Coincidentally, no evidence was found for the participation of M1 in the exciton polaron dynamics. On the contrary, the strongly anharmonic M2 mode was identified to be the primary phonon participating in the non-adiabatic mixing of X A and X B , eventually driving the population exchange between these two states, see Ref. 20. The anharmonic phonons can also be clearly identified to be playing a role in the thermal dephasing of excitons, as reported in Ref. 19. The increase in the homogeneous linewidths of excitonic resonances with temperature can be analysed to estimate the energy of the phonons which scatter the exciton. Such an analysis revealed that average energy of the phonon that broadens X A is about 6 meV, clearly indicating the role of the higher energy anharomonic modes, dominated by M2, in the excitonphonon elastic scatting. The temperature dependence of the X B linewidth, on the other hand, yielded a phonon energy of over 20 meV. However, the vibrational modes at such energies correspond to the motion within the organic layer and thus should not contribute to the scattering of excitons that are confined within the inorganic layer. We consider that this discrepancy is due to inadequacy of the LO phonon scattering model of exciton polarons, which does not explicitly consider the contributions from phononphonon interactions to the exciton dephasing .