Helically π-stacked conjugated polymers bearing photoresponsive and chiral moieties in side chains: Reversible photoisomerization-enforced switching between emission and quenching of circularly polarized fluorescence

Article abstract of DOI:10.1002/adfm.200902059

Novel multifunctional conjugated polymers, (poly(p-phenylene)s and poly(bithienylene-phenylene)s with (R)· and (S)-configurations], which have fluorescence, chirality, and photoresponsive properties, have been designed and synthesized. The polymers are co

Full text of DOI:10.1002/adfm.200902059

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Helically p-Stacked Conjugated Polymers Bearing
Photoresponsive and Chiral Moieties in Side Chains:
Reversible Photoisomerization-Enforced Switching
Between Emission and Quenching of Circularly
Polarized Fluorescence
By Hiroyuki Hayasaka, Tatsuaki Miyashita, Kazuya Tamura, and
Kazuo Akagi*
luminescence.[9–13] Helically p-stacked con-
jugated polymers bearing photoresponsive
and chiral moieties in side chains might be
candidates to enable photo-switching
between emission and quenching of CPF
through reversible photoisomerization.
Recently, the photochemical control of
linearly polarized fluorescence (LPF) has
been performed by using liquid crystalline
and conjugated copolymers with photore-
sponsive dithienylethene moieties in the
side chain.[12e] When the polymer-based
device of LPF is fabricated, the relative
arrangement between the LPFpolymer film
and the linear polarizer should be rigor-
ously controlled. Namely, the aligned LPF
polymer film must be exactly arranged
Novel multifunctional conjugated polymers, [poly(p-phenylene)s and
poly(bithienylene-phenylene)s with (R)- and (S)-configurations], which have
fluorescence, chirality, and photoresponsive properties, have been designed
and synthesized. The polymers are composed of p-conjugated main chains,
where poly(p-phenylene) and poly(bithienylene-phenylene) are fluorescence
moieties, and the side chains of the photochromic dithienylethene moiety are
linked with chiral alkyl groups. The polymer films exhibit right- or left-handed
circularly polarized fluorescence (CPF) and also show reversible quenching
and emitting behaviors as a result of photochemical isomerization of the
dithienylethene moiety upon irradiation with ultraviolet and visible light. This
is the first report realizing the reversible switching of CPF using chirality and
photoresponsive properties.
parallel or perpendicular to the linear polarizer. Otherwise, the
light passing through the LPF film and the polarizer is
insufficiently polarized, which gives rise to incompletely polarized
light. Nevertheless, this type of fabrication becomes much more
difficult and time consuming when the size of the device becomes
smaller in the micro- or nano-order. One way to avoid such a
difficultyinthedevicefabricationofLPFistodealwithCPF. Thisis
because CPF is free from the macroscopic alignment of the
polymer, andthedegreeofcircularpolarizationofthepolymerfilm
depends on that of one-handed screwing in the helical polymer
and/or that of the helical p-stacking of polymers. Besides, CPF is
easily transformed into LPF by passing the light of CPF through a
1/4 (quarter) wave plate.
1. Introduction
Conjugated polymers are promising materials for use in organic
light-emitting diodes (OLEDs), organic field-effect transistors
(OFETs), photovoltaic cells, and biosensors.[1–5] Chiral conjugated
polymers are expected to show circularly polarized luminescence
when they form helical structures. They can be prepared by the
introduction of a chiral moiety into a side chain.[6–8] However, the
circularly polarized fluorescence (CPF) cannot be controlled in
intensity like a switching between emitting and non-emitting
(quenching) states, which is desirable for dynamic control of
Here, we have designed and synthesized multifunctional
conjugated polymers, [poly(p-terphenylene)s and poly(bithienyl-
ene-phenylene)s with (R)- and (S)-configurations], which have
fluorescence, chiral, and photoresponsive properties. The poly-
mers are composed of p-conjugated main chains where poly(p-
terphenylene) and poly(bithienylene-phenylene) are fluorescence
moieties, and photochromic dithienylethene moieties[9] are linked
with chiral alkyl groups in the side chains.
[*] Prof. K. Akagi, Dr. H. Hayasaka, T. Miyashita
Department of Polymer Chemistry
Kyoto University, Katsura
Kyoto, 615-8510 (Japan)
E-mail: akagi@fps.polym.kyoto-u.ac.jp
K. Tamura
Institute of Materials Science
University of Tsukuba, Tsukuba
Ibaraki 305-8573 (Japan)
Scheme 1 depicts the structures of the polymers composed of a
main chain, where the p-conjugated aromatic unit is a fluorescent
moiety (green frame), and a side chain bears a photochromic
DOI: 10.1002/adfm.200902059
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(dimethylamino)pyridine (DMAP) in CH2Cl2. The copolymeriza-
tion between the monomer (R)-5 and 4,40-biphenyldiboronic acid
bis(propyl glycol)cyclic ester in a mixture of THF and water in the
presence of Pd(PPh3)4 as a catalyst was carried out through a
Suzuki coupling reaction to give (R)-P1.[15] The copolymerization
of (R)-5 and 5,50-bis-trimethylstannyl-2,20-bithiophene in THF in
the presence of Pd2(dba)3 (dba ¼ dibenzylideneacetone) and (2-
furyl)3P as catalysts was carried out through a Stille polycondensa-
tionreactiontogive(R)-P2.[16] Thepolymers(S)-P1and(S)-P2were
obtained by synthetic routes similar to those for (R)-P1 and (R)-P2,
respectively.
Scheme 1. Structures of photoresponsive chiral conjugated polymers.
All polymers synthesized were fusible and soluble in organic
solvents such as THF, toluene, and CHCl3. The number-average
molecular weights (Mn) of (R)-P1 and (S)-P1 were 1.4 ꢀ 104 and
1.1 ꢀ 104, respectively, while those of (R)-P2 and (S)-P2 were
1.0 ꢀ 104 and 8.0 ꢀ 103, respectively. The degree of polymerization
(DP) was calculated to be 9–15, indicating that the polymer main
chain consists of 27ꢁ45 aromatic rings.
dithienylethene moiety (red frame) linked with the chiral moiety
(blue frame).
The present polymer films exhibit right- or left-handed CPF
owing to a helically p-stacked or weakly twisted structure, and also
show reversible quenching and emitting behaviors in CPF as a
result of photochemical isomerization of the dithienylethene
moiety upon irradiation of ultraviolet and visible lights. This is the
first report realizing the reversible switching of CPF emission by
using chiral and photoresponsive properties.
Photoisomerization of the dithienylethene moiety upon
irradiation with UV (l ¼ 254 nm) and visible (l > 400 nm) light
was confirmed by 1H NMR analysis in CDCl3. Two broad signals
observed at 5.30 and 5.34 ppm were assigned to the methylene
protons neighboring the dithienylethene moiety with an open
form. Irradiation of UV light (l ¼ 254 nm, 16 W) caused the
photoisomerization, giving new broad signals at 5.05 and
5.08 ppmthatcorrespondedtothemethyleneprotonsneighboring
the dithienylethene moiety with a closed form. The integrated
intensities of the proton signals indicated that the open forms of
44% and 30% were converted into the closed forms in the
photostationary states (PSS) of P1 and P2, respectively. Here, the
PSS is defined as {[closed form]/([open form] þ [closed
form])} ꢀ 100.[9a,12c,e] Inotherwords, thedithienylethene moieties
of 56% and 70% remained unchanged in the open forms of P1 and
P2, respectively, even upon UV light irradiation. Meanwhile, the
degrees of conversion from the open into the closed form in the
cast films of P1 and P2 were 10% and 9–7%,
2. Results and Discussion
2.1. Synthesis and Characterization of Polymers
Syntheticroutesofmonomer(R)-5andpolymers(R)-P1and(R)-P2
are shown in Scheme 2. Ethyl-4-[(R)-1-methyloctoxy]benzoate [(R)-
2] was synthesized by Mitsunobu coupling of 1 with (S)-2-nonanol
in tetrahydrofuran (THF).[14] The hydrolysis of (R)-2 with NaOHin
a mixed solvent of MeOH and water gave 4-[(R)-1-methyloctox-
y]benzoic acid [(R)-3]. The esterification between the hydroxy
group of the dithienylethene derivative 4[12e] and (R)-3 gave (R)-5 in
the presence of dicyclohexylcarbodiimide ( DCC) and 4-
respectively. Note that the degree of conversion
in the cast film was evaluated in the following
way: The cast film, after irradiation by UV light,
was stripped off from the substrate and then
dissolved in CDCl3 for 1H NMR measurement.
After subsequent irradiation with visible
light, all proton signals of the open form
reappeared. The results of polymerization and
the conversion value are summarized in
Table 1.
Thermal properties of the polymers were
examined through differential scanning calori-
metry (DSC) and polarized optical microscopy
(POM). Broad peaks associated with the phase
transition were observed by DSC. The broad-
ening may be attributed to a high viscosity and
wide polydispersity of the polymer. As sum-
marized in Table 1, the phase transition
Scheme 2. Synthetic routes and photoisomerization. Conditions: a) (S)-2-nonanol, DIAD, PPh3,
THF. b) NaOH, H2O, MeOH. c) DCC, DMAP, CH2Cl2. d) 4,40-Biphenyldiboronic acid bis(neo-
pentylglycol)cyclic ether, Pd(PPh3)4, NaHCO3, THF, H2O. e) 5,50-Bis-trimethylstannyl-2,20-bithio-
temperatures during the heating process of
(R)-P1 (open) and (S)-P1 (open) were 69 and
70 8C, respectively, while those in the cooling
one are 65 and 68 8C, respectively. Similarly, the
phase transition temperatures in the heating
phene,
Pd2(dba)3
(2-furyl)3P,
THF.
DCC ¼ dicyclohexylcarbodiimide,
DMAP ¼ 4-
(dimethylamino)pyridine, DIAD ¼ diisopropyl azodicarboxylate, dba ¼ dibenzilideneacetone,
* ¼ chiral substituent.
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Table 1. Polymerization results, conversion rates from the open to the
closed form in the dithienylethene moiety, and transition temperature of
the polymers.
moiety in the side chain, was observed in both polymer
films.
The polymers, P1 and P2, dissolved in CHCl3, toluene, or THF,
showed no Cotton effect in the region of the pꢁpꢂ transition of the
conjugated main chain in circular dichroism (CD) spectra,
althoughtheygaveimperceptiblesignalsintheshorterwavelength
region such as 253–258 nm, due to overlapped absorption bands
between the dithienylethene moiety and the phenylene one linked
with the chiral alkyl moiety (see Supporting Information Fig. S3
and S4). This result suggests that the main chain of the polymer
does not form an intrachain one-handed helical structure in
solution, even though the polymer has a chiral alkyl moiety in the
side chain. This might be rationalized by the fact that the center of
chirality in the side chain is far from the conjugated main chain,
which makes through-bond and/or through-space intramolecular
interactions difficult. The chirality only effects the phenylene and
dithienylethene moieties in the side chain.
Polymer Mn [a] Mw [b] Mw/Mn DP [c]
Conversion
rate [d]
Transition
temperature [e]
[8C]
in CDCl3 film heating cooling
(R)-P1
(S)-P1
(R)-P2
(S)-P2
14 000 255 000
11 000 104 000
10 000 30 000
18
10
15
12
11
9
44
44
30
30
10
10
9
69
70
52
69
65
68
50
64
3.0
1.8
8 000
14 000
7
[a] Number-average molecular weight evaluated with a polystyrene (PS)
standard. [b] Weight-average molecular weight evaluated with a PS stan-
dard. [c] Degree of polymerization. [d] Conversion rate from the open form
into the closed form under irradiation of UV light. [e] Transition tempera-
ture between glass and meso phases in the open form.
However, the cast films showed CD signals with Cotton effects
in the pꢁpꢂ transition region of the polymer main chain. CD
spectra of P1 and P2 films are shown in Figure 2c and 2f,
respectively. The (R)-P1 film exhibited a split CD band, where the
positive and negative Cotton effects were observed from the longer
to shorter wavelengths. The (S)-P1 film also showed a split CD
band, giving a mirror image to that of the (R)-P1 film. This implies
that the polymers in the film are each assembled to form a one-
handed helical interchain p-stacking structure. It is also under-
standable that the direction of the helical p-stacked structure
depends on theconfiguration of the chiral moietyin theside chain.
According to the bisignate exciton coupling theory,[17] it can be
assumed that the (R)-P1 film has a P-helicity with a right-handed
(clockwise) p-stacked structure. The (S)-P1 film has a M-helicity
with a left-handed (counterclockwise) p-stacked structure. On the
other hand, the (R)-P2 and (S)-P2 films showed CD bands with
mirror images of each other. However, the CD bands gave no
splitting shape and relatively weak signals compared with those of
process of (R)-P2 (open) and (S)-P2 (open) were 52 and 69 8C,
respectively, while those in the cooling one are 50 and 64 8C,
respectively (see also Supporting Information Fig. S1 and S2). The
polymers showed mesophases in both heating and cooling
processes over a wide range of temperatures, which indicates
an enantiotropic nature.
2.2. Absorption and CD Spectra
(R)-P1 (open) and (R)-P2 (open) dissolved in CHCl3 showed
absorption bands at 343 and 429 nm, respectively, which
correspond to pꢁpꢂ transitions of the polymer main chains.
Thebandat250 nmintheopenformofthedithienylethenemoiety
decreased in intensity after irradiation with UV light for 1 min. At
the same time, the bands around 350 and 520 nm, attributable to
the closed form of the dithienylethene moiety,
gradually increased in intensity. Subsequent
irradiation with visible light for 5 min caused
an increase in intensity at 250 nm and a
decrease in intensity around 350 and 520 nm,
as shown in Figure 1a and 1c. The cast films of
(R)-P1 and (R)-P2, prepared from the mixture
of CHCl3 and toluene at room temperature,
showed absorption bands at 360 and 470 nm,
respectively, assignable to pꢁpꢂ transitions of
the conjugated main chain. The results are
shown in Figure 2a and 2d. It is worth noting
that the absorption band attributed to the main
chain of the (R)-P2 showed a large red-shift of
41 nm in the cast film, while that of (R)-P1
showed a red-shift of only 17 nm. This is likely
because the coplanarity of the main chain
increased more in the (R)-P2 cast film than in
the (R)-P1 one. Figure 2b and 2e show
differenceabsorptionspectrabetweentheopen
formandthePSSofthe(R)-P1and(R)-P2films,
Figure 1. a) UV-vis absorption and b) fluorescence spectra of (R)-P1 and those (c and d) of (R)-P2
in CHCl3 (4.0 ꢀ 10ꢁ5 M). The wavelength of excitation for fluorescence was 350 nm. Insets show
photographs of emitting and quenching between the open form and the PSS in solution
respectively. Thereversiblechangebetweenthe
open form and the PSS, which is a result of
the photoisomerization of the dithienylethene (excitation wavelength of 370 nm, 4 W, handheld lamp).
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60 s. However, the quenched fluorescence was
regenerated by irradiation with visible light for
5 min, which leads to a reversible photoswitch-
ing of fluorescence, as shown in Figure 1b and
1d. The ratio of fluorescence intensity between
the open form and the PSS (Iopen/IPSS) was 180
for (R)-P1 and 20 for (R)-P2. The fluorescence
quantum yields of the open form and PSS for
(R)-P1 were 0.65 and 0.005, respectively, and
those for (R)-P2 were 0.23 and 0.01, respec-
tively. The quantum yields of theopen form and
PSS for (S)-P1 and (S)-P2 were very similar to
those of the corresponding polymers with (R)-
configurations (see Table 2). The fluorescence
quantum yield was evaluated by using quinine
sulfate in 1.0 M sulfuric acid as a standard
solution. The quenching of the fluorescence
might be a result of an efficient energy transfer
from the excited polymer main chain to the
closed form of the dithienylethene moiety.
However, the excited dithienylethene of the
closed form changes to its ground state through
a non-radiative transition. A similar quenching
behavior in fluorescence was observed in the
cast film, as shown in Figure 3a and 3c. The
results of fluorescence intensity (Iopen/IPSS) in
Figure 2. UV-vis absorption spectra and difference spectra between the PSS and the open form
of (R)-P1 (a and b) and (R)-P2 (d and e) cast films, respectively, and CD spectra of P1 (c) and P2
(f) cast films upon photoisomerization between the open form and the PSS of the dithienylethene
moiety.
P1films.ThissuggeststhattheP2polymersformlooselyp-stacked
helical structures. The non-straight and rather bent backbone of
P2, which consists of bithiophene-monophenylene repeat units,
might be less suitable for the formation of interchain p-stacking,
and results in a weak CD signal.
Interestingly, there is no difference in CD spectra between the
open form and the PSS, irrespective of P1 and P2 films and also of
the (R)- and (S)-configuration. This indicates that the helical p-
stacked structure of the P1 film and the chiral structure of the P2
film remain unchanged even after the reversible photoisomeriza-
tion between the open form and PSS in the side chain. This may
allowustoexploitthechiropticalpropertiessuchasCPFduringthe
photochemical isomerization, as will be mentioned below.
CHCl3 and cast films of P1 and P2 are summarized in Table 2. The
ratio of fluorescence intensity (Iopen/IPSS) at 413 nm in the (R)-P1
film was 240, and the corresponding value at 570 nm in the (R)-P2
film was 80.
Here it is useful to compare the fluorescence quantum yields of
thecastfilmswiththoseinsolution.AsseeninTable2,theabsolute
fluorescence quantum yields of (R)- and (S)-P1 films were 0.16 and
0.14, respectively; those of (R)- and (S)-P2 films were 0.04 and 0.03,
respectively. It is evident that the quantum yields of P1 films are
about4to6timeslargerthanthoseofP2ones.Therelativestrength
in quantum yield between P1 and P2 films is consistent with the
case of solution where the quantum yield (0.65) of P1 dissolved in
chloroform is about three times larger than that (0.23–0.24) of P2
in chloroform. Note that the fluorescence quantum yields of the
polymer films are substantially smaller in absolute value than
those in solution. This may be a result of concentration quenching
in thefilm, because thefilm iscomposedofneat polymer. Whereas
the polymer in solution is dispersed in chloroform, so is free from
concentration quenching.
2.3. Fluorescence Spectra
The fluorescence band at 410 nm of (R)-P1 (open) and that at
530 nmof(R)-P2(open)inCHCl3 drasticallydecreasedinintensity
and then quenched upon the irradiation with UV light after 50 to
Table 2. Fluorescence quantum yields and CPF intensity ratios between the open and PSS states in CHCl3 (4 ꢀ 10ꢁ5 M) and cast films of P1 and P2.
Polymer
In CHCl3
Film
I
open/IPSS (Em [nm]) [a]
fopen (fPSS) [a][b]
Iopen/IPSS (Em [nm])
fopen
DIopen/DIPSS [d] (Em [nm])
gem [e] (ꢃ 0.005)
(R)-P1
(S)-P1
(R)-P2
(S)-P2
180 (410)
130 (410)
20 (530)
24 (530)
0.65 (0.005)
0.65 (0.005)
0.23 (0.01)
0.24 (0.01)
240 (413) [a]
200 (413) [a]
80 (570) [c]
73 (575) [c]
0.16 [a]
0.14 [a]
0.04 [c]
0.03 [c]
13 (414) [a]
12 (422) [a]
7 (650) [c]
5 (630) [c]
ꢁ1.0 ꢀ 10ꢁ2 [a]
þ1.0 ꢀ 10ꢁ2 [a]
þ1.0 ꢀ 10ꢁ2 [c]
ꢁ1.5 ꢀ 10ꢁ2 [c]
[a] Excitation at 350 nm. [b] Quinine sulfate in 1.0 M sulfuric acid as a standard solution. [c] Excitation at 380 nm. [d] DI: CPF intensity. [e] Dissymmetric
factor defined as the ratio between fluorescence and CPF intensities; gem ¼ (IL ꢁ IR)/[(IL þ IR)/2] ¼ DI/I.
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configuration, upon photoisomerization from
the open form to the PSS. Namely, the
quenching of CPF occurs in the PSS, which
is associated with the quenching of fluores-
cence itself. The reverse photoisomerization
from the PSS to the open form causes a
reappearance of the CPF band. Such a photo-
switching behavior was observed over 10 cycles,
as shown in Figure 4. It should be noted that the
(R)- and (S)-P2 films exhibit CPF spectra with
positive and negative signs, respectively, as
shown in Figure 3d. These signs are opposite to
those of the (R)- and (S)-P1 films, which
suggests that the loosely p-stacked structure
of the P2 film has an opposite helical sense to
that of the P1 film, although the detailed
mechanism remains unclear.[8c,18]
The ratio of CPF intensities (DIopen/DIPSS
)
between the open form and the PSS of the (R)-
P1 film at 414 nm and that of the (R)-P2 film at
650 nm were 13 and 7, respectively, which are
smaller than the corresponding ratios of the
Figure 3. Fluorescence spectra of a) (R)-P1 and c) (R)-P2 and CPF spectra of b) P1 and d) P2 cast
films. The wavelength of excitation light for fluorescence was 350 nm for P1 and 380 nm for P2.
The inset shows photographs of the emitting film of the open form and the quenching film of the
PSS of (R)-P1 and (R)-P2 (excitation wavelength l ¼ 370 nm, 4 W, handheld lamp).
fluorescence intensities (240 and 80 in Iopen
/
IPSS for (R)-P1 and (R)-P2, respectively). The
ratios of the CPF intensities (DIopen/DIPSS) in cast films of P1 and
P2 are also summarized in Table 2. The remaining weak CPF
emission observed in the PSS is a result of a small amount of the
openform,whichisomerizedfromtheclosedformduringtheCPF
measurement. The degree of circular polarization in fluorescence
was evaluated using the dissymmetry factor, gem. This factor is
2.4. CPF Spectra
It is of interest that the polymers show CPF as well as CD in cast
films, although they show neither CPF nor CD in solution, except
the weak CD signal that corresponds to overlapped absorption
bands of the dithienylethene and the phenylene moieties linked
with the chiral alkyl moiety. The formation of helical p-stacking
structures of P1 is supported by the observation of CPF in cast
films, as shown in Figure3b. The open forms (R)- and (S)-P1, show
negative and positive signs in the CPF spectra, respectively. The
sign in the CPF spectra is defined as DI ¼ IL – IR, where IL and IR
represent left- and right-handed fluorescence intensities, respec-
tively. The positive and negative signs in CPF indicate the
formation of the left- and right-handed helical structures,
respectively. It follows that the (R)- and (S)-P1 films have right-
and left-handed screw structures, respectively, which is consistent
with the results of CD spectra. Figure 3b also shows that the CPF
intensity of the P1 film drastically decreases, irrespective of the
defined by the equation; gem ¼ (IL – IR)/[(IL þ IR)/2] ¼ DI/I ¼ VAC
/
V
DC. IR and IL denote the right- and left-handed CPF intensities,
respectively,andVDC andVAC aremeasuredvaluesthatcorrespond
to the fluorescence and CPF intensities. As shown in Figure 5 and
Table 2, the gem values for the P1 and P2 films were estimated to be
in the order of 10ꢁ2 at 414 nm and 650 nm, respectively. Finally, it
should be emphasized that the helical p-stacked structure formed
in the films of the present conjugated polymers is so rigid that it is
not affected by the photochemical opening and closing isomeriza-
tion reaction of the dithienylethene moiety in the solid state. This
allowed us to control the reversible switching of the CPF between
emission and quenching states through photochemical irradia-
tions, by maintaining the chirality of the polymers.
3. Conclusions
Novel photoresponsive chiral p-conjugated polymers have been
synthesized by introducing dithienylethene moieties linked with
chiral alkyl groups into the polymer side chains. It is implied that
the cast films of P1 polymers, which consist of a straight backbone
of terphenylene moieties as repeat units, have helical p-stacked
structures of their main chains. Meanwhile, the cast films of P2,
whichconsistsofabentbackboneofbithienylene-monophenylene
moieties as repeat units, are suggested to have a weakly p-stacked
structure. The cast films of the two kinds of conjugated polymers
exhibited right- or left-handed CPF with relatively large dis-
symmetry factors in the order of 10ꢁ2. The emission and
quenching of CPF of the cast films are reversibly switched
Figure 4. Reversible changes of CPF intensities of (R)-P1 and (S)-P1 at
414 nm in a cast film upon alternating irradiations of UV (light blue area)
and visible (yellow area) light.
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carried out using a UV (l ¼ 254 nm, 4 W) or visible (l > 400, 100 W)
mercury lamp as a light source at room temperature.
Samples for UV-vis, CD, PL, and CPF measurements were prepared by
casting the polymer dissolved in a mixture of CHCl3 and toluene on a
quartz substrate. The thickness of the polymer film was in the range of 1.0–
1.2 mm.
Materials: Compound 4 and bis-trimethylstannyl-2,20-bithiophene were
prepared by procedures described in the literature.[12e] 4-Hydroxybenzoic
acid ethyl ester, diisopropylazodicarboxylate (DIAD, 40 wt % in toluene,
ꢄ1.9 M), dicyclohexylcarbodiimide (DCC), and 4-(dimethylamino)pyridine
(DMAP) were purchased from Tokyo Kasei (TCI). Triphenylphosphine
(PPh3), and (R)- and (S)-2-nonanol were purchased from Wako Pure
Chemical Industries. 4,40-Biphenyldiboronic acid bis(neopentylglycol)
cyclic ether, tris(dibenzylideneacetone)dipalladium(0) [Pd2(dba)3], tri-2-
furylphosphine [(2-furyl)3P], and tetrakis(triphenylphosphine)palladium(0)
[Pd(PPh3)4] were purchased from Aldrich Co. Ltd THF was dried and
distilled over sodium benzophenone ketyl under Ar. CH2Cl2 was distilled
over CaCl2 under argon atmosphere. MERCK Silicagel 60 (particle size
0.063–0.200mm) was used for column chromatography.
Ethyl-4-[(R)-1-methyloctoxy]benzoate [(R)-2]: A solution of DIAD
(4.0 mL, 7.69 mmol) in THF (5.0 mL) was added to a mixture of 4-
hydroxybenzoic acid ethyl ester 1 (1.02 g, 6.17 mmol), triphenylphosphine
(1.80 g, 6.96 mmol), and (S)-2-nonanol (1.00 g, 6.94 mmol) in THF
(20 mL). The reaction mixture was stirred at 0 8C for 1 h under Ar
atmosphere. The resulting precipitate was extracted with CHCl3,
thoroughly washed with saturated NaCl solution, and dried over anhydrous
sodium sulfate. The precipitate was removed by filtration, and the filtrate
was evaporated under reduced pressure. The residue was purified by
column chromatography (silica gel, CH2Cl2) to give 1.94 g (99%) of (R)-2 as
a yellow oil. HRMS (EI, m/z):[M]þ calcd. for C18H28O3: 292.2038; found,
1
292.2034. H NMR (400 MHz, CDCl3, d): 0.88 (t, 3H, J ¼ 6.8 Hz, ꢁCH3),
1.27–1.34 (m, 15H, ꢁOCHCH3 and ꢁOCH(CH2)6CH3), 1.37 (t, 3H,
J ¼ 7.2 Hz, ꢁCOOCH2CH3), 4.33 (q, 2H, J ¼ 7.2 Hz, ꢁCOOCH2CH3), 4.43
(sext, 1H, J ¼ 6.8 Hz, ꢁOCH(CH3)C7H15), 6.87 (d, 2H, J ¼ 8.8 Hz, ortho to
ꢁOCH(CH3)C7H15), 7.96 (d, 2H, J ¼ 8.8 Hz, meta to ꢁOCH(CH3)C7H15).
13C NMR (400 MHz, CDCl3, d): 14.0, 14.1, 19.6, 22.6, 25.4, 29.2, 29.5, 31.8,
36.3, 60.2 (sp3, ꢁOCH2CH3), 74.0 (sp3, ꢁOCH(CH3)C7H15), 114.9 (sp2,
phenylene), 120.5 (sp2, phenylene linked to carbonyl moiety), 131.7 (sp2,
phenylene), 162.3 (sp2, phenylene carbon linked to ether type oxygen),
165.7 (sp2, ꢁCOOC2H5).
Figure 5. Dissymmetry factors (gem) of a) P1 and b) P2 films in open form
and the PSS.
through the photoisomerization of the dithienylethene moiety
introduced in the side chain. The present polymerscould be useful
for advanced chiroptical materials with photochemically switch-
able CPF properties.
4-[(R)-1-Methyloctoxy]benzoic acid [(R)-3]: Compound (R)-2 (1.94 g,
6.65 mmol) was hydrolyzed by NaOH (3.10 g, 77.5 mmol) in 10 mL of
water and 120 mL of MeOH at 60 8C for 4 h. The solvent was then
evaporated, and the product was dissolved in water. The mixture was
acidified to pH 1 with hydrochloric acid solution. The resulting precipitate
was extracted with CHCl3, thoroughly washed with saturated NaCl solution,
and dried over anhydrous sodium sulfate. The precipitate was removed by
filtration, and the filtrate was evaporated under reduced pressure to
yield 1.65 g (94%) of a colorless oil. HRMS (EI, m/z): [M]þ calcd. for
C16H24O3: 246.1725; found, 246.1725. 1H NMR (400 MHz, CDCl3, d): 0.88
(t, 3H, J ¼ 6.4 Hz, ꢁCH3), 1.28–1.75 (m, 15H, ꢁOCHCH3 and
ꢁOCH(CH2)6CH3), 4.45 (sext, 1H, J ¼ 6.4 Hz, ꢁOCH(CH3)C7H15), 6.90
(d, 2H, J ¼ 8.7 Hz, ortho to ꢁOCH(CH3)C7H15), 8.04 (d, 2H, J ¼ 8.7 Hz,
meta to ꢁOCH(CH3)C7H15). 13C NMR (400 MHz, CDCl3, d): 14.1, 19.6,
22.6, 25.4, 29.2, 29.5, 31.8, 36.3, 74.0 (sp3, ꢁOCH(CH3)C7H15), 114.9 (sp2,
phenylene), 120.9 (sp2, phenylene linked to carbonyl moiety), 132.9 (sp2,
phenylene), 162.7 (sp2, phenylene carbon linked to ether type oxygen),
171.4 (sp2, ꢁCOOH).
4. Experimental
Measurements: 1H and 13C NMR spectra were measured in CDCl3 using
a JEOL AL-400 spectrometer. Chemical shifts were represented in parts per
million downfield from tetramethylsilane (TMS) as an internal standard.
Mass spectrometry was performed with a JEOL JMS-SX102A spectrometer.
The molecular weights of polymers were determined by gel permeation
chromatography (GPC) using a Shodex A-80M column and a JASCO HPLC
870-UV detector with THF used as solvent during measurements. The
instrument was calibrated with a polystyrene standard. Phase transition
temperatures were determined using a TA Instrument Q-100 differential
scanning calorimeter with a constant heating/cooling rate of 10 8C minꢁ1
,
and texture observations were carried out under crossed nicols by using a
Zeiss AxioImager M1m polarizing microscope equipped with a Zeiss
AxioCam MRc5 digital camera and a Linkam TH-600PM heating and
cooling stage with temperature control.
1-{5-(2,5-Dibromobenzoyloxymethylene)-2-methylthien-3(-yl}-2-[5-{4-
((R)-1-methyloctoxy)benzoyloxymethylene)}-2-methylthien-3-yl]-3,3,4,4,5,5-
hexafluorocyclopentene [(R)-5]: A solution of compound
4 (0.68 g,
Optical absorption (UV-vis) spectra were measured using a JASCO V-
570 spectrometer. CD spectra were measured with JASCO J-820 spectro-
meter. Fluorescence spectra were measured using a JASCO FP-750
spectrometer. Fluorescence quantum yields were measured using a JASCO
FP-6500 spectrometer equipped with an ILF-533 integrating sphere. CPF
measurements were performed with a JASCO CPL 200S spectrometer with
a quartz cell or substrate at room temperature. Photo-irradiation was
0.98 mmol), (R)-3 (0.24 mg, 0.89 mmol), DCC (0.22 mg, 1.0 mmol), and
DMAP (0.13 mg, 1.1 mmol) in CH2Cl2 (20 mL) was stirred for 14 h at room
temperature. The crude product was extracted with CHCl3. The organic
layer was washed with saturated NaCl solution and dried over anhydrous
sodium sulfate. The precipitate was removed by filtration, and the filtrate
was evaporated under reduced pressure. The residue was purified with
column chromatography (silica gel; CHCl3) to give 450 mg (54%) of (R)-5
Adv. Funct. Mater. 2010, 20, 1243–1250
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www.afm-journal.de
www.MaterialsViews.com
as a yellow oil. HRMS (EI, m/z): [M]þ calcd. for C40H16O5Br2F6O2:
934.0432; found, 934.0478. 1H NMR (400 MHz, CDCl3, d): 0.87 (t, 3H,
Technology, Japan. Supporting Information is available online from Wiley
InterScience or from the author.
J ¼ 6.5 Hz,
ꢁCH3),
1.27–1.73
(m,
15H,
ꢁOCHCH3
and
Received: November 3, 2009
Revised: December 13, 2009
Published online: March 15, 2010
ꢁOCH(CH2)6CH3), 1.89 (s, 6H, thienyl-CH3), 4.43 (sext, 1H, J ¼ 6.5 Hz,
ꢁOCH(CH3)C7H15), 5.36 (s, 2H, ꢁCOOCH2ꢁ), 5.40 (s, 2H,
ꢁCOOCH2ꢁ), 6.86 (d, 2H, J ¼ 8.9 Hz, ortho to ꢁOCH(CH3)C7H15),
7.08 (s, 1H, thienyl-H), 7.13 (s, 1H, thienyl-H), 7.45 (d, 1H, J ¼ 8.6 Hz,
phenyl-H), 7.51 (d, 1H, J ¼ 8.6 Hz, phenyl-H), 7.88 (s, 1H, phenyl-H), 7.96
(d, 2H, J ¼ 8.9 Hz, meta toꢁOCH(CH3)C7H15). 13C NMR (400 MHz,
CDCl3, d): 14.1, 14.4 (2 ꢀ sp3 signals, thienyl-CH3), 22.6, 25.4, 29.2, 29.5,
31.7, 36.3, 60.4 (sp3, ꢁOCH2ꢁ), 61.4 (sp3, ꢁOCH2ꢁ), 75.0 (sp3,
ꢁOCH(CH3)C7H15), 115.0, 120.4, 120.9, 121.3 (sp2, phenylene linked to
carbonyl moiety), 124.4, 124.4.,127.3, 128.5, 131.7, 132.9 (sp2, phenylene
linked to carbonyl moiety), 134.1, 135.1, 135.6, 135.7, 136.7, 143.1,
143.7 162.3 (sp2, phenylene carbon linked to ether type oxygen), 164.2 (sp2,
ꢁOCOꢁ), 165.7 (sp2, ꢁOCOꢁ).
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13C NMR (400 MHz,
CDCl3, d): 14.0, 14.3, 19.5, 22.6, 25.4, 29.2, 29.5, 31.7, 36.2, 60.4 (2 ꢀ sp3
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Fig. S5 in the Supporting Information).
(R)-P2: A solution of Pd2(DBA)3 (3.5 mg, 3.4 mmol) and (2-furyl)3P
(3.5 mg, 13.5 mmol) in 1 mL of THF was stirred under Ar at 50 8C for
15 min. 5,50-bis-trimethylstannyl-2,20-bithiophene (191 mg, 0.34 mmol)
and (R)-5 (316 mg, 0.34 mmol) were then added to the mixture. After
stirring at 50 8C for 3 days, the reaction mixture was poured into a large
amount of methanol (400 mL) that contained 12 N HCl (3 mL) and
vigorously stirred for 15 min. The resulting precipitate was collected by
filtration and dissolved in a minimum amount of THF (3 mL) and stirred in
methanol (300 mL) for 24 h. After filtration, the product was dried under
1
vacuum to give 318 mg (99%) of an orange powder. H NMR (400 MHz,
CDCl3, d): 0.83 (br, 3H, ꢁCH3), 1.21–1.28 (m, 15 H, ꢁOCHCH3 and
ꢁOCH(CH2)6CH3), 1.79 (br, 3H, thienyl-CH3), 1.83 (br, 3H, thienyl-CH3),
4.39 (br, 1H, ꢁOCH(CH3)C7H15), 5.28 (br, 2H, ꢁCOOCH2ꢁ), 5.32 (br, 2H,
ꢁCOOCH2ꢁ), 6.83 (d, 2H, J ¼ 8.8 Hz, ortho to ꢁOCH(CH3)C7H15), 6.98
(br, 2H, thienyl-H in dithienylethene), 7.13–7.96 ppm (m, 7H, phenyl-H and
thienyl-H in main chain), 7.92 (d, 2H, J ¼ 8.8 Hz, meta
toꢁOCH(CH3)C7H15). 13C NMR (400 MHz, CDCl3, d): 14.1, 19.5, 22.6,
25.4, 29.2, 29.5, 31.7, 36.2, 60.4 (sp3, ꢁOCH2ꢁ), 61.2 (sp3, ꢁOCH2ꢁ),
74.0 (sp3, ꢁOCH(CH3)C7H15), 114.9 (sp2, phenylene in side chain), 121.3
(sp2, phenylene linked to carbonyl moiety), 124.2, 124.7, 127.3, 128.0,
131.6 (sp2, phenylene in side chain), 136.7, 143.0, 143.5, 162.3 (sp2,
phenylene carbon linked to ether type oxygen), 165.7 (sp2, ꢁOCOꢁ), 167.7
(sp2, ꢁOCOꢁ) (see Fig. S6 in the Supporting Information).
Similar chemical properties were obtained for the enantiomeric
compounds (S)-2, (S)-3, (S)-5, (S)-P1, and (S)-P2.
Acknowledgements
This work was supported by a Grant-in-Aid for Science Research (S) (No.
202250007) and that in a Priority Area ‘Super-Hierarchical Structures’ (No.
446) from the Ministry of Education, Culture, Sports, Science and
Adv. Funct. Mater. 2010, 20, 1243–1250
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