monomers. The origin of this phenomenon is revealed by analyzing the excited state components for all the 496 dimers (Figure ). Similar to the C22-X series, for dimers formed by two monomers with distinct E 5% , their S1 are usually dominated by the LE states of the monomer with lower E 5% . Dimers containing monomers with similar E 5% have similar portions of monomer LE states thus maximizing the TDM cancellation effect and reducing the oscillator strength. Besides, the involvement of CT states is also more prominent between monomers with similar energies, which further decreases the fluorescence intensity.