Perylenediimide (PDI) and its derivatives have often been used as chromophores for singlet fission. The overall kinetics of the singlet fission process are solventdependent, and while CT states in PDI materials appear rapidly in polar solvents, high-yield singlet fission occurs equally rapidly in nonpolar solvents. Here, we use RAS-SF + PCM to explore the impact of solvent polarity on the singlet fission process. FIG. : RAS-SF/cc-pVDZ + PCM results for two geometries of (PDI)2 that have been called (a) "MO" and (b) "C8". Structures are shown on the left and correspond to slightly different offsets in the lateral plane as well as different stacking distances, 3.46 Å for model 1 and 3.28 Å for model 2. Both models give rise to a pair of 1 ME states and the middle panel illustrates the orbitals involved in the two largest CT configurations for both states. Tables on the right quantify the percentage CT character in each of these two configurations, along with the corresponding dipole moment, as a function of the solvent's dielectric constant. The state labeled 1 ME is the higher-energy state.