Synthesis and characterization of 2-alkylbenzotriazole-based donor-π-acceptor-type copolymers

Article abstract of DOI:10.1055/s-0033-1339177

Four donor-π-acceptor-type copolymers were synthesized via palladium-catalyzed Sonogashira coupling reaction. The resulting donor-π-acceptor-conjugated copolymers can show fluorescence emission in the range of λ = 473-568 nm, and the band gaps of the alternating polymers can be tuned in the range 3.09-3.74 eV by using four different donors. Georg Thieme Verlag Stuttgart · New York.

Full text of DOI:10.1055/s-0033-1339177

LETTER
▌1505
lSetyternthesis and Characterization of 2-Alkylbenzotriazole-Based Donor-π-
Acceptor-Type Copolymers
Synthesis of 2-Alkylbenzotriazole-Based Donor-π-Acceptor-Type Copolymers
Xuerong Mao, Xiaoxiang Jiang, Hongwen Hu, Yixiang Cheng,* Chengjian Zhu*
Key Lab of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093,
P. R. of China
Fax +86(25)83317761; E-mail: yxcheng@nju.edu.cn; E-mail: cjzhu@nju.edu.cn
Received: 03.04.2013; Accepted after revision: 08.05.2013
paper we synthesized four novel D-π-A-conjugated copo-
lymers by using alkyl-substituted phenothiazine and thio-
phene as donors, 2-alkylbenzotriazole as acceptor, and
Abstract: Four donor-π-acceptor-type copolymers were synthe-
sized via palladium-catalyzed Sonogashira coupling reaction. The
resulting donor-π-acceptor-conjugated copolymers can show fluo-
rescence emission in the range of λ = 473–568 nm, and the band alkyne linker as π-bridge linker.
gaps of the alternating polymers can be tuned in the range 3.09–3.74
eV by using four different donors.
The monomers and four polymers were synthesized as
1
0
shown in Scheme 1. Compound 2, 3,7-dibromo-10-octa-
Key words: donor-π-acceptor, conjugated copolymers, benzotri-
azoles, fluorescence
11
decyl-10H-phenothiazine (M2), 3,7-dibromo-10-octa-
12
decyl-10H-phenothiazine-5,5-dioxide (M3), and 3,7-
bis(5-bromothiophen-2-yl)-10-octadecyl-10H-phenothi-
1
3
azine (M4), and 3,7-bis(5-bromothiophen-2-yl)-10-
octadecyl-10H-phenothiazine-5,5-dioxide (M5) were
prepared according to the literature. 4,7-Diethynyl-2-
octyl-2H-benzo[d][1,2,3]triazole (M1) could be obtained
by Sonogashira coupling reaction of 4,7-dibromo-2-octyl-
Conjugated polymers (CP) incorporating different elec-
tron-donating (D) units and electron-accepting (A) het-
erocycle groups have attracted much more attention on
many optoelectronic applications of prospective materi-
12
1
als. In recent years, many ground-breaking contributions
2
H-benzo[d][1,2,3]triazole (2) with trimethylsilylacety-
have been devoted to the construction of novel multifunc-
tional polymer materials due to their advantages on low
cost, mechanical flexibility, low weight, large-scale pro-
lene (TMSA), and then the hydrolytic reaction was carried
out by a KOH solution. D-π-A-type copolymers of P1, P2,
P3, and P4 were synthesized via Sonogashira cross-cou-
pling reaction of M1 with M2, M3, M4, and M5 by using
Pd(PPh ) as a catalyst in DMF–Et N at 80 °C for 48 hours
2
duction, and so on. One of the plausible strategies has
been confirmed by designing D-A-type polymers at well-
defined molecular level, which can tune the highest occu-
pied molecular orbital (HOMO) and lowest unoccupied
molecular orbital (LUMO) energy levels to absorb visible
wavelength photons as well as enhance the intramolecular
3
4
3
14
under N atmosphere, respectively. These resulting D-π-
2
A-conjugated copolymers show fluorescence emission in
the range of λ = 473–568 nm, and the band gaps of the co-
polymers can be tuned in the range of 3.09–3.74 eV,
which is attributed to the minimization of steric effects be-
tween donator and acceptor. The newly synthesized poly-
mers are readily soluble in common organic solvents,
such as THF, CHCl , and CH Cl , which is crucial for its
3
charge transfer (ICT) efficiency. Recently, many novel
D-A polymers have been widely explored by introducing
various strong electron-rich groups and electron-accept-
4
ing counterparts in the main chain backbone. Compared
3
2
2
with D-A-type polymers, the D-π-A counterparts can also
exhibit excellent photovoltaic properties due to the effec-
tive charge transport along the delocalized π-conjugation
purification and the deposition of high-quality film for ef-
6a
ficient optoelectronic devices. The number-average mo-
lecular weights (M ), the weight-average molecular
n
5
polymer backbone. To the best of our knowledge, the
weight (M ), and the polydispersity index (PDI) values of
w
work on the design and synthesis of D-π-A-type polymers
still remains elusive.
copolymers are listed in Table 1. M and PDI of the copo-
w
lymers measured by GPC are M = 17240 and PDI = 1.60
w
for P1, M = 15790 and PDI = 1.44 for P2, = 15780
2
-Alkylbenzotriazole (BTA) has been wildly employed as
w
Mw
6
and PDI = 1.23 for P3, and M = 17910 and PDI = 1.78
an electron-accepting moiety in the past years. However,
w
incorporation of BTA into D-π-A-conjugated polymer for P4. As shown in Figure 1, the TGA curves indicate
7
main chain received less attention. Chen reported three that the polymers have relatively high thermal stability
BTA-based conjugated polymers with good solubility in without 5% weight loss before 320 °C, which can provide
8
6b
common organic solvents and good thermal stability. The desirable thermal properties for practical applications.
You group also designed D-π-A-type copolymers based
The absorption spectra of the copolymers P1–P4 were
on the BTA group which show high hole mobility and
measured in CH Cl as shown in Figure 2 and Table 2. In
2
2
9
high power conversion efficiency (PCE) up to 7%. In this
the absorption spectra the following S0→S1 (π–π*) tran-
sitions appear at λ = 438 nm for P1, λ = 399 nm for P2, λ =
394 nm for P3, λ = and 475 nm for P4, and shorter wave-
SYNLETT 2013, 24, 1505–1508
Advanced online publication: 14.06.2013
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6
lengths in the range of λ = 250–360 nm can be ascribed to
the S0→S2 (π–π*) transition. Compared with P1, the
DOI: 10.1055/s-0033-1339177; Art ID: ST-2013-W0300-L
Georg Thieme Verlag Stuttgart · New York
©

1506
X. Mao et al.
LETTER
Table 2 Optoelectronic Properties and Fluorescent Quantum Yields
–
5
(
?) of Four Polymers (1.0·10 mol/L, CH Cl )
2 2
Polymer Absorption Emission Quantum yield HOMO HUMO
(
nm)
(nm)
(%)
(eV)
(eV)
P1
P2
P3
P4
438
399
494
475
505
473
568
528
45a
38
31
40
–5.23
–5.82
–4.96
–5.22
–1.75
–2.09
–1.87
–2.00
The emissive wavelengths of four polymers are observed
at λ = 505, 473, 568, and 528 nm for P1, P2, P3, and P4,
respectively (Figure 3). When thiophene units are intro-
duced into the main chain backbone, the emission peak of
P3 (λ = 568 nm), and P4 (λ = 528 nm) are red-shifted by
Figure 1 TGA curve of the four conjugated copolymers
Table 1 Molecular Weights and Thermal Properties of Copolymers
6
3 nm and 55 nm, referred to P1 and P2, respectively. It
b
b
Polymer
Tempdec. (°C)a M (g/mol)
M (g/mol) PDI
w
n
is also worth mentioning that introduction of the electron-
deficient sulfone group into the conjugated polymer P2
main chain backbone leads to obvious blue-shift (32 nm)
for the emission wavelength. Four polymers have high
quantum yields, such as 45% for P1, 38% for P2, 31% for
P3, and 40% for P4, due to the effective intramolecular
charge transfer between D and A units via the π-bridge
P1
P2
P3
350
370
320
410
10740
10920
12850
10080
17240
15790
15780
17910
1.60
1.44
1.23
1.78
P4
5a
a
linker.
Temperature of 5% weight loss measured by TGA in nitrogen.
Molar mass (M , M ) and polydispersity index (PDI) were deter-
mined by GPC in THF against polystyrene standards with UV detec-
tion set at absorption maxima.
b
n
w
To further shed light on the electronic properties of four
D-π-A-conjugated copolymers, computational studies of
the molecular orbitals of their model compounds were
carried out by using density functional theory (DFT) ap-
maximum absorption peak of the copolymer P3 shows an proaches at the B3LYP/6-31G (d, p) level. All the alkyl
obvious red-shift (63 nm), which can be attributed to the groups were replaced with an ethyl group to simplify the
introduction of two thiophenyl groups to the phenothi- calculation. As is evident from Figure 4, the HOMO iso-
azine moiety. The similar results are obtained for P4 and surfaces of all compounds show delocalization of the
P2.
HOMO across the whole conjugated backbone structure,
1
)
TMS
Pd(PPh3)2Cl2, CuI
1
2
) Br(CH2)7Me
NaOH
Br
Br
N
N
N
) Br2, HBr
N
N
2) KOH, MeOH
HN
N
N
C8H17
N
C8H17
M1
1
2
Pd(PPh3)4, CuI
Ar
Br Ar
Br
+
n
N
N
N
N
N
C8H17
N
C8H17
Ar =
O
O
S
S
S
S
O
O
S
S
N
S
S
N
N
N
C18H37
C18H37
C18H37
C18H37
P1
P2
P3
P4
Scheme 1 Synthesis procedures for the BTA-based conjugated polymers
Synlett 2013, 24, 1505–1508
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of 2-Alkylbenzotriazole-Based Donor-π-Acceptor-Type Copolymers
1507
–
5
Figure 2 UV-vis absorption spectra of P1, P2, P3, and P4 (1.0·10
mol L–1 in CH Cl )
2
2
whereas the LUMOs are mainly localized on the acceptor
core. Compared with model-1, model-2 shows its lower
HOMO level, which can be attributed to the introduction
of the strong electron-deficient sulfone group into the con-
jugated polymer P2 backbone. A smaller HOMO–LUMO
band gap of model-1 than that of model-2 could be ob-
served. The similar result can be found that model-3 has
a lower band-gap energy (13.09 eV) than model-4 (3.22
eV). In addition, when thienyl units were introduced into
the main-chain backbone of the conjugated poymers,
model-3 and model-4 showed lower band-gap energies
than model-1 or model-2. Further, the calculation results
of the model compounds show model-3 < model-4 <
Figure 4 HOMO and LUMO surface plots for model-1, model-2,
model-3, and model-4
Acknowledgment
model-1 < model-2 in the HOMO–LUMO gap, which are This work was supported by the National Natural Science Founda-
excellently identical to the order of the absorption maxima tion of China (No. 21074054, 51173078, 21172106), National
Basic Research Program of China (2010CB923303).
of the UV-vis absorption in the order of P3 > P4 > P1 > P2.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett. SnuIpofoipmngr irtSatnoIuipfog
r
t
iornat
References and Notes
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(
2
(
Figure 3 Fluorescence spectra of P1, P2, P3, and P4
U. Angew. Chem. Int. Ed. 2008, 47, 4070.
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In summary, four 2-alkylbenzotriazole-based donor-π-
acceptor-type copolymers incorporating various donors in
the main chain backbone could be synthesized via palladi-
um-catalyzed Sonogashira coupling reaction and exhibit
high fluorescence quantum yields with tunable band gaps.
They are expected to be used as the potential optical ma-
terials.
Photovoltaics: Materials, Device Physics, and
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©
Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 1505–1508

1508
X. Mao et al.
LETTER
(
3) (a) Kim, J.; Yun, M. H.; Anant, P.; Cho, S.; Jacob, J.; Kim,
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(14) Synthesis Procedures for the BTA-Based Conjugated
Polymers
2
010, 22, 4890. (c) Cui, C. H.; Fan, X.; Zhang, M. J.; Zhang,
J.; Min, J.; Li, Y. F. Chem. Commun. 2011, 47, 11345.
d) Huo, L. J.; Hou, J. H.; Zhang, S. Q.; Chen, H. Y.; Yang,
Synthesis of P1
(
To a 100 mL Schlenk flask, M-1 (0.14 g, 0.05 mmol), M2
(0.31 g, 0.05 mmol), Pd(PPh ) (2.9 mg, 0.03 mmol), and
Y. Angew. Chem. Int. Ed. 2010, 122, 1542. (e) Bronstein, H.;
Chen, Z. Y.; Ashraf, R. S.; Zhang, W. M.; Du, J. P.; Durrant,
J. R.; Tuladhar, P. S.; Song, K.; Watkins, S. E.; Geerts, Y.;
Wienk, M. M.; Janssen, R. A. J.; Anthopoulos, T.;
Sirringhaus, H.; Heeney, M.; McCulloch, I. J. Am. Chem.
Soc. 2011, 133, 3272.
3
4
CuI (0. 5 mg, 0.003 mmol) were added in 10 mL THF and
Et N (6 mL) under N atmosphere. The mixture was stirred
3
2
at 90 °C for 2 d. The solvent was evaporated under vacuum
after the mixture was cooled to r.t. The residue was dissolved
and in CH Cl (100 mL) and filtered; the filtrate was then
2
2
(
5) (a) Ma, X.; Mao, X. R.; Zhang, S. W.; Huang, X. B.; Cheng,
Y. X.; Zhu, C. J. Polym. Chem. 2013, 4, 520. (b) Wu, Y. Z.;
Ma, X.; Jiao, J. M.; Cheng, Y. X.; Zhu, C. J. Synlett 2012,
concentrated and added to MeOH to precipitate the polymer.
The polymer was dried in vacuum to give 210 mg of product
in 58% yield. GPC results: M = 17240, M = 10740,
w
n
1
2
3, 778. (c) Wang, X. C.; Chen, S.; Sun, Y. P.; Zhang, M. J.;
Li, Y. F.; Li, X. Y.; Wang, H. Q. Polym. Chem. 2011, 2,
872. (d) Baek, N. S.; Hau, S. K.; Yip, H. L.; Acton, O.;
Chen, K. S.; Jen, A. K. Y. Chem. Mater. 2008, 20, 5734.
e) Wang, X. C.; Sun, Y. P.; Chen, S.; Guo, X.; Zhang, M.
J.; Li, X. Y.; Li, Y. F.; Wang, H. Q. Macromolecules 2012,
5, 1208. (f) Woo, C. H.; Beaujuge, P. M.; Holcombe, T.
W.; Lee, O. P.; Fréchet, J. M. J. J. Am. Chem. Soc. 2010, 132,
PDI = 1.54. H NMR (300 MHz, CDCl ): δ = 7.24–7.21 (m,
3
6 H), 6.69–6.66 (m, 2 H), 3.77–3.76 (m, 4 H), 1.75–0.85 (m,
50 H). Anal. Calcd for (C H N S) : C, 78.85; H, 9.10; N,
2
4
8
64
4
n
7.66; S, 4.39. Found: C, 78.23; H, 9.16; N, 7.84; S, 4.27.
Synthesis of P2
(
P2 was synthesized from monomers M-1 and M-3 in 70%
yield by following in the same procedure used for the
preparation of P1. GPC results: M = 17240, M = 10050,
4
w
n
1
15547. (g) Zhang, M. J.; Guo, X.; Li, Y. F. Macromolecules
PDI = 1.72. H NMR (300 MHz, CDCl ): δ = 8.45–7.23 (m,
3
2
011, 44, 8798. (h) Bundgaard, E.; Krebs, F. C. Sol. Energy
1 H), 8.21–8.19 (m, 2 H), 7.78–7.16 (m, 5 H), 4.80–4.76 (m,
2 H), 4.20–4.06 (m, 2 H), 1.21–0.85 (m, 50 H). Anal. Calcd
for (C H N O S) : C, 75.55; H, 8.72; N, 7.34; S, 4.20.
Found: C, 75.64; H, 8.63; N, 7.17; S, 4.28.
Synthesis of P3
Mater. Sol. Cells 2007, 91, 954. (i) Cheng, Y. J.; Yang, S.
H.; Hsu, C. S. Chem. Rev. 2009, 109, 5868. (j) Chen, J.; Cao,
Y. Acc. Chem. Res. 2009, 42, 1709. (k) Popere, B. C.; Pelle,
A. M. D.; Thayumanavan, S. Macromolecules 2011, 44,
4
8
62
4
2
n
4
2
767. (l) Duan, C. H.; Huang, F.; Cao, Y. J. Mater. Chem.
012, 22, 10416.
P3 was synthesized from monomers M1 and M4 in
73%yield by following the same procedure used for the
preparation of P1. GPC results: M = 15780, M = 12850,
(
6) (a) Patel, D. G.; Feng, F.; Ohnishi, Y. Y.; Abboud, K. A.;
w
n
1
Hirata, S.; Schanze, K. S.; Reynolds, J. R. J. Am. Chem. Soc.
PDI = 1.23. H NMR (300 MHz, CDCl ): δ = 7.80–8.53 (m,
3
2
012, 134, 2599. (b) Baran, D.; Balan, A.; Celebi, S.;
2 H), 7.40–7.28 (m, 2 H), 7.12–6.81 (m, 6 H), 5.21–4.79 (br,
2 H), 3.83–3.81 (br, 2 H), 2.16–0.84 (m, 50 H). Anal. Calcd
for: (C H N S ) : C, 75.29; H, 7.67; N, 6.27; S, 10.77.
Found: C, 75.18; H, 7.76; N, 6.12; S, 10.95.
Synthesis of P4
Esteban, B. M.; Neugebauer, H.; Sariciftci, N. S.; Toppare,
L. Chem. Mater. 2010, 22, 2978. (c) Hızalan, G.; Balan, A.;
Baran, D.; Toppare, L. J. Mater. Chem. 2011, 21, 1804.
7) Zhang, Z. H.; Peng, B.; Liu, B.; Pan, C. Y.; Li, Y. F.; He, Y.
H.; Zhou, K. C.; Zou, Y. P. Polym. Chem. 2010, 1, 1441.
8) Zhang, L. J.; He, C.; Chen, J. W.; Yuan, P.; Huang, L.;
Zhang, C.; Cai, W. Z.; Liu, Z. T.; Cao, Y. Macromolecules
5
6
68
4 3 n
(
(
P4 was synthesized from monomers M1 and M5 in 73%
yield by following the same procedure used for the
preparation of P1. GPC results: M = 17910, M = 10080,
w
n
1
2
010, 43, 9771.
PDI = 1.78. H NMR (300 MHz, CDCl ): δ = 8.34–8.32 (m,
3
(
9) Price, S. C.; Stuart, A. C.; Yang, L. Q.; Zhou, H. X.; You, W.
2 H), 7.84–7.83 (m, 2 H), 7.60–6.31 (m, 8 H), 4.80–4.82 (br,
2 H), 4.18–4.17 (br, 2 H), 2.26–0.59 (m, 50 H). Anal. Calcd
for (C H N O S ) : C, 72.69; H, 7.41; N, 6.05; O, 3.46; S,
J. Am. Chem. Soc. 2011, 133, 4625.
(
10) Peng, B.; Najari, A.; Liu, B.; Berrouard, P.; Gendron, D.; He,
5
6
66
4
2 3 n
Y.; Zhou, K.; Zou, Y.; Leclerc, M. Macromol. Chem. Phys.
10.40. Found: C, 72.76; H, 7.36; N, 6.01; O, 3.49; S, 10.37.
2
010, 211, 2026.
Synlett 2013, 24, 1505–1508
© Georg Thieme Verlag Stuttgart · New York

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