Confinement fluorescence effect of an aggregation‐induced emission luminogen in crystalline polymer

Despite the impressive progress of stimuli‐responsive fluorescent materials, little is known about the influence of confinement created by crystalline polymer over the fluorescence properties of fluorescent molecules. The effects of confinement on the fluorescence of an aggregation‐induced emission luminogen (AIEgen) are investigated using computational simulations, which reveal that the confined space induces the AIEgens to take a more planar conformation, resulting in a red‐shifted emission spectrum. With this property, the study is extended to explore the confinement generated by various polymer crystalline forms, and it is shown that different fluorescence colors are activated. This confinement fluorescence effect is attributed to the different spatial dimensions of the polymer amorphous layer between lamellar crystals where the AIEgens are located. These results indicate the immediate association between crystalline structure and fluorescence signals, activating unprecedented photophysical properties of luminescent materials, and also providing the possibility for crystalline structure visualization, it is important for the many polymer crystallization processes occurring in the materials processing.

In order to address the above issue, instead of molecularlevel modification, one general approach to achieve smart responsive behavior is to control the intermolecular interactions, molecular conformation, or stacking behavior of fluorophores in different environments, [17,18] providing a highly reversible response upon external stimuli.In particular, confinement fluorescence effect materials are such a type of light emission system constructed between the single molecule fluorophore and the surrounding microenvironment, featuring conformational or morphological change of a single fluorophore. [17]Although many confinementassociated phenomena have been studied in solutions or gel states, in practice, fluorescent materials are often used in the dry solid state for real applications. [19][26] With this property, these AIEgens capable of exhibiting remarkable changes in fluorescent color and intensity under certain confinement not only provide high-quality light-emitting properties for condensed matter structure visualization, [17] but also activate unprecedented photophysical properties for novel luminescent materials development.
The crystalline microstructure is an important characteristic of semicrystalline polymers, determining their mechanical properties and versatile functions, [27][28][29] in which a large number of confined spaces are created originating from intrinsically free volumes between entangled polymer chains. [30]Due to the difference in the way polymer chains are stacked, the size of the nano-confinement in the crystalline and amorphous regions of semicrystalline polymers is different. [31]Our previous studies showed that the single molecule-based AIE system of TPE-EP exhibits distinct emission colors when dispersed in the amorphous polymer phase (green emission) and confined in the crystalline polymer phase (yellow emission). [32]Such phenomenon is ascribed to the changes of the AIE molecular conformation and packing mode when confined between the polymer lamellar crystals. [32]This study shows the potential of polymer networks as constrained environments for fluorescence behavior control of AIE molecules.Therefore, it is very important to study the mechanism and law of the influence of confined space on fluorescence characteristics for the development of fluorescence-responsive materials.
Herein, we perform a systematic investigation of the confinement effects on the fluorescent properties of an AIE molecule, TPE-EP with polymorphic character, which provides an excellent candidate for our study (Figure 1A).Further, theoretical models with a hybrid scheme, in combi-nation with quantum mechanics and molecular mechanics are used to explore molecular conformation and frontier molecular orbitals of TPE-EP in a confined space, demonstrating more planar conformation and then red-shifted fluorescence with greater degrees of confinement.Owing to high practical application value, biodegradable semi-crystalline polymers of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) are selected to create adjustable confined spaces to accommodate TPE-EP molecules (Figure 1B).We then extend the work to investigate the effect of the crystalline structure of PLLA homocrystals (HCs) and PLLA/PDLA stereo-complex crystals (SCs) on the fluorescence properties of TPE-EP (Figure 1C).Our results show different fluorescence colors are generated in various polymer crystalline forms, which is attributed to the different spatial dimensions of the free volumes between lamellar crystals where the TPE-EP are located.This work suggests the confined space of polymer crystals provides a novel way of manipulating fluorescence properties, and also has high potential in the identification of polymer crystal structures, providing a visual method for online detection of polymer structure evolution during the materials processing.

Electronic structures based on quantum mechanics/molecular mechanics simulations
As shown in Figure 1A, we use a polymorph luminogen of TPE-EP as a confinement-responsive material in our study.TPE-EP consists of three parts: a twisted tetraphenylethylene (TPE) as the donor unit, a cationic pyridinium as the acceptor unit, and a carbon-carbon double bond as the spacer unit.In our previous work, [32] it has been demonstrated that the amphiphilic structure forces TPE-EP to form segregated aggregates in hydrophobic PLLA, that is, the green-emissive TPE-EP in the crossed-packed aggregates is favored in the amorphous phase of PLLA, while the yellow-emissive TPE- EP in the parallel-packed aggregates is preferred in the crystalline phase of PLLA (Figures S1 and S2).In the crystalline phase of PLLA, the molecules of TPE-EP are pushed in the amorphous areas between crystalline layers during polymer crystallization, the confined space forces TPE-EP molecules to adopt a parallel packing mode, resulting in redshifted emission when compared with those molecules in amorphous PLLA. [32]In order to understand the confinement fluorescence effect, we studied the molecular behavior in the complex system before and after space compression (Figure 2A and Figure S3).Specifically, the crystalline lattice parameters were reduced by 20% in three axes respectively with parameters in the original and compressed lattices listed in Table S1.We compared the torsion angles before and after the compression in different lattices (Table S2).The results show that the torsion angles defined in Figure 2A turn to be closer to 0 • or 180 • , indicating the increased conformational planarity of the four twisted moieties in TPE-EP.
According to the measurement of the distances between two neighboring TPE-EP molecules in the crystal lattice (Figure 2B; Figure S4), it is noted that the distance along the π⋅⋅⋅π stacking direction decreases more than the distance along the other directions, resulting in the change in the twisted conformation.As Figure 2B shows, the center distances between phenyl rings of TPE-EP are reduced from 7.09 and 6.71 Å to 5.75 and 5.92 Å, respectively along the π⋅⋅⋅π stacking direction.The closer the intermolecular distance of TPE-EP, the closer the torsion angle between phenyl rings is to 0 • or 180 • .Therefore, it is demonstrated that the twisted conformation becomes more planar in the confined space to reduce compression-induced steric effects.
Upon compression, due to the shortened distance between the central TPE-EP molecule (QM region) and its surroundings (MM region), the intermolecular interactions of TPE-EP may be enhanced accordingly.Therefore, we further calculated the intermolecular interactions between TPE-EP molecules in different packing conformations (Figure 2C and Figure S5) at the B3LYP/6-31G(d,p) level.It showed that the van der Waals interactions between TPE-EP molecules could be decomposed into C-H⋅⋅⋅π, C-H⋅⋅⋅C, and π⋅⋅⋅π attractions.Similar to the theoretical investigation by Zheng and her coworkers, the van der Waals interactions dominate intermolecular interactions compared to electrostatic repulsion. [33]As Figure 2C shows, the weak intermolecular interaction between TPE-EP molecules in the native and compressed conformations along the c-axis is indicated by the interaction region indicator (IRI) using the electron density and gradient, which is defined in Equation ( 1). [34]I where ρ is the electron density, r is the coordinate vector, a is an adjustable parameter, and the sign(λ 2 ) is the sign of Hessian second largest eigenvalue of ρ, which are used to distinguish bonding (λ 2 < 0) and non-bonding (λ 2 > 0) interactions.The magnitude of sign(λ 2 )ρ is mapped on the IRI isosurface with different colors for presenting the nature of the interaction region.The relatively stronger intermolecular interactions are demonstrated by relatively higher ρ and larger sign(λ 2 )ρ in Figure 2C.The results demonstrate that in our proposed polymorphic luminescent material, the weak intermolecular interactions are enhanced when TPE-EP molecules are in a compressed confined space.It is noted that despite increased molecular interactions, they remain in the weaker range.The weak intermolecular interaction between TPE-EP molecules makes them easily disturbed by the surrounding microenvironment. [35]n addition to the conformational planarization and intermolecular interactions, analysis of the electronic structure, such as the energy of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), will provide useful information for predicting the confinement fluorescence effect.Frontier molecular orbitals, HOMO and LUMO reveal the charge transfer character in the excited state (Figure 2D and Figure S6), because the HOMO is mainly localized on the TPE unit and LUMO is concentrated on the pyridinium group.Before compression, the HOMO-LUMO gap of TPE-EP is 2.33 eV, while it decreases to 2.11 eV after compression along the c-axis, indicating that compression reduces the HOMO-LUMO energy gap.In addition, the HOMO and LUMO distributions are almost unchanged upon compression, intermolecular exciton coupling could be ignored.These data indicate that the conformation planarization of a single fluorophore made the greatest contribution to the redder-shifted emission upon compression.

Fluorescent response to PLLA homocrystals
From the above theoretical calculations, it has been demonstrated that the fluorescence emission of TPE-EP is highly dependent on the size of the confinement space size.By manipulating the temperatures of isothermal crystallization, the size of the free space between adjacent crystalline layers could be controlled accordingly.For example, the α and δ crystal forms of PLLA could be obtained by different crystallization temperatures.As shown in the layered stack model (Figure 3A), the long period (L), the amorphous layer thickness (L a ), and the crystal thickness (L c ) are identified.In PLLA α form, L a between two crystalline layers is larger than that of δ form.On the other hand, TPE-EP molecules exist as nano-crystalline aggregates confined between polymer lamellae.From the above molecular simulation results, we can conclude that for a single TPE-EP molecule, the local-ized environmental changes induced by crystal compression are consistent with those induced by changing the thickness of the polymer amorphous layer.Therefore, it is anticipated that TPE-EP molecular conformation could be manipulated if they are confined in the different polymer crystals, generating various fluorescence emissions accordingly.
With this special property, we incorporated TPE-EP into the PLLA polymer matrix, followed by a melt crystallization process between two glass slides.Crystallization temperature and isothermal crystallization time were controlled respectively, resulting in PLLA α or δ crystal form with different crystallinities.In our study, PLLA α crystal form was yielded by annealing the melt-quenched sample at a relatively high temperature of 130 • C. The crystalline regions with yellow emission are distinguished from green-emissive amorphous phases as radial spherulites grow (Figure 3B and Figures S7, S8A, and S9).The spherulite crystalline morphology observed under the fluorescent microscope is in agreement with that under the polarized optical microscope.Figure 3C demonstrates the fluorescence sensitivity of TPE-EP in PLLA α crystal form by increasing the crystallization time.A gradually red-shifted emission from green to yellow was revealed.A similar red-shifted trend was observed when doping TPE-EP in PLLA δ crystal form, melt-quenched blends of TPE-EP and PLLA were annealed at a low temperature of 90 • C. With the increase of the crystallization time, numerous granular crystals in yellow emission were generated in green-emissive amorphous film (Figure 3D and Figure S8B), leading to redshifting in fluorescence emission (Figure 3E).It is noted that the δ crystallite size is smaller than that of the α crystal form, which is beneficial for the remarkably tough mechanical property of polylactide materials. [36]he crystallinity (χ α ) of these PLLA samples in α form was calculated by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC).In Figure 3F, at the beginning of crystallization, the melt-quenched film is amorphous without diffraction peaks of the crystalline phase.With the crystallization process proceeding at around 130 • C, the crystalline peaks of the α form started to appear at 2θ values of 14.8 • , 16.8 • , 19.1 • , and 22.4 • , and the intensity increased with crystallization time.The DSC thermograms of a series of crystallized samples are in good agreement with the above WAXD results (Figure S10 and Table S3).Their detailed fluorescence properties were tracked by photoluminescence (PL) spectroscopy.Figure 3G shows the normalized PL spectra of TPE-EP in PLLA α crystalline samples at a crystallinity of 4.60%, 12.7%, 22.9%, 37.0%, 46.2%, and 55.5%, respectively.With an increase of χ α (α crystal form), a red-shifted light emission was observed from 523 nm (Ф F = 74%) to 542 nm (Ф F = 39%) in the PL spectrum.In addition, a linear correlation between PLLA crystallinity (α form) and wavelength maximum highlighted the quantitative sensing capability of TPE-EP (Figure 3H).The crystallinity (Figure S11 and Table S4) and fluorescence emission maximum (Figure S12) of the as-prepared δ crystalline films were measured.A similar linear relationship was also observed for the TPE-EP-dopped PLLA δ crystal form.The 0.4 slope value of the PLLA δ crystal form is larger than that of the PLLA α crystal form (slope value = 0.3), which is ascribed to the smaller thickness of the amorphous layer between two crystalline layers.More confined space pushed TPE-EP to adopt more planar molecular conformation with redder emission, which is supported by small-angle X-ray Scattering (SAXS) measurement.After Lorentz-corrected analysis, L a of α and δ crystal forms were calculated to be 13.8 nm and 12.7 nm (Figure 3I and Figure S13, χ α , χ δ ∼ 30%), respectively.The above results indicate the ability of PLLA HCs with different crystal forms to manipulate the fluorescence behavior of TPE-EP based on the confinement fluorescence effect.The reversibility and repeatability of the sensing behavior of TPE-EP under the polymer crystalline confinement were demonstrated by repeated melting-quenching-crystallization processes (Figure S14).On the other hand, the linear relationship between emission maximum and polymer crystallinity (α and δ crystal forms) provides the possibility to visualize the polymer crystallinity on the basis of the fluorescence output signals.

Fluorescent response to PLLA/PDLA SC crystallites
[38][39][40] It is noted that SCs are created from the PLLA/PDLA blends.The SCs provide a higher melting point (∼230 • C) than that of the α or δ form consisting of PLLA homopolymer (∼170 • C).Besides, SCs also exhibit superior mechanical properties compared to HCs.The improved physical properties of SCs form are mainly attributed to the compact molecular packing and strong interchain interactions between the left-handed PLLA and right-handed PDLA polymer chains (Figure 4A). [41]Therefore, the crystalline structure of SC is important for understanding the crystal structure-physical property relationships of polylactide materials.
In order to evaluate the sensing ability of TPE-EP in SCs, the blend samples of PLLA/PDLA with the various L/D ratios were fabricated from casting the solutions.Here, the L/D ratio stands for the mixing ratio between PLLA and PDLA (weight percent).Figure 4B shows the fluorescence response of TPE-EP in a range of L/D blends.The blend samples with the L/D ratio of 100/0−60/40 showed a blue-shifted emission with increasing D content, while the opposite trend was observed for the blends with the L/D ratio of 40/60−0/100.Yet, the L/D 50/50 gave the reddest emission of 559 nm.Afterward, the WAXD analyses were carried out for these blend samples to correlate the information between crystalline structure and fluorescence behavior (Figure 4C and Figure S15).The results show that the homopolymer of PLLA or PDLA gave the pure α phase, while the L/D 60/40−40/60 blend samples exhibited only the SC phase.Meanwhile, the samples with the L/D ratio 90/10-70/30 and 30/70-10/90 showed a mixture of the α and SC crystallites.Figure 4D summarizes the results of the WAXD characterizations.The integrated area of the (200/110), (203), and (210) diffraction peaks of the α form (A(α)), and those of the ( 110), (300/030), and (220) diffraction peaks of the SC phase (A(SC)) and those of amorphous part A(am) were evaluated from the WAXD profiles shown in Figure 4C.The ratio A(SC)/[A(SC) + A(α) + A(am)], that is, the crystallinity of SCs phase (χ SC ), was plotted versus the L/D ratio in the blend sample.The crystallinity of the α form, χ α ( = A(α)/[A(SC) + A(α) + A(am)]), as well as the sum of the SC fraction (χ SC ) and α fraction (χ α ) are also plotted here with blue hollow triangles and red squares, respectively.The crystalline structure of the samples of L/D 100/0−60/40 is symmetric to the cases of L/D 40/60-0/100.That is, the SC formation area is symmetrical about the center of L/D 50/50.The DSC analyses shown in supporting information (Figure S16 and Tables S5 and S7) are consistent with the WAXD data (Figure 4C).It is noted that the correlation between the emission maximum and the D component is consistent with that of crystalline structure (Figure 4E and Table S8), confirming the capability of TPE-EP in sensing SC of PLLA/PDLA.
As illustrated in Figure 4A, TPE-EP molecules are repelled to the amorphous layer in the layered stack model.After Lorentz-corrected analysis of SAXS data of L/D blend samples, we found that the changes in amorphous lamellar thickness account for the fluorescence process of TPE-EP (Figure 4E, Figure S17, and Table S9).TPE-EP in L/D 50/50 shows the red-shifted emission with the maximum wavelength (λ em = 559 nm) because L/D 50/50 has the smallest L a (15.8 nm), which is consistent with the fluorescence phenomenon.It is worth mentioning that TPE-EP molecules in the pure SC phase gave redder emission than those in α crystal form or δ crystal form, even though the larger amorphous layer thickness was displayed in the SC phase.The reason might be attributed to the tight molecular packing and strong molecular interaction among the L/D SC.The rigid microenvironment of the L/D amorphous layer also promotes the red-shifted emission of TPE-EP, [24] which was supported by their apparent mechanical properties.The rigidity of L/D blend polymers was compared by nanoindentation test.In a typical measurement, the load applied to the tip of the indenter increases as the tip penetrates further into the sample and soon reaches a pre-defined value.After the tip was retracted, the area of the residual indentation was measured.shows load-displacement curves for instrumented nanoindentation tests of the blends with the L/D ratio 50/50, 60/40, and 70/30.The specimen hardness (H) can be defined by the following Equation (2). [42] P max A c (2)   where P max is the load maximum and A c is the residual indentation area.The results indicate SC of L/D 50/50 has the greatest mechanical performance, supporting the fluorescence behavior shown in Figure 4E.The synergistic effect of confined space and rigid microenvironment allows them to manipulate the fluorescence behavior of TEP-EP, in turn, to facilitate TPE-EP to visualize the SC crystalline polylactide materials.

CONCLUSION
In conclusion, we have shown how TPE-EP as a unique sensor can provide high-quality fluorescence response properties toward polymer crystalline structure.A hybrid model combined with quantum mechanics and molecular mechanics reveals that the confined space increases the conformational planarity of the twisted AIEgen, resulting in a red shift in the emission spectrum.During polymer crystallization, the amorphous layer confined between two crystalline lamellae provides a free space to accommodate TPE-EP molecules.The emission of TPE-EP is marked in different colors when confined in various crystalline forms, which originates from different confinement sizes of the corresponding polymer crystals.Excitingly, the relationship between the polymer crystals and fluorescence color has been successfully established, which can be used to construct confinement fluorescence effect-based fluorophores with adjustable fluorescence properties.Moreover, it would facilitate the understanding of fluorescence processes within polymer crystals, and provide guidance for polymer engineering endeavors to use TPE-EP as a "built-in" sensor for in-situ monitoring of the polylactide material manufacturing process, as well as predicting the microscopic condensed matter structure and macroscopic polymer physical properties.

Computational details
The packing conformation of TPE-EP was simulated using the model shown in Figure S3, according to the previously reported polymorphic arrangements of TPE-EP. [32]o save the computational process, a hybrid quantum mechanics/molecular mechanics (QM/MM) approach with an ONIOM scheme was applied, [43] in which the center TPE-EP and PF 6 − anion were calculated at the B3LYP/6-31G(d,p) level and the other molecules were simulated by a universal force field (UFF).We reduced the crystal lattice by 15%-20% along the three lattice axes of TPE-EP, denoted as a-, b-, and c-directions in Figure S3 for simulating compression in experiments.We then optimized the QM regions within the QM/MM (B3LYP/UFF) scheme, while the MM regions were frozen in comparison with the original lattice.Following the optimization, vibrational modes were checked to confirm that the optimized structure was minimum.The change in the energy gap between frontier molecule orbitals could be used as an indicator in molecular spectroscopy, followed by a comparison in the energy difference between the HOMO and LUMO at the B3PW91/cc-pVTZ level.Since the B3PW91/cc-pVTZ method has provided reasonable HOMO-LUMO gaps in conjugated oligomers in a previous study, [44,45] we also applied this approach in calculations for a single TPE-EP molecule, which was extracted from the optimized QM/MM model.All calculations were carried out using the program Gaussian 16 in version C.02. [46] Our simulations could provide insight into the confinement effect on fluorescence spectroscopy, which could be used as a rational design in visualization and performance control of the polymer processing.

Preparation of α and δ crystal forms of TPE-EP-doped PLLA
The TPE-EP powder was dissolved in tetrahydrofuran to produce a stock solution (1 mg/mL).Meanwhile, PLLA (M w = 1.1 × 10 5 g/mol, PDI = 2.92) was dissolved in trichloromethane to make a polymer solution (10 mg/mL).Afterward, a specified amount of TPE-EP solution and PLLA solution was mixed at room temperature, in which the TPE-EP content was 0.50 wt% (Figure S7).The mixture was cast on a quartz sheet to form a film sample by slow evaporation.The obtained film samples were then melted between glass slides at 185 • C for 2 min and rapidly cooled to 130 • C for isothermal crystallization.By controlling different crystallization times, a series of PLLA α crystalline samples with different crystallinities were obtained.To control the formation of PLLA δ crystals, the isothermal crystallization temperature was controlled at 90 • C. The crystallization time was adjusted to obtain PLLA δ crystalline samples with different degrees of crystallinity.PLLA amorphous samples were obtained by the "melting-quenching" process.

Preparation of TPE-EP-dopped poly(lactic acid) SC crystals
PLLA (M w = 2.9 × 10 3 g/mol, PDI = 5.92) and PDLA (M w = 4.5 × 10 4 g/mol, PDI = 1.60) were respectively dissolved in trichloromethane to form 10 mg/mL polymer solutions.They were then mixed in the desired ratios to form a range of PLLA/PDLA blends.Afterward, a certain amount of TPE-EP stock solution was added to the above solutions under vigorous stirring, wherein the TPE-EP content was controlled at 0.50 wt%.Finally, 1.5 mL of the mixed solution was placed in a 2 mL vial, and the solvent was evaporated at 60 • C for crystallization.Here, solvent evaporation-induced crystallization was used because of the high melting temperature (∼230 • C) of PLLA/PDLA SC, TPE-EP molecules may undergo thermal decomposition at such high temperatures.

Measurements
WAXD was measured on a Bruker D2 phaser X-ray diffractometer using Cu Kα radiation.DSC was carried out on a DSC Q20 (TA Instruments) at a heating rate of 10

C O N F L I C T O F I N T E R E S T S TAT E M E N T
The authors declare no conflict of interest.

D ATA AVA I L A B I L I T Y S TAT E M E N T
The data that support the findings of this study are available from the corresponding author upon reasonable request.

F I G U R E 1
Confinement of fluorescence effect of an aggregation-induced emission luminogen in the crystalline polymer.(A) Molecular structure ofTPE-EP.(B) Chemical structure of polymers of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA).(C) The polymer crystals create an adjustable confinement space for the TPE-EP as a "built-in" sensor to achieve adjustable fluorescence.

F I G U R E 2
Confinement fluorescence effect.(A) Schematic diagram of the torsion definition (top) and the torsion angles of TPE-EP before and after compression along the c-direction (bottom).(B) Distances between TPE-EP molecules in the original (top) and compressed (bottom) along c-direction from molecular simulations in the quantum mechanics/molecular mechanics (QM/MM) scheme.(C) IGMH analysis calculated at the B3LYP/6-31G(d,p) level with dispersion corrected between TPE-EP molecules in the original (left) and compressed along the c-direction (right).The bottom is coloring and chemical interpretation of sign(λ 2 )ρ on the interaction region indicator (IRI) isosurfaces.(D) Molecular orbitals of TPE-EP calculated at the B3PW91/cc-pVTZ level in the original (left) and compressed along the c-direction (right).

F I G U R E 3
Polymers of poly(L-lactide) (PLLA) homocrystals visualization.(A) Layered stacking model of PLLA α and δ crystal forms with ideal phase boundary.TPE-EP molecules as a built-in sensor are expelled into the amorphous layers for PLLA crystal form sense. (B, D) Fluorescence (top) and polarized optical (bottom) micrographs of the TPE-EP-dopped PLLA during isothermal crystallization at 130 • C (B) and 90 • C (D), respectively.The scale bar is 50 μm.(C, E) Fluorescence images of TPE-EP-dopped PLLA during isothermal crystallization at 130 • C (C) and 90 • C (E), respectively.UV excitation wavelength: 365 nm.(F) Wide-angle X-ray diffraction (WAXD) profile measured for PLLA α form with increasing crystallization time at a given crystallization temperature of 130 • C. (G) Normalized PL spectra of TPE-EP-dopped PLLA (α crystal form) at different crystallinities.Excitation wavelength: 400 nm.(H) Plots of the estimated crystallinity versus the emission maximum with linear fit relationships.(I) One-dimensional correlation function curves of PLLA α and δ crystal forms, which are calculated from their Lorentz-corrected small-angle X-ray Scattering (SAXS) curves.
• C min −1 under a nitrogen atmosphere.SAXS characterizations were performed on a SAXSessmc2 instrument (Anton Paar).Fluorescence photographs were captured by a Canon EOS 80D camera.PL spectra were recorded using a PTI QM/TM.Fluorescence quantum yield was measured using a Quantaurus-QY C11347-11.Fluorescence and polarizing microscope images were taken on a Nikon EclipseNi-U microscope.Nanoindentation measurements were performed on a Bruker Hysitron TI980 instrument.This work was partially supported by the National Science Foundation of China (51973030, 52127805, 52273031, and 22173017), the Science and Technology Commission of Shanghai Municipality (20JC1414900 and 22511103900), the Shanghai Rising-Star Program (20QA1400100), the China Postdoctoral Science Foundation (2022M710664, 2022M710663, and 2022T150111), the Fundamental Research Funds for the Central Universities (2232021A-06 and 22D210613), "DHU" Distinguished Young Professor Program (LZB2021001) and State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Donghua University.