The excited state population increase seen with amplification of the 161 and 176 cm -1 phonon modes could be the result of modification of singlet fission or exciton transport dynamics. A previous computational study suggests that a 177 cm -1 mode modulates the electronic coupling between singlet and triplet states, which ultimately drives singlet fission via a conical intersection. Our data is consistent with these phonon modes driving singlet fission and therefore increasing the initial triplet population. Because the population increase is consistent across all photoexcitation locations, it is difficult to distinguish between changes in the overall population and changes in transport dynamics. Given that the increase relative to the single pulse is the same order of magnitude at all locations, and in there is still a greater population along the fast axis than the slow axis, it is reasonable to assume amplification of these modes drives the generation of more excited states rather than modifying transport dynamics. It is also possible that the 161/176 cm -1 modes drive more efficient transport along both the slow and fast axes in addition to driving more excited state population, leading to the increase in population at offset locations. In this case, triplet diffusion is still sufficiently slow such that we still see an increase at the fully overlapped region due to the presence of more excited state species during the timeframe of this experiment. While this study cannot detangle these two effects, it is clear that selective amplification of the 161 and 176 cm -1 phonon modes drive an increase in the overall excited state population.