A novel chemosensor-bipyridyl end capped hyperbranched conjugated polymer

Article abstract of DOI:10.1016/j.cclet.2010.12.024

A novel hyperbranched conjugated chemosensor with bipyridyl groups as periphery groups (BPY-HPV) was synthesized. BPY-HPV was highly sensitive to metal ions (Cu²⁺, Ni²⁺) for the strong coordination interaction (K_sv at the

Full text of DOI:10.1016/j.cclet.2010.12.024

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Chinese Chemical Letters 22 (2011) 725–728
www.elsevier.com/locate/cclet
A novel chemosensor-bipyridyl end capped hyperbranched
conjugated polymer
a
a,
Xin Meng a,b, Qing Guo He a, , Hui Min Cao , Jian Gong Cheng
*
*
a State Key Laboratory of Transducer Technology, Shanghai Institute of Microsystem and Information Technology,
Chinese Academy of Sciences, Shanghai 200050, China
b Graduate School of the Chinese Academy of Sciences, Beijing 100039, China
Received 2 September 2010
Abstract
A novel hyperbranched conjugated chemosensor with bipyridyl groups as periphery groups (BPY-HPV) was synthesized. BPY-
HPV was highly sensitive to metal ions (Cu2+, Ni2+) for the strong coordination interaction (Ksv at the order of 107 molꢀ1 L)
monitored by fluorescence spectroscopy. Moreover, by hydrogen bonds and charge transfer interaction, BPY-HPV shows strong
interaction with 1,1,2,2-tetrachloroethane whatever in CH2Cl2 (Ksv ꢁ 106 molꢀ1 L) or film.
# 2010 Qing Guo He. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Hyperbranched conjugated polymer; Hydrogen bonding; Fluorescence; Tetrachloroethane
Conjugated polymers are superior to its organic counterparts in their collective and amplifying response, ease to make
devices and so on. A variety of molecular recognition events based on conjugated polymers have been revealed by
switching or tuning the luminescence of the nearby signaling moieties based charge transfer, photoinduced electron
transfer or electronic-energy transfer [1–4]. The conjugated polymers designed for recognition are focused on those with
linearrigid rodstructure, suchasPPP, PPVandPPE [5,6]. Severallinearcopolymersofbipyridylgroups, akind ofeffective
functional group for ion recognition, and phenylene vinylene or fluorine moieties were reported to have high metal ion
selectivity. Hyperbranched polymer, a kind of polymer of high solubility and thermal stability, is characteristic of global
structure, and the end groups were exposed on the surface of the globe [7,8]. So if bipyridyl groups were incorporated into
the periphery groups of the fluorescent hyperbranched polymer, they would contact with the environment directly. The
high density of end groups will endow this polymer to be high effective and selective for ion or molecular recognition.
Here we report synthesis, characterization of one bipyridyl end-capped hyperbranched phenylene vinylene (BPY-
HPV). The interaction between BPY-HPV and metal ions or 1,1-2,2-tetrachloroethane (TCE) in CH2Cl2 solution was
investigated. Also the switching behavior in film was studied. The chemical structure of BPY-HPVis given in Scheme 1.
To a solution of benzene-1,3,5-trialdehyde 0.3 g (1.85 mmol) and [2,5-dimethoxy-1,4-xylylene]bis(triphen-
ylphosphonium chloride 1.4 g (1.85 mmol) in DMF 15 mL was dropped a solution of CH3OK (3.7 mmol) in CH3OH
under vigorously stirring and a dynamic nitrogen atmosphere at room temperature. After 6 h, 50-methylbipyridyl
monoylid 0.97 g (1.85 mmol) was added followed by the addition of CH3OK 0.13 g (1.85 mmol) in CH3OH under
* Corresponding authors.
E-mail addresses: hqg@mail.sim.ac.cn (Q.G. He), jgcheng@mail.sim.ac.cn (J.G. Cheng).
1001-8417/$ – see front matter # 2010 Qing Guo He. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2010.12.024

[()TD$FIG]
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X. Meng et al. / Chinese Chemical Letters 22 (2011) 725–728
Scheme 1. The synthetic method and chemical structure of BPY-HPV.
vigorously stirring. The reaction was kept at room temperature for 6 h. Then the polymer could be precipitated from
methanol followed by extracting with methanol for two days. The resulting polymer was obtained as a bright-yellow
solid with an overall yield 45%.
FTIR (KBr pellet, cmꢀ1): 3006 (Ar–H, C–H, w), 2929 (CH3, w), 1590, 1542, 1496, 1462, 1407, 1208 (nas = C–O–
C, s), 1042 (ns = C–O–C, s), 964 (d = C–H, trans, ms), 888 (w), 864 (w), 823 (w), 697 (d = CH, cis vw).
1H NMR (400 MHz, CDCl3): d 2.3 (CH3ꢀ, S), 3.2 (s, CH3O–), 3.8 (s, CH3O–), 6.4–7.8 (m, –Ar –H), 8.1–8.8 (m,
bipyridyl-H);13C NMR (400 MHz, CDCl3): d 21.09 (CH3ꢀ), 56.04 (CH3O–), 108.94, 112.89, 118.08, 121.34–129.16,
133.04–133.8, 145.78, 148.04–151.35 (aromatic carbon on double bond and phenyl rings), 155.63–156.60 (aromatic
carbon on bipyridyl groups); calcd. For (C17H15O2N)n (265)n, (%) C 76.9, H 5.66, O 12.07, N 5.28; found (%) C 78.56,
H 5.55, O 10.59, N 5.30; MALDI-TOF (MS): 3051, 2952, 2295, 1651, and 1398.
1
FTIR, H NMR and 13C NMR and elemental analysis results were consistent with the proposed molecular
structures. From both 1H NMR and 13C NMR, the proton signal at 2.3 and 21 ppm could be attributed to methyl groups
on the bipyridyl groups, which could be clearly discerned from the signal of methoxy groups on the distylrylbenzene
units. Also, the signal of bipyridyl groups could be found at 8.1–8.8 ppm and 155–156 ppm different from the signal of
phenyl and vinylene double bonds, which could be further confirmed by elemental analysis with a percentage of
nitrogen at 5.3%. MALDI–TOF was used to determine the molecular weight of the polymer, since GPC for its linear
standard (polystyrene) is not suitable for the determination of a polymer with a hyperbranched structure.
The main absorption peak of BPY-HPV in CH2Cl2 is located in 323 nm and 395 nm corresponding to the stilben
and distyrylbenzene units. The main emission peak located at 455 nm with a shoulder at about 480 nm corresponding
to the emission of distyrylbenzene units [8]. Thus in BPY-HPV, the periphery units act as the light-harvesting antenna,
which funnel the energy to the distyrylbenzene units, then it emits from the low energy of distyrylbenzene moieties.
The energy transfer could be supported by investigation of the lifetime of BPY-HPV in CH2Cl2, The decay curve
exhibited biexponential fitting with a major fast-decay component (1.33 ns (65.41%)) along with a slow decay
component (2.58 ns (34.56%)).
The fluorescence of BPY-HPV in CH2Cl2 could be quenched significantly by the addition of increasing amounts of
metal ions, such as nickel, copper, etc. The quenching behavior of the emission peak maximum obeys Stern–Volmer
equation, namely, F0/F = 1+Ksv[CM]. Where F0 is the fluorescence intensity in the absence of metal perchlorate salt,
F is the intensity of fluorescence in the presence of metal ions; Ksv is the Stern–Volmer quenching constant and CM is
the concentration of metal ions. The quenching constant was determined to be 1.6 ꢂ 107 molꢀ1 L and
1.1 ꢂ 107 molꢀ1 L for copper and nickel ions respectively (see Fig. 1). For Ag+, the Ksv is 4.4 ꢂ 104 molꢀ1 L.
The strong interaction and high selectivity may arise from the well-matched size between copper ions and bipyridyl
groups. And the strong coordination interaction will change the electron density and conformation of bipyridyl groups,
then the electron or energy transfer between bipyridyl–metal ion complex and distyrylbenzene moieties would result

[()TD$FIG]
X. Meng et al. / Chinese Chemical Letters 22 (2011) 725–728
727
3.5
200
3.0
2.5
2.0
150
1.5
1.0
0.0
0.5
1.0
1.5
2.0
2.5
[Ni ]x 10 /M
100
50
0
300 350 400 450 500 550 600 650 700
wavelength(nm)
Fig. 1. Fluorescence quenching of BPY-HPV by Cu(ClO4)2 with the excitation wavelength at 320 nm and the concentrations of Cu2+ are 0,
2.96 ꢂ 10ꢀ8, 6 ꢂ 10ꢀ8, 8.96 ꢂ 10ꢀ8, 1.19 ꢂ 10ꢀ7, 1.49 ꢂ 10ꢀ7, 1.79 ꢂ 10ꢀ7, 2.08 ꢂ 10ꢀ7 mol Lꢀ1 and BPY-HPV is 1.5 ꢂ 10ꢀ2 mg/mL respec-
[()TD$FIG]
tively. The inset is the corresponding Stern–Volmer curve.
800
600
400
200
0
3.0
2.5
2.0
1.5
1.0
0.0
0.5
1.0
1.5
2.0
[CHCl2CHCl2] x107/M
400 450 500 550 600 650 700 750 800
wavelength(nm)
Fig. 2. Fluorescence quenching of BPY-HPV by TCE, the concentrations of TCE are 0, 5 ꢂ 10ꢀ8, 1 ꢂ 10ꢀ7, 1.5 ꢂ 10ꢀ7, 2.0 ꢂ 10ꢀ7, 2.5 ꢂ 10ꢀ7
,
3.0 ꢂ 10ꢀ7 mol Lꢀ1 respectively, and BPY-HPV is 1.5 ꢂ 10ꢀ2 mg/mL. The inset is the corresponding Stern–Volmer curve.
[()TD$FIG]
Scheme 2. The proposed interaction mode between BPY-HPV and 1,1,2,2-tetrachloroethane.

[()TD$FIG]
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X. Meng et al. / Chinese Chemical Letters 22 (2011) 725–728
160
quenched
recovered
140
original
120
100
80
60
40
20
0
400
450
500
550
600
650
700
wavelength(nm)
Fig. 3. Fluorescence spectra of BPY-HPV before (solid line) and after being exposed to TCE solution (dashed line) and TEA (dotted line) vapor.
in the fluorescence quenching of BPY-HPV3, which is contrast to the conjugation length change for its linear
counterpart arising from metal-complexation induced conformation change [2].
Moreover, the emission of BPY-HPV could also be quenched greatly (Ksv 6 ꢂ 106 molꢀ1 L) (see Fig. 2) by TCE.
The quenching behavior also obeys Stern–Volmer equation. Considering the chemical structure of TCE, the electron-
withdrawing effect of the chloride atoms will make the hydrogen atom act as naked protons. The two protons may
interact with nitrogen atom of the bipyridyl groups by a hydrogen bonding-like interaction. Also because the electron-
accepting ability of the four chlorine atoms, charge transfer interaction may happen between polymer and TCE
through hydrogen atoms, which could be partly supported by the interaction between BPY-HPV and glycol, since
glycol could also be expected to have a stronger hydrogen bonds forming ability, which the quenching constant is very
low (Ksv 3.28 molꢀ1 L). So the interaction may be a cooperative mode of hydrogen bonding and charge transfer. The
proposed interactive mode between BPY-HPV and TCE was given in Scheme 2.
Compared with the strong fluorescence of the film spin-coated from a solution in CH2Cl2, the fluorescence of that
with TCE as solvent was quenched completely. And while the spin-coated film from CH2Cl2 solution was dipped into a
solution of TCE in cyclohexane (10ꢀ3 mol Lꢀ1), the fluorescence of BPY-HPV was quenched gradually with
increasing of the time. But when the film was dipped into triethylamine, the fluorescence could be completely
recovered as shown in Fig. 3. Thus, a chemosensory device based on BPY-HPV could be realized.
To our knowledge, this is the first example of chemosensory based on hyperbranched conjugated polymers
containing bipyridyl groups on the periphery positions. It shows high sensitivity to metal ions and 1,1,2,2-
tetracholoethane by coordination or hydrogen bonding interaction.
Acknowledgments
We are grateful to NSFC (No. 20773156) and the Ministry of Science and Technology of China (No.
2007AA06A408), the ‘‘Bairen program’’ of CAS, and the Shanghai Science and Technology Committee (Nos.
09XD1405000 and 08JC1421900).
References
[1] J. Wang, D. Wang, E.K. Miller, et al. Macrolmolecules 33 (2000) 5152.
[2] B. Wang, M. Wasielewski, J. Am. Chem. Soc. 119 (1997) 1221.
[3] M. Kimura, T. Horai, K. Hanabusa, et al. Adv. Mater. 10 (1998) 459.
[4] (a) K.D. Ley, K.S. Schanze, J. Am. Chem. Soc. 119 (1997) 3423;
(b) K.A. Walters, K.D. Ley, K.S. Schanze, Chem. Commun. (1998) 1115.
[5] (a) D.T. McQuade, A.E. Pullen, T.M. Swager, Chem. Rev. 2537 (2000) 100;
(b) S.W. Thomas III, G.D. Joly, T.M. Swager, Chem. Rev. 107 (2007) 1339.
[6] A.P. de Silva, H.Q.N. Gunaratne, T. Gunnlaugsson, et al. Chem. Rev. 97 (1997) 1515.
[7] Q. He, H. Huang, F. Bai, et al. Macromol. Rapid Commun. 27 (2006) 302.
[8] Q. He, F. Bai, J. Yang, et al. Thin Solid Film 417 (2002) 183.