Fig. 1. (a) Schematic view of a Drude sphere with a dye shell under study. The vectors e_X, e_Y, and e_Z show the basis for the permittivity tensor of the shell material: e_Z is directed normally to the surface, while e_X and e_Y lie in the tangential plane. (b)–(j) Light extinction cross section of a Drude sphere with a dye shell with varying reduced oscillator strength, f_J, and different molecular arrangements in the organic shell. (b)–(d) Results are obtained for f_J = 0.15 and (b) isotropic (equiprobable) J-aggregate orientation, (c) tangential J-aggregate orientation, and (d) normal J-aggregate orientation in the dye shell. In (e)–(g) and (h)–(j), the same results are calculated for f_J = 0.08 and f_J = 0.03, respectively.

Fig. 2. (a) Light extinction cross section of a bare Drude sphere and a Drude sphere with a dye shell of isotropic J-aggregate orientation with f_J = 0.15 [see Fig. 1(b)]. (b)–(i) Electromagnetic energy density distributions in the plane lying along the light polarization and passing through the particle center. Results are presented for light wavelengths, λ, corresponding to different resonances in the light extinction spectra (see Fig. 1). (b) Bare Drude sphere, λ = 485 nm. (c)–(e) Drude sphere with a dye shell with isotropic J-aggregate orientation: (c) λ = 458 nm, (d) λ = 490 nm, and (e) λ = 517 nm. (f)–(g) Normal J-aggregate orientation: (f) λ = 433 nm and (g) λ = 512 nm. (h)–(i) Tangential J-aggregate orientation: (h) λ = 470 nm and (i) λ = 510 nm. The reduced oscillator strength of a dye shell, f_J = 0.15 for all cases. Light polarization is parallel to the horizontal axis. The color maps represent the electromagnetic energy density in the logarithmic scale.

Fig. 3. (a)–(c) Light extinction spectra of bare nanorods of different sizes: (a) 11 nm, (b) 18 nm, and (c) 34 nm. For the sake of brevity, the results for 37 nm are not shown because they are similar to those for 34 nm. In these figures, the solid orange lines represent the experimental results^[30], and the solid black lines represent our calculations. (d) Schematic view of a TDBC-coated gold nanorod. (e)–(h) and (i)–(l) Light extinction spectra of TDBC-coated gold nanorods of different diameters: (e) and (i) 11 nm, (f) and (j) 18 nm, (g) and (k) 34 nm, and (h) and (l) 37 nm. (e)–(h) show a comparison of experimental results^[30] (solid orange lines) and numerical simulations performed with the heuristic quantum model^[30] (dashed–dotted blue lines) with our results obtained with the classical anisotropic model for tangential J-aggregate orientation in the TDBC shell (solid black lines). (i)–(l) show the effect of J-aggregate orientation: the solid orange lines represent the experimental results^[30], the solid black lines represent tangential orientation, the thin red lines with dashes represent isotropic (equiprobable) orientation, and the dotted green lines represent normal orientation.

Fig. 4. (a)–(c) Light extinction cross sections of a TDBC-coated gold nanorod of size 34 nm for (a) isotropic, (b) normal, and (c) tangential J-aggregate orientations in a shell. The black curves (A) are orientation-averaged cross sections, ⟨σ^(ext)⟩. The red curves (B) and blue curves (C) are cross section contributions from cases of light polarization parallel and perpendicular to the nanorod axis, respectively (i.e., σ_Y^(ext)/3 and 2σ_Z^(ext)/3). (d)–(o) Electromagnetic energy density distributions in the Y–Z plane passing through the nanorod center [see Fig. 3(d)]. Results are presented for light wavelengths, λ, corresponding to different resonances in the light extinction spectra. (d)–(i) Isotropic J-aggregate orientation: (d) λ = 551 nm, (e) λ = 580 nm, (f) λ = 635 nm, (g) λ = 520 nm, (h) λ = 570 nm, and (i) λ = 590 nm. (j)–(l) Normal J-aggregate orientation: (j) λ = 635 nm, (k) λ = 546 nm, and (l) λ = 566 nm. (m)–(o) Tangential J-aggregate orientation: (m) λ = 577 nm, (n) λ = 625 nm, and (o) λ = 520 nm. The direction of the light polarization is shown in the upper right corner of each figure. The nanorod size is 34 nm in all cases. The color maps represent the electromagnetic energy density in the logarithmic scale.