Novel Zinc(II) Phthalocyanine Dyes for Color Photoresists

Abstract

Color photoresists are the key materials for the fabrication of color filters (CFs). Organic dyes offer a promising alternative to the conventional pigment-based system to make CFs with higher resolution. However, the stability of dye molecules is an urgent problem to be solved. Herein, we designed and synthesized a series of highly stable zinc phthalocyanine dyes containing polymerizable acrylamide groups. Upon light exposure, dense and insoluble network structures were formed in the prepared CFs, which increase the thermal stability and anti-migration capacity of these dyes.

Currently, liquid crystal display (LCD) remains the mainstream among various new display technologies due to its huge industrial base, relatively mature production technology, continuously optimized performance, and declining cost. The color filter (CF) is one of the most important components in thin-film-transistor liquid crystal display (TFT-LCD) modules. It converts the white backlight into multiple color lights.[1] The RGB (red, green, and blue) pixels arranged in regular black matrixes in the CF determine its resolution and color gamut. Color photoresists (CRs), which comprise red (R), green (G), and blue (B) photoresists to form color pixels capable of displaying color images, are the primary raw materials of CFs.[2]

RGB color photoresists can form RGB pixels patterned in regular black matrixes after a photolithographic process. Generally, CRs contain photoinitiators, colorants, monomers, and additives that are dispersed in solvents. Among these components, colorants determine the resolution and color properties of CF. The industry currently uses pigments as colorants. Pigments have a large particle size, broad absorption spectra, high photostability, and good heat resistance. However, with the emergence of HD 8K display, flexible display, and virtual reality technologies, pigment-based CF has reached the resolution limit, and it is challenging to further improve color performance.[3] This is ascribed to the broad absorption spectra and large sizes of pigments that cause reduced transmittance, plain brightness, and low contrast.[4] Miniaturization of the pigment’s particle size from 100 to 50 nm by a grinder is a promising approach to enhance the color performance of pigment-based CFs. However, it involves exploring complicated grinding processes that put forward extremely high requirements for equipment and materials. Additionally, to avoid the agglomeration of fine pigments into large aggregations in the photoresists, more dispersants are required, which may cause issues, such as increased CF thickness and high cost.[5]

An alternative scenario is using dyes instead of pigments as CR colorants. Dyes exhibited narrower absorption bands, higher transmittance, and superior color-saturation properties compared to the pigments. Furthermore, using dyes in CRs should overcome the intrinsic inferior thermal stability, which can be improved by tailoring the dye molecules.[6] Additionally, dyes should have good solubility in industrial solvents, such as PGMEA, and good compatibility with other components in CRs.[7] Therefore, systematic investigations on the inherent relationship between the structure and properties of dyes lay the foundation for realizing the use of dyes in CRs.

Herein, three zinc(II) phthalocyanine dyes with cross-linkable bonds were designed and synthesized, as shown in Scheme [1]. Phthalocyanines were used as the primary structure for molecular design and synthesis. Due to having a planar macrocyclic with a large conjugate structure of an 18-π electron system, the complexes of phthalocyanine exhibit excellent photochemical and photophysical properties and high stability.[8]

The characteristics of dyes may be adjusted by altering the functional substituents on the zinc(II) phthalocyanine ring. For example, aryloxy and chlorine[9] and amide substituents can improve the solubility of dyes and compatibility with other CR components. Additionally, cross-linkable bonds[10] were engineered into dyes so that they may be copolymerized with monomers and binders to form a network structure, increasing the stability of the CFs.[11] The effects of molecular structure on the spectral properties, solubility, compatibility, and thermal stability of the dyes are discussed in this paper.

Synthesis and Geometry Optimization

The synthetic procedures of all dyes are shown in Scheme [1], and they were characterized by ¹H NMR spectroscopy and mass spectrometry. The experiment details are described in the References and Notes section.[24] [25]

Figure [1] shows the optimization of the ground-state geometry of the synthesized dyes. The phenyl substituents[12] around the phthalocyanine core can provide an effective steric strain with the planes of the Pc core and the phenyl forming twisted angles that should not be disregarded. The steric strain induced by nonperipheral (α) position substituents is larger than that caused by peripheral (β) position substituents.[13] Thus, the vertical axial bulkiness of the phthalocyanine core plane of β-N-ZnPc (0.06 Å) is lower than that of α-N-ZnPc (0.19 Å) and Cl-N-ZnPc (0.92 Å).[9] [14] Furthermore, because chlorine atoms with high steric strain can distort the Pc core, the vertical axial bulkiness of Cl-N-ZnPc is greatly enhanced.[9] The vertical axial bulkiness of dyes can influence their intermolecular interactions and hence their physical, chemical, and electronic characteristics, such as solubility and thermal stability.[15]

Spectral Properties of the Synthesized Dyes

The UV/Vis absorption spectra of the dyes α-N-ZnPc, β-N-ZnPc, and Cl-N-ZnPc are shown in Figure [2]. Their absorption spectra were measured and compared using a UV/Vis spectrophotometer. The structure of the substituents on the Pc cores can significantly impact Pc conjugation and, therefore, the UV/Vis absorption spectrum bands of dyes. Furthermore, the UV/vis absorption spectra of metal PCs have two characteristic bands: one is the B band between 250–450 nm and the other is the Q band at 600–800 nm.[16] These two characteristic bands are formed by the transition of the π electron system of PCs, so different structures will show different characteristic spectral bands.[17]

All the synthesized dyes presented maximum absorption in the 680–700 nm range and provided colors from cyan to green, as shown in Figure [2]. The dyes for the CFs should absorb light in the 690–700 nm range to transmit light evenly in the green area of 500–550 nm. CFs should have outstanding color-filtering capabilities at the target wavelength. The greater the molar extinction coefficients (ε), the smaller the amount of dye required. The molar extinction coefficients of the dyes were substantially higher than those of the pigments,[9] exceeding 50000 L/mol/cm.

As shown in Table [1], the maximum absorption of β-N-ZnPc appeared at 681 nm, while those of dyes, α-N-ZnPc and Cl-N-ZnPc, appeared at 694 and 695 nm, respectively. The conjugate substituents of the nonperipheral locations on the Pc cores caused a bathochromic shift[5] [9] of around 15 nm in the maximum absorption wavelength of α-N-ZnPc and Cl-N-ZnPc compared to β-N-ZnPc. Based on the calculation of the phthalocyanine molecular orbitals, the linear combination of atomic orbitals (LCAO) coefficients of the HOMO level at the α-position are larger than those at the β-position.[18] Thus, the substituents at the α-position have a stronger effect on the HOMO level than the β-position, which narrows the energy gap between the HOMO and LUMO levels to a greater extent and causes a bathochromic shift in Q-band absorption.

Thermal Stability of the Synthesized Dyes

Herein, the thermal stability of the produced dyes was evaluated by thermogravimetric analysis (TGA). The CRs were maintained at 230 °C for 30 min during production. According to the percentage of thermal weightlessness at 230 °C for 30 min, as shown in Figure [3], the thermal stability of the dyes was assessed. Under these conditions, the weight loss of all synthetic dyes was only approximately 1 wt%, far less than 5 wt%. Since the amide substituents on the dyes can create intermolecular hydrogen bonds and increase the intermolecular interactions, the dyes have improved thermal stability.[19] In conclusion, the synthesized dyes have high thermal stability and can tolerate the temperature necessary for CF production.

Solubility of the Synthesized Dyes

The main difference between dye- and pigment-based CRs is the dissolved state of the colorants in the CRs. Pigment-based colorants for CRs are nanoparticles of a certain size that are dispersed in photoresists and insoluble, while dye-based colorants can be dissolved in photoresists.

As the dyes are dissolved as molecules in the dye-based CR, the solubility of the dyes in the photoresist must be high. The solubility of dyes in solvents is required to be no less than 5 wt%.[20] To achieve greater dispersion and compatibility with binders, traditional pigment-based photoresist solvents are primarily lipids, ethers, and a few ketones. Some solvents are occasionally mixed to adjust the boiling point and viscosity to prevent them from erupting into a boil or evaporating too quickly during prebaking, resulting in undesirable film surfaces. We tested the synthesized dyes in various typical photoresist solutions. As shown in Table [2], α-N-ZnPc showed good performance in all solvents, which might be due to the steric hindrance of large steric substitutions on nonperipheral positions.[21] All dyes were more than 10 wt% soluble in DMF, far exceeding the industry standard of 5 wt%.

Furthermore, when choosing solvents for photoresists, we should consider solubility, surface tension, volatility, and compatibility with other photoresist components.[15b] The best CFs can only be coated when all aspects are well-matched. When DMF was used as the solvent in our experiments, the films had relatively flat surfaces with no obvious particles, and the coffee ring effect was weak.[22]

Characterization of the Spin-Coated Films

Transmission Spectra and Color Coordinates of CFs

In this study, α-N-ZnPc was used to prepare the CRs due to its superior thermal stability, solubility, and color performance, and the transmission spectra and color coordinates of the CFs[11] were evaluated by changing the dye content in the CRs to determine the most suitable.

Through coating, prebaking, exposure, and postbaking, CFs were prepared. The specific wavelength transmittance and color coordinates of CFs are closely connected to the display efficiency of LCDs and can be used to evaluate the performance of dyes as CR colorants. The CFs should have a high transmittance in the green range of 500–550 nm and efficiently absorb light in the other regions.[21]

The transmittance of the CFs prepared at all dye concentrations was higher than 70%, as shown in Figure [4] and Table [3]; the transmission spectrum of the CFs produced with 5 wt% dye concentration had a sharp peak shape near the wavelength of 530 nm, indicating that the filter had greater filtering capacity and chromaticity. In subsequent studies, we may alter the color purity by adding yellow dyes to the CRs, which can absorb light intensely under 500 nm with no residual absorption over 500 nm and can efficiently cut off unwanted transmittance of provided green dyes while preserving the required transmittance range.[23]

Anti-Migration and Thermal Stability of Green Spin-Coated CFs

The synthesized dyes in this study have cross-linkable methacrylamide substituents. During exposure, the binders and monomers can undergo polymerization with the cross-linkable bonds of the dyes, generating patterns insoluble in alkali.[10] This can, to some extent, prevent dye migration and aggregation and allow the dyes to have good thermal stability.

During the simulation of the exposure process, the green spin-coated CFs were treated to partial UV irradiation and partial shading for comparison purposes. These CFs were then postbaked at 230 °C for 30 min.[9] The thermal stability and anti-migration capacity of the manufactured filter films were determined by comparing the color difference values (ΔE_abs) of the CFs before and after the filters were postbaked again. As shown in Table [4], the color difference value (1.3968) in the exposed area of the CR was less than that (2.3328) in the unexposed region. This means that following exposure, cross-linking reactions occurred in the UV-irradiated area, resulting in the dense network structure that made the films more resistant to dye migration and aggregation and reduced color difference values.

Chemical Stability of Green Spin-Coated CFs

To evaluate the chemical stability of the prepared green filters, they were immersed in solvents (PGMEA, ethyl lactate, and DMF) commonly used in CFs for 10 min, and the color-difference values were measured before and after the treatment.[10]

As shown in Table [5], the color-difference values of the fabricated films before and after dipping in PGMEA, ethyl lactate, and DMF were 0.22, 0.18, and 3.56, respectively. The color-difference values are not significant in most solvents except in DMF. In other words, the fabricated green-filter films were chemically stable.

To summarize this study, we designed, synthesized, and studied a series of cross-linkable and highly stable zinc phthalocyanine dyes.[24] [25] The effects of substituents on the spectrum characteristics, thermal stability, and solubility of the dyes were examined, and the experimental data were evaluated theoretically. The results suggest that α-N-ZnPc, which possesses large steric effect substituents in nonperipheral positions, has outstanding thermal stability and color characteristics and may be employed as a dye-based colorant for CRs. Furthermore, the green spin-coated CFs manufactured with target dye had excellent chemical and thermal stability, as well as the capacity to successfully resist dye migration and aggregation. Our work is meaningful for exploring dye-based CFs.

Conflict of Interest

The authors declare no conflict of interest.

Acknowledgment

The authors acknowledge the assistance of DUT Instrumental Analysis Center.

• References and Notes

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• 24 Synthesis of N-MP p-Aminophenol (10.00 g, 91.64 mmol, 1.00 equiv) and acetonitrile (70 mL) were added to a flask (250 mL). Under a nitrogen atmosphere, an acetonitrile solution (20 mL) of methacrylic anhydride (13.72 mL, 91.64 mmol, 1.00 equiv) was added dropwise to the flask within 30 min. The reaction was then transferred to an oil bath and refluxed for 3 h until the cloudy solution gradually transformed into a light-yellow transparent liquid with no obvious turbidity. Next, the reaction was allowed to cool to room temperature. After filtering, the product was crystallized from the filtrate as a white solid; yield 56%. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.52 (s, 1 H), 9.20 (s, 1 H), 7.53–7.31 (m, 2 H), 6.79–6.62 (m, 2 H), 5.75 (s, 1 H), 5.44 (s, 1 H), and 1.93 (s, 3 H). ¹³C NMR (151 MHz, DMSO-d₆ ): δ = 166.71, 154.02, 141.03, 131.01, 122.59, 119.76, 115.36, 19.28. TOF LC–MS: m/z [M – H]^– calcd for C₁₀H₁₀NO₂ ^–: 177.0790; found: 177.0705. Synthesis of α-N-MP2 3-Nitrophthalonitrile (6.5 g, 37.54 mmol, 1.00 equiv), N-MP (7.98 g, 45.05 mmol, 1.20 equiv), and DMF (40 mL) were added to a flask (250 mL). Under nitrogen atmosphere, the mixture was stirred for 30 min. Then, anhydrous potassium carbonate (7.78 g, 56.32 mmol, 1.50 equiv) was added to the flask within 1 h. The reaction’s temperature was gradually increased to 80 °C for 8 h under N₂ protection. Next, the reaction was cooled to room temperature and later poured into 1500 mL water, and the crude product was precipitated. The crude product was filtered and dried; then purified by column chromatography (silica gel, DCM/ethyl acetate) to yield α-N-MP2 (9.48 g, 83%) as a white solid. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.92 (s, 1 H), 7.91–7.57 (m, 4 H), 7.49–6.94 (m, 3 H), 5.82 (s, 1 H), 5.64–5.33 (m, 1 H), 1.96 (s, 3 H). ¹³C NMR (151 MHz, DMSO-d ₆): δ = 167.32, 160.80, 149.71, 140.77, 137.40, 136.48, 128.40, 122.38, 121.94, 120.90, 120.58, 116.30, 116.13, 113.90, 105.10, 19.18. TOF LC–MS: m/z [M + Cl]^– calcd for C₁₈H₁₃ClN₃O₂ ^–: 338.0702; found: 338.0695. Synthesis of β-N-MP2 β-N-MP2 was synthesized following a similar process for α-N-MP2 by using 4-nitrophthalonitrile as starting material. The crude product was purified by column chromatography (silica gel, DCM/ethyl acetate); yield 49%. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.92 (s, 1 H), 8.08 (d, J = 8 Hz, 1 H), 7.86–7.79 (m, 2 H), 7.75 (d, J = 4 Hz, 1 H), 7.36 (dd, J = 8, 4 Hz, 1 H), 7.21–7.13 (m, 2 H), 5.81 (s, 1 H), 5.56–5.48 (m, 1 H), 1.96 (s, 3 H). ¹³C NMR (151 MHz, DMSO-d ₆): δ = 167.32, 161.97, 149.43, 140.81, 137.35, 136.75, 122.74, 122.39, 122.01, 121.17, 120.54, 117.12, 116.41, 115.88, 108.32, 19.19. TOF LC–MS: m/z [M + Cl]^– calcd for C₁₈H₁₃ClN₃O₂ ^–: 338.0702; found: 338.0696. Synthesis of Cl-N-MP2 Cl-N-MP2 was synthesized following a similar process for α-N-MP2 by using tetrachlorophthalonitrile as starting material. The crude product was purified by column chromatography (silica gel, DCM/ethyl acetate); yield 37%. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.81 (s, 1 H), 7.67 (d, J = 8 Hz, 2 H), 6.97 (d, J = 12 Hz, 2 H), 5.78 (s, 1 H), 5.52 (s, 1 H), 1.94 (s, 3 H). ¹³C NMR (151 MHz, DMSO-d ₆): δ = 167.11, 152.41, 151.69, 140.74, 137.12, 135.66, 135.46, 132.66, 122.36, 120.47, 117.81, 115.52, 115.46, 113.43, 113.29, 19.17. TOF LC–MS: m/z [M + Cl]^– calcd for C₁₈H₁₀Cl₄N₃O₂ ^–: 441.9533; found: 441.9500. Synthesis of α-N-ZnPc α-N-MP2 (1 g, 3.30 mmol, 3.00 equiv), anhydrous zinc acetate (0.15 g, 1.10 mmol, 1.00 equiv), and anhydrous N,N-dimethylethanolamine (30 mL) were added to a 100 mL flask, and the reaction was conducted at 140 °C for 12 h under nitrogen atmosphere. Next, the reaction was cooled to room temperature and later poured into 500 mL water, and the crude product was precipitated. The crude product was filtered and dried, then purified by column chromatography (silica gel, DCM/methyl alcohol). Finally, it was subjected to a 48 h Soxhlet extraction with toluene, dichloromethane, and ethyl acetate to yield α-N-ZnPc (0.40 g, 28%) as a green solid. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.78 (t, J = 8 Hz, 4 H), 9.18 (d, J = 8 Hz, 2 H), 8.81 (t, J = 8 Hz, 1 H), 8.70 (d, J = 8 Hz, 1 H), 8.27–8.06 (m, 3 H), 8.01 (s, 1 H), 7.89–7.62 (m, 10 H), 7.56–7.38 (m, 6 H), 7.23–7.18 (m, 4 H), 5.83 (dd, J = 24, 12 Hz, 4 H), 5.50 (d, J = 24 Hz, 4 H), 2.07– 1.87 (m, 12 H). MALDI-TOF-MS: m/z [M]^– calcd for C₇₂H₅₂N₁₂O₈Zn: 1276.3; found: 1276.3. Synthesis of β-N-ZnPc β-N-ZnPc was synthesized following a similar process for α-N-ZnPc by using intermediate β-N-MP2 as starting material; yield 39%. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.96 (dd, J = 24, 12 Hz, 4 H), 8.78 (dd, J = 24, 16 Hz, 4 H), 8.36 (d, J = 24 Hz, 4 H), 7.96 (dt, J = 28, 12 Hz, 8 H), 7.71 (dd, J = 20, 12 Hz, 4 H), 7.63–7.37 (m, 8 H), 5.90 (s, 4 H), 5.58 (d, J = 8 Hz, 4 H), 2.03 (s, 12 H), MALDI-TOF-MS: m/z [M]^– calcd for C₇₂H₅₂N₁₂O₈Zn: 1276.3; found: 1276.3. Synthesis of Cl-N-ZnPc
  Cl-N-ZnPc was synthesized following a similar process for α-N-ZnPc by using Cl-N-MP2 as starting material; yield 23%. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.79 (d, J = 20 Hz, 4 H), 7.68 (d, J = 20 Hz, 8 H), 7.11 (s, 6 H), 6.92 (s, 2 H), 5.80 (d, J = 12 Hz, 4 H), 5.49 (d, J = 8 Hz, 4 H), 1.94 (d, J = 8 Hz, 12 H). MALDI-TOF-MS: m/z [M]⁺ calcd for C₇₂H₄₀Cl₁₂N₁₂O₈Zn: 1691.9; found: 1691.9.
• 25 Measurement of the Solubility of Synthesized Dyes A 2 mL brown bottle was filled with 0.075 g of the produced dye and 0.5 g of the solvent. The vial was subjected to ultrasonography for 10 min and kept standing for 24 h. After filtering the mixture over a 0.1 micron polytetrafluoroethylene membrane, the filtrate was dried for 1 h at 150 °C to extract the dissolved dye solid. Then, the solubility of the dyes was calculated. Preparation of Dye Solutions and CRs Preparation of the green dye solution for a color filter: 0.05 g prepared dye and 0.45 g DMF were placed in a 2 mL vial and sonicated thoroughly. Preparation of the Basic Photoresist 0.765 g photoresist special acrylic binder 1 (AR1, 37wt%), 0.417 g dipentaerythritol hexaacrylate (DPHA), 0.05 g photoinitiator (PI-1), and 0.02 g leveling additive (L, 10wt%) were dissolved in 0.698 g PGMEA and treated with sonication thoroughly. Preparation of the Green Photoresist for a CF 0.20 g of basic photoresist and 0.5 g of green dye solution were placed into a 2 mL brown bottle. After sufficient ultrasonic mixing, it was used as the green photoresist for a CF. Fabrication of the Green Spin-Coated CFs Green photoresists were dropped onto transparent glass substrates with dimensions of 5 × 5 × 0.07 cm. The coating speed was maintained at 500 rpm/min for 12 s. The wet CFs were then baked at 100 °C for 100 s before exposure to UV light (365 nm, 120 mW/cm², 10 s) and then baked at 230 °C for 30 min.

Corresponding Author

Publication History

Received: 14 March 2023

Accepted after revision: 26 April 2023

Accepted Manuscript online:
26 April 2023

Article published online:
26 June 2023

© 2023. Thieme. All rights reserved

Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany

• References and Notes

• 1 Tsuda K. Displays 1993; 14: 115
  CrossrefSearch in Google Scholar
• 2 Sabnis RW. Displays 1999; 20: 119
  CrossrefSearch in Google Scholar
• 3 Wang D, Zhang S.-k, Wan J.-y, Chen W.-t, Yuan J.-f. Dig. Tech. Pap. – Soc. Inf. Disp. Int. Symp. 2019; 50: 912
  CrossrefSearch in Google Scholar
• 4 Kim T.-H, Lee B.-J, An S.-O, Lee J.-H, Choi J.-H. Dyes Pigm. 2020; 174: 108053
  CrossrefSearch in Google Scholar
• 5 Namgoong JW, Kim HM, Kim SH, Yuk SB, Choi J, Kim JP. Dyes Pigm. 2021; 184: 108737
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• 6 Hye KG, Yong LJ, Rim KN, Yoon C, Kim J.-P, Hong CJ. Mol. Cryst. Liq. Cryst. 2012; 563: 36
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• 24 Synthesis of N-MP p-Aminophenol (10.00 g, 91.64 mmol, 1.00 equiv) and acetonitrile (70 mL) were added to a flask (250 mL). Under a nitrogen atmosphere, an acetonitrile solution (20 mL) of methacrylic anhydride (13.72 mL, 91.64 mmol, 1.00 equiv) was added dropwise to the flask within 30 min. The reaction was then transferred to an oil bath and refluxed for 3 h until the cloudy solution gradually transformed into a light-yellow transparent liquid with no obvious turbidity. Next, the reaction was allowed to cool to room temperature. After filtering, the product was crystallized from the filtrate as a white solid; yield 56%. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.52 (s, 1 H), 9.20 (s, 1 H), 7.53–7.31 (m, 2 H), 6.79–6.62 (m, 2 H), 5.75 (s, 1 H), 5.44 (s, 1 H), and 1.93 (s, 3 H). ¹³C NMR (151 MHz, DMSO-d₆ ): δ = 166.71, 154.02, 141.03, 131.01, 122.59, 119.76, 115.36, 19.28. TOF LC–MS: m/z [M – H]^– calcd for C₁₀H₁₀NO₂ ^–: 177.0790; found: 177.0705. Synthesis of α-N-MP2 3-Nitrophthalonitrile (6.5 g, 37.54 mmol, 1.00 equiv), N-MP (7.98 g, 45.05 mmol, 1.20 equiv), and DMF (40 mL) were added to a flask (250 mL). Under nitrogen atmosphere, the mixture was stirred for 30 min. Then, anhydrous potassium carbonate (7.78 g, 56.32 mmol, 1.50 equiv) was added to the flask within 1 h. The reaction’s temperature was gradually increased to 80 °C for 8 h under N₂ protection. Next, the reaction was cooled to room temperature and later poured into 1500 mL water, and the crude product was precipitated. The crude product was filtered and dried; then purified by column chromatography (silica gel, DCM/ethyl acetate) to yield α-N-MP2 (9.48 g, 83%) as a white solid. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.92 (s, 1 H), 7.91–7.57 (m, 4 H), 7.49–6.94 (m, 3 H), 5.82 (s, 1 H), 5.64–5.33 (m, 1 H), 1.96 (s, 3 H). ¹³C NMR (151 MHz, DMSO-d ₆): δ = 167.32, 160.80, 149.71, 140.77, 137.40, 136.48, 128.40, 122.38, 121.94, 120.90, 120.58, 116.30, 116.13, 113.90, 105.10, 19.18. TOF LC–MS: m/z [M + Cl]^– calcd for C₁₈H₁₃ClN₃O₂ ^–: 338.0702; found: 338.0695. Synthesis of β-N-MP2 β-N-MP2 was synthesized following a similar process for α-N-MP2 by using 4-nitrophthalonitrile as starting material. The crude product was purified by column chromatography (silica gel, DCM/ethyl acetate); yield 49%. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.92 (s, 1 H), 8.08 (d, J = 8 Hz, 1 H), 7.86–7.79 (m, 2 H), 7.75 (d, J = 4 Hz, 1 H), 7.36 (dd, J = 8, 4 Hz, 1 H), 7.21–7.13 (m, 2 H), 5.81 (s, 1 H), 5.56–5.48 (m, 1 H), 1.96 (s, 3 H). ¹³C NMR (151 MHz, DMSO-d ₆): δ = 167.32, 161.97, 149.43, 140.81, 137.35, 136.75, 122.74, 122.39, 122.01, 121.17, 120.54, 117.12, 116.41, 115.88, 108.32, 19.19. TOF LC–MS: m/z [M + Cl]^– calcd for C₁₈H₁₃ClN₃O₂ ^–: 338.0702; found: 338.0696. Synthesis of Cl-N-MP2 Cl-N-MP2 was synthesized following a similar process for α-N-MP2 by using tetrachlorophthalonitrile as starting material. The crude product was purified by column chromatography (silica gel, DCM/ethyl acetate); yield 37%. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.81 (s, 1 H), 7.67 (d, J = 8 Hz, 2 H), 6.97 (d, J = 12 Hz, 2 H), 5.78 (s, 1 H), 5.52 (s, 1 H), 1.94 (s, 3 H). ¹³C NMR (151 MHz, DMSO-d ₆): δ = 167.11, 152.41, 151.69, 140.74, 137.12, 135.66, 135.46, 132.66, 122.36, 120.47, 117.81, 115.52, 115.46, 113.43, 113.29, 19.17. TOF LC–MS: m/z [M + Cl]^– calcd for C₁₈H₁₀Cl₄N₃O₂ ^–: 441.9533; found: 441.9500. Synthesis of α-N-ZnPc α-N-MP2 (1 g, 3.30 mmol, 3.00 equiv), anhydrous zinc acetate (0.15 g, 1.10 mmol, 1.00 equiv), and anhydrous N,N-dimethylethanolamine (30 mL) were added to a 100 mL flask, and the reaction was conducted at 140 °C for 12 h under nitrogen atmosphere. Next, the reaction was cooled to room temperature and later poured into 500 mL water, and the crude product was precipitated. The crude product was filtered and dried, then purified by column chromatography (silica gel, DCM/methyl alcohol). Finally, it was subjected to a 48 h Soxhlet extraction with toluene, dichloromethane, and ethyl acetate to yield α-N-ZnPc (0.40 g, 28%) as a green solid. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.78 (t, J = 8 Hz, 4 H), 9.18 (d, J = 8 Hz, 2 H), 8.81 (t, J = 8 Hz, 1 H), 8.70 (d, J = 8 Hz, 1 H), 8.27–8.06 (m, 3 H), 8.01 (s, 1 H), 7.89–7.62 (m, 10 H), 7.56–7.38 (m, 6 H), 7.23–7.18 (m, 4 H), 5.83 (dd, J = 24, 12 Hz, 4 H), 5.50 (d, J = 24 Hz, 4 H), 2.07– 1.87 (m, 12 H). MALDI-TOF-MS: m/z [M]^– calcd for C₇₂H₅₂N₁₂O₈Zn: 1276.3; found: 1276.3. Synthesis of β-N-ZnPc β-N-ZnPc was synthesized following a similar process for α-N-ZnPc by using intermediate β-N-MP2 as starting material; yield 39%. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.96 (dd, J = 24, 12 Hz, 4 H), 8.78 (dd, J = 24, 16 Hz, 4 H), 8.36 (d, J = 24 Hz, 4 H), 7.96 (dt, J = 28, 12 Hz, 8 H), 7.71 (dd, J = 20, 12 Hz, 4 H), 7.63–7.37 (m, 8 H), 5.90 (s, 4 H), 5.58 (d, J = 8 Hz, 4 H), 2.03 (s, 12 H), MALDI-TOF-MS: m/z [M]^– calcd for C₇₂H₅₂N₁₂O₈Zn: 1276.3; found: 1276.3. Synthesis of Cl-N-ZnPc
  Cl-N-ZnPc was synthesized following a similar process for α-N-ZnPc by using Cl-N-MP2 as starting material; yield 23%. ¹H NMR (400 MHz, DMSO-d ₆): δ = 9.79 (d, J = 20 Hz, 4 H), 7.68 (d, J = 20 Hz, 8 H), 7.11 (s, 6 H), 6.92 (s, 2 H), 5.80 (d, J = 12 Hz, 4 H), 5.49 (d, J = 8 Hz, 4 H), 1.94 (d, J = 8 Hz, 12 H). MALDI-TOF-MS: m/z [M]⁺ calcd for C₇₂H₄₀Cl₁₂N₁₂O₈Zn: 1691.9; found: 1691.9.
• 25 Measurement of the Solubility of Synthesized Dyes A 2 mL brown bottle was filled with 0.075 g of the produced dye and 0.5 g of the solvent. The vial was subjected to ultrasonography for 10 min and kept standing for 24 h. After filtering the mixture over a 0.1 micron polytetrafluoroethylene membrane, the filtrate was dried for 1 h at 150 °C to extract the dissolved dye solid. Then, the solubility of the dyes was calculated. Preparation of Dye Solutions and CRs Preparation of the green dye solution for a color filter: 0.05 g prepared dye and 0.45 g DMF were placed in a 2 mL vial and sonicated thoroughly. Preparation of the Basic Photoresist 0.765 g photoresist special acrylic binder 1 (AR1, 37wt%), 0.417 g dipentaerythritol hexaacrylate (DPHA), 0.05 g photoinitiator (PI-1), and 0.02 g leveling additive (L, 10wt%) were dissolved in 0.698 g PGMEA and treated with sonication thoroughly. Preparation of the Green Photoresist for a CF 0.20 g of basic photoresist and 0.5 g of green dye solution were placed into a 2 mL brown bottle. After sufficient ultrasonic mixing, it was used as the green photoresist for a CF. Fabrication of the Green Spin-Coated CFs Green photoresists were dropped onto transparent glass substrates with dimensions of 5 × 5 × 0.07 cm. The coating speed was maintained at 500 rpm/min for 12 s. The wet CFs were then baked at 100 °C for 100 s before exposure to UV light (365 nm, 120 mW/cm², 10 s) and then baked at 230 °C for 30 min.

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