Plexcitons: The Role of Oscillator Strengths and Spectral Widths in Determining Strong Coupling

Journal Article · Fri Jan 05 00:00:00 EST 2018 · ACS Nano

DOI:https://doi.org/10.1021/acsnano.7b06589· OSTI ID:1426223

Thomas, Reshmi ^[1]; Thomas, Anoop ^[1]; Pullanchery, Saranya  ^[1]; Joseph, Linta ^[1]; Somasundaran, Sanoop Mambully ^[1]; Swathi, Rotti Srinivasamurthy  ^[1]; Gray, Stephen K. ^[2]; Thomas, K. George  ^[1]

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1. School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram (IISER-TVM), Vithura, Thiruvananthapuram 695551, India
2. Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, United States

Strong coupling interactions between plasmon and exciton-based excitations have been proposed to be useful in the design of optoelectronic systems. However, the role of various optical parameters dictating the plasmon-exciton (plexciton) interactions is less understood. Herein, we propose an inequality for achieving strong coupling between plasmons and excitons through appropriate variation of their oscillator strengths and spectral widths. These aspects are found to be consistent with experiments on two sets of free-standing plexcitonic systems obtained by (i) linking fluorescein isothiocyanate on Ag nanoparticles of varying sizes through silane coupling and (ii) electrostatic binding of cyanine dyes on polystyrenesulfonate-coated Au nanorods of varying aspect ratios. Being covalently linked on Ag nanoparticles, fluorescein isothiocyanate remains in monomeric state, and its high oscillator strength and narrow spectral width enable us to approach the strong coupling limit. In contrast, in the presence of polystyrenesulfonate, monomeric forms of cyanine dyes exist in equilibrium with their aggregates: Coupling is not observed for monomers and H-aggregates whose optical parameters are unfavorable. The large aggregation number, narrow spectral width, and extremely high oscillator strength of J-aggregates of cyanines permit effective delocalization of excitons along the linear assembly of chromophores, which in turn leads to efficient coupling with the plasmons. Further, the results obtained from experiments and theoretical models are jointly employed to describe the plexcitonic states, estimate the coupling strengths, and rationalize the dispersion curves. The experimental results and the theoretical analysis presented here portray a way forward to the rational design of plexcitonic systems attaining the strong coupling limits.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States)
• Sponsoring Organization: Council of Scientific and Industrial Research (CSIR); USDOE Office of Science (SC)
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1426223
• Journal Information: ACS Nano, Vol. 12, Issue 1; ISSN 1936-0851
• Publisher: American Chemical Society (ACS)
• Country of Publication: United States
• Language: English