This data set contains all data necessary to generate the figures in the manuscript. Detailed information on how the data was obtained may be found in the open access manuscript which has been deposited in this repository. Figure 1 - structure and general photo physics of the DT-Mes molecule. Figure 2 - determination of the energy levels of DT-Mes and multiple emissive species. Figure 3 - Transient absorption spectroscopy and excited state evolution. Figure 4 - Transient absorption spectroscopy and varying TT/CT balance. Figure 5 - TT and CT action spectra. Figure 6 - switching between coherent and incoherent singlet fission Figure 7 - multidimensional plot of the surfaces participating in the last part of singlet fission. Figure 8 - summary of singlet fission mechanism.