Effect of Stokes shift on molecular polariton dynamics

Strong coupling between molecules and confined light, like surface plasmon polaritons (SPP) or cavity photons (CP), leads to a formation of polariton states manifested by a Rabi split in the absorption spectrum. This changes the energy landscape of the molecules and can alter their chemical behavior. However, the Stokes shift of the molecule can play an essential role here.

We have studied molecular polaritons involving SPPs or optical cavities and different molecules. While the emission of SPP is purely transverse magnetic (TM), that of a SPP-molecule polariton has also a transverse electric (TE) component with the TE/TM ratio following the molecular contribution. Interestingly, we observe that the larger the Stokes shift of the molecule is, the lower is the TE emission. For cavities, the angle dependent emission of the lower CP-molecule polariton while exciting the upper polariton, reveals different pathways depending again on the Stokes shift. While molecules with high Stokes shift seem to induce regular molecule relaxation and excitation of the lower polariton via the fluorescing state, the molecules with no Stoke shift relax to the lower polariton via coupling to vibrational states. In both cases the effect of the molecular relaxation is eminent.