Coupled Molecular Emitters in Superstructures Interact with Plasmonic Nanoparticles

Using hyperspectral measurements, J-aggregate nanorods of porphyrin molecules embedded in plasmonic Au nanoparticles arrays are studied. Measurements of J-aggregate nanorods that cross onto a plasmonic array exhibit a shift in their absorption peak, and display weak coupling properties only for the embedded part. Furthermore, a significant thickness-dependent redshift in the plasmonic resonance for the J-aggregate clusters is observed. Such redshift is also dependent on the ratio of J-aggregate in the plasmonic dipole interaction area, reaching values of up to 120 meV for approximate to 40% coverage. In addition, for large clusters of J-aggregates, the plasmonic spectrum shows coupling behavior between the systems indicated by a small Rabi splitting. The findings are validated by a quasi-static model based on the change of the dielectric environment around the embedded nanoparticles. Using the model, the fraction of embedding J-aggregates in the plasmonic interaction area is correlated with the change in plasmonic resonance peak. These results offer insight into the coupled nature of molecular emitters in supramolecular structures and their interaction with plasmonic nanoparticles and can lead to new types of sensitive optical detectors based on these interactions.