Double click synthesis and second-order nonlinearities of polystyrenes bearing donor - Acceptor chromophores

Article abstract of DOI:10.1021/ma100869m

Donor - acceptor chromophores were almost quantitatively introduced into the side chains of a polystyrene derivative by sequential click chemistry-type addition reactions as an efficient postfunctionalization method. The first click reaction is the conven

Full text of DOI:10.1021/ma100869m

Macromolecules 2010, 43, 5277–5286 5277
DOI: 10.1021/ma100869m
Double Click Synthesis and Second-Order Nonlinearities of Polystyrenes
Bearing Donor-Acceptor Chromophores
Yongrong Li,† Kazuma Tsuboi,† and Tsuyoshi Michinobu*,‡,§
†Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1 Ookayama,
Meguro-ku, Tokyo 152-8552, Japan, ‡Global Edge of Institute, Tokyo Institute of Technology, 2-12-1
Ookayama, Meguro-ku, Tokyo 152-8550, Japan, and §PRESTO, Japan Science and Technology
Agency (JST), Kawaguchi, Saitama, Japan
Received April 20, 2010; Revised Manuscript Received May 18, 2010
ABSTRACT: Donor-acceptor chromophores were almost quantitatively introduced into the side chains of
a polystyrene derivative by sequential “click chemistry”-type addition reactions as an efficient postfunctio-
nalization method. The first click reaction is the conventional Cu(I)-catalyzed azide-alkyne cycloaddition
(CuAAC), and the second one is the atom-economic addition of strong acceptor molecules, such as
tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoquinodimethane (TCNQ), to the aniline-substituted
electron-rich alkynes. Steric hindrance was found to be an important factor in determining the reactivity
of alkyne-acceptor addition reactions. All obtained polymers showed good solubility in common organic
solvents, and they were fully characterized by GPC, 1H NMR and IR spectroscopy, and elemental analysis.
After the acceptor addition, the polymers showed an intense charge-transfer (CT) band centered at ca. 480 nm
for the TCNE adducts and ca. 710 nm for the TCNQ adducts. Electrochemical measurements of these
polymers also revealed well-defined oxidation and reduction potentials, offering consistency between the
electrochemical and optical band gaps. The second harmonic generation (SHG) coefficients (d33 and d15) of
the polymer thin films were evaluated by SHG measurements before and after corona poling at 150 ꢀC, a
temperature that was determined on the basis of thermal analyses. The results show that the TCNE adducted
polymers possess better SHG properties than the corresponding TCNQ adducted polymers, probably
reflecting the superior chromophore mobility within the polymers.
Introduction
We recently focused on the highly efficient addition reactions
between electron-rich alkynes and strong acceptor molecules,
Click chemistry became one of the most important techniques
to prepare functional polymers with well-defined chemical
structures.1 In particular, when click chemistry is applied as a
postfunctionalization method, desired functional moieties can be
introduced into polymer side chains and the polymer properties
are greatly improved.2 One of the most powerful and well-studied
click chemistry reactions is probably the Cu(I)-catalyzed azide-
alkyne cycloaddition (CuAAC) reaction, originated by Sharpless
and co-workers, which is capable of selectively combining two
components in terms of covalent bonds in excellent yields.3
However, this reaction has several limitations, such as the need
for a metal catalyst for the control of high yield and regioselec-
tivity, the explosive nature of some azide substances, and the poor
optoelectronic properties of the 1,4-triazole ring. In order to
solve these problems, metal-free azide-alkyne click chemistry
has been developed.4 Moreover, thiol-ene/thiol-yne reactions
and Diels-Alder reactions were recently applied as a metal- and
azide-free click chemistry to preparation of a series of macro-
molecular architectures.5-7 Nevertheless, there are few reports
that can solve the last limitation of the poor optoelectronic
properties.
such as tetracyanoethylene (TCNE) and 7,7,8,8-tetracyanoqui-
nodimethane (TCNQ), forming nonplanar donor-acceptor
chromophores via the thermal [2 þ 2] cycloaddition followed by
the ring-opening (Scheme 1).8 The reactivity largely depends on
the electron-donating groups substituted by the alkyne moiety,
and dialkylanilino donors were found to afford the desired
donor-acceptor structures in a quantitative yield at room
temperature.9 No special purification process is necessary be-
cause of the absence of byproducts. Therefore, this reaction
satisfies most of the requirements of click chemistry suggested
in the original review,3a and it can be classified as a new metal-free
click chemistry that further improves optoelectronic properties
of organic materials. Some small nonplanar donor-acceptor
molecules prepared by these reactions were demonstrated to
show excellent second-order10 andthird-order11 nonlinear optical
effects.
We have already succeeded in introducing these donor-
acceptor chromophores in aromatic polymers by the high-yield-
ing postfunctionalization method using TCNE as an acceptor
molecule.12 Note that the postfunctional preparation of do-
nor-acceptor structures within polymers has previously been
reported using the tricyanovinylation of electron-rich aromatic
rings with TCNE, but this reaction requires harsh conditions and
produces hydrogen cyanide (HCN) as a byproduct.13 Therefore,
the efficiency is much less than that of our approach. However,
we have not yet attempted double postfunctionalization using
this reaction. Double postfunctionalization is a convenient method-
ology to prepare more complex functional polymers from a
readily available precursor polymer in a controlled manner.
Tuning of the electronic HOMO and LUMO levels is crucial in
improving the optoelectronic properties of organic materials.
Design of new donor-acceptor type π-conjugated molecules
is one solution because through-bond interactions between donor
and acceptor moieties result in narrow band gaps originat-
ing from the elevated HOMO and lowered LUMO levels.
*Corresponding author. E-mail: michinobu.t.aa@m.titech.ac.jp.
r 2010 American Chemical Society
Published on Web 05/24/2010
pubs.acs.org/Macromolecules

5278 Macromolecules, Vol. 43, No. 12, 2010
Li et al.
Scheme 1. Thermal Addition Reaction between Alkynes Activated by
Electron-Donating Groups (EDGs) and Strong Acceptor Molecules
treatment with hexamethyldisilazane before use.18 Residual
solvents were removed by heating the films in vacuum at 70 ꢀC.
NLO Measurements. Second-order optical nonlinearity of the
polymers was determined by second harmonic generation
(SHG).18 The poling of polymer films was performed in a
wire-to-plane geometry under in situ conditions. The dischar-
ging wire to plane distance was 10 mm. As the temperature
gradually increased to a point 15-20 ꢀC higher than Tg, 9.0 kV of
corona voltage was applied and kept for 30 min. The films were
cooled to 20 ꢀC in the presence of the electric field, after which
the SHG measurements were carried out with a Nd:YAG laser
LOTIS TII LS-2132UTF operating at the 15 Hz repetition rate
and 5-6 ns pulse duration at 1064 nm. The electric field vector
of the incident beam was either parallel (p-polarization) or per-
pendicular (s-polarization) to the plane of incidence. SHG
signals are corrected with a photomulitiplier after through a couple
of blocking filters. The electric field of vector of SHG signals was
selected with a polarizer to be either p- or s-polarization. A Y-cut
crystal served as the reference.
The key requirements for achieving desired polymers are for
quantitative yield and orthogonality to occur in both reactions.
There is in fact increasing interest in the development of double
click postfunctionalization, and many complex macromolecular
architectures have successfully been synthesized.14
In this paper, we report for the first time the combination of the
conventional CuAAC and alkyne-acceptor click reaction for
establishment of the new double click postfunctionalization.15
We selected the azide-functionalized polystyrene as a readily
available and universally applicable precursor polymer, which
was applied to the sequential click chemistry reactions. This
report also demonstrates the applicability of the alkyne-TCNQ
reaction to the postfunctional modification of polymers. The
final polymer products contain densely attached donor-acceptor
chromophores, featuring strong charge-transfer (CT) bands in
the visible and near-IR region as well as redox activities in both
anodic and cathodic directions. Therefore, the nonlinear optical
properties of the polymers were evaluated by second-harmonic
generation (SHG) measurements, and the structure-property
relationship was summarized.
N,N-Dihexadecyl-4-iodoaniline (1). To a solution of 4-iodoa-
niline (5.30 g, 24.2 mmol) in dehydrated DMF (50 mL), 1-io-
dohexadecane (28.0 g, 79.5 mmol) and sodium carbonate
(4.50 g, 42.5 mmol) were added under nitrogen. The mixture
was stirred at 95 ꢀC for 20 h. After cooling to 20 ꢀC, the
mixture was washed with water (200 mL) and extracted by
dichloromethane (200 mL). The organic phase was collected and
dried over sodium sulfate. Evaporation and column chroma-
tography (SiO2, hexane) afforded the desired product (13.0 g,
78%). 1H NMR (300 MHz, CDCl3): δ 0.88 (m, 6 H), 1.26 (s, 52
H), 1.52 (m, 4 H), 3.18 (m, 4 H), 6.38 (d, J = 9.0 Hz, 2 H), 7.39 (d,
J = 9.0 Hz, 2 H). 13C NMR (75 MHz, CDCl3): δ 14.13, 22.70,
27.02, 27.11, 28.56, 29.37, 29.43, 29.51, 29.56, 29.61, 29.67,
29.70, 30.52, 31.94, 33.58, 50.99, 75.29, 113.95, 137.60, 147.56.
N,N-Dihexadecyl-4-({4-[(triisopropylsilyl)ethynyl]phenyl}-
ethynyl)aniline (2p). To a degassed solution of [(4-ethynyl-
phenyl)ethynyl](triisopropyl)silane (1.00 g, 3.54 mmol) and 1
(2.36 g, 3.53 mmol) in diisopropylamine (40 mL), bis(triphenyl-
phosphine)palladium(II) dichloride (50 mg, 0.070 mmol) and
cuprous iodide (25 mg, 0.13 mmol) were added under argon. The
mixture was stirred at 20 ꢀC for 18 h. After removal of the pre-
cipitated salt by filtration, evaporation and column chromato-
graphy (SiO2, hexane) afforded the desired product (2.16 g, 74%)
as a viscous liquid. 1H NMR (300 MHz, CDCl3): δ 0.89 (m, 6 H),
1.14 (s, 18 H), 1.27 (m, 52 H), 1.58 (m, 7 H), 3.27 (m, 4 H), 6.57
(d, J = 8.7 Hz, 2 H), 7.36 (d, J = 8.7 Hz, 2 H), 7.41 (s, 4 H). 13C
NMR (75 MHz, CDCl3): δ 11.33, 14.12, 18.67, 22.68, 27.17,
29.54, 31.95, 50.95, 87.00, 91.98, 92.99, 107.01, 108.35, 111.17,
122.16, 124.33, 130.89, 131.85, 132.93, 148.07. IR (KBr): 2923,
2853, 2208, 2152, 1610, 1596, 1521, 1465, 1401, 1368, 1195, 1134,
882, 835, 812 cm-1. MALDI-TOF MS (dithranol): m/z: calcd for
C57H95NSiþ: 821.72 g mol-1; found: 823.5 g mol-1 [M þ H]þ.
N,N-Dihexadecyl-4-({3-[(triisopropylsilyl)ethynyl]phenyl}-
ethynyl)aniline (2m). To a degassed solution of [(3-ethynyl-
phenyl)ethynyl](triisopropyl)silane (1.00 g, 3.54 mmol) and
1 (2.36 g, 3.53 mmol) in diisopropylamine (40 mL), bis(triphenyl-
phosphine)palladium(II) dichloride (50 mg, 0.070 mmol) and
cuprous iodide (25 mg, 0.13 mmol) were added under argon.
The mixture was stirred at 20 ꢀC for 18 h. After removal of the
precipitated saltbyfiltration, evaporationandcolumnchromato-
graphy (SiO2, hexane) afforded the desired product (1.98 g, 68%)
as a viscous liquid. 1H NMR (300 MHz, CDCl3): δ 0.81 (m, 6 H),
1.07 (s, 18 H), 1.22 (m, 52 H), 1.51 (m, 7 H), 3.19 (m, 4 H), 6.49 (d,
J = 7.2 Hz, 2 H), 7.17 (m, 1 H), 7.28 (m, 3 H), 7.34 (m, 1 H), 7.53
(s, 1 H). 13C NMR (75 MHz, CDCl3): δ 11.31, 14.13, 18.67, 22.70,
22.17, 29.54, 31.94, 50.96, 86.30, 90.86, 91.56, 106.49, 108.38,
111.15, 123.65, 124.55, 128.13, 130.74, 131.00, 132.92, 134.62,
148.03. IR (KBr): 2924, 2853, 2203, 2150, 1608, 1590, 1519, 1465,
1399, 1368, 1221, 1189, 1125, 1074, 883, 811, 790 cm-1. MALDI-
Experimental Section
Materials. All reagents were purchased from Kanto, Tokyo
Kasei, Wako, and Aldrich and used as received. [(4-Ethynyl-
phenyl)ethynyl](triisopropyl)silane,16 [(3-ethynylphenyl)ethynyl]-
(triisopropyl)silane,16 and poly(4-azidomethylstyrene) (4)17 were
synthesized according to the reported methods.
General Measurements. 1H and 13C NMR spectra were
measured on a JEOL model AL300 spectrometer at 20 ꢀC.
Chemical shifts are reported in ppm downfield from SiMe4,
using the solvent’s residual signal as an internal reference. The
resonance multiplicity is described as s (singlet), br s (broad
singlet), d (doublet), and m (multiplet). Infrared (IR) spectra
were recorded on a JASCO FT/IR-4100 spectrometer. Gel
permeation chromatography (GPC) was measured on a Shodex
system equipped with polystyrene gel columns using THF as an
eluent at a flow rate of 1.0 mL min-1. Relative molecular
weights were determined by comparison with the calibrated
standard polystyrenes. Absolute molecular weights were deter-
mined by using the detector miniDAWN Tristar. UV-vis
spectra were recorded on a JASCO V-550 spectrophotometer.
Elemental analysis was performed on a PerkinElmer 2400-Series
II CHNS/O analyzer. Thermogravimetric analysis (TGA) and
differential scanning calorimetry (DSC) measurements were
carried out on a Seiko SII TG 6220 and a Seiko SII DSC
6200, respectively, under nitrogen flow at a scanning rate of
10 ꢀC min-1. Thickness of films was measured on a Dektak3ST
surface profiler. Electrochemical measurements were carried
out at 20 ꢀC in dehydrated CH2Cl2 containing 0.1 M (nC4H9)4-
NClO4 in a classical three-electrode cell. The working and
auxiliary electrodes were a glassy carbon disk electrode (2 mm
in diameter) and a platinum wire, respectively. The reference
electrode was Ag/AgCl/CH3CN/(nC4H9)4NPF6. All potentials
are referenced to the ferricinium/ferrocene (Fcþ/Fc) couple used
as an internal standard.
Film Fabrication. Polymers were dissolved in dehydrated
toluene at a concentration of ∼3 wt % and then filtered through
a 0.2 μm syringe filter. Polymer solutions were spin-coated on a
glass slide, which has sequentially been cleaned by detergent,
pure water, and acetone in an ultrasonic bath, followed by the
TOF MS (dithranol): m/z: calcd for C57H95NSiþ: 821.72 g mol-1
found: 823.5 g mol-1 [M þ H]þ.
;

Article
4-[(4-Ethynylphenyl)ethynyl]-N,N-dihexadecylaniline (3p). To
Macromolecules, Vol. 43, No. 12, 2010 5279
(8.6 mM, 3.2 mL) was added under air. The mixturewas stirredat
20 ꢀC for 1 h. The solution was evaporated to afford 6m (26.2 mg,
100%). H NMR (300 MHz, CDCl3): δ 0.86 (m, 6n H), 1.24
a solution of 2p (1.00 g, 1.21 mmol) in tetrahydrofuran (12 mL),
tetrabutylammonium fluoride (1 M in tetrahydrofuran) (2.4 mL)
was added under air. The mixture was stirred at 0 ꢀC for 20 min.
Column chromatography (SiO2, CH2Cl2) afforded the desired
1
(s, 52n H), 1.59 (s, 7n H), 3.34 (br s, 4n H), 5.36 (br s, 2n H), 6.63
(s, 7n H), 7.46 (br s, 2n H), 7.76 (br s, 2n H), 8.00 (br s, n H), 8.44
(br s, n H). IR (KBr): 2923, 2852, 2214, 1603, 1490, 1417, 1342,
1211, 1183, 819, 701 cm-1. Elemental analysis calcd for (C63H84-
N8)n: C 79.37, H 8.88, N 11.75; found: C 79.44, H 8.99, N 11.57%.
1
product (786 mg, 95%) as a yellow solid. H NMR (300 MHz,
CDCl3):δ0.90(m,6H), 1.31(m, 52H), 1.55(m,4H), 3.15(s, 1H),
3.34 (m, 4 H), 6.58 (d, J = 9 Hz, 2 H), 7.37 (d, J = 9 Hz, 2 H), 7.44
(s, 4 H). 13C NMR (75 MHz, CDCl3): δ 14.11, 22.69, 27.17, 29.61,
31.93, 50.94, 78.32, 83.57, 86.76, 93.24, 108.26, 111.17, 120.67,
124.97, 120.67, 124.97, 130.99, 131.92, 132.94, 148.11. IR (KBr):
3308, 2919, 2850, 2206, 2098, 1611, 1595, 1524, 1467, 1398, 1352,
1132, 842, 820 cm-1. MALDI-TOF MS (dithranol): m/z: calcd for
C48H75Nþ: 665.59 g mol-1; found: 667.1 g mol-1 [M þ H]þ.
4-[(3-Ethynylphenyl)ethynyl]-N,N-dihexadecylaniline (3m). To
a solution of 2m (650 mg, 0.790 mmol) in tetrahydrofuran
(8 mL), tetrabutylammonium fluoride (1 M in tetrahydrofuran)
(2.4 mL) was added under air. The mixture was stirred at 0 ꢀC for
20 min. Column chromatography (SiO2, CH2Cl2) afforded the
desired product (520 mg, 99%) as a yellow solid. 1H NMR (300
MHz, CDCl3): δ 0.88 (m, 6 H), 1.29 (m, 52 H), 1.56 (s, 4 H), 3.07
(s, 1 H), 3.27 (m, 4 H), 6.56 (d, J = 9 Hz, 2 H), 7.29 (m, 1 H),
7.36 (m, 3 H), 7.46 (d, J = 7.5 Hz, 1 H), 7.52 (s, 1 H). 13C NMR
(75 MHz, CDCl3): δ 14.13, 22.70, 27.15, 29.62, 31.94, 50.93,
83.04, 86.10, 91.75, 108.19, 111.10, 122.21, 124.70, 128.24,
130.76, 131.45, 132.92, 134.68, 148.01. IR (KBr): 3309, 2923,
7p. To a solution of 5p (21.0 mg, 0.0254 mmol repeat unit-1
)
in o-dichlorobenzene, a TCNQ solution in 1,2-dichloroethane
(7.0 mM, 3.6 mL) was added under nitrogen. The mixture was
stirred at 160 ꢀC for 24 h. The solution was evaporated to afford
7p (26.1 mg, 100%). 1H NMR (300 MHz, CDCl3): δ 0.87 (m, 6n
H), 1.26 (s, 52n H), 1.60 (s, 7n H), 3.33 (m, 4n H), 5.15-5.50
(br s, 2n H), 6.42-6.70 (br s, 6n H), 6.72-7.07 (br s, 4n H),
7.37-7.50 (br s, 4n H), 7.70-8.00 (s, n H). IR (KBr): 2922,
2852, 2202, 1581, 1522, 1458, 1401, 1348, 1178, 826, 715 cm-1
.
Elemental analysis calcd for (C69H88N8)n: C 80.50, H 8.62,
N 10.88; found: C 81.07, H 8.93, N 10.00%.
7m. To a solution of 5m (23.4 mg, 0.0284 mmol repeat unit-1
)
in o-dichlorobenzene, a TCNQ solution in 1,2-dichloroethane
(7.0 mM, 4.0 mL) was added under nitrogen. The mixture was
stirred at 160 ꢀC for 24 h. The solution was evaporated to afford
7m (29.0 mg, 99%). 1H NMR (300 MHz, CDCl3): δ 0.86 (m, 6n
H), 1.24 (s, 52n H), 1.60 (s, 7n H), 3.33 (m, 4n H), 5.15-5.50 (br
s, 2n H), 6.47-6.75 (br s, 6n H), 6.80-7.05 (br s, 4n H),
7.37-7.90 (br s, 7n H). IR (KBr): 2920, 2851, 2203, 1581,
1521, 1465, 1400, 1347, 1176, 822 cm-1. Elemental analysis
calcd for (C69H88N8)n: C 80.50, H 8.62, N 10.88; found: 81.02, H
8.67, N 10.11%.
2852, 2200, 1611, 1591, 1419, 1466, 1398, 1369, 1122, 811, 791 cm-1
.
MALDI-TOF MS (dithranol): m/z: calcd for C48H75Nþ: 665.59
g mol-1; found: 667.1 g mol-1 [M þ H]þ.
5p. To a solution of 4 (31 mg, 0.20 mmol repeat unit-1
)
in DMF (8 mL), 3p (130 mg, 0.20 mmol), sodium ascorbate
(3.9 mg, 0.012 mmol), and copper(II) sulfate pentahydrate
(2.3 mg, 0.0098 mmol) were added under argon. The mixture
was stirred at 20 ꢀC for 24 h, yielding a yellow precipitate. The
precipitate was filtered and washed with DMF, followed by
methanol and water to afford the yellow solid (135 mg, 87%).
The filtrate was poured into methanol to yield the residual
desired polymer (total: 152 mg, 98%). 1H NMR (300 MHz,
CDCl3): δ 0.86 (m, 6n H), 1.25 (s, 52n H), 1.57 (m, 7n H), 3.19
(br s, 4n H), 5.47 (s, 2n H), 6.48 (br s, 2n H), 6.75 (br s, 2n H), 7.30
(d, J = 12.6 Hz, 4n H), 7.74 (br s, 5n H). 13C NMR (75 MHz,
CDCl3): δ 14.13, 22.69, 26.01, 27.15, 29.73, 31.92, 50.88, 87.13,
92.04, 108.51, 111.09, 123.98, 125.38, 127.55, 129.41, 131.66,
132.93, 147.27, 147.85. IR (KBr): 2923, 2852, 2207, 1603, 1524,
Results and Discussion
Monomer Synthesis. For the sequential and double click
reactions, orthogonality in each reaction is important. We
designed new molecules 3p and 3m having two kinds of
alkyne groups: one a terminal alkyne and the other an
internal electron-rich alkyne. The terminal alkynes will
selectively react with azide substances under the CuAAC
conditions, whereas the internal alkynes will be inert under
those conditions. On the other hand, only the internal
alkynes will display sufficient reactivity toward acceptors
because of the activation by the dialkylanilino groups. In
order to enhance the solubility of the final polymers, long
alkyl chains of hexadecyl groups were introduced.
1458, 1368, 1190, 1136, 842, 812 cm-1
.
5m. To a solution of 4 (47.7 mg, 0.300 mmol repeat unit-1) in
DMF (12 mL), 3m (200 mg, 0.300 mmol), sodium ascorbate
(6.0 mg, 0.030 mmol), and copper(II) sulfate pentahydrate
(3.7 mg, 0.0015 mmol) were added under argon. The mixture
was stirred at 20 ꢀC for 24 h, yielding a yellow precipitate. The
precipitate was filtered and washed with DMF, followed by
methanol and water to afford the yellow solid (209 mg, 87%).
The filtrate was poured into methanol to yield the residual desired
polymer (total: 235 mg, 98%). 1H NMR (300 MHz, CDCl3): δ
0.86 (m, 6n H), 1.24 (s, 52n H), 1.50 (m, 7n H), 3.18 (br s, 4n H),
5.30 (s, 2n H), 6.19 (br s, 2n H), 6.49 (br s, 4n H), 6.72 (br s, 3n H),
7.68 (br s, 2n H), 7.96 (br s, 2n H). IR (KBr): 2923, 2852, 2210,
Starting from N,N-dihexadecyl-4-iodoaniline (1), prepared
from 4-iodoaniline and 1-iodohexadecane, Sonogashira cou-
pling with HCtCPhCtCSi(iPr)3 followed by silyl deprotec-
tion with (nC4H9)4NF afforded the desired key molecules 3p
and 3m in moderate yields (67-70% in two steps) (Scheme 2).
The terminal alkynes of 3p and 3m were stable under ambient
conditions, which were verified by the 1H NMR spectra in
CDCl3 with a sharp peak at 3.19 ppm for 3a and 3.15 ppm
for 3m.
Polymer Synthesis. Poly(4-azidomethylstyrene) (4) was
prepared as a precursor polymer by radical polymerization
of 4-chloromethlystyrene with azobis(isobutyronitrile), fol-
lowed by substitution of chlorine atoms with azide groups.17
The molecular weight (Mn) and the polydispersity (Mw/Mn)
determined by GPC relative to standard polystyrenes were
11 500 and 1.75, respectively. The azide group was confirmed
by IR spectra with a strong vibrational peak at 2095 cm-1
(Figure 1), and the content was determined to be 96% by
elemental analysis.
1603, 1579, 1519, 1458, 1368, 1198, 1130, 1045, 812, 791 cm-1
6p. To a solution of 5p (24.5 mg, 0.0295 mmol repeat unit-1
.
)
in chloroform (0.3 mL), a TCNE solution in 1,2-dichloroethane
(0.163 M, 0.18 mL) was added under air. The mixture was stirred
at 20 ꢀC for 1 h. The solution was evaporated to afford 6p (28.2 mg,
1
100%). H NMR (300 MHz, CDCl3): δ 0.86 (m, 6n H), 1.24 (s,
52n H), 1.59 (s, 7n H), 3.34 (m, 4n H), 5.48 (s, 2n H), 6.68 (br s,
4n H), 7.69 (br s, 8n H), 7.98 (s, n H). IR (KBr): 2923, 2852, 2214,
1604, 1489, 1418, 1346, 1212, 1182, 971, 820 cm-1. Elemental
analysis calcd for (C63H84N8)n: C 79.37, H 8.88, N 11.75; found:
C 79.56, H 9.27, N 11.17%.
The terminal alkynes of 3p or 3m were selectively reacted
with azide groups of 4 in the presence of Cu(I) catalysts,
yielding the tolane-appended polymers 5p and 5m (Scheme 3).
We found that when the reaction is performed in DMF, the
resulting high molecular weight polymers are deposited from
6m. To a solution of 5m (22.7 mg, 0.0275 mmol repeat unit-1
)
in chloroform (4 mL), a TCNE solution in 1,2-dichloroethane

5280 Macromolecules, Vol. 43, No. 12, 2010
Li et al.
Scheme 2. Synthesis of Tolane Monomersa
a Reagents and conditions: (a) HCtCPhCtCSi(iPr)3, PdCl2(PPh3)2, CuI, iPr2NH, N2, 18 h; (b) (nC4H9)4NF, THF, 0 ꢀC, 20 min.
and a new CT band with the most intense peak at 481 nm for
5p f 6p and 483 nm for 5m f 6m appeared (Figure 3). The
peak positions of the CT bands were unchanged, while the
intensities almost linearly increased with the increasing
amount of added TCNE, finally leading to completely red
solutions. The presence of the isosbestic points at 308 and
382 nm for 5p and at 306 and 377 nm for 5m indicates no side
reactions.
The same titration experiments were carried out for 5p and
5m by using TCNQ as an expanded acceptor. Although the
TCNQ addition to the monomeric electron-rich alkyne
molecules proceeded at room temperature,19 the polymeric
reaction required heating. After a TCNQ solution was added
to the precursor polymer solutions in o-dichlorobenzene, the
mixtures were heated to 160 ꢀC. The reaction temperature
was carefully determined on the basis of thermal analyses of
both precursor and produced polymers (vide infra). The
solution color was gradually changed from yellow to green,
and the UV-vis spectral changes suggested reaction com-
pletion in 40 min in the case of 5p f 7p and 90 min in the case
of 5m f 7m. Stepwise addition of TCNQ to the precursor
polymers 5p and 5m followed by heating to 160 ꢀC for 40 and
90 min, respectively, provided clear spectral changes with the
isosbestic points at 335 and 383 nm for 5p and at 310 and
372 nm for 5m, implying the absence of any undesired side
reactions (Figure 4). The generated CT bands bathochromi-
cally shifted compared to the TCNE adducts, and the end
absorptions reached the near-IR region. Thus, the most
intense CT band was centered at 712 nm for 7p and 715 nm
for 7m, resulting in the green color.
Figure 1. IR spectra of polymers (a) 4, (b) 5p, (c) 6p, and (d) 7p.
the solutions. Thus, a simple filtration of the deposited
precipitates after the reaction for 24 h provided the desired
polymers 5p and 5m in a fairly good yield of 87%. Evapora-
tion of the filtrate and subsequent precipitation into a water/
methanol (4:1) mixture afforded the residual desired polymers
in a combined yield of 98%. The GPC measurements revealed
a reasonable molecular weight increase. The Mn and Mw/Mn
values determined by GPC relative to standard polystyrenes
are 52 300 and 1.55 for 5p and 49 000 and 1.85 for 5m
(Table 1). The slightly lower molecular weight and higher
polydispersity of the m-phenylene-linked 5m than the
p-phenylene-linked 5p seem to reflect the different hydro-
dynamic volumes in the GPC measurements. The absence
of the terminal alkynes and the presence of the internal
1
alkynes were confirmed by the H NMR and IR spectra
The acceptor titration experiments revealed that TCNQ
showed lower reactivity than TCNE, despite the similar first
reduction potential of TCNQ (Ered,1 = -0.25 V vs Fcþ/Fc)
to that of TCNE (Ered,1 = -0.32 V vs Fcþ/Fc).8c Further-
more, the m-phenylene-linked bent side chain needed a
longer reaction time than the p-phenylene-linked straight
side chain. These results indicate that the reactivity of the
alkyne-acceptor addition is governed not only by the elec-
tron density of the alkyne moieties but also by steric factors.
The larger molecular size of TCNQ compared to TCNE
made the reactions more difficult on the confined polymer
side chains, and this effect was more significant for the
m-phenylene-linked 5m than for the p-phenylene-linked 5p.
The UV-vis titration experiments enabled us to prepare
the full TCNE and TCNQ adducted polymers without any
special purification processes. Addition of a stoichiometric
amount of TCNE at room temperature and TCNQ at 160 ꢀC
to 5p and 5m, followed by evaporation of the solvents,
quantitatively furnished the desired polymers, 6p, 6m, 7p,
and 7m (Scheme 3). GPC measurements revealed a slight
increase in the relative Mn values and a greater increase in the
relative Mw values compared with the corresponding pre-
cursor polymer values (Table 1). These molecular weight
of 5p and 5m. In the IR spectra, both the strong azide
vibrational peak at 2095 cm-1 and the vibrational peak at
3308 cm-1 ascribed to the terminal alkynes of 3p and 3m
disappeared, whereas the vibrational peak at 2207 cm-1
originating from the internal alkynes of 3p and 3m remained
(Figure 1). In the 1H NMR spectra, the benzyl proton peak
of 4 at 4.60 ppm completely shifted to 5.47 ppm for 5p and
5.30 ppm for 5m (Figure 2). Moreover, the terminal alkyne
proton peak for 3m centered at 3.07 ppm disappeared and
the dialkylaniline peaks appeared after the CuAAC click
modification. The 13C NMR spectrum of 5p also revealed
the presence of the internal alkynes (Figure 1SI).
Subsequently, the second postfunctionalization was per-
formed by adding acceptor molecules to 5p and 5m in
chlorinated solvents. Because the resulting donor-acceptor
chromophores usually feature well-defined CT bands in the
visible region, the reactions were initially investigated by
UV-vis spectroscopic titration experiments. When TCNE
was selected as a compact acceptor molecule, the reaction
immediately proceeded at room temperature, suggesting the
occurrence of click postfunctionalization. Thus, the absorp-
tion intensities of the precursor polymers started to decrease,

Article
Macromolecules, Vol. 43, No. 12, 2010 5281
Scheme 3. Sequential Double Click Postfunctionalization of Polystyrene Derivative 4a
a Reagents and conditions: (a) CuSO4 5H2O, sodium ascorbate, DMF, 24 h; (b) TCNE, CHCl3, 1 h; (c) TCNQ, o-dichlorobenzene, 160 ꢀC, 24 h.
3
Table 1. Summary of Molecular Weights and Thermal Properties of
the Polymers
bulky and nonplanar acceptor moieties (Figure 2). This
broadening was more significant in the case of the TCNQ
adducted polymers, probably reflecting the larger chromo-
phore size. The same tendency was observed for the 13C
NMR spectra (Figure 1SI). In the IR spectra, a weak alkyne
vibrational peak ascribed to the tolane moieties of the
precursor polymer 5p was replaced by a strong cyano peak
at 2214 cm-1 for 6p and 2202 cm-1 for 7p (Figure 1). The
elemental analyses of all polymers 6p, 6m, 7p, and 7m showed
good agreement with the calculated values. All of these
results support the perfect postfunctionalization by the
alkyne-acceptor addition reactions.
UV-vis absorption spectra of the chromophore-appended
polymers were investigated in various solvents. Addition of
trifluoroacetic acid (TFA) to the polymer solutions provided
evidence of the CT bands. Because protonation of the dihex-
adecylaniline moieties results in a dramatic decrease in the
electron-donating power, it is concluded that the decreased
low-energy bands in the presence of TFA are derived from the
CT bands (Figure 2SI). These bands were almost fully regene-
rated when the solutions were neutralized with triethylamine,
suggesting good reversibility under the employed acid-base
conditions.
Absorption and emission spectra of 6p and 6m were mea-
sured in various organic solvents, and the data were summari-
zed as a function of solvent polarity ET(30) (Figure 3SI and
Table 1SI).20 Similarly to the small donor-substituted 1,1,4,
4-tetracyanobutadienes (TCBDs), both polymers displayed
positive solvatochromism in the absorption spectra (Figure
4SI). Emission spectra were very weak and were composed of
two peaks. The longer wavelength emission at ∼670 nm is
assumed to originate from the excimers, and these excimers
tended to be predominantly formed in less polar solvents
a
a
b
b
polymer
Mn
Mw/Mn
Mn
Mw/Mn
Tg/ꢀCc T5%/ꢀCd
4
11 500
52 300
49 000
58 500
51 000
53 200
42 200
1.75
1.55
1.85
1.80
1.99
2.55
2.39
5p
5m
6p
6m
7p
7m
217 000
215 000
306 000
222 000
131 000
181 000
1.64
1.72
1.33
1.42
1.16
2.10
361
371
313
321
315
318
130
134
127
129
a Molecular weights determined by GPC (eluent: THF, calibrated by
standard polystyrenes). b Molecular weights determined by GPC-MALS
(multiangle light scattering). c Glass transition temperatures determined
by DSC at the scanning rate of 10 ꢀC min-1 d The 5% weight loss
.
temperatures determined by TGA at the heating rate of 10 ꢀC min-1
.
increases are consistent with the definition of Mn and Mw.
Accordingly, the polydispersities became larger after the
acceptor additions, and this tendency is more significant
when TCNQ was employed as an acceptor. The absolute
molecular weights were also measured for the clicked poly-
mers. They were ∼4 times larger than the corresponding
relative molecular weights, except for 7p (Table 1). The
apparent decrease in the absolute Mn after TCNQ addition
is probably ascribed to the low solubility of the products in
the GPC eluent, THF.
The chemical structures of the chromophore-appended
polymers were further characterized. The 1H NMR and IR
spectral changes of p-phenylene-linked and m-phenylene-
linked derivatives were similar, so the representative spectra
are shown in Figures 1 and 2. In the 1H NMR spectra, some
peaks such as the benzyl and aromatic protons became
broader after the acceptor additions, implying the increased
rotational barriers of parts of the single bonds due to the

5282 Macromolecules, Vol. 43, No. 12, 2010
Li et al.
such as cyclohexane and diethyl ether. This tendency is
remarkable in the case of 6m, probably representing the
confined polymer environments.
Electrochemistry. One of the most important features of
donor-acceptor chromophores is the redox activities. The
obtained polymers were soluble in common organic solvents,
such as CHCl3, CH2Cl2, and THF. Thus, cyclic voltammo-
grams (CVs) were measured in CH2Cl2 with 0.1 M
(nC4H9)4NClO4 at 20 ꢀC.
Figure 5 shows the typical CV curves of the polymers. The
tolane-appended polymers 5p and 5m displayed the only
aniline-centered quasi-reversible oxidation waves at 0.28 and
0.22 V (vs Fcþ/Fc), respectively (Table 2). On the other hand,
the TCNE adducted polymers 6p and 6m showed anodically
shifted first oxidation potentials (Eox,1) at 0.84 and 0.79 V,
respectively, as well as the TCBD-centered reversible first
reduction potentials (Ered,1) at -0.91 and -0.95 V, respec-
tively. In contrast to the small donor-substituted TCBD
molecules showing two well-resolved reduction steps,21 the
polymers displayed only single reduction waves. This is
because the polymers tended to adsorb on the electrode
surface during the voltage sweep. The anodic shift of Eox,1
can be explained by the efficient interaction of the dihexa-
decylanilino moiety with the TCBD acceptor, which makes
the oxidation more difficult. The TCNQ adducted polymers
7p and 7m exhibited easier oxidations (Eox,1 at 0.42 and 0.47
V, respectively) and reductions (Ered,1 at -0.68 and -0.76 V,
respectively) than the corresponding TCNE adducted poly-
mers, probably caused by the expanded π-conjugation of
the acceptor moieties. This result means that the acceptor
moieties of 7p and 7m more weakly interact with the dihexa-
decylanilino donors than the TCBD moieties of 6p and 6m.
Consequently, the electrochemical band gaps Δ(Eox,1
-
Ered,1) of the TCNQ adducted polymers were much smaller
than those of the TCNE adducted polymers, as summarized
in Table 2. These electrochemical band gaps were in good
agreement with the optical band gaps determined by the end
absorptions in chlorinated solvents.
Thermal Properties. Thermal stability is very important
for application of functional polymers in organic devices. To
reveal the thermal properties of the postfunctionalized poly-
mers in this work, thermogravimetric analysis (TGA) and
differential scanning calorimetry (DSC) measurements were
performed at a scanning rate of 10 ꢀC min-1 under flowing
nitrogen. In contrast to the previous report that demon-
strated the thermal improvements in aromatic polyamine by
the TCNE addition,12a the 5% decomposition temperatures
(T5%) of the TCNE adducted polymers 6p and 6m were lower
than those of the corresponding precursor polymers 5p and
5m (Table 1 and Figure 6). A similar decrease in T5% was also
observed for the TCNQ adducted polymers 7p and 7m. These
results may be derived from the intrinsic electron-accepting
nature of the triazole ring. The T5%s of the p-phenylene-
linked 6p and 7p are slightly lower than those of the
corresponding m-phenylene-linked 6m and 7m due to the
efficient through-bond communication between the triazole
ring and the acceptor moieties. However, it was also shown
that all the obtained polymers are thermally stable without
any decomposition at least up to 200 ꢀC.
Figure 2. 1H NMR spectra of (a) 4, (b) 5m, (c) 6m, and (d) 7m in CDCl3
at 20 ꢀC.
DSC measurements of the chromophore-appended polymers
were performed to estimate the glass transition temperatures
Figure 3. UV-vis spectral changes of (a) 5p and (b) 5m upon titration with TCNE (0-1.0 equiv) in chloroform at 20 ꢀC.

Article
Macromolecules, Vol. 43, No. 12, 2010 5283
Figure 4. UV-vis spectral changes of (a) 5p and (b) 5m upon titration with TCNQ (0-1.0 equiv) in o-dichlorobenzene at 160 ꢀC.
Figure 5. Cyclic voltammograms of (a) 5p, (b) 6p, (c) 7p, (d) 5m, (e) 6m, and (f) 7m in CH2Cl2 (þ0.1 M (nC4H9)4NClO4) at 20 ꢀC.
Table 2. Summary of the Electrochemistry Data of the Postfunc-
(Tgs), but they did not show any well-defined transitions in
the range from -50 to 200 ꢀC. Therefore, the synthesized
polymers with unknown Tg values were homogeneously
mixed with poly(methyl methacrylate) (PMMA; Mw =
250 000, Mn = 178 000) at various ratios, and the mixtures
were subjected to the DSC measurements. PMMA displayed
a Tg of 115 ꢀC, and this value gradually increased with the
increasing synthesized polymer content (see Figure 5SI as
an example of 6m). Plots of the synthesized polymer con-
tent vs Tg values were analyzed according to the Fox
tionalized Polymers in CH2Cl2 (þ 0.1 M (nC4H9)4NClO4)a
polymer
Eox,1/V
Ered,1/V
Δ(Eox,1 - Ered,1)/V
λend/nm (eV)
5p
5m
6p
6m
7p
7m
0.28
0.22
0.84
0.79
0.42
0.47
-0.91
-0.95
-0.68
-0.76
1.75
1.74
1.10
1.23
750 (1.65)
760 (1.63)
1150 (1.08)
1130 (1.15)
a Potentials vs Fcþ/Fc. Working electrode: glassy carbon electrode;
-1
equation (Tg = w1/Tg1 þ w2/Tg2, where w is the weight
counter electrode: Pt; reference electrode: Ag/AgCl.

5284 Macromolecules, Vol. 43, No. 12, 2010
Li et al.
Figure 6. TGA curves of polymers (a) 5p, 6p, and 7p and (b) 5m, 6m, and 7m at the heating rate of 10 ꢀC min-1 under flowing nitrogen.
Table 3. Summary of SHG Measurements
polymer
λ
max/nm (eV)a
480 (2.58)
Φb
film thickness/nmc
110
polingd
d15/pm V-1
d33/pm V-1
d33/d15
6p
0.10
before poling
after poling
before poling
after poling
before poling
after poling
before poling
after poling
1.1
1.6
1.9
5.3
0.63
1.8
0.27
0.32
2.3
1.6
3.2
1.6
1.9
0.69
0.81
2.4
2.4
6m
7p
482 (2.57)
0.04
0.51
0.17
150
165
140
0.40
0.97
0.40
0.40
0.95
1.2
712.5 (1.74)
711.5 (1.74)
7m
2.8
a Measured as a thin film state on a glass slide. b Order parameter Φ = 1 - A1/A0, where A0 and A1 are the absorbance of the polymer films before and
after corona poling, respectively. c Measured by a Dektak3ST. d At 9.0 kV and 150 ꢀC for 30 min.
Figure 7. SHG response from film of 6p after poling. (a) Angular dependence of SHG signals. (b, c) Polarization dependence of p-polar and s-polar
SHG signal measured at incident angle of 45ꢀ, respectively. In (b) and (c) polarization angle 0ꢀ corresponds to s-polarization of incident fundamental
field.
fraction and Tg1 and Tg2 are the glass transition temperatures
of each polymer), which enabled estimation of the unknown
Tgs of the chromophore-appended polymers. The estimated
Tg values ranged from 127 to 134 ꢀC (Table 1).
NLO Properties. To evaluate the second-order NLO acti-
vities of the obtained polymers bearing donor-acceptor
chromophores, their thin films were prepared by spin-coating
of the toluene solutions on a hydrophobically treated glass

Article
Macromolecules, Vol. 43, No. 12, 2010 5285
substrate with hexamethyldisilazane. The film thicknesses
were controlled in the range of 110-165 nm. The most
efficient technique for studying the second-order NLO activ-
ities was to investigate the second harmonic generation (SHG)
processes characterized by SHG coefficients (d15 and d33).22
The noncentrosymmetric alignment of the donor-acceptor
chromophores is essential for high SHG, and this is usually
achieved by corona poling. Taking into account the thermal
properties of the polymers, the corona poling was performed
at 9.0 kV and 150 ꢀC, slightly above Tg, for 30 min. Figure 6SI
shows the UV-vis spectra of 6p, 6m, 7p, and 7m before and
after the poling. The λmax values of the polymer thinfilms were
almost the same as those in chlorinated solvents (Table 3). The
solvatochromic investigations of 6p and 6m suggest that the
solid state environment of these polymers corresponds to an
ET(30) of ca. 40 kcal mol-1. Although the absorption wave-
lengths or the CT bands were unchanged, the intensities
explicitly decreased after the poling. The absorbance decrease
in the p-phenylene-linked side chain polymers 6p and 7p was
more significant than that in the corresponding m-phenylene-
linked side chain polymers 6m and 7m. The order parameters
(Φ) are summarized in Table 3.
The SHG measurements were performed at a fundamental
wavelength of 1064 nm using a Nd:YAG laser at 20 ꢀC. From
the angular dependence of the SHG signals, the SHG
coefficients (d15 and d33) were calculated with respect to the
d11 of the quartz crystals (0.50 pm V-1).23 Figure 7 shows an
example of the measured data for the film of 6p after poling.
The specific symmetric shapes of the plots in Figure 7b,c
suggest C¥v symmetry in chromophore ordering, where only
d15 and d33 contribute to the SHG response. The d33 value of
6p after the poling was the largest (5.3 pm V-1) among the
measured polymer samples (Table 3). After the corona
poling of the 6p thin film, the ratio of d33/d15 was almost
doubled and was slightly larger than the theoretical value of
3.24 Although the d33 of 6m and 7m also increased due to the
corona poling, their d33/d15 values were almost unchanged.
This result means that the number of the poled chromo-
phores increased after the poling, but the chromophores
were assumed to obliquely align due to the restricted move-
ments. This effect was most remarkable in the case of 7p. The
d15 is larger than d33 both before and after the poling,
implying the difficulty of the chromophore alignment even
by the poling above the estimated Tg. All of these results
indicate the importance of the isolated space for chromo-
phore alignment. Thus, 6p with the small sized and less
hindered compact donor-acceptor chromophores displayed
the best SHG result. The reasons why the SHG activities
were observed before poling and that the ratio of d33/d15 was
above 3 for 6p are probably attributable to the specific
interfacial interactions between the hydrophobically treated
glass surface and the polymer peripheral substituents, such
as aliphatic chains.
mainly reflects the steric factors in the congested polymer
environments. The final polymers bearing donor-acceptor chro-
mophores displayed intense CT bands at ca. 480 nm for the
TCNE adducts and ca. 710 nm for the TCNQ adducts. Thus, the
polymer colors aretunable from yellow (precursor) to red (TCNE
adducts) and green (TCNQ adducts). The UV-vis absorption
spectra were substantiated by the electrochemical measurements.
The electrochemical band gaps were consistent with the corres-
ponding optical band gaps determined by the end absorptions.
There were no noticeable differences in the linear absorption and
electrochemical properties between the straight p-phenylene
spacer and the bent m-phenylene spacer in the side chain
structure, namely 6p vs 6m or 7p vs 7m. However, when we
further advanced into the SHG measurements with sufficient
thermal stability in mind, a great difference resulted. Polymer 6p
with the straight p-phenylene spacer and the compact TCBD
acceptor moiety in the side chains displayed a much larger d33
value than those of 6m with the bent m-phenylene spacer as well
as 7p and 7m with bulky TCNQ adducted acceptor moieties. This
result clearly indicates the importance of sufficient space for
chromophore movement upon poling. The recent trend in design-
ing organic electrooptic materials is directed toward dendritic
structures utilizing the inner nanospaces.25 Application of the
double click postfunctionalization to the synthesis of dendritic
donor-acceptor molecules and polymers will be worthwhile for
future projects.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research and the Special Coordination Funds
for Promoting Science and Technology from MEXT, Japan.
Supporting Information Available: 13C NMR spectra of
5p, 6p, and 7p, and UV-vis and fluorescence spectral behavior
of 6p, 6m, 7p, and 7m in various solvents and glass transition
temperatures of 6m/PMMA mixtures. This material is available
free of charge via the Internet at http://pubs.acs.org.
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