As can be seen, population from the S N is split in sub-100 fs reactions with the majority undergoing intersystem crossing into the T N states and a smaller portion undergoing internal conversion to the S 1 state. From the S 1 state, all population relaxes to the S 0 ground state on a 20 fs time scale. The population in the higher-lying triplet states T N is transferred to the T 1 state on a 150 fs time scale, before the population in the triplet manifold relaxes back to the S 0 . This triplet-to-singlet back intersystem crossing occurs on a 750 fs time scale, accounting for the slower component in the rise of the S 0 population.