A polymer based fluorescent sensor for Zn2+ detection and its application for constructing logic gates

Article abstract of DOI:10.1016/j.polymer.2011.10.034

A polymer-based fluorescent sensor was synthesized by polymerization of (S)-6,6′-dibutyl-3,3′-(di-5-salicylde-ethynyl)-2, 2′-binaphthol (M-1) with (R,R)-1,2-diaminocyclohexane (M-2) via nucleophilic addition-elimination reaction. The responsive optical pr

Full text of DOI:10.1016/j.polymer.2011.10.034

Polymer 52 (2011) 5811e5816
Contents lists available at SciVerse ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
A polymer based fluorescent sensor for Zn2þ detection and its application
for constructing logic gates
,
,
a
Yu Dong a, Yuanzhao Wu a, Xiaoxiang Jiang a, Xiaobo Huang a b, Yixiang Cheng a , Chengjian Zhu
*
a Key Lab of Mesoscopic Chemistry of MOE, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
b College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325027, China
a r t i c l e i n f o
a b s t r a c t
A polymer-based fluorescent sensor was synthesized by polymerization of (S)-6,60-dibutyl-3,30-(di-5-
salicylde-ethynyl)-2,20-binaphthol (M-1) with (R,R)-1,2-diaminocyclohexane (M-2) via nucleophilic
additioneelimination reaction. The responsive optical properties of the polymer on transition metal ions
were investigated by fluorescence and UVevis spectra. The polymer (1.0 ꢀ 10ꢁ5 mol/L in THF) could emit
fluorescence at 550 nm and exhibit high selectivity for sensing Zn2þ with 36.1-fold fluorescence
enhancement. Three logic gates were designed according to the different fluorescence responses of this
Article history:
Received 25 June 2011
Received in revised form
4 September 2011
Accepted 19 October 2011
Available online 25 October 2011
polymer sensor to Zn2þ and Cu2þ
.
Keywords:
Polymer
Fluorescence
Zn2þ
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
fluorescence sensors have been reported [15]. An advantage of
fluorescent conjugated polymers over small molecules is that signal
amplification occurs from electronic communication along the
polymer backbone. Swager et al. [16] reported that the delocaliz-
As is known to all, Zn2þ is the second most abundant transition
metal ion in human body and plays a great role in many biology
processes, such as DNA binding, gene expression, metalloenzyme
catalysis, apoptosis, neurotransmission, brain function and
pathology, immune function, and mammalian reproduction [1].
Disorders of zinc metabolism could lead to an increasing risk of
several diseases, such as Alzheimer’s disease, Parkinson’s disease,
prostate cancer, epilepsy, ischemic stroke, and infantile diarrhea
[2]. In addition, high concentration of Zn2þ has a detrimental effect
on biological systems, as well as natural environment [3]. There-
fore, developing a highly selective detection method for Zn2þ is of
considerable importance and in great need. In the past few years,
many analytical methods have been developed for the detection of
zinc, including atomic absorption spectrometry [4], UVevis spec-
trometry [5], electrochemical [6], and potentiometry [7]. The
superiority of fluorescent sensor over other type sensors lies in its
sensitivity, selectivity, rapid response and high spatial resolution
via microscopic imaging [8].
able p-electronic conjugated “molecular wire” polymer can greatly
amplify the fluorescence responsive change due to facile energy
migration along the polymer backbone upon light excitation.
Molecular logic gates were developed to meet the need of
miniaturization in computer industry [17]. It is such a hot research
field that various logic gates have been designed and fabricated
recently [18]. Normally, an excellent chemosensor that can respond
differently to the stimuli from external environment changing can
be used for constructing molecular logic gate. In this research, three
logic gates were developed via carefully modulating the “Inputs”,
which show distinct functions with the fluorescent polymer sensor.
2. Experiment part
2.1. Materials and methods
To the best of our knowledge, most of the fluorescent sensors for
Zn2þ are based on small molecules, which contain DPA [9], quino-
line [10], bipyridine [11], acyclic and cyclic polyamines [12], triazole
[13], or Schiff-base [14]. However, very few polymer-based
All solvents and reagents were commercially available and
analytical-reagent-grade. THF was purified by distillation from
sodium in the presence of benzophenone and Et3N was newly
distilled before using. NMR spectra were collected on a 300-Bruker
spectrometer 300 MHz for 1H NMR and 75 MHz for 13C NMR and
reported as parts per million (ppm) from the internal standard TMS.
MS was determined on a Micromass GCT. FT-IR spectra were taken
on a Nexus 870 FT-IR spectrometer. Fluorescence spectra were
* Corresponding author.
E-mail address: yxcheng@nju.edu.cn (Y. Cheng).
0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2011.10.034

5812
Y. Dong et al. / Polymer 52 (2011) 5811e5816
obtained from an RF-5301PCspectrometer. Ultravioletevisible
(UVevis) spectra were obtained using a PerkineElmer Lambda 25
spectrophotometer. Specific rotation was determined with a Ruo-
lolph Research Analyfical Autopol I. C, H and N of elemental anal-
yses were performed on an Elementar Vario MICRO analyzer.
Molecular weight was measured by GPC with Waters-244 HPLC
pump and THF was used as solvent and relative to polystyrene
standards. TGA was conducted on a PerkineElmer Pyris-1 instru-
ment under N2 atmosphere.
Calcd. for C24H22N2O2: C, 77.81; H, 5.99; N, 7.56. Found: C, 77.81; H,
6.01; N, 7.58.
2.4. (S)-6,60-2,20-bis(methoxymethoxy)-1,10-binaphthyl (5)
(S)-6,60-Dibromo-2,20-bis(methoxymethoxy)-1,10-binaphthyl
(4) (5.9 g, 11.1 mmol) was dissolved in anhydrous THF (50 mL), n-
BuLi (15.0 mL, 2.5 mol/L in hexanes, 37.5 mmol) was added by
syringe injection at ꢁ78 ꢂC under a N2 atmosphere. After the
reaction mixture was stirred for 20 min, n-C4H9Br (5.3 g,
38.7 mmol) was added to the above solution at ꢁ78 ꢂC under a N2
atmosphere. The reaction mixture was gradually warmed to room
temperature and stirred overnight. The reaction was quenched by
adding saturated NH4Cl solution, and the mixture was extracted
with ethyl acetate (2 ꢀ 50 mL). The combined organic layers were
washed with water and brine respectively, and then dried over
anhydrous Na2SO4. After removal of solvent under reduced pres-
sure, the crude product was purified by column chromatography
(petroleum ether/ethyl acetate) (30: 1, v/v) to afford a colorless
2.1.1. Metal ion titration
Each metal ion titration experiment was started with a 3.0 mL
polymer with a known concentration (1.0 ꢀ 10ꢁ5 mol/L corre-
sponding to the (R,R)-salen moiety in THF solution). Zn(NO3)2 salt
and other various metal salts (nitrate, 1.0 ꢀ 10ꢁ3 mol/L, H2O) were
used for the titration. Polymer-metal complexes were produced by
adding aliquots of a solution of the selected metal salt to a THF
solution of the polymer sensor.
2.2. 5-ethynylsalicylaldehyde (2)
viscous oil product (S)-6,60-dibutyl-2,20-bis(methoxymethoxy)-
25
1,10-binaphthyl (5) in 70.4% yield (3.8 g). [
a]
¼ ꢁ38.0ꢂ (c ¼ 0.5,
D
Compound (1) was prepared according to a reported method
[19a]. To a mixture of 5-bromo- salicylaldehyde (5.0 g, 24.87 mmol),
Pd (PPh3)2Cl2 (174 mg, 0.25 mmol), and CuI (47 mg, 0.25 mmol) in
80 mL of Et3N (newly distilled), trimethylsilylacetylene (17.7 mL,
124.3 mmol) was added. The mixture was stirred for 12 h at
85e90 ꢂC. After cooling, the resulting ammonium salt was filtered
though a celite pad, and the filtrate was concentrated, following
purified by chromatography on silica gel with petroleum ether and
acetate as eluent (30: 1). Removal of solvent under vacuum affor-
ded a yellow powder, and the product was identified as 5-
trimethylethynylsilylsalicylaldehyde (4.0 g, 74%). Mp: 96-97 ꢂC;
CH2Cl2). 1H NMR (300 MHz, CDCl3):
d
7.90 (d, 2H, J ¼ 9.0 Hz), 7.65
(s, 2H), 7.56-7.52 (d, 2H, J ¼ 9.0 Hz), 7.09 (s, 4H), 5.08-5.05 (d, 2H,
J ¼ 6.9 Hz), 4.98-4.95 (d, 2H, J ¼ 6.6 Hz), 3.16 (s, 6H), 2.73 (t, 4H,
J ¼ 7.5 Hz), 1.69-1.64 (m, 4H), 1.43-1.35 (m, 4H), 0.98-0.92 (t, 6H,
J ¼ 7.2 Hz); 13C NMR (75 MHz, CDCl3):
d152.6, 138.5, 132.9, 130.4,
129.0, 128.1, 126.6, 125.9, 121.7, 117.5, 95.3, 55.7, 35.9, 33.8, 22.8,
14.3. FT-IR (KBr, cmꢁ1): 2956, 2929, 2857, 1596, 1500, 1480, 1241,
1151, 1028. MS (EI, m/z): 486 (Mt, 7%), 410 (100%), 382 (48%), 339
(34%).
2.5. (S)-6,60-dibutyl-2,20-binaphthol (model compound 6) [19c]
1H NMR (300 MHz, CDCl3):
d 11.12 (s, 1H), 9.87 (s, 1H), 7.72 (d,
J ¼ 2.1 Hz, 1H), 7.64-7.60 (d, J ¼ 8.7 Hz, 1H), 6.97-6.93 (d, J ¼ 8.7 Hz,
Compound (5) was dissolved in the mixed solvents of 10 mL
ether and 10 mL methanol. 15 mL of hydrochloric acid (12 mol/L)
solution was added to the above solution. The solution was stirred
at room temperature for 8 h. After removal of all solvents under
reduced pressure, the residue was extracted with ethyl acetate
(2 ꢀ 30 mL). The combined organic layers were washed with 2 mol/
L NaHCO3 solution and brine twice, and then dried over anhydrous
Na2SO4. The crude product was purified by column chromatog-
raphy on silica gel (petroleum ether/ethyl acetate) (20:1 v/v) to
1H), 0.27 (s, 9H).
5-Trimethylethynylsilylsalicylaldehyde (4.36 g, 20.0 mmol) was
dissolved in 30 mL CH2Cl2. KOH (1.12 g, 20.0 mmol) was dissolved in
15 mL MeOH and added to the CH2Cl2 solution. The reaction
mixture was stirred at room temperature for 3 h, and then the
solvent was concentrated under reduced pressure. To the residue
was added a mixture of H2O (40 mL) and CH2Cl2 (50 mL) to afford
a two-phase solution. The aqueous layer was further extracted with
CH2Cl2 (2 ꢀ 50 mL), and the combined CH2Cl2 layers were washed
with H2O twice, and dried over anhydrous Na2SO4. The solution
was filtered, and the solvent was removed by rotary evaporation to
obtain a light yellow powder identified as 5-ethynylsalicylaldehyde
afford a white solid product (0.71 g, 93.4% yield). Mp: 72w74 ꢂC
20
[
d
a
]
¼ þ82.9 (c ¼ 0.31, CH2Cl2). 1H NMR (300 MHz, CDCl3)
D
7.94e7.90 (d, J ¼ 9.0 Hz，2H), 7.68 (s, 2H), 7.38-7.35 (d, J ¼ 8.9 Hz，
2H), 7.20-7.16 (dd, J ¼ 8.6 Hz，2H), 7.12-7.09 (d, J ¼ 8.6 Hz，2H,),
4.98 (s, 2H), 2.77-2.72 (t, J ¼ 7.7 Hz，4H), 1.70-1.67 (m, 4H), 1.44-
1.36 (m, 4H), 0.98-0.93 (t, J ¼ 7.3 Hz，6H). 13C NMR (75 MHz, CDCl3)
(2) (2.6 g, 88%). Mp: 121-122 ꢂC; 1H NMR (300 MHz, CDCl3):
d 11.15
(s, 1H), 9.89 (s, 1H), 7.75 (d, J ¼ 2.0 Hz, 1H), 7.66 (dd, J ¼ 8.6, 2.1 Hz,
1H), 6.99 (d, J ¼ 8.7 Hz, 1H), 3.06 (s, 1H).
d
152.5, 139.0, 132.1, 131.2, 130.0, 129.4, 127.3, 124.6, 118.0, 111.3,
35.9, 33.9, 22.8, 14.4. FT-IR (KBr, cmꢁ1): 3503.4, 3421.9, 2950.1,
2921.8, 1598.1, 1507.3, 1474.1, 1363.7, 1214.1, 1142.6, 1124.5, 952.2,
2.3. Model compound 3 [19b]
880.6, 827.1 cmꢁ1
.
A mixture of 5-ethynylsalicylaldehyde (584.6 mg, 4.0 mmol) and
(R,R)-1,2-diaminocyclo-hexane (228.4 mg, 2.0 mmol) was dissolved
in 20 mL methanol. The obtained solution was stirred at 40 ꢂC for
12 h. After cooling to room temperature, the solvent was removed
by a rotary evaporator. The crude product was recrystallized from
2.6. (S)-6, 60-dibutyl-3, 30-diiodo-2, 20-binaphthol (7)
Compound (5) (3.69 g, 7.58 mmol) was dissolved in 30 mL of
anhydrous THF. 10.6 mL of n-BuLi (2.5 mol/L in hexane,
26.53 mmol) was added by syringe injection to the above solution
at room temperature under N2 atmosphere. The solution was
stirred for 6 h at room temperature, and then the solution of
iodine (7.7 g, 30.32 mmol in 30 mL of THF) was slowly injected to
the mixed solution at ꢁ78 ꢂC. The mixture was then stirred
overnight while the temperature was gradually warmed to room
temperature. The reaction was quenched with 10% aqueous
Na2S2O3 (30 mL). After removal of the solvent under reduced
ethyl acetate and petroleum ether to afford a yellow solid 4
25
(592 mg, 80% yield). Mp: 146-148 ꢂC; [
a
]
D
¼ ꢁ0.059 (c ¼ 0.49,
THF); 1H NMR (300 Hz, CDCl3):
d 13.54 (br, 2H), 8.23 (s, 2H), 7.39
(dd, J ¼ 8.4, 1.8 Hz, 2H), 7.34 (d, J ¼ 1.8 Hz, 2H), 6.87 (d, J ¼ 8.4 Hz,
2H), 3.34-3.37 (m, 2H), 2.97 (s, 2H), 1.45-1.97 (m, 8H). 13C NMR
(75 Hz, CDCl3):
d 163.9, 161.5, 135.9, 135.3, 118.2, 117.3, 112.2, 83.0,
75.7, 72.4, 32.8, 24.0. FT-IR (KBr, cmꢁ1): 3299, 3281, 2941, 2863,
1633, 1587, 1486, 1286, 826,585. MS (FAB): m/z 370.2 (Mþþ1). Anal.

Y. Dong et al. / Polymer 52 (2011) 5811e5816
5813
pressure, the residue was extracted with ethyl acetate (2 ꢀ 50 mL),
3. Results and discussion
the combined organic layers were washed with water and brine
twice. The solution was concentrated to give a crude product of
3.1. Syntheses and feature of the polymer sensor
(S)-6,60-dibutyl-3,30-diiodo-2,20-bismethoxy-
methoxy-1,10-
binaphthyl which was directly used without purification. The
crude product was dissolved in the mixed solvents of 30 mL of
ether and 30 mL of methanol, and then 35 mL of HCl (12 mol/L)
solution was added to the above solution. The solution was stirred
at room temperature for 8 h. After the removal of the solvent
under reduced pressure, the residue was extracted with ethyl
acetate (2 ꢀ 50 mL). The combined organic layers were washed
with 8% aqueous NaHCO3 and brine twice, and then dried over
anhydrous Na2SO4. After removal of solvent, a yellow viscous
5-Ethynylsalicylaldehyde (2) was synthesized by a two-step
reaction from the starting material 5-bromosalicylaldehyde [19a].
Model compound 3 could be synthesized in 80.0% yield according
to the reported literatures [19b]. Model compound 6 could be ob-
tained in 93.4% yield [19c]. (S)-6,60-Dibutyl-3,30-diiodo-2,20-
binaphthol (7) was obtained by a five-step reaction from (S)-BINOL
in 27.3% yield according to literatures [19d]. Monomer M-1, (S)-6,60-
dibutyl-3,30-di-(salicylal-5-ethynyl)-2,20-binaphthol, was synthe-
sized through a typical Sonogashira reaction from (7) and (2) in
30.0% yield. The polymer could be obtained by Schiff base forma-
tion between dialdehyde (M-1) and (R,R)-1,2-diaminocyclohexane
(M-2) under a mild condition in 70.0% yield (Fig. 1). Mw, Mn and
PDI of the polymer were determined by gel permeation chroma-
tography using polystyrene standards in THF, and the values of
them are 12090, 10310 and 1.17, respectively. The GPC result of the
polymer shows the moderate molecular weight. The polymer is an
air stable powder with light yellow color and shows good solubility
in common organic solvents, such as toluene, THF, CHCl3, CH2Cl2,
and DMF, which can be attributed to the nonplanarity of the
twisted polymer backbone and the flexible n-butoxy group. The (S)-
BINOL and (R,R)-salen moieties can orient a well-defined spatial
arrangement in the main chain backbone of the polymer, mean-
while salen-based moieties can form stable complexes with various
metal ions due to the potentially tetradentate N2O2 donor [22].
product (S)-6,60-dibutyl-3,30-diiodo-2,20-binaphthol was obtained
25
in the yield of 38.8% (1.91 g). [
a]
¼ ꢁ65.0 (c ¼ 0.3, CH2Cl2). Mp:
D
58e60 ꢂC. 1H NMR (300 MHz, CDCl3):
d 8.45 (s, 2H), 7.57 (s, 2H),
7.19 (dd, 2H, J ¼ 8.7 Hz, 1.5 Hz), 7.03 (d, 2H, J ¼ 8.7 Hz), 5.36 (s, 2H),
2.74 (t, 4H, J ¼ 7.5 Hz), 1.69-1.61 (m, 4H), 1.43-1.34 (m, 4H), 0.98-
0.92 (m, 6H); 13C NMR (75 MHz, CDCl3):
d149.5, 139.7, 139.3, 131.5,
130.8, 129.5, 125.6, 124.3, 112.5, 86.3, 35.4, 33.3, 22.3, 13.9. FT-IR
(KBr, cmꢁ1): 3476, 2925, 2854, 1572, 1500, 1441, 1362, 1143. MS
(EI, m/z): 650 (Mt, 100%), 607 (100%).
2.7. (S)-6,60-dibutyl-3,30-di-(salicylal-5-ethynyl)-2,20-binaphthol
(M-1) [20]
An oven-dried Schlenk flask equipped with a magnetic stirring
bar was charged with Pd(PPh3)2Cl2 (4.31 mg, 6.15
(1.17 mg, 6.15 mol), and 5-ethynylsalicylaldehyde (2) (89.89 mg,
615 mol). After the flask was capped with a rubber septum, the
mmol), and CuI
m
m
3.2. UVevis titration of the polymer sensor on Zn2þ
flask was evacuated and backfilled with nitrogen for three circles.
Then (S)-6,60-dibutyl-3,30-diiodo-2,20-binaphthol (7) (200 mg,
308 mmol) was added by syringe in THF, followed by TEA (5 mL) and
THF (5 mL). The Schlenk flask was then sealed and stirred at
ambient temperature for 20 h. Diluted with THF, and filtered
through a celite pad, then the crude product was purified by
As can be seen from Fig. 2, UVevis spectra of the polymer exhibit
a maximal absorption at 262 nm and a broad band situated at
353 nm. Upon addition of Zn2þ, the absorbance peaks at 262 and
284 nm show a significant reduction with the increasing amount of
Zn2þ. Simultaneously, the absorbance peak at 353 nm appears red-
shift to 368 nm. Moreover, there are three isosbestic points at 275,
297 and 355 nm, which indicate the formation of a stable complex
with a certain stoichiometric ratio.
column chromatography (30: 1-10: 1, v/v) to afford a white powder
25
(30.7 mg) in 30.0% yield. [
a
]
¼ ꢁ83.1 (c ¼ 0.5, THF). Mp:
D
132e134 ꢂC. 1H NMR (300 MHz, CDCl3):
d
11.03 (s, 2H), 9.56 (s, 2H),
8.09 (s, 2H), 7.78 (s, 2H), 7.76 (s, 2H), 7.71 (s, 2H), 7.33-7.29 (d, 2H,
J ¼ 9.0 Hz), 7.11 (s, 2H), 7.08 (s, 2H), 6.93-6.90 (d, 2H, J ¼ 9.0 Hz),
2.81-2.75 (t, 4H, J ¼ 7.5 Hz), 1.76-1.65 (m, 4H, J ¼ 7.5 Hz), 1.47-1.39
(m, 4H, J ¼ 7.5 Hz), 1.00-0.95 (t, 6H, J ¼ 7.5 Hz); 13C NMR (75 MHz,
3.3. The selective and sensitive recognition of the polymer sensor on
Zn2þ
CDCl3):
d
196.2, 161.8, 156.4, 152.0, 138.6, 133.5, 131.3, 130.1, 129.7,
The fluorescence titration of the polymer sensor with Zn2þ was
presented in Fig. 3. The polymer sensor can lead to a specific
response toward Zn2þ, and the fluorescent intensity of Zn2þ-con-
taining polymer complex shows gradual enhancement as high as
36.1-fold upon the concentration molar ratio addition of Zn2þ from
0.1 to 1.5 (Fig. 3). Moreover, the maximum emission wavelength of
the polymer is remarkably blue shifted from 550 to 485 nm along
129.2, 127.0, 126.3, 125.7, 122.3, 120.1, 118.5, 118.1, 112.1, 100.4, 35.5,
33.3, 22.4, 13.9. FT-IR (KBr, cmꢁ1): 2923, 1661, 1478, 1282. MS (EI, m/
z): 685.7 (Mþ-1). Anal. Calcd. for C46H38O6: C, 80.45; H, 5.58. Found:
C, 80.37; H, 5.37.
2.8. Polymer sensor [21]
with a dramatic enhancement of fluorescence intensity. The Zn2þ
-
A
mixture of M-1 (0.15 g, 0.22 mmol) and (R,R)-1, 2-
polymer solution can emit green fluorescence and is readily
detected by naked eyes (Fig. 3, inset). The obvious fluorescence
enhancement response and blue shift can be attributed to three
reasons: Firstly, a relatively high-energy non-bonding electron pair
of the nitrogen atom arisen from the imine group transfers an
electron to the excited fluorophore, which results in the fluores-
cence quenching. But when the electron pair is bound by coordi-
nation of Zn2þ, the redox potential of the receptor is raised so that
the HOMO of the receptor becomes lower in energy than that of the
fluorophore. Thus, the PET process from the receptor to the fluo-
rophore is suppressed, and the fluorescence is switched on [8a].
Secondly, the formation of Zn2þ-polymer complex can enhance the
planarity and rigidity of the polymer and tend to produce fluores-
cence enhancement [23]. Thirdly, when salen-based N2O2 receptor
diaminocyclohexane (24.9 mg, 0.22 mmol) was dissolved in
8 mL of chloroform. The obtained solution was stirred at 50 ꢂC for
6 h concentrated to 1 ml and the residual was dropped into
methanol (15 mL) to precipitate the yellow Salen polymer. The
resulting polymer was filtrated and washed with methanol several
times, and then dried in vacuo to afford 70 mg light yellow
powder in the yield of 70.0%. GPC results: Mw
¼
12090,
¼ ꢁ723.7 (c ¼ 0.10, THF); 1H NMR
25
Mn ¼ 10310, PDI ¼ 1.17; [
a
]
D
(300 Hz, CDCl3):
d
8.34-7.58 (8H), 7.01-6.63 (10H), 3.35-2.74 (4H),
1.89-1.62 (4H), 1.41-1.27 (10H), 0.95-0.92 (10H). FT-IR (KBr, cmꢁ1):
2927, 2360, 1688, 1635, 1629, 1525, 1491, 1487，1285. Anal. Calcd.
for C52H48N2O4: C, 81.65; H, 6.32; N, 3.66. Found: C, 81.38; H, 6.31;
N, 3.64.

5814
Y. Dong et al. / Polymer 52 (2011) 5811e5816
TMS
PdCl2(PPh3)2
CuI,
H
N
N
Br
CHO
OH
CHO
OH
CHO
OH
H2N
NH2
KOH
OH HO
MeOH
TEA
MeOH
Model compound 3
2
1
n-Bu
OH
OH
HCl
Br
n-Bu
n-Bu
n-Bu
(1) Br2
Model compound 6
n-Bu
OH
(1) n-BuLi
(2) n-BuBr
OMOM
OMOM
OMOM
OMOM
I
OH
(2) NaH/MOMCl
Br
(1) n-BuLi
OH
OH
(2) I2
S-BINOL
4
5
(3) HCl
n-Bu
I
CHO
7
OH
n-Bu
n-Bu
H2N
NH2
N
N
2
OH
OH
M-2
[
OH HO
PdCl2(PPh3)2,
CuI
n-Bu
n
CHCl3
OH
OH
n-Bu
chiral polymer sensor
M-1
OH
CHO
Fig. 1. Synthesis procedures of model compounds 3, 6 and polymer sensor.
in the main chain backbone of the polymer sensor coordinates with
Zn2þ, a large blue shift of 50 nm for the emission spectrum of the
polymer is observed (Fig. 5a), which suggests that an ICT process is
also involved in. The donating character of the salen-based receptor
containing cyclohexyl electron-donating group is reduced when
the binding event occurs, which leads to a blue shift of the fluo-
rescence sensor [8a].
In this paper, we further investigated the selectivity of the
polymer to various metal ions. The fluorescence titration experi-
ment was carried out under the conditions mentioned above. As
can be seen from Fig. 4, the polymer sensor exhibits the highest
sensitivity and selectivity to Zn2þ among tested metal ions. Addi-
tion of 1.0 equiv Naþ, Kþ, Mg2þ, Ca2þ, Agþ, Cd2þ, Hg2þ, Pb2þ, Cr3þ
,
Fe3þ can only cause slight fluorescence enhancement (I/I0-1<1.2).
Whereas Ni2þ and Cu2þ lead to nearly complete quenching for the
polymer fluorescence on the ion addition at a concentration of
1:1 molar ratio, which can be attributed to the intramolecular
photoinduced electron transfer (PET) or photoinduced charge
transfer (PCT) between the polymer backbone and binding metal
complexes. Moreover, we also found that Cd2þ gives no interfer-
ence in the detection, which means that this polymer provides an
alternative way to distinguish Zn2þ from Cd2þ under our reported
350
1.2
P
P+Zn
300
250
200
150
100
50
0
0.1
0.2
0.3
0.4
1.0
0.8
0.5
0.6
0.6
0.4
0.2
0.0
0.7
0.8
0.9
1.0
1.2
1.5
0
400
450
500
550
600
650
250
300
350
400
450
500
Wave Length(nm)
Wave Length(nm)
Fig. 3. Fluorescence spectra of the polymer (1.0
ꢀ
10ꢁ5 mol/L) with increasing
Fig. 2. UVevis spectra of the polymer (1.0 ꢀ 10ꢁ5 mol/L) with increasing amounts of
Zn2þ (0e1.5 equiv.).
amounts of Zn2þ (0, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 8.0, 10.0, 15.0, 20.0, 25.0, 30.0,
40.0 ꢀ 10ꢁ6 mol/L) (lex ¼ 350 nm).

Y. Dong et al. / Polymer 52 (2011) 5811e5816
5815
35
30
25
20
15
10
5
0
Na+ Mg2+ K+ Ca2+ Cr3+ Fe3+ Co2+ Ni2+ Cu2+ Zn2+ Ag+ Cd2+ Hg2+ Pb2+
Fig. 6. INH logic gate with Zn2þ (10
mM) and EDTA (10 mM) as “input”.
Fig. 4. Relative fluorescence intensity of polymer-metal ions complex. In these
M of
the polymer in THF at room temperature and in the absence and presence of 1.0 equiv.
of a metal ion.
experiments, the fluorescence measurement was taken at lex ¼ 350 nm from 10
m
procedure. Most importantly, based on the fluorescence image of
the polymer sensor in the absence and presence of 1.0 equiv. of
a metal ion, we can easily distinguish Zn2þ by the distinctive bright
green fluorescence under the UV lamp (
l
¼ 365 nm) by naked eyes.
In addition, the competing experiment of the polymer towards
Zn2þ was conducted by treating a solution of Zn-polymer complex
with other metal ions. The fluorescence intensities of the polymer
do not appear obvious difference in the presence of other metal
ions even at a higher concentration. But the coexisted ions (Cr3þ
,
Co2þ, Ni2þ and Cu2þ) showed interference in Zn2þ detection to
some extent (SI2, Fig. 1).
3.4. Logic gate development
Fig. 7. IMP logic gate with Cu2þ (100
mM) and EDTA (100 mM) as “input”.
Based on the different fluorescence responses of this polymer
sensor towards Cu2þ and Zn2þ, three logic gates were designed
accordingly. EDTA was introduced into the process of constructing
logic gates as a result of its strong chelating property for metal ions.
Fig. 5 illustrated an INH logic gate that combine a NOT gate to an
AND gate. The fundamental INH action was obtained with Zn2þ
leading to the output as “1”. Under other conditions fluorescence is
quenched, resulting in output “0”. The central metal displacement
occurred when Cu2þ was added to a high fluorescence solution of
polymer sensor and Zn2þ, which caused fluorescence quenching
[24]. Fig. 6 also showed an INH logic gate with Zn2þ (10
mM) and
(10
m mM) as input. High FL intensity was observed
M) and Cu2þ (10
only in the presence of 1.0 equiv. of Zn2þ and the absence of Cu2þ
,
EDTA (10
mM) as input. The mechanism for Fig. 6 is due to the strong
chelating property of EDTA, which caught Zn2þ tightly and made
the solution’s fluorescence return to its initial state. Fig. 7 showed
another type of logic gate that incorporating a NOT gate and an OR
gate (Implication). It also can be basically understood as a reversed
INH operation with the same mechanism as Fig. 6.
4. Conclusions
A novel polymer-based fluorescence sensor incorporating salen
moieties in the main chain backbone was used as an excellent
probe for the detection of Zn2þ. Compared with other cations, such
as Naþ, Kþ, Mg2þ, Ca2þ, Cr3þ, Fe3þ, Co2þ, Ni2þ, Cu2þ, Agþ, Cd2þ
,
Hg2þ, and Pb2þ, Zn2þ produced the most pronounced fluorescence
enhancement response as well as a large blue shift of the polymer
sensor. Most importantly, we can identify Zn2þ with naked eye
under UV excitation (
l
¼ 365 nm). Three logic gates were designed
with two different interaction mechanisms. The results indicated
that this polymer-based fluorescence sensor can be employed to
selectively sensing Zn2þ and construct molecular logic gates to
meet computing needs.
Fig. 5. INH logic gate with Zn2þ (10 M) and Cu2þ (10
m mM) as “input”.

5816
Y. Dong et al. / Polymer 52 (2011) 5811e5816
(c) Tomat E, Nolan M, Jaworski J, Lippard SJ. J Am Chem Soc 2008;130:
Acknowledgments
15776e7;
(d) Komatsu K, Urano Y, Kojima H, Nagano T. J Am Chem Soc 2007;129:
13447e54.
[9] (a) Nolan EM, Ryu JW, Jaworski J, Feazell RP, Sheng M, Lippard SJ. J Am Chem
This work was supported by the National Natural Science
Foundation of China (No. 21074054, 51173078), National Basic
Research Program of China (2010CB923303), the Bureau of Science
and Technology of Wenzhou (No. S20100007) and the Fundamental
Research Funds for the Central Universities (1082020502).
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(b) Hanaoka K, Muramatsu Y, Urano Y, Terai T, Nagano T. Chem-Eur J 2010;16:
568e72;
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You Y, Tomat E, Hwang K, Atanasijevic T, Nam W, Jasanoffc AP, et al. Chem
Commun 2010;46:4139e41.
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Appendix. Supplementary material
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.polymer.2011.10.034.
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