Use of Equation by Manian and co-workers to study the exciton dynamics of di-keto pyrrolopyrrole show internal conversion to be the primary loss mechanism for every electronic state save for the S 1 state (Table ). Detailed examination of these rates highlighted that Franck-Condon the nuclear-electronic couplings between same-spin states was calculated from the residues of the imaginary component of the non-adiabatic matrix element as shown by Send & Furche , this work used the spinflip TDDFT method, as implemented in the Q-chem software package . The difference between the two methods is a factor of ∼1.5, explained by Manian and co-workers as being due to the residue method not accounting for the final state correctly.