English

• Recently, complementary metal-oxide-semiconductor (CMOS) image sensors have garnered significant attention due to their potential applications across various next-generation industrial fields, including autonomous vehicles, medical imaging, machine vision, security, virtual reality, and augmented reality. The color-film technology utilized in CMOS image sensors demands increasingly finer pixel sizes and higher contrast ratios to produce high-quality, realistic images [1-5]. Traditionally, the pigment dispersion method has been the most widely employed technique for fabricating color films, owing to the high thermal-, chemical-, and light-stability of pigments. However, this method faces persistent challenges by the low solubility of pigments, commonly leading to light scattering by aggregated particles and bad contrast ratios of image sensors [6-9]. To resolve these problems, dye-based color films have been explored as an alternative. The higher solubility of dyes in solvents effectively prevents light scattering caused by particle aggregation, thereby improving the transmittance of the color film and enhancing image brightness [10-16]. Among synthetic dyes, azo dyes are the most widely used class of synthetic dyes with great solubility in industrial solvent and high extinction coefficients which could contribute to achieve finer pixel sizes, high brightness, as well as higher contrast ratios [12-16]. However, a significant drawback of azo dyes is their generally inadequate thermal and light stability due to the high density of electron cloud on the azo bond [14-17]. Furthermore, molecular isomerization of azo dyes, which can induce severe molecular torsion, frequently occurs in the ground state, leading to compromised thermal and light stability. These limitations significantly restrict the application of azo dyes in color films.

  Various strategies have been investigated to enhance the stability of azo dyes. For example, introducing electron-withdrawing groups such as -CN, -NO₂, and -COOH into the azo parent structure could significantly reduce the electron cloud density of azo dyes, thereby inhibiting oxidation and thermal degradation during the baking process of color film preparation [15,16,18-23]. Additionally, complexes formed from pyridone-based azo dyes have found application in optical recording layers, where they exhibit enhanced light stability along with good thermal and light stability [18-24]. However, the use of metal complex dyes limits the overall performance of color films [28-33]. Recently, the exceptional light stability of dyes containing pyrazolone groups has attracted considerable attention [17,24-27]. Consequently, designing highly thermally stable azo dyes with pyrazolone groups has emerged as a promising strategy for achieving dyes and dye-based color films with improved thermal and light stability.

  Herein, a series of azo dyes were designed by selecting 5-methyl-2-phenyl-4-(2-phenylhydrazo)−2,4-dihydro-3H-pyrazol-3-one, a heterocyclic structure that could endow azo dyes good light stability as mentioned above, as the coupling component. Notably, arylazo pyrazolone dyes are prone to azo-hydrazo tautomerism, while the formation of stable hydrazo form is generally depends on the intramolecular hydrogen bond interactions. The designed azo dyes’ structures were simulated, and the effects of intramolecular hydrogen bonding on the molecular dihedral angle and the vertical axial bulkiness of the azo dyes were theoretically analysed. Based on the results, the designed azo dyes were synthesized with the purpose of studying the correlation between the intramolecular hydrogen bonding and hydrazo isomer formation and the thermal stability. The mechanism of thermal stability for the target azo dyes was further revealed at the molecular engineering level through insights from ultraviolet–visible (UV–vis) absorptions spectra and time-depending infrared correlation analysis [34-42]. As a validation of the design concept, the color films based on the synthesized dyes were prepared using a spin-coating process and the related properties were studied to achieve the improvements in thermal stability, light stability, solubility, and solvent resistance of azo dyes in color films simultaneously.

  To develop ultra-highly thermal stable dye-based color films, a series of different azo derivatives were designed by applying 5-methyl-2-phenyl-4-(2-phenylhydrazono)−2,4-dihydro-3H-pyrazol-3-one as hydrogen bonding maker in Fig. 1a. One of the most interesting features regarding arylazo pyrazolone dyes is the possible occurrence of azo-hydrazone tautomerism, and the hydrazo form is generally more stable due to the generation of stable six-membered ring by intramolecular hydrogen bonding and the introduction of the electron-withdrawing groups (NO₂, CN, Br) (Table S1 in Supporting information) which reduces the electron cloud density (ECD) and further stabilizes the hydrogen bonded structure [19-24,43,44]. Thus, the hydrazo structure with intramolecular hydrogen bonding were optimized and electrostatic potential surface by density functional theory (DFT) to predict the thermal stability of the designed dyes [24,31,32]. As is shown in Fig. 1a, the existence of intramolecular hydrogen bonding between N—H and C=O increases the planarity of P-1–P-5, restricts the azo- hydrazone tautomerism, strongly stabilizes hydrazo isomers, which may lead to improve the thermal stability of dyes [25-33]. As is shown in Fig. 1b, there is no intramolecular hydrogen bonding in P-6, the dihedral angle of the plane of 2,6-dibromo-4-nitrophenyl to the azo bond plane (64.10°), leading to the low planarity of the molecules, which may result in the worst thermal stability [4,33]. Furthermore, the molecular bulkiness of P-1–P-5 with pyrazolone group (~3.00 Å) stabilized by hydrogen bonding is lower than that of P-6 (6.18 Å), the low bulkiness of a molecule would increase intermolecular interactions and thus enhance the thermal stability of molecules [33,44]. The electrostatic potential surface of the hydrazo structure stabilized by intramolecular hydrogen bonding was calculated to further predict the stability of the designed azo dyes in Fig. 1c. Compared to the negative charge value for P-1 (−0.0024) without electron-withdrawing groups, the charge value of the center of azo bond for the other five dyes (P-2–P-6) with electron-withdrawing groups is close to 0. As the number of substituted electron-withdrawing groups increases, the charge values of dyes change from negative to positive. These are attributed to the fact that strong induced effect by the electron-withdrawing groups reduced the ECD of azo bond in the molecules, which further inhibits the oxidization of the molecules. Altogether, the P-2, P-3, P-4 and P-5 theoretically show better thermal stability than P-1 and P-6 due to the introduction of intramolecular hydrogen bonding and institution of electron-withdrawing groups.

  Figure 1

  

  Figure 1.  Molecular structure analysis of synthesized azo dyes. (a) The molecular structures of six dyes. (b) Optimized structures (TPSSh.S0.ESA (d, p) of the six designed dyes. (c) Electrostatic potential surface maps of the six dyes. H-bond: hydrogen bonding.

  DownLoad: Full-Size Img PowerPoint

  Afterwards, to verify the feasibility for the designed dyes, the six dyes were synthesized (Scheme S1 in Supporting information), their comprehensive details for structure characterization (Fourier transform infrared (FTIR) spectrum, ¹H NMR spectrum, and mass spectrum) are shown in Figs. S1–S18 (Supporting information). Among the characterization, spectral data (FTIR and NMR) of dyes P-1–P-5 suggest the existence of azo-hydrazone tautomerism in the solid state and in the CDCl₃ solution. The UV–vis absorbance spectra of azo dyes P-1–P-6 at different pH values in methanol solutions, which is often used as a common solvent for the detection of azo-hydrazone isomerism were measured to further confirm the main structure of the six synthesized dyes (Fig. S19a in Supporting information) [27,43-47]. The methanol solution of P-1, showed two distinct absorption peaks located at 402 nm, which were attributed to the π-π* transitions between the pyrazole ring and the phenyl ring in the hydrazo tautomer [47,48]. Another weak peak was observed near 368 nm, which corresponded to the π-π* transition between the pyrazole ring and the phenyl ring in the azo isomer [48]. While, for P-6, there is only one peak at 450 nm (Fig. S19b in Supporting information), reflecting the fact that P-6 always keeps in azo structure. After adding ammonia to P-1 methanol solution to finely adjust the pH value, the strength of absorption peaks of P-1 spectrum at 402 and 368 nm changes accordingly, namely, the former is weakened and the latter is enhanced. It is concluded that there is a “hydrazo ⇌ azo” tautomeric equilibrium in solution and the hydrazo isomers of P-1 are dominating under neutral pH conditions [49,50]. However, the absorption peak shape of P-6 remains unchanged at different pH, which demonstrates that P-6 keeps in the azo structure. Moreover, the UV–vis absorbance spectra of P-2–P-5 in different pH environments are similar to P-1. Thus, based on the above results, P-1–P-5 mainly exists in hydrazo form while P-6 keep in azo form.

  To investigate the thermal stability of the six dyes, the thermal decomposition temperature (T_d) (Fig. 2a), and the changes in mass loss of the dyes at 230 ℃ for 30 min (the general manufacturing temperature of transparent color films is 230 ℃) were measured to investigate the thermal stability of six dyes and the results are shown in Fig. 2b. The decomposition temperature (T_d) values of P-1, P-2, P-3, P-4, P-5 and P-6 were 222, 275, 275, 250, 270 and 220 ℃, respectively (Table S2 in Supporting information), which indicated that the dyes P-2–P-5 have higher thermal stability than P-6. This may attribute to the high planarity caused by the intermolecular hydrogen bonding between N—H and C=O in dyes (P-2–P-5) which led to high crystallinity and outstanding intermolecular forces. Consequently, the energy of the excited state was converted into heat energy by energy transfer between molecules, thereby improving the antioxidant energy of the derivative molecule [44]. As a result, the improvement of molecular planarity could strengthen the stability to thermal degradation [11]. In addition, the occurrence of the intermolecular hydrogen bonding prevents the transformation of hydrazo isomer to azo isomer and stabilized the hydrazo isomer, which further improve the thermal stability of dyes. Notably, the T_d of P-1 without electron-withdrawing is higher than that of P-6 substituted by electron-withdrawing groups, this further demonstrated that the introduction of the intermolecular hydrogen bonding contributed to the improvement of dyes’ thermal stability. Furthermore, the mass loss of P-1 and P-6 at 230 ℃ for 30 min is more than 8.00 wt% (Fig. 2c), indicating a thorough decomposition process of P-1 and P-6, while the mass losses of P-2, P-3, P-4, P-5 are less than 5.00 wt%, which could further indicate that the dyes P-2–P-5 has higher thermal stability than P-6 due to the high planarity caused by the intermolecular hydrogen bonding. P-1 has worse thermal stability due to the much high ECD in azo bond which make it easier to be oxidized than the other four dyes, it is align with above DFT results. Thus, referring to the thermal stability requirements of commercial filters (mass loss should not exceed 5.00 wt%), dyes P-2, P-3, P-4, and P-5 have great thermal stability and are suitable to make for color films.

  Figure 2

  

  Figure 2.  TGA analysis of the synthesized dyes. (a) Dyes were heated to 500 ℃, (b) dyes were heated to 230 ℃ and held in this temperature for 30 min, then heated to 300 ℃, (c) the mass loss of the synthesized dyes heated to 230 ℃ for 30 min.

  DownLoad: Full-Size Img PowerPoint

  The preceding characterizations have highlighted the critical role of intramolecular hydrogen bonding of hydrazo isomers in the thermal stability. To substantiate this hypothesis, the FTIR spectra and ¹H NMR were used to confirm the occurrence of the intramolecular hydrogen bonding in hydrazo form [30]. The infrared spectra of P-2, P-3, P-4, and P-5 at 25 ℃ were shown in Fig. 3a. The peaks of ~3440 and ~1668 cm⁻¹ are attributed to the N—H and C=O stretching vibration peaks of the bonding, which demonstrated that there is an intramolecular hydrogen bonding between P-1 and P-5 at 25 ℃ [19]. The stretching vibration peaks of the N—H of P-4 are red-shifted to 3336–3150 cm⁻¹, which is significantly lower than in the case of the corresponding analogues forming a single intramolecular hydrogen bond (~3440 cm⁻¹) and the C=O stretching vibration peaks of P-4 are shifted to ~1707 cm⁻¹ compared with those of P-2, P-3, and P-5 (~1668 cm⁻¹), thus suggesting that intramolecular crossed hydrogen bonds may be formed in the P-4 molecule [19,31]. In addition, the ¹H NMR spectra of the six dyes are shown in Fig. S20 (Supporting information), with the hydrogen proton peak (α-position) of the hydrazo form N—H of P-2 at the chemical shift of 13.7 ppm, and the same pattern is also shown for P-3 and P-5, the chemical shift of N—H in P-4 is shifted to the lower field, i.e., from 13.5 ppm to 14.3 ppm, due to the hydrogen bonds between NO₂ and N—H, and the competing effect of hydrogen bonds between carbonyl and N—H [47]. Thus, the results of ¹H NMR reaffirm the formation of intramolecular hydrogen bonding in P-2, P-3, P-4, P-5. The existence of intramolecular hydrogen bonds between N—H and C=O not only increase the planarity of molecules but also decrease the bulkiness of a molecule, resulting in the dyes with great thermal stability [33].

  Figure 3

  

  Figure 3.  The structural characterize of the synthesized azo dyes. (a) The FTIR spectra and structure of the designed azo dyes P-2–P-5 measured at 25 ℃. (b) Schematic illustration for the azo-hydrazone tautomerism of P-2. (c) Temperature-dependent FTIR spectra of P-2 in the N—H and C=O vibration regions acquired during heating. (d) Synchronous and asynchronous 2D COS derived from the stretching peak of the N—H group of P-2 during heating. (e) Synchronous and asynchronous 2D COS derived from the stretching peak of the C=O on the 1D FTIR spectra of P-2 during heating. (f) Synchronous and asynchronous 2D COS derived from the bending peak of the N—H group of P-2 during heating.

  DownLoad: Full-Size Img PowerPoint

  We also employed temperature-variable FTIR spectroscopy to evaluate the thermal sensitivities of the internal interactions in dyes to detect different state of hydrazo molecules (Figs. 3b–f) [24,32-35]. Taking P-2 as an example (Fig. 3c), with increasing temperature from 50 ℃ to 150 ℃, the spectral intensities of all the hydrogen bonded groups declined, while those of free groups increased, suggesting the heat-induced dissociation of hydrogen bonds between C=O and N—H. Two-dimensional correlation spectra (2D COS) were further generated to determine the thermal-responsive sequence of all the species. On the basis of Noda's judging rule, with the consideration of both signs in the synchronous and asynchronous spectra (Figs. 3d–f) [31-36], the responsive order of different groups to temperature increase is as follows: ν(N—H) (associated N—H of stable hydrazo isomer for P-2 (Fig. 3b), 3440 cm⁻¹) → ν(N—H) (free N–H of temporary hydrazo isomer for P-2 (Fig. 3b), 3460 cm⁻¹); ν(C=O) (associated, 1650 cm⁻¹) → ν(C=O) (free, 1660 cm⁻¹); δ(N—H) (associated, 1610 cm⁻¹) → δ(N—H) (free, 1505 cm⁻¹), (→ indicates “prior to”), which are consistent with the 1D FTIR results (Fig. 3c). Notably, 2DCOS record different state hydrazo structure (stable hydrazo isomer, temporary hydrazo isomer). This phenomenon is also observed in the spectra of P-3–P-5 (Figs. S21–S23 in Supporting information). Altogether, the response of hydrogen-bond-related species again highlighted the dominant role of hydrogen bonds in regulating molecular structure and the resistance to heat [30,33,36,43-47].

  Based on above results, dyes P-2–P-5 is suitable to prepare the color films. To further verify the photophysical properties feasibility of color film preparation, UV–vis absorption spectra of the synthesized azo dyes in propylene glycol monomethyl ether acetate (PGMEA) which is usually used as the industrial solvent to make for color films were measured. As the spectra shown in Fig. S24 (Supporting information), the λ_max of the dyes P-2, P-3, P-4, P-5 was 399, 390, 401, and 367 nm, respectively, which indicates that P-5 have dull yellow, while the three synthesized azo dyes (P-2, P-3, P-4) exhibit bright yellow color same as in methanol solutions. The absorbance of the synthesized azo dyes in PGMEA maintained the single molecule spectral characteristics at much higher concentration of 50 µmol/L, which indicated that there were few aggregates formed in the solution. Furthermore, the corresponding molar extinction coefficients were calculated based on the Lambert-Beer law, which are larger than 2.0 × 10⁴ L mol⁻¹ cm⁻¹ (Table S3 in Supporting information). Altogether, the photophysical properties of three dyes (P-2, P-3, P-4) are suitable to make for color films [49,50].

  Accordingly, the solubility of dyes was studied by using PGMEA as solvent, and the results are shown in Table S3. The solubility of dye P-4 is the smallest among six dyes (4.2 g/100 g). The solubility of P-2 and P-3 in PGMEA at 25 ℃ was 6.6 and 6.4 g/100 g, respectively, which was greater than 5.0 g/100 g and met the requirement of color film preparation [33,50-52].

  Based on above discussion, representative yellow dyes with ultra-highly thermal stability, great solubility, P-2 and P-3, were selected as the candidates for the preparation of color films. The synthesized dye-based color films constructed from the synthesized azo dyes and polysulfone (PSU) composite were prepared by spin-coating process (Fig. 4a), their optical quality and heat resistance were characterized. C.I. Pigment Yellow 138 (Fig. S25 in Supporting information), a commercial yellow pigment that was usually used as colorant in color-film devices, was selected as reference. The optical microscopy images of the derivative-based PSU composite and C.I. Pigment Yellow 138 color films (concentration: 1.25 wt%) are shown in Fig. 4b. For the same paper, the black characters were observed under normal incident light when two novel color films were placed on that as shown in Fig. 4b. However, the characters were obscured when placed under the commercial pigment-based films due to the multiple scattering caused by pigment particles. This is due to the better dispersion characteristics of the synthesized azo dyes in the PSU compared to the pigments, which avoids optical loss of the color films owing to the scattering effect (Fig. 4c). Additionally, the transmittance of the synthesized dye-based color films (P-2, P-3) exceeds 90% within the 550–780 nm range, significantly higher than that of the C.I. Pigment Yellow 138 based films (67%, Fig. 4d). This result further supports the suitability of dyes P-2 and P-3 for the production of color films with high transmittance [48].

  Figure 4

  

  Figure 4.  Performance analysis of azo dye-based color films. (a) Fabrication of the yellow color films and spin-coated films using the synthesized azo dyes (P-2, P-3) and commercial filter pigment in the same mass fraction (1.25 wt%). (b) The optical image of the color films. (c) Possible diagram of strong internal interactions of dye molecules with polysulfone (PSU). (d) Transmittance of the color films. (e) Transmittance at the range of 550–780 nm of the novel color films before and after baking. (f) Transmission at the range of 550–780 nm of the novel color films before and after irradiation at 365 nm.

  DownLoad: Full-Size Img PowerPoint

  In order to evaluate the thermal stability of the synthesized dye-based color films and pigment-based film, the transmittance spectra of the dye-based color films were measured before and after baking at 230 ℃ for 30 min. As shown in Fig. 4e, the transmittance of P-2 and P-3 dye-based color films between 550 nm and 780 nm remained ~90% before and after baking. The transmittance spectra of P-2 and P-3 dye-based color film keep unchanged, which is similar to the transmittance of commercial pigment-based film (Fig. S26 in Supporting information) [51]. This is because the dyes P-2, and P-3 consist of the heterocyclic structure (5-methyl-2-phenyl-4-(2-phenylhydrazone)−2,4-dihydro-3H-pyrazol-3-one) in the coupling component, which could generate intramolecular hydrogen bonding, form six-membered ring conjugation system in the molecule and increase the planarity of molecules, resulting in the strong intermolecular π-π interaction between dye molecules with phenyl rings of polysulfone, which decrease of migration between dye molecules (Fig. 4c) [27,31,32,52-58]. Thus, P-2 and P-3 are suitable for preparing yellow-colored transparent films because of their high and commercial pigment comparable light stability.

  The color difference (ΔE) was measured before and after baking to further evaluate the thermal stability of the synthesized dye-based color films. As is shown in Table S4 (Supporting information), the color difference values of the dye-based color films P-2 and P-3 were less than 3, with no significant change in the color. This is consistent with the above thermogravimetric analysis (TGA) results. Therefore, the thermal stability of the color films prepared with the dyes P-2 and P-3 meets the requirements of commercial color films [46].

  The light stability of the synthesized dye-based color films (P-2, P-3) and pigment-based film was also evaluated, the transmittance spectra are shown in Fig. 4f. The transmission of color films prepared by the synthesized azo dyes and PSU remained almost unchanged, (Fig. S27 in Supporting information) and with the extension of the exposure time under light emitting diode (LED)-lamp irradiation, the ΔE of the synthesized dye-based color films are less than 3 (Table S5 in Supporting information), which is similar to the result of C.I. Pigment Yellow 138 and difficult to be distinguished with the naked eye. So, the synthesized azo dyes (P-2, P-3) are suitable for preparing yellow films [48].

  To further evaluate the practical application stability of the novel color films, the solvent resistance of the synthesized dye-based color films after immersion in organic solvents with different polarity (petroleum ether, methanol, N,N′-dimethylformamide (DMF) and PGMEA) was further measured (Fig. S28 in Supporting information). After soaking in different organic solvents for five days at 25 ℃, the synthesized dye-based color films keep in yellow (Fig. S28a), and the transmittance of the synthesized dye-based color films varied less than 5% (Fig. S28b). The solubility of the dyes depends on the intermolecular interaction between the dye molecule and the solvent, and the higher the solubility of the dye is, the worse its solvent resistance is. The novel dye-based film (P-2 and P-3) showed great solvent resistant at room temperature (above 90%), this could be attributed to the high planarity of the molecules caused by intramolecular intramolecular hydrogen bonding, resulting in strong intermolecular π-π force between the benzene ring of dyes and the benzene ring in the PSU [27,53-57]. Thus, the P-2 and P-3 dye-based color films have great solvent resistance, meeting with the practical requirement of CMOS image sensor.

  In conclusion, six yellow azo dyes utilizing 5-methyl-2-phenyl-4-(2-phenylhydrazono)−2,4-dihydro-3H-pyrazol-3-one as the coupling component and aromatic amines with various electron-withdrawing groups as diazo components were designed and synthesized. The relationship between the dye structures and their properties has been studied and shown that the presence of intermolecular hydrogen bonding between the hydrogen atom on the N—H group and the oxygen atom of the C=O group of the hydrazo structure facilitates the formation of a stable six-membered ring, strongly increases the planarity of molecules, restricts the azo-hydrazone tautomerism, and the electron-withdrawing groups in the diazo component further stabilize this hydrogen-bonded structure, that is hydrazo isomers, thereby reducing thermal oxidation and degradation of the azo dyes. Consequently, four dyes (P-2, P-3, P-4, P-5) with excellent thermal and light stability (T_d > 260 ℃) were obtained. Among them, the two synthesized dyes (P-2 and P-3) with great bright yellow color (~400 nm), proper solubility (up to 6.00 g/100 g) were selected to make for color films. Their dye-based color films displayed ultra-highly thermal and light stability (T_d > 230 ℃, color difference ΔE < 3). Notably, the increase of molecular structure planarity by hydrogen bonding for the novel dyes balance the high transmittance (>90%) at the range of 550–780 nm) and the solvent resistance of the dye-based color films, showing potential as a replacement for CMOS color films or other organic electronic devices.

  Declaration of competing interest

  The authors declare that they have no known competing financialinterestsor personal relationships that could have appeared to influence the work reported in this paper.

  CRediT authorship contribution statement

  Shi Li: Writing – review & editing, Writing – original draft, Visualization, Validation, Methodology, Investigation, Formal analysis, Data curation. Wenshuai Zhao: Conceptualization. Yong Qi: Formal analysis. Wenbin Niu: Investigation. Wei Ma: Supervision, Methodology. Bingtao Tang: Validation, Methodology. Shufen Zhang: Writing – review & editing, Writing – original draft, Supervision, Resources, Funding acquisition.

  Acknowledgments

  This work is supported by the Program of the National Natural Science Foundation of China (No. 22238002), the Fundamental Research Funds for the Central Universities (No. DUT22LAB610), Research and Innovation Team Project of Dalian University of Technology (No. DUT2022TB10), and China Postdoctoral Science Foundation (No. 2022M720639).

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2024.110653.

  
  
• 1. [1]

     Y. Horie, S. Han, J. Lee, et al., Nano Lett. 17 (2017) 3159–3164. doi: 10.1021/acs.nanolett.7b00636

  2. [2]

     Y. Mao, C. Zhou, C. Wang, et al., Chin. Chem. Lett. 34 (2023) 425–428.

  3. [3]

     W. Peng, Y. Fu, L. Wang, et al., Chin. Chem. Lett. 32 (2021) 2544–2550. doi: 10.1016/j.cclet.2021.01.028

  4. [4]

     W. Ma, X. He, T. Chen, et al., Chin. Chem. Lett. 35 (2024) 109099. doi: 10.1016/j.cclet.2023.109099

  5. [5]

     K. Mishima, K. Matsuyama, H. Ishikawa, K. Hayashi, S. Maeda, Fluid Phase Equilib. 194 (2002) 895–904.

  6. [6]

     C.R. Souza, D.H. Bandoni, A.P.A. Bragotto, et al., Compr. Rev. Food Sci. Food Saf. 22 (2022) 380–407.

  7. [7]

     F.A. Saad, H.A. El-Ghamry, M.A. Kassem, Appl. Organomet. Chem. 33 (2019) 4965–4979. doi: 10.1002/aoc.4965

  8. [8]

     B.K. Jeon, S.H. Jang, S.H. Kim, et al., Opt. Mater. 147 (2024) 114676. doi: 10.1016/j.optmat.2023.114676

  9. [9]

     Y.L. Oon, S.A. Ong, L.N. Ho, et al., Bioresour. Technol. 266 (2018) 97–108. doi: 10.1016/j.biortech.2018.06.035

  10. [10]

      U. Daswani, U. Singh, P. Sharma, et al., J. Phys. Chem. C 122 (2018) 14390–14401. doi: 10.1021/acs.jpcc.8b04070

  11. [11]

      J.W. Namgoong, H.M. Kim, S.H. Kim, et al., Dyes Pigments 184 (2021) 108737. doi: 10.1016/j.dyepig.2020.108737

  12. [12]

      G.F. Pereira, A.E. Ghenymy, A. Thiam, et al., Sep. Purif. Technol. 160 (2016) 145–151. doi: 10.1016/j.seppur.2016.01.029

  13. [13]

      Y. Tian, D. Zhao, C.M. Shu, et al., Process Saf. Environ. 155 (2021) 219–229. doi: 10.1016/j.psep.2021.09.018

  14. [14]

      N. Katsuumi, R. Miyazaki, D. Nakane, et al., J. Mol. Struct. 1285 (2023) 135465. doi: 10.1016/j.molstruc.2023.135465

  15. [15]

      S. Debnath, G. Mohiuddin, S. Turlapati, et al., Dyes Pigments 99 (2013) 447–455. doi: 10.1016/j.dyepig.2013.05.029

  16. [16]

      L. Yu, M.Y. Cao, P.T. Wang, Appl. Environ. Microb. 83 (2017) e00508–17.

  17. [17]

      H.F. Rizk, S.A. Ibrahim, M.A. El-Bora, et al., Dyes Pigments 112 (2015) 86–92. doi: 10.1016/j.dyepig.2014.06.026

  18. [18]

      J. Lađarević, L. Radovanović, B. Božić, et al., Appl. Organomet. Chem. 37 (2023) e7219. doi: 10.1002/aoc.7219

  19. [19]

      A.D. Maˇsulović, J.M. Lađarevi, A.M. Ivanovska, et al., Dyes Pigments 195 (2021) 109741. doi: 10.1016/j.dyepig.2021.109741

  20. [20]

      J. Mirković, B. Božić, V. Vitnik, et al., Color Technol. 134 (2017) 33–43.

  21. [21]

      J. Mirković, J. Rogan, D. Poleti, et al., Dyes Pigments 104 (2014) 160–168. doi: 10.1016/j.dyepig.2014.01.007

  22. [22]

      S. Chen, L. Li, Song S, et al., Cryst. Growth Des. 23 (2023) 4970–4978. doi: 10.1021/acs.cgd.3c00215

  23. [23]

      L. Zhang, J.M. Cole, X. Liu, J. Phys. Chem. C 117 (2013) 26316–26323. doi: 10.1021/jp4088783

  24. [24]

      P. Gilli, V. Bertolasi, V. Ferretti, et al., J. Am. Chem. Soc. 122 (2000) 10405–10417. doi: 10.1021/ja000921+

  25. [25]

      W. Liu, Y. Hou, W. Wu, et al., Ind. Eng. Chem. Res. 50 (2011) 6952–6956. doi: 10.1021/ie102586u

  26. [26]

      X. Liang, J. Liu, Y. Fu, et al., Sep. Purif. Tecnnol. 163 (2016) 258–266. doi: 10.1016/j.seppur.2016.03.006

  27. [27]

      V. Deneva, A. Lyčka, S. Hristova, et al., Dyes Pigments 165 (2019) 157–163. doi: 10.1016/j.dyepig.2019.02.015

  28. [28]

      A. Alimmari, D. Mijin, R. Vukićević, et al., Chem. Cent. J. 6 (2012) 71. doi: 10.1186/1752-153X-6-71

  29. [29]

      T. Lu, F. Chen, J. Comput. Chem. 33 (2012) 580–592. doi: 10.1002/jcc.22885

  30. [30]

      P.S. Patil, P.O. Gupta, N. Sekar, ChemistrySelect 7 (2022) e202203075. doi: 10.1002/slct.202203075

  31. [31]

      J. Lađarevića, B. Božićb, L. Matović, et al., Dyes Pigments 162 (2019) 562–557.

  32. [32]

      H.F. Qian, J. Geng, D. Xu, et al., Dyes Pigments 160 (2019) 853–862. doi: 10.1016/j.dyepig.2018.09.018

  33. [33]

      J.W. Namgoong, S.H. Kim, S.W. Chung, et al., Dyes Pigments 154 (2018) 128–136. doi: 10.1016/j.dyepig.2018.01.024

  34. [34]

      S. Li, Y. Qi, W. Niu, et al., Dyes Pigments 229 (2024) 112260. doi: 10.1016/j.dyepig.2024.112260

  35. [35]

      Y.W. Wen, M. Li, L.F. Fan, et al., Adv. Mater. 36 (2024) 2406574. doi: 10.1002/adma.202406574

  36. [36]

      J. Chen, Z. Wang, B. Yao, et al., Adv. Mater. 36 (2024) 2401178. doi: 10.1002/adma.202401178

  37. [37]

      H. Qiao, B. Wu, S. Sun, et al., J. Am. Chem. Soc. 146 (2024) 7533–7542. doi: 10.1021/jacs.3c13392

  38. [38]

      I. Noda, J. Am. Chem. Soc. 111 (1989) 8116–8118. doi: 10.1021/ja00203a008

  39. [39]

      I. Noda, Appl. Spectrosc. 47 (1993) 1329–1336. doi: 10.1366/0003702934067694

  40. [40]

      C. Bilton, F.H. Allen, G.P. Shields, et al., Acta Crystallogr. B 56 (2000) 849–856. doi: 10.1107/S0108768100003694

  41. [41]

      R.K. Castellano, Y. Li, E.A. Homan, et al., Eur. J. Org. Chem. 2012 (2012) 4483–4492. doi: 10.1002/ejoc.201200438

  42. [42]

      E. Benassi, K. Akhmetova, H. Fan, Phys. Chem. Chem. Phys. 21 (2019) 1724. doi: 10.1039/c8cp04789h

  43. [43]

      A. Quirk, B. Unni, I.J. Burgess, Langmuir 32 (2016) 2184. doi: 10.1021/acs.langmuir.5b04178

  44. [44]

      Y.D. Kim, J.P. Kim, O.S. Kwon, I.H. Cho, Dyes Pigments 81 (2009) 45–52. doi: 10.1016/j.dyepig.2008.09.006

  45. [45]

      H. Ma, X. Zhao, S. Yan, et al., Dyes Pigments 207 (2022) 110726. doi: 10.1016/j.dyepig.2022.110726

  46. [46]

      S. Li, C. Gao, J. Xue, et al., Dyes Pigments 224 (2024) 112023. doi: 10.1016/j.dyepig.2024.112023

  47. [47]

      A. Singh, R. Choi, B. Choi, et al., Dyes Pigments 95 (2012) 580–586. doi: 10.1016/j.dyepig.2012.06.009

  48. [48]

      M.H. Habibi, A. Hassanzadeh, A. Zeini-Isfahani, Dyes Pigments 69 (2006) 93–101. doi: 10.1016/j.dyepig.2005.02.011

  49. [49]

      D. Nedeltcheva, L. Antonov, A. Lyčka, et al., Curr. Org. Chem. 13 (2009) 217. doi: 10.2174/138527209787314832

  50. [50]

      W. You, H.Y. Zhu, W. Huang, et al., Dalton Trans. 39 (2010) 7876–7880. doi: 10.1039/c0dt00101e

  51. [51]

      X.C. Chen, T. Tao, Y.G. Wang, et al., Dalton Trans. 41 (2012) 11107–11115. doi: 10.1039/c2dt31102j

  52. [52]

      A. Fulara, W. Dzwolak, J. Phys. Chem. B 114 (2010) 8278–8283. doi: 10.1021/jp102440n

  53. [53]

      S. Kim, T.G. Hwang, W.J. Choi, et al., Prog. Org. Coat. 191 (2024) 108399. doi: 10.1016/j.porgcoat.2024.108399

  54. [54]

      E.M. Zahran, E.M. Fatila, C. Chen, et al., Anal. Chem. 90 (2018) 1925–1933. doi: 10.1021/acs.analchem.7b04008

  55. [55]

      E. Zhang, L. Jiang, H. Li, et al., Dyes Pigments 219 (2023) 111616. doi: 10.1016/j.dyepig.2023.111616

  56. [56]

      T. Tao, X.L. Zhao, Y.Y. Wang, et al., Dyes Pigments 166 (2019) 226–232. doi: 10.1016/j.dyepig.2019.03.046

  57. [57]

      A. Lyčka, Dyes Pigments 165 (2019) 341–345. doi: 10.1016/j.dyepig.2019.02.024

  58. [58]

      T.H. Kim, B.J. Lee, S.O. An, J.H. Lee, J.H. Choi, Dyes Pigments 174 (2020) 108053. doi: 10.1016/j.dyepig.2019.108053

• 

  Figure 1  Molecular structure analysis of synthesized azo dyes. (a) The molecular structures of six dyes. (b) Optimized structures (TPSSh.S0.ESA (d, p) of the six designed dyes. (c) Electrostatic potential surface maps of the six dyes. H-bond: hydrogen bonding.

  下载: 全尺寸图片 幻灯片
  

  Figure 2  TGA analysis of the synthesized dyes. (a) Dyes were heated to 500 ℃, (b) dyes were heated to 230 ℃ and held in this temperature for 30 min, then heated to 300 ℃, (c) the mass loss of the synthesized dyes heated to 230 ℃ for 30 min.

  下载: 全尺寸图片 幻灯片
  

  Figure 3  The structural characterize of the synthesized azo dyes. (a) The FTIR spectra and structure of the designed azo dyes P-2–P-5 measured at 25 ℃. (b) Schematic illustration for the azo-hydrazone tautomerism of P-2. (c) Temperature-dependent FTIR spectra of P-2 in the N—H and C=O vibration regions acquired during heating. (d) Synchronous and asynchronous 2D COS derived from the stretching peak of the N—H group of P-2 during heating. (e) Synchronous and asynchronous 2D COS derived from the stretching peak of the C=O on the 1D FTIR spectra of P-2 during heating. (f) Synchronous and asynchronous 2D COS derived from the bending peak of the N—H group of P-2 during heating.

  下载: 全尺寸图片 幻灯片
  

  Figure 4  Performance analysis of azo dye-based color films. (a) Fabrication of the yellow color films and spin-coated films using the synthesized azo dyes (P-2, P-3) and commercial filter pigment in the same mass fraction (1.25 wt%). (b) The optical image of the color films. (c) Possible diagram of strong internal interactions of dye molecules with polysulfone (PSU). (d) Transmittance of the color films. (e) Transmittance at the range of 550–780 nm of the novel color films before and after baking. (f) Transmission at the range of 550–780 nm of the novel color films before and after irradiation at 365 nm.

  下载: 全尺寸图片 幻灯片
•