For better comparison of geometries, the xyz coordinates for each conformer of each dimer were transformed into new coordinates that describe the dimers in terms of rotation and displacement along the long axis, short axis, and perpendicular axis. That is, one monomer was chosen as the reference monomer, while the other is considered the displaced monomer, and both monomer centres of mass were determined. For DBTO, the oxygen atom was omitted from centre of mass computations, to keep the centre of mass in the plane of the aromatic system. The long and short axes are indicated by blue and red dashed lines, respectively, in Figure , with the direction of positive displacement indicated by arrows, where applicable. In general, the long axis passes through the two most distant carbon atoms of the molecule, while the short axis is perpendicular to the long axis, and bisects the central bond which connects the most distant aromatic rings to each other. The normal, or z, axis is that line which is perpendicular to both the long and short axes (and thus to the best-fit plane of the monomer) through the point of their intersection. Separation between centres of mass was described as translation of the displaced centre of mass along the long, short, and normal axes of the reference monomer. Rotation of the displaced monomer was described by three angles: a) the angle between the reference long axis and the projection of the displaced long axis into the plane of the reference monomer, b) the inclination of the displaced long axis with respect to the plane of the reference monomer, and c) the inclination of the displaced short axis with respect to the plane of the reference monomer. This gives us a coordinate system which ignores the small intramonomer distortions, and describes any dimer using only six degrees of freedom. Further details on these definitions, including on positive vs. negative displacements and rotations for specific monomers are provided in the Supplementary Information, Section S1. Transformed coordinates for each dimer can also be found in the SI.