Synthesis and properties of folded π-stacking polymers having J-aggregative, alternative, and staggered assembling structures

Article abstract of DOI:10.1016/j.polymer.2016.05.075

Three types of folded polymers showing alternative stacking of two different π-units (A-3), J-aggregate (J-3), and staggered stacking (S-3) structures of π-modules were designed and synthesized using 2-substituted 1,3-diaryl tethering units. The UV-absorbing and fluorescent emission properties of these polymers were investigated and compared to those of the corresponding single structural π-molecule component and H-type stacking polymer (H-3). These three types of polymers exhibited unique optical properties as a result of a distinctive arrangement of π-units.

Full text of DOI:10.1016/j.polymer.2016.05.075

Polymer 97 (2016) 550e558
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Polymer
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Synthesis and properties of folded
p-stacking polymers having
J-aggregative, alternative, and staggered assembling structures
,
Sentaro Okamoto a *, Masaru Kudo a, Ryosuke Nomura a, Ryota Moriai a, Yusuke Naito a,
Shigeaki Funyu b, Ken-ich Ishitsuka b, Naoki Asano b
a Department of Materials and Life Chemistry, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama, 221-868, Japan
b Tsukuba Research Laboratory, Hitachi Chemical Co., Ltd, 48 Wadai, Tsukuba-shi, Ibaraki, 300-4247, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Three types of folded polymers showing alternative stacking of two different
p-units (A-3), J-aggregate
Received 30 March 2016
Received in revised form
24 May 2016
Accepted 31 May 2016
Available online 31 May 2016
(J-3), and staggered stacking (S-3) structures of
substituted 1,3-diaryl tethering units. The UV-absorbing and fluorescent emission properties of these
polymers were investigated and compared to those of the corresponding single structural -molecule
component and H-type stacking polymer (H-3). These three types of polymers exhibited unique optical
properties as a result of a distinctive arrangement of -units.
p-modules were designed and synthesized using 2-
p
p
© 2016 Elsevier Ltd. All rights reserved.
Keywords:
Folded polymers
p-Stacking
J-stacking
1. Introduction
This stacking of
p-units (form V), similar to that found unique to H-
type aggregates of
p-molecules, provides the polymers with a large
Polymeric molecules, particularly those showing ordered as-
sembly of p-moieties, are of interest as optical and/or electronically
ultra violet (UV) absorption hypochromic shift that is unique to H-
aggregation materials [15e20]. V polymers (H-3) were synthesized
active polymers because of their low processing costs and desirable
mechanical properties. Thus, the two-dimensional orientation of
from p-units (2) and tethering units (1) by Suzuki-Miyaura
coupling polymerization (Equation (3) in Scheme 1).
p
ꢀmolecules (e.g., J- and H-aggregations) provides these materials
Herein, in addition to folded H-stacking polymers, we designed
with arrange of photophysical, electronic, and photoelectronic
novel folded
p
-stacking polymers with J-type
p
-stacking, alterna-
properties [1e8].
tive stacking of two different
structures (Scheme 2).
p
-units, and staggered -stacking
p
We recently developed folded
of 2-substituted 1,3-diarylpropane structures and subsequently
studied their properties [9e11]. 2-Substituted 1,3-
diphenylpropanes predominantly exist in conformation III for
bulky Z substituents (Equation (1) in Scheme 1), as suggested by
MM2 calculations of I, II, and III simplified conformers. These were
confirmed by 1H NMR analyses (i.e., chemical shift of aromatic
protons by shielding effect) [12,13] and fluorescence (i.e., pre-
dominant emission of benzene excimer) measurements [14]. Based
on these results, we synthesized polymers composed of 2-
p-stacking polymers composed
Folded polymers with H-type stacking of
synthesized by A2þB2 type polymerization of turn-up tethering
unit 1 and -units 2, as previously reported by our group. Once
units are selectively connected to two tethering units to yield 4,
polymerization of monomer 4 with different -units 2′ may pro-
duce alternative stacking polymers (A-3). -Unit 6, bearing two
spacer units added to 2, may react with monomer 4 to afford J-type
stacking polymers (J-3). Polymerization of monomer 5, bearing a
p-units (H-3) can be
p
p-
p
p
p
-
unit and a spacer at one end of 1, will result in staggered stacking
polymers (S-3).
substituted 1,3-phenylpropane and
p-modules. We found that
these polymers spontaneously fold to the
p-stacking V conformer;
this configuration being favored over the linear stretched form IV
both in solution and film state (Equation (2) in Scheme 1) [9,10].
2. Experimental
2.1. General
* Corresponding author.
E-mail address: okamos10@kanagawa-u.ac.jp (S. Okamoto).
NMR spectra were recorded in CDCl3 at 600 and 500 MHz for 1H
http://dx.doi.org/10.1016/j.polymer.2016.05.075
0032-3861/© 2016 Elsevier Ltd. All rights reserved.

S. Okamoto et al. / Polymer 97 (2016) 550e558
551
Scheme 1. Basis of folded H-stacking polymers.
Scheme 2. Synthetic approach for H-, J-, alternative, and staggered stacking polymers.

552
S. Okamoto et al. / Polymer 97 (2016) 550e558
Scheme 3. Preparation of monomers 4 and 5.
and 150 and 125 MHz for 13C, respectively, on JEOL JMN-ECA600
and 500 spectrometers. Chemical shifts are reported in part per
measured on JEOL Accu TOF T-100 equipped with ESI ionization.
The UV-Vis absorption spectra were recorded with a UV-2450
SHIMADZU spectrophotometer. Fluorescence emission spectra
(FL) and excitation spectra were recorded with a RF-5300PC SHI-
MADZU spectrophotometer. All reactions sensitive to oxygen and/
or moisture were performed under an argon atmosphere. Dry sol-
vents (THF, DMF, CH2Cl2) were purchased from Kanto Chemical Co.,
Inc., and used as received without any additional purification and
degassing procedure.
Polymers H-3A, H-3B, and H-3C were synthesized according to
the similar procedure to that for synthesis of A-3. Polymer H-3D
was prepared by a similar protocol for synthesizing J-3. For syn-
thetic procedures for monomers 4 and 5, see Supplementary
million (ppm,
d
) relative to Me4Si (
d
0.00) or residual CHCl3 (
d 7.26
for 1H NMR), or a center peak of CDCl3
(d
77.0 for 13C NMR). IR
spectra were recorded on an FT/IR 4100 (JASCO) and are reported in
wave numbers (cmꢀ1). The Mn and Mw of polymers were measured
with a TOSOH HLC-8020 gel-permeation chromatography (GPC)
unit (eluent: THF; calibration: polystyrene standards) using two
TSK-gel columns (2 Multipore HXL-M). MALDI-TOF (matrix-assisted
laser desorption ionization time-of-flight) mass spectra were
recorded by a Shimadzu Biotech Axima CFR plus curved field
reflection (CFR) in the reflection ion mode by use of a laser
(l
¼
337 nm). High-resolution mass spectra (HR-MS) were

S. Okamoto et al. / Polymer 97 (2016) 550e558
553
Scheme 4. Synthesis of polymers A-, J-, and S-3.
Materials. Model compounds OBu-BStB and F-BStB were prepared
by the similar procedure to the reported synthesis of BStB [9].
(n-Bu)4NBr (161 mg, 0.500 mmol), 2b (227 mg, 0.500 mmol), 2 M
aqueous K2CO3 (1.00 mL), and THF (1.67 mL) was added a solution
of Pd(PPh3)4 (23.1 mg, 0.020 mmol) in THF (1.67 mL) at room
temperature. After the mixture was stirred for 3 days at 80 ꢁC,
saturated aqueous NaHCO3 (3 mL) was added and the mixture was
extracted with CH2Cl2. The combined organic layers were washed
2.2. Polymer A-3
Under Ar atmosphere, to a mixture of 4b (582 mg, 0.500 mmol),

554
S. Okamoto et al. / Polymer 97 (2016) 550e558
Scheme 5. Synthesis of H-stacking polymer H-3.
with H2O, dried over Na2SO4, and filtered. Residue obtained by
concentration of the filtrate was dissolved in CH2Cl2 and the solu-
tion was poured into MeOH. The obtained polymer precipitate was
collected by filtration, washed with Et2O and dried under reduced
pressure. Polymer A-3 (313 mg) was obtained in 52% yield as a
days at 120 ꢁC. The reaction was quenched by addition of saturated
aqueous NaHCO3 and the aqueous layer was extracted with CH2Cl2.
The combined organic layers were washed with H2O, dried over
Na2SO4. After filtration and evaporation, the residues was dissolved
in CH2Cl2 and poured into MeOH. The obtained polymer precipitate
was washed Et2O several times and dried under reduced pressure.
Polymer J-3 (164 mg) was obtained in 22% yield as a yellow solid:
yellow solid: 1H NMR (600 MHz, CDCl3)
d 7.45e6.77 (br m, overlap
with CHCl3 peak, 26H, Ar and CH]CH), 4.10e3.82 (br, 4H,
OCH2CH2CH2CH3), 3.02e2.85 (br, 4H, CH2Ar), 2.52e2.31 (br, 4H,
CH2Ar), 2.16e2.01 (br, 2H, CHCH2Ar), 1.89e1.72 (br, 4H,
OCH2CH2CH2CH3), 1.60e1.48 (br, 4H, OCH2CH2CH2CH3), 1.27e1.13
(br, 12H, (CH3)2C), 1.04e0.80 (br m, 24H, (CH3CH2)3Si and
OCH2CH2CH2CH3), 0.66e0.47 (br, 12H, (CH3CH2)3Si). IR (film) 2954,
1H NMR (600 MHz, CDCl3)
d 7.57e6.57 (br m, overlap with CHCl3
peak, 36H, Ar and CH]CH), 4.11e3.84 (br, 12H, ArCH2OAr and
OC4H9), 3.02e2.77 (br, 4H, CH2Ar), 2.48e2.24 (br, 4H, CH2Ar),
2.10e1.97 (br, 2H,CHCH2Ar), 1.91e1.65 (br, 8H, OC4H9), 1.65e1.38
(br, 8H, OC4H9), 1.65e1.11 (br, 12H, (CH3)2C), 1.11e0.72 (br m, 30H,
(CH3CH2)3Si and OC4H9), 0.72e0.49 (br, 12H, (CH3CH2)3Si). IR (film)
3421, 2954, 2871, 1668, 1510, 1417, 1200, 1012, 963.3, 802.2,
720.3 cmꢀ1. Mn ¼ 1.36 ꢂ 104, Mw ¼ 6.50 ꢂ 104, Mw/Mn ¼ 4.77 based
on GPC analysis.
2933, 2873, 1606, 1482, 1417, 1203, 1011, 965.2, 721.2 cmꢀ1
.
Mn ¼ 1.05 ꢂ 104, Mw ¼ 2.83 ꢂ 104, Mw/Mn ¼ 2.70 based on GPC
analysis.
2.3. Polymer J-3
2.4. Polymer S-3
The mixture of 4a (520 mg, 0.500 mmol), 6a (306 mg,
0.500 mmol) and NMP (5.00 mL) were added K2CO3 (276 mg,
2.00 mmol) at room temperature. The mixture was stirred for 3
To a mixture of 5a (109.6 mg, 0.133 mmol) and NMP (0.90 mL)
was added K2CO3 (73.4 mg, 0.532 mmol), and the mixture was

S. Okamoto et al. / Polymer 97 (2016) 550e558
555
Fig. 1. (a) UV-Vis Absorption (UV) and Fluorescence (FL) Spectra of OBu-BStB, F-BStB, A-3, H-3A (x 10), and He3B in CH2Cl2 (10ꢀ6 M). FL: Excited at 337 nm for OBu-BStB, 355 nm
for F-BStB, 336 nm for A-3, 341 nm for H-3A (measured using a 10ꢀ7 M solution and spectra are indicated using tenfold intensity), and 343 nm for He3B. (b) Fluorescence (FL) and
excitation (EX) spectra of A-3 (film), H-3A (film), He3B (film), F-BStB (10ꢀ7 M in CH2Cl2), and OBu-BStB (10ꢀ7 M in CH2Cl2). FL (normalized): excited at 340 nm for A-3, 390 nm for H-
3A, 443 nm for He3B, 355 nm for F-BStB, and 388 nm for OBu-BStB. EX (normalized): monitored at 530 nm for A-3, 443 nm for H-3A, and 420 nm for He3B.
stirred at 120 ꢁC for 3 days. The reaction was quenched by addition
of saturated aqueous NaHCO3 and the aqueous layer was extracted
with CHCl3. The combined organic layers were dried over Na2SO4.
After filtration and evaporation, the residues was dissolved in CHCl3
and poured into a large amount of MeOH. The obtained polymer
was washed with hexane several times and dried under reduced
pressure to give polymer S-3 (43 mg) in 44% yield as a brown solid:
3. Results and discussion
3.1. Synthesis
3.1.1. Synthesis of monomers
As required by the synthetic approach herein designed, mono-
mers 4 and 5 were prepared following the procedure shown in
Scheme 3. Triethyl methanetricarboxylate was alkylated with p-
BrC6H4CH2Br followed by mono-decarboxylation to afford 7 that
was further alkylated with benzyl bromide derivatives 8a or 8b and
subsequently decarboxylated to afford 1,3-diarylpropanes 9a and
9b, respectively. 9a (Y ¼ OCH2CH]CH2) was reacted with MeMgI
and subsequenly silylated with Et3SiCl. Deallylation of the resulting
silyl ether gave phenol derivative 9a’ (26% yield from 7). Suzuki-
Miyaura coupling of 9a’ and diboronate 2a furnished monomer
4a (30% yield). Similarly, iodobromo compound 9b was coupled
with 2a to provide dibromo compound 9’ (24% yield) after reaction
with excess MeMgI. Diol 9b’ was silylated to give monomer 4b (76%
yield). Moreover, AB-monomer 5a was prepared from diphenol
1H NMR (600 MHz, CDCl3)
d 7.87e6.39 (br, overlap with CHCl3 peak,
20H in one unit, Ar), 5.17e4.64 (br, 2H in one unit, OCH2), 3.84e3.15
(br, 4H in one unit, SiOCH2), 3.15e2.61 (br, 2H in one unit,
CHCH2Ar), 2.61e2.06 (br, 3H in one unit, CCHCH2), 1.19e0.59 (br,
21H in one unit, SiCCH3, CCH3), 0.24e0.29 (br, overlap with TMS
peak, 12H in one unit, SiCH3). 13C NMR (150 MHz, CDCl3)
d 156.7,
142.8, 136.9, 136.6, 136.3, 129.8, 129.2, 128.6, 128.6, 128.4, 127.9,
127.7, 127.0, 126.8, 126.7, 126.6, 126. 114.5, 69.8, 65.3, 44.1, 26.0, 18.3,
16.0, -5.5, -5.6. IR (film) 3023, 2952, 2926, 2854, 1509, 1250, 1086,
960.4, 773.3, 664.4 cmꢀ1. Mn ¼ 1.02 ꢂ 104, Mw ¼ 2.10 ꢂ 104, Mw/
Mn ¼ 2.06 based on GPC analysis.

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S. Okamoto et al. / Polymer 97 (2016) 550e558
Fig. 2. (a) UV-Vis absorption and FL spectra of J-3 (10ꢀ6 M in CH2Cl2), H-3A (2 ꢂ 10ꢀ6 M in CH2Cl2), H-3D (2 ꢂ 10ꢀ6 M in CH2Cl2), and OBu-BStB (10ꢀ7 M in CH2Cl2). FL: excited at
390 nm for J-3, 390 nm for H-3A, 387 nm for H-3D, and 388 nm for OBu-BStB. (b) FL and EX spectra of J-3 and H-3D films. FL: excited at 412 nm for J-3, 340 nm for H-3D, and 388 nm
for OBu-BStB. EX: monitored at 503 nm for J-3, 472 nm for H-3D, and 443 nm for OBu-BStB.
compound 10 [11] by conversion into the mono trifluoromethnane
sulfonate 11 (54%) followed by Heck coupling (41%) with 12, acetal
cleavage under acidic conditions, reduction of the resulting alde-
hyde, and finally conversion of the alcohol to the corresponding
bromide (see Scheme 3).
with the corresponding diboronate 2a, 2b, or 2c, respectively
(Scheme 5). Ether tethered polymer H-3D was also prepared from
1b [11] and 6a by Williamson etheration.
3.2. Optical properties
3.1.2. Synthesis of polymers A-, J-, S-, and H-3
3.2.1. Polymer A-3
Once monomers 4 and 5 were obtained, polymers A-3, J-3, and
S-3 were synthesized (Scheme 4). Polymer A-3 (Mn: 1.05 ꢂ 104, Mw:
2.83 ꢂ 104, Mw/Mn: 2.70, determined by GPC analysis with poly-
styrene standard), composed of an alternative stacking structure of
UV-Vis absorption (UV) and fluorescence (FL) spectra of CH2Cl2
solutions of A-3, H-3A, H-3B, and model compounds OBu-BStB and
F-BStB are shown in Fig. 1(a). The concentration (M) of the polymer
solutions refers to the molar amount of the repeat unit per volume of
solution (L). For A-3, the concentration refers to the total molar
two different
p-units, was obtained in 52% yield (after re-
precipitation from MeOH) by Suzuki-Miyaura coupling polymeri-
zation of 4b and fluoro diboronate compound 2b. J-Stacking poly-
mer J-3 (Mn: 1.36 ꢂ 104, Mw: 6.50 ꢂ 104, Mw/Mn: 4.77) was prepared
in 22% yield (after re-precipitation from MeOH) by Williamson
etheration polymerization of diphenol derivative 4a with dibro-
mide 6a under basic conditions. Polymer S-3 (Mn: 1.02 ꢂ 104, Mw:
amount of two
similar to its single
sorption of A-3 (labs max: 337 nm) and H-3B (labs max: 340 nm)
showed hypochromic shifts, compared to model compounds, which
suggested their H-type aggregating orientation of
to F-BStB (lem max: 420 nm) and OBu-BStB (lem max: 443 nm),
emission spectra for polymers A-3 (lem max: 448 nm), H-3A (lem max:
475 nm), and H-3B (lem max: 4461 nm) bathochromically shifted.
Emission from A-3 was mainly ascribed to emission from OBu-BStB
units in the polymer but not to that of F-BStB, probably due to
intramolecular energy transfer from F-BStB units to OBu-BStB units.
Fig. 1(b) shows the FL and excitation (EX) spectra of A-3, H-3A,
and H-3B films. These films were simply prepared by applying a
p
-units. Although UV of H-3A (labs max: 392 nm) was
p-model OBu-BStB (labs max: 385 nm), UV ab-
p-units. Compared
2.10 ꢂ 104, Mw/Mn: 2.08) with staggered-stacking structure of
p-
units (44% yield after re-precipitation from MeOH) was readily
synthesized by Williamson etheration polymerization of bromo
phenol monomer 5a.
With the aim to compare the properties of A-3, J-3, and S-3
polymers with their corresponding H-stacking counterparts, homo
polymers H-3A, H-3B, and H-3C were prepared by reacting 1a [10]

S. Okamoto et al. / Polymer 97 (2016) 550e558
557
Fig. 3. (a) UV-Vis Absorption (UV) and Fluorescence (FL) Spectra of BStB, S-3, He3C, and He3B in CH2Cl2 (10ꢀ6 M). FL: Excited at 364 nm for BStB (measured using a 10ꢀ7
M
solution), 362 nm for S-3, and 383 nm for He3C. (b) FL and EX spectra of S-3 (film), He3C (film), and BStB (10ꢀ7 M in CH2Cl2). FL (normalized): excited at 347 nm for S-3, 342 nm for
He3C, and 326 nm for BStB. EX (normalized): monitored at 467 nm for S-3, 426 nm for He3C and 466 nm for BStB.
CH2Cl2 solution containing the polymers to a quartz glass and
subsequently removing the solvent. The spectra of F-BStB and OBu-
BStB (CH2Cl2 solutions) are also shown for comparison. Compared
to F-BStB and OBu-BStB, the H-stacking H-3A (lem max: 508 nm) and
H-3B (lem max: 496 nm) polymers showed FL emission spectra with
a large red-shifting, this being mainly ascribed to the excimer-like
3.2.2. Polymer J-3
The UV-Vis absorption and FL spectra of CH2Cl2 solutions of J-
type (J-3) and H-stacking (H-3A and H-3D) polymers are summa-
rized in Fig. 2(a). The spectra of a single p-unit model OBu-BStB are
also given for comparison. The concentration (M) of the polymer
solutions refers to the molar amount of the repeat unit per volume
of solution (L). Therefore, the concentration of H-3A and H-3D
polymers was adjusted to be twice than that of J-3. In terms of
emission by H-type aggregation of
bathochromic shift (lem max: 539 nm), potentially attributed to
exciplex-like emitting of the two different -units, was observed
p-units. Interestingly, a larger
p
shape and lmax
(ca 390 nm), these polymers showed nearly
abs
for A-3. This large shift of emission for A-3 was unique to the film
form and quite different from its behavior in a CH2Cl2 solution. A-3
similar normalized UV spectra. J-3, H-3A, and H-3D polymers
exhibited red-shifted FL emission compared to a single -unit OBu-
p
possesses an alternative stacking structure of two different
p
-units
BStB. It can be noted that the emission spectra of the J-like stacking
polymer J-3 were more intense as compared to H-3A and H-3D. The
fluorescence quantum efficiencies (FF) of J-3 (FF 0.23), H-3A (FF
0.10), and H-3D (FF 0.14) polymers were relatively determined by
comparing with that of 9,10-diphenylanthracene (FF 0.81). Fig. 2(b)
shows the FL and EX spectra of J-3 and H-3D films. Unlike FL spectra
in solution (Fig. 2(a)), emission spectra of films bathochromically
shifted to a large extent compared to the single p-unit model OBu-
BStB (CH2Cl2 solution). J-like stacking polymer J-3 showed larger
bathochromic shifts as compared to its analogous H-stacking H-3D.
with the same -length as those of H-type aggregation materials,
p
thereby leading to similar stacking arrangement for both types of
polymers. Thus, compared to F-BStB and OBu-BStB, A-3 showed EX
spectra with a large hypochromic shift. Hypochromic shift of UV
absorption and excitation (EX) spectra are an unique phenomenon
to H-type aggregation polymers. The difference of FL behavior be-
tween a solution and film can be rationalized by assuming that
polymer folded stacking structure may be tighter in film than in a
solution.

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S. Okamoto et al. / Polymer 97 (2016) 550e558
3.2.3. Polymer S-3
Acknowledgments
The UV-absorption and emission properties of the staggered p-
stacking polymer S-3 in a CH2Cl2 solution are shown in Fig. 3(a).
The spectra of H-3C and BStB were also investigated for the sake of
comparison. The UV-spectra of S-3 (labs max: 362 nm) was similar to
We thank the Ministry of Education, Culture, Sports, Science,
and Technology (MEXT) [#26620109 and Supported Program for
the Strategic Research Foundation at Private Universities,
2008e2012], Japan, for financial support.
those of BStB (labs max: 364 nm) in terms of shape and labs max
.
However, S-3 (lem max: 427 nm) exhibited red-shifted emission
than BStB (lem max: 414 nm). Interestingly, emission of S-3 indicated
a similar shape and labs max to those of H-3C (lem max: 426 nm) but
showed higher intensity. Fig. 3(b) summarizes the FL and EX
spectra of S-3 in film. As we reported previously, the H-stacking
polymer H-3C exhibits large hypochromic UV (and EX) and bath-
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.polymer.2016.05.075.
ochromic FL shifts compared to the single
BStB. This hypochromic shift is a characteristic of the H-aggregate
of -modules, whereas the bathochromic phenomenon may be
attributed to excimer-type emission by the stacked structure of
moieties within the polymer. In contrast, the J-stacking structure
resulted in broadened bathochromic shifted absorption (Fig. 2).
p-unit model compound
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aggregate (J-3), and staggered stacking (S-3) structures of
p-mod-
ules. The UV-absorbing and fluorescent emission properties of
these three polymers were compared with those of the corre-
sponding single structural
stacking polymer (H-3). As a result of the distinctive arrangement
of -units, each polymer exhibited unique optical properties. These
p-molecule component and H-type
p
characteristics were observed more prominently in film than in a
solution.