The C22-X and PC113-X series. To study the impact of monomer properties on the dimer fluorescence, we constructed the "C22-X series" including 132 dimers, each with monomer C22 paired with one of the 132 monomers, X. In the cartesian coordinate, the C22 and X are assembled by aligning their axes of maximum moment of inertia along the z-axis and then placing their centroids on the z-axis with a separation of 3.7 Å (see Supplementary Material Figure ). To explore the effects of dimer conformation, we then created two conformers for each dimer, namely the TDM-parallel conformer and the TDM-perpendicular conformer, by rotating their monomers along the z-axis. The TDM-parallel conformer has its two monomers' S1 TDMs aligned both along the x-axis, while the TDM-perpendicular conformer has the two TDMs aligned along the x and y axes respectively (see Supplementary Material Figure ). The PC113-X series was constructed following the same procedure. These structures were the starting point of further DFT geometry optimizations.