Dynamic control of full-colored emission and quenching of photoresponsive conjugated polymers by photostimuli

Article abstract of DOI:10.1002/adfm.201500136

A series of photoresponsive and full-colored fluorescent conjugated copolymers is synthesized by combining phenylene- and thienylene-based main chains with photochromic dithienylethene (DE) side chains. Solutions and cast films of the polymers exhibit var

Full text of DOI:10.1002/adfm.201500136

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Dynamic Control of Full-Colored Emission and Quenching
of Photoresponsive Conjugated Polymers by Photostimuli
Kazuyoshi Watanabe, Hiroyuki Hayasaka, Tatsuaki Miyashita, Kenta Ueda, and Kazuo Akagi*
and aggregation-enhanced emission (AEE)
A series of photoresponsive and full-colored fluorescent conjugated copoly-
mers is synthesized by combining phenylene- and thienylene-based main
chains with photochromic dithienylethene (DE) side chains. Solutions and
cast films of the polymers exhibit various colored fluorescence in visible
wavelengths of 400−700 nm corresponding to emissions of the conjugated
main chain. The fluorescence is reversibly photoswitched between emission
and quenching through DE photoisomerization using external stimuli from
ultraviolet and visible light irradiation. The reprecipitation method with ultra-
sonication enables the polymers to form spherical aggregates with diameters
of 20−70 nm in water. After investigating and comparing the optical proper-
ties, the resulting nanosphere solutions are assumed to exist in an interme-
diate state between an isolated state (i.e., in solution) and an aggregated state
in cast film. The majority of the nanosphere solutions also exhibit the same
photoswitchable fluorescence behavior as those in the solutions and the cast
films. The results demonstrate that the visible fluorescence of the conjugated
copolymers is reversibly switchable between emission and quenching using
the photoisomerizing DE side chain regardless of the fluorescent colors and
the polymer chain aggregation.
characteristics were reported in selected
ACPs.[14–16] Therefore, it is of great interest
to investigate ACPs in the aggregated state
that are quite different from those the iso-
lated chain state.
The polymer nanosphere solution
can be treated as an intermediate state
between a solution state and a solid film
state because the polymer nanoparticles
uniformly disperse in a solvent, similar
to their behavior in solution, whereas the
polymer chains aggregate with each other,
similarly to their behavior in a solid film.
In other words, the polymer nanosphere
solution can be regarded as a dispersed
nano-ordered crystalline polymer system.
This bilateral character of the nanosphere
solution causes the polymer to exhibit high
processability and fluidity as well as aggre-
gation effects. In addition, the polymer
nanosphere solution enables quantitative
analysis of the aggregated state of poly-
mers from the spectroscopic point of view.
Hence, the polymer nanosphere solution is useful for under-
standing the aggregation effect on ACPs as compared with the
solution and solid film states.
1. Introduction
Aromatic π-conjugated polymers (ACPs) are promising can-
didates for advanced functional materials and are expected to
be applied in such organic devices as organic light-emitting
diodes, organic field-effect transistors, organic photovoltaic
cells, and chemical biosensors due to their semiconductive and
optoelectronic properties.[1–8] The ACPs exhibit various colored
fluorescence in the visible region due to changes in the main
chain structures because their properties are fundamentally
determined by the primary structure of the conjugated back-
bones. Furthermore, the fluorescent property can be modified
and functionalized by controlling the secondary or higher-
ordered structures of the main chains in an aggregated state. It
is well known that linearly aligned and helically π-stacked ACPs
show linear and circular dichroism in luminescence, respec-
tively.[9–13] In another case, aggregation-induced emission (AIE)
Dynamic control of the fluorescence of ACPs using an
external light stimulus is of particular interest because such
photoresponsive polymers are essential for next-generation
optoelectronic materials. Dithienylethene (DE) derivatives[17–20]
are one class of the most attractive photoresponsive materials
because of their outstanding fatigue resistance, thermal sta-
bility, and ability to undergo conformational changes between
open and closed forms via photoisomerization, and therefore
they are regarded as promising materials for the fabrication
of photodynamically controllable luminescent devices[21,22] as
well as photodynamically color-tunable systems.[23–27] The DE
derivatives are also known to display luminescent color changes
via photoisomerization.[20,28–37] Similarly, conjugated polymers
that contain DE moieties in the polymer backbones exhibit
photochromism.[20,38–41] The chromism in both absorption
and luminescence of the conjugated polymers is attributed to
structural changes in the conjugated backbones resulting from
the DE photoisomerization. Hence, it is necessary to properly
design the molecular structure to realize the desired switching
behavior and fluorescent colors.
K. Watanabe, Dr. H. Hayasaka, T. Miyashita,
K. Ueda, Prof. K. Akagi
Department of Polymer Chemistry
Kyoto University, Katsura
Nishikyo-ku, Kyoto 615–8510, Japan
E-mail: akagi@fps.polym.kyoto-u.ac.jp
It is well known that in ACP nanoparticles doped with
luminescent dopants, the ACP fluorescence is almost com-
pletely quenched and the fluorescence of the dopant is mainly
DOI: 10.1002/adfm.201500136
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DE
DE
DE
DE
O
O
O
O
O
O
O
O
S
S
n
n
n
n
C6H13
C6H13
C6H13
C6H13
P1
P2
P3
P4
DE
DE
DE
O
O
O
O
O
O
S
S
S
S
S
n
n
n
P5
"Photoresponsive" moiety
P6
P7
F
F
F F
F
F
F
F
F
F
F
F
UV
C8H17
C6H13
C8H17
C6H13
DE =
O
O
O
O
Vis.
O
O
S
S
S
S
Open form
Scheme 1. Structures of photoresponsive conjugated polymers.
Closed form
observed.[42] This is due to the intraparticle energy transfer
from the ACP backbone to the dopant. Thus, it was previously
reported that the ACP nanoparticles doped with photochromic
dyes showed reversible fluorescence photoswitching between
emission and quenching by photoisomerization of the dyes
upon irradiation of external light stimuli.[42–45] On the other
hand, it was also reported that the ACPs incorporated with
photochromic moieties showed reversible photomodulation of
the fluorescence by using light stimuli.[46–48] In these polymer
systems, the fluorescent moiety is independent of the pho-
tochromic moiety, resulting in high flexibility on the molecular
design.
By introducing the DE moiety into the side chains of ACPs,
the polymer fluorescence in solution and solid film was switch-
able between emission and quenching via reversible DE photoi-
somerization. In previous work, we reported the photodynamic
ON/OFF switching of linearly polarized luminescence (LPL) in
macroscopically aligned ACPs and also that of circularly polar-
ized luminescence (CPL) in helically π-stacked ACPs using UV–
vis light stimuli.[49,50] In these cases, the fluorescent conjugated
backbones of the polymers were unchanged before and after
DE photoisomerization, and therefore, the interchain structures
were maintained. In addition, this material offers the advantage
of free design of the fluorescent color because the fluorescent
polymer backbone and the photoisomerized DE side chain are
independent of each other from the viewpoint of the π-electronic
structure. Very recently, we reported that three types of ACPs
with the DE side chains showed red-, green-, and blue-colored
fluorescence in the nanosphere solution, and they exhibited
photoswitching behavior between emission and quenching
by external light stimuli.[51] However, the red-colored fluores-
cent ACP showed bluish purple-colored fluorescence in chlo-
roform solution although it exhibited red-colored fluorescence
in nanosphere solution and solid film. This is because the main
chain of the red-colored fluorescent ACP consists of a polyflu-
orene backbone containing a very small amount of 4,7-di(2-
thienyl)-2,1,3-benzothiadiazole (DBT) moiety, and the red-
colored fluorescence of the DBT moiety is only observable in
the aggregated state. This means that the photodynamic ON/
OFF switching behavior of full-colored fluorescence has not
been completely achieved in the isolated chain state such as in
the chloroform solution.
In this work, we designed and synthesized several types of
photoresponsive ACPs by incorporating a DE side chain into
various conjugated main chains, i.e., poly(p-terphenylene)
[P1], poly(fluorene-phenylene) [P2], poly(biphenylene-thie-
nylene) [P3], poly(fluorene-thienylene) [P4], poly(p-phenylene-
vinylene) [P5],[49] poly(bithienylene-phenylene) [P6],[49] and
poly(terthiophene) [P7] (Scheme 1). The polymers exhibited
various blue−red colored fluorescence corresponding to the
conjugated length of the main chains. In solution and solid
film, it was successfully demonstrated that the fluorescence
of ACPs in the whole visible region was reversibly switchable
between emission and quenching through photoisomeriza-
tion of the DE side chains regardless of the fluorescence wave-
lengths (Figure 1). The quenching efficiency in cast films was
higher than that in solutions as a result of the aggregation
effect. The reprecipitation method with ultrasonication enabled
the polymers to form spherical aggregates with diameters of
20−70 nm in water. The resulting nanosphere solutions exhib-
ited moderate fluorescent properties between those of solutions
and solid films, and the fluorescence was also photoswitchable,
except for the red-colored fluorescence of P7. Herein, we con-
ducted a comprehensive investigation of the photoswitchable
full-colored fluorescence of ACPs bearing DE side chains in
both the isolated chain and the aggregated states.
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Figure 1. Scheme of photoswitching behavior of multicolored fluorescence between emission and quenching by using DE photoisomerization.
After subsequent irradiation with visible light (λ > 400 nm), all
proton signals corresponding to the DE open form were regen-
erated. These results indicated that reversible photoisomeriza-
tion of DE moiety occurred even in the polymer side chains.
2. Results and Discussion
2.1. Synthesis and Characteristics of Photoresponsive Conju-
gated Polymers
The synthetic routes of the photoresponsive monomers and
polymers are shown in Scheme 2. 2,5-Dibromobenzoic acid
and 2,5-dibromo-3-thenoic acid were esterified with the DE
derivative 2 via Mitsunobu reaction to give 3 and 4, respec-
tively. Esterification of the intermediate products with 1 in
the presence of both N,N’-dicyclohexylcarbodiimide (DCC)
and 4-(dimethylamino)pyridine (DMAP) yielded the photore-
sponsive monomers, M1 and M2, respectively. The photore-
sponsive conjugated polymers P1−P4 were synthesized via a
Suzuki coupling reaction between the monomers and diborate
monomers, i.e., 4,4′-biphenyldiboronic acid cyclic ester and
9,9-dihexylfluorene-2,7-diboronic acid cyclic ester, in the pres-
ence of tetrakis(triphenylphosphine)palladium(0) [Pd(PPh3)4]
as a catalyst. The P5−P7 polymers were synthesized through
a Stille coupling reaction between the monomers and dis-
tannyl monomers, i.e., 1,2-bis(tributylstannyl)ethylene and
5,5′-bis(trimethylstannyl)-2,2′-bithiophene, in the presence of
tris(dibenzylideneacetone)dipalladium(0) [Pd2(dba)3] and tri-
2-furylphosphine [(2-furyl)3P] as catalysts.
The molecular structures of the monomers and the polymers
were confirmed using nuclear magnetic resonance (NMR)
measurements, mass spectrometry, and elemental analysis.
All synthesized polymers were fusible and soluble in such
organic solvents as tetrahydrofuran (THF), toluene, and chloro-
form (CHCl3). Table 1 shows the average molecular weights of
the polymers as evaluated by gel permeation chromatography
(GPC). The number- and weight-average molecular weights (Mn
and Mw) of the polymers range from 1.1 × 104 to 2.0 × 104 and
1.2 × 104 to 1.5 × 105, respectively, resulting in a polydispersity
index (PDI, Mw/Mn) of 1.1−7.5. The degree of polymerization
(DP) was estimated as 10−19 using the Mn values. The DE
moiety in the side chains successfully photoisomerized from
the open form to closed form upon irradiation by UV light
(λ = 254 nm). The level of DE conversion to closed form in a pho-
tostationary state (PSS) was estimated as 42%−47% by using 1H
NMR results (see the Experimental Section for more detail). In
this work, a PSS is an equilibrium state between the open form
and the closed form of the DE moiety under UV irradiation.
2.2. Absorption and Fluorescence of P1−P7 Solutions
and Cast Films
First, we investigated the optical properties of the P1−P7 solu-
tions and cast films. The absorption peaks of P1−P7 in CHCl3
solution (c = 4.0 × 10−5 M) and cast film are summarized in
Table 2. The polymer cast films were prepared from CHCl3−
toluene solutions of the corresponding polymers. As shown
in Figure 2a, the polymer solutions in an open state showed
various absorption bands in the visible region of 300−600 nm,
which corresponds to π–π* transition of the polymer conju-
gated backbone. The polymer cast films showed absorption
bands in a longer wavelength region than those of the CHCl3
solutions (Figure 2b) because the effective conjugated length of
the polymer main chains were increased in the solid state. More
specifically, the absorption bands of P1−P7 were red-shifted by
11, 0, 19, 14, 11, 35, and 40 nm, respectively (see Table 2). It
is worth noting that the thienylene-containing polymers of P3,
P4, P6, and P7 exhibited larger red shifts in absorption than
those of the thienylene-free polymers P1, P2, and P5. This
effect results from the high π-stacking feature of the thienylene
ring, which enhances the coplanarity of the polymer conjugated
backbone in a solid state. This observation is also supported by
the fact that the degree of red shift increases with the number
of thienylene rings in a polymer repeating unit, i.e., the absorp-
tion peak shift is 0−11 nm for thienylene-free polymers P1, P2,
and P5; 14−19 nm for monothienylene-containing polymers P3
and P4; 35 nm for the bithienylene-containing polymer P6; and
40 nm for terthienylene-containing polymer P7.
Figure 2c,d displays the photoluminescence (PL) spectra of
the polymers in the open state with excitation wavelengths at
either 350 or 380 nm. The CHCl3 solutions and cast films of
the polymers exhibited various colored fluorescence that cor-
responded to π*−π transition of the polymer conjugated back-
bone. As shown in Figure 2c,d, 3, the fluorescent color of the
polymer solutions and cast films changed from blue to red with
an increasing number of thienylene rings in the repeating unit,
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(A)
(B)
1) 2-Hexyl-1-decanol,
DIAD, TPP, THF
C8H17
C6H13
2) KOH, water, MeOH
O
O
OH
O
1) 1-Bromo-2-hexyldecane,
K2CO3, 18-crown-6, acetone
MeO
HO
1
2) KOH, water, MeOH
F
F
F
F
O
F
F
F
F
F
F
F
F
OH
C8H17
Br
Br
DIAD, TPP
O
O
1
O
O
O
C6H13
S
S
S
S
O
O
OH
DCC, DMAP
THF
Br
Br
CH2Cl2
Br
Br
F
F
M1
3
F
F
F
F
F
F
F
F
O
F
F
F
F
F
F
F
OH
Br
S
S
HO
OH
F
C8H17
C6H13
2
O
O
Br
1
S
O
O
O
S
S
S
S
O
O
DIAD, TPP
THF
DCC, DMAP
OH
CH2Cl2
Br
Br
Br
Br
S
S
M2
4
O
B
O
O
B
O
O
O
O
O
DE
B
B
DE
O
O
O
O
Pd(PPh3)4, Na2CO3
THF/water
Pd(PPh3)4, Na2CO3
THF/water
M1
M2
S
n
n
P1
P3
O
O
O
B
O
O
O
O
O
B
B
B
DE
DE
O
O
C6H13
C6H13
C6H13
C6H13
O
O
Pd(PPh3)4, Na2CO3
THF/water
Pd(PPh3)4, Na2CO3
THF/water
S
n
n
C6H13
C6H13
C6H13
C6H13
P2
P4
S
SnMe3
Bu3Sn
SnBu3
DE
Me3Sn
DE
O
O
S
O
O
Pd2(dba)3, (2-furyl)3P
DMF
Pd2(dba)3, (2-furyl)3P
THF
S
S
S
n
n
P7
P5
S
SnMe3
Me3Sn
DE
S
O
O
Pd2(dba)3, (2-furyl)3P
THF
S
S
n
P6
Scheme 2. Synthetic routes of photoresponsive conjugated polymers, P1−P7.
except for the PPV derivative P5. Specifically, thienylene-free P1
and P2 showed blue fluorescence, monothienylene-containing
P3 and P4 displayed bluish-green fluorescence, bithienylene-
containing P6 displayed green and yellow fluorescence, and ter-
thienylene-containing P7 displayed red fluorescence. The fluo-
rescence peak wavelengths of the polymers are listed in Table 3.
This result also indicates that the thienylene ring enhances the
coplanarity of the polymer main chain, and hence, the effec-
tive conjugated length. The fluorescence quantum yields of
the polymer solutions in the open state (Φopen) were evaluated
using quinine sulfate in 1.0 M sulfuric acid as a standard, as
summarized in Table 3. Thienylene-free P1 and P2, which con-
sist of phenylene and fluorene rings, showed high Φopen values
of 62% and 85%, respectively. However, thienylene copolymers
P3, P4, and P6 and PPV derivative P5 showed lower Φopen
values of 23%−26%. Furthermore, PT derivative P7 showed a
significant low Φopen value of 5%, which might be due to a so-
called “concentration quenching in fluorescence” phenomenon
resulting from the high π-stacking feature of the thienylene
rings.[52–54]
2.3. Photoswitching Behavior in Absorption and Fluorescence of
P1−P7 Solutions and Cast Films
Next, we investigated the absorption and fluorescence changes
upon irradiation by external light sources for P1−P7 solutions
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Table 1. Molecular weights of P1−P7 and level of DE conversion to closed form in a PSS.
Polymer
Mn
Mw
Mw/Mn
DPa)
Level of DE conversion to
closed form in a PSSb) [%]
P1
10 700
15 500
20 000
20 000
13 000
14 200
17 000
12 200
31 000
148 000
150 000
36 000
18 800
51 000
1.1
2.2
7.5
7.4
2.7
1.3
3.0
10
12
19
16
14
14
16
45
45
42
42
47
42
45
P2
P3
P4
P5c)
P6c)
P7
a)Degree of polymerization; b)The values were estimated by using 1H NMR results of the polymers in CDCl3; c)Previous study.[49]
and cast films. Figure 4 shows the spectral changes of the
CHCl3 solution of P2 in an open state and a PSS. As shown in
Figure 4a, the absorption band at approximately 255 nm gradu-
ally decreased in intensity as the DE moiety changed from the
open form to the closed form upon irradiation by UV light (λ =
254 nm). At the same time, other absorption bands at approxi-
mately 360 and 520 nm increased in intensity, which corre-
spond to the DE closed form. The absorption changes stopped
after 50 s of UV irradiation because P2 reached the PSS. Subse-
quent irradiation by visible light (λ > 400 nm) for 5 min caused
photoisomerization of the DE moiety from the closed form to
the open form, resulting in regeneration of the absorption spec-
trum of P2 in the open state. The inserted images show the
color change of the P2 solution in the open state and PSS. All
of the other polymer solutions also exhibited the same photos-
witching behavior in absorption, as shown in Figure S1 (Sup-
porting Information). It is worthy to emphasize that the DE
moiety in the polymers can photoisomerize by external light
stimuli although all the absorption bands overlap those of the
polymer conjugated main chains (see Figure S7a,b, Supporting
Information). This suggests that the DE moiety receives pho-
tonic energy enough to be photoisomerized even if the conju-
gated backbone coexists.
fluorescence of the other polymer solutions was also quenched
by UV irradiation (see Figure 3 and Figure S2, Supporting
Information). The fluorescence intensity ratios between the
open state and PSS (Iopen/IPSS) of the polymer solutions were
estimated as 50−190 and are summarized in Table 3. Fluores-
cence quenching might occur due to efficient energy transfer
from the excited polymer conjugated backbone to the DE side
chain in the closed form, and the DE side chain subsequently
releases the energy through nonradiative transition from the
excited to ground states.[49–51] The quenched fluorescence was
regenerated by irradiation with visible light (λ > 400 nm),
which photoisomerized the DE closed form to the open form.
As a result, CHCl3 solutions of the polymers exhibited revers-
ible photoswitching behavior in fluorescence between emission
and quenching using external UV and visible light stimuli.
Similar to the CHCl3 solutions, P1−P7 cast films also exhib-
ited reversible spectral changes in absorption and fluorescence
(Figures S3 and S4, Supporting Information). Interestingly,
the polymer cast films showed the distinct photoswitching
behavior in fluorescence with high Iopen/IPSS values of 80−790
(see Table 3). The Iopen/IPSS values of the cast films are larger
than those of the CHCl3 solutions, indicating that the energy
of the excited polymer backbone efficiently transfers to the DE
side chain in a solid state, i.e., in a cast film where the polymer
chains are located close to each other. Figure 3 shows photo-
graphs of the CHCl3 solutions and cast films of P1−P7 in the
open state and the PSS, which visually demonstrates the revers-
ible photoswitching behavior of various colored fluorescence.
Figure 4b shows the fluorescent change of the CHCl3 solu-
tion of P2 via DE photoisomerization. The blue fluorescence
band of P2 in the open state drastically decreased in intensity
upon irradiation by UV light (λ = 254 nm) and was completely
quenched when P2 reached the PSS. The various colored
Table 2. Absorption peaks of CHCl3 solutions, nanosphere solutions, and cast films of P1−P7 in an open state.
Polymer
CHCl3 solutiona)
Nanospheres solution
Δλmax
Cast film
b)
b)
λmax
λmax
λmax
Δλmax
[nm]
[nm]
[nm]
11
1
[nm]
[nm]
11
0
P1
P2
P3
P4
P5
P6
P7
342
358
370
394
414
426
508
353
359
385
402
417
450
531
353
358
389
408
425
461
548
15
8
19
14
11
35
40
3
24
23
a)Polymer concentration: 4.0 × 10−5 M; b)Absorption peak shift from the λmax of the polymer CHCl3 solution.
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Figure 2. a,b) UV−vis absorption and c,d) normalized PL spectra of P1−P7 in an open state. a,c) CHCl3 solutions (c = 4.0 × 10−5 M) and b,d) cast films.
Excitation wavelength: 350 nm for all CHCl3 solutions and P1 and P2 cast films; 380 nm for P3−P7 cast films.
It should be noted that the DE moiety in an open state has
no absorption band in the region of 350−800 nm (see Figure S8,
Supporting Information), and hence no photoisomerization
occurs on the DE moiety upon the irradiation of excitation
light of λ = 350 and 380 nm. On the other hand, the DE moiety
in a PSS has an absorption band covering the wavelength of
Figure 3. Photoswitching behavior between emission and quenching of full-colored fluorescence of P1−P7 CHCl3 solutions (upper), nanosphere solu-
tions (middle), and cast films (lower) by UV and visible light stimuli. Excitation wavelength: λ = 370 nm.
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Table 3. Fluorescence properties of P1−P7 in CHCl3 solution, nanosphere solution, and cast film.
Polymer
CHCl3 solutiona)
Nanosphere solution
Cast film
b)
d)
b)
d)
b)
d)
c)
Emmax
Iopen/IPSS
Emmax
Iopen/IPSS
Emmax
Iopen/IPSS
Φopen
[nm]
[nm]
414e)
420e)
481f)
480f)
539f)
571f)
648f)
[nm]
[%]
62
85
26
24
24
23
5
P1
P2
P3
P4
P5
P6
P7
410e)
422e)
474e)
480e)
492e)
528e)
593e)
120
190
80
140
320
270
235
375
180
30
412e)
419e)
478f)
478f)
536f)
575f)
647f)
490
790
360
290
530
320
80
50
120
90
60
a)Polymer concentration: 4.0 × 10−5 M; b)Fluorescence peak of the polymer in an open state; c)Fluorescence quantum yield in an open state evaluated by using quinine sul-
fate in 1.0 M sulfuric acid as a standard; d)Fluorescence intensity ratio between the open state and PSS; e)Excitation wavelength: 350 nm; f)Excitation wavelength: 380 nm.
300−400 nm. Thus, the DE moiety may partially photoisomerize
from the closed to open form under irradiation of the excitation
light, resulting in changes in the absorption spectra. To avoid
the photoisomerization, the photoluminescence spectra of the
polymers in a PSS were measured in a short time (less than
14 s).
suppressing the full regeneration of the polymer fluorescence.
Because the UV light (λ = 254 nm) used for DE photoisomeri-
zation has relatively high energy and can damage the pho-
tochromic conjugated structure of DE, the unphotochromic
byproduct might be formed. This is also supported by the spec-
tral change in UV−vis absorption of the DE moiety, 2, during
the photoisomerization cycle (Figure S7a,b, Supporting Infor-
mation). In both the open state and PSS, the absorption band at
250 nm decreased in intensity with repeating the photoisomeri-
zation cycle, whereas the absorption band at 300 nm increased
in intensity. This result indicates that the DE moiety gradually
changed into an unphotochromic byproduct. The extinction
coefficient at 518 nm, which corresponds to the DE closed form,
also decreased to 30.2% after 5 cycles of the photoisomeriza-
tion (see Figure S7c, Supporting Information), implying a loss
of the photochromic property. The decrease in fatigue resist-
ance of all the polymers, therefore, is due to the degradation of
the DE moiety. Interestingly, the absorption band of P5 main
chain decreased in intensity and blue-shifted with every pho-
toisomerization cycle, as shown Figure S10e, Supporting Infor-
mation (green arrow). Such a change in absorption denotes
a decrease in the conjugated length of P5 main chain, indi-
cating that the polymer conjugated backbone is photo-oxidized
by irradiating UV light. However, P5 showed relatively better
2.4. Fatigue Resistance in Fluorescence Photoswitching of
Polymers
We investigated the fatigue resistance of all the polymer
films. As shown in Figure S9 (Supporting Information), the
photoswitching behavior was maintained after repeating the
photoisomerization cycle 5 times although the PL intensity
decreased to 2.6%−25.4%. Moreover, Figure S10 (Supporting
Information) shows spectral changes in UV−vis absorption of
the polymer films in an open state. As indicated by the black
arrows, the absorption band at 250 nm, corresponding to the
DE moiety, also decreased in intensity with repeating the pho-
toisomerization cycle. On the other hand, the absorption bands
corresponding to the conjugated main chains were unchanged,
except the case of P5. These results indicate that the DE
moiety partially changed into an unphotochromic byproduct,
Figure 4. Spectral changes in a) UV−vis absorption and b) PL spectra of P2 CHCl3 solution (c = 4.0 × 10−5 M) under UV irradiation (λ = 254 nm). Insets
show the photo images of P2 CHCl3 solution in the open state and PSS. Excitation wavelength: 350 nm.
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polymers form spherical aggregates with an
average particle size of 20−70 nm in diam-
eter. The size distribution was also estimated
using the SEM images, as summarized in
Table 4.
2.7. Photoswitching Behavior in Absorption
and Fluorescence of Polymer Nanospheres
Figure 7 shows the UV−vis absorption and PL
spectra of nanosphere solutions of P1−P7 in
the open state. Similar to both of the CHCl3
solutions and the cast films, the nanosphere
solutions showed absorption and fluores-
cence bands corresponding to the π–π* and
π*–π transitions of the polymer conjugated
backbones. Thus, the peak wavelengths in
both absorption and fluorescence were red-
shifted with the increase in the effective con-
jugated length of the polymer backbone in
the order of P1−P7. Namely, the fluorescence
color gradually changed from blue to red.
The absorption and fluorescence peak wave-
lengths are summarized in Tables 2 and 3.
Interestingly, the absorption peaks in the
nanosphere solutions exhibited intermediate
values between those of the solutions and the
cast films. This result implies that the nano-
sphere solution represents an intermediate
Figure 5. a) Schematic procedure of reprecipitation method. b) Photo images of P1−P7 nano-
sphere solutions in water.
fatigue resistance from the viewpoint of PL intensity, as shown
in Figure S9 (Supporting Information). Thus, in this case, the
photoswitching behavior of the fluorescence is affected by the
degradation of DE moiety rather than the photo-oxidization of
the conjugated main chain.
state between an isolated state and an aggregated state. At the
same time, the fluorescence peak wavelengths were similar to
those in the cast films. It is well known that the fluorescence
of conjugated polymers involve quasi-localized chromophores
in the polymer backbone.[56,57] In addition, the energy in the
excited conjugated backbone transfers intramolecularly and is
finally trapped in low-transition-energy regions, the so-called
“exciton traps.” Thus, the fluorescence spectra tend to reflect
the fluorescent property of the exciton traps rather than that of
the average of the entire conjugated backbone.[58] Hence, these
2.5. Preparation Method for Polymer Nanosphere Solutions
Polymer nanospheres dispersed in water were prepared using
the reprecipitation method with ultrasonication.[55] A schematic
of the procedure is shown in Figure 5a, and the process details are
described as follows. Solutions of the polymers (0.31−0.48 mg,
see Table 4) in THF (1.5 mL) were added dropwise into water
(10 mL) at 0 °C under ultrasonication using an ultrasonic
homogenizer (130 W, 20 kHz). The THF solvent was removed
under reduced pressure at 55 °C to give the polymer nano-
sphere solutions in water. Figure 5b shows photo images
of P1−P7 nanosphere solutions. The polymer nanospheres
remained dispersed in water even if they were held at room
temperature for several months, indicating the high stability of
the nanospheres.
Table 4. Conditions for nanosphere preparation and the particle size of
the nanospheres.
Conditions for nanosphere
preparationa)
Particle size
[nm]
Polymer amount
Average
Distribution
[mg]
0.479
0.464
0.452
0.312
0.398
0.428
0.412
[µmol]
0.47
0.38
0.44
0.25
0.44
0.41
0.39
P1
P2
P3
P4
P5
P6
P7
50
40
45
60
70
20
35
30−80
30−60
30−50
40−75
50−90
15−50
25−50
2.6. Morphology of Polymer Nanospheres
The morphology of the polymer nanospheres was observed
using scanning electron microscopy (SEM). Figure 6 shows
the SEM images of P1−P7 nanospheres, which indicate that all
a)The polymers were dissolved in THF (1.5 mL) and then added dropwise into
water (10 mL) under ultrasonication.
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Figure 6. SEM images of polymer nanospheres. a) P1, b) P2, c) P3, d) P4, e) P5, f) P6, and g) P7.
results indicate that P1−P7 nanospheres have exciton traps sim-
ilar to those of the cast films because the polymers exist in an
aggregated state in both the nanosphere solutions and the cast
films.
as summarized in Table 3, and represent intermediate values
between those of the solutions and the cast films, except for
P7 (see Figure 9). This result also implies that the nanosphere
solution is an intermediate state between an isolated state and
an aggregated state.
The photoinduced spectral changes in both absorption and
fluorescence were also investigated. Figure 8a shows the absorp-
tion change of the P2 nanosphere solution induced by external
light stimuli. The absorption spectra show that the band at
approximately 255 nm decreased in intensity with irradia-
tion by UV light, whereas the bands at approximately 350 nm
and 520 nm increased. This result indicates that the DE side
chains photoisomerize from the open form to the closed form
even in the polymer nanospheres. Subsequent irradiation by
visible light regenerated the original absorption spectrum of
P2 in the open state through reverse photoisomerization of
the DE moiety. Figure 8b shows the fluorescence change of the
polymer nanosphere solution. Similarly to the CHCl3 solutions
and the cast films, the fluorescence of P2 nanospheres were
quenched by UV irradiation and subsequently regenerated
upon irradiation with visible light. The other nanosphere solu-
tions of P1 and P3−P7 also exhibited the same behavior in both
absorption and fluorescence regardless of the fluorescent colors
(see Figure 3, Figures S5 and S6, Supporting Information).
These results successfully demonstrated that the multi-colored
fluorescence of the polymer nanospheres was photoswitchable
between emission and quenching using external light stimuli.
In addition, the Iopen/IPSS values were evaluated as 30−375,
It is worth noting that the red-colored fluorescence of P7
nanosphere solution is unexpectedly weak in intensity, and
therefore, it is difficult to visually observe the fluorescence
photoswitching on a photo image (Figure 3). This is due to
the high π-stacking feature of the PT backbone consisting only
of thienylene rings with a planar structure, which causes a
decrease in the fluorescence intensity in a solid state. In addi-
tion, the energy in the excited PT backbone is easily decayed
due to the polarizable environment of the surrounding water
solvent. The red-colored fluorescence of P7 nanosphere solu-
tion is therefore too weak to be observed.
2.8. Mechanism of Fluorescence Quenching
As shown in Figure S8 (Supporting Information), the absorp-
tion band of the DE moiety 2 in a PSS overlaps the fluorescence
bands of all the polymers although the absorption band of 2 in
an open state does not. This is because the absorption band at
518 nm corresponding to the DE closed form extends over the
visible region. It is therefore anticipated that the fluorescence
of the polymers may be quenched through an energy transfer
Figure 7. a) UV−vis absorption and b) normalized PL spectra of P1−P7 nanosphere solutions in water.
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Figure 8. a) UV−vis absorption and b) PL spectra of polymer nanosphere solutions of P2 in an open state and a PSS.
such as Förster resonance energy transfer (FRET) from the
polymer conjugated backbone to the DE closed form, which
requires the spectral overlap between the luminescence of
donor (polymer conjugated backbone, herein) and the absorp-
tion of acceptor (DE closed form).
open form to the polymer conjugated backbone. Because the
DE open form shows no luminescence, this result implies that
the energy transfer between the polymer conjugated backbone
and the DE moiety may occur through the FRET mechanism,
suggesting the fluorescence quenching process via FRET. How-
ever, it should be emphasized that the distance between the
polymer conjugated backbone and the DE moiety is estimated
to be 4−6 Å by using molecular mechanics calculation. Hence,
Dexter type energy transfer, which can occur at a short distance
within 10 Å via an electron-exchange process, is also regarded
as an alternative mechanism of the energy transfer from the
polymer backbone to the DE closed form. The detail mecha-
nism of the fluorescence quenching still remains unclear and
needs further investigation.
Furthermore, we investigated whether the energy transfer
from the DE open form to the polymer conjugated backbone
occurs or not. As mentioned above, the DE open form is par-
tially degraded through the photoisomerization, which causes a
decrease in intensity of the absorption band at around 250 nm
even in CHCl3 solution (see Figure S11, Supporting Informa-
tion). Thus, if there might be any energy transfer from the DE
open form to the polymer conjugated backbone, the polymer
fluorescence excited by UV light of λ = 250 nm also should
decrease in intensity after the photoisomerization. If not, the
polymer fluorescence intensity should keep unchanged. Hence
we measured excitation spectra of CHCl3 solutions of the poly-
mers in an open state, and then compared the spectra before
and after 1 cycle of the photoisomerization (Figure S12, Sup-
porting Information). The result of the excitation spectra of
P3−P6 showed that the PL intensity was kept unchanged even
after the photoisomerization of the DE moiety (see, black arrows
in Figure S12, Supporting Information). This indicates that the
PL intensity is not affected by the decrease in relative amount
of DE open form, i.e., there is no energy transfer from the DE
3. Conclusion
Full-colored fluorescent conjugated copolymers with photo-
switchable emissions were synthesized by combining phe-
nylene- and thienylene-based main chains with photochromic
DE side chains. The CHCl3 solutions and cast films of the
polymers exhibited various colored fluorescence in visible
wavelengths of 400−700 nm corresponding to their main chain
structures. The fluorescence was reversibly photoswitched
between emission and quenching via DE
photoisomerization using external UV and
visible light stimuli. The reprecipitation
method with ultrasonication enabled the
polymers to form spherical aggregates with
diameters of 20−70 nm in water. After inves-
tigating and comparing the optical proper-
ties, the resulting nanosphere solutions were
estimated to exist in an intermediate state
between an isolated state in solution and an
aggregated state in cast film from the view-
point of the luminescent properties. The flu-
orescence photoswitching behavior was also
observed in the nanosphere solutions, except
for the PT derivative. The current study dem-
onstrated that the visible fluorescence of con-
jugated polymers were reversibly switchable
between emission and quenching using the
photoisomerizing DE side chain regardless
Figure 9. Fluorescence intensity ratios (Iopen/IPSS) in CHCl3 solutions, nanosphere solutions,
and cast films of P1−P7.
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oil was dissolved in MeOH (250 mL), mixed with a solution of KOH
(11.2 g, 200 mmol) in water (40 mL), and then stirred for 12 h at 50 °C.
After removing MeOH under reduced pressure, HCl was added into the
aqueous solution at 0 °C. The crude product was extracted with CHCl3,
washed with a saturated NaCl aqueous solution, and then dried over
anhydrous Na2SO4. The precipitate was removed by filtration and the
filtrate was evaporated under reduced pressure. The residue was purified
by column chromatography (silica gel; CHCl3) to give 1 as light yellow
oil (12.8 g, 88%): 1H NMR (400 MHz, CDCl3, TMS): δ = 0.88 (m, 6H;
(CH2)5CH3 and (CH2)7CH3), 1.27−1.44 (m, 24H; OCH2CH(CH2)5CH3
and OCH2CH(CH2)7CH3), 1.79 (m, 1H; OCH2CH(C6H13)C8H17), 3.90
(d, J = 5.9 Hz, 2H; OCH2CH), 6.93 (d, J = 8.8 Hz, 2H; Ph-H ortho to
OCH2CH(C6H13)C8H17), 8.06 ppm (d, J = 8.8 Hz, 2H; Ph-H meta to
OCH2CH(C6H13)C8H17); 13C NMR (100 MHz, CDCl3, TMS): δ = 14.1,
22.7, 26.82, 26.85, 29.3, 29.6, 29.7, 30.0, 31.32, 31.34, 31.86, 31.93, 37.9,
71.2, 114.3, 121.4, 132.3, 164.0, 172.1 ppm; HRMS (ESI, m/z): [M − H+]
calcd for C23H38O3: 361.2748; Found: 361.2754; Anal. calcd for C23H38O3:
C 76.20, H 10.57; Found: C 76.09, H 10.69. [Route B]: 1 was synthesized
by using the same procedure with our previous study.[49]
1-{5-(2,5-Dibromo-3-thenoyloxymethyl)-2-methyl-3-thienyl}-2-(5-
hydroxymethyl-2-methyl-3-thienyl)-3,3,4,4,5,5-hexafluorocyclopentene (4):
To a mixture of 2 (2.50 g, 5.84 mmol), TPP (1.70 g, 6.48 mmol), and
2,5-dibromo-3-thenoic acid (1.67 g, 5.84 mmol) in THF (100 mL) was
added dropwise a solution of DIAD (3.4 mL, 6.46 mmol) in THF (20 mL)
via a dropping funnel at 0 °C. The reaction mixture was stirred overnight
at room temperature. After removing the solvent under reduced
pressure, the residue was purified by column chromatography (silica gel;
CHCl3) to give 4 as a pale yellow solid (1.88 g, 46%): 1H NMR (400 MHz,
CDCl3, TMS): δ = 1.87 (s, 3H; thienyl-CH3), 1.92 (s, 3H; thienyl-CH3),
4.75 (s, 2H; CH2OH), 5.35 (s, 2H; COOCH2), 6.95 (s, 1H; thienyl-H
in DE), 7.08 (s, 1H; thienyl-H in DE), 7.34 ppm (s, 1H; thienyl-H); 13C
NMR (100 MHz, CDCl3, TMS): δ = 14.46, 14.48, 59.9, 60.9, 111.7, 119.9,
124.3, 124.6, 124.8, 128.4, 131.1, 131.6, 135.5, 142.2, 142.4, 143.6,
160.3 ppm; HRMS (ESI, m/z): [M + Na+] calcd for C22H14Br2F6O3S3:
718.8248; Found: 718.8226; Anal. calcd for C22H14Br2F6O3S3: C 37.95,
H 2.03, Br 22.95, S 13.81; Found: C 37.85, H 2.08, Br 22.88, S 13.67.
1-{5-(2,5-Dibromo-3-thenoyloxymethyl)-2-methyl-3-thienyl}-2-[5-
{4-(2-hexyldecyloxy)benzoyloxymethyl}-2-methyl-3-thienyl]-3,3,4,4,5,5-
hexafluorocyclopentene (M2): A solution of 1 (1.15 g, 3.17 mmol), 4 (1.66
g, 2.38 mmol), DCC (0.641 g, 3.11 mmol), and DMAP (0.324 g, 2.65
mmol) in CH2Cl2 (80 mL) was stirred for 60 h at room temperature. The
precipitate was removed by filtration and the filtrate was evaporated under
reduced pressure. The residue was purified by column chromatography
(silica gel; hexane/ethyl acetate = 19:1) to give M2 as colorless oil
(2.30 g, 93%): 1H NMR (400 MHz, CDCl3, TMS): δ = 0.87 (m, 6H;
(CH2)5CH3 and (CH2)7CH3), 1.27−1.43 (m, 24H; OCH2CH(CH2)5CH3
and OCH2CH(CH2)7CH3), 1.79 (m, 1H; OCH2CH(C6H13)C8H17), 1.87
(s, 3H; thienyl-CH3), 1.88 (s, 3H; thienyl-CH3), 3.88 (d, J = 5.8 Hz, 2H;
OCH2CH), 5.34 (s, 2H; COOCH2), 5.37 (s, 2H; COOCH2), 6.90 (d,
J = 8.8 Hz, 2H; Ph-H ortho to OCH2CH(C6H13)C8H17), 7.09 (s, 2H;
thienyl-H in DE), 7.33 (s, 1H; thienyl-H), 7.97 (d, J = 8.8 Hz, 2H; Ph-H
meta to OCH2CH(C6H13)C8H17); 13C NMR (100 MHz, CDCl3, TMS):
δ = 14.1, 14.4, 22.7, 26.80, 26.82, 29.3, 29.6, 29.7, 30.0, 31.29, 31.31,
31.8, 31.9, 37.9, 60.5, 60.9, 71.2, 111.6, 114.2, 119.9, 121.6, 124.3, 124.5,
127.6, 128.2, 131.1, 131.6, 131.7, 135.6, 136.9, 143.2, 143.7, 160.3, 163.5,
166.0 ppm; HRMS (ESI, m/z) [M + NH4+] calcd for C45H50Br2F6O5S3:
1058.1409; Found: 1058.1389; Anal. calcd for C45H50Br2F6O5S3: C 51.93,
H 4.84, Br 15.35, S 9.24; Found: C 52.08, H 4.79, Br 15.31, S 9.21.
Photoresponsive Poly(para-phenylene) Derivative (P1): To a solution of
M1 (130 mg, 0.13 mmol), 4, 4′-biphenyldiboronic acid bis(neopentyl
glycol) cyclic ester (47.2 mg, 0.13 mmol), and Pd(PPh3)4 (1.5 mg,
1.3 µmol) in THF (2 mL) was added 40% Na2CO3 aqueous solution
(2 mL) and then the mixture was stirred overnight at 60 °C. The
reaction mixture was poured into a large amount of water (300 mL)
and vigorously stirred for 1 h. The resulting precipitate was collected
by filtration, dissolved in minimum amount of THF (3 mL), and
of the fluorescent color and polymer chain aggregation. It is
expected that the polymers synthesized in this work will be
useful for creating photoresponsive optoelectronic devices.
4. Experimental Section
Measurements: NMR spectra were measured with JEOL EX-270,
JEOL AL-400, and JEOL EX-400 spectrometers. Chemical shifts were
represented in parts per million downfield from tetramethylsilane (TMS)
as an internal standard. High-resolution mass spectra (HRMS) were
obtained by using JEOL JMS-SX102A mass spectrometer. Elemental
analyses were performed by Yanako CHN Corders (MT-3, MT-5, and
MT-6), JSL JM-10, Mitsubishi chemical analytech AQF-100, and Dionex
ICS-1500. UV−vis absorption spectra were measured with JASCO V-570
UV/VIS/NIR spectrophotometer, and PL spectra were measured with
JASCO FP-750 spectrofluorometer. All optical measurements were
performed using a quartz cell or a quartz substrate. SEM was performed
with JEOL JSM-7500F. The samples were coated with Pt-Pd alloy by
using JEOL JFC-1600 ion coater before measurements of SEM. GPC was
performed at 40 °C with a system consisting of Agilent Technologies
PLgel 5 µm MIXED-D column, JASCO CO-2065 Plus column oven,
JASCO UV-2070 Plus UV/VIS detector, and JASCO PU-2080 Plus HPLC
pump, where the instrument was calibrated by polystyrene standard.
THF was used as an eluent and the flow rate was 1.0 mL min−1
.
Photoirradiation was carried out at room temperature by using a UV
mercury lamp (λ = 254 nm, 4 W) or a visible lamp (λ > 400 nm, 100 W)
as the light source. The level of DE conversion from the open form
to the closed form, which is defined as {[closed form]/([open form] +
[closed form])} × 100, was confirmed through 1H NMR measurement
in CDCl3. Ratio of the open form and the closed form was determined
by using the integration values of CH2 protons neighboring a thienylene
ring of DE. The relative fluorescence quantum yield (Φ) was evaluated by
using quinine sulfate in 1.0 M sulfuric acid as a standard. Ultrasonication
was carried out using SONICS VCX 130.
Materials: All chemicals were used as purchased. Diisopropyl
azodicarboxylate (40 wt% in toluene, ≈1.9 M; DIAD), DCC, and
DMAP were purchased from Tokyo Chemical Industry Co., Ltd.
Triphenylphosphine (TPP) was purchased from Wako Pure Chemical
Industries,
Ltd.
2,5-Dibromobenzoic
acid,
2-hexyl-1-decanol,
4,4′-biphenyldiboronic acid bis(neopentyl glycol) cyclic ester,
9,9-dihexylfluorene-2,7-diboronic acid bis(1,3-propanediol) cyclic ester,
Pd2(dba)3, (2-furyl)3P and Pd(PPh3)4 were purchased from Aldrich Co.,
Ltd. Methyl 4-hydroxybenzoate, sodium carbonate (Na2CO3), potassium
hydroxide (KOH), THF, dichloromethane (CH2Cl2), CHCl3, and
methanol (MeOH) were purchased from Nacalai Tesque, Inc. THF was
freshly dried and distilled over sodium benzophenone ketyl under Ar.
CH2Cl2 was distilled over CaCl2 under argon atmosphere. MERCK silica
gel 60 (particle size 0.063−0.200 mm) was used to purify compounds
by column chromatography. DE derivative 2 was synthesized according
to previous literature.[59,60] Compounds 1, 3, M1, 2,5-dibromo-3-thenoic
acid, and 5,5′-bis(trimethylstannyl)-2,2′-bithiophene were prepared
according to our previous works.[49,61] 4,4′-Biphenyldiboronic acid
bis(1,3-propanediol) cyclic ester was synthesized by esterification of
4,4′-biphenyldiboronic acid with 1,3-propanediol. 9,9-Dihexylfluorene-
2,7-diboronic acid bis(pinacol) cyclic ester was prepared according
to previous literature.[62] Photoresponsive polymers P5 and P6 were
synthesized and reported in our previous work.[49]
Synthesis and Characterization: All syntheses were carried out under
argon atmosphere. 4-(2-Hexyldecyloxy)benzoic acid (1): [Route A]: To a
mixture of 2-hexyl-1-decanol (9.70 g, 40.0 mmol), TPP (11.5 g, 44.0 mmol),
and methyl p-hydroxybenzoate (6.70 g, 44.0 mmol) in THF (70 mL)
was added dropwise a solution of DIAD (23.2 mL, 44.1 mmol) in THF
(20 mL) via a dropping funnel at 0 °C. The reaction mixture was stirred
overnight at room temperature. After removing THF under reduced
pressure, the residue was purified by column chromatography (silica
gel; CHCl3) to give methyl 4-(2-hexyldecyloxy)benzoate as yellow oil. The
reprecipitated by stirring in methanol (300 mL) for
1 h. After
filtration, the product was dried under vacuum to give white powder
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(115 mg, 89%): 1H NMR (400 MHz, CDCl3, TMS): δ = 0.89 (m, 6H,
(CH2)5CH3 and (CH2)7CH3), 1.18 (m, 24H, OCH2CH(CH2)5CH3 and
OCH2CH(CH2)7CH3), 1.33 (m, 1H, OCH2CH(C6H13)C8H17), 1.71 (s,
3H, thienyl-CH3), 1.76 (s, 3H, thienyl-CH3), 3.78 (d, 2H, J = 5.6 Hz,
OCH2CH), 5.15 (s, 2H, COOCH2), 5.27 (s, 2H, COOCH2), 6.81 (d, 2H,
J = 8.2 Hz, Ph-H ortho to OCH2CH(C6H13)C8H17), 6.92 (s, 1H thienyl-H
in DE), 6.98 (s, 1H, thienyl-H in DE), 7.16−7.77 (m, 10H, Ph-H in main
chain), 7.88 (d, 2H, J = 8.2 Hz, Ph-H meta to OCH2CH(C6H13)C8H17),
8.07 (m, 1H, Ph-H in main chain).
Photoresponsive Poly(fluorene phenylene) Derivative (P2): The same
procedure with P1 was employed by using M1 (172.0 mg, 0.17 mmol),
9,9-dihexylfluorene-2,7-diboronic acid bis(1,3-propanediol) cyclic ester
(83.5 mg, 0.17 mmol), Pd(PPh3)4 (1.96 mg, 1.7 µmol), THF (2 mL), and
40% Na2CO3 aqueous solution (2 mL). The product was obtained as
white powder (184 mg, 92%): 1H NMR (400 MHz, CDCl3, TMS): δ =
0.69 (m, 6H, C((CH2)5CH3)2), 0.80 (m, 6H, (CH2)5CH3 and (CH2)7CH3),
1.02 (m, 16H, C(CH2(CH2)4CH3)2), 1.20 (m, 24H, OCH2CH(CH2)5CH3
and OCH2CH(CH2)7CH3), 1.33 (m, 1H, OCH2CH(C6H13)C8H17), 1.72 (s,
3H, thienyl-CH3), 1.74 (s, 3H, thienyl-CH3), 1.98 (m, 4H, C(CH2C5H11)2),
3.79 (d, 2H, J = 6.0 Hz, OCH2CH), 5.09 (s, 2H, COOCH2), 5.28 (s, 2H,
COOCH2), 6.82 (d, 2H, J = 8.8 Hz, Ph-H ortho to OCH2CH(C6H13)
C8H17), 6.88 (s, 1H thienyl-H in DE), 7.00 (s, 1H, thienyl-H in DE),
7.16−7.79 (m, 8H, Ph-H and fluorene-H in main chain), 7.89 (d, 2H, J
= 8.8 Hz, Ph-H meta to OCH2CH(C6H13)C8H17), 8.05 (m, 1H, Ph-H in
main chain).
4H; COOCH2), 6.78 (br, 2H; thienylene-H in main chain), 6.86 (d, J =
8.8 Hz, 2H; Ph-H ortho to OCH2CH(C6H13)C8H17), 7.11 (br, 2H;
thienyl-H in DE), 7.21 (br, 3H; thienylene-H in main chain), 7.95 (d, J =
8.8 Hz, 2H; Ph-H meta to OCH2CH(C6H13)C8H17).
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgments
The authors thanked Kazuya Tamura for his valuable cooperation in
synthesis and spectroscopic measurements. This work was supported
by Grants-in-Aid for Science Research (A) (Grant No. 25246002) from
the Ministry of Education, Culture, Sports, Science and Technology,
Japan.
Received: January 12, 2015
Revised: February 27, 2015
Published online: March 30, 2015
Photoresponsive Poly(biphenylene thiophene) Derivative (P3): The same
procedure with P1 was employed by using M2 (136 mg, 0.13 mmol),
4,4′-biphenyldiboronic acid bis(1,3-propanediol) cyclic ester (42.0 mg,
0.13 mmol), Pd(PPh3)4 (1.50 mg, 1.30 µmol), THF (20 mL), and 40%
Na2CO3 aqueous solution (12 mL). The product was obtained as yellow
[1] J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R. N. Marks,
K. Mackay, R. H. Friend, P. L. Burns, A. B. Holmes, Nature 1990,
347, 539.
[2] R. H. Friend, R. W. Gymer, A. B. Holmes, J. H. Burroughes,
R. N. Marks, C. Taliani, D. D. C. Bradley, D. A. Dos Santos,
J. L. Bredas, M. Logdlund, W. R. Salaneck, Nature 1999, 397, 121.
[3] C. V. Hoven, A. Garcia, G. C. Bazan, T. Q. Nguyen, Adv. Mater. 2008,
20, 3793.
[4] S. Guenes, H. Neugebauer, N. S. Sariciftci, Chem. Rev. 2007, 107,
1324.
[5] D. T. McQuade, A. E. Pullen, T. M. Swager, Chem. Rev. 2000, 100,
2537.
1
powder (130 mg, 97%): H NMR (400 MHz, CDCl3, TMS): δ = 0.87 (m,
6H, (CH2)5CH3 and (CH2)7CH3), 1.25 (m, 24H, OCH2CH(CH2)5CH3
and OCH2CH(CH2)7CH3), 1.36 (m, 1H, OCH2CH(C6H13)C8H17), 1.83
(s, 3H, thienyl-CH3), 1.86 (s, 3H, thienyl-CH3), 3.85 (d, 2H, J = 5.6 Hz,
OCH2CH), 5.30 (s, 2H, COOCH2), 5.35 (s, 2H, COOCH2), 6.87 (d, 2H, J
= 8.8 Hz, Ph-H ortho to −OCH2CH(C6H13)C8H17), 7.07 (s, 2H thienyl-H
in DE), 7.68 (m, 8H, Ph-H in main chain), 7.79 (s, 1H, thienylene-H in
main chain), 7.96 (d, 2H, J = 8.8 Hz, Ph-H meta to −OCH2CH(C6H13)
C8H17).
[6] S. W. Thomas III, G. D. Joly, T. M. Swager, Chem. Rev. 2007, 107,
1339.
Photoresponsive Poly(fluorene thiophene) Derivative (P4): The same
procedure with P1 was employed by using M2 (117 mg, 0.11 mmol),
9,9-dihexylfluorene-2,7-diboronic acid bis(pinacol) cyclic ester (66.0 mg,
0.11 mmol), Pd(PPh3)4 (1.27 mg, 1.1 µmol), THF (20 mL), and 40%
Na2CO3 aqueous solution (12 mL). The product was obtained as yellow
[7] H. E. A. Huitema, G. H. Gelinck, J. B. P. H. van der Putten,
K. E. Kuijk, C. M. Hart, E. Cantatore, P. T. Herwig, A. J. J. M. van
Breemen, D. M. de Leeuw, Nature 2001, 414, 599.
[8] C. D. Dimitrakopoulos, P. R. L. Malenfant, Adv. Mater. 2002, 14, 99.
[9] A. C. Grimsdale, K. L. Chan, R. E. Martin, P. G. Jokisz, A. B. Holmes,
Chem. Rev. 2009, 109, 897.
[10] K. Akagi, Bull. Chem. Soc. Jpn. 2007, 80, 649.
[11] L. A. P. Kane-Maguire, G. G. Wallace, Chem. Soc. Rev. 2010, 39,
2545.
[12] K. Watanabe, K. Suda, K. Akagi, J. Mater. Chem. C 2013, 1, 2797.
[13] K. Watanabe, K. Akagi, Sci. Technol. Adv. Mater. 2014, 15, 044203.
[14] A. Qin, J. W. Y. Lam, B. Z. Tang, Prog. Polym. Sci. 2012, 37, 182.
[15] R. Hu, J. Luis Maldonado, M. Rodriguez, C. Deng, C. K. W. Jim,
J. W. Y. Lam, M. M. F. Yuen, G. Ramos-Ortiz, B. Z. Tang, J. Mater.
Chem. 2012, 22, 232.
[16] X. Liu, J. Jiao, X. Jiang, J. Li, Y. Cheng, C. Zhu, J. Mater. Chem. C
2013, 1, 4713.
[17] M. Irie, Chem. Rev. 2000, 100, 1685.
[18] K. Matsuda, M. Irie, J. Photochem. Photobiol. C 2004, 5, 169.
[19] H. Tian, S. J. Yang, Chem. Soc. Rev. 2004, 33, 85.
[20] H. Tian, S. Wang, Chem. Commun. 2007, 781.
[21] Z. Zhang, X. Liu, Z. Li, Z. Chen, F. Zhao, F. Zhang, C. Tung, Adv.
Funct. Mater. 2008, 18, 302.
1
powder (122 mg, 89%): H NMR (400 MHz, CDCl3, TMS): δ = 0.77 (m,
6H, C((CH2)5CH3)2), 0.87 (m, 6H, (CH2)5CH3 and (CH2)7CH3), 1.11
(m, 16H, C(CH2(CH2)4CH3)2), 1.26 (m, 24H, OCH2CH(CH2)5CH3 and
OCH2CH(CH2)7CH3), 1.38 (m, 1H, OCH2CH(C6H13)C8H17), 1.85 (s, 3H,
thienyl-CH3), 1.87 (s, 3H, thienyl-CH3), 2.06 (m, 4H, C(CH2C5H11)2),
3.86 (d, 2H, J = 5.2 Hz, OCH2CH), 5.29 (s, 2H, COOCH2), 5.36 (s,
2H, COOCH2), 6.89 (d, 2H, J = 8.4 Hz, Ph-H ortho to OCH2CH(C6H13)
C8H17), 7.07 (s, 1H thienyl-H in DE), 7.10 (s, thienyl-H in DE), 7.45−7.79
(m, 7H, fluorene-H and thienylene-H in main chain), 7.96 (d, 2H, J =
8.4 Hz, Ph-H meta to OCH2CH(C6H13)C8H17).
PhotoresponsivePolythiopheneDerivative(P7):AsolutionofM2(104mg,
0.10 mmol), Pd2(dba)3 (0.92 mg, 1.00 µmol), and (2-furyl)3P (0.93 mg,
4.00 µmol) in THF (2 mL) was stirred at 50 °C for 30 min, followed
by addition of 5,5′-bis(trimethylstannyl)-2,2′-bithiophene (49.2 mg,
0.10 mmol). After stirred at 50 °C for 25 h, the reaction mixture was
poured into a large amount of methanol (100 mL) containing HCl and
then vigorously stirred for 3 h. The resulting precipitate was collected
by filtration, dissolved in minimum amount of THF (3 mL), and
reprecipitated by stirring in methanol (100 mL) for 30 min. After filtration,
the product was dried under vacuum to give dark red powder (90 mg,
86%): 1H NMR (400 MHz, CDCl3, TMS): δ = 0.85 (t, J = 6.6 Hz, 6H;
(CH2)5CH3 and (CH2)7CH3), 1.24−1.42 (m, 24H; OCH2CH(CH2)5CH3
and OCH2CH(CH2)7CH3), 1.74 (m, 1H; OCH2CH(C6H13)C8H17), 1.89
(br, 6H; thienyl-CH3), 3.82 (d, J = 5.2 Hz, 2H; OCH2CH), 5.34 (br,
[22] P. Zacharias, M. C. Gather, A. Koehnen, N. Rehmann, K. Meerholz,
Angew. Chem. Int. Ed. 2009, 48, 4038.
[23] H. K. Bisoyi, Q. Li, Acc. Chem. Res. 2014, 47, 3184.
©
wileyonlinelibrary.com
Adv. Funct. Mater. 2015, 25, 2794–2806
2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
2805

www.afm-journal.de
www.MaterialsViews.com
[24] Y. Li, M. Wang, A. Urbas, Q. Li, J. Mater. Chem. C 2013, 1, 3917.
[25] Y. Li, C. Xue, M. Wang, A. Urbas, Q. Li, Angew. Chem. Int. Ed. 2013,
52, 13703.
[26] K. Rameshbabu, A. Urbas, Q. Li, J. Phys. Chem. B 2011, 115,
3409.
[46] J. Finden, T. K. Kunz, N. R. Branda, M. O. Wolf, Adv. Mater. 2008,
20, 1998.
[47] N. Anwar, T. Willms, B. Grimme, A. J. C. Kuehne, ACS Macro Lett.
2013, 2, 766.
[48] Y. Chan, M. E. Gallina, X. Zhang, I. Wu, Y. Jin, W. Sun, D. T. Chiu,
Anal. Chem. 2012, 84, 9431.
[49] H. Hayasaka, K. Tamura, K. Akagi, Macromolecules 2008, 41,
2341.
[50] H. Hayasaka, T. Miyashita, K. Tamura, K. Akagi, Adv. Funct. Mater.
2010, 20, 1243.
[51] J. Bu, K. Watanabe, H. Hayasaka, K. Akagi, Nat. Commun. 2014, 5,
3799.
[27] K. Rameshbabu, L. Zou, C. Kim, A. Urbas, Q. Li, J. Mater. Chem.
2011, 21, 15673.
[28] T. Fukaminato, M. Irie, Adv. Mater. 2006, 18, 3225.
[29] T. B. Norsten, N. R. Branda, Adv. Mater. 2001, 13, 347.
[30] T. B. Norsten, N. R. Branda, J. Am. Chem. Soc. 2001, 123, 1784.
[31] S. Lim, B. An, S. D. Jung, M. Chung, S. Y. Park, Angew. Chem. Int.
Ed. 2004, 43, 6346.
[32] T. Kawai, T. Sasaki, M. Irie, Chem. Commun. 2001, 711.
[33] G. Y. Jiang, S. Wang, W. F. Yuan, L. Jiang, Y. L. Song, H. Tian,
D. B. Zhu, Chem. Mater. 2006, 18, 235.
[52] B. M. W. Langeveld-Voss, R. A. J. Janssen, M. P. T. Christiaans,
S. C. J. Meskers, H. P. J. M. Dekkers, E. W. Meijer, J. Am. Chem. Soc.
1996, 118, 4908.
[34] L. Giordano, T. M. Jovin, M. Irie, E. A. Jares-Erijman, J. Am. Chem.
Soc. 2002, 124, 7481.
[53] E. Peeters, A. Delmotte, R. A. J. Janssen, E. W. Meijer, Adv. Mater.
1997, 9, 493.
[35] S. Murase, M. Teramoto, H. Furukawa, Y. Miyashita, K. Horie,
Macromolecules 2003, 36, 964.
[54] B. M. W. Langeveld-Voss, R. A. J. Janssen, E. W. Meijer, J. Mol.
Struct. 2000, 521, 285.
[36] M. Berberich, A. Krause, M. Orlandi, F. Scandola, F. Würthner,
Angew. Chem. Int. Ed. 2008, 47, 6616.
[55] N. Kurokawa, H. Yoshikawa, N. Hirota, K. Hyodo, H. Masuhara,
ChemPhysChem 2004, 5, 1609.
[37] S. Yagai, K. Iwai, T. Karatsu, A. Kitamura, Angew. Chem. Int. Ed.
2012, 51, 9679.
[56] S. Mukamel, S. Tretiak, T. Wagersreiter, V. Chernyak, Science 1997,
277, 781.
[38] T. Kawai, T. Kunitake, M. Irie, Chem. Lett. 1999, 28, 905.
[39] C. P. Harvey, J. D. Tovar, Polym. Chem. 2011, 2, 2699.
[40] Q. Luo, H. Cheng, H. Tian, Polym. Chem. 2011, 2, 2435.
[41] T. Kawai, Y. Nakashima, M. Irie, Adv. Mater. 2005, 17, 309.
[42] A. Kaeser, A. P. H. J. Schenning, Adv. Mater. 2010, 22, 2985.
[43] Z. Tian, J. Yu, C. Wu, C. Szymanski, J. McNeill, Nanoscale 2010, 2,
1999.
[44] E. J. Harbron, C. M. Davis, J. K. Campbell, R. M. Allred, M. T. Kovary,
N. J. Economou, J. Phys. Chem. C 2009, 113, 13707.
[45] C. M. Davis, E. S. Childress, E. J. Harbron, J. Phys. Chem. C 2011,
115, 19065.
[57] A. Kohler, D. A. dos Santos, D. Beljonne, Z. Shuai, J. L. Bredas,
A. B. Holmes, A. Kraus, K. Mullen, R. H. Friend, Nature 1998, 392,
903.
[58] J. Yu, D. H. Hu, P. F. Barbara, Science 2000, 289, 1327.
[59] S. L. Gilat, S. H. Kawai, J. M. Lehn, Chem. Eur. J. 1995, 1, 275.
[60] G. Sevez, J. Gan, J. Pan, X. Sallenave, A. Colin, H. Saadoui, A. Saleh,
F. Voegtle, J.-L. Pozzo, J. Phys. Org. Chem. 2007, 20, 888.
[61] K. Watanabe, I. Osaka, S. Yorozuya, K. Akagi, Chem. Mater. 2012,
24, 1011.
[62] S. P. Dudek, M. Pouderoijen, R. Abbel, A. P. H. J. Schenning,
E. W. Meijer, J. Am. Chem. Soc. 2005, 127, 11763.
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