Synthesis and fluorescence study of conjugated polymers based on 2,4,6-triphenylpyridine moieties

Article abstract of DOI:10.1039/c5nj03722k

Three novel conjugated polymers based on 2,4,6-triphenylpyridine moieties were synthesized by a Pd-catalyzed Sonogashira coupling reaction. The three polymers P-1, P-2 and P-3 showed strong fluorescence emission with large Stokes' shifts and high quantum yields. We also performed a theoretical calculation analysis to predict the electrochemical and optical properties of the conjugated polymers. The results indicated that although the calculated energy levels were higher than those determined by experiments, the trends of P-1, P-2 and P-3 in the band gaps were in good agreement with the ones obtained by UV-vis and CV measurements of the polymers.

Full text of DOI:10.1039/c5nj03722k

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Synthesis and fluorescence study of conjugated
polymers based on 2,4,6-triphenylpyridine moieties†
Cite this:DOI: 10.1039/c5nj03722k
Qianping Ran,a Jianfeng Ma,a Tao Wang,a Shimin Fan,a Yong Yang,a Shuai Qi,a
Yixiang Cheng*b and Fengyan Song*a
Three novel conjugated polymers based on 2,4,6-triphenylpyridine moieties were synthesized by a Pd-catalyzed
Sonogashira coupling reaction. The three polymers P-1, P-2 and P-3 showed strong fluorescence emission with
large Stokes’ shifts and high quantum yields. We also performed a theoretical calculation analysis to predict the
electrochemical and optical properties of the conjugated polymers. The results indicated that although the
calculated energy levels were higher than those determined by experiments, the trends of P-1, P-2 and P-3 in
the band gaps were in good agreement with the ones obtained by UV-vis and CV measurements of the
polymers.
Received (in Montpellier, France)
29th December 2015,
Accepted 28th April 2016
DOI: 10.1039/c5nj03722k
www.rsc.org/njc
not only increases the electron affinity of the polymer,8a,b which
makes the polymer more resistant to oxidation and also gives the
Introduction
Conjugated polymers (CPs) have received much attention due to polymer better electron-transporting properties, but also avoids
their remarkable optical and electrochemical applications fluorescence quenching due to the intersystem crossing (ISC)
including chemical sensors,1 electroluminescent devices,2 field- effect of the heavy atom.10 Some of them have been introduced
effect transistors,3 solar cells,4 and so on. In comparison with the into the polymer backbones to realize the desirable opto-
inorganic counterparts, the main advantages of the organic electronic materials.8,9 So far, however, there have been few
conjugated polymers are their light weight, flexible nature, reports on 2,4,6-triphenylpyridine-based conjugated polymers
solution processability and tunable properties.5 Additionally, with tunable band gaps.
these delocalizable p-electronic conjugated ‘‘molecular wire’’
In this paper, we designed and synthesized three novel
polymers can greatly amplify the fluorescence response signal conjugated polymers based on 2,4,6-trisphenylpyridine moieties
due to facile energy migration along the polymer backbone upon via Sonogashira polymerization. The three polymers P-1, P-2
light excitation.1,6 Moreover, the conjugated polymers can be and P-3 showed strong fluorescence emission with large Stokes’
systematically modified by the incorporation of rational donor and shifts and high quantum yields. The large Stokes’ shifts and
acceptor moieties into the polymer backbone in an alternating relatively high quantum yields not only provide the feasibility
fashion.7
for biological imaging and biosensing applications,11 but also
2,4,6-Triphenylpyridine, as a well-known electron-deficient can achieve high solid state emission intensity or serve as
heterocyclic unit, has been widely used as the conjugated promising electron transporting materials in OLEDs.12 We also
molecular bridge linker to the polymer main chain.8 Pyridine performed a theoretical calculation analysis to predict the
and aromatic heterocyclic derivatives have been widely used as electrochemical and optical properties of the conjugated poly-
electron transporting/hole blocking materials in LED devices mers. The results indicated that although the calculated energy
and LED blends because these units have many excellent levels were higher than those determined by experiments, the
properties of being a better chromophore, with high electron trends of P-1, P-2 and P-3 in the band gaps were in good
affinity, high thermal and oxidative stability, and ability for good agreement with the ones obtained by UV-vis and CV measure-
charge injection and transporting building blocks.9 In addition, ments of the polymers.
introduction of the pyridinyl moiety into the polymer backbone
a State Key Laboratory of High Performance Civil Engineering Materials (HPCEM),
Experimental section
Jiangsu Research Institute of Building Science, Nanjing 210008, Jiangsu, China.
E-mail: songfengyan@cnjsjk.cn
Materials and measurements
b Key Lab of Mesoscopic Chemistry of MOE and Collaborative Innovation Center of
Chemistry for Life Sciences, School of Chemistry and Chemical Engineering,
Nanjing University, Nanjing 210093, P. R. China. E-mail: yxcheng@nju.edu.cn
All solvents and reagents were commercially available and were
of analytical reagent grade. THF and Et3N were distilled from
† Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nj03722k sodium in the presence of benzophenone. NMR spectra were
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obtained using a Bruker Avance 300 spectrometer with 300 MHz 6.99 (dd, J1 = 6.9 Hz, J2 = 3.0 Hz, 2H), 4.02 (t, J = 5.7 Hz, 2H), 1.82
for 1H NMR and 75 MHz for 13C NMR, and reported as parts per (dd, J1 = 7.5 Hz, J2 = 3.6 Hz, 2H), 1.55 (dd, J1 = 8.1 Hz, J2 = 3.6 Hz,
million (ppm) referenced to TMS as the internal standard. 2H), 0.99 (t, J = 6.6 Hz, 3H); 13C NMR (75 MHz, CDCl3): d 160.5,
Electrospray ionization mass spectra (ESI-MS) were measured 156.3, 149.8, 138.6, 132.3, 129.6, 127.9, 127.7, 123.6, 116.5, 115.2,
on a Thermo Finnigan LCQ Fleet system. UV-vis spectra were 67.7, 31.4, 19.3, 13.8. FT-IR (KBr, cmÀ1): 3021, 2954, 2873, 1543,
obtained on a Perkin-Elmer Lambda 25 spectrometer. Fluores- 1364, 1210, 752, 633. Anal. calcd for C27H25NO: C, 85.45; H, 6.64;
cence spectra were obtained from a RF-5301PC spectrometer. N, 3.69. Found: C, 85.53; H, 6.72; N, 3.52.
FT-IR spectra were measured on a Nexus 870 FT-IR spectrometer.
Compound c. A mixture of 4-(diethylamino)benzaldehyde
Elemental analyses were performed on an Elementar Vario (3.54 g, 20 mmol), acetophenone (4.81 g, 40 mmol), ammonium
MICRO analyzer. Thermogravimetric analyses (TGA) were performed acetate (24.0 g, 312 mmol) and acetic acid (100 mL) was heated
on a PerkinElmer Pyris-1 instrument under a N2 atmosphere. and reacted at 115 1C for 24 h. After cooling to 0 1C, the
Molecular weight was determined by gel permeation chromato- precipitates were filtered. The obtained crude product was
graphy (GPC) using a Waters 244 HPLC pump, and THF was recrystallized by methanol to afford the residue. The residue
used a solvent relative to polystyrene standards.
was purified by silica gel chromatography (petroleum ether/
The electrochemical measurements were carried out in ethyl acetate, v/v, 8/1) to afford 4-(2,6-diphenylpyridin-4-yl)-N,N-
1
anhydrous DCM with 0.1 mol LÀ1 tetrabutylammonium hexa- diethylaniline (3.32 g, 43.9%) as a deep yellow solid. H NMR
fluorophosphate (Bu4NPF6) as the supporting electrolyte at a (300 MHz, CDCl3): d 8.05 (d, J = 7.8 Hz, 4H), 7.79 (s, 2H), 7.73
scan rate of 0.05 V sÀ1 at room temperature under the protec- (s, 2H), 7.58–7.67 (m, 6H), 6.78 (d, J = 6.3 Hz, 4H), 3.43 (dd, J1 =
tion of nitrogen. A gold disk was used as a working electrode, 8.7 Hz, J2 = 3.9 Hz, 4H), 1.23 (t, J = 6.9 Hz, 6H); 13C NMR
platinum wire was used as a counter electrode and Ag/AgCl (75 MHz, CDCl3): d 160.7, 156.2, 150.4, 138.3, 131.8, 128.1,
(3.0 mol LÀ1 KCl solution) was used as a reference electrode. 127.9, 123.3, 115.7, 111.9, 44.9, 12.4. FT-IR (KBr, cmÀ1): 3294,
The fluorescence quantum yields were determined by the equation: 3058, 2975, 2137, 1630, 1486, 1281, 787, 632. Anal. calcd for
FF(sample) = (Fsample/Fref)(Aref/Asample)(nsample2/nref2)FF(ref),13 where
F, A and n are the measured fluorescence (area under the emission 7.03; N, 7.13.
C27H26N2: C, 85.68; H, 6.92; N, 7.40. Found: C, 85.81; H,
peak), the absorbance at the excitation position, and the refractive
M-2. A mixture of benzaldehyde (2.12 g, 20 mmol), 1-(4-
index of the solvent, respectively. Rhodamine B (f) = 0.6514 in EtOH bromophenyl)ethanone (7.96 g, 40 mmol), ammonium acetate
and ZnPc (f) = 0.2815 in DMF were used as the reference.
(24.0 g, 312 mmol) and acetic acid (100 mL) was heated and
Density functional theory (DFT) calculations were performed reacted at 115 1C for 24 h. After cooling to 0 1C, the precipitates
on polymer repeat units and the highest occupied molecular were filtered. The obtained crude product was recrystallized by
orbital (HOMO) and the lowest unoccupied molecular orbital methanol to furnish the desired product (yellowish needle
(LUMO) energy levels were estimated from the optimized product, yield: 45.7%, 4.24 g). 1H NMR (300 MHz, CDCl3): d
geometry using the B3LYP functional and the 6-31G(d,p) basis 8.05 (d, J = 8.1 Hz, 4H), 7.85 (s, 2H), 7.71 (d, J = 5.7 Hz, 2H), 7.63
set.16
(d, J = 7.8 Hz, 4H), 7.48–7.57 (m, 3H); 13C NMR (75 MHz, CDCl3):
d 160.5, 156.4, 150.6, 138.6, 138.2, 132.5, 129.2, 128.7, 127.2,
123.7, 117.2. FT-IR (KBr, cmÀ1): 1596, 1533, 1240, 1113, 1054,
Syntheses
Compound a. A mixture of benzaldehyde (2.12 g, 20 mmol), 869, 735, 587. Anal. calcd for C23H15Br2N: C, 59.38; H, 3.25; N,
acetophenone (4.81 g, 40 mmol), ammonium acetate (24.0 g, 3.01. Found: C, 59.13; H, 3.32; N, 3.10. MS (ESI, m/z): 465.0.
312 mmol) and acetic acid (100 mL) was heated and reacted at
M-3. A mixture of 4-(diethylamino)benzaldehyde (3.56 g,
115 1C for 24 h. After cooling to 0 1C, the precipitates were 20 mmol), 1-(4-bromophenyl)ethanone (7.96 g, 40 mmol),
filtered. The obtained crude product was recrystallized by ammonium acetate (24.0 g, 312 mmol) and acetic acid (100 mL)
methanol to furnish the desired product a (colorless crystal, was heated and reacted at 115 1C for 24 h. After cooling to 0 1C,
1
yield: 56.5%, 3.47 g). H NMR (300 MHz, CDCl3): d 8.05 (d, J = the precipitates were filtered. The obtained crude product was
8.1 Hz, 4H), 7.84 (s, 2H), 7.77 (s, 2H), 7.72 (d, J = 6.0 Hz, 2H), recrystallized by methanol to afford the residue. The residue
7.63 (d, J = 7.8 Hz, 4H), 7.46–7.57 (m, 3H); 13C NMR (75 MHz, was purified by silica gel chromatography (petroleum ether/
CDCl3): d 160.4, 156.4, 150.6, 138.4, 137.9, 132.5, 129.1, 128.7, ethyl acetate, v/v, 10/1) to afford 2,6-bis(4-bromophenyl)-4-(4-
127.3, 123.6, 117.2. FT-IR (KBr, cmÀ1): 1632, 1573, 1264, 1135, butoxyphenyl)pyridine (4.75 g, 44.2%) as a colorless crystal.
735, 587. Anal. calcd for C23H17N: C, 89.87; H, 5.57; N, 4.56. 1H NMR (300 MHz, CDCl3): d 8.02 (d, J = 8.4 Hz, 4H), 7.78 (s,
Found: C, 89.80; H, 3.37; N, 3.01.
2H), 7.58–7.67 (m, 6H), 7.02 (dd, J1 = 6.6 Hz, J2 = 2.7 Hz, 2H),
Compound b. A mixture of 4-butoxybenzaldehyde (3.56 g, 4.02 (t, J = 5.4 Hz, 2H), 1.81 (dd, J1 = 7.2 Hz, J2 = 3.3 Hz, 2H),
20 mmol), acetophenone (4.81 g, 40 mmol), ammonium acetate 1.53 (dd, J1 = 8.7 Hz, J2 = 3.9 Hz, 2H), 1.00 (t, J = 6.3 Hz, 3H);
(24.0 g, 312 mmol) and acetic acid (100 mL) was heated and 13C NMR (75 MHz, CDCl3): d 160.3, 156.3, 150.1, 138.3,
reacted at 115 1C for 24 h. After cooling to 0 1C, the precipitates 132.7, 129.6, 128.3, 128.1, 123.6, 116.5, 115.1, 67.9, 31.3, 19.3,
were filtered. The obtained crude product was recrystallized by 13.9. FT-IR (KBr, cmÀ1): 3021, 2931, 2854, 2837, 1599, 1375,
methanol to furnish the desired product b (colorless crystal, 1137, 1086, 823, 752, 633. Anal. calcd for C27H23Br2NO: C,
yield: 50.8%, 3.86 g). 1H NMR (300 MHz, CDCl3): d 8.03 60.36; H, 4.31; N, 2.61. Found: C, 60.57; H, 4.48; N, 2.65. MS
(d, J = 8.1 Hz, 4H), 7.83 (s, 2H), 7.75 (s, 2H), 7.54–7.66 (m, 6H), (ESI, m/z): 537.0.
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M-4. A mixture of 4-(diethylamino)benzaldehyde (3.54 g, Then the mixture was cooled to room temperature and filtered
20 mmol), 1-(4-bromophenyl)ethanone (7.96 g, 40 mmol), through a short silica gel column. Then the polymer was precipitated
ammonium acetate (24.0 g, 312 mmol) and acetic acid (100 mL) in methanol (80 mL). The polymer was filtered and washed with
was heated and reacted at 115 1C for 24 h. After cooling to 0 1C, the methanol several times. Further purification could be con-
precipitates were filtered. The obtained crude product was recrys- ducted by dissolving the polymer in THF to precipitate in
tallized by methanol to furnish the desired product M-4 (yellow methanol again. The polymer was dried in vacuum to afford
solid, yield: 49.5%, 5.31 g). 1H NMR (300 MHz, CDCl3): d 8.05 (d, J = P-3 (48.9 mg, 58.1%) as a deep red solid. GPC results:
1
8.1 Hz, 4H), 7.77 (s, 2H), 7.60–7.66 (m, 6H), 6.79 (d, J = 5.7 Hz, 4H), Mw = 9470, Mn = 6330, PDI = 1.49. H NMR (300 MHz, CDCl3):
3.43 (dd, J1 = 9.3 Hz, J2 = 4.2 Hz, 4H), 1.22 (t, J = 6.6 Hz, 6H); 13C d 8.13–8.42 (m, 3H), 8.04 (d, J = 6.0 Hz, 4H), 7.86 (s, 2H), 7.52–7.71
NMR (75 MHz, CDCl3): d 156.2, 150.3, 138.7, 131.8, 128.1, 127.9, (m, 8H), 7.30–7.48 (m, 3H), 6.78 (d, J = 6.6 Hz, 2H), 4.23–4.31
123.3, 115.8, 112.3, 44.7, 12.6. FT-IR (KBr, cmÀ1): 3342, 3187, 2935, (m, 3H), 3.44 (dd, J1 = 8.7 Hz, J2 = 3.6 Hz, 2H), 1.69–1.88 (m, 3H),
2200, 1566, 1486, 1367, 1217, 1030, 787, 632. Anal. calcd for 1.51–1.62 (m, 2H), 1.01–1.47 (m, 38H), 0.87 (s, 6H). FT-IR (KBr,
C27H24Br2N2: C, 60.47; H, 4.51; N, 5.22. Found: C, 60.72; H, 4.68; cmÀ1): 3342, 3187, 2935, 2854, 2837, 2200, 1933, 1748, 1566, 1486,
N, 5.09. MS (ESI, m/z): 536.0.
1367, 1157, 1049, 775, 632. Anal. calcd for (C61H67N3)n: C, 86.99; H,
P-1. A mixture of M-1 (46.7 mg, 0.1 mmol), M-2 (46.5 mg, 8.02; N, 4.99. Found: C, 86.57; H,7.94; N, 4.85.
0.1 mmol), Pd(PPh3)4 (5.8 mg, 5% mmol), and CuI (1.0 mg,
5% mmol) was added to THF (6 mL) and Et3N (6 mL) under a N2
atmosphere. The reaction mixture was stirred at 75 1C for 48 h.
Then the mixture was cooled to room temperature and filtered
Results and discussion
Synthesis and structural features of the monomers and the
through a short silica gel column. Then the polymer was
precipitated in methanol (80 mL). The polymer was filtered and
washed with methanol several times. Further purification could
be conducted by dissolving the polymer in THF to precipitate in
methanol again. The polymer was dried in vacuum to afford P-1
(43.7 mg, 56.8%) as a deep yellow solid. GPC results: Mw = 12 410,
polymers
The synthetic routes to the monomers and polymers are shown in
Scheme 1. 3,6-Diethynyl-9-octadecyl-9H-carbazole (M-1)17 was pre-
pared according to reported literature methods. M-2 was synthesized
by the reaction of benzaldehyde, 1-(4-bromophenyl)ethanone, and
ammonium acetate in HAc in 45.7% yield. M-3 and M-4 were
synthesized according to the synthetic method of M-2. P-1, P-2 and
P-3 were synthesized by a Pd-catalyzed Sonogashira coupling reac-
tion from M-1 and M-2/M-3/M-4 in yields of 56.8, 61.5 and 58.1%,
respectively (Scheme 2). The chemical structures of the polymers
1
Mn = 7020, PDI = 1.77. H NMR (300 MHz, CDCl3): d 8.13–8.34
(m, 2H), 8.06 (d, J = 6.0 Hz, 4H), 7.86 (s, 2H), 7.72 (d, J = 6.6 Hz,
3H), 7.64 (d, J = 6.6 Hz, 4H), 7.41–7.57 (m, 4H), 4.27(s, 2H), 1.84
(s, 2H), 0.82–1.47 (m, 38H), 0.86 (s, 4H). FT-IR (KBr, cmÀ1): 2237,
1839, 1716, 1596, 1533, 1358, 1240, 1113, 1054, 869, 735, 587.
Anal. calcd for (C57H58N2)n: C, 88.79; H, 7.58; N, 3.63. Found: C,
88.73; H, 7.41; N, 3.54.
1
could be verified by H NMR and IR spectroscopy. The complete
disappearance of the alkyne proton signals at d B 3.3 confirms
the efficient coupling reaction of the alkyne. Meanwhile, the IR
spectrum of P-1/P-2/P-3 also shows no absorption bands at about
B3300 cmÀ1 which are assignable to the stretching vibrations
of RCH. This demonstrates the successful preparation of the target
polymers. As expected, the resonance peaks in the 1H NMR spectra
of polymers are broader than those of monomers due to part to their
longer rotational correlation times. The resulting polymers show
excellent solubility in common organic solvents including THF,
CHCl3 and CH2Cl2. Table 1 summarizes the polymerization results
and thermal properties of the polymers. The number average
molecular weight and the polydispersity index (PDI) of the polymers
measured by GPC were Mn = 7420 and PDI = 1.77 for P-1, Mn = 5970
and PDI = 1.85 for P-2, and Mn = 6330 and PDI = 1.49 for P-3. As
shown in Fig. 1, the TGA curves reveal that the degradation
temperature (Td) of 5% weight loss of P-1, P-2 and P-3 is 254,
226 1C and 279 1C, respectively, which indicates the excellent
thermal stability of the polymers.
P-2. A mixture of M-1 (46.7 mg, 0.1 mmol), M-3 (53.7 mg,
0.1 mmol), Pd(PPh3)4 (5.8 mg, 5% mmol), and CuI (1.0 mg,
5% mmol) was dissolved in THF (6 mL) and Et3N (5 mL) under
a N2 atmosphere. The reaction mixture was stirred for 48 h at
75 1C. Then the mixture was cooled to room temperature and
filtered through a short silica gel column. Then the polymer
was precipitated in methanol (80 mL). The polymer was filtered
and washed with methanol several times. Further purification
could be conducted by dissolving the polymer in THF to
precipitate in methanol again. The polymer was dried in
vacuum to afford P-2 (51.8 mg, 61.5%) as a pale blue solid.
GPC results: Mw = 11 020, Mn = 5970, PDI = 1.85. 1H NMR
(300 MHz, CDCl3): d 8.04–8.33 (m, 3H), 7.98 (d, J = 8.7 Hz, 3H),
7.78 (s, 2H), 7,47–7.70 (m, 7H), 7.32–7.40 (m, 2H), 6.96 (d, J =
8.1 Hz, 2H), 4.12–4.27 (m, 2H), 3.94–4.01 (m, 2H), 1.68–1.87
(m, 4H), 1.47–1.52 (m, 3H), 1.00–1.37 (m, 37H), 0.82–1.00
(m, 4H), 0.74–0.82 (m, 5H). FT-IR (KBr, cmÀ1): 3021, 2931,
2854, 2837, 2237, 1937, 1756, 1599, 1375, 1259, 1137, 1086, 823,
752, 633. Anal. calcd for (C61H66N2O)n: C, 86.89; H, 7.89; N,
3.32. Found: C, 86.67; H, 7.73; N, 3.28.
Optical properties
The UV-vis absorption and fluorescence spectra of the poly-
P-3. A mixture of M-1 (46.7 mg, 0.1 mmol), M-4 (53.6 mg, mers, a, b and c are shown in Fig. 2, and the corresponding
0.1 mmol), Pd(PPh3)4 (5.8 mg, 5% mmol), and CuI (1.0 mg, optical data are listed in Table 2. As shown in UV-vis absorption
5% mmol) was dissolved in THF (6 mL) and Et3N (6 mL) under a spectra (Fig. 2a) measured in solutions (1.0 Â 10À5 mol LÀ1 in
N2 atmosphere. The reaction mixture was stirred for 48 h at 75 1C. CH2Cl2), a, b and c displayed one peak centered at 265 nm,
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Scheme 1 Synthesis of monomers and polymers.
Scheme 2 Chemical structures of the polymers.
274 nm and 255 nm, respectively. P-1, P-2 and P-3 show two
distinct bands in the absorption spectra. One band at the
shorter wavelength region at around 250–295 nm is assigned
to their localized p–p* transition, and the other band at a longer
wavelength at around 350–375 nm is attributed to the intra-
molecular charge transfer (ICT)18 between electron-rich donors
and electron-deficient acceptors. As shown in the emission
spectra of Fig. 2b, the model compounds a, b and c can emit
fluorescence concerted at 359 nm, 354 nm and 415 nm. While
the 2,4,6-trisphenylpyridine unit is introduced into the main
chain backbone of the conjugated polymer, the maximum
Table 1 Molecular weight and thermal properties of polymers
a
b
b
Polymer
Td (1C)
Mw (g molÀ1
)
Mn (g molÀ1
)
PDI
P-1
P-2
P-3
254
226
279
12 410
11 020
9470
7020
5970
6330
1.77
1.85
1.49
a
b
Temperature of 5% weight loss measured by TGA in nitrogen. Molar
mass (Mn, Mw) and polydispersity index (PDI) were determined by GPC
in THF against polystyrene standards with UV detection set to absorp-
tion maxima.
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Table 2 Summary of optical properties of P-1, P-2 and P-3 (1.0 Â
10À5 mol LÀ1, CH2Cl2)
lex (nm) lmax (nm) Stokes shift (cmÀ1
)
FF
a
b
labs (nm)
a
b
c
265, 318
274
255, 292, 353 295
263
264
359
354
415
439
430
470
9.88 Â 103
8.24 Â 103
1.39 Â 104
1.57 Â 104
1.06 Â 104
1.84 Â 104
—
—
—
0.37
0.43
0.26
P-1 260, 319, 355 355
P-2 295, 352 361
P-3 252, 318, 353 365
a
The emission wavelength lmax of the conjugated polymers P-1, P-2 and
b
P-3. Quantum yields were determined with ZnPc as fluorescence
reference in DMF (F = 0.28).
Fig. 1 TGA curves of the conjugated polymers P-1, P-2 and P-3.
Fig. 2 (a) Normalized UV-vis absorption spectra in CH2Cl2 solutions and (b)
normalized emission spectra in CH2Cl2 solutions of a, b, c, P-1, P-2, and P-3.
emission peaks of P-1 (439 nm), P-2 (430 nm) and P-3 (470 nm)
appear red-shifted by 80, 76 and 65 nm, respectively, indicating
an efficient extension of p-conjugation along the linkers. Such
an obvious result suggests that the 2,4,6-trisphenylpyridine
based polymer shows large Stokes’ shifts and obvious fluores-
cence emission, which is expected to be used as potential
fluorescent materials.
Electrochemical properties
The redox behaviors of the three polymers were measured by
cyclic voltammetry (CV) in a deoxygenated CH2Cl2 solution at a Fig. 3 Cyclic voltammograms of the polymers P-1, P-2 and P-3.
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Table 3 Electrochemical data for P-1, P-2 and P-3, and the calculated
HOMO and LUMO energy values
are shown in Fig. 3, and the electrochemical data are summar-
ized in Table 3. The three conjugated polymers underwent
irreversible or quasi-reversible oxidation and reduction waves.
In their oxidation traces, the onset potentials of P-1, P-2 and P-3
occurred at +0.87 eV, +0.9 eV and +0.85 eV, respectively,
essentially arising from the oxidation of electron-donating
carbazole units. In their reduction traces, P-1, P-2 and P-3
exhibited similar onset potentials at À0.72 eV, À0.87 eV and
À0.68 eV, which can be assigned to the reduction of the
electron-accepting 2,4,6-tris(4-phenoxy)-pyridine moiety. The
highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) energy levels of the
polymers can be calculated according to the equations HOMO =
Àe(Eooxnset + 4.8) (eV) and LUMO = Àe(Eroendset + 4.8) (eV).19 On the
From CVa
From calculation
onset b
ox
onset b
red
c
d
E
HOMOc
E
LUMOc Eg
HOMOd LUMOd Eg
(V)
(eV)
(V)
(eV)
(eV) (eV)
(eV)
(eV)
P-1 0.87
P-2 0.90
P-3 0.85
À5.67
À5.70
À5.65
À0.72 À4.08 1.59 À5.15
À0.87 À3.93 1.77 À5.21
À0.68 À4.12 1.53 À5.24
À2.64
À2.47
À2.92
2.51
2.74
2.32
a
The ferroncene–ferrocenium couple (Fc/Fc+) was used as the internal
reference and under our experimental conditions, E(Fc+/Fc) = 0.42 V vs.
Ag/AgCl. Eox and Ered determined from the onset potentials of the
b
c
d
oxidation and reduction waves. Eg = LUMO À HOMO. DFT quantum
mechanical calculations (B3LYP/6-31G*).
scan rate of 50 mV sÀ1. All measurements were performed in basis of these onset potentials, the HOMO/LUMO energy levels
N2-saturated solutions containing 0.1 M tetrabutylammonium of P-1, P-2 and P-3 were determined to be À5.67/À4.08 eV,
hexafluorophosphate (Bu4NPF6) as the supporting electrolyte, and À5.70/À3.93 eV and À5.65/À3.93 eV with the corresponding
redox potentials were calibrated using a ferrocene–ferrocenium electrochemical band gaps of 1.59, 1.77 eV and 1.53 eV,
(Fc–Fc+) redox couple as an external standard. Platinum wire was respectively. This demonstrated that the energy levels of con-
used as a counter electrode and a Ag/AgCl electrode was used as a jugated polymers can be effectively tuned by changing the
reference electrode. The polymers were deposited onto the working donor and acceptor moieties in the polymer main-chain
electrode from CH2Cl2 solution. The CV curves of P-1, P-2 and P-3 backbone.
Fig. 4 The LUMO and HOMO energy levels of the repeating unit from DFT calculations.
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Molecular orbital calculations
Acknowledgements
¨
According to Hoger’s report and Huang’s report, there is a
This work was supported by the National Natural Science
Foundation of China (No. 51278232, 51408274 and 51508242)
and Natural Science Foundation of Jiangsu Province of China
(BK20130048, BK20131011 and BK20151012).
nearly proportional relationship between the experimentally
determined (CV) and the theoretically calculated energy levels
for the HOMOs and LUMOs of these polymers.5b,20 The result
indicates that the frontier molecular orbital energy levels of
polymers could be predictably tuned through theoretical calcu-
lations of model molecules. To gain a better insight into the Notes and references
geometric and electronic structures, we performed a theoretical
1 (a) F. Song, G. Wei, L. Wang, J. Jiao, Y. Cheng and C. Zhu,
calculation analysis on the model molecules 1, 2 and 3 con-
stituting the corresponding repeat units (Fig. 4). All calcula-
tions were performed using the Gaussian 09 program suite by
using the B3LYP method and the 6-31G* basis set.16 Moreover,
all the alkyl chains were replaced by methyl and methoxy
groups in the calculation for simplicity. Fig. 4 displays the
LUMO and the HOMO of model 1–3. The calculated HOMO,
LUMO and energy gaps (Eg) of the three models are listed in
Table 3. As shown in Fig. 4, the LUMO of the three model
compounds is mainly localized at the central core of 2,4,6-
tris(4-phenoxy)-pyridine with a strong contribution to the nitro-
gen atom, whereas the HOMO localization is not only centered
on the core of the tris(4-phenoxy)-pyridine unit with small
coefficients, but also partially at the donor carbazole moiety
in the polymer backbone. The calculated data show that the
model molecules of P-1, P-2 and P-3 have the LUMO and HOMO
energy levels in the range of À2.47 to À2.92 eV and À5.15 to
À5.24 eV, respectively. The band gaps were determined to be
2.51 eV, 2.74 eV and 2.32 eV for P-1, P-2 and P-3. The LUMO
energy level of model 2 is higher than that of models 1 and 3
indicating that the electron accepting ability of M-2 is stronger
than that of M-1 and M-3. It can also be found that the order of
band gap (Eg) was model 2 4 model 1 4 model 3, which is
almost consistent with the UV-vis absorption maxima of the
polymers in the order P-3 o P-1 o P-2. Although the calculated
energy levels were higher than those determined by experi-
ments, the trends of P-1, P-2 and P-3 in the band gaps were in
good agreement with the ones obtained by UV-vis and CV
measurements of the polymers.
J. Org. Chem., 2012, 77, 4759–4764; (b) J. Hou, F. Song,
L. Wang, G. Wei, Y. Cheng and C. Zhu, Macromolecules,
2012, 45, 7835–7842; (c) F. Song, N. Fei, F. Li, S. Zhang,
Y. Cheng and C. Zhu, Chem. Commun., 2013, 49, 2891–2893;
(d) G. Wei, S. Zhang, C. Dai, Y. Quan, Y. Cheng and C. Zhu,
Chem. – Eur. J., 2013, 19, 16066–16071; (e) G. Wei, Y. Jiang,
F. Li, Y. Quan, Y. Cheng and C. Zhu, Polym. Chem., 2014, 5,
5218–5222; ( f ) F. Li, G. Wei, Y. Sheng, Y. Quan, Y. Cheng
and C. Zhu, Polymer, 2014, 55, 5689–5694; (g) F. Song,
G. Wei, X. Jiang, F. Li, Y. Cheng and C. Zhu, Chem. Com-
mun., 2013, 49, 5772–5774.
2 (a) B. G. Kang, H. Kang, N. G. Kang, C. L. Lee, K. Lee and
J. S. Lee, Polym. Chem., 2013, 4, 969–977; (b) L. P. Lu, D. Kabra
and R. H. Friend, Adv. Funct. Mater., 2012, 22, 4165–4171;
(c) J. J. Intemann, E. S. Hellerich, B. C. Tlach, M. D. Ewan,
C. A. Barnes, A. Bhuwalka, M. Cai, J. Shinar, R. Shinar and
M. Jeffries-EL, Macromolecules, 2012, 45, 6888–6897;
(d) P. Zalar, Z. B. Henson, G. C. Welch, G. C. Bazan and
T. Q. Nguyen, Angew. Chem., Int. Ed., 2012, 51, 7459–7498;
(e) C. C. Cheng, Y. L. Chu, P. H. Huang, Y. C. Yen, C. W. Chu,
A. C. M. Yang, F. H. Ko, J. K. Chen and F. C. Chang, J. Mater.
Chem., 2012, 22, 18127–18131.
3 (a) C. Cheng, C. Yu, Y. Guo, H. Chen, Y. Fang, G. Yu and
Y. Liu, Chem. Commun., 2013, 49, 1998–2000; (b) J. Kim,
S. H. Kim, T. K. An, S. Park and C. E. Park, J. Mater. Chem.,
2013, 1, 1272–1278; (c) W. Zhou, Y. Wen, L. Ma, Y. Liu and
X. Zhan, Macromolecules, 2012, 45, 4115–4121.
4 (a) Z. Li, S. W. Tsang, X. Du, L. Scoles, G. Robertson,
Y. Zhang, F. Toll, Y. Tao, J. Lu and J. Ding, Adv. Funct.
Mater., 2011, 21, 3331–3336; (b) Y. Wu, Y. Jing, X. Guo,
S. Zhang, M. Zhang, L. Huo and J. Hou, Polym. Chem., 2013,
4, 536–541; (c) Y. J. Cheng, S. H. Yang and C. S. Hsu, Chem.
Rev., 2009, 109, 5868–5923; (d) L. Dou, J. Gao, E. Richard,
J. You, C. C. Chen, K. C. Cha, Y. He, G. Li and Y. Yang, J. Am.
Chem. Soc., 2012, 134, 10071–10079; (e) A. Balan, D. Baran
and L. Toppare, Polym. Chem., 2011, 2, 1029–1043; ( f ) J.-T.
Chen and C.-S. Hsu, Polym. Chem., 2011, 2, 2702–2722.
5 (a) X. Ma, X. Mao, S. Zhang, X. Huang, Y. Cheng and C. Zhu,
Polym. Chem., 2013, 4, 520–527; (b) X. Ma, X. Jiang, S. Zhang,
X. Huang, Y. Cheng and C. Zhu, Polym. Chem., 2013, 4,
4396–4404; (c) X. Jiang, X. Liu, Y. Jiang, Y. Quan, Y. Cheng
and C. Zhu, Macromol. Chem. Phys., 2014, 215, 358–364;
(d) X. Ma, E. A. Azeem, X. Liu, Y. Cheng and C. Zhu, J. Mater.
Chem. C, 2014, 2, 1076–1084; (e) S. Zhang, Y. Sheng, G. Wei,
Y. Quan, Y. Cheng and C. Zhu, J. Polym. Sci., Part A: Polym.
Chem., 2014, 52, 1686–1692.
Conclusions
In summary, we have successfully synthesized three novel
polymers P-1, P-2 and P-3 containing carbazole units and
2,4,6-trisphenylpyridine moieties in the main chain by a Pd-
catalyzed Sonogashira coupling reaction. The UV-vis absorption
and fluorescence spectra indicate that the introduction of
2,4,6-trisphenylpyridine moieties into the conjugated polymer
could significantly affect the optical properties of the polymers.
Also, the CV and calculated data further demonstrate that
although the calculated energy levels were higher than those
determined by experiments, the trends of P-1, P-2 and P-3 in the
band gaps were in good agreement with the ones obtained by
UV-vis and CV measurements of the polymers. These photo-
physical and electrochemical properties indicate that the poly-
mers might have potential device-based applications.
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6 (a) S. W. Thomas III, G. D. Joly and T. M. Swager, Chem. Rev.,
2007, 107, 1339–1386; (b) S. Rochat and T. M. Swager, ACS
Appl. Mater. Interfaces, 2013, 5, 4488–4502.
7 (a) B. S. Harrison, M. B. Ramey, J. R. Reynolds and K. S. Schanze,
J. Am. Chem. Soc., 2000, 122, 8561–8562; (b) D. L. Wang, J. Wang,
D. Moses, G. C. Bazan and A. J. Heeger, Langmuir, 2001, 17,
1262–1266; (c) N. DiCesare, M. R. Pinto, K. S. Schanze and
J. R. Lakowicz, Langmuir, 2002, 18, 7785–7787; (d) M. R. Pinto,
Y. Zhong, S. Wu, B. Chu, Y. Su and Y. He, J. Am. Chem. Soc.,
2016, 138, 4824–4831.
12 (a) Y. Zhou, J. W. Kim, R. Nandhakumar, M. J. Kim, E. Cho,
Y. S. Kim, Y. H. Jang, C. Lee, S. Han, K. M. Kim, J.-J. Kim and
J. Yoon, Chem. Commun., 2010, 46, 6512–6514; (b) X. Ma,
J. Jiao, J. Yang, X. Huang, Y. Cheng and C. Zhu, Polymer,
2012, 53, 3894–3899; (c) D. Frath, J. Massue, G. Ulrich and
R. Ziessel, Angew. Chem., Int. Ed., 2014, 53, 2290–2310.
B. M. Kristal and K. S. Schanze, Langmuir, 2003, 19, 6523–6533. 13 D. F. Eaton, Pure Appl. Chem., 1988, 60, 1107–1114.
8 (a) J. A. Mikroyannidis, P. A. Damouras, V. G. Maragos, 14 G. E. Crosby and J. N. Denmas, J. Phys. Chem., 1971, 75,
L. R. Tsai and Y. Chen, Eur. Polym. J., 2009, 45, 284–294;
(b) A. Kraft, A. C. Gromsdale and A. B. Holmes, Angew. 15 X. J. Jiang, S. L. Yeung, P. C. Lo, W. P. Fong and D. K. P. Ng,
Chem., Int. Ed., 1998, 37, 402–444; (c) T. Kanbara, N. Saito, J. Med. Chem., 2011, 54, 320–330.
T. Yamamoto and K. Kubota, Macromolecules, 1991, 24, 16 (a) R. Yoshii, A. Nagai and Y. Chujo, J. Polym. Sci., Part A: Polym.
991–1024.
5883–5885; (d) T. Kanbara, T. Kushida, N. Saito,
I. Kuwajima, K. Kubota and T. Yamamoto, Chem. Lett.,
1992, 583–586; (e) Y. W. Wang, D. D. Gebler, D. K. Fu,
T. M. Swager, A. G. MacDiarmid and A. J. Epstein, Synth.
Met., 1997, 85, 1179–1182.
Chem., 2010, 48, 5348–5356; (b) R. Gresser, H. Hartmann,
M. Wrackmeyer, K. Leo and M. Riede, Tetrahedron, 2011, 67,
7148–7155; (c) M.-J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M.-A. Robb, J. R. Cheeseman, J. A. Montgomery and
J.-A. Pople, et al., Gaussian 03, Revision C. 02, Gaussian, Inc.,
Wallingford CT, 2004.
9 (a) K. J. Fallon, N. Wijeyasinghe, N. Yaacobi-Gross, R. S.
Ashraf, D. M. E. Freeman, R. G. Palgrave, M. Al-Hashimi, 17 T. Kanbara, N. Saito, T. Yamamoto and K. Kubota, Macro-
T. J. Marks, I. McCulloch, T. D. Anthopoulos and H. Bronstein, molecules, 1991, 24, 5883–5885.
Macromolecules, 2015, 48, 5148–5154; (b) D. Liu, W. Zhao, 18 (a) X. Peng, F. Song, E. Lu, Y. Wang, W. Zhou, J. Fan and
S. Zhang, L. Ye, Z. Zheng, Y. Cui, Y. Chen and J. Hou, Macro-
molecules, 2015, 48, 5172–5178; (c) Y. Kim, D. X. Long, J. Lee,
G. Kim, T. J. Shin, K. W. Nam, Y. Y. Noh and C. Yang,
Macromolecules, 2015, 48, 5179–5187; (d) J. H. Wu and
G. S. Liou, Polym. Chem., 2015, 6, 5225–5232.
Y. Gao, J. Am. Chem. Soc., 2005, 127, 4170–4171; (b) G. Qian,
Z. Zhong, M. Luo, D. Yu, Z. Zhang, D. Ma and Z. Y. Wang,
J. Phys. Chem. C, 2009, 113, 1589–1595; (c) F. Song, X. Ma,
J. Hou, X. Huang, Y. Xiang and C. Zhu, Polymer, 2011, 52,
6029–6036.
10 N. J. Turro, Modern molecular Photochemistry, Benjamin/ 19 (a) C.-C. Ho, Y.-C. Liu, S.-H. Lin and W.-F. Su, Macromolecules,
Cummings Publ. Co., New York, 1978, p. 48.
2012, 45, 813–820; (b) X. Ma, J. Jiao, J. Yang, X. Huang,
Y. Cheng and C. Zhu, Polymer, 2012, 53, 3894–3899; (c) Y. Ie,
J. Huang, Y. Uetani, M. Karakawa and Y. Aso, Macromolecules,
2012, 45, 4564–4571.
11 (a) X. Zhang, J. Yu, Y. Rong, F. Ye, D. T. Chiu and K. Uvdal,
Chem. Sci., 2013, 4, 2143–2151; (b) I. Wu, J. Yu, F. Ye,
Y. Rong, M. E. Gallina, B. S. Fujimoto, Y. Zhang, Y.-H.
Chan, W. Sun, X.-H. Zhou, C. Wu and D. T. Chiu, J. Am. 20 (a) F. M. Pasker, S. M. Le Blanc, G. Schnakenburg and
¨
Chem. Soc., 2015, 137, 173–178; (c) S.-Y. Liou, C.-S. Ke, J.-H.
Chen, Y.-W. Luo, S.-Y. Kuo, Y.-H. Chen, C.-C. Fang and
C.-Y. Wu, ACS Macro Lett., 2016, 5, 154–157; (d) B. Song,
S. Hoger, Org. Lett., 2011, 13, 2338–2341; (b) T. Tao,
Y. X. Peng, W. Huang and X. Z. You, J. Org. Chem., 2013,
78, 2472–2481.
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