The strong coupling between photoactive molecules and confined light, like surface plasmon polaritons (SPP) or cavity photons (CP), manifests itself by Rabi splitting at the matching energy of the molecular absorption and the light mode. The split is due to formation of hybrid polariton states between the light and the molecules. These states affect the energy landscape of the molecules and can thus alter also their chemical behavior. This has evolved to a new field of research called polariton chemistry. However, the relaxation pathways within strongly coupled systems are not fully known yet. This is a highly important question since it determines whether the polariton lifetime is sufficient for the chemical control.<br/><br/>We have studied the dynamics of polaritons by analyzing their emission in cases including SPPs or CP. While the emission of SPP is purely transverse magnetic (TM), the strong coupling with molecules induces transverse electric (TE) component to the emission of a SPP-molecule polariton. In the case of randomly oriented molecules the TE/TM ratio of the polariton emission clearly follows its molecular contribution but is influenced also by the Stokes shift of the molecule - the larger the shift the lower the TE emission. For optical cavities, the angle dependent emission of CP-molecule polaritons reveals different relaxation pathways depending on the Stokes shift. While molecules with high Stokes shift seem to undergo regular molecular relaxation and emit a polariton at the fluorescence wevelength, the system with no Stoke shift will relax to the lower polariton via coupling to vibrational states.<br/><br/>Our recent quantum mechanical molecular dynamic simulations show that in the case of high Stokes shift the polariton indeed very rapidly localizes to a single molecule excitation and decays to the fluorescing state. This supports well the experiments and above explanation, and can be also directly utilized in for example for coherent polaritonic light harvesting.

Effect of Stokes shift on strongly coupled hybrid states between organic molecules and confined light

2019 Fall National Meeting

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