Mechanical,thermal,and optical properties of yellow fluorescent molecule/polyimide composite films

Abstract

In recent years, polyimides (PIs) with fluorescent properties have attracted special attention. In this study, the yellow fluorescent compound 2-(4-(diphenylamino)benzylidene)malononitrile (Y) was synthesized. Then, a series of yellow fluorescent molecule/polyimide composite films were prepared using 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) and 1,2,3,4-cyclobutane tetracarboxylic dianhydride (CBDA) as the monomers, followed by thermal imidization. To explore the structures and properties, the obtained PI(6FAPB-CBDA)-Y composite films were characterized in detail. The test results showed that as the Y content increased from 0% to 1.2%, the glass transition temperature (T_g) of the PI(6FAPB-CBDA)-Y composite films decreased from 328°C to 308°C, and the tensile strength declined from 119.1 MPa to 78.4 MPa. When the Y ratio reached 1.2%, the PI(6FAPB-CBDA)-1.2Y film exhibited an optimal fluorescence performance, along with excellent stability. Additionally, all the composite films maintained good transparency and were soluble in some polar aprotic solvents. In brief, the PI(6FAPB-CBDA)-Y composite films demonstrate outstanding comprehensive properties, making them suitable for applications in anti-counterfeiting, optoelectronic devices, and smart responsive materials.

Keywords

polyimide composite films fluorescence performance thermal performance mechanical properties

Introduction

Polyimide (PI), as a high-performance polymer material, demonstrates immense application potential in cutting-edge fields such as aerospace, electronic packaging, and membrane separation technology due to its exceptional thermal stability, mechanical strength, dielectric insulation, chemical inertness, and optical transparency.^1–8 In particular, fluorescent polyimides not only retain the superior properties of conventional PIs but also exhibit excellent fluorescence characteristics, enabling their use in advanced applications such as optical anti-counterfeiting labels, novel optoelectronic display devices, and high-sensitivity sensors.^9–14 By rationally designing the molecular structure and incorporating specific fluorescent groups into the polyimide backbone or side chains, people can endow the polyimide with unique fluorescence properties.^13,15–17 For instance, Yu et al.¹⁸ synthesized a hyperbranched tetra-phenylethylene (TetraPE)-based fluorescent PI. The distorted TetraPE structure and semi-aromatic dianhydride monomer effectively suppressed the charge transfer (CT) effect, resulting in enhanced PL emission in the solid film with a light-yellow fluorescence peak at 535 nm. Qu et al.¹⁹ developed two diamine monomers TPCDA and TPNDA containing pendant triphenylamine (TPA) groups, which were polymerized with two dianhydrides to form four PI films. Due to the aggregation induced emission (AIE) phenomenon, two diamines demonstrate intense emission at 395 and 447 nm, respectively. Moreover, the TPCDA-based PI films exhibited bright orange photoluminescence at 565 nm and 585 nm, respectively.

At present, the development and application of fluorescent polyimides are still in the laboratory research stage due to complex synthesis processes and high costs. The preparation of polyimide composite film by compositing with fluorescent substances is a simple and feasible method. Researchers have reported some polymer composite films with fluorescent properties.^20–22 Fluorescent small molecules (e.g., fluorescent dyes) or nanoparticles (e.g., quantum dots) can be incorporated into the polymer matrix through in-situ polymerization or direct blending methods, followed by thermal treatment to form fluorescent polyimide composites.^23–25 The fluorescence properties of the resulting films can be flexibly tuned by varying the type and concentration of the fluorescent additives.^19,26,27 For example, Khalid et al.²⁸ synthesized mesoporous silica (mSiO₂) and diatomite particles with CdS quantum dots and carbon quantum dots (CDs) and blended them into polyimide derived from pyromellitic dianhydride (PMDA) and 4,4′-diaminodiphenyl ether (ODA) as monomers. The mechanical properties of the composite film deteriorate as the content of the inorganic component increases. Furthermore, the luminescence performance of PI/mSiO₂@CdS@CDs is 7.6 times that of PI/diatomite@CdS@CDs. In another study, Hang et al.²⁹ developed yttrium oxide (Y₂O₃) with fluorescent characteristics and embedded it into polyimide films. The introduction of Y₂O₃ not only endowed the films with fluorescence but also enhanced their thermal stability while maintaining mechanical integrity. The composite films exhibited a glass transition temperature (T_g) of approximately 300°C and a tensile strength exceeding 85 MPa, surpassing industry application standards.

For composite materials, uneven component dispersion and poor interfacial compatibility can significantly affect various properties of the composite material.^28–30 Compared with inorganic functional particles, organic fluorescent molecules demonstrate better compatibility with polymer matrix. However, the high-temperature processing required for polyimide synthesis imposes stringent thermal stability requirements on the fluorescent compounds to ensure their structural integrity within the polymer matrix. Furthermore, the inherent chemical structure of the polyimide matrix plays a crucial role in determining the optical properties of the final composite.^31–33 Notably, colorless and transparent polyimide film used as the matrix is more attractive because of reducing charge transfer (CT)³⁴ effects.^35–37 It is worth noting that the introduction of organic small molecules can also change the aggregation state of large molecular chains, which has a significant impact on the structure and properties of composite materials. Therefore, the balance between various performance factors needs to be carefully considered.

Herein, we synthesized a yellow fluorescent compound 2-(4-(diphenylamino)benzylidene)malononitrile (Y) with aggregation-induced emission (AIE) characteristic. Subsequently, polymerization reaction was carried out using 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) and 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) as monomers to obtain a poly(amic acid) (PAA) solution. Different proportions of compound Y were then added to the PAA solution, which were uniformly mixed and cast on a clean glass plate. Next, thermal imidization was performed to prepare the PI(6FAPB-CBDA)-Y composite films. The rigid and bulky tristyrene structure and highly polar -CN group endow compound Y with excellent thermal stability. Meanwhile, the alicyclic structure of dianhydride monomer CBDA can more effectively prevent charge transfer (CT) and reduce the occurrence of non-radiative transitions. The resulting yellow fluorescent molecular/PI composite films exhibited excellent mechanical properties, thermal stability, fluorescence performance, transparency, and solubility. This study provides a simple and feasible approach for developing functional PI film materials.

Experimental section

Raw materials

2-(4-(Diphenylamino)benzylidene)malononitrile (Y) was synthesized according to the literature.³⁸ 1,4-Bis(4-aminophenoxy-2-trifluoromethyl)benzene (6FAPB) was bought from China Tech (Tianjin) Chemical Co., Ltd. 1,2,3,4-Cyclobutanetetracarboxylic dianhydride (CBDA) was purchased from Liaoning Oxiran Huahui New Material Co., Ltd. (China). N,N-Dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), and tetrahydrofuran (THF) were obtained from the National Pharmaceutical Group Chemical Reagent Co., Ltd. (China).

Preparation of PI(6FAPB-CBDA)-Y composite films

The 2.142 g (5.000 mmol) of 6FAPB was weighed and poured into a 250 mL of two-necked flask. Then, 17.000 g of DMAc was weighed into a bottle and dissolved by mechanically stirring. After 30 min, 0.981 g (5.000 mmol) of CBDA was slowly added to the flask. The mixture was continuously stirred for 10 h in an ice-water bath to form a light-color and viscous poly(amic acid) (PAA) solution. Subsequently, a certain amount of Y compound was added and stirred for another 3 h under ultrasonic treatment to yield a Y-containing PAA solution. The mixed solution was cast onto a clean glass plate, pre-treated on a 60°C hot plate, and then subjected to stepwise heating in a far-infrared drying oven with the following temperature program: 80°C to 120°C (held for 10 min), 120°C to 160°C (held for 10 min), 160°C to 200°C (held for 10 min), 200°C to 240°C (held for 10 min), and finally 240°C to 290°C (held for 15 min). After natural cooling, the PI(6FAPB-CBDA)-Y composite films were released from the glass substrate. According to the Y concentration, including 0%, 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, and 1.2%, the PI(6FAPB-CBDA), PI(6FAPB-CBDA)-0.05Y, PI(6FAPB-CBDA)-0.1Y, PI(6FAPB-CBDA)-0.2Y, PI(6FAPB-CBDA)-0.4Y, PI(6FAPB-CBDA)-0.6Y, and PI(6FAPB-CBDA)-1.2Y samples were prepared. The preparation route of PI(6FAPB-CBDA)-Y composite films is illustrated in Scheme 1.

Characterization

The number-average molecular weight (M_n) and weight-average molecular weight (M_w) of the polymer were measured using a Waters E2695 gel permeation chromatograph (GPC, USA). The chemical structures of the PI composite films were characterized using a Nicolet iS10 Fourier-transform infrared spectrometer (FT-IR, USA) with a wavenumber range of 500–4000 cm⁻¹. Mechanical properties were evaluated by testing the strain-stress curves on a HY-0580 tensile testing machine (Shanghai Hengyi, China) at room temperature (22°C–26°C). The film specimens were cut into strips with dimensions of 7 cm in length and 1 cm in width (gauge length: 5 cm), and the tensile speed was 10 mm/min. Thermal stability was investigated by using a Netzsch STA 449F3 simultaneous thermal analyzer (TGA, Germany) under N₂ atmosphere (50 mL/min) with a heating rate of 10°C/min from room temperature to 800°C. Furthermore, glass transition temperatures (T_g) were explored by examining the tanδ-T curves of the PI(6FAPB-CBDA)-Y composite films on a PerkinElmer DMA 8000 dynamic mechanical analyzer (DMA, USA) under N₂ purge (80 mL/min) at a heating rate of 10°C/min and frequency of 1 Hz over a temperature range of 50°C–400°C. Optical performance was investigated by recording the light transmittance at a wavelength range of 200–800 nm using a PerkinElmer Lambda-750S UV-vis spectrophotometer (USA). Solid fluorescence properties of both Y compound and PI(6FAPB-CBDA)-Y composite films were characterized with an FS5 fluorescence spectrometer (Edinburgh Instruments, UK) at ambient temperature. The attenuation rate of fluorescence intensity is calculated according to formula (1).

Attenuation rate = \frac{I_{0} - I_{t}}{I_{0}} \times 100 %

(1)

Among them, I₀ is the initial fluorescence intensity, and I_t is the intensity at time t. In addition, the microstructures of the PI(6FAPB-CBDA)-Y composite films were determined using a Bruker D8 X-ray diffractometer (XRD, Germany) at a scanning range of 2θ = 10–80°. The chain spacing d value was calculated, according to Bragg’s law nλ = 2dsinθ (λ = 0.154 nm, n = 1).

Results and discussion

Performance characterization of compound Y

Initially, the optical properties of 2-(4-(diphenylamino)benzylidene)malononitrile (Y) were measured by a solid-state fluorescence test, as shown in Figure 1(a). Clearly, its optimal excitation wavelength was 500 nm, while the maximum emission wavelength appeared at 590 nm (yellow color). Subsequently, thermal stability testing of compound Y was conducted, and the obtained TGA and DTG curves are presented in Figure 1(b). The results demonstrate that during heating, the primary weight loss occurs predominantly at 380°C, mainly attributed to chemical bond cleavage. Thus, the compound Y exhibits favorable thermal stability and fluorescence characteristics.

Structures of PI(6FAPB-CBDA)-Y composite films

The M_n and M_w of the pure PI(6FAPB-CBDA) were obtained as 83,974 and 111,085 g/mol, respectively, and the polydispersity index (PDI) was approximately 1.32. High molecular weight means that the molecular chains of PI are long and prone to entanglement between them. Narrow distribution indicates that the length of molecular chains is relatively close and there are fewer internal defects. Figure 2 presents the FT-IR spectra of PI(6FAPB-CBDA)-Y composite films to determine their chemical structures. Two characteristic absorption peaks are observed at approximately 1782 cm⁻¹ and 1713 cm⁻¹, corresponding to the asymmetric and symmetric stretching vibrations of C=O in the imide ring, respectively. Additionally, the special peak at 1370 cm⁻¹ is typically attributed to the C-N stretching vibration within the imide ring. The appearance of these characteristic peaks confirms the successful formation of imide ring structures in the polymer backbone.^39–42 Since the incorporated Y content is minimal, the FT-IR spectra of PI(6FAPB-CBDA)-Y composites remain essentially consistent with the pure PI(6FAPB-CBDA).

XRD analysis was employed to investigate the microstructures of the PI(6FAPB-CBDA)-Y composite films, and the d values were determined using Bragg’s law. As shown in Figure 3, the XRD patterns exhibit a broad diffraction peak, indicating that all PI(6FAPB-CBDA)-Y composite films possess an amorphous structure. Calculations based on Bragg’s law reveal that the d value of PI(6FAPB-CBDA)-Y composites is slightly larger than that of the pristine PI(6FAPB-CBDA) film without Y fluorescent molecules (2θ = 16.22°, d = 0.546 nm). Moreover, the d relatively increases with the increase of Y concentration. This increase is primarily attributed to the incorporation of fluorescent molecules, which disrupts the tight packing of PI polymer chains and expands the interchain distance.⁴⁰

Mechanical properties of PI(6FAPB-CBDA)-Y composite films

Figure 4 demonstrates the stress-strain curves of PI(6FAPB-CBDA)-Y composite films, and the corresponding mechanical properties are summarized in Table 1. The flexible ether linkages in 6FAPB contribute to high elongation at break, while the cyclobutane structure in CBDA imparts chain rigidity that maintains good tensile strength. As the Y content increases from 0% to 1.2%, the mechanical properties exhibit a gradual deterioration. The tensile strength decreases from 119.1 MPa to 78.4 MPa, with elongation at break ranging between 8.0% and 15.3%. This reduction likely results from the Y fluorescent molecules disrupting the regular packing and tight entanglement of polyimide chains and weakening intermolecular interactions. Moreover, due to the gradual aggregation of fluorescent molecules, non-uniform dispersion is formed, thereby compromising the mechanical performance of PI(6FAPB-CBDA)-Y.^41,42

Table 1.

Thermal and optical properties of PI(6FAPB-CBDA)-Y composite films.

Samples	Thickness (μm)	T_g (°C)	Tensile strength (MPa)	Broken elongation (%)	T₅₀₀ (%)
PI(6FAPB-CBDA)	50	328	119.05 ± 3.0	15.3 ± 0.2	88.1
PI(6FAPB-CBDA)-0.05Y	50	327	108.37 ± 2.0	16.2 ± 0.2	84.7
PI(6FAPB-CBDA)-0.1Y	49	325	102.82 ± 3.0	10.1 ± 0.1	83.9
PI(6FAPB-CBDA)-0.2Y	49	317	98.75 ± 2.0	17.1 ± 0.1	77.3
PI(6FAPB-CBDA)-0.4Y	50	311	93.91 ± 2.0	12.8 ± 0.1	65.4
PI(6FAPB-CBDA)-0.6Y	50	309	90.37 ± 2.0	7.8 ± 0.1	52.6
PI(6FAPB-CBDA)-1.2Y	48	308	78.38 ± 2.0	7.9 ± 0.2	17.8

Note. T₅₀₀, transmittance at 500 nm.

Thermal performance of PI(6FAPB-CBDA)-Y composite films

To evaluate the thermal properties of the composite films, TGA and DMA tests were conducted. Figure 5(a) shows the TGA and DTG curves of PI(6FAPB-CBDA)-Y composite films. During heating, the initial decomposition temperature is approximately 400°C, with the major weight loss occurring around 500°C, primarily attributed to the thermal decomposition of the PI polymer backbone.⁴³ When compared with conventional aromatic PIs, these PI(6FAPB-CBDA)-Y composite films display relatively lower thermal decomposition temperatures. This is predominantly attributed to the somewhat diminished thermal stability of the alicyclic structure derived from the CBDA monomer, which has inherent structural features that make it less resistant to thermal degradation.³⁷ Furthermore, the thermal degradation process of the PI(6FAPB-CBDA)-Y composites shows no significant changes compared to the pristine PI(6FAPB-CBDA), indicating that the incorporation of small amounts of Y does not substantially alter the thermal decomposition behavior of the macromolecular chains.

Figure 5(b) presents the tanδ-T curves of PI(6FAPB-CBDA)-Y composite films. During heating, the polymer film transitions from the glassy state to the rubbery state, exhibiting a distinct tanδ peak whose corresponding temperature represents the glass transition temperature (T_g).⁴⁴ As shown in Table 1, the T_g values of the PI(6FAPB-CBDA)-Y composite films decrease from 328°C to 308°C as the Y content increases from 0% to 1.2%. This reduction primarily results from the fluorescent small molecules disrupting the ordered arrangement of PI macromolecular chains and weakening intermolecular interactions, thereby facilitating chain segment mobility.⁴⁵ In addition, the gradual widening of the tanδ peak in dynamic mechanical analysis suggests heterogeneous viscoelastic behavior, which may arise from aggregation of fluorescent molecules and/or weak interfacial interactions between the aggregated fluorescent molecules and the polymer matrix. Therefore, the strain-stress and tanδ-T curves indicate that the dispersion of fluorescent molecules changes from uniform to non-uniform with increasing addition amount.

Optical performance of PI(6FAPB-CBDA)-Y composite films

Fluorescence performance tests were carried out on the PI(6FAPB-CBDA)-Y composite films, as illustrated in Figure 6. Owing to the incorporation of Y, the fluorescence intensity of the PI(6FAPB-CBDA)-Y composite films is significantly enhanced compared to that of the pure PI(6FAPB-CBDA) sample. This result indicates that the fluorescent compound Y is relatively stable during the preparation process of the composite films, without significant thermal decomposition. Moreover, as the concentration of Y increases from 0% to 1.2%, the fluorescence intensity shows an upward trend. Specifically, when excited at 410 nm, the PI(6FAPB-CBDA)-1.2Y sample shows the highest fluorescence intensity. Moreover, as the concentration of Y increases, the intermolecular interaction among small fluorescent molecules is enhanced. The aggregation of fluorescent molecules significantly increases the fluorescence intensity of composite films and exhibits inherent AIE characteristics. Simultaneously, the interactions between the PI macromolecular chains are weakened. These changes lead to a red shift of the emission wavelength, but all emissions still fall within the yellow light region.⁴⁵ As shown in Figure 6(a), the pristine PI(6FAPB-CBDA) film exhibits emission wavelengths between 500 and 520 nm, corresponding to a green color in theory, but the fluorescence intensity is very low. In Figure 6(b) and (c), when the concentration of Y compound is 0.05% and 0.1%, the maximum emission wavelength is 546 nm and 548 nm, respectively. When the Y content reaches 0.2%, the emission wavelength is 550 nm, the fluorescence color is yellow-green, as shown in Figure 6(d). At higher doping levels of 0.6 and 1.2%, intensified intermolecular interactions among the Y molecules induce further color evolution. The emission wavelengths appear at 568 nm and 598 nm, so the PI(6FAPB-CBDA)-0.6Y and PI(6FAPB-CBDA)-1.2Y films exhibit distinct yellow fluorescence under UV illumination (Figure 6(e) and (f)).

Figure 7(a) and (b) shows the images of PI(6FAPB-CBDA)-Y composite films under natural light and UV light. It is obvious that in visible light, the film sample is transparent, but the color shifts from nearly colorless to yellow as the concentration of Y components in the film increases. Under UV light, the visual color transforms from blue through white (blue and yellow) to yellow due to the activation of specific Y fluorescent substances in the film. These results indicate that even if the content of Y is relatively low, the fluorescence characteristics of the composite films are very obvious. This is consistent with the result in Figure 6.

The fluorescence stability of the PI(6FAPB-CBDA)-1.2Y sample was investigated through isothermal treatments at various temperatures for 30 min. As depicted in Figure 8(a) and (b), the sample exhibits no significant changes in fluorescence intensity after thermal treatment at 20°C–300°C, but shows a small decrease after treatment at −40°C, with an attenuation rate of 3.3%. Furthermore, long-term fluorescence stability tests were conducted by placing the sample under room temperature and natural light for 200 days (Figure 8(c)). Based on the calculations of fluorescence intensity data, the attenuation rate has reached 7.0% after 200 days, indicating exceptional performance stability. Furthermore, under UV light, the PI(6FAPB-CBDA)-Y composite films still demonstrate significant fluorescence characteristic when placed on a hot-plate at 100°C, 200°C, and 300°C, as depicted in Figure 8(d). These results confirm that the PI(6FAPB-CBDA)-Y composite films possess outstanding optical stability, making them suitable for applications at high-temperature conditions.

The UV-visible spectra of the PI(6FAPB-CBDA)-Y composite films are presented in Figure 9, and the light transmittance at 500 nm is listed in Table 1. The pristine PI(6FAPB-CBDA) film exhibits particularly good transparency in the visible light region (400–700 nm), with a cutoff wavelength of 302 nm and a transmittance of 88.1% at 500 nm. The steric hindrance effect of -CF₃ groups in 6FAPB can effectively suppress intermolecular charge transfer complex (CTC) formation, while the alicyclic structure in CBDA can reduce the conjugation effect, thereby achieving colorless and transparent characteristics.⁴⁶ As the concentration of Y increases, these composite films demonstrate a gradually increasing UV absorption, leading to a decline of light transmittance at 500 nm and an increase of cutoff wavelength.⁴⁷ When the proportion of Y is 1.2%, the optical transmittance of the PI(6FAPB-CBDA)-1.2Y sample at 500 nm dramatically drops to 17.8% and the cutoff wavelength reaches about 465 nm. Thus, to maintain the light color and transparent properties of the PI film, the amount of compound Y added should be appropriate.

Solubility of PI(6FAPB-CBDA)-Y composite films

The solubility tests were carried out in several solvents. As summarized in Table 2, the PI(6FAPB-CBDA)-Y composite films demonstrate good solubility in polar aprotic solvents (DMF, DMSO, DMAc, and NMP), with limited solubility in ethyl acetate and THF upon heating. This excellent dissolution behavior originates from two key structural features: (1) The -CF₃ groups in the 6FAPB diamine monomer create substantial free volume and increase interchain spacing within the polymer matrix; (2) The flexible ether linkages in 6FAPB improve chain mobility and conformational flexibility, thereby facilitating solvent molecule diffusion.^48,49 These PI(6FAPB-CBDA)-Y composite films with excellent solubility overcome the limitations of traditional PI materials that are notoriously difficult to dissolve and demonstrate significant advantages in material processing and functional design.

Table 2.

Solubility of PI(6FAPB-CBDA)-Y composite films.

Sample/Solvent	DMF	DMAc	DMSO	NMP	Ethyl acetate	THF	Ethanol
PI(6FAPB-CBDA)	++	++	++	++	+-	+-	--
PI(6FAPB-CBDA)-0.05Y	++	++	++	++	+-	+-	--
PI(6FAPB-CBDA)-0.1Y	++	++	++	++	+-	+-	--
PI(6FAPB-CBDA)-0.2Y	++	++	++	++	+-	+-	--
PI(6FAPB-CBDA)-0.4Y	++	++	++	++	+-	+-	--
PI(6FAPB-CBDA)-0.6Y	++	++	++	++	+-	+-	--
PI(6FAPB-CBDA)-1.2Y	++	++	++	++	+-	+-	--

Solubility test: 1 mg PI(6FAPB-CBDA)-Y sample in 10 mL solvent; ++: completely soluble at room temperature, +: soluble upon heating, +-: partially soluble upon heating, --: insoluble even with heating.

Conclusions

In this study, a yellow fluorescent compound 2-(4-(diphenylamino)benzylidene) malononitrile (Y) was firstly synthesized. Then, the PI(6FAPB-CBDA)-Y composite films were prepared through polymerization of 6FAPB and CBDA monomers, followed by blending with varying concentrations of compound Y and thermal imidization. With the increase in Y content from 0 to 1.2%, fluorescent molecules gradually aggregated, thereby leading to a decrease in the tensile strength of the PI(6FAPB-CBDA)-Y composite films from 119.05 MPa to 78.38 MPa. Meanwhile, the glass transition temperature (T_g) dropped from 328°C to 308°C. With the increase of the Y content, the fluorescence intensity of the PI(6FAPB-CBDA)-Y composite film significantly increased. When the Y concentration reached 1.2%, the fluorescence intensity of PI(6FAPB-CBDA)-1.2Y was the highest. After high/low temperature treatment or long-time placement, these composite films showed excellent fluorescence stability. As the Y content increased from 0 to 1.2%, the color of the composite film gradually deepened, and the light transmittance at 500 nm decreased from 88.1% to 17.8%. Moreover, these composites exhibited good solubility in some organic solvents. Therefore, by regulating the concentration of compound Y, the as-prepared PI(6FAPB-CBDA)-Y composite film materials can emit fluorescence in various colors (blue-white-yellow) and maintain excellent transparency, remarkable mechanical properties, and outstanding thermal properties, which can be applied in certain special optical fields.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The present research work was supported by the National Natural Science Foundation of China (22278051) and CNPC Innovation Found (2022DQ02-0608).

ORCID iD

Yunhua Lu

Data Availability Statement

Data will be made available on request.

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