Intrinsic and Extrinsic Circular Dichroism in Linear Arrays of Anisotropic Chiral Nanoparticles

Abstract

Controlling the collective optical properties of chiral plasmonic systems is essential for advancing photonic and chiral sensing technologies. Using template-assisted self-assembly, we engineered one-dimensional chiral plasmonic linear arrays composed of highly anisotropic chiral gold nanoparticle chains in an end-to-end configuration, achieving tunable plasmonic and chiroptical properties. While isolated chiral NPs exhibit intrinsic plasmonic circular dichroism (CD), their periodic arrangement introduces surface lattice resonances, yielding sharp extrinsic CD peaks. Orientation- and angle-dependent CD measurements enable a clear differentiation between intrinsic and extrinsic CD contributions. Notably, at specific angles of incidence, the assembled arrays exhibit a significant enhancement in the chiroptical response, demonstrating the dynamic tunability of their optical activity. The chiroptical properties of the arrays can be transferred to a luminescent dye, thereby yielding circularly polarized emission. These chiral superlattices supporting intrinsic and extrinsic chiroptical properties offer a robust platform for photonic devices, ultrasensitive chiral sensing, and enantioselective applications.

Chirality is central to photonics, as chiral media interact asymmetrically with circularly polarized (CP) light, giving rise to circular dichroism (CD) (i.e., the differential extinction of left and right circularly polarized (LCP and RCP) light by chiral molecules or nanostructures). In plasmonic nanostructures, engineered chirality and controlled assembly (spacing, orientation, and resonance coupling) boost collective modes, which strengthen light–matter interactions. − Chiral plasmonic structures can be created via top-down or bottom-up routes. Lithographic (top-down) methods yield either intrinsically chiral shapes (e.g., helices or spirals) or extrinsically chiral superstructures but suffer from complexity, low yield, and challenges in ultrafine 3D features. Seed-mediated (bottom-up) growth in the presence of enantiopure small molecules produces intrinsically chiral Au nanostructures (e.g., nanorods, nanocubes, and nanoplates) with sharp features and high optical activity, reaching anisotropy g-factors of ∼0.20, , even up to ∼0.44 with CP light-assisted growth. These colloidal building blocks offer broadband, morphology-dependent chiroptical responses and uniform near-field enhancement.

On the other hand, ordered nanoparticle (NP) arrangements produce narrower CD bands. Hexagonal arrays of chiral Au NPs were shown to produce collective, sharper CD signals and uniform hotspots, improving enantioselective sensing. Square arrays on Au films couple CD with surface plasmon resonances for sensitive biosensing. Template-assisted extrinsic superlattices (triskelion arrays) achieved a maximum g-factor magnitude (|g _max|) of 1.2 at a 14° incidence angle, with <15 nm full width at half-maximum (fwhm) in the NIR, enabling tunable polarization filters and optical rotators.

Compared with low-aspect-ratio (AR) plasmonic particles, elongated NPs show stronger polarization- and angle-dependent near-field enhancement and thus are highly sensitive to orientation. Template-assisted self-assembly can be used to program NP arrangement into hierarchical arrays with collective modes across the visible–NIR. However, controlling the orientation of anisotropic chiral NPs remains challenging, which limits interparticle coupling and the collective chiroptical response. Although wrinkle-assisted assembly produced ordered linear arrays of Au nanorods (NRs), , poly­(dimethylsiloxane) (PDMS) channels can crack from corrugation, resulting in reduced filling yield.

Here, we adapted a reported protocol to overgrow highly anisotropic chiral NPs from silver-free pentatwinned Au NRs and formed periodic end-to-end linear arrays via template-assisted self-assembly. Orientation-dependent and angle-resolved CD allowed us to separate intrinsic plasmonic CD from extrinsic surface lattice resonance (SLR)-induced CD. Extrinsic CD shows sharp features (fwhm <15 nm), tunable with the angle of incidence of CP light, whereas intrinsic CD remains comparatively unaltered. Improved end-to-end alignment was found to strengthen the extrinsic response, and this deterministic orientation enables precise and tunable modulation of the nanorods’ intrinsic chiroptical response through their coupling to SLRs. In addition, chirality transfer was confirmed by mirror-image circularly polarized luminescence (CPL) from lattices of opposite handedness.

Elongated pentatwinned Au nanorods (PT–Au NRs; AR > 10) were synthesized using a modified oleic acid-assisted seed-mediated method. Building on the micelle-induced chiral growth method, , achiral PT–Au NRs (Figure S1) were subsequently overgrown in the presence of binary micelles formed by 1,1′-binaphthyl-2,2′-diamine (BINAMINE) and cetyltrimethylammonium chloride (CTAC) to yield elongated chiral Au NRs (Figure a–c, see results for various growth conditions in Figure S2). We define long S-rod and long R-rod samples according to their growth using S- or R-BINAMINE/CTAC mixtures, respectively. The selected long S-rod and R-rod samples had average dimensions of 264 ± 33 nm × 54 ± 3 nm (AR = 4.9 ± 0.7) and 280 ± 36 nm × 55 ± 3 nm (AR = 5.1 ± 0.7), respectively. They both exhibited a sharp extinction peak at 540 nm with a weak shoulder near 780 nm and strong plasmonic CD across the visible–NIR region, with maximum g-factor values of ca. +0.10 and −0.10, respectively, at ∼780 nm.

1.

Structure and chiroptical response of long chiral PT–Au NRs. (a) Representative SEM images of long chiral PT–Au NRs synthesized using achiral PT NR seeds in the presence of S- and R-BINAMINE/CTAC mixtures (long S-rod and long R-rod, respectively). (b, c) Extinction (b) and g-factor (c) spectra of long chiral PT–Au NRs in aqueous colloidal dispersion. (d–i) Representative HAADF-STEM images (d, g), 3D tomography reconstructions (e, h), and helicity characterization (f, i) of a long S-rod (325 × 52 nm²) (d–f) and a long R-rod (273 × 54 nm²) (g–i).

High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and electron tomography (Figure d,e,g,h) revealed a wrinkled morphology, with wrinkles wrapping around the central Au NR with left- and right-handed inclinations in the S- and R-rod samples, respectively (further detail in Figure S3). These wrinkles leverage optically chiral localized surface plasmon resonance (LSPR) modes that selectively enhance the extinction of the LCP and RCP light. To further investigate the morphology and chiroptical properties of the chiral NRs, helicity analysis was conducted using electron tomography reconstructions as previously reported. , Positive helicity values correspond to overall right-handed helicity; negative values indicate overall left-handed helicity. Helicity analysis revealed a helicity of −0.045 for the long S-rod (left-handed helical structure) and +0.076 for the long R-rod with a right-handed helical structure (Figure f,i).

Finite-difference time-domain (FDTD) simulations were carried out directly on 3D electron-tomography reconstructions (instead of simplified models) to more accurately predict the plasmonic behavior. Simulated extinction spectra for the representative long R-rod (Figure S4a) and long S-rod (Figure S5a) show a sharp peak at ∼540 nm and a second peak at around 790/880 nm, accounting for the experimental shoulder near 780 nm. The second peak is regarded as a chiral mode originating from the wrinkled NR surface with increasing intensity for deeper wrinkles. Simulated g-factor spectra (Figures S4b and S5b) display opposite handedness for the long R-rod and S-rod, as expected from their chiral features. The simulated g-factor spectrum exhibits a shift at the lower-energy (longer-wavelength) band compared to the experimental one, which features a broader band due to subtle variations in the actual chiral NPs that affect the ensemble-averaged response. The spatial distribution of electric field enhancement (|E/E₀|²) and magnetic field enhancement (|H/H₀|²) maps at selected wavelengths reveals polarization-selective hotspots and mirror-symmetric patterns under opposite polarizations (Figures S4–S6 and Supporting Information additional discussion). Wrinkled PT–Au NRs produce enhanced directional near-fields compared to more isotropic chiral NPs. This single-rod chiral response provides the basis for collective effects in ordered arrangements.

For further comparison in the assembly and properties of aligned chiral NRs, single-crystalline (SC)–Au NRs (AR = 6.0) were synthesized by seeded-mediated growth (Figure S7a,b). Chiral overgrowth with S-BINAMINE/CTAC mixtures yielded “normal S-rods” with a positive helicity (right-handed) determined by electron tomography (Figure S7c–e). Despite using S-BINAMINE as the chiral inducer in both syntheses, the SC S-rod exhibited opposite helicity to the PT long S-rod, in agreement with our previous report. To provide a direct comparison and serve as a control, FDTD simulations of a representative S-rod are included (Figure S8), demonstrating how reduced AR leads to a weaker circular-polarization-dependent near-field enhancement relative to the long chiral rods.

To manipulate collective plasmonic and chiroptical properties, we assembled wrinkled Au NRs into one-dimensional (1D) arrays. Template-assisted self-assembly creates patterned plasmonic arrays with well-defined periodicity. PDMS stamps were prepared with linear grooves of carefully chosen dimensions to control the orientation and interparticle distance (Figure S9). As a result, linear arrays were obtained with different lattice parameters (Figure a) on conductive indium tin oxide (ITO)-coated glass slides, as required for SEM imaging. , Self-assembly of chiral NRs was achieved by slow solvent evaporation of thiol-terminated poly­(ethylene glycol) (PEG)-coated chiral NRs confined under a patterned PDMS mold. NR concentration (50–100 mM in Au⁰) and solvent composition (33 vol% H₂O, 67 vol% ethanol, ∼100 μM CTAC) were optimized for end-to-end alignment of NR chains. After carefully removing the PDMS mold, linear NR arrangements remained, forming chiral plasmonic superlattices with periodicity Λ defined by the mold’s geometry (Supporting Information Tables S1 and S2). For simplicity, Λ represents the master periodicity, whereas the actual 1D linear array periodicities were 3–5% smaller. An index-matching medium enhanced SLR visualization by creating a more homogeneous dielectric environment (Figure S10).

2.

Linear chiral plasmonic arrays and their orientation-dependent chiroptical responses. (a) Schematics of the fabrication of NP arrays using template-assisted self-assembly. (b–g) Representative SEM images, CD and LD spectra measured with different orientations (θ = 0°, β = 0°; θ = 90°, β = 0; θ = 0°, β = 180°; and θ = 90°, β = 180°, where θ represents azimuthal (in-plane) rotation and β denotes vertical-axis rotation (i.e., sample flipping) of 1D linear arrays made of long R-rods (b–d) and normal S-rods (e–g) with Λ = 400 nm. The inset in (c) presents a magnified view of the 575–615 nm wavelength region.

Two sets of chiral plasmonic NRs with different ARs (∼4.3 and ∼ 1.9) and comparable g-factors (0.025 and 0.030 for long S-rods and normal R-rods; −0.042 and −0.032 for normal S-rods and long R-rods) were prepared for self-assembly into linear arrays (Figure S11). Both sets have similar NP volumes and intrinsic g-factors, minimizing size- or chirality-induced bias. The use of chiral long NRs (AR ≈ 4.3) and chiral normal NRs (AR ≈ 1.9) enables a clear assessment of AR-dependent shifts in collective CD after assembly. Using a patterned PDMS mold (Λ = 400 nm, 194 nm lateral groove size), we obtained highly ordered end-to-end single chains with minimal side-by-side assembly. For comparison, we selected the long R-rod and normal S-rod 1D linear arrays with Λ = 400 nm (Figures b,e and S12).

Wrinkled NRs with random orientations in aqueous colloidal dispersions show intrinsic plasmonic CD (Figures c and S11g,h). In contrast, optical anisotropy from linear assembly (linear dichroism (LD) and linear birefringence (LB)) originating from the collective interactions and spatial arrangement of the ensemble can induce extrinsic CD. In our system, “intrinsic CD” originates from the chiral surface morphology of the nanorods, while “extrinsic CD” refers to the orientation- and angle-dependent lattice-induced chiroptical response that arises from the collective anisotropy of the nanorod assemblies. , Therefore, CD and LD (under transversal LCP and RCP excitation at normal incidence) were measured at four different orientations (see the schemes in Figure S13). We denote the azimuthal (in-plane) rotational angle as θ and the vertical-axis rotation (sample flipping) as β. Averaging over four scans eliminates linear dichroism–linear birefringence (LDLB) interactions and photoelastic modulator-induced artifacts. ,

For a 1D linear lattice, the Rayleigh–Wood anomaly is ${\lambda }_{\mathrm{RW}}^{(m)}=\frac{\mathrm{\Lambda }}{|m|}(n_{\mathrm{medium}}\pm \sin {\theta }_{\mathrm{AOI}})$ , where Λ is the lattice parameter, m is a factor related to the diffraction order, n _medium is the effective refractive index around the lattice, and θ_AOI is the illumination angle. Using an ITO substrate (effective n = 2.0, 1.9, and 1.8 for Λ = 400, 500, and 600 nm, respectively), the estimated λ_RW values are 800, 950, and 1080 nm; exact values depend on the local dielectric environment. Long R-rod arrays (Λ = 400 nm) exhibit a θ-dependent collective CD signal originating from SLR, with peaks at 600 nm (θ = 0°, black and red curves; fwhm ≈ 10 nm with Q-factor ≈ 63) and slightly split into 598 and 604 nm at θ = 90° (blue and green curves; fwhm ≈ 12 nm with Q-factor ≈ 52). Despite the small shift relative to the fwhm, the splitting reflects a strong orientation sensitivity from SLR-induced CD (Figure c). These Q-factors are fully consistent with plasmonic SLR systems operating in the visible–NIR regions, where intrinsic ohmic losses in Au suppress ultrahigh Q-factors as compared to dielectric metasurfaces based on bound states in the continuum (BICs) or (leaky) guided-mode resonances. −

Sharp LD changes at these wavelengths further confirm the SLR spectral position (Figure d). LD values at β = 0 and 180° (same θ) are nearly identical, displaying bands of the same sign, whereas a 90° in-plane rotation (different θ) results in bands with opposite signs. The intrinsic CD at 745 nm is largely θ- or β-invariant. Normal S-rod arrays (Λ = 400 nm) exhibit pronounced extrinsic CD with a sharp peak at ∼604 nm at θ = 90° (fwhm ≈ 14 nm with Q-factor ≈ 43) and concomitant LD changes (Figure f,g). The intrinsic CD for the normal S-rod arrays appears at >950 nm (discussed below).

We further investigated how the PDMS mold geometry (channel width and lattice parameter Λ) affects the chiroptical response of linear arrays. As summarized in Table S1, a larger Λ yields wider channels, altering the degree of linear arrangement. For long S-rod arrays, increasing Λ produces double- and triple-chain structures due to the broader channel width, while generally preserving tip-to-tip configuration (Figure a–c). CD spectra show extrinsic CD peaks at approximately 600 and 750 nm (Λ = 400 and 500 nm, respectively) which become significantly weaker or vanish for Λ = 600 nm (Figure d–f). The sharpness of the SLR-induced CD also decreases with increasing Λ, reflecting a reduced structural order. A similar trend holds for the long R-rod arrays, where extrinsic CD diminishes with increasing Λ, whereas intrinsic CD retains opposite handedness (Figures S14 and S15). This attenuation of extrinsic CD likely arises from variations in the linear arrangement between samples and from the specific angle of incidence (AOI) used during measurements, which may not efficiently excite the SLR. Compared with colloidal long rods, the intrinsic CD peaks of the arrays blue shift to 730–760 nm while retaining comparable four-scan-averaged |g _max| = 0.02–0.03 under transverse excitation and normal incidence (Figure g). This blue shift does not originate from longitudinal dipole coupling. Instead, the intrinsic CD is governed by the chiral surface plasmon mode produced by helicoidal wrinkles on the nanorod surface, which is spectrally decoupled from longitudinal LSPR.

3.

Influence of channel width and lattice parameter of the PDMS mold. (a–f) Representative SEM images and corresponding CD spectra of 1D linear arrays of long S–Au NRs (length: 270 ± 30 nm, width: 64 ± 5 nm; AR:4.2 ± 0.6) fabricated with Λ = 400 nm (a,d), 500 nm (b,e), and 600 nm (c,f). (g,h) Averaged g-factor spectra (from four scans) for 1D linear arrays of long chiral PT–Au NR and normal chiral SC–Au NR samples with different lattice parameters (Λ = 400, 500, and 600 nm). The corresponding extinction spectra are shown in Figure S19. Note: (1) even after four-scan averaging, minor extrinsic CD contributions persist, likely from macroscopic anisotropy such as “pairwise” interference, which slightly complicates isolation of intrinsic CD; (2) artificial peaks and dips around 900 nm in the four-scan averaged g-factor spectra arise from concatenation of two CD spectra (850–950 nm) and detector-edge noise.

Normal S-rod arrays (Λ = 500 nm) show a strong reduction of the 742 nm extrinsic CD at θ = 90° (Figure S16), with a broad band emerging at 625 nm, assigned to a collective plasmon-coupled asymmetry driven by more vertical rods and increased side-by-side, side-to-end, and stacked NP arrangements. , At Λ = 600 nm, the expected extrinsic CD > 900 nm is absent, whereas strong bands appear in the 590–640 nm range across all four configurations (Figure S17). Notably, a sharp band at ∼590 nm arises at θ = 90° and β = 180°, indicating asymmetric arrangements. Normal R-rod arrays exhibit similar behavior: extrinsic CD weakens with increasing Λ, whereas intrinsic CD retains an opposite handedness (Figure S18). Intrinsic CD is blue-shifted relative to colloidal samples with a smaller shift for larger Λ (Figure h). Reduced intrinsic g-factors at Λ = 500 and 600 nm likely reflect stronger transverse plasmon mode coupling from increased side-by-side arrangements, which reduces the longitudinal chiroptical response. Despite variations in the degree of linear arrangement and multichain formation, comparisons remain valid: intrinsic peaks from single-rod chirality keep their handedness and similar magnitude, enabling the isolation of AR-dependent effects.

These superlattices combine intrinsic (wrinkled morphology) and extrinsic (SLR) effects, producing strong, orientation-dependent CD. Controlled linear assembly thus enables the manipulation and amplification of plasmonic and chiroptical responses. Moreover, arrays of long chiral NRs show stronger, sharper SLR-CD with higher g-factors, owing to superior end-to-end alignment and uniform lattices that suppress side-by-side assembly. To isolate the contribution of intrinsic chirality, 1D arrays of achiral rods (Figure S20) showed minimal, nearly symmetric g-factor spectra under two different orientations. Only a sharp ∼610 nm extrinsic CD band remained, which is reduced by four-scan averaging. Thus, achiral arrays contribute solely to extrinsic CD, confirming that intrinsic CD originates from the chiral morphology of the wrinkled NRs.

To understand the Λ-dependent decrease in SLR-induced CD and further clarify the photonic nature of intrinsic and extrinsic CD in chiral plasmonic systems, we performed angular dispersion measurements on our linear arrays using a custom-built setup (Figure S21). Angle-resolved g-factor maps were calculated from the LCP and RCP transmittance, with the g-factor defined as

$$g‐\mathrm{f}\mathrm{actor}=\frac{A_{\mathrm{LCP}}-A_{\mathrm{RCP}}}{\frac{1}{2}(A_{\mathrm{LCP}}+A_{\mathrm{RCP}})}=\frac{-\log T_{\mathrm{LCP}}+\log T_{\mathrm{RCP}}}{\frac{1}{2}(-\log T_{\mathrm{LCP}}-\log T_{\mathrm{RCP}})}$$ 1

where A _LCP and A _RCP represent the absorbance of the sample and T _LCP and T _RCP represent transmittance, under both LCP and RCP light. Figure a and Figure S22 show distinct Rayleigh–Wood anomaly modes (m = ±1 for both the air superstrate and the substrate) for long R-rod arrays (Λ = 400 nm). The g-factor map demonstrates spectral splitting and broadband tunability (400–800 nm), with a nearly linear dependence on the AOI. The intrinsic CD regions above the m = ±1 line remain nondispersive with the AOI, whereas the SLR-induced extrinsic CD regions closely follow the diffraction edges. Normal S-rod arrays (Λ = 400 nm) exhibit the same trend but weaker intrinsic CD and less pronounced dispersion (Figure b). Thus, dispersive bands correspond to extrinsic CD, while nondispersive bands are intrinsic.

4.

Experimental angle-resolved g-factor of linear chiral plasmonic arrays. (a–d) Angle-resolved g-factor maps (AOI ranging from – 30 to 30°) and extracted g-factor spectra (AOI ranging from 0 to 30°) for 1D linear arrays of long R-rods (a, c) and normal S-rods (b, d) with Λ = 400 nm. The dashed lines in panel (a) show the theoretical Rayleigh–Wood anomaly lines ${\lambda }_{\mathrm{RW}}^{(m)}=\frac{\mathrm{\Lambda }}{|m|}(n_{\mathrm{medium}}\pm \sin {\theta }_{\mathrm{AOI}})$ , where we consider the air superstrate (n _air = 1) and the substrate (n _sub = 1.5).

Long R- and S-rod arrays (Λ = 400, 500 nm) show clear AOI-dependent SLR dispersion in the g-factor maps (Figure S23). At Λ = 600 nm, maps are noisier with no spectral splitting, indicating that the missing ∼900 nm extrinsic CD arises from reduced order, not AOI effects. Normal R-rod arrays (Λ = 400, 500, and 600 nm) show the same trend with the SLR dispersion at Λ = 400 and 500 nm but none at 600 nm (Figure S24). Intrinsic CD is predominantly positive, reflecting opposite handedness relative to the long R-rod and normal S-rod sets. Overall, extrinsic modes are dispersed along the Rayleigh–Wood lines, whereas intrinsic bands remain nondispersive, confirming photonic and morphology-driven origins, respectively. The absence of extrinsic peaks at Λ = 600 nm is attributed to diminished lattice order rather than angular excitation.

The extracted g-factors for long R-rod and normal S-rod arrays in the visible (500–700 nm) exceed 0.04 and 0.03, respectively, across AOI 0–30° (Figure c,d). Long R-rods reach maximum g-factor values of +0.085 at 752 nm (AOI = 26°) and −0.115 at 599 nm (AOI = 2°), whereas normal S-rods reach +0.048 at 598 nm (AOI = 2°) and −0.097 at 600 nm (AOI = 0°). Notably, spectral splitting within AOI = 0–10° follows a “+ – +” pattern for the long R-rod arrays but a “– + −” pattern for the normal S-rod arrays (Figure S25). These patterns are inverted when comparing AOI ranges of 0° to 10° and 0° to −10°.

Linear arrays of chiral NRs are potential platforms for CPL, upon the deposition of a luminescent dye. Recent studies have shown that chiral plasmonic and photonic architectures can induce CPL from initially achiral emitters by selectively enhancing and outcoupling one optical handedness through chiral near-field interactions and polarization-dependent radiative channels. Examples include directional chiral emission mediated by extrinsic chiral quasi-bound states in the continuum, CPL from nanostructured emitter arrays, spin-dependent emission from planar chiral nanoantennas, and chirality transfer from plasmonic superlattices to adjacent emitters. Ordered 1D arrays provide a well-defined chiral environment, ensuring reproducible CPL over large areas. As discussed above, linear arrangements show collective interactions that are hard to achieve in random films. We spin-coated a thin film of resist (SU8) doped with an achiral organic dye, Rhodamine B (∼250 nm) onto pre-formed chiral arrays and racemic (1:1 mixture of long S- and R-rods) controls. We anticipate mirror-image CPL from S- and R-arrays via chirality transfer and no CPL from racemic samples. This effect can be quantified by the luminescence asymmetry factor (g _lum), defined as

$$g_{\mathrm{lum}}=2\frac{(I_{\mathrm{LCP}}-I_{\mathrm{RCP}})}{(I_{\mathrm{LCP}}+I_{\mathrm{RCP}})}$$ 2

where I _LCP and I _RCP are the LCP and RCP emission intensities. This parameter accounts for the degree of chirality in the excited state, spin polarization of the emitted light, chiral emission efficiency, and interaction between the electric and magnetic transition moments of the molecules.

We determined g _lum values at each sample’s emission maximum (CPL measurement details in Supporting Information), showing a slight Δλ shift between samples functionalized with opposite enantiomers, +9.29 × 10^–3 (λ = 590 nm) for the S-rod array and −1.09 × 10^–2 for the long R-rod array (λ = 604 nm) (Figure ). The shift in emission maxima likely stems from minor differences in dimensional and morphological variations between the chemically synthesized R- and S-rods, surface functionalization, or local overlap/stacking on the substrate, also manifested in the emission intensity of the samples. The presence of a nonhomogeneous or anisotropic environment can alter luminescence processes via surface-related effects that can influence both the radiative and nonradiative pathways, resulting in observable differences in emission characteristics. Also, the variation in λ_max (wavelength with maximum g _lum) may arise from differences in the extinction and CD spectral profiles of both arrays (Figure S26), which affect the degree of plasmon–exciton coupling between dye emission and the plasmonic mode. Additionally, the g _lum value reflects how the dye emission couples to the near-field polarization environment rather than far-field CD only, leading to asymmetric plasmon–exciton interactions that modify both the polarization and the shape of the emission spectrum.

5.

Chiral plasmonic platforms for circularly polarized light emission. Raw CPL (a) and corresponding g _lum (b) spectra are shown for long S-rod arrays, long R-rod arrays, and racemic arrays (1:1 mixture of long S- and R-rods) with Λ = 400 nm, all covered by a RhB-doped SU-8 resin.

In summary, highly anisotropic chiral Au NRs (g-factor of ± 0.1) were assembled into 1D tip-to-tip superlattices via template-assisted patterning. Intrinsic CD from single NRs can be decoupled from extrinsic SLR in such ordered arrays. Angle-resolved CD reveals sharp, tunable extrinsic peaks that shift linearly with AOI. Improved end-to-end alignment strengthens the extrinsic signal, whereas the intrinsic CD remains largely unchanged. The arrays act as active chiral photonic platforms, exhibiting near-mirror-image CPL from achiral dyes, evidencing chirality transfer. These results provide a reproducible route to controllable chiroptical activity for CPL emitters, ultrasensitive chiral sensing, and enantioselective photonics, opening alternative photonic modes with dispersion characteristics beyond leaky guided modes and quasi-BICs for enhancing chiroptical responses.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.nanolett.5c05530.

• Materials and methods and supplementary data (PDF)

• Electron tomography reconstructions and related orthoslices for a representative long R-rod (MPG)

• Electron tomography reconstructions and related orthoslices for a representative long R-rod (MPG)

• Electron tomography reconstructions and related orthoslices for a representative long R-rod (MPG)

• Electron tomography reconstructions and related orthoslices for a representative long S-rod (MPG)

• Electron tomography reconstructions and related orthoslices for a representative long S-rod (MPG)

• Electron tomography reconstructions and related orthoslices for a representative long S-rod (MPG)

• Electron tomography reconstructions and related orthoslices for a representative normal S-rod (MPG)

• Electron tomography reconstructions and related orthoslices for a representative normal S-rod (MPG)

T.H.C., A.M., and L.M.L.-M. conceived and designed the study. T.H.C. carried out the nanoparticle synthesis and self-assembly, performed the structural and optical characterization, and wrote the manuscript. Y.L. prepared the PDMS stamp and helped with self-assembly. S.J. helped with optical measurement and performed the FDTD simulations. I.R. acquired the CPL data. M.M. and S.B. conducted the electron tomography and subsequent analysis. T.H.C., A.M., and L.M.L.-M. supervised the research. The manuscript was written through the contributions of all authors. All authors have given approval to the final version of the manuscript.

T.H.C. and L.M.L.-M. acknowledge funding from the European Commission under grant HORIZON-TMA-MSCA-PFEF, SEP-210883629 (ChirPlasBiosensing). S.B. and L.M.L.-M. acknowledge funding from the European Research Council (ERC Synergy grant no. 101166855 CHIRAL-PRO). A.M. acknowledges funding from the Spanish Agencia Estatal de Investigación (MCIN/AEI/10.13039/501100011033) through grants PID2022-141956NB-I00 (OUTLIGHT) and CEX2023-001263-S (Spanish Severo Ochoa Centre of Excellence program). I.R. acknowledges funding from Grant PID2023-151549NB-I00 funded by MICIU/AEI/10.13039/501100011033, by FSE; grant IT1553-22 funded by the Basque Government and CEX2023-001296-S (Spanish Severo Ochoa Centre of Excellence program).

The authors declare no competing financial interest.