Plasmon-exciton coupling in Au nanosphere/carbocyanine J-aggregate hybrids assessed by magnetic circular dichroism (MCD) spectroscopy

In this study, we evaluate plasmon-exciton coupling in Au nanosphere/carbocyanine J-aggregate hybrids by magnetic circular dichroism (MCD) spectroscopy. The carbocyanine dye we used is JC-1, which adsorbs onto Au nanospheres to form J-aggregates. The hybrids exhibit a double-peaked extinction spectrum, and a shallow dip appears at the resonance position of the native J-aggregates, indicating the presence of plasmon-exciton in-teractions. MCD spectra of the hybrids show a derivative-like profile originated from the surface plasmon resonance of Au nanospheres accompanied by an additional distinct dip (or bump) caused by the exciton resonance of the adsorbed J-aggregates. Importantly, the MCD dip (or bump) position does not correspond to that of the observed new extinction peak, but agrees well with the extinction dip. Moreover, we find that the linewidths of the MCD dip (or bump) are narrow and comparable to that of the J-band of the dye aggregates. All the results suggest that the present hybrid systems are categorized in a weak-coupling regime. Hence we believe that MCD will be a useful spectroscopic method to effectively assess the plasmon-exciton interactions in various kinds of plasmonic-excitonic nanohybrid systems.