Table : QM/MM average energies E S 0 !T together with their standard deviation (in kJ.mol ) over five independent trajectories for several QM subsystems (either featuring a single thymine (1T) or the TTTT stack (4T). Interestingly, when including the entire TTTT strand (4T model)in the the QM partition, we observe a non-negligible stabilization of T whose E drops to an average of 299 kJ.mol 1 . This e↵ect is indeed compatible with the enhanced treatment of multichromophoric coupling and polarization e↵ects, which are not included in our force field based on fixed-charge and hence in the MM embedding. It is also in line with experimental evidences pointing to the decrease of the triplet energy in the DNA environment. 17 However, if the decrease of the triplet energy is undeniable, a finer analysis of the QM/MM-MD simulation reveals a more contrasted behavior. Indeed, the 4T model experiences the most prominent oscillations, globally spanning an interval of 99.6 kJ.mol 1 on the ensemble of the five replicas. As a matter of fact, while trajectory number 1 provides a relative low energy (268 kJ.mol 1 ) trajectory 5 yields an average E of 316 kJ.mol 1 , i.e. a value that is comparable to the ones obtained for the 1T model. Globally our results are in reasonable agreement with the experimental determination of the triplet energy in thymine, the value of 270 kJ.mol 1 being comprised in our confidence interval. However, our data also o↵er a more complex scenario, in which the energy of the triplet state is strongly dependent on the precise, and instantaneous, arrangement of the DNA and solvent structural parameters, leading to the coexistence of higher and lower energy situations, which thus can be accessible for triplet energy transfer or not. This aspect can have a strong influence in dictating the overall characteristic time for the energy transfer, but also the final quantum yield, especially in presence of competitive channels, such as those due to triplet quenchers.