Quinizarin Derivatives as Photoinitiators for Free-Radical and Cationic Photopolymerizations in the Visible Spectral Range

Article abstract of DOI:10.1021/acs.macromol.9b02448

We report the use of efficient visible-light sensitive allyl (QA) and epoxidized (QE) quinizarin derivatives as photoinitiating systems when combined with an appropriate electron donor (methyldiethanol amine, MDEA), an electron acceptor (iodonium salt, Iod), or a H donor (thiol derivative), for free-radical photopolymerization (FRP), cationic photopolymerization (CP), and a thiol-ene process. These systems have demonstrated excellent initiating properties under air or in laminated conditions under visible-light irradiation (LEDs?405, 455, and 470 nm or Xe lamp) for FRP, CP, or the thiol-ene process and appear more efficient than the well-known camphorquinone-based photoinitiating systems. As highlighted by electron paramagnetic resonance (EPR) and laser flash photolysis experiments, QA (or QE) acts either as an electron donor via a photoinduced electron transfer pathway with Iod or as a proton/proton-coupled electron transfer promoter with MDEA or a thiol derivative. Two types of interpenetrated polymer networks have been synthesized either by CP and the thiol-ene process with di(ethylene glycol) divinyl ether/trithiol or by a concomitant free-radical and cationic photopolymerization with an epoxide/acrylate blend mixture upon LED?455 or 470 nm exposure. Interestingly, the resulting quinizarin-derived materials showed antiadherence properties under visible-light exposure even after two cycles of antibacterial experiments. Quinizarin derivatives can not only initiate photopolymerization but also generate singlet oxygen on the surface of the materials for preventing the adhesion and proliferation of bacteria under visible-light activation.

Full text of DOI:10.1021/acs.macromol.9b02448

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Article
Quinizarin Derivatives as Photoinitiators for Free-Radical and
Cationic Photopolymerizations in the Visible Spectral Range
́
Pauline Sautrot-Ba, Steffen Jockusch, Jean-Pierre Malval, Vlasta Brezova, Michael Rivard,
Samir Abbad-Andaloussi, Agata Blacha-Grzechnik, and Davy-Louis Versace*
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ABSTRACT: We report the use of efficient visible-light sensitive
allyl (QA) and epoxidized (QE) quinizarin derivatives as
photoinitiating systems when combined with an appropriate
electron donor (methyldiethanol amine, MDEA), an electron
acceptor (iodonium salt, Iod), or a H donor (thiol derivative), for
free-radical photopolymerization (FRP), cationic photopolymeriza-
tion (CP), and a thiol−ene process. These systems have
demonstrated excellent initiating properties under air or in
laminated conditions under visible-light irradiation (LEDs@405,
455, and 470 nm or Xe lamp) for FRP, CP, or the thiol−ene
process and appear more efficient than the well-known
camphorquinone-based photoinitiating systems. As highlighted by
electron paramagnetic resonance (EPR) and laser flash photolysis
experiments, QA (or QE) acts either as an electron donor via a photoinduced electron transfer pathway with Iod or as a proton/
proton-coupled electron transfer promoter with MDEA or a thiol derivative. Two types of interpenetrated polymer networks have
been synthesized either by CP and the thiol−ene process with di(ethylene glycol) divinyl ether/trithiol or by a concomitant free-
radical and cationic photopolymerization with an epoxide/acrylate blend mixture upon LED@455 or 470 nm exposure. Interestingly,
the resulting quinizarin-derived materials showed antiadherence properties under visible-light exposure even after two cycles of
antibacterial experiments. Quinizarin derivatives can not only initiate photopolymerization but also generate singlet oxygen on the
surface of the materials for preventing the adhesion and proliferation of bacteria under visible-light activation.
ing systems.10 Surprisingly, anthraquinone-derived photoinitiat-
ing systems have scarcely been studied, despite their interesting
INTRODUCTION
■
Over the past 10 years, photoinitiated photopolymerization has
light-absorbing properties. A few examples are however
gained great interest in many domains and has been the
described in the literature; Xiao et al. have thus developed a
cornerstone of many conventional applications in coatings,
three-component photoinitiating system based on an anthra-
microelectronics, adhesive inks, dentistry, and the fabrication of
biomaterials or three-dimensional objects.1,2
Photon-driven chemical processes are undoubtedly indis-
quinone derivative Oil Blue N, iodonium salt (Iod), and N-
vinylcarbazole (NVK), for the concomitant free-radical and
cationic polymerizations, as well as the thiol−ene click
reactions.11
The ability of three monoamino-substituted anthraquinone
derivatives as potential photoinitiators when combined with Iod
has been investigated by Zhang et al. for initiating the cationic
photopolymerization of epoxy monomers upon LED irradi-
ation.12 Coote et al. have described the initiating properties of
multihydroxy-anthraquinone derivatives with various additives
[e.g., Iod, tertiary amine, NVK, or 2-(4-methoxystyryl)-4,6-
pensable techniques for the synthesis of original materials since
these offer undeniable advantages over the thermal route, e.g.,
low-temperature polymerization conditions without any harm-
ful solvent, spatial control, reduced reaction times, and the
capability to tune overall properties of the cross-linked
materials.3 However, several limitations exist such as oxygen-
induced inhibition that remains the main issue of concern in
FRP or the use of UV-light irradiation.4,5 In light of these
considerations, many efforts have been made to develop new
visible-light photosensitive systems to overcome the previously
described drawbacks.6−8 Both cleavable and Norrish II type
photoinitiating systems, acting in the visible range, are well
known to perform the FRP under air.9 A review has moreover
described the recent progress in cationic and free-radical
photopolymerizations using visible-light-sensitive photoinitiat-
Received: November 20, 2019
Revised: January 11, 2020
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Table 1. Structure of the Compounds Used in This Study
bis(trichloromethyl)-1,3,5-triazine (R-Cl)] for different types of
photopolymerization reactions (cationic photopolymerization
of epoxides or divinyl ethers and free-radical polymerization of
methacrylates) under green LED.11 Similar results have been
demonstrated by Xiao et al. using four dihydoxyanthraquinone
derivatives upon blue LED irradiation.13 More recently, a new
efficient three-component photoinitiating system based on 2,6-
diaminoanthraquinone was used to initiate upon visible-light
exposure, the cationic polymerization of epoxy monomers
concomitantly with the photoinduced sol−gel process of a
reactive hybrid organic−inorganic precursor.14
The limited investigations concerning the use of anthraqui-
none (AQ) derivatives as visible-light-absorbing photoinitiators
for the free-radical and cationic photopolymerizations prompted
us to develop new AQ structures. The novelty of such AQ
derivatives is to be used as (i) a visible photosensitizer and a
photopolymerizable monomer since allyl and epoxy photo-
polymerizable moieties have been added to the AQ structures
and (ii) an antibacterial agent since these new molecules can
generate singlet oxygen. In the present investigation, two
anthraquinone derivatives are synthesized and their photo-
chemical behavior is evaluated under visible-light irradiation
(LED@405, 455, or 470 nm). The performance of AQ
derivatives as efficient photoinitiators for free-radical or cationic
polymerizations and thiol−ene reactions when combined with
methyldiethanol amine (MDEA, an electron donor), iodonium
salt (Iod, an electron acceptor), or a thiol derivative (H-donor
molecule) is investigated by real-time FT-IR spectroscopy.
Mechanistic details are evaluated by steady-state photolysis and
nanosecond laser flash experiments and fluorescence and
electron paramagnetic resonance techniques. In addition, the
antimicrobial properties of AQ-derived materials are tested
against Staphylococcus aureus under visible-light exposure after
many cycles of antibacterial experiments, which had never been
demonstrated in the literature yet.
B
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derivatives/Iod/RhB were conducted in acetonitrile, under air, and
upon LED@405 nm exposure (44 mW/cm2).
Steady-State Fluorescence Measurements. Steady-state fluo-
rescence measurements were carried out on a FluoroMax-4
spectrofluorometer. The fluorescence quantum yields were determined
relatively to rhodamine 101 in EtOH (Φf = 0.92) and corrected for the
solvent refractive index.
Phosphorescence Experiments. The phosphorescence measure-
ments were performed using a FluoroMax-4 spectrofluorometer, which
is equipped with a Xe-pulsed lamp operating at up to 25 Hz.
Luminescence measurements were performed in ethanol at 77 K. The
samples are placed in a 5 mm diameter quartz tube inside a Dewar filled
with liquid nitrogen.
Electronic Paramagnetic Resonance (EPR). Electronic para-
magnetic resonance (EPR) spectra in X-band were carried out by
means of an EMXplus spectrometer (Bruker) with a high-sensitivity
probe head (Bruker) or by an EMX spectrometer (Bruker) with the
standard TE102 (ER 4102 ST) rectangular cavity using thin-walled
quartz EPR tubes (Bruker) according to the general procedure
described in ref 15. The experimental EPR spectra were analyzed by
Bruker software WinEPR, and the simulated spectra were calculated
using Winsim2002 software16 or with the EasySpin toolbox.17
Laser Flash Photolysis. Laser flash photolysis experiments
employed the pulses from a Spectra Physics GCR-150-30 Nd:YAG
laser (355 nm, 7 ns pulse length) and a computer-controlled system that
has been described elsewhere.18 For recording the transient absorption
spectra and quenching studies, solutions of QA or QE were prepared at
concentrations such that the absorbance was ∼0.3 at the excitation
wavelength (355 nm) at a path length of 1 cm.
EXPERIMENTAL SECTION
■
Materials. Quinizarin (1,4-dihydroxyanthraquinone, QZ), 3,4-
epoxycyclohexane)methyl-3,4-epoxycyclohexylcarboxylate (EPOX),
trimethylolpropane tris(3-mercaptopropionate) (trithiol, >95%), di-
(ethylene glycol)divinyl ether (DVE), camphorquinone (CQ, >97%),
3-chloroperbenzoic acid (m-CPBA), 2,3,5,6-tetramethyl-1-nitrosoben-
zene (nitrosodurene, ND), and 5,5-dimethyl-pyrroline N-oxide
(DMPO, distilled prior to the application) were purchased from
Sigma-Aldrich, and trimethylolpropane triacrylate (TMPTA) was from
Sartomer. N-Methyldiethanol amine (>98%) and allyl bromide (99%,
stab. with 300−1000 ppm propylene oxide) were from Alfa Aesar, and
4-(2-methylpropyl)phenyl iodonium hexafluorophosphate (Iod) was
kindly provided by BASF. 1,3-Diphenylisobenzofuran (DPBF) (Acros
Organics, purity >97%) in methanol (Acros Organics, 99.9%) were
used as specific 1O2 quenchers. Ethanol (EtOH), methanol (MeOH),
molecular sieves (3 Å), silica gel, ethyl acetate (EtOAc), cyclohexane
(CyH), and diethyl ether (Et2O) were obtained from commercial
suppliers. Table 1 summarizes the chemical structures of the main
compounds used in this study.
Synthesis of Allyl Quinizarin (QA). A mixture of NaOH (120 mg,
3 mmol, 2 equiv) and K2CO3 (1.66 g, 12 mmol, 8 equiv) was powdered
in a mortar. To the resulting powder were successively added 1,4-
dihydroxyanthraquinone (QZ) (360.3 mg, 1.5 mmol, 1 equiv) and
NEt4Br (96.7 mg, 0.3 mmol, 0.2 equiv). The solid mixture was then
added portionwise and under agitation into a 20 mL microwave tube
equipped with a magnetic stirrer and containing allyl bromide (6 mL, 46
equiv). The heterogeneous mixture was let to react under pressure at 85
°C for 30 min under microwave exposure. After completion of the
reaction, H2O was added (100 mL) and the expected product was
extracted with Et2O (3 × 50 mL). The combined organic layers were
washed with H2O, then dried over anhydrous Na2SO4, and
concentrated under vacuum. The crude product was purified by
chromatography (SiO2, CyH/EtOAc 80/20). Expected allyl quinizarin
(QA) was obtained as a yellow powder (85%, mp = 105 2 °C). 1H
NMR (400 MHz, CDCl3, ppm) δ 8.18 (m, 2H, J = 5.8, 3.3 Hz, H2),
7.71 (m, 2H, J = 5.8, 3.3 Hz, H1), 7.30 (s, 2H, H10), 6.14 (ddt, 2H, J =
17.2, 10.6, 5.0 Hz, H8), 5.61 (dd, 2H, J = 17.2, 1.5 Hz, H9a), 5.37 (dd,
2H, J = 10.6, 1.5 Hz, H9b), 4.71 (dt, 4H, J = 5, 1.4 Hz, H7). 13C NMR
(100 MHz, CDCl3, ppm) δ 183.3 (C4), 153.5 (C6), 134.4 (C3), 133.4
(C1), 132.8 (C8), 126.6 (C2), 123.8 (C5), 122.4 (C10), 118.3 (C9),
71.1 (C7). IR (neat, cm−1) 1658, 1562, 1401 (νCC); 1236 (νAr‑O‑C);
929, 976 (δRCHCH2); 803, 859 (δC‑H).
Irradiation Sources. Three light-emitting diodes (LEDs), i.e.,
LED@405 nm (60 mW/cm2), LED@455 nm (38 mW/cm2), and
LED@470 nm (25 mW/cm2), and a polychromatic Xenon lamp
(Hamamatsu, Lightningcure LC8-03, xenon lamp, 200 W, 60 mW/
cm2) were used to initiate the cationic or free-radical photo-
polymerization.
Cyclic Voltammetry. Cyclic voltammetry measurements of QA
and QE were performed in a classical three-electrode cell equipped
using an AUTOLAB potentiometer/galvanometer employing GPES
electrochemical software version 4.9 (Utrecht, The Netherlands). A
standard three-electrode cell configuration was employed using a
platinum working electrode, a saturated calomel electrode (SCE), and a
gold wire as a counter electrode. nBu4NBF4 (0.1 M, acetonitrile
solution) was used as the supporting electrolyte. QA or QE was
introduced at 1 mM concentration, and the electrochemical cell was
placed under inert conditions by argon flow prior to analysis. The free
energy change, ΔGeT, for an electron transfer between QA (QZ or QE)
and Iod can be calculated for the classical Rehm−Weller equation.19
Photopolymerization Kinetic Studies. All of the photochemical
conditions for the photopolymerization experiments are described in
the figure captions. The photosensitive formulations were laid down on
a BaF2 pellet and irradiated under air or in laminate conditions with
different light sources. The thickness of the coatings was 25 μm for all of
the experiments. The decrease of the epoxy group contents of EPOX
and the acrylate functions of TMPTA are continuously followed by real-
time Fourier transform infrared spectroscopy (RT-FT-IR, Jasco FT-IR
4700) at 790 and 1636 cm−1, respectively.
Singlet Oxygen Detection. Singlet oxygen photogeneration of the
coatings was investigated using 0.05 mM solution of 1,3-diphenyliso-
benzofuran (DPBF) in MeOH.20,21 The progress of the singlet oxygen
formation was followed by the oxidation of DPBF and consequently by
following the decrease of its absorbance at 410 nm by means of a
Hewlett Packard 8452A UV−vis spectrometer. The quartz cuvette
applied in the measurements has a 10 mm path length for UV−vis
measurements. The surface of the sample (0.5 cm2; thickness, 2 mm)
was illuminated under a Xenon lamp source (Figure S4). Additionally,
the blank test was done, i.e., the absorbance of DPBF was monitored
when its solution was irradiated in the absence of the photoactive layer.
The reported decrease of the absorbance of DPBF during the
irradiation of photoactive polymeric films is given with respect to the
blank test.
Synthesis of Epoxidized Quinizarin (QE). Into a 100 mL one-
necked flask equipped with a magnetic stirrer, allyl quinizarin QA (0.5 g,
1.6 mmol, 1 equiv) was dissolved in degassed CH2Cl2 (50 mL). m-
CPBA was added at 0 °C 4 times over 10 h (4 × 0.5 g, 16 mmol, 10
equiv), and the mixture was allowed to warm to room temperature
between each addition. After completion of the reaction, the mixture
was concentrated under vacuum and purified by chromatography
(SiO2, CyH/EtOAc 40/60). Epoxidized quinizarin (QE) was obtained
1
as a yellow powder (80%, mp = 160 2 °C). H NMR (400 MHz,
CDCl3, ppm) δ 8.17 (m, 2H, J = 5.8, 3.3 Hz, H2), 7.72 (m, 2H, J = 5.8,
3.3 Hz, H1), 7.38 (s, 2H, H10), 4.44 (d, 2H, J = 11.4 Hz, H7a), 4.15
(dd, 2H, J = 11.4, 4.8 Hz, H7b), 3.48 (dd, 2H, J = 4.8, 2.6 Hz, H8), 3,04
(dd, 2H, J = 4.9, 2.6 Hz, H9a), 3.01−2.93 (m, 2H, J = 4.9 Hz, H9b). 13C
NMR (100 MHz, CDCl3, ppm) δ 183.0 (C4), 153.8 (C6), 134.2 (C3),
133.5 (C1), 126.6 (C2), 124.1 (C5), 123.3 (C10), 70.9 (C7), 50.4
(C8), 44.8 (C9). IR (neat, cm−1) 1664, 1565, 1402 (νCC); 1239
(νAr‑O‑C); 910 (δCH2‑O‑CH); 845, 765 (δC‑H).
Characterization. NMR spectra were recorded with a Bruker
Avance II (400 MHz for 1H and 100 MHz for 13C NMR) instrument.
1D and 2D NMR experiments were performed in CDCl3. IR spectra
were recorded on a PerkinElmer FT-IR spectrometer. UV−vis spectra
were obtained on a PerkinElmer Lambda 2 UV−vis spectrophotometer
in the 200−800 nm wavelength range, using 1 cm path length cuvettes
at room temperature. Melting points of both modified monomers were
̈
measured in capillary tubes on a Buchi B-545 apparatus.
Steady-State Photolysis. Steady-state photolysis of quinizarin
derivatives (QA or QE), quinizarin derivatives/Iod, and quinizarin
C
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Scheme 1. General Procedures for the Synthesis of QA and QE
Antibacterial Assays. Antibacterial tests were performed using S.
aureus ATCC6538 on the quinizarin derivative-coatings under visible-
light irradiation according to a previously described procedure.22,23 The
emission spectrum of the visible emitted lamp used in the antibacterial
tests is given in Figure S4. The total bacterial adhesion was determined
by counting the number of CFUs. Levels of adhesion were reported as
numbers of cells per square centimeter. Experiments were conducted 4
times for each sample. Finally, the quinizarin derivatives films were
intensively rinsed with ethanol and dried under vacuum for one night at
40 °C. After 1 week of storage in the dark, the same samples were
subjected to the same described antibacterial tests under visible-light
exposure.
RESULTS AND DISCUSSION
■
Figure 1. UV−vis spectra of quinizarin (QZ), allyl quinizarin (QA),
epoxidized quinizarin (QE), and camphorquinone (CQ) in acetoni-
trile.
Synthesis and Absorption Properties of QA and QE.
The general procedure for the synthesis of QA and QE is
summarized in Scheme 1. 1H, 13C, and HSQC NMR of QA and
QE are described in the Supporting Information (Figures S1−
S3). Allylation of quinizarin (QZ) followed a previously
reported procedure24 to give aromatic ethers according to the
Williamson reaction. The synthesis proceeded in a sealed vial
under microwave irradiation, using allyl bromide as the reaction
solvent, in the presence of NaOH, K2CO3, and NEt4Br. The
reaction was completed after 30 min at 85 °C. The purification
of the crude by flash chromatography on silica gel gave the
expected allylated quinizarin (QA) in a good yield of 85%. 1H
NMR analysis of QA confirmed the presence of two allyl groups
per quinizarin moiety. The 1H signals at 6.15 ppm (m, 1H), 5.6
ppm (d, 1H), and 5.35 ppm are assigned to the protons of the
allyloxy group of QA and are in agreement with literature
data.24,25
The oxidation of QA was performed in CH2Cl2 by the action
of m-CPBA added portionwise over 10 h to convert the allyl
bonds into epoxides.25 This quantitative reaction was done
under mild conditions and expected to yield high conversions.
After purification of the crude by flash chromatography on silica
gel, the epoxidized quinizarin derivative (QE) was isolated in
80% yield. Comparison with the NMR spectrum of QA, the
complete disappearance of the allyl protons between 5.30 and
6.20 ppm in the structure of QE is observed and consequently
new signals originating from the protons of the epoxy group26,27
between 2.9 and 3.5 ppm appear, thus confirming the isolation of
a bis-epoxidized compound.
anthraquinone derivatives in combination with different
additives are described in the literature and have been used as
photoinitiating systems to promote CP or FRP. According to
literature studies,13 QZ has not demonstrated any interesting
photoinitiating properties, which motivated us to focus our
attention on the properties of new quinizarin derivatives QA and
QE. The overall photochemical reactivities of QA and QE in the
presence of Iod, MDEA, or trithiol have been first studied by
steady-state photolysis. As demonstrated in Figure 2A, the
absorbance of QA slightly decreases upon LED@405 nm
exposure under air, indicating weak photobleaching and low
photochemical reactivity. On the contrary, when QA is
combined with Iod, a significant decrease of the absorbance of
QA is observed (Figure 2B), thus demonstrating a synergetic
interaction between QA and Iod. Notably, the photolysis of the
QA/Iod photoinitiating system under visible-light irradiation
results in the formation of protonic acid, H+, as demonstrated by
rhodamine B (RhB) as an acid indicator22 (Figure 2C). As
shown in Figure 2C, the irradiation of the QA/Iod system at 405
nm leads to a significant increase in the acid form of RhB at 550
nm. Interestingly, the addition of MDEA or trithiol to QA lead
to a fast decrease of the absorbance of QA, along with the
appearance of new UV−visible bands below 400 nm and above
500 nm (Figure 2D,E, respectively). These new species have
been attributed to semiquinone-like radical species.28,29 Results
with QE are similar to those observed with QA (see the
Supporting Information, Figure S5).
The UV−vis absorption spectra of QA (λmax = 415 nm, εmax
=
6000 M−1 cm−1) and QE (λmax = 407 nm, εmax = 5530 M−1
cm−1) in Figure 1 show high molar absorption coefficients than
the common visible-light photoinitiator camphorquinone (CQ)
The fluorescence and phosphorescence properties of both QA
and QE are displayed in Figure 3, respectively. All of the
photochemical properties of the anthraquinone derivatives are
summarized in Table 2. QA and QE showed only very week
fluorescence (fluorescence quantum yield: Φf ∼ 0.002), and no
changes in fluorescence were observed in the presence of
additives (Iod, MDEA, or trithiol). These results suggest short
singlet excited-state lifetimes and high intersystem crossing
efficiencies for both quinizarin derivatives. To investigate the
used in free-radical or cationic photopolymerization (CQ, λmax
=
466 nm, εmax = 38 M−1 cm−1). The overlaps between the
emission spectra of the household LEDs@405, 455, and 470 nm
with the absorption spectra of QA or QE make them interesting
and potential visible-light photoinitiators.
Photochemical Reactivity of QA and QE with Some
Additives, i.e., Iod, MDEA, or Trithiol. The reactivities of
D
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Figure 2. Steady-state photolysis of (A) QA, (B) QA/Iod, (C) QA/Iod/rhodamine B (D) QA/MDEA, and (E) QA/trithiol in acetonitrile after
LED@405 nm irradiation under air. [QA] = 0.14 mM, [Iod] = 13 mM, [MDEA] = 30 mM, [trithiol] = 10 mM, and [RhB] = 10−6 M.
triplet states, transient absorption measurements using nano-
second laser flash photolysis of QA and QE were performed in
deoxygenated acetonitrile and are displayed in Figure 4. Several
triplet-state absorption peaks for QA and QE were observed
below 600 nm (295, 340, 490, and 580 nm). The triplet states of
QE and QA decayed with lifetimes of 28 and 40 μs, respectively,
under the recovery of the ground state, which was observable at
410 nm.
As expected, the triplet states were quenched by molecular
oxygen efficiently (quenching rate constants: kqO2 (QA) = (1.7
0.1) × 109 M−1 s−1 and kqO2 (QE) = (1.5 0.1) × 109 M−1 s−1;
see the Supporting Information, Figure S6).
When Iod is added to a deoxygenated solution of QA or QE in
acetonitrile, their triplet lifetimes decreased. The bimolecular
rate constants for quenching of triplet states of QA and QE were
Figure 3. Normalized absorption, fluorescence, and luminescence
determined from the plot of the slope of the inverse triplet
spectra of quinizarin derivatives. Absorption and fluorescence spectra of
lifetime vs the Iod concentration (see the Supporting
Information, Figure S7). The resulting quenching rate constants
of kqIod (QA) = (8.9 0.4) × 106 M−1 s−1 and kqIod (QE) = (9.3
0.3) × 106 M−1 s−1 (Supporting Information, Figure S7)
QA and QE were done in MeCN (λex = 400 nm). Phosphorescence
spectra of QA and QE were collected in a glassy matrix of EtOH (λex =
430 nm, delay = 1 ms, and time-gate = 20 ms). No phosphorescence was
observed with QZ.
E
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Table 2. Photophysical Properties of QZ, QA, and QE
a
a
a
a
a
b
b
εabs /M−1 cm−1
λabs /nm
λfluo /nm
Φfluo
ES1 /eV
ET1 /eV
τp /ms
Eοx (V)
QZ
QA
QE
6950
6000
5530
475
415
407
558
541
539
0.13
0.002
0.002
2.37
1.61
1.66
1.70
c
2.64
2.30
2.37
44
39
c
2.68
a
b
c
In MeCN. In EtOH at 77 K, ET1 was determined from the onset of the phosphorescence spectrum. ES1 ≈ 1/2hc(νabs + νfluo).
Figure 4. Transient absorption spectra of QA (left) and QE (right) in a deoxygenated MeCN solution at 0−8 μs after laser pulse (355 nm, 7 ns pulse
width). The insets at the top show traces of the triplet excited-state decay at 580 nm and ground-state recovery at 410 nm.
indicate electron transfer between the excited triplet states of
quinizarin derivatives and the ground state of Iod. The negative
free energy changes (ΔGT (QA/Iod) = −0.44 eV; ΔGT (QE/Iod)
=
−0.47 eV) for the 3QA/Iod (or 3QE/Iod) system as calculated
with the Rehm−Weller equation using the oxidation potentials
for QA or QE of Eox,QA = 1.66 V/SCE and Eox, QE = 1.70 V/SCE,
respectively (measured by cyclic voltammetry; see Supporting
Information, Figure S8), the reduction potential of Iod, ERed
,
Iod
= −0.2 V, and the excited triplet-state energies of ET,QA = 2.30 eV
and ET,QE = 2.37 eV (extracted from the phosphorescence
spectrum) are in agreement with a favorable electron transfer
reaction from 3QA* (or 3QE*) to Iod.
These statements are further confirmed indirectly by EPR
spin-trapping experiments under light irradiation (Figure 5).
EPR results indicate the formation of a stable adduct of
nitrosodurene (ND) with the 4-methylphenyl radical15 (•ND-
(4-methylphenyl)). According to our previous discussion,
various active radical species are expected to be formed under
visible-light exposure of the QA (or QE)/Iod systems, and a
proposed mechanism is displayed in eqs 1 and 2 and is in
agreement with published mechanistic studies of iodonium salt
photolysis.30−32
Figure 5. Experimental (1) and simulated (2) EPR spectra obtained
after 900 s exposure (LED@400 nm) of QA/Iod/ND in C6H6 under
argon (initial concentrations: [QA] = 5 mM; [Iod] = 35 mM; and
[ND] = 20 mM). EPR spectrometer settings: microwave frequency,
∼9.43 GHz; microwave power, 1.1 mW; center field, ∼336 mT; sweep
width, 4.5 or 5 mT; gain, 1.00 × 105; modulation amplitude, 0.02 mT;
sweep time, 125 s; time constant, 20.48 ms; and number of scans, 5. The
inset shows the structure of the ND spin-adduct assigned from the
simulated EPR spectrum.
3
QA + hv → Q A*
(1)
3QA* + (MePh)2I+(Iod)
rapidly quenched by MDEA with rate constants of kqMDEA (QA)
= (5.4 0.2) × 108 M−1 s−1 and kqMDEA (QE) = (6.1 0.2) ×
108 M−1 s−1 (see the Supporting Information for details, Figure
S9) (Table 3).
→ QA•+ + (MePh)2I•
•
→ QA•+ + MePh + MePhI
(2)
The tertiary amine MDEA is a coinitiator that is frequently used
with ketone-based photoinitiators. The reactivities of triplet
excited states of QA and QE with MDEA were investigated by
laser flash photolysis. The triplet states of QA and QE were
In addition to LFP experiments, EPR investigations show the
formation of aminoalkyl radical DMPO-adducts resulting from
the photolysis of the QA/MDEA photoinitiating system (Figure
6). The spin-Hamiltonian parameters elucidated from the
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Table 3. EPOX Final Conversions Determined by IR under Air or in Laminate upon Exposure to Different Visible-Light Sources
a b
,
for 800 s, in the Presence of CQ/Iod, QZ/Iod, QA/Iod, and QE/Iod
epoxy conversion under air determined by IR (%)
xenon lamp
LED@405 nm
LED@455 nm
LED@ 470 nm
CQ/EPOX/Iod
QZ/EPOX/Iod
QA/EPOX/Iod
QE/EPOX/Iod
np
np
76
57
np
np
56
72
np
np
43
58
np
np
52
50
a
b
np = no polymerization. Photoinitiator/Iod (0.5/2.0%, w/w).
Figure 7. Experimental (1) and simulated (2) EPR spectra obtained
during 600 s in situ exposure (LED@400 nm) of QA/trithiol/DMPO
in C6H6 under argon (initial concentrations: [QA] = 5 mM; [trithiol] =
0.08 M; [DMPO] = 0.08 M). EPR spectrometer settings: microwave
frequency, ∼9.439 GHz; microwave power, 1.1 mW; center field, ∼336
mT; sweep width, 7 mT; gain, 1.00 × 105; modulation amplitude, 0.025
mT; sweep time, 60 s; time constant, 20.48 ms; and number of scans,
10. The inset shows the structure of the DMPO-adduct assigned from
the simulated EPR spectrum.
Figure 6. Experimental (1) and simulated (2) EPR spectra obtained
during 900 s in situ exposure (LED@400 nm) of QA/MDEA/DMPO
in C6H6 under argon (initial concentrations: [QA] = 5 mM; [MDEA] =
0.08 M; [DMPO] = 0.08 M). EPR spectrometer settings: microwave
frequency, ∼9.433 GHz; microwave power, 11 mW; center field, ∼336
mT; sweep width, 7 mT; gain, 1.00 × 105; modulation amplitude, 0.025
mT; sweep time, 90 s; time constant, 20.48 ms; and number of scans,
10. The inset shows the structure of the DMPO-adduct assigned from
the simulated EPR spectrum.
Cationic Polymerization of Epoxides. Different polymer-
ization kinetic profiles (epoxy conversion vs irradiation time) for
EPOX in the presence of QA (or QE)/Iod photoinitiating
systems under air and different visible-light irradiation sources
are displayed in Figure 8. Table 4 summarizes the final epoxy
conversion of EPOX after 800 s of irradiation with different
visible LED systems. CQ/Iod and QZ/Iod have been used as
reference initiating systems for comparison. No photopolyme-
rization of EPOX is observed under visible-light irradiation
when Iod is used alone because it absorbs below 300 nm. The
cationic polymerization of EPOX successfully occurs (Figure 8)
when using the QA (or QE)/Iod system under multiple
wavelength exposures (405, 455, and 470 nm). Accordingly, the
final conversions of epoxy groups into polymer reach more than
50% after 800 s exposure without any period of inhibition. These
results are in accordance with the production of photoacids
(Figure 2C) responsible for cationic photopolymerization of
EPOX. In comparison, the CQ/Iod photoinitiating system was
also tested. CQ is well adapted as its absorption maxima is in the
420−470 nm range and the photosensitized decomposition of
Iod occurs via an electron transfer reaction with CQ, leading to
simulated spectra (i.e., aN = 1.481 0.003 mT, aHβ = 1.848
0.014 mT, aHγ = 0.080 0.001 mT, aHγ = 0.074 0.003 mT; g =
2.0058 0.0001) are compatible with the aminoalkyl radical
DMPO-adduct.15 The EPR results indirectly confirm the
electron transfer reaction, followed by a proton transfer reaction
from MDEA to QA (eq 3).
•
QA + MDEA + hv → QAH• + MDEA (−H)
(3)
Finally, the addition of a thiol derivative, trithiol, to the QA (or
3
3
QE) solution has led to quenching of QA* and QE*. The
bimolecular quenching rate constants, kq, of the QA and QE
triplet states by trithiol were evaluated at (8.1 0.2) × 106 and
(8.0 0.2) × 106 M−1 s−1, respectively (see the Supporting
Information for details, Figure S10). These quenching rate
constants are typically associated with an H-abstraction
reaction; this statement was confirmed by EPR by the formation
of thiyl radicals when QA (or QE)/trithiol systems are irradiated
(Figure 7). Indeed, the spin-Hamiltonian parameters elucidated
β
from the simulated spectra (i.e., aN = 1.348 0.001 mT, aH
=
̈
the generation of Bronsted acid and the cationic polymerization
1.175 0.002 mT, aH = 0.092 0.004 mT, aH = 0.094 0.004
mT; g = 2.0061 0.0001) are well compatible with the thiyl
radical DMPO-adduct33 (eq 4).
of EPOX.34−37 However, under the same irradiation conditions,
the photopolymerization of EPOX fails with the CQ/Iod
system, therefore highlighting the superior initiating properties
of QA (or QE)/Iod photoinitiating systems.
QA + RSH + hv → QAH• + RS•
(4)
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Figure 9. Kinetics profiles of TMPTA in the presence of QA/MDEA
(0.5/2%, w/w) (A) under air and (B) in laminate conditions upon
exposure to (1) LED@405 nm, (2) LED@455 nm, (3) Xe lamp, and
(4) LED@470 nm irradiation. Thickness of the film = 25 μm.
Figure 8. Kinetic profiles of EPOX (epoxy function) under air in the
presence of (A) QA/Iod (0.5/2%, w/w) and (B) QE/Iod (0.5/2%, w/
w) upon exposure to (1) xenon lamp, (2) LED@405 nm, (3) LED@
470 nm, and (4) LED@455 nm. Thickness of the film = 25 μm.
or in laminate. This better performance of QA and QE is
probably caused by the higher molar absorption coefficients of
QA and QE compared to that of CQ. These kinetic results
confirm the formation of α-aminoalkyl radicals identified by our
previous EPR studies (Figure 6). Surprisingly, under given
experimental conditions, no free-radical polymerization occurs
with CQ/MDEA under air, which is probably caused by the low
initiation rate, due to the poor light absorption of CQ that
cannot compete with oxygen inhibition and oxygen diffusion in
the thin films.
Not surprisingly, the QZ/MDEA photoinitiating system
appears not as efficient as that containing QA or QE. Indeed,
phenolic derivatives are well known to interact with the active
radical species generated in the medium at each step of the
photoinduced polymerization reaction:39,40 the photoinduced
phenoxyl radicals known as efficient termination agents39 can
quench the growing polymer chains and inhibit the radical
photopolymerization.
Free-Radical Polymerization of TMPTA with Quinizar-
in Derivatives/MDEA Photoinitiating Systems. The free-
radical polymerizations of TMPTA under air or in laminate in
the presence of the QA/MDEA photoinitiating system using
visible-light sources (Xe lamp and LEDs@405, 455, and 470
nm) are described in Figure 9. The corresponding final
conversions are summarized in Table 5. The well-known
photoinitiating system, i.e., CQ/MDEA, has also been studied
for comparison (Figure S12); the FRPs of TMPTA with QZ/
MDEA and QE/MDEA systems in the same reported
conditions are displayed in the Supporting Information (Figures
S11 and S13). CQ derivatives when coupled with MDEA have
been intensively studied and have demonstrated very efficient
initiating properties. The photolysis of CQ/MDEA systems
leads to the formation of α-aminoalkyl radicals that can initiate
the FRP.9,36,38
As can be seen from Table 5, QA/MDEA (or QE/MDEA)
shows superior photoinitiating efficiencies compared to those of
the conventional photoinitiating system (CQ/MDEA) when
irradiated with a Xe lamp and LEDs@455 and 470 nm under air
Free-Radical Polymerization of TMPTA with Quinizar-
in Derivatives/Iod Photoinitiating Systems. The FRP of
TMPTA was investigated with the QA (or QE)/Iod photo-
Table 4. Double Bond Conversion Determined by IR for the Free-Radical Polymerization of TMPTA under Air or in Laminate
upon Exposure to Different Visible-Light Sources for 800 s in the Presence of CQ/MDEA, QZ/MDEA, QA/MDEA, and QE/
a b
,
MDEA
double bond conversion determined by IR in laminate and under air (%)
xenon lamp
LED@ 405 nm
LED@ 455 nm
LED@ 470 nm
CQ/MDEA/TMPTA
QZ/MDEA/TMPTA
QA/MDEA/TMPTA
QE/MDEA/TMPTA
39 (np)
30 (np)
55 (54)
57 (40)
40 (np)
28 (np)
54 (55)
55 (43)
44 (np)
12 (np)
44 (50)
50 (33)
37 (np)
69 (67)
57 (50)
a
b
np = no polymerization, ( ) = experiments and conversions under air. Photoinitiator/MDEA (0.5/2%, w/w).
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Table 5. Double Bond Conversion Determined by IR for the Free-radical Polymerization of TMPTA under Air or in Laminate
a b
,
upon Exposure to Different Visible-Light Sources for 800 s, in the Presence of CQ/Iod, QZ/Iod, QA/Iod, and QE/Iod
double bond conversion determined by IR in laminate and under air (%)
xenon Lamp
LED@405 nm
LED@455 nm
LED@470 nm
CQ/Iod/TMPTA
QZ/Iod/TMPTA
QA/Iod/TMPTA
QE/Iod/TMPTA
45 (np)
np (np)
70 (5)
50 (np)
np (np)
65 (np)
66 (np)
32 (np)
np (np)
50 (np)
36 (np)
15 (17)
77 (np)
80 (12)
75 (np)
a
b
np = no polymerization, ( ) = experiments and conversions under air. Photoinitiator/Iod (0.5/2.0%, w/w).
initiating systems (Figures 10 and S15) in comparison with CQ/
Iod and QZ/Iod systems used as references (Figures S14 and
addition, the initiator radical formation step, the formation of
phenyl radicals, is probably slower and less efficient than for α-
amino radicals from MDEA (see 3QA* rate constants with Iod
and MDEA). Interestingly, under laminate conditions, where
oxygen diffusion into the polymerizing film is eliminated, the
kinetics of TMPTA polymerization obtained with quinizarin
derivatives/Iod systems are highly efficient (final acrylate
conversions >50% whatever the visible-light sources used) and
remain higher than those with the CQ/MDEA system. The
inefficient FRP of TMPTA with the QZ/Iod photoinitiating
system is similar to that observed with the QZ/MDEA system
and can also be explained by the capability of phenoxyl radicals
to be used as terminating agents.39
Free-Radical Polymerization of a TMPTA/Trithiol
Blend with Quinizarin Derivatives or Quinizarin Deriv-
atives/Iod Photoinitiating Systems: Effect of Iod.
Quinizarin derivatives are highly performing photoinitiating
systems when combined with trithiol. As expected, the final
acrylate conversions for the FRP of TMPTA with the QA (or
QE)/trithiol system under air is similar to those obtained in
laminate without any period of inhibition (Table 7, Figure 11,
and Figures S17−S19). According to EPR experiments (Figure
7), the photolysis of QA (or QE)/trithiol systems leads to the
formation of thiyl radicals (RS•), which form peroxyl radicals
(RSOO•) in the presence of dissolved oxygen. The following
hydrogen transfer reaction between RSOO• and trithiol
regenerates thiyl radicals that can add to acrylates to initiate
polymerization.41 The addition of Iod significantly increases the
final acrylate conversion and the initial polymerization rate
whether under air or in laminated conditions, as expected
according to eqs 5 and 6. Surprisingly, the S−H conversions
slightly increase but remain lower than the acrylate conversions.
This suggests that phenyl-derived radicals (derived from the
photolysis of QA (or QE)/Iod systems) may participate in the
FRP of TMPTA by adding to acrylate double bonds or favor a
Figure 10. Photopolymerization profiles of TMPTA (acrylate
function) in the presence of QA/Iod (0.5/2.0%, w/w) in laminate
and upon exposure to (1) LED@405 nm, (2) Xe lamp, (3) LED@455
nm, and (4) LED@470 nm. Thickness of the film = 25 μm.
S16). When QA (or QE) are combined with Iod, the
polymerization of TMPTA occurs under our experimental
conditions in laminate only (Table 6). This supports the
formation of phenyl-derived radicals as demonstrated by EPR
spin trapping; such radicals can initiate the free-radical
polymerization. However, under air, phenyl-derived radicals
are scavenged by oxygen, thus forming peroxyl radicals that are
not reactive toward acrylates and cannot initiate the FRP. The
lower efficiency of Iod than that of MDEA as a coinitiator for
polymerization under air is probably caused by the high
reactivity of phenyl radicals (from Iod) that react indiscrimina-
torily with organic molecules (H-abstraction). These competing
side reactions reduce the fraction of initiator radicals, adding to
acrylate double bonds for the initiation of polymerization. In
Table 6. Double Bond Conversion Determined by IR of a TMPTA/Trithiol Blend (43/57%, w/w) under Air or in Laminate upon
Exposure to Different Visible-Light Sources for 800 s in the Presence of CQ, QZ, QA, QE, CQ/Iod, QZ/Iod, QA/Iod, and QE/
a b
,
Iod
double bond conversion determined by IR in laminate and under air (%)
xenon lamp
LED@ 405 nm
LED@ 455 nm
LED@ 470 nm
CQ/trithiol/TMPTA
CQ/Iod/trithiol/TMPTA
QZ/trithiol/TMPTA
QZ/Iod/trithiol/TMPTA
QA/trithiol/TMPTA
QA/Iod/trithiol/TMPTA
QE/trithiol/TMPTA
81 (40)
73 (np)
75 (42)
91 (62)
79 (70)
98 (97)
75 (80)
90 (98)
100 (89)
90 (57)
86 (90)
90 (73)
60 (67)
92 (95)
90 (45)
90 (98)
97 (68)
87 (76)
67 (np)
80 (15)
57 (25)
86 (84)
59 (np)
70 (40)
85 (90)
90 (85)
92 (91)
98 (95)
90 (96)
93 (100)
QE/Iod/trithiol/TMPTA
a
b
np = no polymerization, ( ) = experiments and conversions under air. Photoinitiator alone (0.5 wt %). Photoinitiator/Iod (0.5/2.0%, w/w).
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Table 7. Vinyl Double Bond Conversions Determined by IR
of DVE/Trithiol Formulation (43/57%, w/w) Obtained in
Laminate and in Air Conditions upon 800 s Light Exposure
with Different LEDs in the Presence of CQ (0.5 wt %), CQ/
Iod (0.5/2.0%, w/w), QA (0.5 wt %), and QA/Iod (0.5/2.0%,
R′‐CH•‐CH2‐SR + RS‐H → R′‐CH2‐CH2‐SR + RS•
(7)
Thiol−Ene Reaction and Cationic Photopolymeriza-
tion of a DVE/Trithiol Blend with QA and QA/Iod
Photoinitiating Systems: Effect of Iod. Excellent kinetic
profiles for the thiol−ene photopolymerization of the DVE/
trithiol blend mixture are obtained when using QA and QA/Iod
systems under LEDs@455 and 470 nm exposure (Figures 12
a
w/w)
vinyl double bond conversions determined by
IR in laminate and under air (%)
LED@455 nm
LED@470 nm
CQ/DVE/trithiol
CQ/Iod/DVE/trithiol
QA/DVE/trithiol
65 (71)
99 (88)
89 (70)
100 (99)
41 (39)
90 (64)
83 (49)
100 (85)
QA/Iod/DVE/trithiol
a
( ) = experiments and conversions under air.
Figure 12. Kinetic profiles of the allyl and thiol functions in the DVE/
trithiol formulation (43/57%, w/w) in the presence of (A) QA (0.5 wt
%) and (B) QA/Iod (0.5/2.0%, w/w) in laminate upon LED@455 nm
(curves 1 and 2) and LED@470 nm (curves 3 and 4) exposure. Curves
1 and 3 = acrylate conversions; curves 2 and 4 = thiol conversions.
Thickness of the film = 25 μm.
Figure 11. Photopolymerization profiles of a TMPTA/trithiol blend
(43/57%, w/w) in the presence of (A) QA (0.5%) and (B) QA/Iod
(0.5/2.0%, w/w) in laminate upon LED@405 nm (curves 1 and 2), Xe
lamp (curves 3 and 4), and LED@455 nm (curves 5 and 6). Curves 1, 3,
and 5 = acrylate conversions; curves 2, 4, and 6 = thiol conversions.
Thickness of the film = 25 μm.
and S24 under air). The vinyl double bond conversions after 800
s of irradiation are summarized in Table 7 and compared with
those of CQ and CQ/Iod photoinitiating systems used as
references (Figures S25 and S26). The vinyl double bond
conversions in the presence of QA in laminate (89 and 83% with
LED@455 nm and LED@470 nm, respectively) are slightly
higher than those of S−H (78 and 69%); the vinyl groups
disappear according to the thiol−ene process; indeed, thiyl
radicals generated from the H-atom abstraction reaction
between trithiol and QA are reactive toward vinyl double
bonds. Interestingly, when QA is combined with Iod, the final
double bond conversions reach 100% (S−H conversions: 90
and 86% with LED@455 nm and LED@470 nm, respectively).
This highly efficient double bond conversion could be explained
by the fact that DVE can polymerize according to a cationic
reaction initiated by photoacids43 that have been generated
during the photolysis of the QA/Iod system or through a thiol−
ene reaction.44 Finally, the high final conversions of S−H
demonstrate that the DVE photopolymerization mainly occurs
through a thiol−ene process and albeit to a lesser extent in a
cationic process. Photopolymerizations under air are similar to
H-atom abstraction reaction, according to eqs 5−7. In this
multicomponent QA/Iod/trithiol system, the formation of thiyl
radicals is dominant. Surprisingly, high conversions for the FRP
of TMPTA in laminate (Figure S20) are observed with QZ when
coupled with trithiol and/or Iod: H-atom abstraction reactions
from trithiol by phenoxyl radicals42 are possible, thus generating
thiyl radicals that are reactive toward allyl functions. The
formation of thiyl radicals can also explain why the FRP of
TMPTA under air with QZ in the presence of trithiol is
effective37 (Figure S21).
•
MePh + RS‐H (trithiol) → MePh‐H + RS•
(5)
RS• + R′‐CH = CH2(TMPTA) → R′‐CH•‐CH2‐SR
(6)
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those under laminate as thiol−ene chemistry is less sensitive to
oxygen (Figure S24).
forming units (CFUs) of an interpenetrated polymer network
after 16 h of incubation against S. aureus with and without light
irradiation and after a second cycle of the antibacterial test. The
CFU number reaches 1.36 × 106 after 16 h of incubation without
any light exposure. Interestingly, the CFU number drastically
drops down to 4.1 × 104 on the surface of the irradiated coatings.
After intensive rinsing and drying under vacuum, the films were
reused and tested a second time as antibacterial materials under
visible-light irradiation. Interestingly, the CFU number after this
second cycle of antibacterial experiments slightly decreases to
3.9 × 104. This result is due to the production of singlet oxygen
at the surface of the irradiated films, as demonstrated by DPBF
experiments (see the Supporting Information, Figure S29).
Singlet oxygen can oxidize the olefinic double bonds in fatty
acids necessary for S. aureus growth, leading thus to their
death.22,47 It is also interesting to notice that visible-light
irradiation does not lead to the growth/death of bacteria.
Interpenetrated Polymer Network. An interpenetrated
polymer network has been synthesized according to a
concomitant free-radical and cationic photopolymerization of
the TMPTA/EPOX blend in the presence of QA/Iod or QE/
Iod systems under air or in laminate upon LED@455 nm
exposure. Our results are in full agreement with our previous
investigations;15 the final acrylate conversions are higher in
laminate than under air; the opposite is observed for the epoxy
polymerization of EPOX (Table 8, see Supporting Information,
Table 8. Epoxy and Double Bond Conversions Determined
by IR of a TMPTA/EPOX Blend (50/50%, w/w) under Air or
in Laminate in the Presence of QA/Iod (0.5/2.0%, w/w) and
QE/Iod (0.5/2.0%, w/w) after 800 s of LED@455 nm Light
Exposure
QA/Iod/TMPTA/EPOX
QE/Iod/TMPTA/EPOX
CONCLUSIONS
■
epoxy
epoxy
conversion
(%)
double bond
conversion
(%)
QA and QE have demonstrated excellent initiating properties in
combination with coinitiators such as iodonium salt (Iod), N-
methyldiethanol amine (MDEA), or a thiol derivative for both
free-radical and cationic photopolymerizations under visible-
light irradiation (LEDs@405, 455, and 470 nm or Xe lamp).
Notably, final conversions obtained under air with these
quinizarin-derived photoinitiating systems are excellent and
more effective than common CQ-based photoinitiating systems.
We also demonstrated that the QA/Iod system could efficiently
promote both the thiol−ene reaction and the cationic
photopolymerization of a DVE/trithiol blend and could lead
to interpenetrated polymer networks according to a concom-
itant free-radical and cationic photopolymerization of the
epoxide/acrylate blend mixture upon LED@455 or 470 nm
exposure. Interestingly, the resulting coatings incorporating
quinizarin derivatives have shown excellent antiadherence
properties under visible-light exposure even after two cycles of
antibacterial experiments that have never been demonstrated yet
in the literature.
conversion
(%)
double bond
systems
conversion (%)
under air
in laminate
72
52
48
76
49
39
50
87
Figures S27 and S28). Indeed, radicals are highly consumed by
oxygen-limiting FRP under air rather than by the cationic
polymerization of EPOX. It should be underlined that the final
acrylate conversions of TMPTA in the blend formulation are
higher than those of the monomer used alone when photo-
polymerization occurs under air. This interesting effect is due to
the hydrogen donation capability of the EPOX monomer for
generating additional reactive radical species, as observed for
some other photoinitiating systems.45,46
Antibacterial Assays on the Interpenetrated Polymer
Networks. Quinizarin-derived films have been exposed to a
fixed concentration of S. aureus solution overnight. After 16 h of
incubation, half of the samples are irradiated under white visible
light at 37 °C and the others are stored in the dark at 37 °C. The
same experiment has been performed a second time to
demonstrate the reuse of the samples as antibacterial films.
Interestingly, no diffusion of QA from the samples was observed
during the time of incubation into a bacterial solution. This
demonstrates that QA is successfully and covalently linked to the
polymer network. Figure 13 displays the number of colony-
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.macromol.9b02448.
NMR spectra of QA and QE; additional steady-state
photolysis experiments; determination of quenching rate
constants kq by laser flash photolysis; cyclic voltammetry
of QZ, QA and QE; additional photopolymerization
kinetics; singlet oxygen analysis with 1,3-diphenylisoben-
zofuran (PDF)
AUTHOR INFORMATION
■
Corresponding Author
́
Davy-Louis Versace − Institut de Chimie et des Materiaux Paris-
̀
̀
Est (ICMPE) − UMR-CNRS 7182 Equipe Systemes Polymeres
Complexes (SPC), 94320 Thiais, France; orcid.org/0000-
0002-4272-5021; Email: versace@icmpe.cnrs.fr
Authors
́
Pauline Sautrot-Ba − Institut de Chimie et des Materiaux Paris-
̀
̀
Est (ICMPE) − UMR-CNRS 7182 Equipe Systemes Polymeres
Figure 13. Antibacterial properties of the quinizarin-derived films
against S. aureus, with and without visible-light exposure.
Complexes (SPC), 94320 Thiais, France
K
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(10) Xiao, P.; Zhang, J.; Dumur, F.; Tehfe, M. A.; Morlet-Savary, F.;
Steffen Jockusch − Department of Chemistry, Columbia
University, New York, New York 10027, United States;
orcid.org/0000-0002-4592-5280
́
Graff, B.; Gigmes, D.; Fouassier, J. P.; Lalevee, J. Visible light sensitive
photoinitiating systems: Recent progress in cationic and radical
photopolymerization reactions under soft conditions. Progr. Polym.
Sci. 2015, 41, 32−66.
́
Jean-Pierre Malval − Institut de Chimie des Materiaux de
Mulhouse (IS2M)-UMR 7361, 68057 Mulhouse, France;
́
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orcid.org/0000-0002-7642-6636
Schmidt, T. W.; Kable, S. H.; Stenzel, M. H.; Coote, M. L.; Xiao, P.
Multihydroxy-Anthraquinone Derivatives as Free Radical and Cationic
Photoinitiators of Various Photopolymerizations under Green LED.
Macromol. Rapid Commun. 2018, 39, No. 1800172.
́
Vlasta Brezova − Institute of Physical Chemistry and Chemical
Physics, Department of Physical Chemistry, Slovak University of
Technology in Bratislava, SK-812 37 Bratislava, Slovak Republic
́
Michael Rivard − Institut de Chimie et des Materiaux Paris-Est
́
(12) Zhang, J.; Lalevee, J.; Hill, N. S.; Peng, X.; Zhu, D.; Kiehl, J.;
̀
̀
(ICMPE) − UMR-CNRS 7182 Equipe Systemes Polymeres
Complexes (SPC), 94320 Thiais, France; orcid.org/0000-
0002-5487-1595
Morlet-Savary, F.; Stenzel, M. H.; Coote, M. L.; Xiao, P. Photoinitiation
Mechanism and Ability of Monoamino-Substituted Anthraquinone
Derivatives as Cationic Photoinitiators of Polymerization under LEDs.
Macromol. Rapid Commun. 2019, 40, No. 1900234.
́
́
Samir Abbad-Andaloussi − Universite Paris-Est Creteil (UPEC),
̀
Laboratoire Eau, Environnement, Systemes Urbains (LEESU),
́
(13) Zhang, Z.; Lalevee, J.; Zhao, J.; Graff, B.; Stenzel, M. H.; Xiao, P.
́
UMR-MA 102, 94010 Creteil, France
Agata Blacha-Grzechnik − Faculty of Chemistry, Silesian
University of Technology, 44-100 Gliwice, Poland
Dihydroxyanthraquinone derivatives: natural dyes as blue-light-
sensitive versatile photoinitiators of photopolymerization. Polym.
Chem. 2016, 7, 7316−7324.
́
(14) Tomane, S.; Sautrot-Ba, P.; Mazeran, P.-E.; Lalevee, J.; Graff, B.;
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.macromol.9b02448
Morlet-Savary, F.; Abbad-Andaloussi, S.; Langlois, V.; Versace, D.-L.
Photoinitiating Systems Based on Anthraquinone Derivatives: Syn-
thesis of Antifouling and Biocide Coatings. ChemPlusChem 2017, 82,
1298−1307.
Author Contributions
The manuscript was written through the contributions of all
authors. All authors have given approval to the final version of
the manuscript.
́
(15) Breloy, L.; Brezova, V.; Malval, J.-P.; Rios de Anda, A.; Bourgon,
J.; Kurogi, T.; Mindiola, D. J.; Versace, D.-L. Well-Defined Titanium
Complex for Free-Radical and Cationic Photopolymerizations under
Visible Light and Photoinduction of Ti-Based Nanoparticles. Macro-
molecules 2019, 52, 3716−3729.
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
■
́
Dr. Versace Davy-Louis and Prof. Vlasta Brezova would like to
thank the French National Research Agency (ANR), UPEC,
ICMPE, Slovak Research and Development Agency, and
Ministry of Education, Science, Research and Sport of the
Slovak Republic for financial support (Contract no. APVV-15-
0053).
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