Fluorescent OFF-ON polymer chemosensor bonded alternatively with 1,4-dioctyloxybenzene and (R,R)-salen for cascade Zn2+ and chiral recognition

Article abstract of DOI:10.1016/j.tetasy.2012.04.015

The synthesis of the chiral main chain polymers 1a-b bonded alternatively with (R,R)-salen and 1,4-dioctyloxybenzene has been described employing a palladium-catalyzed C-C cross-coupling reaction as the key step. They are soluble in common organic solvent

Full text of DOI:10.1016/j.tetasy.2012.04.015

Tetrahedron: Asymmetry 23 (2012) 570–576
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Tetrahedron: Asymmetry
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Fluorescent OFF–ON polymer chemosensor bonded alternatively with
1,4-dioctyloxybenzene and (R,R)-salen for cascade Zn2+ and chiral recognition
⇑
Sekarpandi Sakthivel, Tharmalingam Punniyamurthy
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of the chiral main chain polymers 1a–b bonded alternatively with (R,R)-salen and 1,4-dioc-
tyloxybenzene has been described employing a palladium-catalyzed C–C cross-coupling reaction as the
key step. They are soluble in common organic solvents and act as a highly selective ‘OFF–ON’ fluorescent
chemosensors toward Zn2+. The resultant Zn(II)-polymer complexes exhibit significant chiral recognition
toward (R)- and (S)-1-phenyl-N-[(pyridin-2-yl)methylene]ethanamines 9 under ambient conditions.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 13 March 2012
Accepted 25 April 2012
Available online 24 May 2012
1. Introduction
optical response in comparison to small molecules as chemosen-
sors.15f,g In continuation of our studies on stereoregular poly-
The detection of metal ions found in biological systems and in
the environment has received considerable attention in recent
years, as these ions can be either beneficial or toxic to human
health.1 Among them, Zn2+ is the second most essential transition
metal ion for the human body, and plays an indispensable role in
various biological processes, such as gene transcription, cell apop-
tosis, regulation of metalloenzymes, neural signal transmission,
and insulin secretion.2 The deviation of Zn2+ concentration from
normal levels causes diabetes and many severe neurological dis-
eases including epilepsy and Alzheimer’s disease.3 Thus, the selec-
tive detection of Zn2+ in various samples is of vital toxicological
and environmental importance. However, unlike other transition
metal ions such as Cu2+, Co2+, and Ni2+, Zn2+ does not give any spec-
troscopic or magnetic signals due to its complete valence shell
electronic configuration. In this context, the fluorometric detection
of Zn2+ has been appealing since it is easy to perform with high
sensitivity.4 Numerous scientific endeavors have thus been made
in the development of fluorescent Zn2+ probes based on small mol-
ecules, such as quinolines,5 rhodamine,6 bis(benzoxazole),7 bipyri-
dine,8 spirobenzopyravarien,9 anthracene,10 naphthalimide11 and
tricarbocyanine,12 peptides,13 and nanoparticles.14 More recently,
a few studies have focused on the use of stereoregular organic
polymers for this purpose,4a,15 because the selective coordination
and binding of certain metal ions to the chromophoric site of the
polymers can greatly influence the optical properties of the mate-
rials, making them promising candidates for sensors.16 In conju-
gated polymers, a small change in the chromophoric site can
generate a signal, which can be amplified through the delocalized
mers,4a,17a,b we herein report the synthesis and application of
new chiral main chain polymers 1a–b for the highly selective rec-
ognition of Zn2+ as OFF–ON fluorescent chemosensors. The resul-
tant Zn(II)-polymer complexes exhibited significant chiral
recognition toward (R)- and (S)-1-phenyl-N-[(pyridin-2-yl)methy-
lene]ethanamines 9 under ambient conditions.
2. Results and discussion
The reaction of 1,4-hydroquinone 4 with 1-bromooctane in the
presence of K2CO3 gave 1,4-dioctyloxybenzene, which could be
brominated using Br2 to afford 1,4-dibromo-2,5-dioctyloxyben-
zene 5 in 85% yield. Compound 5 was then reacted with trim-
ethoxyborane in the presence of n-BuLi followed by acid
hydrolysis to give 2,5-dioctyloxyphenyldiboronate 6 in 80% yield
(Scheme 1).17b,c
OH
OC8H17
Br
OC8H17
B(OH)2
(i)
Br
(ii)
(HO)2B
OH
OC8H17
OC8H17
4
5
6
Scheme 1. Reagents and conditions: (i) C8H17Br (2.5 equiv), K2CO3 (2.5 equiv),
EtOH, 70 °C, 24 h, 80%; (ii) Br2, CHCl3, 0 °C to rt, 27 h, 90%; (iii) n-BuLi (2.3 equiv),
B(OMe)3 (2.5 equiv), Et2O, ꢀ20 °C to rt, 12 h, 2 N HCl, rt, 0.5 h, 80%.
p
-electron cloud of the polymer backbone to produce an effective
The chemoselective reaction of 2,4-dihydroxybenzaldehyde 7
with trifluoromethanesulfonic anhydride in the presence of pyri-
dine gave 4-formyl-3-hydroxyphenyl trifluoromethanesulfo-
nate4a,18 8 in 60% yield, which could be C-C cross-coupled with 6
⇑
Corresponding author. Tel.: +91 361 2582309; fax: +91 361 2690762.
E-mail address: tpunni@iitg.ernet.in (T. Punniyamurthy).
0957-4166/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetasy.2012.04.015

S. Sakthivel, T. Punniyamurthy / Tetrahedron: Asymmetry 23 (2012) 570–576
571
CHO
CHO
HO
OC8H17
OH
OH
(i)
(ii)
OHC
CHO
H17C8O
OH
OH
OTf
7
8
2
Scheme 2. Reagents and conditions: (i) Tf2O (1 equiv), pyridine (1 equiv), CH2Cl2, 0 °C-rt, 27 h, 60%; (ii) 2,5-dioctyloxyphenyldiboronate 6 (0.5 equiv), Pd(PPh3)2Cl2 (3 mol %),
PPh3 (9 mol %), K2CO3 (3 equiv), THF, reflux, 24 h, 80%.
using Pd(PPh3)2Cl2 to afford the desired dialdehyde 2 in 80% yield
(Scheme 2).19
ca.289
(
e
= 2.60 ꢁ 104 Mꢀ1cmꢀ1
)
and 349 nm
(
e
= 2.98 ꢁ 104
Mꢀ1cmꢀ1) for 1a, and 290 (
e
= 2.77 ꢁ 104 Mꢀ1cmꢀ1) and 352 nm
Dialdehyde 2 was then used in a Schiff base formation with
(R,R)-1,2-diaminocyclohexane 3a and (R,R)-1,2-diphenylethylen-
ediamine 3b upon heating in CHCl3 to give the polymers 1a-b as
yellow powders (Schemes 3 and 4).4a,17a–b,20 The octyloxy substitu-
ent on the polymer backbone helps them to be soluble in common
organic solvents such as THF, CHCl3, and CH2Cl2. GPC analysis, with
polystyrene as an internal standard and THF as an eluent, was used
to determine their average molecular weights, which corresponded
to ca. 27 repeating units for 1a (Mw = 16771, Mn =12261 and PDI =
1.37) and ca. 23 repeating units for 1b (Mw = 19274, Mn = 12449
and PDI = 1.55). The 1H NMR spectra recorded at 400 MHz were
found to be consistent with their structures.
(
e
= 3.21 ꢁ 104 Mꢀ1cmꢀ1) for 1b, respectively, due to
p–
p⁄ transi-
tion. Regarding fluorescence, 1a emitted a weak blue light at 423
and 521 nm (kex = 360 nm), and 1b at 421 and 519 nm (kex
=
360 nm). Thermal analysis showed that the polymers 1a-b were
thermally stable up to ca. 270 °C and a total weight loss of 58–
68% was observed upon a gradual increase in temperature to
600 °C.
The fluorescent nature of polymers 1a–b prompted us to evalu-
ate them as chemosensors for the detection of various common
metal ions. Interestingly, polymers 1a–b exhibited the best selec-
tivity toward Zn2+ as an OFF–ON hemosensor compared with other
metal ions such as Na+, Ag+, Fe3+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Pb2+
,
Figure 1 illustrates the UV-vis, fluorescence and TGA of poly-
mers 1a–b. The UV–vis spectra showed absorption maxima at
Al3+, and Ce3+ (Fig. 2). Polymer 1b was found to be superior to 1a
with an enhancement in the fluorescence. Figure 3 illustrates the
Polymer 1a
Mw = 16771, Mn = 12261, PDI =1.37
n = 27, [α]D20 = −570 (c 0.02, CHCl3)
N
N
N
N
OH HO
OH HO
H17C8O
OC8H17
H17C8O
OC8H17
(i)
H2N
NH2
3a
n
OC8H17
H17C8O
H17C8O
OC8H17
OH
N
HO
N
OH HO
N
N
Scheme 3. Reagent and conditions: (i) dialdehyde 2 (1 equiv), CHCl3, 45 °C, 3 h, 91%.
Polymer 1b
Mw = 19274, Mn = 12449, PDI =1.55
n = 23, [α]D20 = −126 (c 0.03, CHCl3)
N
N
N
N
OH HO
OH HO
H17C8O
OC8H17
H17C8O
OC8H17
(i)
H2N
NH2
3b
n
OC8H17
H17C8O
H17C8O
OC8H17
OH
N
HO
N
OH HO
N
N
Scheme 4. Reagent and conditions: (i) dialdehyde 2 (1 equiv), CHCl3, 45 °C, 3 h, 97%.

572
S. Sakthivel, T. Punniyamurthy / Tetrahedron: Asymmetry 23 (2012) 570–576
Figure 1. The polymers 1a–b: (a) UV–vis and fluorescence spectra (1 ꢁ 10ꢀ5 M in
Figure 2. Fluorometric titration: (a) 1a (kex = 360 nm) and (b) 1b (kex = 360 nm)
(1 ꢁ 10ꢀ5 M in THF) with different metal nitrate salts (3 ꢁ 10ꢀ4 M in water, 1 equiv
with respect to the monomeric unit).
THF) and (b) TGA.
images of fluorescence of 1b without (a) and with (b) Zn2+, while
(c) shows the graphical presentation of the selectivity of 1b with
different metal ions. Polymer 1b with Zn2+emits a strong blue fluo-
rescence, which could be attributed to the reduced non-radiative
decay of the Zn(II)-polymer complex excited state and the quench-
ing contributed from the lone pair of electrons of the nitrogen
through internal charge transfer (ICT).1b,21 In addition, a blue shift
(ꢂ50 nm) in the emitted light was observed, which could be
caused by a decrease in energy of the HOMO of the polymer upon
the formation of the Zn(II)-polymer complex.22
Polymer 1b was further studied with various Zn2+ concentra-
tions (Fig. 4). The absorption band at 290 nm slightly shifted to
293 nm with a gradual decrease of intensity. The isosbestic points
at 296 and 366 nm indicate the formation of a Zn(II)-polymer
complex.
Next, the sensing selectivity of polymer 1b with different
Zn2+concentrations was studied (Fig. 5a). The weakly emissive 1b
(THF, 1 ꢁ 10ꢀ5 M) at ca. 519 nm, upon addition of Zn2+ (3 ꢁ 10ꢀ4
M), exhibited a blue-shifted emission at 471 nm. The enhancement
in intensity of the emission band was proportional to the Zn2+ con-
centration. When the Zn2+concentration was 1.1 equiv with re-
spect to the monomer unit of the polymer 1b, the fluorescence
intensity increased to a maximum 22-fold enhancement. Further
enhancement in the addition of Zn2+ concentration led to no
change in the fluorescence intensity. By applying a Hill plot to this
titration data (Fig. 5b), the stability constant of Zn(II)-polymer 1b
Figure 3. The polymer 1b (1 ꢁ 10ꢀ5 M in THF): (a) fluorescence image without Zn2+
and (b) fluorescence image with 1 equiv Zn2+ (3 ꢁ 10ꢀ4 M in water) (both are
excited using a commercially available UV lamp (k = 360 nm). (c) The selectivity of
1b (1 ꢁ 10ꢀ5M in THF) with metal ions (3 ꢁ 10ꢀ4 M in water).
The use of fluorometric titration for the enantioselective recog-
nition of chiral compounds has received considerable attention in
recent years.24 Since the Zn(II)-polymer complexes are optically
active and pyridine is known to cause chelation to Zn2+ with
complex was calculated as 1.62 ꢁ 108 Mꢀ1 23
.

S. Sakthivel, T. Punniyamurthy / Tetrahedron: Asymmetry 23 (2012) 570–576
573
Figure 4. UV–vis titration of 1b (1 ꢁ 10ꢀ5 M in THF) with 0.1–1.1 equiv of Zn2+ ion
(3 ꢁ 10ꢀ4 M in water with respect to the monomeric unit of 1b).
Figure 6. Fluorescence spectra (kex = 360 nm): (a) 1a, 1a + Zn2+ and 1a + Zn2++ R-9
and (b) 1b, 1b + Zn2+ and 1b + Zn2++ R-9 (1 ꢁ 10ꢀ5 M in THF) [12 equiv of (R)-9 with
respect to Zn(II)-polymer complex].
The Zn(II)-polymer complexes exhibited significant enantioselec-
tive recognition toward (R)-1-phenyl-N-[(pyridin-2-yl)methylene]
ethanamine (R)-9 and (S)-1-phenyl-N-[(pyridin-2-yl)- methy-
lene]ethanamine (S)-9. In these experiments, an excess of imines
(R)- or (S)-9 (1–18 equiv) could drive the equilibrium toward the
right to ensure enantiomeric differentiation through distinct en-
hanced fluorescence difference (Scheme 5).25b Thus, the fluorescent
‘OFF’ polymers 1a–b may form complexes with Zn2+ to give fluores-
cent ‘ON’ Zn(II)-polymer complexes that could enantioselectively
recognize (R)-9 and (S)-9 to afford enhanced fluorescent Zn(II)-poly-
mer-9 complexes. Experiments with (R)-9 ((IR/Io)max = 6.78 and 3.19,
respectively, for 1a and 1b) showed higher fluorescence intensity
compared to that with (S)-9 [(IS/Io)max = 5.94 and 2.58, respectively,
for 1a and 1b]. The enhancement in the fluorescence of the Zn(II)-
polymer-9 complex was due to the reduced secondary Zn—O inter-
actions between the salen unit.4a,26 The
D(I/Io)max corresponds to
0.91 and 0.61 for the Zn(II)-polymer 1a and Zn(II)-polymer 1b
complexes, respectively, which suggests that the Zn(II)-polymer 1a
complex could strongly discriminate between enantiomers (R)-9
and (S)-9 compared with Zn(II)-polymer 1b complex.
Figure 5. (a) Fluorometric titration of 1b (1 ꢁ 10ꢀ5 M in THF, kex = 360 nm) with
0.1–1.1 equiv of Zn2+ ion (3 ꢁ 10ꢀ4 M in water, with respect to the monomeric unit
of 1b). (b) Hill plot of 1b with 0.1–1.1 equiv of Zn2+ (with respect to monomeric unit
of 1b).
3. Conclusion
enhanced fluorescence,4a,25 the in situ generated Zn(II) complexes
of polymers 1a–b with Zn2+ were studied for the selective recogni-
tion of chiral imines (R)-9 and (S)-9 bearing the pyridine moiety
(Figs. 6 and 7 and Table 1).
The synthesis of chiral main chain polymers 1a–b with (R,R)-
salen and 1,4-dioctyloxybenzene moieties has been accomplished
via a C–C cross-coupling reaction as the key step. These chiral mate-

574
S. Sakthivel, T. Punniyamurthy / Tetrahedron: Asymmetry 23 (2012) 570–576
Zn2+
1a b
1a-b-Zn(II)
1a-b-Zn(II)
Enhanced
-
OFF
ON
Fluorescence
Fluorescence
= (R)-9 or (S)-9
Scheme 5. Plausible mechanism for fluorescence chiral recognition.
enantioselective discrimination toward (R)- and (S)-1-phenyl-N-
[(pyridin-2-yl)methylene]ethanamines under ambient conditions.
4. Experimental section
4.1. General
2,4-Dihydroxybenzaldehyde (98%), trifluoromethane-sulfonic
anhydride (P99%), hydroquinone (P99%), (trimethylsilyl)acety-
lene (98%), octyl bromide (99%), trimethyl borate (P98%), n-BuLi
(2.0 M in cyclohexane), Pd(PPh3)2Cl2 (98%), CuI (98%), PPh3 (99%)
Ce(NO3)3ꢃ6H2O (P98%), Cd(NO3)2ꢃ4H2O (P99%) and Zn(NO3)2ꢃ
6H2O (98%) were purchased from Aldrich. Co(NO3)2ꢃ6H2O (97%),
Cu(NO3)2ꢃ3H2O (P99%), Ni(NO3)2ꢃ6H2O (98%), Al(NO3)3ꢃ9H2O
(P95%) and NaNO3 (P99%) were purchased from Merck.
Fe(NO3)3ꢃ9H2O (98%), Pb(NO3)2 (98%) and AgNO3 (99%) were
purchased from Rankem and used as received without further
purification. Et2O and THF were freshly distilled from sodium
and benzophenone under nitrogen prior to use. Column chroma-
tography was carried out with Rankem 60–120 mesh silica gel.
Analytical TLC was performed with Rankem silica gel G and GF
254 plates. NMR spectra (400 MHz for 1H and 100 MHz 13C) were
recorded on a DRX-400 Varian spectrometer using CDCl3 as solvent
and Me4Si as an internal standard. Chemical shifts (d) are reported
in ppm and spin–spin coupling constants (J) are given in Hz.
Melting points were determined using a Buchi B-540 and are
uncorrected. IR spectra were recorded using a Perkin–Elmer
spectrum one spectrometer. UV-vis spectra were recorded on
Perkin–Elmer Lambda 25 UV/vis spectrometer. Fluorescence spec-
tra were recorded on a Varian Carey Eclipse fluorescence spectro-
photometer. GPC analysis was performed with the stationary
phase column StyragelÒ WAT044221 using polystyrene as an inter-
nal standard and THF as eluent. The optical rotation was measured
on a PerkinElmer model-343. Thermal gravimetric analysis was
performed on SDT Q600 under a nitrogen atmosphere. Elemental
analysis was carried out using a Perkin–Elmer 2400 CHNS analyzer.
Figure 7. Chiral recognition of the Zn(II)-polymer 1a–b complexes (generated
in situ from 1 ꢁ 10ꢀ5 M of 1a–b in THF and 12 ꢁ 10ꢀ4 M of Zn2+in water (1:1.1))
with 1–18 equiv of (R)-9 and (S)-9 (6 ꢁ 10ꢀ3 M in THF).
D(I/Io)max corresponds to
0.91 and 0.61, respectively, for (a) and (b).
Table 1
Chiral recognition of (R)-9 and (S)-9 with Zn2+-polymer complexes
N
N
4.2. Preparation of the dialdehyde 2
N
N
4-Formyl-3-hydroxyphenyl trifluoromethanesulfonate 8 (7.2
Me
(R)-9
Me
(S)-9
mmol, 1.94 g), 2,5-di(octyloxy)phenyldiboronate
6 (3.4 mmol,
1.44 g), Pd(PPh3)2Cl2 (6 mol %), PPh3(18 mol%) and K2CO3 (20.4
mmol, 2.8 g) were stirred at reflux for 24 h in THF (30 mL) under
a nitrogen atmosphere. The solvent was then evaporated on a ro-
tary evaporator to give a residue, which was dissolved in EtOAc
(30 mL) and washed with brine (5 mL) and water (2 ꢁ 10 mL). Dry-
ing (Na2SO4) and evaporation of the solvent gave a solid, which
was purified by silica gel column chromatography using EtOAc
and hexane as eluent to give 2 as a yellow solid in 80% yield. Mp
115 °C; 1H NMR (400 MHz, CDCl3) d 11.07 (s, 2H), 9.92 (s, 2H),
7.57 (d, J = 8.4 Hz, 2H), 7.27 (t, J = 8.0 Hz, 2H), 7.19 (s, 2H), 6.96
(s, 2H), 3.93 (t, J = 6 Hz, 4H), 1.69 (t, J = 6.8 Hz, 4H), 1.35–1.23 (m,
20H) 0.85 (t, J = 6.2 Hz, 6H); 13C NMR (100 MHz, CDCl3) d 196.2,
161.5, 150.5, 147.4, 133.2, 130.3, 121.8, 119.6, 118.5, 115.8, 69.7,
32.0, 29.4, 26.2, 22.8, 14.3; FT-IR (KBr) 3055, 2923, 2853, 1645,
1621, 1557, 1520, 1493, 1467, 1434, 1392, 1371, 1317, 1266,
1211, 1198, 1134, 1055, 1030, 971, 939, 904, 883, 818, 741, 717,
.
b
Zn2+-polymer [c1]a
Enantiomer
(I/Io)max
K (Mꢀ1
)
Zn2+-1a
Zn2+-1a
Zn2+-1b
Zn2+-1b
(R)-9
(S)-9
(R)-9
(S)-9
6.78
5.94
3.19
2.58
3.02 ꢁ 104
2.04 ꢁ 104
6.60 ꢁ 104
5.62 ꢁ 104
a
[c1] = 1 ꢁ 10ꢀ5 M in THF.
b
K = stability constant calculated from a linear Hill plot with 1:1 binding model
to the fluorescence enhancement.
rials are soluble in common organic solvents and serve as highly
selective fluorescent chemosensors toward Zn2+. Polymer 1b with
(R,R)-1,2-diphenylethylenediamine and Zn2+ exhibited the best
fluorescence enhancement as an OFF–ON chemosensor. In addition,
the resultant Zn(II)-polymer complexes showed significant

S. Sakthivel, T. Punniyamurthy / Tetrahedron: Asymmetry 23 (2012) 570–576
575
587, 513 cmꢀ1. Anal. Calcd for C36H46O6: C, 75.23; H, 8.07. Found:
C, 75.19; H, 8.11.
1.2 Hz, 1H), 7.44 (d, J = 8.4 Hz, 2H), 7.39–7.23 (m, 4H), 4.65 (q,
J = 13.2, 6.8 Hz, 1H), 1.62 (d, J = 6.8 Hz, 3H); 13C NMR (100 MHz,
CDCl3) d 160.5, 154.8, 149.4, 144.6, 136.6, 128.6, 127.1, 126.8,
124.8, 121.5, 69.6, 24.6; FT-IR (neat) 3060, 2972, 2926, 2861,
1587, 1567, 1467, 1436, 1371, 1080, 993, 908, 762, 699,
4.3. Synthesis of polymers 1a–b
4.3.1. Polymer 1a
549 cmꢀ1; (R)-enantiomer (R)-9 ½a 2D0
¼ ꢀ34:1 (c 1.05, CHCl3). Anal.
ꢄ
To a stirred solution of dialdehyde 2 (1.8 mmol, 1.04 g) in CHCl3
(5 mL) was added (1R,2R)-diamino-cyclohexane 3a (1.8 mmol,
0.205 g) and the resultant mixture was stirred at 45 °C for 3 h.
The reaction mixture was then concentrated (ca. 2 mL) and treated
with MeOH (3 mL). The resultant precipitate 1a was collected by
Calcd for C14H14N2: C, 79.97; H, 6.71; N, 13.32. Found: C, 79.90; H,
6.73; N, 13.37. (S)-enantiomer (S)-9 ½a D20
¼ þ34:8 (c 1.04, CHCl3);
ꢄ
lit.27b
½
a 2D0
ꢄ
¼ þ85 (c 0.6, CHCl3). Anal. Calcd for C14H14N2: C,
79.97; H, 6.71; N, 13.32. Found: C, 79.92; H, 6.73; N, 13.35.
filtration as
a yellow powder in 91% (1.06 g) yield. GPC:
4.6. Enantioselective fluorescent recognition
Mw = 16771, Mn = 12261 (PDI 1.37); 1H NMR (400 MHz, CDCl3) d
8.33 (s, 2H), 7.21–7.07 (m, 6H), 6.91 (s, 2H), 3.84 (t, J = 8.6 Hz,
4H), 3.35 (s, 2H), 1.92–1.20 (m, 32 H), 0.83 (t, J = 7 Hz, 6H); 13C
NMR (100 MHz, CDCl3) d 164.5, 160.8, 150.4, 142.6, 131.0, 130.4,
120.4, 117.8, 117.6, 116.1, 72.8, 69.6, 33.4, 31.9, 29.3, 26.1, 24.4,
22.8, 14.3; FT-IR (KBr) 3440, 2926, 2855, 1622, 1563, 1491, 1468,
1367, 1205, 1142, 1037, 936, 863, 813 cmꢀ1; UV-vis (CHCl3): kmax
A solution of polymers 1a–b (3 mL, 1 ꢁ 10ꢀ5 M in THF with re-
spect to monomeric unit) and Zn(NO3)2ꢃ6H2O (28
l
L, 12 ꢁ 10ꢀ4
M
in H2O, 1.1 equiv) was thoroughly mixed at ambient temperature
to produce the respective Zn(II)-polymer complexes. After 5 min,
they were treated with (R)-9 or (S)-9 (5–90 lL (1–18 equiv),
6 ꢁ 10ꢀ3 M in THF). The solutions were mixed and left for 5 min
at ambient temperature to generate the corresponding Zn(II)-poly-
mer-(R)-9 or (S)-9 complexes. The fluorescence of the respective
solutions was measured with kex = 360 nm.
(e
) = 289 (2.60 ꢁ 104), 349 (2.98 ꢁ 104) nm (Mꢀ1cmꢀ1); fluores-
cence (THF): kex = 360 nm; kem = 423, 521 nm; ½a D20
¼ ꢀ570 (c
ꢄ
0.02, CHCl3). Anal. Calcd for (C42H56N2O4)n: C, 77.26; H, 8.65; N,
4.29. Found: C, 77.19; H, 8.67; N 4.23.
Acknowledgment
4.3.2. Polymer 1b
To a stirred solution of dialdehyde 2 (1.8 mmol, 1.04 g) in CHCl3
(5 mL) was added (1R,2R)-diphenylethylenediamine 3b (1.8 mmol,
0.382 g) and the resultant mixture was stirred at 45 °C for 3 h. The
isolation of 1b was carried out as described for 1a as a yellow pow-
der in 97% (1.26 g) yield. GPC: Mw = 19274, Mn = 12449 (PDI 1.55);
1H NMR (400 MHz, CDCl3) d 8.34 (s, 2H), 7.19–7.08 (m, 16H), 6.92
(s, 2H), 4.77 (s, 2H), 3.84 (t, J = 6.4 Hz, 4H), 1.62–1.19 (m, 24 H),
0.80 (t, J = 6.6 Hz, 6H); 13C NMR (100 MHz, CDCl3) d 166.0, 160.8,
150.4, 143.1, 139.8, 131.2, 130.4, 128.5, 128.1, 127.8, 120.7,
117.9, 117.6, 116.1, 80.4, 69.7, 31.9, 29.4, 26.2, 22.8, 14.3; FT-IR
(KBr) 3435, 3029, 2924, 2853, 1622, 1561, 1490, 1467, 1454,
This work was supported by the Department of Science and
Technology, New Delhi, and the Council of Scientific and Industrial
Research, New Delhi.
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1367, 1260, 1207, 1137, 1027, 935, 865, 812, 766, 698, 603 cmꢀ1
;
UV-vis (CHCl3): kmax
(
e
) = 290 (2.77 ꢁ 104), 352 (3.21 ꢁ 104) nm
(Mꢀ1cmꢀ1); fluorescence (THF): kex = 360 nm; kem = 421, 519 nm;
½
a 2D0
ꢄ
¼ ꢀ126 (c 0.03, CHCl3). Anal. Calcd for (C50H58N2O4)n: C,
79.96; H, 7.78; N, 3.73. Found: C, 79.91; H, 7.81; N, 3.76.
4.4. Metal ion titration
The solutions of polymers 1a-b (3 mL, 1 ꢁ 10ꢀ5 M in THF with
respect to the monomeric unit) and metal nitrate salts (100 lL,
3 ꢁ 10ꢀ4 M in water, 1 equiv) were thoroughly mixed at ambient
temperature to produce the corresponding metal-polymer com-
plexes (Fig. 2). After 5 min, the fluorescent properties of the solu-
tion with the in situ generated metal-polymer complexes were
measured.
4.5. Preparation of 1-phenyl-N-[(pyridin-2-yl)methyl-ene]eth-
anamines (R)-9 and (S)-927a–b
To a stirred solution of pyridine-2-carboxaldehyde (1 mmol,
107 mg) in CH3OH (1 mL), (R)- or (S)-1-phenylethanamine
(1 mmol, 121 mg) was added and the resulting solution was stirred
at room temperature for 3 h. The solvent was evaporated on a ro-
tary evaporator to give a residue, which was dissolved in EtOAc
(10 mL) and washed with brine (5 mL) and water (2 ꢁ 10 mL). Dry-
ing (Na2SO4) and evaporation of the solvent gave a residue, which
was purified on basic silica gel column chromatography using
EtOAc and hexane as eluent to give (R)-9 or (S)-9 as a yellow liquid
in 97% (203 mg) yield. 1H NMR (400 MHz, CDCl3): d 8.62 (d,
J = 4.8 Hz, 1H), 8.47 (s, 1H), 8.08 (d, J = 8 Hz, 1H), 7.71 (dt, J = 7.6,

576
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