Probing the role of oscillator strength and charge of exciton forming molecular J-aggregates in controlling nanoscale plasmon–exciton interactions

In this study, we probe into the roles of exciton oscillator strength and charge of J-aggregates as well as nanoparticle's surface capping ligands in dictating the plasmon–exciton interaction. We systematically compare the plasmon–exciton coupling strengths of two hybrid plexcitonic systems involving CTAB-capped hollow gold nanoprisms (HGNs) and two different cyanine dyes, TDBC and PIC, having very similar J-band spectral positions and linewidths, but different oscillator strengths and opposite charges. Both HGN–PIC and HGN–TDBC systems display large Rabi splitting energies which are found to be extremely dependent on dye-concentrations. Interestingly, for our plexciton systems we find that there is interplay between the exciton oscillator strength and the electrostatic interaction amid dyes and HGN-surfaces in dictating the coupling strength. The oscillator strength dominates at low dye-concentrations resulting in larger Rabi splitting in the HGN–PIC system while at high concentrations, a favorable electrostatic interaction between TDBC and CTAB-capped HGN results in larger exciton population of the HGN-surface and in turn larger Rabi splitting for the HGN–TDBC system than the HGN–PIC system even though TDBC has a lower oscillator strength than PIC. The trend in Rabi splitting is just reversed when the HGN surface is modified with a negatively charged polymer, confirming the role of electrostatic interactions in influencing the plasmon–exciton coupling strength.