous. Note that, for monomers of lower symmetry, such as BzQuin, multiple dimer conformers may be homologous to the same (computed or hypothetical) dimer conformer of the higher-symmetry species, in this case, phenanthrene. In such cases, the multiple conformers of the lower-symmetry dimer can also be considered to be homologous to each other.