Designing Plasmon-Molecule Interactions

In this work we show theoretically and experimentally that a molecular system at very low concentration can be strongly coupled to plasmonic modes. Upon coupling new hybrid states are formed, lower and higher polaritons. These modes have the characteristics of both molecular and plasmonic states and also new characteristic different from those of the molecular and plasmonic states. As the coupling strength grows increasing of molecular concentration asymmetric splitting is observed giving rise to enhanced transmission through metallic hole arrays. Moreover, we have also succeeded in reaching a linear dependency of the Rabi splitting value on the square root of the absorbance which is another proof for strong coupling.

We also show that by tuning the plasmonic modes we are able to be on/off resonance with respect to the molecular system and therefore generate new photonic-exciton hybrid states at different energies and as a consequence with unique properties. Moreover, we show that by changing the distance between the plasmons and the molecules we can design the strong interactions between the two systems.

(a) Schematic illustration of the system used. The system is composed from fabricated Ag film placed between glass and PVA or porphyrin derivative embedded in PVA. (b) Absorbance spectrum of porphyrin derivative embedded in PVA spin coated onto glass. The absorbance is ca. 0.016. The inset is a SEM image of the fabricated Ag film.