The new design is generally based on the improvement of existing commercial photoinitiators as well as the introduction of new building blocks aimed at improving the properties of polymerized materials. A photoinitiator named 1,4-bis(4-bromophenyl)-2,5-bis(4-(trifluoromethyl)phenyl)-1,4-dihydropyrrolo[3,2-b]pyrrole (PyBF) with a symmetric trifluoromethyl (-CF3) end groups was synthesized through a one-step aldehyde–ketone condensation reaction. The -CF3 groups are introduced on the 2,5-position phenyl rings of the pyrrolo[3,2-b]pyrrole core, and PyBF shows visible light photoinitiation ability that matching with light-emitting diode (LED) of 405 nm. Both acrylate prepolymer and monomer have been applied to our photopolymerization formulas using PyBF as one-component photoinitiator. The thermal stability of PyBF is compared with commercial photointiator (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, TPO) with a comparable thermal decomposition temperature (Td) temperature above 300 oC. The SEM results show that the cured materials of PyBF/TPO/PEGDA mixture using PyBF/TPO as two-component photoinitiator system have smooth surface, instead of PyBF/PEGDA and TPO/PEGDA systems. Therefore, both the potential pyrrole-based one- and two-component photoinitiator for rational design is worth expected for visible light photopolymerization.
Research Article
A pyrrolo[3,2-b]pyrrole derivative used for one- and two-component radical photoinitiators for photopolymerization under 405 nm
https://doi.org/10.21203/rs.3.rs-3365038/v1
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Photopolymerization Photoinitiator Pyrrolo[3
2-b]pyrrole Trifluoromethyl groups Visible light
Photopolymerization is a light-induced reaction, which converts liquid monomer and prepolymer into solid polymers, and these reactions require the use of an appropriate photoinitiator[1–4]. The advantages of photopolymerization technology are in terms of economical, efficient, energy saving, enabling and environmental friendly[5, 6]. Due to unique technical advantages, photopolymerization has been widely used in popular applications such as coatings, inks and adhesives. In addition, photopolymerization also plays an irreplaceable role in advanced high-technology purposes such as 3D printing[7], microelectronics[8] and biological materials[9]. Photoinitiators are a key component in the photopolymerization systems because they have a significant influence on the photopolymerization rate and the performance of photopolymerized materials[10–13]. In recent technology, heat-assistant light curing 3D printing become popular[14], which requires cured materials to achieve high curing degree and thermal stability, to guarantee strong mechanical properties. Thus, photointiators with rapid initiating rate also need good thermal stability.
Radical photoinitiator can absorb light in the ultraviolet (250–420 nm) or visible region (400-800nm), generate free radicals, and induce the polymerization of monomers to cross link[15–16]. One-, two- and multi-component photoinitiators have been reported for visible light range to match present applications[17–23]. Radical photoinitiators based on conjugated skeleton including carbazole[3, 18, 24–27], phenothiazine and thioxanthone [28] exhibit broad absorption bands. Conventional commercial photoinitiators ensure the wide development of photopolymerizations in practical applications in terms of rapid photoinitiation speed and high photopolymerization conversion[29]. Under 405 nm LED irradiation, commercial phosphine oxide (TPO) is commonly used [30, 31].
New symmetric-structured photoinitiators have been synthesized possessing comparative photoinitiation efficiency and good sufficient thermostability. Hu et al. have synthesized a series of symmetric bifunctional photoinitiators comprising oxime-ester moieties as latent initiation functionalities and conjugated carbazole as chromophores in an electron acceptor (A)-π-electron donor (D)-π-electron acceptor (A) structure for reliable 3D printing process under visible light[27]. Xu et al. have developed six ketones as visible light sensitive photoinitiators in combination with an amine and an iodonium salt for the free radical polymerization of acrylates upon LED irradiation at 405 nm[32]. Deng et al. have designed and synthesized a series of bis-chalcone-based visible light photoinitiators with the maximum absorption wavelengths redshifted, formulas in three-component system including iodonium and amine for coating and low migration ratio[33]. Zhu and co-workers have developed outstanding homosubstituted thiazolothiazole-based photoinitiators coupled with one or two additives exhibiting effective photoinitiation abilities on both the free radical and the cationic photopolymerization upon the light irradiation from LED@410 nm with minor shrinkage[34]. Jia and co-workers have reported the designing of symmetric D-π-A structures, which extend π-conjugation, gain good intramolecular charge transfer (ICT) characteristic, and at the same time good initiating ability[35]. Therefore, a proper molecular design based on symmetric structures have a great attraction on developing more efficient photoinitiators, which may provide new characteristics for present applications.
Pyrrole is a five-membered ring heterocycle characterized by an easiness of chemical modification, low oxidation potential, high thermal and chemical stability.[36] Recently, pyrrole is found by researchers to be an interesting scaffold for the design of photoinitiators[37]. Xue et al. obtained high final monomer conversions with the symmetric bifunctional pyrrole-based dyes, which exhibit high reactivity due to high rate constants of intermolecular interactions and generation of efficiently initiating radicals[36]. Xue et al. also have studied a pyrrole-based enone dyeto react with amine as additive and combined with commercial iodonium salt [38].Tang et al. have developed a conjugated 1,3-bis(1-methyl-1H-2-yl)prop-2-en-1-one with two pyrrole rings as high-performance LED photoinitiator [39]. This photoinitiator has a high molar extinction coefficient from 365 to 425 nm, and interacts with a commercial diphenyliodonium salt to initiate cationic and free radical photopolymerization. These results demonstrate pyrrole groups are optional functional building blocks for radical photoinitiators. Li and co-workers have reported a novel synthesis route to obtain a bifunctional pyrrole-carbazole-based photoinitiator via one-step reaction, exhibiting excellent absorption at 405 nm and the ability for hydrogen donation used to sensitize commercial triarysulfonium salts and extend the absorption window of the onium salts into the visible light region[41]. As mentioned above, the five-membered heterocyclic thiazole modified by symmetrically substituted groups as both photoinitiators and dyes for 3D printing under violet LED, which also indicates good potential of five-membered heteroaromatic rings in long-wavelength photopolymerization[34]. Li et al. have designed three novel pyrrole chalcones with D-π-A structures were designed and characterized as Norrish II photoinitiators. The photochemistry activity with common amine coinitiator of pyrrole chalcones exhibited the excellent initiating ability for blue LED free radical photopolymerization of acrylates via photopolymerization kinetics. [42]Therefore, pyrrole and other five-membered heterocyclic rings can be promising candidates for long-wavelength photopolymerization and have good photoreaction activity with co initiators and commercial photointiators. In recent study, symmetric -CF3 groups introduced on pyrrolo[3,2-b]pyrrole core generate a A-D-A molecule structure for radical photopolymerization. The introduction of -CF3 bring an extended absorption band as compared with that previously symmetric bifunctional by -NO2 only as UV photoinitiator. The -CF3 groups were found as substituents to improve the photoinitiation ability of pyrrolo[3,2-b]pyrrole photoinitiators under LED of 405 nm.
In this work, we focused on 1,4-dihydropyrrolopyrroles discovered by Gryko and coworkers [43, 44]. A photoinitiator, 1,4-bis(4-bromophenyl)-2,5-bis(4-(trifluoromethyl)phenyl)-1,4-dihydropyrrolo[3,2-b]pyrrole (PyBF), with symmetric bifunctional trifluoromethyl end groups was synthesized through one-step aldehyde–ketone condensation reaction. The visible light initiation ability of PyBF, relationships with different components and surface morphology of the corresponding cured materials has been studied. PyBF was not only investigated as one-component free radical photoinitiator by itself under LED lamps of 365 nm and 405 nm, but also studied for co-initiation with either amines or commercial photoinitiators (TPO) under 405 nm. Both acrylate prepolymer and monomers have been applied to the photopolymerization formulas. The thermal stability of PyBF was compared with TPO. The surface morphology of the cured materials from different photopolymerization systems containing PyBF has also been explored by scanning electron microscope (SEM). The potential pyrrole photoitiator for rational design is worth expected.
Materials
The 4-trifluoromethylbenzaldehyde, 4-bromoaniline, 2, 3-butanedione, p-toluene sulfonic acid, anhydrous acetic acid and 2, 4, 6-trimethylbenzoyl diphenylphosphine oxide (TPO) were purchased from Energy Chemical. The acrylate resins includes trimethylolpropane triacrylate (TMPTA) and polyethylene glycol acrylate (PEGDA), which were purchased from Tokyo Chemical Industry.
Methods
The nuclear magnetic resonance (NMR) spectra were recorded in deuterated chloroform (CDCl3) with a Bruker AM-400 spectrometer (400 MHz for 1H NMR and 100 MHz for 13C NMR). Ultraviolet − visible measurements were performed on a SHIMADZU UV-2600 spectrometer. For the fluorescence spectra, a HITACHI F-4500 fluorescence spectrometer was used. Cyclic voltammetry (CV) measurements were conducted with a CHI660D electrochemical workstation in a deoxygenated dichloromethane solution of tetrabutylammonium hexafluorophosphate (n-Bu4NPF6) under a nitrogen atmosphere (the concentration is 0.1 mol L− 1). A glassy carbon dish (working electrode), platinum electrode (counter electrode) and Ag/AgCl electrode (reference electrode) were used. Measurements were carried out with ferrocene as the standard. Thermogravimetric (TG) analyses were conducted on a DSC 200 F3 Maia (NETZSCH, Germany) at a heating rate of 10°C/min under a nitrogen atmosphere. Mass spectra (MS, Shimadzu, Japan) were conducted for the study on the photolysis of PyBF. The light sources were an FUV-6BK UV curing machine connected to LED irradiators of 365 and 405 nm (Guangzhou Banwoo Electronic Technology Co., Ltd.).
Synthesis of PyBF
The preparation of PyBF was carried out following the original procedure discovered by Gryko and coworkers[43]. The synthetic route of PyBF is displayed in Fig. 1.
The 4-trifluoromethylbenzaldehyde (1.007g, 5.8 mmol), 4-bromoaniline (1.147g, 6.7 mmol), and p-toluene sulfonic acid (0.287g, 1.7 mmol) were put into a two-necked bottle and then stirred in hydrous acetic acid of 25 mL at 90°C for 0.5 h. Then, butane-2,3-dione (0.127g, 1.5 mmol) was added and the resulting mixture was stirred at 90°C for 3.5 h. After cooling, the precipitate was filtered and washed with glacial acetic acid. The pure product was obtained by recrystallization from ethyl acetate.
PyBF: light yellow solid, 48% yield. 1H NMR (400MHz, chloroform-d) δ7.52 (m, 8H), δ7.30 (d, J = 8.80Hz, 4H), δ7.15 (d, J = 8.80Hz, 4H), δ6.45 (s, 2H). 13C NMR (101MHz, chloroform-d) δ138.59, 136.45, 135.19, 132.78, 132.43, 128.31, 128.09, 126.85, 125.56, 125.52, 119.95, 77.36. HRMS(ESI)(m/z): [M+H]+calcd. For C32H18Br2F6N2, 701.9741; found: 701.4982.
Steady State Photolysis
The absorbance of the maximum absorption peaks of PyBF and TPO were measured with a UV-vis spectrophotometer. The concentration of PyBF was 5×10− 6 M in dichloromethane solution, and that of TPO was 1×10− 4 M. The solutions were irradiated at intervals under different LED light source. The light intensity of 365 and 405 nm are 1.0 and 15 mW cm− 2, respectively.
Gel Fraction
The gel fraction method was selected in this study to obtain the degree of conversion value of monomer and prepolymer, and it is a convenient method to measure the insoluble fractions, such as the cross-linked or network polymers[45–47]. Formulations of PyBF(0.5 wt%)/PEGDA under 365 and 405 nm were used in this study for gel fraction testing. Formulation of PyBF(0.5 wt%)/TMPTA under 405 nm was conducted for comparing different resins. PyBF(0.5 wt%)/TPO/PEGDA with different weight ratio of TPO (1 wt% and 0.5 wt%) and TPO/PEGDA with different weight ratio of TPO (1 wt% and 0.5 wt%) were also tested for promoting component interactions and comparing the photoinitiation ability of PyBF. The blank glass sheets are numbered, weighed and recorded, respectively. Then, a sample of photopolymerization system was dropped on the glass sheet, and recorded the weighted as m1. The LED lamp was used to irradiated the sample at intervals. After irradiation, the glass sheets were immersed in ethanol solution sufficiently, and it was put into the oven for drying to constant weight. Then, the remaining solid weight was recorded as m2. The gel fraction rate is calculate according to ω= (m2/m1) × 100% (Eq. (1)). Moreover, Formulations of PyBF(0.5 wt%)/triethylamine (TEA)/PEGDA and PyBF/N-methylpyrrolidone (NMP)/PEGDA are also prepared for further investigating the interactions in these two-component photoinitiation systems. The amount of TEA and NMP are the same as 150 µL.
Synthesis
PyBF was synthesized through one-pot reaction, and can easily purify by recrystallization. The corresponding 1H NMR and 13C NMR was provided in Fig. S1 of Supporting Information (SI).
Spectroscopic properties, theoretical calculations and thermogravimetric analysis
UV absorption spectra of three photoinitiators (PyBF and TPO) were measured, as it is expected for well matching with different-wavelength LED light sources. The corresponding absorption spectra are shown in Fig. 1, and the photochemistry parameters are summarized in Table 1. PyBF displayed two main absorption bands around 256 and 368 nm. The main absorption band of PyBF well matches with near UV and visible light range around 350–420 nm. PyBF is very promise for pyrrolo[3,2-b]pyrrole-based photoinitiator to apply in LED photopolymerization under 405 nm. The corresponding concentrations of PyBF and TPO are 5×10− 6 and 1×10− 4 M, respectively. TPO is the commercial radical photoinitiator, and its maximum absorption wavelength (λabsmax) is at 295 nm as determined. As shown in Table 1, the maximum molar extinction coefficients of PyBF, and TPO are 292200 and 1640 M cm− 1, separately. The maximum emission wavelengths (λflmax) of PyBF and TPO were also measured as 424 and 460 nm with its concentration of 1×10− 4 M (Fig. S2).
|
Compound |
PyBF |
TPO |
|---|---|---|
|
λabsmax (nm) |
368 |
292 |
|
λflmax (nm) |
424 |
460 |
|
ɛmax(L · mol− 1 · cm− 1) |
333600 |
1640 |
|
Eox(V) |
0.864 |
-0.511 |
|
Ered(V) |
1.062 |
0.910 |
|
E00(eV) |
3.09 |
3.08 |
To gain insight into the electronic properties and geometries of PyBF, quantum chemical calculations based on DFT at the B3LYP/6-31G level were carried out[48]. All structural optimization and energy calculations were performed using the GAUSSIAN 09 program. The frontier orbitals of PyBF and the electrostatic potential surface (ESP) profile for PyBF are shown in Fig. 3. ESP result exhibits the inductive effect of electron-withdrawing groups makes the negative charge of the -CF3 groups. Especially, the charge distribution of pyrrolo[3,2-b]pyrrole core on PyBF still shows negative, indicating pyrrolo[3,2-b]pyrrole electron-rich property. The highest occupied molecular orbital (HOMO) of PyBF mainly locates among pyrrolo[3,2-b]pyrrole and the 2,5-diphneyl containing -CF3, while the lowest unoccupied molecular orbital (LUMO) almost delocalize over the whole molecule. As shown in Table 1, the E00 values calculated from optical results are 3.09 eV for PyBF.
Thermal properties of PyBF and TPO were investigated by TGA analysis[49]. The temperature range of the weight loss curves is from 25 to 550 oC. Figure 4 presents the weight loss curves of PyBF and TPO, respectively. The decomposition temperatures (Td) values of PyBF and TPO are 340.5 and 295 oC, respectively. The thermal stability of PyBF is sufficient for usual storage and processing. The new photoinitiator with -CF3 exhibited Td values higher than 200 oC, which indicated that the good heat-resistance property of PyBF based on the pyrrolo[3,2-b]pyrrole core.
Steady state photolysis
Steady-state photolysis experiment was conducted to investigate the photochemical reaction of PyBF[50, 51]. As shown in Fig. 5 (a) and (b), the photolysis of individual PyBF under 365 and 405 nm is very efficient within 60 s. The absorption band of PyBF declined continuously after irradiation time, indicating the ICT band gradually decreased. New shoulder bands are around 250–350 nm, suggesting a new blue-shift intermediate generate after decomposition of D-A structure, which is in accordance with that of our previous study[40]. NMR and MS results also indicate photolysis occurred during the light irradiation. 1H NMR spectrum after irradiation is shown in Fig. S3. MS spectra before and after photolysis are shown as Fig. S4 (a) and (b). The characterized peaks on 1H NMR spectra of PyBF were gradually transformed after light exposure. As shown in Fig. S3, the chemical shift δ of PyBF at 6.46 ppm is attributed to the C-H on the pyrrolo[3,2-b]pyrrole structure, and new peaks were shown at around 6.66 ppm after 480 s irradiation by LED lamp of 365 nm. This means that a new pyrrolo[3,2-b]pyrrole structure was generated after bond fraction of the -CF3 groups during light irradiation. Fig. S4 shows the mass spectrum change of PyBF from initial to irradiated by 365-nm LED for 480 s. MS spectrum of PyBF shows a peak at m/z = 701, corresponding to the exact mass of PyBF. A new peak is observed at m/z = 566 after 480 s irradiation, which indicates the formation of a new structure. The peak at m/z = 566 possibly corresponds to the photolysis product with its structure shown in schematic diagram of mechanism as Fig. S5. The efficient photolysis of PyBF under 405-nm LED lamp reveals that its good photoreaction activity for visible light-induced photopolymerizations of acrylate photosensitive resins.
Photopolymerizations of different resins at different wavelengths and improvement by amines
The gel fraction method was used to directly compare the curing conversions of PyBF(0.5 wt%)/PEGDA system under LED lamps of 365/405 nm and PyBF(0.5 wt%)/TMPTA. Figure 6(a) displays the effects of different irradiation wavelengths on the photoinitiation ability of the new pyrrolo[3,2-b]pyrrole-based radical photoinitiator, and Fig. 6(b) shows difference of gel fractions between the bi-functional acrylate prepolymer PEGDA and tri-functional acrylate monomer TMPTA induced by PyBF.
The maximum gel fraction rate value of PyBF(0.5 wt%)/PEGDA under 405 nm light source is 61.3%, and that of PyBF(0.5 wt%)/PEGDA under 365 nm light source is 45.3%. Figure 6(a) suggests PyBF shows better photoinitiation ability under irradiation wavelength of 405 nm than 365 nm. Figure 6 (b) shows the gel fraction rate of PyBF(0.5 wt%)/TMPTA under 405 nm is around 40%. It can be seen from the Fig. 6 (b) that both the bifunctional acrylate prepolymer of PEGDA and trifunctional acrylate monomer of TMPTA are successfully polymerized by the photoinitiation of PyBF under LED lamp of 405 nm.
In order to improve the polymerization performance of the curing system, triethylamine (TEA) and N,N-methylpyrrolidone (NMP) were added to the formulas with PyBF as the photoinitiator and PEGDA as the curing resin[52]. According to Fig. 6(c), after adding TEA, the gel fraction rate was increased from 64.3–80.0%, while the addition of NMP increases the final conversion to 65.4%. These experiments exhibit PyBF not only can be used as one-component photoinitiator but also as two-component with amines under 405 nm.
Photopolymerizations incorporation with commercial TPO
In order to further extend the applications of pyrrolo[3,2-b]pyrrole photoinitiators, we also cooperated PyBF with commercial visible-light radical photoinitiators. The corresponding gel fraction curves versus irradiation time are exhibited in Fig. 7. The absorption of commercial TPO well matches with the 405 nm light source for light-curing 3D printing technology in additive manufacturing. The final gel fraction rates of PyBF(0.5 wt%)/TPO(1 wt%)/PEGDA and TPO(1 wt%)/PEGDA systems are 100%, and those at 1s are 93.8% and 87.5%, respectively. When the addition of 0.5 wt% TPO, the highest gel fraction rate of PyBF(0.5 wt%)/TPO(0.5 wt%)/PEGDA also can reach nearly 100%, and those at 1s are 92.6% and 87.5%, respectively.
In addition, the synergistic effect of TPO and PyBF was proved by studying the spectral and electrochemical behavior of PyBF/TPO two-component systems. The free energy change (ΔGel) of the photoelectron reaction between the excited state of PyBF as electron donor and TPO as electron acceptor are calculated based on the Rehm-Weller equation[41]. CV results provide the oxidation potential (Eox) of electron donor (PyBF) and the reduction potentials (Ered) of electron acceptor (TPO). In a separate experiment (Fig.S2), the oxidation potential of PyBF is 0.864V. The reduction potential of TPO is -0.910V. The singlet excited state energy (E00) of PyBF is calculated as 3.09 eV, according to the intersection wavelength of its absorption spectrum and emission spectrum on basis of E00 = hcN/λ. The PyBF/TPO pair is calculated ΔGel is -3.14 eV, indicating that the photoelectron transfer between the excited state of PyBF and TPO is thermodynamically allowed. The negative free energy change of PyBF/TPO favors photoelectron transfer reactions.
\(\Delta {G}_{\text{e}\text{l}}={E}_{\text{o}\text{x}}\left(\frac{\text{D}}{{\text{D}}^{\bullet +}}\right)-{E}_{\text{r}\text{e}\text{d}}\left(\frac{{\text{A}}^{\bullet -}}{\text{A}}\right)-{E}_{00}\) Eq. (2)
When commercial photoinitiators were co-initiated with PyBF, the resistance to shrinkage[29, 34] and migration of cured polymers were found to be improved[12, 33, 53]. Figure 8 (a)-(c) are surface morphology images of the cured materials of PyBF(0.5 wt%)/PEGDA, TPO(1 wt%)/PEGDA and PyBF(0.5 wt%)/TPO(1 wt%)/PEGDA observed by scanning electron microscope (SEM), respectively. The cured materials of the three photopolymerization systems were prepared under a 405nm LED lamp with a light intensity of 15 mW cm− 2 for 480 s. When the curing system is PyBF(0.5 wt%)/PEGDA, the surface is with uneven and some extent textured morphology (Fig. 8 (a)). It can be seen from (Fig. 8 (b)) that there are obvious folds on the surface of the samples polymerized by TPO(1 wt%)/PEGDA. The flat and smooth surface of the sample obtained by PyBF(0.5 wt%)/TPO(1 wt%)/PEGDA is without wrinkles and no folds, as shown in Fig. 8(c), indicating low curing shrinkage after polymerized for the same period.
To investigation of migration properties, cured materials were weighed and then soaked in 3 mL acetonitrile solution. Figure 9 (a) and (b) show the absorption spectra changes at λabsmax with the increase of soaking time for PyBF(0.5 wt%)/PEGDA and TPO(1 wt%)/PEGDA, respectively. Figure 9(c) exhibits the absorbance changes at their maximum absorption wavelengths after the cured film soaked in acetonitrile for one day. Table 2 sums up the migration ratio and extraction weight for PyBF and TPO from their cured materials. The migration ratio of PyBF has a comparable scale with commercial TPO, which is calculated by Eq. (3)[54]. The extraction weight is calculated from Eq. (4)[55]. Based on the absorptions at λabsmax of the leaching solution, the concentration of the photoinitiators were calculated, and low leaching of photoinitiator compounds favor the increase of the hardness of the cured films[30, 33]. The molecular weight of PyBF is 704.3 g mol− 1, which is larger than that of commercial TPO (348.4 g mol− 1).
|
Photoinitiator |
Absorbance |
Extraction Weight (10-5m, g) |
Original quality(10− 5, g) |
Extraction ratio(wt%) |
|---|---|---|---|---|
|
PyBF |
0.168 |
0.1064 |
1.5 |
7.09 |
|
TPO |
0.209 |
13.3192 |
30 |
44.40 |
A photoinitiator, 1,4-bis(4-bromophenyl)-2,5-bis(4-(trifluoromethyl)phenyl)-1,4-dihydropyrrolo[3,2-b]pyrrole (PyBF), with symmetric trifluoromethyl end groups was synthesized through a one-step aldehyde–ketone condensation reaction. The introduction of symmetric -CF3 moieties have been studied for visible light initiation ability, relationships with different components and surface morphology of the cured materials. PyBF has been not only investigated as a one-component free radical photoinitiator by itself under 365 nm and 405 nm LED lamp, but also discussed co-initiation with TEA, NMP and TPO under 405 nm. Both prepolymer and monomers have been applied to the photopolymerization formulas. The thermal stability of PyBF is comparable with commercial TPO. PyBF/PEGDA system gets curing conversion about 60%. The gel faction result of PyBF/TEA/PEGDA shows the presence of TEA increase curing conversion beyond 80%. The conversion of the PyBF/TPO/PEGDA reach near 100%, and SEM results reveal the surface morphology show the synergistic effect between PyBF and TPO. The negative ΔGel value indicates that the photoelectron transfer between the excited state of PyBF and TPO is thermodynamically allowed. It is believed that new pyrrole derivatives will further expanding the toolbox for photoinitiators with different absorption characteristics, photophysical properties and interaction with components.
Acknowledgments The authors gratefully thanks for the financial support of the Natural Science Foundation of Tianjin City (22YDTPJC00620).
Ethical Approval Not applicable.
Funding The authors received the financial support of the Natural Science Foundation of Tianjin City (22YDTPJC00620) for the research publication of this article.
Availability of data and materials All data generated or analyzed during this study are included in this published article [and its supplementary information files].
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No competing interests reported.