Squarylium-triazine dyad as a highly sensitive photoradical generator for red light

Article abstract of DOI:10.1002/chem.201300622

New dyads, based on squarylium dye and substituted-triazine, were synthesized that exhibit an intramolecular photodissociative electron-transfer reaction. The compounds were used as a red-light photoradical generator. The photochemical activity of the dyad was compared to the corresponding unlinked systems (S+T) by determining the rate constant of electron transfer. The efficiency of the radical generation from the dyad compared to the unlinked system was demonstrated by measuring the maximum rate of free radical polymerization of acrylates in film. An excellent relationship between the rate of electron transfer and the rate of polymerization was found, evidencing the interest of this new approach to efficiently produce radicals under red light. Put on the red light: Diads based on a squarylium dye and triazine derivatives absorb light in the red region strongly, giving rise to an intramolecular photodissociative electron-transfer reaction that releases radicals (see figure). Copyright

Full text of DOI:10.1002/chem.201300622

FULL PAPER
DOI: 10.1002/chem.201300622
Squarylium-Triazine Dyad as a Highly Sensitive Photoradical Generator for
Red Light
Koichi Kawamura,* Julien Schmitt, Maxime Barnet, Hanene Salmi, Christian Ley, and
Xavier Allonas*[a]
Abstract: New dyads, based on squary-
lium dye and substituted-triazine, were
synthesized that exhibit an intramolec-
ular photodissociative electron-transfer
reaction. The compounds were used as
a red-light photoradical generator. The
photochemical activity of the dyad was
compared to the corresponding un-
linked systems (S+T) by determining
the rate constant of electron transfer.
The efficiency of the radical generation
from the dyad compared to the un-
linked system was demonstrated by
measuring the maximum rate of free
radical polymerization of acrylates in
film. An excellent relationship between
the rate of electron transfer and the
rate of polymerization was found, evi-
dencing the interest of this new ap-
proach to efficiently produce radicals
under red light.
Keywords: donor–acceptor
sys-
tems · dyads · electron transfer ·
photochemistry · polymerization
Introduction
UV additives in photopolymerization. However, this could
also be a drawback when developing new applications with
new irradiation sources such as laser diodes or light-emitting
diodes (LED) that are found to be quite inexpensive when
emitting in the green or red region.
Generating radicals is considered as one of the most impor-
tant route of synthesis in organic chemistry. Among the dif-
ferent ways used to produce efficiently different radicals,
photochemistry appears as very popular, affording a good
and clean control of the release process, with high yields
and without thermal heating. Therefore, development of
photoradical generators (PRG) is still a lively topic that
finds attractive applications in many different fields such as
cosmetics, medicals, microelectronics, optics, and photore-
sists. Indeed, modern applications use PRG in triggering bi-
oactivity,[1] in drug[2] or fragrance[3] release, in the fields of
microelectronics.[4] The term of phototrigger is often em-
ployed, specifying that the PRG is used to launch a given
chemical process.[5] Organic synthesis can take advantage of
such PRG by building photolabile protective groups that
could be released under irradiation by light.[6,7] In photo-
Therefore, there is a need to design new PRG that can be
irradiated in the green to red region of the electromagnetic
spectrum. In this paper, we have developed a new approach
in which a photodissociative electron transfer within a dyad
based on a dye linked to a releasing group produces a radi-
cal. As a first target, squarylium dye was chosen as a highly
absorbing dye in the red region.[10–12] Squarylium dyes have
unique photophysical and photochemical features and have
found many technological applications in non-linear
optics,[13] electrochromic materials,[14] electroluminescent ma-
terials,[15] and photoconductive materials.[16] Recently, some
squarylium dyes together with initiators have been used in
photopolymerization for potential applications in holograph-
ic information recording.[17,18] Positive photoresists using
squarylium dyes/trichloromethyltriazine combinations are
also reported.[19] On the other side of the molecule, a tri-
chloromethyltriazine derivative was selected as a photo-
ACHTUNGTRENNUNGpolymerization, the term of photoinitiator underlines the
role of the PRG to prompt the initiation of the polymeriza-
tion through a chain reaction.[8]
Whatever the application cited, most of the PRG exhibit
absorption spectra in the UV-blue region of the electromag-
netic spectrum.[9] Although this generally occurs at high
quantum yields, irradiation in this high energy region limits
the use of PRG in medical or cosmetic application, as well
as preventing the use of other chemical additives that
should absorb in the same region, such as pigments or anti-
AHCTUNGTRENNUNG
between the dye and the triazine moiety, which leads to the
[20]
ꢀ
dissociation of a C Cl bond.
As a result, a C-centered
radical is produced that could effectively initiate a polymeri-
zation reaction.[21–24] Therefore, we expect an efficient elec-
tron-transfer reaction between the squarylium and the tri-
ꢀ
AHCTUNGTREGaNNUN zine moieties followed by a fast C Cl bond cleavage that
[a] Dr. K. Kawamura, J. Schmitt, M. Barnet, H. Salmi, Prof. C. Ley,
Prof. X. Allonas
would lead to the formation of radicals. Spectroscopic ex-
periments were performed to support this contention and
the efficiency of a photopolymerization reaction of an acryl-
ate initiated by this dyad was compared to that obtained by
a physical mixture of dye and triazine derivative. It is clearly
Laboratory of Macromolecular Photochemistry
and Engineering, University of Haute Alsace
3b, rue Alfred Werner, 68093 Mulhouse (France)
E-mail: koichi.kawamura@uha.fr
xavier.allonas@uha.fr
Chem. Eur. J. 2013, 19, 12853 – 12858
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Scheme 1. Compounds used in this work.
shown that the dyad performs more efficiently, evidencing
the high reactivity of the dyad.
It is shown that after irradiation, an electron transfer
occurs between the dye and the triazine moiety, which leads
[20]
ꢀ
Scheme 2. Synthesis of triazine-linked squarylium dye S-2-T; CDI=1,1’-
carbonyldiimidazole.
to the dissociation of a C Cl bond. As a result, a C-cen-
tered radical is produced that could effectively initiate a pol-
ymerization reaction.[21–24] Therefore, we expect an efficient
electron-transfer reaction between the squarylium and the
ꢀ
triazine moieties followed by a fast C Cl bond cleavage,
which would lead to the formation of radicals. Spectroscopic
experiments were performed to support this contention and
the efficiency of a photopolymerization reaction of an acryl-
ate initiated by this dyad was compared to that obtained by
a physical mixture of dye and triazine derivative. It is clearly
shown that the dyad performs more efficiently, evidencing
the high reactivity of the dyad.
Results and Discussion
Excited state reactivity of the S-n-T dyad: Linked com-
pounds S-2-T and S-6-T were synthesized by using a proce-
dure adapted from the literature (Scheme 2).[25,26]
Figure 1. Photolysis of S-2-T in ethyl acetate followed under irradiation
(630 nm, 0.1 mWcmꢀ2).
The photophysical properties of the dyads S-2-T, S-6-T
and the parent dye S were measured in ethyl acetate. All
compounds were found to have similar absorption and fluo-
rescence features (Table 1), indicating that there is no ap-
preciable ground-state interaction between the two groups
in the dyads. Upon irradiation at 630 nm, the absorbance of
S-2-T decreased rapidly, whereas no change was observed in
the equimolar mixture of S and T (Figure 1).
for S-6-T and S-2-T, respectively (Table 1). This indicates
that the intramolecular interaction in S-2-T is more effective
than the physical mixture of S and T under irradiation.
A clear evidence of intramolecular electron transfer in
S-2-T was obtained with femtosecond pump-probe transient
absorbance spectroscopy by irradiating ethyl acetate solu-
tion of S-2-T with 610 nm light pulses of 100 fs duration.
The corresponding transient spectra are given in Figure 2
for pump-probe delays ranging from 2.2 ps to 2.6 ns. The
positive band before 500 nm is ascribed to the transient ab-
sorbance of the emissive excited state of the chromophore
in S-2-T.[27,28] The negative band with a maximum at 630 nm
is assigned to the (S-2-T) bleaching and stimulated emissions
of the (S-2-T) emissive excited state. All bands decay quite
homothetically in the first hundred femtoseconds. Interest-
ingly, for delays higher than 150–200 ps, a positive band
grows around 650–700 nm. This positive band was observed
in all solvents with the linked compound (S-2-T), but was
When compared to the initial dye S, steady-state fluores-
cence show a decrease of the emission down to 55 and 7%
Table 1. Absorption and fluorescence properties of the compounds stud-
ied in ethyl acetate.
Compound
Absorption
Fluorescence
lmax [nm] (loge)
lmax [nm] (rel. int. [%])
S
633 (5.58)
633 (5.58)
636 (5.47)
645 (100)
645 (7)
648 (55)
S-2-T
S-6-T
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Squarylium-Triazine Dyad
FULL PAPER
Scheme 3. Reaction mechanism of S-n-T.
from which a photodissociative electron transfer occurs to
ꢀ
the triazine moiety T. This leads to a fast C Cl bond cleav-
age preventing back-electron-transfer and a carbon-centered
radical is formed.
The radicals produced during the photolysis of S-2-T or
S-6-T can be used to photoinitiate the free-radical polymeri-
zation of acrylate. Therefore, it was tempting to test the
photopolymerization efficiency of dyads compared to that of
physical mixture of S in the presence of various concentra-
tion of T. Such experiments were performed in films at a
concentration of 0.03m for S-2-T, S-6-T and S. The dyads
were compared to physical S+nT mixtures in which the
concentration of added triazine in the matrix is increased
from 0.03 to 0.21m (S+T and S+7T, respectively; Table 2).
The results are shown in Figure 3 and the relative rates of
photopolymerization are collected in Table 2.
Figure 2. Femtosecond pump-probe transient spectroscopy of (S-2-T):
a) in the ethyl acetate spectrum, and b) fourth first orthogonal kinetics
obtained by singular value decomposition (SVD) analysis. Plain lines rep-
resent the best corresponding fit.
Table 2. Relative rate of polymerization Rp for the different systems
studied.[a]
Combination
[T]
Rp
(rel.)
Fluorescence
lifetime [ns]
ket
[109 sꢀ1
]
[m]
N
U
S
0
0
2.90
2.84
2.54
2.37
2.18
2.17
2.63
–
not present in experiments conducted with the unlinked
chromophore squarylium S in ethyl acetate, acetonitrile, di-
S+T
S+3T
S+5T
S+7T
S-2-T
S-6-T
0.03
0.09
0.15
0.21
0
1.0
3.5
6.2
7.3
16.3
4.9
0.01
0.05
0.08
0.11
0.11
0.03
chloromethane, and chloroform. Moreover the positive ab-
+
C
sorption band matches the radical cation S of the chromo-
phore S, which was generated by photoionization and pulse
0
radiolysis as reported in the literature.[27–29] This indicates
[a] [S]=[S-2-T]=[S-6-T]=0.03m.
that the intramolecular electron transfer occurs from S to T
+
C
and this process generates the cation radical S in the
S-2-T-linked molecule. It is worth noting also the photo-
bleaching band around 630 nm indicating no ground state
recovery in the time window of the apparatus.
The kinetic analysis of the spectro-temporal data was per-
formed by singular value decomposition.[30–32] The best fit of
the four first weighted orthogonal kinetics leads to three
time constants and one step function. The two short kinetics
(0.98 and 32.6 ps) are ascribed to the complex formation of
the emissive state of the dye.[33,34] The longer one of 215 ps,
corresponds to the lifetime of the emissive excited state in
the linked compound, in agreement with the value obtained
in ethyl acetate solution of S-2-T by using time-correlated
single-photon counting (TCSPC). The step function is ascri-
bed to the formation of transient species that do not recom-
bine in the time window and is ascribed to the formation of
the radical cation of the dye and the subsequent permanent
bleaching.
Figure 3. Real-time photopolymerization experiments.
As can be seen, the photopolymerization reaction is much
more efficient for both S-2-T and S-6-T systems compared
with the S+T system. The S-2-T system even outperforms
the efficiency of the physical mixture S+7T in which the tri-
azine is in large excess (0.21m). This effect clearly demon-
According to these experiments, the general mechanism
of reaction is given in Scheme 3. Under irradiation, the
squarylium moiety S is excited into its first excited state,
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12855

K. Kawamura, X. Allonas et al.
strates that the efficiency of radical generation is related to
the intramolecular electron-transfer process.
To get more insight into this reaction, the electron-trans-
fer rates were calculated from time-resolved fluorescence
decays in films of the dyad S-2-T, S-6-T and the unlinked
systems S+T to S+7T.
As it was seen that no ground state interaction occurs in
the dyads, the fluorescence lifetime t0 of the dye alone (S)
was taken as a reference for measuring the intrinsic rate of
electron transfer occurring in the dyads. The rates were cal-
culated according to Equation (1):
1
1
ket ¼ = ꢀ =
t0
ð1Þ
t
Figure 4. Plot of the maximum rate of polymerization versus the
in which t the fluorescence lifetime of the dyad or, in the
case of physical mixture, the fluorescence lifetime of S in
the presence of T. The results collected in Table 2 show that
S-2-T exhibits a higher rate constant of electron transfer
than S-6-T, and is quite similar to the physical mixture S+
7T. These results are in line with the close proximity be-
tween S and T in S-2-T (which is almost the same in S+7T)
than in S-6-T.
electron-transfer rate for S-2-T, S-6-T, and S+nT.
dyads outperform the physical mixtures: two regression
lines with different coefficients are obtained, separating
linked and unlinked systems in two groups. Thus, linear re-
gression coefficient of the linked systems is higher than that
of the physical mixtures. This could be ascribed to the yield
of radical generation (frad) after electron transfer, which
may differ for linked and unlinked systems in the matrix.
Indeed frad could be related to the rate of dissociation of tri-
azine kdis and the rate of back-electron-transfer kbet
(Scheme 3) according to the following Equation (5):
It is worth noting that the rates of polymerization exhibit
the same trend, that is, they increase with increasing rates of
electron transfer in physical mixtures S+nT and in the
dyads S-2-T and S-6-T. However, the rate of polymerization
is larger in S-2-T compared with the unlinked S+7T system,
even if they have the same rate of electron transfer.
Assuming a monomolecular termination reaction for the
polymerization process, the maximum rate of polymeriza-
tion Rp is given by Equation (2):[35,36]
kdis
kdis þ kbet
ð5Þ
ꢀrad
¼
ꢀ
One can assume that the rate constant of C Cl bond
cleavage is the same for all the systems. Consequently, the
differences in frad can be ascribed to variation of kbet. The
kbet depends on the energetics of the reaction as well as the
distance between the reactants. Obviously, the latter factor
clearly differs for linked and unlinked systems, and as a con-
sequence, a higher quantum yields should be the conse-
quence of a lower kbet in the dyads compared with the physi-
cal mixtures.
ꢀ
ꢁ
ꢀi Iabs
kt
Rp ¼ kp
½Mꢁ
ð2Þ
in which kp and kt are the rate constants of propagation and
termination, respectively, Iabs is the absorbed light intensity
and [M] is the concentration of the monomer. fi stands for
the initiation quantum yield, which is related to Equa-
tion (3):
Conclusion
ꢀi ¼ t ꢂ ket ꢂ ꢀrad
ð3Þ
in which frad is the yield of radical formation. Then, Equa-
tion (2) turns into Equation (4):
In this paper new dyads were synthesized, based on squary-
lium dye and triazine derivatives, which absorb strongly the
light in the red region. It was shown that excitation of the
dyad leads to an intramolecular photodissociative electron
transfer and then to the formation of radicals. Rate con-
stants for electron transfer were measured within the dyad
and compared with that obtained for a physical mixture of
the dye and substituted-triazine in solid film, showing that
the photo-process occurs much more efficiently in former
case. To exemplify this effect, photopolymerization experi-
ments were performed, exhibiting higher rates of polymeri-
zation when the dyads are used. The outstanding perform-
ance of the dyad compared with the physical mixture of re-
Rp ¼ K ꢂ t ꢂ ket ꢂ ꢀrad
ð4Þ
in which K is a constant that depends on experimental con-
ditions. Figure 4 shows the plot of the relative polymeriza-
tion rate as a function of ket ꢁt for linked and unlinked sys-
tems. A linear relationship is outlined between the two pa-
rameters.
These results confirm the fact that there is a direct rela-
tionship between Rp and the primary photochemical process,
the photodissociative electron transfer. Interestingly, both
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Chem. Eur. J. 2013, 19, 12853 – 12858

Squarylium-Triazine Dyad
FULL PAPER
tiator (a squarylium dye/triazine combination or a triazine-linked squary-
lium dye), a polyfunctional acrylate monomer (pentaerythritol tetraacry-
actants places this compound as a very efficient dissociative
photoinitiator for free radical photopolymerization or as
phototrigger. This concept of visible light absorbing dye
linked to a dissociative electron acceptor open new opportu-
nities for the development of photoradical generators ab-
sorbing in the green–red region of the electromagnetic spec-
trum.
late) and
a
polymeric binder (polymethyl methacrylate MW =
35000 gmolꢀ1) were dissolved in a 16:1:1 (w/w/w) mixture of solvent
(methyl ethyl ketone/1-methoxy-2-propanol/THF), and the solution was
cast on a glass or on a polypropylene film by using a 24 mm RKprint K
Hand Coater. The solvent was evaporated by heating at 908C for 2 min.
The thickness of the film thus prepared was about 4 mm. Films were over-
coated by a polyvinyl alcohol film (MW =2000 gmolꢀ1) to prevent diffu-
sion of atmospheric oxygen.
The photosensitivity of the dyad were measured by Real-Time FTIR and
performed by using a 635 nm laser diode as an irradiation source with
the irradiance intensity at the surface of the sample adjusted to
10 mWcmꢀ2. The kinetics of the polymerization were measured by fol-
lowing the disappearance of the acrylic double bond at 1410 cmꢀ1. The
degree of acrylate double bond conversion (C) was calculated from the
decrease of the area of the IR absorption peak between 1402 and
1418 cmꢀ1 of the sample after exposure using the following Equation (6):
Experimental Section
Triazine-linked squarylium dyes S-n-T: Synthesis of linked compound S-
2-T and S-6-T was performed according to the general procedure[11,25,26]
shown in Scheme 2.
Synthesis of S-2-T:
(trichloromethyl)-1,3,5-triazin-2-yl]benzoate (2.00 g, 3.42 mmol) and 3-hy-
droxy-4[4-(N,N-dibutylanilino)]cyclobut-3-ene-1,2-dione (1.03 g,
A mixture of [2-(N-ethylanilino)ethyl] 4-[4,6-bis-
ACHTUNGTRENNUNG
C ð%Þ ¼ ðA0ꢀAtÞ=A0 ꢂ 100
ð6Þ
3.13 mmol) in dry 2-propanol/triethylorthoformate (20 mL, 5:1, v/v) was
heated at reflux for 5 h under nitrogen, under green light because of the
red sensibility of the product. The reaction was then stopped by addition
of a mixture of cyclohexane/ethyl acetate (60 mL, 5:1, v/v). The solvent
was evaporated, and the residue was purified by using column chroma-
tography (cyclohexane/ethyl acetate=1:1, v/v as eluent), to afford the
product as a green solid (0.703 g, 0.81 mmol, 26%). 1H NMR (CDCl3):
d=0.99 (t, J=7.2 Hz, 6H), 1.20–1.48 (m, 8H), 3.44 (t, J=7.5 Hz, 4H),
3.63 ( q, J=6.9 Hz, 2H), 3.90 (t, J=5.7 Hz, 2H), 4.61 (t, J=5.7 Hz, 2H),
6.72 (d, J=9.0 Hz, 2H), 6.86 (d, J=8.7 Hz, 2H), 8.16 (d, J=7.5 Hz, 2H),
8.37 (d, J=8.7 Hz, 4H), 8.75 ppm (d, J=7.5 Hz, 2H); HRMS: m/z calcd
for C40H40N5O4Cl6: 866.1181 [M+H+]; found: 866.1164.
in which A0 represent the initial peak area before irradiation and At rep-
resent the peak area of the acrylic double bond at time, t.[38]
Acknowledgements
The Cercle Gutenberg, Strasbourg is fully acknowledged for the Chaire
dꢂExcellence provided to K.K.
Synthesis of S-6-T: S-6-T was synthesized by following the above proce-
dure using [6-(N-ethylanilino)hexyl] 4-[4,6-bis(trichloromethyl)-1,3,5-tri-
ACHTUNGTRENNUNG
azin-2-yl]benzoate as a starting material. Yield: 25%; 1H NMR (CDCl3):
[1] X. Wang, S. Werner, T. Weiss, K. Liefeith, C. Hoffmann, RSC Adv.
2012, 2, 156–160.
d=0.99 (t, J=7.3 Hz, 6H), 1.31–1.90 (m, 19H), 3.43 (t, J=7.7 Hz, 6H),
3.52 ( q, J=7.1 Hz, 2H), 4.39 (t, 6.9 Hz, 2H), 6.69 (d, J=2.7 Hz, 2H),
6.73 (d, J=2.7 Hz, 2H), 8.24 (d, J=8.7 Hz, 2H), 8.34 (d, J=0.7 Hz, 2H),
8.37 (d, J=0.7 Hz, 2H), 8.77 ppm (d, J=8.7 Hz, 2H); HRMS: m/z calcd
for C44H48Cl6N5O4: 922.1808 [M+H+]; found: 922.1807.
[2] T. Muraoka, C. Y. Koh, H. Cui, S. I. Stupp, Angew. Chem. 2009, 121,
6060–6063; Angew. Chem. Int. Ed. 2009, 48, 5946–5949.
[3] A. Herrmann, Photochem. Photobiol. Sci. 2012, 11, 446–459.
[4] K. Dietliker, in A Compilation of Photoinitiators Commercially
Available for UV Today, SITA Technology Limited, 2002.
[5] F. Ercole, T. P. Davis, R. A. Evans, Polym. Chem. 2010, 1, 37–54.
[6] C. G. Bochet, J. Chem. Soc. Perkin Trans. 1 2002, 125–142.
Methods: Absorbance spectra of solutions were recorded on a Cary 4000
UV-Visible Spectrophotometer (Varian) and absorbance spectra of films
were recorded on Agilent 8453E spectroscopy system (Agilent Technolo-
gies). HRMS were performed on Agilent Technologies Mass Spectrome-
ter Detector 6510 (MSD; Q-TOF, LC/Mass) in positive Electro Spray
Ionization (ESI) source mode. Monomer polymerization was monitored
by RT-FTIR spectroscopy using a Vertex 70 FTIR spectrometer (Bruker
Optik).[37]
ˇ
[7] P. Klꢃn, T. Solomek, C. G. Bochet, A. Blanc, R. Givens, M. Rubina,
V. Popik, A. Kostikov, J. Wirz, Chem. Rev. 2013, 113, 119–191.
[8] J. P. Fouassier, X. Allonas, J. Lalevꢄe, C. Dietlin, in Photochemistry
and Photophysics of Polymer Materials (Ed.: N. S. Allen), Wiley,
Hoboken, 2010, pp. 351–419.
[9] C. G. Bochet, Tetrahedron Lett. 2000, 41, 6341–6346.
[10] S. Yagi, H. Nakazumi, in Functional Dyes (Ed.: S.-H. Kim), Elsevier,
Amsterdam, 2006, p.215.
[11] Y. Hyodo, H. Nakazumi, S. Yagi, Dyes Pigm. 2002, 54, 163.
[12] S. Yagi, Y. Hyodo, S. Matsumoto, N. Takahashi, H. Kono, H. Naka-
zumi, J. Chem. Soc. Perkin Trans. 1 2000, 599–604.
A FluoroMax-4 (Horiba, Jobin–Yvon) spectrofluorometer coupled with a
TCSPC accessory was used to measure steady-state fluorescence spectra
and fluorescence decays. A 607 nm NanoLEDs (duration 1.7 ns) was
used as pulsed excitation source leading to a time resolution, after decon-
volution, of around 200 ps.
Femtosecond time-resolved transient absorption experiments were per-
formed by using Excipro pump-probe apparatus (CDP corp). Femtosec-
ond laser excitation wavelength was adjusted to 610 nm by mean of col-
linear 800 nm pumped CDP2017 (CDP corp) optical parametric amplifi-
er. The 100 fs laser pulses (800 nm) were provided by a Spectra-Physics
Tsunami Ti:Sa oscillator coupled to a Spitfire pro Spectra-physics regen-
erative amplifier. The resulting pump-probe cross-correlation of the
setup was found to be about 200 fs.
[13] C. Prabhakar, K. Bhanuprakash, V. J. Rao, M. Balamuralikrishna,
D. N. Rao, J. Phys. Chem. C 2010, 114, 6077.
[14] S.-H. Kim, S.-K. Han, Color. Technol. 2001, 117, 61–67.
[15] M. Matsui, S. Tanaka, K. Funabiki, T. Kitaguchi, Bull. Chem. Soc.
Jpn. 2006, 79, 170–176.
[16] N. A. Davidenko, Y. P. Get’manchuk, E. V. Mokrinskaya, L. N. Gu-
menyuk, V. A. Pavlov, N. G. Chuprina, N. N. Kuranda, S. V. Khutor-
nyi, A. A. Ishchenko, N. A. Derevenko, A. V. Kulinich, V. V. Kur-
dyukov, L. I. Kostenko, J. Opt. Technol. 2008, 75, 182.
[17] H. Yong, W. Zhou, G. Liu, L. M. Zhen, E. Wang, J. Photopolym.
Sci. Technol. 2000, 13, 253.
UV-grade acetonitrile was purchased from Fluka and UV-grade ethyl
acetate, dichloromethane, chloroform were purchased from Aldrich. An-
other solvents and chemicals were of reagent grade quality and used
without further purification. Pentaerythritol tetraacrylate (PETTA,
SR295) was supplied by Sartomer and used as received.
[18] Y. He, W. Zhou, F. Wu, M. Li, E. Wang, J. Photochem. Photobiol. A
2004, 162, 463.
Films for the measurement of photophysical behavior and photopolyme-
rization were typically prepared in the following manner. The photoini-
[19] S. Noppakundilograt, N. Miyagawa, S. Takahara, T. Yamaoka, J.
Photopolym. Sci. Technol. 2001, 14, 273.
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12857

K. Kawamura, X. Allonas et al.
[20] G. Pohlers, J. C. Scaiano, R. Sinta, R. Brainard, D. Pai, Chem. Mater.
1997, 9, 1353–1361.
[31] I. H. M. van Stokkum, D. S. Larsen, R. van Grondelle, Biochim. Bio-
phys. Acta 2004, 1657, 82–104.
[21] C. Grotzinger, D. Burget, P. Jacques, J. P. Fouassier, Macromol.
Chem. Phys. 2001, 202, 3513.
[22] J. Kabatc, M. Zasada, J. Paczkowski, J. Polym. Sci. Part A 2007, 45,
3626–3636.
[32] J. Brazard, C. Ley, F. Lacombat, P. Plaza, M. M. Martin, G. Checcuc-
ci, F. Lenci, J. Phys. Chem. B 2008, 112, 15182–15194.
[33] C. Cornelissen-Gude, W. Rettig, R. Lapouyade, J. Phys. Chem. A
1997, 101, 9673–9677.
[23] O. I. Tarzi, X. Allonas, C. Ley, J. P. Fouassier, J. Polym. Sci. Part A
2010, 48, 2594–2603.
[24] K. Kawamura, Y. Aotani, H. Tomioka, J. Phys. Chem. B. 2003, 107,
4579–4586.
[34] C. Gude, W. Rettig, J. Phys. Chem. A 2000, 104, 8050–8057.
[35] E. Andrzejewska, Prog. Polym. Sci. 2001, 26, 605–665.
[36] A. Ibrahim, V. Maurin, C. Ley, X. Allonas, C. Croutxe-Barghorn, F.
Jasinski, Eur. Polym. J. 2012, 48, 1475–1484.
[25] H. Nakazumi, Y. Hyodo, S. Yagi, Synth. Met. 2003, 137, 1395.
[26] D. Keil, H. Hartmann, Dyes Pigm. 2001, 49, 161.
[27] P. V. Kamat, S. Das, K. G. Thomas, M. V. George, J. Phys. Chem.
1992, 96, 195–199.
[37] X. Allonas, C. Ley, A. Ibrahim, O. Tarzi, A. C. Yong, C. Carrꢄ, R.
Chevallier, Photochem. Photobiol. Sci. 2012, 11, 1682–1690.
[38] C. Decker, K. Moussa, Macromolecules 1989, 22, 4455–4462.
[28] A. Wojcik, R. Nicolaescu, P. V. Kamat, Y. Chandrasekaran, S. Patil,
J. Phys. Chem. A 2010, 114, 2744–2750.
[29] L. Eberson, J. Phys. Chem. 1994, 98, 752–756.
[30] N. P. Ernsting, S. A. Kovalenko, T. Senyushkina, J. Saam, V. Farztdi-
nov, J. Phys. Chem. A 2001, 105, 3443–3453.
Received: February 18, 2013
Revised: June 3, 2013
Published online: August 5, 2013
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