Fig. , shows the time-dependent polariton eigenenergies when photon frequency is close to the molecular excitation (∼ resonant). As the upper polariton is energetically close to the dark states, nonadiabatic transitions lead to the transfer of population from the upper polariton to the dark states. In the same way, the lower polariton gets populated by dark states through nonadiabatic transitions. Thus, at low detunings (or at resonance), the PL intensity congregates at the lower polariton as a result of both significant population and photonic character. Thus, in summary, this work 32 concludes that the congregation of the PL intensity results from an interplay among phonon-mediated nonadiabatic transitions between polaritons, cavity loss, and the angle-dependent photonic character of the polariton branches. The resulting angular resolved PL spectra with various detuning (at zero angle) obtained experimentally and through direct quantum dynamics simulations are presented in Fig. -f and Fig. -i respectively.