G Model
CCLET-3728; No. of Pages 7
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J.-Y. Yao et al. / Chinese Chemical Letters xxx (2016) xxx–xxx
[27–31], in this text we explored quinoxaline containing photo-
cleavable thioether group as hybrid photoinitiator. With the
quinoxaline as a typical hydrogen abstraction group, we intro-
ethanol in 85 8C and stirred for 12 h under nitrogen protection. The
mixture was then evaporated to remove most of the solvent and
recrystallized. The precipitant was filtered from ethanol and dried
to get 2, 3-bis (4-fluorophenyl) quinoxaline (DF-Q).
duced phenyl thioether group into
a series of quinoxaline
skeletons, which was proved to be cleavable by irradiation of
UV-light. This system possesses the advantage of both Type I and
Type II mentioned above, such as the adjustable absorption
wavelength and more active or not easily quenched radicals. The
involved photochemical mechanisms were investigated by UVꢀvis
photolysis, electron spin resonance spin trapping (ESR-ST) and
high-performance liquid chromatography/mass spectrum (HPLC/
MS) techniques. Then we studied the kinetics for polymerization of
multifunctional acrylates by Real Time Fourier Transform Infrared
(FT-IR).
10 mmol of DF-Q and three times equivalent of thiophenol
(30 mmol) were put into 150 mL three-necked round bottom flask
equipped with magnetic stirrer. After the addition of 50 mL N, N-
dimethylformamide (DMF), one times equivalent of KOH and
toluene were added to accelerate reaction rate. The reaction was
under the gas protection and equipped with water separator to
remove water. The mixture was stirred at 130 8C for 24 h.
Appropriate addition of toluene should be done after the toluene
was evaporated. The mixture was slowly trickled into 10 times
ethanol. The precipitant was filtered from ethanol and dried to get
2, 3-bis (4-(phenylthio) phenyl) quinoxaline (SQ1).
2. Experimental
2.3. Instruments
2.1. Materials
1H NMR and 13C NMR spectra were recorded on a Varian
Mercury Plus-400 nuclear magnetic resonance spectrometer
(400 MHz) using CDCl3 and DMSO-d6 as solvents. FT-IR spectra
were recorded on a Thermo Scientific IS10 Fourier Transform
Infrared Spectrometer. Mass spectra were determined on ACQUI-
TYTM UPLC&Q-TOF MS Premier Ultra Performance Liquid Chro-
matography & Quadrupole-Time-of-Flight Mass Spectrometer.
UVꢀvis absorption spectra and dynamics were conducted on a
Perkin-Elmer LS-50B spectrophotometer. SQs were dissolved in
chloroform at a concentration about 5 ꢁ 10ꢀ5 mol/L. Elemental
analysis was conducted on an Elementar Vario ELIII. ESR (electron
spin resonance) experiments were carried out with a Bruker EMX
EPR spectrometer.
[1,10-Biphenyl]-3,30,4,40-tetraamine,1,2-bis(4-fluorophenyl)
ethane-1,2-dione, naphthalene-2,3-diamine were obtained from
TCI (Shanghai) Development Co., Ltd. Benzene-1,2-diamine,
[1,10:20,100-terphenyl]-40,50-diamine were purchased from Meryer
(Shanghai) Chemical Technology Co., Ltd. 2-Mercaptobenzothia-
zole (MBO) was obtained from J&K Chemical Co., (Shanghai, China).
N-methyldiethanolamine (MDEA) and ethyl, 4-(dimethylamino)-
benzoate (EDB) were purchased from Alfa Aesar. ((2-((2-(Acry-
loyloxy)propoxy)methyl)propane-1,3-diyl)bis(oxy))bis(propane-
2,1-diyl) diacrylate (G3POTA) and 2-phenoxyethyl acrylate
(EM2102) were provided by Eternal Chemical Co., CTD. 2, 2-Bis
(4-(acryloxypolyethoxy) phenyl) propane (A-BPE-10) was provid-
ed by Shin-Nakamura Chemical Co., Ltd. Other chemicals were
obtained from China National Pharmaceutical Group Co. (Shang-
hai, China). All reagents were used as received except as noted.
2.4. ESR spin trapping (ESR-ST) experiment
ESR (electron spin resonance) experiments were carried out
with a Bruker EMX EPR spectrometer at 9.5 GHz with a modulation
frequency of 200 kHz with 5, 5-dimethyl-1- pyrroline-N-oxide
(DMPO) as radical capturing agent. A high-pressure mercury lamp
with a cut-off filter (365 nm) was used for irradiation in the ESR
spectrometer cavity. The concentrations of SQ4 dissolved in
mL of each sample
was transformed into a quartz ESR tube and then purged with
nitrogen to get rid of oxygen.
2.2. Synthesis of 2, 3-diphenylquinoxaline derivatives
Four phenylquinoxalines with thioether group (SQ), 2, 3-bis-
(4-(phenylthio)phenyl)quinoxaline (SQ1), 2, 20, 3, 30-tetrakis- (4-
(phenylthio)phenyl) -6, 60-biquinoxaline (SQ2), 2, 3-bis (4-(phe-
nylthio)phenyl) benzo[g] quinoxaline (SQ3), and 2, 3-diphenyl-5, 6-
bis (4-(phenylthio)phenyl) pyrazine (SQ4) were synthesized accord-
ing to Scheme 1, as well as phenyl quinoxalines (Q) as reference. Take
SQ1 as example, 10 mmol of benzene-1, 2-diamine and 10 mmol 1,
2-bis(4-fluorophenyl)- ethane-1, 2-dione were dissolved in 20 mL of
dichloromethane were 1 ꢁ 10ꢀ4 mol/L. 25
2.5. Radical photopolymerization with real time Fourier transform
Infrared spectra
Photopolymerization of different monomers (Scheme 2)
initiated by SQs was carried out while acquiring real time
Fourier Transform Infrared Spectroscopy (FT-IR, Thermo Scien-
tific IS10) with a high-pressure mercury lamp as the light source.
The intensity of light is about 10 mW/cm2. Here, the sample
consists of 4 mmol/L SQs and without any solvent. An
approximately 2 mg film sample of 50
mm thickness was held
on KBr for 3 min while irradiated under the protection of
nitrogen. The change of Peak area in about 1640 cmꢀ1 is directly
proportional to the amount of acrylate reacted in the system. By
integrating the area under the characteristic peak, the double
bond conversion (DBC) of the HDDA was determined according
to Eq. (1) [32,33]:
D
ðS0ꢀStÞ
DBC ¼
(1)
St
Scheme 1. Process for the synthesis of SQs based on quinoxalines and their
structures. (i, 85 8C ethanol as solvent. ii, DMF as solvent, toluene to take away
moisture, KOH as catalyzer in 130 8C).
Where St is the characteristic peak area in about 1640 cmꢀ1
evolved at time t and S0 is the peak area before irradiation.
Please cite this article in press as: J.-Y. Yao, et al., Combining photo-cleavable and hydrogen-abstracting groups in quinoxaline with