The fluorescence energy was calculated as the vertical emission energy at the S1 minimum geometry as all systems obey Kasha's rule. After optimizing the structures to their groundstate minimum geometry, S1 geometry minimizations were performed at TD-wB97X-D3/6-31G* level of theory, with the same geometry optimization parameters as the ground-state optimization and no constrains. Unconstrained relaxation of the dimer geometry may change the orientation of the two monomers' S1 transition dipole moments, making them not strictly parallel or perpendicular. However, the geometry optimization results show that the angular change does not exceed 30° for any dimer in this study (Figure ). Hence, our discussions of TDM-parallel vs. TDM-perpendicular conformers are still valid.