Programmable chiroptical multilayer films assembled from self-healing stretchable elastomers for information encryption

Abstract

Flexible chiroptical materials with strong and tunable optical activity are highly desirable for applications in optical encryption, quantum communication, and wearable photonic devices. Recently, various strategies have been developed for constructing flexible chiral plasmonic films. Among these, combining uniaxial alignment with twisted multilayer stacking offers an effective and scalable route to generate strong chiroptical signals using achiral building blocks. However, a key challenge remains in achieving highly ordered plasmonic nanostructures within deformable polymer matrices, which is essential for constructing tunable and robust chiral optical systems. Herein, we report a self-healing, ultra-stretchable hybrid elastomer composed of silver nanowires (AgNWs), waterborne polyurethane (WPU), and tempo-oxidized cellulose nanofibers (TOCNF), which enables the efficient formation of aligned anisotropic structures via uniaxial wet-stretching. The resulting AgNWs@WPU/TOCNF films exhibit ultrahigh stretchability (>1000%) and retain their orientation after drying. Importantly, the intrinsic self-healing capability enables seamless twist-stacking of pre-aligned films through water-assisted interfacial fusion, resulting in robust multilayer architectures with strong circular dichroism signals, characterized by a maximum ellipticity of 13.3° and an absorption dissymmetry factor exceeding 0.6. Further integration with a fluorescent layer yields circularly polarized emission films with a luminescence dissymmetry factor up to 0.5. Leveraging the programmable optical responses, a multilayer encryption device was fabricated for information encoding and decoding based on polarization states. This work provides a scalable and modular platform for developing self-healing chiroptical devices with tunable optical functionalities and high potential for photonic encryption and smart wearable technologies.

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1. Introduction

Chiroptical materials with strong and tunable optical activity are emerging as powerful platforms in diverse applications such as broadband optical communication, quantum computing, sensing and wearable devices.^1–4 Compared to traditional solution systems and rigid counterparts, soft plasmonics that integrate anisotropic plasmons with deformable polymer matrices are particularly attractive,^5–8 owing to their ability to couple mechanical actuation with optical signal modulation, enabling external-force-induced tuning of circular dichroism (CD) or circularly polarized light (CPL).^5,7,9,10 To realize such mechanically tunable optical responses, the polymer matrix must possess high stretchability and mechanical robustness, which not only facilitates the formation of nanoscale anisotropy in embedded plasmonic components – a key to achieving strong optical activity – but also ensures reliable mechanical responsiveness and structural stability under large deformation.^11–16

Among various strategies developed for constructing chiral plasmonic materials, self-assembly of plasmonic nanostructures represents an elegant bottom-up approach to generate strong optical activity through precise control over nanoparticle arrangement.^17,18 However, these systems often suffer from limited scalability, poor structural stability, and challenges in dynamic modulation. Alternatively, surface patterning or template-assisted methods offer higher structural regularity and stronger chiroptical signals,^19,20 yet they typically involve complex fabrication processes or rigid substrates, which hinder their practical application. In contrast, incorporating plasmonic nanoparticles into stretchable polymer matrices has emerged as a particularly promising strategy.^7,21–23 This approach not only simplifies the fabrication process but also provides inherent adaptability to external deformation, making it highly suitable for developing mechanically tunable chiroptical systems. To this end, we recently reported a wet-stretching strategy using polyvinyl alcohol (PVA) as a stretchable substrate to co-align surface-coated gold nanorods (AuNRs), achieving exceptional optical activity (ellipticity ∼10⁴ mdeg) and ultrabroadband CD responses spanning 200–2500 nm after subsequently twist-stacking.⁷ Benefiting from the plastic deformation behavior of PVA, the strain-induced anisotropy could be well preserved after stretching.

Nevertheless, achieving both extreme stretchability and stable anisotropic structures remains a fundamental challenge for the construction of soft chiroptical systems. Polymers like PVA enable fixation of nanoparticle alignment but suffer from limited stretchability (<500%). In contrast, highly stretchable elastomers such as polyurethanes or silicone rubbers allow large deformation but inevitably recover upon release,^24,25 disrupting the strain-induced anisotropy. This intrinsic trade-off severely limits the development of soft chiroptical materials capable of large, programmable, and stable optical modulation.

To address this critical trade-off, we herein present a new class of highly stretchable and structurally stable chiroptical materials, constructed from a waterborne polyurethane (WPU) elastomer reinforced with tempo-oxidized cellulose nanofibers (TOCNF). The incorporation of TOCNF effectively suppresses the elastic recovery of the WPU matrix upon deformation, thereby preserving the strain-induced anisotropic alignment of embedded nanostructures even under ultrahigh elongation (>1000%) (Fig. 1a). Silver nanowires (AgNWs) were introduced as the plasmonic component, affording pronounced optical activity with an ellipticity exceeding 13° and an absorption dissymmetry factor (g_abs) greater than 0.6 in the visible region (Fig. 1b). In addition, integration with fluorescent layers enabled the generation of circularly polarized light (CPL), with a luminescent dissymmetry factor (g_lum) reaching 0.5 (Fig. 1c), thus enriching the functional output of the system. Notably, the excellent flexibility of the WPU substrate allows for efficient modulation of the ellipticity, wavelength, and handedness of CD/CPL signals via external mechanical stimuli (Fig. 1d). More importantly, the intrinsic self-healing capability of the WPU matrix enables the fusion of multilayered films into a continuous monolithic structure, eliminating interfacial defects and significantly improving device stability and reproducibility (Fig. 1a).

Fig. 1 (a) Schematic illustration of the fabrication process for chiroptical multilayer films. Uniaxial wet-stretching of AgNWs@WPU/TOCNF hybrid elastomer films induces highly aligned anisotropic structures (>1000% elongation). Two pre-oriented films are then twist-stacked and fused via water-assisted self-healing to form CD active multilayers. Further integration with a fluorescent layer yields CPL emission films upon UV excitation. (b) Representative CD spectra of the self-healed AgNWs@WPU/TOCNF films (twist angle θ = ±45°), showing a maximum ellipticity of 13.3° and g_abs value up to 0.6. (c) Corresponding CPL spectra of the self-healed CPL hybrid films (CPL-HF) with θ = ±45°, exhibiting a g_lum value of 0.5. Inset: Optical images of CPL-HF film under UV light (300 nm). (d) Schematic representation of the tunability of chiroptical properties – such as handedness, ellipticity, and wavelength – achieved by structural programming of the AgNWs@WPU/TOCNF films.

2. Results and discussion

2.1. Construction and orientation of the hybrid films

Following this design strategy, flexible hybrid films composed of AgNWs embedded within a WPU and TOCNF composite matrix were fabricated, hereafter referred to as AgNWs@WPU/TOCNF. In this system, WPU served as a highly stretchable soft matrix, while TOCNF acted as a rigid and hydrophilic reinforcement to suppress elastic recovery and enable shape retention after stretching (Fig. S1–S3, ESI†). AgNWs, with a high aspect ratio (length ∼20 μm, diameter ∼40 nm), were incorporated as plasmonic components to induce strong optical activity upon alignment within the polymer matrix (Fig. S4, ESI†).

The fabrication process involved mixing aqueous dispersions of WPU, TOCNF, and AgNWs in appropriate proportions under vigorous stirring to form a homogeneous hybrid solution. This mixture was then cast and dried at ambient conditions to obtain uniform AgNWs@WPU/TOCNF hybrid films (Fig. S5, ESI†). Extinction spectra of the as-prepared films showed no obvious redshift of the AgNWs plasmonic absorption peak (Fig. S6, ESI†), indicating good dispersion without severe aggregation, which was further verified by scanning electron microscopy (SEM) images (Fig. S7, ESI†).

The obtained films were subsequently subjected to uniaxial wet-stretching, during which both the polymer chains and the embedded AgNWs were simultaneously aligned along the stretching direction (Fig. 1a). Benefiting from the physical confinement and abundant hydrogen bondings (HBs) provided by TOCNF, the hybrid films effectively maintained over 1000% strain ratio of its deformed shape after drying when the TOCNF content was 5 wt%, but further increasing the TOCNF content resulted in a gradual decline in the achievable wet-stretching ratio, likely due to the disruption of the WPU molecular network by the excessive incorporation of rigid TOCNF (Fig. S8, ESI†).

SEM images clearly revealed the evolution of AgNWs alignment with increasing stretching ratios (Fig. 2a–c). The unstretched films exhibited a random distribution of AgNWs, while films stretched to 600% showed partial alignment, and films stretched to 1000% displayed highly ordered and densely packed AgNWs along the stretching direction. The orientation evolution was further supported by 2D wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) measurements (Fig. 2d–f). The unstretched film displayed isotropic scattering patterns, whereas the stretched one exhibited pronounced equatorial reflections in WAXS and elongation of scattering in SAXS, indicating the formation of anisotropic structures.^26,27 According to the WAXS and SAXS results, the quantified Herman's orientation factors (f_c) of the AgNWs@WPU/TOCNF film gradually increased from 0.073 to 0.23 and 0.008 to 0.49, respectively (Fig. S9, ESI†).²⁶ In addition, the polarized UV-vis absorption spectra demonstrated increasing dichroic behavior with higher stretching ratios, with the corresponding polar plots evolving from circular to highly elliptical shapes, reflecting the progressive improvement in orientation (Fig. 2g–i and Fig. S10, ESI†). The stretched hybrid films also exhibited pronounced birefringence under polarized optical microscopy (POM), further confirming the successful formation of anisotropic structures (Fig. S11, ESI†).

Fig. 2 Characterization of orientation evolution in AgNWs@WPU/TOCNF hybrid films under different stretching ratios. (a)–(c) SEM images of the film surface at different stretching ratios: (a) 0%; (b) 600%; (c) 1000%. White arrows indicate the stretching direction. (d)–(f) 2D WAXS (top) and SAXS (bottom) patterns of the corresponding samples, showing the progressive alignment of AgNWs and polymer chains with increasing strain: (d) 0%; (e) 600%; (f) 1000%. (g)–(i) Polar plots at different stretching ratios: (g) 0%; (h) 600%; (i) 1000%, demonstrating enhanced optical anisotropy and uniaxial alignment as strain increases of monolayer films.

2.2. Tunable CD response

The ultrahigh stretchability of the AgNWs@WPU/TOCNF hybrid films enabled the formation of highly aligned anisotropic nanostructures, which serve as the structural basis for constructing chiral architectures with tunable CD responses. To this end, a bilayer assembly strategy was employed to fabricate twist-stacked chiral films via water-induced self-healing: Two hybrid films with pre-stretched, oriented AgNWs networks were twisted at a defined angle (θ) and brought into contact under humid conditions. Upon drying, HBs between TOCNF and WPU chains across the interface re-established spontaneously (Fig. S12, ESI†), resulting in seamless fusion into an integrated bilayer film with stable chiral alignment (Fig. 3a). The self-healed film exhibits excellent mechanical properties, with a tensile strength of 127 MPa and a fracture strain of 84%, indicating both robustness and flexibility (Fig. S13, ESI†).

Fig. 3 Tunable chiroptical response of twist-stacked AgNWs@WPU/TOCNF hybrid films. (a) Schematic illustration of the self-healing assembly process triggered by water molecules. HBs dissociated by water re-form upon contact between twisted films, enabling seamless fusion. Inset: The optical image of a self-healed film under ambient light. Functional groups responsible for HBs reformation are highlighted. (b) CD spectra of bilayer films with different twist angles (θ = ±45°, ±30°, ±15°, and 0°), showing increasing ellipticity with larger θ. (c) Polar coordinate diagram of ellipticity at 384 nm as a function of θ, revealing centrosymmetric evolution and enantiomeric behavior between ±θ configurations. (d) CD spectra of bilayer films with different stretching ratios (0–1000%) were used for monolayer alignment. (e) CD spectra of films with varying AgNWs content, demonstrating signal enhancement with increasing AgNWs loading. (f) CD spectra measured from the front and back sides of the bilayer, showed nearly identical responses, indicating direction-independent optical behavior.

The optical activity of the chiral films was investigated by CD spectroscopy. To verify that the CD response originates from the twist-induced chiral stacking rather than the intrinsic anisotropy of the monolayer, control experiments were first conducted on the oriented AgNWs@WPU/TOCNF single-layer films. As shown in Fig. S14 and S15 (ESI†), only negligible CD signals (∼0.15°) were detected for the monolayer films, in sharp contrast to the pronounced CD intensity (>10°) observed in the twist-stacked bilayer films. Subsequently, the effect of interlayer twist angle θ on the CD response was systematically examined. As shown in Fig. 3b, the CD intensity increased with θ and reached a maximum ellipticity of 13.3° at 384 nm when θ = ±45°, accompanied by a g_abs value exceeding 0.6. The angle-dependent evolution of CD was further visualized by plotting the ellipticity at 384 nm against θ, showing a centrosymmetric pattern (Fig. 3c). Notably, configurations with ±θ angles exhibited mirrored CD spectra with opposite signs, confirming the formation of well-defined enantiomeric structures. In addition to twist angle, the CD intensity can also be tuned by modulating intrinsic structural parameters of the monolayer films. Increasing the stretching ratio of the AgNWs@WPU/TOCNF films led to enhanced CD intensity in the longer wavelength region (>600 nm), likely due to improved AgNWs orientation and localized aggregation (Fig. 3d and 2b,c). Furthermore, increasing the AgNWs content significantly amplified the CD signals, while AgNWs-free films exhibited negligible optical activity (Fig. 3e and Fig. S16, ESI†).

Due to the elimination of interfacial discontinuities via self-healing, together with the fully equivalent roles of the two oriented films acting as the combination of retarder and polarizer, the CD spectra remained nearly identical when measured from either side of the bilayer films (Fig. 3f). This unique structural configuration enables the construction of a robust and direction-independent chiral optical system, offering practical advantages over conventional circular polarizers composed of stacked linear polarizers and quarter-wave plates.^28–30

2.3. Construction and control of CPL-emitting devices

Building on the excellent chiroptical properties and programmable CD response of the twist-stacked AgNWs@WPU/TOCNF hybrid films, the construction of CPL-emitting devices was further explored. The selective absorption theory, known as the “Matching Rule”, indicates that CPL can be generated in non-chiral luminophores when their emission bands overlap with the CD-active absorption bands of adjacent chiral materials, even without direct chemical or physical interactions.^31,32 To realize this, fluorescent films with emission wavelengths of 580 nm were fabricated by incorporating rhodamine 6G (R6G) into the WPU matrix (Fig. S17, ESI†). Subsequently, leveraging the same water-induced self-healing strategy as for the bilayer construction, the WPU-R6G fluorescent film was assembled onto the surface of the twist-stacked AgNWs@WPU/TOCNF films, yielding a three-layer CPL hybrid film (CPL-HF) (Fig. 4a).

Fig. 4 CPL performance of the CPL-HF. (a) Schematic illustration of the CPL-HF, constructed by self-healing assembly of a fluorescent layer and a twisted bilayer via water-induced HBs. Inset: Optical image of the CPL-HF film under ambient light. (b) CPL spectra of CPL-HF with different twist angles (θ = ±45°, ±30°, ±15°, and 0°). Inset: Corresponding g_lum spectra. (c) and (d) CPL spectra of CPL-HF fabricated from AgNWs@WPU/TOCNF with different stretching ratios (c) and varying AgNWs contents (d). Inset: Corresponding g_lum spectra.

The CPL performance of the resulting CPL-HF was closely related to the structural parameters of the underlying biayer. As shown in Fig. 4b, adjusting the interlayer twist angle (θ) from −45° to +45° gradually decreased the CPL ellipticity, while the CPL spectra exhibited nearly perfect mirror-image profiles at opposite angles. The maximum CPL ellipticity exceeded 2°, and the corresponding g_lum reached 0.5. Moreover, the CPL signals could be further modulated by tailoring the structural parameters of the AgNWs@WPU/TOCNF layers. Increasing the stretching ratio of the chiral layer led to a gradual increase in g_lum value, although the overall CPL intensity remained relatively constant (Fig. 4c). In addition, increasing the AgNWs content significantly enhanced both the CPL intensity and g_lum values (Fig. 4d). These results demonstrate the versatile tunability of CPL performance in CPL-HF through macroscopic structural regulation of the flexible chiral framework.

2.4. Application for information encryption

The programmable chiroptical properties of twist-stacked hybrid films offer promising opportunities for advanced information encryption.^33–36 In particular, the tunable CD response enables encoding based on ellipticity values that are undetectable by the naked eye, thus enhancing data security.

To demonstrate the feasibility of such applications, a multi-level information encryption strategy was developed based on the precisely programmable ellipticity of the twist-stacked hybrid films. As illustrated in Fig. 5, the interlayer twist angle θ was employed as the key encoding parameter, directly correlated with specific CD ellipticity values. In this demonstration, seven twist angles (−45°, −30°, −15°, 0°, 15°, 30°, and 45°) were selected as the coding basis, corresponding to distinct ellipticity values and module units (top table in Fig. 5). Notably, this system could be further expanded by increasing the number of twist angles within the −45° to +45° range, thereby enhancing the encryption capacity (Fig. S18, ESI†).

Fig. 5 Schematic illustration of information encryption and decryption based on the programmable ellipticity of AgNWs@WPU/TOCNF films. Top: Lookup table showing the relationship between interlayer twisted angles and their corresponding CD ellipticity values, each representing an encrypted module unit. Bottom: Multilevel encryption-decryption process. Step I, the original information (e.g., text of “CHIRAL”). Step II, the encoded data are mapped into a matrix of five basic module units. Step III, each module is translated into a specific twist angle based on the CD–ellipticity correspondence. Step IV, the encrypted film is fabricated by assembling twist-stacked AgNWs@WPU/TOCNF bilayers via wet stretching and self-healing. The optical image shows the resulting chiral QR code–like film under ambient light. Step V, decryption is performed by measuring the ellipticity at fixed positions via CD spectroscopy. The measured ellipticity values are then decoded back into twist angles and module identities to reconstruct the original encrypted information.

To visualize the encryption process, the word “CHIRAL” was encoded as an example (Fig. 5-I). Each letter was assigned a specific matrix combination of five basic module units (Fig. 5-II), and subsequently converted into corresponding twist angles according to the established coding table (Fig. 5-III). Following the fabrication protocol described in Fig. 1a, a 5 × 6 matrix encryption film was assembled via wet-stretching and water-assisted self-healing, generating an integrated encrypted film that appeared featureless under normal observation (Fig. 5-IV). For the decryption process, the ellipticity of each module within the film was measured using a CD spectrometer to extract specific ellipticity values (Fig. 5-V). These values were then translated back into corresponding module units based on the decoding table, allowing the retrieval of the encrypted information.

This encryption system achieves a three-level information security strategy by combining material chirality, programmable ellipticity, and structural coding. The excellent environmental stability ensures effective concealment of information under various application scenarios while enabling accurate decoding only through chiroptical analysis (Fig. S19, ESI†). Moreover, the flexible and scalable design of the CPL-HF provides new possibilities for developing 2D soft encryption devices with enhanced information capacity, security, and adaptability, holding promise for future practical and industrial applications.

3. Conclusion

In summary, we have developed a new class of flexible and structurally stable chiroptical materials based on AgNWs@WPU/TOCNF hybrid films. The monolayer film exhibits ultrahigh stretchability (>1000%) and excellent shape retention, enabling the formation of highly oriented anisotropic structures through wet-stretching. Upon twist-stacking and water-assisted self-healing of two pre-oriented films, robust chiral architectures were constructed, showing strong CD signals with a maximum ellipticity of 13.3° and a g_abs exceeding 0.6. The intrinsic self-healing ability of the WPU-based matrix not only ensures seamless multilayer integration, but also enhances structural stability. Based on this, CPL-HF was fabricated by incorporating a fluorescent WPU-R6G layer, achieving tunable CPL with a maximum ellipticity over 2° and a g_lum of 0.5. Furthermore, a multilevel information encryption strategy was demonstrated by exploiting the fully programmable CD properties of the films. This work presents a versatile and scalable platform for constructing flexible, self-healing chiroptical materials with integrated optical functionality, offering promising prospects for applications in soft photonics, secure information storage, and wearable optical devices.

4. Methods

4.1. Materials

Isophorone diisocyanate (IPDI), poly(tetramethylene ether glycol) (PTMG 2000, average Mn of ∼2000), dimethylolpropionic acid (DMPA), butanediol (BDO), Di-n-butyltin dilaurate (DBTDL) and rhodamine 6G were purchased from Macklin. Triethylamine (TEA) and acetone were purchased from National Medicine. TEMPO-oxide cellulose nanofibers (solid content: 0.5wt%, –COOH content: 1.4 mmol g⁻¹) were purchased from Jinjiahao nanomaterials Inc. China. The AgNWs solution with a diameter of 40 nm and a concentration of 10 mg mL⁻¹ was purchased from XFNANO Inc. China.

4.2. Synthesis of WPU emulsion

First, pre-dried PTMG (20.6 g), IPDI (8.2 g) and DBTDL (0.15 mL) were added into a three-necked flask equipped with a condenser and a N₂ inlet. The reaction mixture was stirred at 400 rpm and heated to 80 °C for 1.5 h under a nitrogen atmosphere. Second, DMPA (1.8 g) and BDO (0.7 g) were added for chain extension, and the reaction was continued for an additional 3.5 h at the same temperature. During this process, a small amount of acetone was added as needed to adjust the viscosity. Third, the reaction temperature was lowered to 45 °C, and the mixture was neutralized with TEA (1.7 mL) under stirring for 15 min. Finally, the resulting prepolymer was dispersed in DI water (66.7 mL) under vigorous stirring at 1000 rpm at room temperature for 40 min to obtain a stable WPU emulsion with solid content of 30 wt%.

4.3. Preparation of AgNWs@WPU/TOCNF hybrid film

First, 6 g pre-diluted WPU emulsion (10 wt%) was mixed with 6.3 g TOCNF solution (0.5 wt%) under stirring at 1500 rpm for 2 h at room temperature. Then 0.4 g AgNWs solution (10 mg mL⁻¹) was added and continually stirred for 2 h to obtain uniform AgNWs@WPU/TOCNF hybrid solution. To obtain hybrid films, a specific amount of the AgNWs@WPU/TOCNF solution was poured onto a 5 cm × 5 cm plate, and placed in an oven at 40 °C for about 12 h.

4.4. Preparation of twist-stacked AgNWs@WPU/TOCNF film

To construct the self-healed bilayers of twisted stacking AgNWs@WPU/TOCNF films, the hybrid film was first cut into 15 mm wide strips. Next, the film strips were wet-stretched using a stretch machine (speed: 10 mm min⁻¹) equipped with a flat port fixture and an axial pulley device. Then, the two oriented wet films were contacted and twist-stacked at a certain angle. After drying, the interface of the film self-healed due to the recombination of HBs and the orientation structure was fixed.

4.5. Preparation of CPL-HF

The WPU-R6G fluorescent film was first prepared: 1 mg rhodamine 6G powder was dissolved in 10 mL of deionized water at room temperature. Then, take 1 g R6G solution dispersed into 2 g WPU emulsion under stirring (1500 rpm) for 1 h. After mixing, a specific amount of the WPU-R6G solution was poured onto a 5 cm × 5 cm plate and placed in an oven at 40 °C for about 12 h to obtain a fluorescent film.

To fabricate the multilayer CPL-HF, one side of the WPU-R6G fluorescent film was moistened with water vapor and brought into contact with the AgNWs@WPU/TOCNF chiral film under a certain gravitational pressure. After drying, a CPL-HF was obtained through self-healing assembled.

4.6. Preparation of integrated encryption film

First, a 5 × 6 matrix of encryption film units was constructed based on the combination encryption module corresponding to the word “CHIRAL” (Fig. 5-II). For each encryption module, a specific torsion angle was assigned, and 30 oriented AgNWs@WPU/TOCNF films (5 × 5 mm²) were used as the upper layers. These were assembled via water vapor-induced self-healing with a base AgNWs@WPU/TOCNF film (3 × 35 mm²) at their respective torsion angles. After drying, an integrated bilayer structure was formed. Notably, the torsion angle of each film unit is not visible to the eyes once fabrication is complete. As such, determining the CD value of each film unit becomes a key step in the decryption process (Fig. 5-V). Subsequently, the CD (or corresponding torsion angle) values of each unit on the encrypted film were translated back into their respective encryption modules, and the final encrypted information was reconstructed through module recombination (Fig. 5-II, I).

4.7. Characterization

Transmission electron microscopy (TEM) images were recorded on a JEM-2100 (JEOL, Japan) electron microscope. Scanning electron microscope (SEM) images were obtained using a Sigma 500 Field emission scanning electron microscopy. Linear birefringence of the films was measured with a Berek compensator on an Olympus BX51 microscope equipped with a Linkam LTS420E hot stage and a T95-HS controller. All UV-vis spectra were recorded on a SHIMADZU UV-3600 plus. The tensile stress–strain tests were conducted using an Instron 5969 instrument equipped with a 1 kN load cell at a speed of 10 mm min⁻¹ at room temperature, with a gauge length of 20 mm maintained between the clamps. All specimens were conditioned at a relative humidity of 50% for 48 hours before testing. Circular dichroism was measured using a JASCO-1500 spectrometer adapted for film samples. The sample was rotated in-plane in 45° increments, resulting in eight measurements. The values from these eight measurements were averaged to obtain the CD response, eliminating potential angle-dependent side effects from linear dichroism and linear birefringence. Fluorescence spectra were measured by an FLS1000 fluorescence spectrophotometer. Circularly polarized luminescence spectra were measured by a JASCO CPL-300 spectrometer with excitation/emission bandwidths of 10 nm. All fluorescent films were observed using a reflective UV camera obscura and captured by a camera to avoid direct exposure of ultraviolet light to the human eye. Wide-angle X-ray scattering (WAXS) and Small-angle X-ray scattering (SAXS) experiments were carried out on point 2.0 of Anton Paar under vacuum.

4.8. Calculation of Herman's orientation parameter

The 2D SAXS and WAXS scattering patterns in Fig. 2 were analyzed with Igor Pro software. Herman's orientation parameter (f_c) was calculated from the azimuthal integrated intensity distribution curves, based on the following equations:
and
where φ is azimuthal distribution, I(φ) is the intensity at φ in the azimuthal scan, and 〈cos² φ〉 is calculated by integrating the intensity of the specific 2θ diffraction peak along φ.²⁶

Conflicts of interest

The authors declare no conflict of interest.

Data availability

The data supporting this article have been included as part of the ESI.†

Acknowledgements

We gratefully acknowledge financial support from the National Natural Science Foundation of China (52373217 to X.-C. Ye, 92356306 to F. Liu), Shaanxi Provincial Science and Technology Department (2024GH-ZDXM-15 to X.-C. Ye). We thank the Instrument Analysis Center of Xi’an Jiaotong University for providing material characterization facilities. We also thank the School of Chemistry and Chemical Engineering, Shaanxi Normal University for their instrument support.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: https://doi.org/10.1039/d5tc01653c

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