Photosensitized isomerization of olefin with benzophenone-conjugated amphiphilic graft copolymers

Article abstract of DOI:10.1016/j.jphotochem.2010.05.003

Two kinds of amphiphilic graft copolymers, PAA-g-P(MMA-co-BP) and P(AA-co-BP)-g-PMMA, consisting of polar poly(acrylic acid) (PAA), less polar poly(methyl methacrylate) (PMMA), and benzophenone (BP) photosensitizing units, have been synthesized. These pol

Full text of DOI:10.1016/j.jphotochem.2010.05.003

Journal of Photochemistry and Photobiology A: Chemistry 213 (2010) 80–86
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Photosensitized isomerization of olefin with benzophenone-conjugated
amphiphilic graft copolymers
∗
Yasuhiro Shiraishi , Takeshi Suzuki, Takayuki Hirai
Research Center for Solar Energy Chemistry, and Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University,
1-3 Machikaneyama-cho, Toyonaka 560-8531, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Two kinds of amphiphilic graft copolymers, PAA-g-P(MMA-co-BP) and P(AA-co-BP)-g-PMMA, consisting
of polar poly(acrylic acid) (PAA), less polar poly(methyl methacrylate) (PMMA), and benzophenone (BP)
photosensitizing units, have been synthesized. These polymers, when used as a photosensitizer for iso-
merization of trans-ˇ-methylstyrene, show a sensitization activity controlled by solvents. In benzene
and chloroform, P(AA-co-BP)-g-PMMA forms a micelle structure consisting of aggregated P(AA-co-BP)
core with dissolved PMMA units at the outer sphere. This suppresses a triplet energy transfer (TET) from
the excited state BP units to olefin and, hence, shows lower sensitization activity than a bulk sensitizer
Received 10 February 2010
Received in revised form 20 April 2010
Accepted 1 May 2010
Available online 9 May 2010
Keywords:
Amphiphilic polymer
Graft copolymer
Photosensitizer
Photoisomerization
Olefin
(4-methoxybenzophenone: MBP). In methanol, both polymers form a weak aggregate of less polar PMMA
units containing dissolved PAA units. The internal cavity of the aggregate is less polar and stabilizes the
excited state BP units. This accelerates a TET from the excited state BP units to olefin and shows higher
sensitization activity than MBP.
©
2010 Elsevier B.V. All rights reserved.
1
. Introduction
amphiphilic graft copolymers in different solvents have been stud-
ied extensively [16], and the polymers have been applied to various
kinds of functional materials such as solubilizer [17], drug deliv-
ery media [18], catalyst [19], and adsorbent [20]. Although some
amphiphilic polymers containing photosensitizing units have been
used for photoreaction [21], there is no report of amphiphilic graft
copolymer containing a photosensitizing unit.
Design of polymers containing photosensitizing units has
attracted much attention in photochemical organic transformation
[
[
1] because polymer microenvironment provides various functions
2], such as accumulation of substrates [3], stabilization of excited
state sensitizers [4], and enhancement of energy transfer to sub-
strate [5]. Amphiphilic polymers containing both polar and less
polar units have attracted a great deal of attention because of their
unique properties. Notably, different solubility of the respective
units in solvents usually leads to a self-assembly of the polymers
In the present work, we synthesized amphiphilic graft copoly-
mers consisting of less polar poly(methyl methacrylate) (PMMA),
polar poly(acrylic acid) (PAA), and photosensitizing benzophenone
(BP) units by the grafting through method. Two copolymers con-
taining BP units either in PAA or PMMA unit, PAA-g-P(MMA-co-BP)
and P(AA-co-BP)-g-PMMA, were synthesized (Scheme 1). These
copolymers were used as a photosensitizer for isomerization of
trans-ˇ-methylstyrene (trans-MS) to cis-MS. We found that the
sensitization activity of these copolymers strongly depends on sol-
[
6], forming several kinds of nanostructures such as spheres [7],
vesicles [8], and rods [9]. Various kinds of amphiphilic polymers
have been proposed such as graft copolymers [10], block copoly-
mers [11], star polymers [12], and hyperbranched polymers [13].
Among them, amphiphilic graft copolymers have been studied
extensively because of their synthesis simplicity [14]. These poly-
mers are usually synthesized via one of three methods [15]: (i)
1
vents. H NMR and dynamic light scattering (DLS) analysis indicate
that this is due to the self-assembly of polymers in different sol-
vents, leading to a change in location of BP moieties and polarity
around the BP moieties.
“
grafting from” reaction involving a growth of side chains from the
initiating groups on the polymer backbone; (ii) “grafting onto” reac-
tion involving a coupling of side polymer chains onto the polymer
backbone, and (iii) “grafting through” reaction involving a copoly-
merization of macromonomers. The morphology and structure of
2. Experimental
2.1. General
∗ Corresponding author. Tel.: +81 6 6850 6271; fax: +81 6 6850 6273.
E-mail address: shiraish@cheng.es.osaka-u.ac.jp (Y. Shiraishi).
All of the reagents used were supplied from Wako, Aldrich, and
Tokyo Kasei and used without further purification. Water was puri-
1
010-6030/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2010.05.003

Y. Shiraishi et al. / Journal of Photochemistry and Photobiology A: Chemistry 213 (2010) 80–86
81
◦
◦
Scheme 1. Synthesis of amphiphilic graft copolymers containing a photosensitizing unit. (i) AET, AIBN, toluene, 70 C; (ii) acryloyl chloride, TEA, DMF, 65 C; (iii) AIBN, DMSO,
◦
6
5
C.
fied by the MilliQ system. PAA-g-P(MMA-co-BP) and P(AA-co-BP)-
g-PMMA were synthesized according to procedure summarized
in Scheme 1. A hemicyanine dye (4-(4-dimethylaminostyryl)-1-
methylpyridinium iodide) was synthesized according to literature
procedure [22].
(br, 3H, C(CH )), 1.78–1.85 (d, J = 18.72 Hz, 2H, –CHCH –), 3.56 (s,
3
2
br, 3H, COOCH ), 6.96 (br, ArH), 7.67 (br, ArH).
3
2.1.3. Synthesis of Ac-PAA and Ac-P(AA-co-BP)
Ac-PAA was synthesized as follows: AET-PAA (1.12 g), triethy-
lamine (TEA) (0.30 g, 3.0 mmol), and acryloyl chloride (0.30 g,
3.3 mmol) were dissolved in DMF (5 mL). The mixture was stirred
for 14 h under dry N2 at room temperature, and a HCl salt of TEA
formed was removed by filtration. The resultant was added slowly
to diethyl ether (100 mL). The precipitate formed was collected by
centrifugation and purified by reprecipitation with MeOH (1 mL)
and diethyl ether (100 mL), affording Ac-PAA (1.2 g) as a white solid.
Ac-P(AA-co-BP) was synthesized in a manner similar to that of Ac-
2
.1.1. Synthesis of AET-PAA and AET-P(AA-co-BP)
AET-PAA was synthesized as follows: AA (1.40 g, 20 mmol),
aminoethanthiol (AET) (0.5 g, 6.5 mmol), and AIBN (0.09 g,
.55 mmol) were dissolved in toluene (5 mL), and the solution was
0
degassed by twice freeze–pump–thaw cycles. The solution was
kept at 65 C for 14 h under dry N2 and added slowly to diethyl
ether (100 mL). The precipitate formed was collected by centrifuga-
tion and purified by reprecipitation with MeOH (1 mL) and diethyl
ether (100 mL), affording AET-PAA as a white solid (1.7 g). AET-
P(AA-co-BP) was synthesized in a manner similar to that of AET-PAA
◦
PAA with AET-P(AA-co-BP) (1.1 g) as a white solid (0.9 g). Ac-PAA:
1
H NMR (400 MHz; DMSO-d ; TMS): ı (ppm) = 1.60–1.83 (br, 2H,
6
–CHCH –), 2.30 (d, J = 5.23 Hz, 1H, –CHCH –), 5.56 (m, –CH CH ),
2
2
2
1
with 4-allyloxyBP (0.25 g, 1.1 mmol) [23] as a white solid (1.6 g).
AET-PAA: H NMR (400 MHz; DMSO-d ; TMS): ı (ppm) = 1.57–1.83
6.08 (m, –CH CH ), 11.6 (br, COOH). Ac-P(AA-co-BP): H NMR
2
1
(400 MHz; DMSO-d ; TMS): ı (ppm) = 1.53–1.77 (br, 2H, –CHCH –),
6 2
6
(
br, 2H, –CHCH –), 2.30 (d, J = 5.12 Hz, 1H, –CHCH –), 11.6 (br,
2.24 (d, J = 5.44 Hz, 1H, –CHCH –), 5.56 (m, –CH CH ), 6.08 (m,
–CH CH ), 7.05 (br, ArH), 7.63 (br, ArH), 12.1 (br, COOH).
2
2
2
2
2
1
COOH). AET-P(AA-co-BP): H NMR (400 MHz; DMSO-d ; TMS):
6
ı (ppm) = 1.56–1.83 (br, 2H, –CHCH –), 2.30 (d, J = 5.25 Hz, 1H,
2
–
CHCH –), 7.02 (br, ArH), 7.60 (br, ArH), 11.6 (br, COOH).
2
2.1.4. Synthesis of Ac-PMMA and Ac-P(MMA-co-BP).
Ac-PMMA was synthesized as follows: AET-PMMA (1.0 g), TEA
2
.1.2. Synthesis of AET-PMMA and AET-P(MMA-co-BP)
AET-PMMA was synthesized as follows: MMA (2.0 g, 20 mmol),
(0.30 g, 3.0 mmol), and acryloyl chloride (0.30 g, 3.3 mmol) were
dissolved in DMF (5 mL). The mixture was stirred under dry N2
for 14 h at room temperature, and a HCl salt of TEA formed
was removed by filtration. The resultant was added slowly to
diethyl ether (100 mL). The precipitate formed was collected by
centrifugation and purified by reprecipitation with MeOH (1 mL)
and diethyl ether (100 mL), affording Ac-PMMA (1.0 g) as a white
solid. Ac-P(MMA-co-BP) was synthesized in a manner similar to
that of Ac-PMMA with AET-P(MMA-co-BP) (1.07 g) as a white
AET (0.6 g, 7.8 mmol), and AIBN (0.09 g, 0.55 mmol) were dis-
solved in toluene (5 mL), and the solution was degassed by twice
freeze–pump–thaw cycles. The solution was kept at 65 C for 14 h
under dry N2 and added slowly to methanol (100 mL). The precipi-
tate formed was collected by centrifugation, affording AET-PMMA
◦
(
1.3 g) as a white solid. AET-P(MMA-co-BP) was synthesized in a
manner similar to that of AET-PMMA with 4-allyloxyBP (0.25 g,
.1 mmol) as a white solid (1.2 g). AET-PMMA: 1H NMR (400 MHz;
DMSO-d ; TMS): ı (ppm) = 0.82–0.98 (br, 3H, C(CH )), 1.78–1.85 (d,
1
solid (1.0 g). Ac-PMMA: 1H NMR (400 MHz; DMSO-d ; TMS): ı
6
(ppm) = 0.84–0.98 (br, 3H, C(CH )), 1.78–1.85 (d, J = 18.34 Hz, 2H,
6
3
3
J = 18.67 Hz, 2H, –CHCH –), 3.56 (s, br, 3H, COOCH ). AET-P(MMA-
–CHCH –), 3.56 (s, br, 3H, COOCH ), 5.50 (m, –CH CH ), 6.08
2
3
2
3
1
2
1
co-BP): H NMR (400 MHz; DMSO-d ; TMS): ı (ppm) = 0.82–0.98
(m, –CH CH ). Ac-P(MMA-co-BP): H NMR (400 MHz; DMSO-
6
2

8
2
Y. Shiraishi et al. / Journal of Photochemistry and Photobiology A: Chemistry 213 (2010) 80–86
Table 1
Property of polymers.
Polymer
x/ya
Mn b (g mol−1
)
Mw b (g mol−1
)
BP unit c (␮mol g−1
)
ES d (kJ mol−1
)
ET d (kJ mol−1
)
Ac-PMMA
Ac-PAA
Ac-P(MMA-co-BP)
Ac-P(AA-co-BP)
PAAx-g-P(MMA-co-BP)y
P(AA-co-BP)x-g-PMMAy
14,500
17,000
15,400
11,800
45,700
27,600
60,000
67,100
36,000
26,100
151,700
87,500
69.7
256
18.0
88.4
329
329
334
332
289
288
289
287
65/35
81/19
a
Determined by 1H NMR analysis.
Determined by GPC analysis.
Determined from absorption spectra.
b
c
d
Excited state energies estimated by absorption, fluorescence, and phosphorescence (77 K) analysis.
DMSO (ε = 1.62 × 10 M cm ) at 298 K. 1H NMR spectra were
obtained by JEOL JNM-AL400 (400 MHz). Fluorescence and phos-
phorescence spectra (77 K) were measured on a Hitachi F-4500
fluorescence spectrophotometer (resolution, 1 nm; band-path
length, 2.5 nm) [25], with an EtOH/diethyl ether glass (2/1 v/v).
Singlet and triplet energy of the polymers were determined accord-
ing to literature procedure [26]. DLS analysis was performed on a
laser light scattering spectrometer (LB-500, HORIBA) [27]. Molec-
ular weight of the polymers was determined by gel permeation
chromatography (GPC) using a JASCO HPLC system equipped with a
PU-980 pump (JASCO) and refractive index detector RI-930 (JASCO)
with KF-806L column (Shodex). Polystyrene standards were used
4
−1
−1
d ; TMS): ı (ppm) = 0.84–0.98 (br, 3H, C(CH )), 1.78–1.85 (d,
6
3
J = 18.56 Hz, 2H, –CHCH –), 3.56 (s, br, 3H, COOCH ), 5.50 (m,
2
3
–
CH CH ), 6.09 (m, –CH CH ), 6.97 (br, ArH), 7.67 (br, ArH).
2
2
2.1.5. Synthesis of PAA-g-P(MMA-co-BP) and
P(AA-co-BP)-g-PMMA
PAA-g-P(MMA-co-BP) was synthesized as follows: Ac-PAA
(
0.4 g), Ac-P(MMA-co-BP) (0.4 g), and AIBN (0.1 g, 0.6 mmol) were
dissolved in DMSO (5 mL), and the solution was degassed by
◦
twice freeze-pump-thaw cycles. The solution was kept at 65 C
for 14 h under dry N2 and added slowly to diethyl ether (100 mL).
The precipitate formed was collected by centrifugation and puri-
fied by reprecipitation with MeOH (1 mL) and diethyl ether
◦
for calibration. The oven temperature was 40 C, and DMF con-
taining LiBr (0.01 M) was used as a carrier solvent (flow rate:
(
100 mL), affording PAA-g-P(MMA-co-BP) (0.40 g) as a white solid.
0
.6 mL/min), where the polymers containing PAA units were ana-
P(AA-co-BP)-g-PMMA was obtained in a manner similar to that
of PAA-g-P(MMA-co-BP) with Ac-P(AA-co-BP) (0.3 g) and Ac-
lyzed after esterification of –COOH units with BF /MeOH [28].
3
PMMA (0.3 g) as a white solid (0.48 g). PAA-g-P(MMA-co-BP): 1
H
NMR (400 MHz; DMSO-d ; TMS): ı (ppm) = 0.82–0.98 (br, 3H,
3. Results and discussion
6
C(CH )), 1.59–1.78 (br, 2H, –CHCH –), 1.78–1.85 (d, J = 18.55 Hz,
3
2
2
3
H, –CHCH –), 2.30 (d, J = 5.02 Hz, 1H, –CHCH –), 3.56 (s, br,
3.1. Properties of polymers
2
2
H, COOCH ), 6.97 (br, ArH), 7.67 (br, ArH), 11.7 (br, COOH).
3
−1
IR (KBr): ꢀ (cm ) = 3438, 3001, 2954, 2889, 1730, 1445, 1383,
Two kinds of amphiphilic graft copolymers containing pho-
tosensitizing BP units, PAA-g-P(MMA-co-BP) and P(AA-co-BP)-g-
PMMA, were synthesized via a grafting through method [15],
according to procedure depicted in Scheme 1. The properties of
the polymers are summarized in Table 1. As shown in Fig. 1,
absorption spectra of both polymers show a distinctive absorp-
tion band of the BP moieties at 260–330 nm, which is similar to
that of 4-methoxybenzophenone (MBP) used as a reference sen-
1
273, 1239, 1201, 1151, 987, 835, 747. P(AA-co-BP)-g-PMMA:
1
H NMR (400 MHz; DMSO-d ; TMS): ı (ppm) = 0.82–0.98 (br, 3H,
C(CH )), 1.58–1.78 (br, 2H, –CHCH –), 1.78–1.85 (d, J = 18.62 Hz,
2
6
3
2
H, –CHCH –), 2.30 (d, J = 5.13 Hz, 1H, –CHCH –), 3.56 (s, br, 3H,
2
2
COOCH ), 7.03 (br, ArH), 7.59 (br, ArH), 12.1 (br, COOH). IR (KBr):
3
1
−
ꢀ
1
(cm ) = 3435, 3000, 2957, 2838, 1730, 1600, 1452, 1397, 1259,
192, 1152, 989, 800, 752.
sitizer (spectrum c). In addition, singlet energy (E ) and triplet
S
2.2. Photoreaction
energy (ET) of the polymers are similar to that of MBP (ES = 325
and ET = 289 kJ mol ).
−
1
Each polymer was dissolved in benzene, chloroform, or
methanol (5 mL) containing trans-MS within a Pyrex glass tube
(
capacity: 20 mL). The tube was sealed using a rubber septum cap.
◦
Argon gas was bubbled through the solution for 5 min at 5 C. The
tube was photoirradiated with magnetic stirring by a high-pressure
Hg lamp (100 W; Eikohsha Co. Ltd., Osaka, Japan), filtered through
an aqueous CuSO4 (10 wt%) solution to give light wavelengths of
ꢁ
> 320 nm. The light intensity at 320–400 nm (through the filter)
−2
is 905 mW m , and the temperature of the solution is 298 K dur-
ing photoirradiation. Substrate and product concentrations were
measured by a gas chromatography (Shimadzu GC-1700, equipped
with FID).
2.3. Analysis
Absorption spectra were recorded on an UV–vis photodiode-
array spectrophotometer (Shimadzu; Multispec-1500; resolution,
nm; band-path length, 1.5 nm) [24]. The amounts of BP
1
units on the polymers were determined by comparison of
absorbance (A290 nm) with 4-methoxybenzophenone (MBP) in
−1
Fig. 1. Absorption spectra of (a) PAA-g-P(MMA-co-BP) (0.2 g L ), (b) P(AA-co-BP)-
−
1
g-PMMA (0.2 g L ), and (c) MBP (0.17 ␮M) measured in DMSO at 298 K.

Y. Shiraishi et al. / Journal of Photochemistry and Photobiology A: Chemistry 213 (2010) 80–86
83
Table 2
Cis-MS yields obtained by 12 h photoirradiation of trans-MS in (a) benzene, (b)
a
chloroform, and (c) methanol with the respective sensitizers.
Solvent
Sensitizer
cis-MS yield (%)
Benzene
MBP
17.4
14.5
3.8
PAA-g-P(MMA-co-BP)
P(AA-co-BP)-g-PMMA
Chloroform
MBP
10.4
9.2
3.8
PAA-g-P(MMA-co-BP)
P(AA-co-BP)-g-PMMA
Methanol
MBP
3.0
8.1
12.0
PAA-g-P(MMA-co-BP)
P(AA-co-BP)-g-PMMA
a
−1
The sensitizers are MBP (5.0 ␮M), PAA-g-P(MMA-co-BP) (0.56 g L ), P(AA-co-
−1
BP)-g-PMMA (0.11 g L ), respectively, where the polymer solutions contain 5.0 ␮M
BP units.
Photosensitization activities of these polymers were estimated
with an isomerization of trans-ˇ-methylstyrene (trans-MS) to
cis-MS, a typical isomerization reaction promoted by a triplet
3
energy transfer (TET) from the excited state BP ( BP*) to trans-
MS [29]. The photoreaction was performed by photoirradiation
(
ꢁ > 320 nm) of different organic solvents such as benzene, chlo-
roform, and methanol containing trans-MS (25 ␮mol) and the
respective polymers (containing 0.025 ␮mol BP unit) under Ar
atmosphere. Photoirradiation of all solutions containing respective
polymers gives rise to cis-MS as a sole product, as does MBP. Other
products such as oxetanes and olefin dimers are not observed, as is
the case with unpolymerized BP sensitizer [29], and the mass bal-
ances of the reactions are more than 90%. Table 2 summarizes the
cis-MS yields (based on the initial amount of trans-MS) obtained
by 12 h photoirradiation. Fig. S1 (Supplementary material) shows
the time-dependent change in cis-MS yields. The yields increase
with time and are not saturated at 12 h photoirradiation. This indi-
cates that the isomerization does not achieve the photostationary
state after 12 h photoirradiation. With MBP, the cis-MS yield lies
in the order of benzene > chloroform > methanol. This is because,
as reported [30], the n,ꢂ* triplet excited state of BP unit is destabi-
lized in polar solvent. The solvent polarity parameter, ꢃf, is defined
as the following equation [31]:
ꢀ
ꢁ
Fig. 2. 1H NMR spectra of (A) PAA-g-P(MMA-co-BP) and (B) P(AA-co-BP)-g-PMMA
measured in (i) chloroform-d and (ii) methanol-d4.
2
ε − 1
n − 1
ꢃf =
−
(1)
2
2
ε + 1
2n + 1
where ε is the dielectric constant and n is the refractive index of the
solvents, respectively [32]. The ꢃf values lie in the order of benzene
P(AA-co-BP) units and the dissolution of PMMA units are confirmed
1
by H NMR analysis of the polymer in chloroform-d. As shown in
(
0.003) < chloroform (0.147) < methanol (0.309), indicating that the
Fig. 2B.i, methyl and methylene signals (a and b) of the PMMA units
appear at 0.8–2.0 ppm [33], whereas the signals of PAA units (c and
d) do not. This suggests that P(AA-co-BP) units are indeed aggre-
gated, while PMMA units are dissolved in solution [34]. This is also
confirmed by dynamic light scattering (DLS) analysis. As shown in
Fig. 3b, P(AA-co-BP)-g-PMMA in benzene and chloroform shows
a formation of polymer particle with 10–20 nm diameter. In con-
trast, Ac-PMMA polymer with no PAA unit (Scheme 1) does not
show scattered light in these solvents (Fig. 3e). This again suggests
that P(AA-co-BP) units are aggregated, while PMMA units are dis-
solved. As shown in Fig. 3d, Ac-P(AA-co-BP) with no PMMA unit
shows polymer particles with 10–20 nm diameter in benzene and
chloroform, which is similar to P(AA-co-BP)-g-PMMA (Fig. 3b). This
suggests that, as shown in Scheme 2b, P(AA-co-BP)-g-PMMA in
these solvents indeed forms a micelle structure consisting of the
aggregated PAA core with the dissolved PMMA units at the outer
sphere. The low cis-MS yield in benzene and chloroform (Table 2)
is therefore because strong aggregation of P(AA-co-BP) units sup-
presses TET from 3BP* to trans-MS.
solvent polarity increases in this order. These data clearly sug-
gest that isomerization of trans-MS indeed occurs efficiently in
less polar solvents. Amphiphilic graft copolymers, however, show
different sensitization activity (Table 2). PAA-g-P(MMA-co-BP) con-
taining BP units in less polar PMMA units shows a cis-MS yield
similar to MBP in benzene and chloroform, but shows much higher
yield in methanol. In contrast, P(AA-co-BP)-g-PMMA containing BP
units in polar PAA units shows a cis-MS yield much lower than
MBP in benzene and chloroform, but shows much higher yield in
methanol.
3
.2. Photosensitization in benzene and chloroform
The very low sensitization activity of P(AA-co-BP)-g-PMMA in
benzene and chloroform (Table 2) is because, in these solvents, the
polymer forms a “micelle” structure consisting of strongly aggre-
gated PAA core with dissolved PMMA units at the outer sphere,
as schematically shown in Scheme 2b. The BP units are confined
within the aggregate, and the TET from 3BP* to trans-MS is sup-
pressed, resulting in very low cis-MS yield. The aggregation of
1
Fig. 2A.i shows H NMR spectrum of PAA-g-P(MMA-co-BP) mea-
sured in chloroform-d, which contains BP units in less polar PMMA

8
4
Y. Shiraishi et al. / Journal of Photochemistry and Photobiology A: Chemistry 213 (2010) 80–86
Scheme 2. Schematic representation of the structure of amphiphilic graft copolymers in different solvents.
units. As is the case for P(AA-co-BP)-g-PMMA (Fig. 2B.i), methyl
and methylene signals for PMMA units (a and b) appear, whereas
the signals for PAA units do not. This indicates that PAA units are
aggregated, while P(MMA-co-BP) units are dissolved. As shown in
Fig. 3a, PAA-g-P(MMA-co-BP) in benzene and chloroform shows
a formation of 10–20 nm polymer particles, which is similar to
that of P(AA-co-BP)-g-PMMA (Fig. 3b). Ac-P(MMA-co-BP) in ben-
zene and chloroform does not show particle formation (Fig. 3c),
whereas Ac-PAA shows a formation of 10–20 nm particles (Fig. 3f).
These indicate that PAA-g-P(MMA-co-BP) in these solvents forms a
micelle structure similar to that of P(AA-co-BP)-g-PMMA, as shown
in Scheme 2a, where the dissolved BP units are located at the
outer sphere. The sensitization activity of PAA-g-P(MMA-co-BP)
comparable to that of MBP in benzene and chloroform (Table 2)
is therefore due to the dissolution of BP units in a bulk solu-
tion.
Fig. 3. Hydrodynamic diameter (D) of (a) PAA-g-P(MMA-co-BP) (0.56 g L 1), (b) P(AA-co-BP)-g-PMMA (0.11 g L−1), (c) Ac-P(MMA-co-BP) (0.07 g L ), (d) Ac-P(AA-co-BP)
(
−
−1
− −1 −1
1
0.02 g L ), (e) Ac-PMMA (0.07 g L ), and (f) Ac-PAA (0.02 g L ) measured in different solvents.

Y. Shiraishi et al. / Journal of Photochemistry and Photobiology A: Chemistry 213 (2010) 80–86
85
Table 3
Spectral data of
ridinium iodide) obtained in methanol.
is isomerized efficiently by TET from 3BP*. The formation of weak
a hemicyanine dye (4-(4-dimethylaminostyryl)-1-methylpy-
aggregate with a less polar domain (Scheme 2c and d) is, there-
fore, probably the major factor for high photosensitization activity
of both PAA-g-P(MMA-co-BP) and P(AA-co-BP)-g-PMMA polymers
in methanol.
Polymer
ꢁmax (nm)
Absorption
Fluorescence
Stokes shift (cm−1)
None
475
476
476
588
585
584
4000
3900
3900
PAA-g-P(MMA-co-BP)
P(AA-co-BP)-g-PMMA
4. Conclusion
Effect of solvents on photosensitization activity of amphiphilic
graft copolymers containing a BP photosensitizing unit, PAA-g-
P(MMA-co-BP) and P(AA-co-BP)-g-PMMA, has been studied for
isomerization of trans-MS, with the following results:
3
.3. Photosensitization in methanol
As shown in Table 2, in methanol, sensitization activity of both
PAA-g-P(MMA-co-BP) and P(AA-co-BP)-g-PMMA are much higher
than that of MBP. This is because these polymers form a weak
aggregate containing a “less polar domain” (Scheme 2c and d),
which stabilizes the n, ꢂ* triplet excited state BP moieties [30]
and enhances TET to trans-MS. The formation of less polar domain
is confirmed by absorption and fluorescence analysis with a flu-
orescent dye. As reported [35], a hemicyanine dye shows a red
shift of absorption band and a blue shift of fluorescence band
(
1) In benzene and chloroform, P(AA-co-BP)-g-PMMA shows much
lower sensitization activity than a bulk MBP sensitizer. The
polymer forms a micelle structure consisting of strongly aggre-
gated P(AA-co-BP) core with dissolved PMMA units at the outer
sphere. The confinement of the BP units within the core sup-
presses the triplet energy transfer from 3BP* to trans-MS and,
hence, results in lower sensitization activity.
(
2) In methanol, both PAA-g-P(MMA-co-BP) and P(AA-co-BP)-g-
PMMA show higher sensitization activity than MBP. These
polymers form a weak aggregate of less polar PMMA units,
which contains dissolved PAA units. The less polar domain
−
1
with a decrease in polarity of the media. The Stokes shift (cm
)
between the absorption and fluorescence maxima is therefore cor-
related with the polarity of media [36]. Table 3 summarizes the
spectral data of a hemicyanine dye (4-(4-dimethylaminostyryl)-
formed within the aggregate stabilizes the excited state BP moi-
1
-methylpyridinium iodide) measured in methanol without and
eties. This enhances the TET from 3BP* to trans-MS and, hence,
with polymers. The Stokes shifts obtained with both polymers
are lower than that obtained without polymer, indicating that the
dye is located in a less polar part formed within the polymers.
In the present reaction, accumulation of trans-MS around the BP
units is also a possible reason for isomerization enhancement.
However, stirring a methanol solution containing the respective
polymers and trans-MS (298 K, 12 h) does not show any change
in the trans-MS concentration in solution. This suggests that sub-
strate accumulation within the polymer [3] does not contribute to
the isomerization enhancement, leaving the formation of less polar
domain within the polymer being the major factor.
results in isomerization enhancement.
Acknowledgments
This work was supported by the Grant-in-Aid for Scientific
Research (No. 19760536) from the Ministry of Education, Culture,
Sports, Science and Technology, Japan (MEXT).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jphotochem.2010.05.003.
The less polar domain is formed by a weak aggregation of
PMMA units less soluble in methanol. In alcoholic solvents, polar
PAA units are soluble, while less polar PMMA units tend to aggre-
gate [37]. Fig. 2ii shows 1H NMR spectra of PAA-g-P(MMA-co-BP)
References
[
1] (a) J. Wahlen, D.E. De Vos, P.A. Jacobs, P.L. Alsters, Adv. Synth. Catal. 346 (2004)
52–164;
and P(AA-co-BP)-g-PMMA measured in methanol-d . As expected,
4
1
strong c and d signals for PAA units appear. In addition, the sig-
nal a for PMMA units also appears, although at the decreased
level. This indicates that less polar PMMA units in both polymers
are partly soluble in methanol [34]. As shown in Fig. 3a and b,
DLS analysis of PAA-g-P(MMA-co-BP) and P(AA-co-BP)-g-PMMA
in methanol detect polymer particles with 40–100 nm diameter,
although smaller particles (10–20 nm) form in benzene and chloro-
form. This implies that weak aggregation of less polar PMMA units
in methanol leads to a formation of large polymer particles with a
less polar character.
The formation of weakly aggregated large polymer particles is
because the polar PAA units are located within the PMMA aggre-
gate, as schematically shown in Scheme 2c and d. As shown in
Fig. 3c and e, Ac-P(MMA-co-BP) and Ac-PMMA in methanol show
a formation of polymer particles with 20–40 nm diameter, which
are much smaller than the particles of PAA-g-P(MMA-co-BP) and
P(AA-co-BP)-g-PMMA polymers in methanol (40–100 nm, Fig. 3a
and b). The presence of polar PAA units suppresses the aggregation
of less polar PMMA units. This probably leads to a weak aggrega-
tion of the PMMA units and results in the formation of large polymer
particles. As a result of this, for both P(AA-co-BP)-g-PMMA and PAA-
g-P(MMA-co-BP), the BP units exist within the less polar domain
(b) S.A. Chavan, W. Maes, L.E.M. Gevers, J. Wahlen, I.F.J. Vankelecom, P.A. Jacobs,
W. Dehaen, D.E. De Vos, Chem. Eur. J. 11 (2005) 6754–6762.
2] (a) N. Kitamura, K. Yamada, K. Ueno, S. Iwata, J. Photochem. Photobiol. A: Chem.
[
184 (2006) 170–176;
(
b) M.J. Fuchter, B.M. Hoffman, A.G.M. Barrett, J. Org. Chem. 71 (2006) 724–729;
(c) A.G. Griesbeck, A. Bartoschek, T.T. El-Idreesy, O. Hoinck, C. Miara, J. Mol.
Catal. A: Chem. 251 (2006) 41–48;
(
d) A.G. Griesbeck, T.T. El-Idreesy, Photochem. Photobiol. Sci. 4 (2005) 205–209.
[
3] (a) W.R. Dichtel, K.-Y. Baek, J.M.J. Frechet, I.B. Rietveld, S.A. Vinogradov, J. Polym.
Sci. Part A: Polym. Chem. 44 (2006) 4939–4951;
(
(
b) S. Hecht, J.M.J. Frechet, J. Am. Chem. Soc. 123 (2001) 6959–6960;
c) A.W. Jensen, B.S. Maru, X. Zhang, D.K. Mohanty, B.D. Fahlman, D.R. Swanson,
D.A. Tomalia, Nano Lett. 5 (2005) 1171–1173.
[4] (a) S. Irie, M. Irie, Y. Yamamoto, K. Hayashi, Macromolecules 8 (1975) 424–427;
b) P. Bhyrappa, J.K. Young, J.S. Moore, K.S. Suslick, J. Am. Chem. Soc. 118 (1996)
708–5711;
c) P. Bhyrappa, J.K. Young, J.S. Moore, K.S. Suslick, J. Mol. Catal. A: Chem. 113
(
5
(
(1996) 109–116.
[5] (a) M.A. Oar, W.R. Dichtel, J.M. Serin, J.M.J. Frechet, J.E. Rogers, J.E. Slagle,
P.A. Fleitz, L.-S. Tan, T.Y. Ohulchanskyy, P.N. Prasad, Chem. Mater. 18 (2006)
3682–3692;
(b) T. Nishikubo, J. Uchida, K. Matsui, T. Iizawa, Macromolecules 21 (1988)
1583–1589;
(
2
c) I. Nishimura, A. Kameyama, T. Nishikubo, Macromolecules 31 (1998)
789–2796.
[
[
6] (a) S-i. Yusa, A. Sakakibara, T. Yamamoto, Y. Morishima, Macromolecules 35
(2002) 10182–10188;
(
b) T. Noda, Y. Morishima, Macromolecules 32 (1999) 4631–4640.
7] (a) M. Li, W. Yang, Z. Chen, J. Qian, C. Wang, S. Fu, J. Polym. Sci. Part A: Polym.
Chem. 44 (2006) 5887–5897;
(
Scheme 2c and d), in which their excited states are stabilized. The
substrate, trans-MS, is able to diffuse inside the weak aggregate and
(b) Y. Deng, Y. Li, X. Wang, Macromolecules 39 (2006) 6590–6598.

8
6
Y. Shiraishi et al. / Journal of Photochemistry and Photobiology A: Chemistry 213 (2010) 80–86
[8] (a) S.Y. Kim, K.E. Lee, S.S. Han, B. Jeong, J. Phys. Chem. B 112 (2008) 7420–7423;
[22] Y. Shiraishi, R. Miyamoto, T. Hirai, Langmuir 24 (2008) 4273–4279.
(
b) K.-J. Gao, G. Li, H. Shi, X. Lu, Y. Gao, B.-Q. Xu, J. Polym. Sci. Part A: Polym.
[23] B. Leshem, G. Sarfati, A. Novoa, I. Breslav, R.S. Marks, Luminescence 19 (2004)
69–77.
Chem. 46 (2008) 4889–4904.
[
9] (a) K.-H. Han, E. Lee, J.S. Kim, B.-K. Cho, J. Am. Chem. Soc. 130 (2008)
[24] Y. Shiraishi, R. Miyamoto, T. Hirai, Org. Lett. 11 (2009) 1571–1574.
[25] Y. Shiraishi, Y. Furubayashi, G. Nishimura, T. Hirai, J. Lumin. 126 (2007) 68–76.
[26] (a) W. Adam, G. Fragale, D. Klapstein, W.M. Nau, J. Wirz, J. Am. Chem. Soc. 117
(1995) 12578–12592;
1
3858–13859;
(
b) D.M. Kuntz, L.M. Walker, Soft Matter 4 (2008) 286–293.
[
[
10] (a) J.H. Yao, K.Y. Mya, L. Shen, B.P. He, L. Li, Z.H. Li, Z.-K. Chen, X. Li, K.P. Loh,
Macromolecules 41 (2008) 1438–1443;
(b) W.S. Jenks, W. Lee, D. Shutters, J. Phys. Chem. 98 (1994) 2282–2289;
(c) T. Shen, Z.-G. Zhao, Q. Yu, H.-J. Xu, J. Photochem. Photobiol. A: Chem. 47
(1989) 203–212.
(
b) D. Peng, C. Feng, G. Lu, S. Zhang, X. Zhang, X. Huang, J. Polym. Sci. Part A:
Polym. Chem. 45 (2007) 3687–3697.
11] (a) Y. Wang, Y. Tan, X. Huang, Y. Che, X. Du, J. Appl. Polym. Sci. 112 (2009)
[27] Y. Shiraishi, Y. Kimata, H. Koizumi, T. Hirai, Langmuir 24 (2008) 9832–9836.
[28] (a) M.S.F. Lie Ken Jie, O. Bakare, J. Chem. Soc. Perkin Trans. 2 (1989) 2121–2125;
(b) U. Ackermann, H.J. Tochon-Danguy, A.M. Scott, J. Label. Compd. Radiopharm.
47 (2004) 523–530.
[29] (a) A.A. Lamola, G.S. Hammond, J. Chem. Phys. 43 (1965) 2129–2135;
(b) T. Arai, H. Sakuragi, K. Tokumaru, Bull. Chem. Soc. Jpn. 55 (1982) 2204–2207.
[30] R.G. Zepp, M.M. Gumz, W.L. Miller, H. Gao, J. Phys. Chem. A 102 (1998)
5716–5723.
[31] (a) J. Hayakawa, M. Ikegami, T. Mizutani, M. Wahadoszamen, A. Momotake, Y.
Nishimura, T. Arai, J. Phys. Chem. A 110 (2006) 12566–12571;
(b) A. Chakraborty, S. Kar, N. Guchhait, J. Photochem. Photobiol. A: Chem. 181
(2006) 246–256;
1
425–1435;
(
b) E. Martinelli, S. Agostini, G. Galli, E. Chiellini, A. Glisenti, M.E. Pettitt, M.E.
Callow, J.A. Callow, K. Graf, F.W. Bartels, Langmuir 24 (2008) 13138–13147.
12] (a) H. Mori, H. Ookuma, T. Endo, Macromolecules 41 (2008) 6925–6934;
[
[
(
b) Y. Liu, X. Cao, M. Luo, Z. Le, W. Xu, J. Colloid Interface Sci. 329 (2009) 244–252.
13] (a) Q. Tang, F. Cheng, X.-L. Lou, H.-J. Liu, Y. Chen, J. Colloid Interface Sci. 337
(
(
2009) 485–491;
b) Y. Kitajyo, Y. Nawa, M. Tamaki, H. Tani, K. Takahashi, H. Kaga, T. Satoh, T.
Kakuchi, Polymer 48 (2007) 4683–4690.
[
[
[
14] D. Neugebauer, Polymer 48 (2007) 4966–4973.
15] K. Matyjaszewski, J. Xia, Chem. Rev. 101 (2001) 2921–2990.
16] (a) X. Zhang, Z. Shen, C. Feng, D. Yang, Y. Li, J. Hu, G. Lu, X. Huang, Macro-
molecules 42 (2009) 4249–4256;
(c) P.D. Zoon, A.M. Brouwer, Chem. Phys. Chem. 6 (2005) 1574–1580;
(d) A.C. Benniston, A. Harriman, J.P. Rostron, Phys. Chem. Chem. Phys. 7 (2005)
3041–3047.
(
b) O.V. Borisov, E.B. Zhulina, Macromolecules 38 (2005) 2506–2514.
[
[
17] (a) J. Chojnowski, W. Fortuniak, M. Scibiorek, K. Rozga-Wijas, A. Grzelka, U.
Mizerska, Macromolecules 40 (2007) 9339–9347;
[32] (a) T.R. Griffiths, D.C. Pugh, Coord. Chem. Rev. 29 (1979) 129–211;
(b) M. Chastrette, M. Rajzmann, M. Chanon, K.F. Purcell, J. Am. Chem. Soc. 107
(1985) 1–11;
(
b) Y. Iwasaki, K. Akiyoshi, Biomacromolecules 7 (2006) 1433–1438.
18] (a) Y. Zhai, Y. Qiao, C. Xie, X. Lin, Y. Ma, A. Dong, L. Deng, J. Appl. Polym. Sci. 110
(c) R.S. Ruoff, D.S. Tse, R. Malhotra, D.C. Lorents, J. Phys. Chem. 97 (1993)
3379–3383.
(
(
2008) 3525–3531;
b) T. Jiang, J.B. Chang, C. Wang, Z. Ding, J. Chen, J. Zhang, E.-T. Kang, Biomacro-
[33] B.M. Baysal, N. Kayaman, J. Chem. Phys. 109 (1998) 8701–8707.
[34] (a) A. Matsuo, T. Watanabe, A. Hirao, Macromolecules 37 (2004) 6283–6290;
(b) S. Angot, D. Taton, Y. Gnanou, Macromolecules 33 (2000) 5418–5426.
[35] (a) H. Wang, R. Helgeson, B. Ma, F. Wudl, J. Org. Chem. 65 (2000) 5862–5867;
(b) Y. Huang, T. Cheng, F. Li, C. Luo, C.-H. Huang, Z. Cai, X. Zeng, J. Zhou, J. Phys.
Chem. B 106 (2002) 10031–10040;
molecules 8 (2007) 1951–1957.
[
19] (a) S.B. Clendenning, S. Fournier-Bidoz, A. Pietrangelo, G. Yang, S. Han, P.M.
Brodersen, C.M. Yip, Z.-H. Lu, G.A. Ozin, I. Manners, J. Mater. Chem. 14 (2004)
1
686–1690;
(
b) J. Ruokolainen, R. Makinen, M. Torkkeli, T. Makela, R. Serimaa, G. ten Brinke,
O. Ikkala, Science 280 (1998) 557–560.
20] (a) L.-B. Feng, S.-X. Zhou, B. You, L.-M. Wu, J. Appl. Polym. Sci. 103 (2007)
(c) S.-L. Wang, T.-I. Ho, Chem. Phys. Lett. 268 (1997) 434–438;
(d) A. Mishra, N.S. Haram, Dyes Pigments 63 (2004) 191–202.
[36] (a) X. Cao, R.W. Tolbert, J.L. McHale, W.D. Edwards, J. Phys. Chem. A 102 (1998)
2739–2748;
[
[
1
458–1465;
(
b) Z. Yuan, M. Gauthier, Macromolecules 39 (2006) 2063–2071.
21] (a) P. Wang, S.M. Zakeeruddin, J.E. Moser, M.K. Nazeeruddin, T. Sekiguchi, M.
Gratzel, Nat. Mater. 2 (2003) 402–407;
(b) M. Tsukada, Y. Mineo, K. Itoh, J. Phys. Chem. 93 (1989) 7989–7992.
[37] (a) W. Hyk, M. Ciszkowska, J. Phys. Chem. B 106 (2002) 11469–11473;
(b) J. Gonzalez-Benito, J.L. Koenig, Polymer 47 (2006) 3065–3072.
(
b) Y. Shiraishi, H. Koizumi, T. Hirai, J. Phys. Chem. B 109 (2005) 8580–8586.