Figure 1.

Experimental extinction spectra of the aqueous solution of (a) JC1 dye (inset: chemical structure of JC1 dye, sketch of J-aggregates and J-band exciton) and (b) bare core–shell Au@Ag nanorods of varying aspect ratios (solid lines), overlaid with theoretical predictions (dashed lines). The multiple peaks below 500 nm, caused by the excitation of transverse dipolar and higher-order plasmon modes of Au@Ag nanorods, are not fully captured by our quasistatic model, which treats them as simple spheroids.^31,32 (Inset) Sketch of the transverse and longitudinal plasmon modes of core–shell Au@Ag nanorods. (c) TEM images of core–shell Au@Ag nanorods with aspect ratios varying from 2.5 to 4.5 from which the extinction spectra in panel b were obtained; scale bars are 50 nm.