TCNE-decorated triphenylamine-based conjugated polymer: Click synthesis and efficient turn-on fluorescent probing for Hg2+

Article abstract of DOI:10.1016/j.dyepig.2013.12.016

A type of triphenylamine-based conjugated polymer with cyano-containing chromophore in side chain, poly[(9,9-dioctyl)-2,7-fluorene-co-N-4-(1,1,4,4- tetracyanobuta-1,3-dienyl)-4,4′-triphenylamine] (P3) was successfully synthesized by catalyst-free and efficient click reaction between poly[(9,9-dioctyl)-2,7-fluorene-co-N-4-ethynyl-4,4′-triphenylamine] (P2) and tetracyanoethylene (TCNE). Chemical structures of intermediates and target polymer were verified by FT-IR and ¹H NMR analyses. Fluorescence of P3's THF solution was specifically quenched by the introduction of I ^-, accompanied by the change of its apparent color from pale brown to light yellow. With the introduction of Hg²⁺, fluorescence of P3/I^- complex recovered quickly and even exceeded the initial intensity of pristine P3 (when the concentration of Hg²⁺ above ～6.65 × 10^-5 M). Other common cations brought very slight interference for P3/I^- complex's response of Hg²⁺, and the detection limit of Hg²⁺ reached ～6.9 nM for such probing system.2013 Elsevier Ltd. All rights reserved.

Full text of DOI:10.1016/j.dyepig.2013.12.016

Dyes and Pigments 104 (2014) 1e7
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
TCNE-decorated triphenylamine-based conjugated polymer: Click
synthesis and efficient turn-on fluorescent probing for Hg2þ
*
*
Wei Shi , Fudong Ma, Yonghai Hui, Hongyu Mi, Yong Tian, Yanli Lei, Zhengfeng Xie
Key Laboratory of Oil & Gas Fine Chemicals, Ministry of Education, College of Chemistry and Chemical Engineering, Xinjiang University, Urumqi 830046,
Xinjiang, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A type of triphenylamine-based conjugated polymer with cyano-containing chromophore in side chain,
poly[(9,9-dioctyl)-2,7-fluorene-co-N-4-(1,1,4,4-tetracyanobuta-1,3-dienyl)-4,40-triphenylamine] (P3) was
successfully synthesized by catalyst-free and efficient click reaction between poly[(9,9-dioctyl)-2,7-
fluorene-co-N-4-ethynyl-4,40-triphenylamine] (P2) and tetracyanoethylene (TCNE). Chemical structures
of intermediates and target polymer were verified by FT-IR and 1H NMR analyses. Fluorescence of P3’s
THF solution was specifically quenched by the introduction of Iꢀ, accompanied by the change of its
apparent color from pale brown to light yellow. With the introduction of Hg2þ, fluorescence of P3/Iꢀ
complex recovered quickly and even exceeded the initial intensity of pristine P3 (when the concentration
of Hg2þ above w6.65 ꢁ 10ꢀ5 M). Other common cations brought very slight interference for P3/Iꢀ
complex’s response of Hg2þ, and the detection limit of Hg2þ reached w6.9 nM for such probing system.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 27 September 2013
Received in revised form
18 November 2013
Accepted 16 December 2013
Available online 25 December 2013
Keywords:
Triphenylamine
TCNE-decorated
Conjugated polymer
Fluorescent probe
Turn-on
Mercury ion
1. Introduction
selective turn-off fluorescent probes for Iꢀ, moreover, owing to the
high association constant and matching ratio between Iꢀ and Hg2þ
,
Hg2þ is a type of tremendous poisonous pollutant and the high-
efficiency detection of Hg2þ by practical-simple and low-cost pro-
tocol is still a challenging issue [1e4]. Considerable efforts have
been devoted to detect Hg2þ via different approaches, such as
neutron activation analysis [5], anodic stripping voltammetry [6,7],
inductively coupled plasma mass spectrometer [8], optical probes
[9e12] and so on. Among these reported methods, optical probes,
especially conjugated polymers (CPs)-based optical probes sprung
up in recent years displayed interesting advantages, such as good
optical stability [13,14], high sensitivity and excellent selectivity
[15e17], and thus have drawn increasing attention. Despite of the
great advance achieved in recent years, most of reported CPs-based
Hg2þ probes are turn-off mode, and the fluorescence turn-on
detection is much more preferable than the quenching mecha-
nism due to the ease of detection and less interference [18e20].
Recently, Iyer et al. reported a type of thiazole-containing CP as a
visual and fluorometric sensor for Iꢀ (turn-off mode) and Hg2þ
(turn-on mode) [21]. It was also reported by our group that tri-
phenylamine or carbazole-containing CPs can be utilized as
theses probes can realize the efficient turn-on detection for Hg2þ
[22,23]. These materials represent a series of promising probing
substrates and the detection limit for Hg2þ reached w2.4 ꢁ 10ꢀ7 M
[22]. How to further modify their probing performance is an
interesting issue remains to be solved, which might be explored by
investigating the relationship between the chemical structure-
probing properties of these polymeric fluorescent sensors.
Recently, Kaur et al. reported a charge-transfer compound of
cyano-containing N-methylpyrrole derivative [24], which exhibits
good selectivity and reasonably sensitivity (with detection limit of
w10 ppm) for Hg2þ. The intramolecular charge-transfer (ICT) in
this compound was quenched due to the interaction between
dicyano-substituted olefinic carbon atom and Hg2þ, which is
responsible for the alteration of its optical properties [24]. This
finding give us an inspiration that the introduction of electron-
withdrawing cyano groups into Hg2þ-responsive CPs might
simultaneously tune their electron energy and modify the inter-
action between these CPs and Hg2þ. Tetracyanoethylene (TCNE) is
one type of typical cyano-containing strong electron acceptors and
has been successfully introduced into carbazole and thiophone-
based CPs by catalyst-free, ethynyl-TCNE addition click reaction
[25e29]. But to the best of our knowledge, although the TCNE-
decorated small-molecular triphenylamine derivatives have been
* Corresponding authors. Tel.: þ86 0991 8588368; fax: þ86 0991 8582809.
E-mail addresses: xjuwshi@gmail.com, shiwei@xju.edu.cn (W. Shi), xiezhf72@
gmail.com (Z. Xie).
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.12.016

2
W. Shi et al. / Dyes and Pigments 104 (2014) 1e7
successfully synthesized [30,31] and applied as the optical probe
for cysteine [31], the introduction of TCNE to triphenylamine-based
CP as well as using it as Hg2þ optical probe has not been reported up
to now.
sodium at the presence of benzophenone and degassed before use.
N, N-bis(4-bromophenyl)-4-(triisopropylsilyl-alkynyl)aniline (3)
was synthesized according to the method reported previously by
our group [32]. 2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-
yl)-9,9-dioctylfluorene (4) was synthesized according to reported
literature [33].
Inspired by above-mention knowledge and in order to
modify the turn-on Hg2þ probing performance of triphenylamine-
based CPs, a kind of triphenylamine-based CP with chromophore in
side chain, poly[(9,9-dioctyl)-2,7-fluorene-co-N-4-(1,1,4,4-tetracy-
anobuta-1,3-dienyl)-4,40-triphenylamine] (P3), was successfully
synthesized by catalyst-free and efficient click reaction between
acetylene (^CeH) pendent-substituted precursor polymer, poly
[(9,9-dioctyl)-2,7-fluorene-co-N-4-ethynyl-4,40-triphenylamine]
(P2) and TCNE. The sensing properties of P3 to Iꢀ and the further
P3/Iꢀ complex to Hg2þ was investigated systematically in this
effort.
Solutions of Fꢀ, Clꢀ, SO42ꢀ, HCO3ꢀ, SCNꢀ, H2PO4ꢀ, CO32ꢀ, NO3ꢀ and Iꢀ
were prepared from their sodium salts. Brꢀ and Acꢀ were prepared
from their potassium salts. Solutions of Ba2þ, Al3þ, Cu2þ, Co2þ
,
Mg2þ, Ni2þ, Zn2þ Pb2þ, Fe3þ, Cd2þ, Agþ and Ca2þ were prepared
from their nitrate salts. Hg2þ was prepared from its acetate salt.
Concentrations of above-mentioned solutions were controlled at
10ꢀ1 M in deionized water and were diluted subsequently to
different concentration stocks for next use.
2.3. Synthesis
2. Experimental section
2.3.1. Synthesis of poly[(9,9-dioctyl)-2,7-fluorene-co-N-4-
triisopropylsilyl-alkynyl-4,40-triphenylamine] (P1)
2.1. Measurements and characterization
N,
N-bis(4-bromophenyl)-4-(triisopropylsilyl-alkynyl)aniline
IR spectra were recorded on an EQUINOX 55 FT-IR spectrometer
with KBr pellets. 1H NMR spectra were collected on a VARIAN
INOVA-400 spectrometer operating at 400 MHz in deuterated
chloroform solution with tetramethylsilane as the internal stan-
dard. UVevisible absorption spectra were recorded on a SHIMADZU
UV-2450 UVevis spectrophotometer. PL spectra were recorded on
SHIMADZU RF-5301pc spectrophotometer. Number-average (Mn)
and weight-average (Mw) molecular weights were determined by
UltiMate3000 in THF using a calibration curve of polystyrene
standards. Cyclic voltammogram were carried out on a CHI660D
electrochemical workstation with platinum electrodes at scan rate
of 50 mV/s against saturated calomel reference electrode (SCE) with
nitrogen-saturated solution of 0.1 M tetrabutylammonium hexa-
fluorophosphate (n-Bu4NPF6) in CH3CN.
(3) (0.350 g, 0.60 mmol), 2,7-bis(4,4,5,5-tetramethyl-1,3,2-
dioxaborolan-2-yl)-9,9-dioctylfluorene (4) (0.360 g, 0.60 mmol)
were added in toluene (16 mL) and 0.2 M potassium carbonate
aqueous solution (3.0 mL). Under nitrogen, Pd(OAc)2 (0.006 g,
0.026 mmol) and 3 drops of Aliquat 336 were placed. The above
mixture was degassed for several times, tricyclohexyl phosphine
(0.012 g, 0.042 mmol) was added afterward. The reaction mixture
was refluxed for 3 days under nitrogen before it was cooled to room
temperature. The crude product was reprecipitated into methanol
(250 mL) and the formed precipitate was purified by flash column
chromatography using toluene as eluant. The target polymer was
obtained by reprecipitation in methanol and dried in vacuum at
50 ꢂC overnight (0.400 g, 79%). FT-IR (KBr, cmꢀ1): 3033, 2925, 2860,
2150 (C^C), 1597, 1504, 1486, 1381, 1315, 1285 (CeN), 1178, 1071,
883, 817, 668. 1H NMR (400 MHz, CDCl3)
d (ppm): 7.81e7.72 (m,
2.2. Materials
1.98H), 7.64e7.52 (m, 6.02H), 7.39e7.33 (m, 4.05H), 7.18e7.07 (m,
2.94H), 7.04e6.98 (m, 2.18H), 6.95e6.91 (m, 1.18H), 2.15e1.93 (m,
4.00H, fluorene eCH2e), 1.19e1.09 (m, 45.28H, alkyl H), 0.85e0.78
(m, 6.06H, alkyl H). Gel permeation chromatography (GPC):
Mw ¼ 11,822, Mn ¼ 9173, and Mw/Mn ¼ 1.29.
All reagents, unless otherwise specified, were purchased from
Aldrich, Acros and TCI Chemical Co. and used without further pu-
rification. Tetrahydrofuran (THF) and toluene were distilled from
Scheme 1. Synthesis of monomers and polymers.

W. Shi et al. / Dyes and Pigments 104 (2014) 1e7
3
2.3.2. Synthesis of poly[(9,9-dioctyl)-2,7-fluorene-co-N-4-ethynyl-
4,40-triphenylamine] (P2)
2.3.3. Synthesis of poly[(9,9-dioctyl)-2,7-fluorene-co-N-4-(1,1,4,4-
tetracyanobuta-1,3-dienyl)-4,40-triphenylamine] (P3)
A solution of P1 (0.211 g, 0.25 mmol) in anhydrous THF
(10 mL) was vigorously stirred under nitrogen in a round-bottom
flask and n-tetrabutylammoniumfluoride (n-Bu4NF) (1 M in THF,
1.27 mL, 1.27 mmol) was added to this solution. The mixture was
stirred at room temperature overnight. The crude product was
purified by flash column chromatography, using toluene as an
eluant, then concentrated and reprecipitated in methanol. The
final product was obtained after vacuum drying at 50 ꢂC over-
night (0.190 g, 90%). FT-IR (KBr, cmꢀ1): 3293 (^CeH), 3032,
2923, 2851, 2104 (C^C), 1597, 1504, 1462, 1315, 1285 (CeN), 1267,
TCNE (4.5 mg, 0.035 mmol) was added to a solution of P2
(24.0 mg, 0.035 mmol) in CHCl3 (5.0 mL). After stirring at room
temperature for 1 h under nitrogen, the solvent was vacuum-
evaporated to yield the desired product as brown-black solid
(27.9 mg, 98%). FT-IR (KBr, cmꢀ1): 3032, 2922, 2850, 2220 (C^N),
1590, 1486, 1321, 1285 (CeN), 1267, 1182, 1070, 887, 814, 620. 1H
NMR (400 MHz, CDCl3)
d (ppm): 8.09e8.00 (m, 1.08H), 7.84e7.64
(m, 4.92H), 7.63e7.45 (m, 5.26H), 7.45e7.31 (m, 4.15H), 7.18e7.10
(m, 2.07H), 7.08e6.98 (m, 0.96H), 6.89e6.71 (m, 0.64H), 2.19e1.84
(m, 4.00H, fluorene eCH2e), 1.31e0.95 (m, 24.14H, alkyl H), 0.81e
0.74 (m, 6.22H, alkyl H).
1176, 1071, 887, 815, 644. 1H NMR (400 MHz, CDCl3)
d (ppm):
7.81e7.73 (m, 1.80H), 7.65e7.51 (m, 6.74H), 7.43e7.33 (m, 3.87H),
7.18e7.12 (m, 1.96H), 7.06e7.00 (m, 2.11H), 6.98e6.88 (m, 0.98H),
3.10e3.00 (m, ^CeH, 1.07H), 2.12e1.87 (m, 4.00H, fluorene e
CH2e), 1.22e0.98 (m, 24.35H, alkyl H), 0.80e0.74 (m, 5.86H, alkyl
H).
3. Results and discussion
3.1. Synthesis and characterization
The synthetic route of intermediates and target polymer is
shown in Scheme 1. P1 was successfully obtained via Suzuki
coupling reaction and deprotected by the disilylation of n-Bu4NF in
THF at room temperature to afford acetylene-pendent substituted
polymer, P2, with high yield (90%). The target polymer, P3, was
synthesized by using P2 and TCNE as starting materials via atom-
economic click postfunctionalization at room temperature
without the involvement of any catalyst and demonstrated excel-
lent yield (98%). The number-average molecular weight of P1 was
measured by means of gel permeation chromatography (GPC)
analysis using THF as eluant against polystyrene standards, to be
9173 and with the polydispersity of 1.29. Considering that the
backbone of P1 should not be affected by subsequent disilylation
and click reaction, the molecular weight of P2 and P3 should be
close to that of P1.
The chemical structures of P1, P2 and P3 were verified by FT-IR
and 1H NMR analyses. As shown in Fig. S1, notable difference ap-
pears in FT-IR spectra between P1 and P2, i.e., in the spectrum of
P2, absorption signal intensity at w2104 cmꢀ1 (corresponds to the
C^C stretching vibration) weakened significantly as compared to
that of P1 (at w2150 cmꢀ1), and a new band at w3293 cmꢀ1 ap-
pears, which can be assigned to the typical stretching absorption
signal of ^CeH [34,35]. This indicates that the disilylation of trii-
sopropylsilyl (TIPS) groups successfully occurred. The ^CeH
stretching vibration signal fades significantly in the spectrum of P3,
and there is a new absorption signal appears at w2220 cmꢀ1, which
Fig. 1. Normalized UVevis (a) and PL spectra (b) of P1, P2 and P3 in THF
(w1.0 ꢁ 10ꢀ5 M) (inset in (a) is the visual photograph of polymers solutions).
Fig. 2. Cyclic voltammogram of P3 in CH3CN with 0.1 M n-Bu4NPF6 at room
temperature.

4
W. Shi et al. / Dyes and Pigments 104 (2014) 1e7
corresponds to the C^N stretching vibration of the cyano groups in
P3 [27].
(UVevis) absorption and fluorescence spectrometry. Fig.1a displays
the UVevis spectra of these polymers in normalization. From Fig. 1a
one can find that the absorption maxima of these three polymers
1H NMR spectra of polymers are shown in Fig. S2. 1H NMR
spectra of P1 and P2 are similar to each other as a whole, except
locate at w365 nm, which stem from the
pep* transition along
that a proton signal at w
d
3.08 ppm appears exclusively in the
polymer backbones. Different from other polymers, a new ab-
sorption band between 400 and 600 nm appears exclusively in the
spectrum of P3, which might be due to the interaction between the
electron-withdrawing 1,1,4,4-tetracyanobuta-1,3-dienyl pendent
and electron-donating triphenylamine moiety in polymer back-
bone [27]. Solutions of P1 and P2 are close to colorless, and the
apparent color of P3 is pale brown (seen from the inset in Fig. 1a).
Fig. 1b displays corresponding emission spectra of polymers in THF
solution. Spectra of P1, P2 and P3 are similar to each other and
display emission maxima at w431 nm.
spectrum of P2, which corresponds to the signal of deprotected
acetylene (^CeH) groups [34,35]. This result is consistent with the
finding in FT-IR analysis, by which one can conclude that the
desilylation reaction happened successfully. From spectrum of P3
one can find that the proton signal at w
Meanwhile, a new proton signal emerges at w
spectrum of P3 but not present in the spectra of P1 and P2, which
corresponds to the characteristic signal of olefinehydrogen in
1,1,4,4-tetracyanobuta-1,3-dienyl [31]. FT-IR and 1H NMR analyses
strongly support that P3 has been successfully synthesized by click
reaction between P2 and TCNE.
d
3.08 ppm almost vanishes.
8.04 ppm in the
d
3.3. Electrochemical properties
Electrochemical redox properties of P1, P2 and P3 have been
investigated via cyclic voltammogram (CV) using n-tetrabuty-
lammonium hexafluorophosphate (n-Bu4NPF6, 0.1 M) as sup-
porting electrolyte in acetonitrile at room temperature to reveal
3.2. Optical properties
Optical properties of three polymers were investigated in THF
(with the concentration of w1 ꢁ 10ꢀ5 M) by ultravioletevisible
Fig. 3. The UVevis absorption (a) and fluorescence response (b) of P3 (with the
concentration of 1.0 ꢁ 10ꢀ5 M) in the presence of common anions (with concentration
of 3.5 ꢁ 10ꢀ4 M for each ion).
Fig. 4. UVevis absorption (a) and fluorescence (b) alteration of P3 in THF (with con-
centration of w1.0 ꢁ 10ꢀ5 M) in the presence of various background anions and with
sequential addition of Iꢀ (with concentration of w3.5 ꢁ 10ꢀ4 M).

W. Shi et al. / Dyes and Pigments 104 (2014) 1e7
5
the redox activities of the polymers and estimate their energy
levels. For P1 and P2, we just obtained their oxidation curves and
the corresponding reduction process was not recorded after
several trials. The oxidation onset potentials (Eoxonset) of P1 and
P2 appear at w1.10 V and 1.06 V (Fig. S3), respectively, and the
corresponding the highest occupied molecular orbital (HOMO)
levels are wꢀ5.50 and wꢀ5.46 eV, respectively, according to an
empirical formula, EHOMO ¼ ꢀe(Eoxonset þ 4.4) (eV) [36]. In
contrast, the TCNE adducted polymer P3 exhibits both anodic
and cathodic profiles under the same measurement condition
(Fig. 2), which might be ascribed to the coexistence of triphe-
nylamine donor and tetracyanobuta-1,3-dienyl acceptor moieties.
The Eoxonset of P3 appears at w0.90 V, which is lower than that of
P1 and P2. This is consistent with previous report that donore
acceptor type CPs generally possess narrower band gaps with an
elevated HOMO level and a lowered the lowest occupied mo-
lecular orbital (LUMO) level, as compared to the neutral or
donor-type polymers [28]. During the cathodic scanning, there
are two-step reduction processes of P3 and with the first
reduction onset potential (Eredonset) at wꢀ1.02 V. The HOMO
level of P3 is wꢀ5.30 eV and the LUMO level of P3 can be
calculated according to ELUMO ¼ ꢀe(Ereonset þ 4.4) (eV), to be
wꢀ3.38 eV [36]. The corresponding bandgap of P3 can be ob-
tained by the subtraction of its HOMO and LUMO levels, to be
w1.92 eV.
of Iꢀ led to tremendous fluorescence quenching while other an-
ions brought inconspicuous influence toward fluorescence in-
tensity of P3.
Fig. S4 displays detailed fluorescent response of P3 toward Iꢀ.
Upon addition of increasing amount of Iꢀ, fluorescence intensity of
P3 decreased gradually, accompanied by the alteration of its
apparent color (Fig. S5). The detection limit of Iꢀ by P3 reaches
w9.7 ꢁ 10ꢀ8 M (according to 3
s rule) [39] as is reflected by its PL
spectra (Fig. S4). The mechanism of fluorescence quenching in this
case might via “heavy-atom” effect [22,23,37,38]. Here, the “heavy-
atom” interaction exists between the excited state of
triphenylamine-containing polymer and Iꢀ, which lead to an
enhancement of the spin-orbit coupling [22,23,37,38].
To evaluate the selectivity of P3 toward Iꢀ, competition exper-
iments were carried out. As is shown in Fig. 4, the background
anions brought slight influence for P3’s optical response toward Iꢀ.
It suggests that this polymer possess excellent selectivity and anti-
interference toward Iꢀ.
3.4. Optical response of P3 toward Iꢀ
According
to
previous
investigation,
carbazole
or
triphenylamine-based conjugated systems can be applied as
sensitive and selective Iꢀ optical probe [22,23,37,38]. Spectral
response of P3 (with the concentration of w1.0 ꢁ 10ꢀ5 M in THF)
toward Iꢀ was thus investigated. Various anionic ions were
introduced into solution of P3, and corresponding UVevis spectra
are illustrated in Fig. 3a. From Fig. 3a one can note that the
distinct enhancement in absorbance was detected exclusively
with the addition of Iꢀ, and other anions just brought slight in-
fluence. Fig. 3b exhibits fluorescence spectra of P3 toward
various anions. In consistent with our previous results about
triphenylamine or carbazole-containing CPs [22,23], the addition
Fig. 6. Fluorescence intensity changes of P3/Iꢀ in THF (concentrations of P3 and Iꢀ
were 1.0 ꢁ 10ꢀ5 and 3.5 ꢁ 10ꢀ4 M, respectively) in the presence of incremental Hg2þ
(a) (inset is the enlarged region of spectrum with low concentration of Hg2þ) and
relationship between I/I0 and Hg2þ (b) (inset is the fitting curve with concentration of
Hg2þ lower than 9.24 ꢁ 10ꢀ7 M).
Fig. 5. UVevis absorption changes of P3/Iꢀ in THF (concentrations of P3 and Iꢀ were
1.0 ꢁ 10ꢀ5 and 3.5 ꢁ 10ꢀ4 M, respectively) in the presence of various metal ions
(w7.5 ꢁ 10ꢀ5 M).

6
W. Shi et al. / Dyes and Pigments 104 (2014) 1e7
better than reported CPs-based turn-on type Hg2þ probes
[21,41,42].
In order to propose the possible reason for such impressive
fluorescence enhancement of P3/Iꢀ toward Hg2þ, the correspond-
ing control experiments were carried out to use P1/Iꢀ and P2/Iꢀ as
probing substrates. From Fig. S6, with the addition of Iꢀ, one can
also find the obvious fluorescence quenching for both P1 and P2
solutions. This result is reasonable due to the presence of triphe-
nylamine segment in these two polymers [22]. With the following
addition of Hg2þ (1.5 ꢁ 10ꢀ4 M), fluorescence of P1 and P2-involved
systems recovered to w90% and 81% of their initial values, and the
fluorescence intensity of both systems altered slightly with the
Fig. 7. Photograph of P3/Iꢀ in THF (concentrations of P3 and Iꢀ were 1.0 ꢁ 10ꢀ5 and
3.5 ꢁ 10ꢀ4 M, respectively) under natural light (upper) and ultraviolet light (365 nm)
(bottom) with the addition of various metal ions (w7.5 ꢁ 10ꢀ5 M).
further addition of Hg2þ
.
Interestingly, P3/Iꢀ displays different performance from P1 and
P2. When the concentration of Hg2þ reaches w6.65 ꢁ 10ꢀ5 M, the
fluorescence intensity of P3/Iꢀ system has exceeded the corre-
sponding value of pristine P3 (Fig. S6c). When the concentration of
Hg2þ came up to w8.30 ꢁ 10ꢀ5 M, the fluorescence intensity of P3/
Iꢀ/Hg2þ system even as high as two folds of the initial value of P3
(Fig. S6c) (the fluorescence with more Hg2þ could not be recorded
due to the corresponding value has surpassed the equipment’s
measurement range with the fixed slit width). Given the same
maintain structures of these three polymers, such difference in
their fluorescence recovery might be attributed to their different
tethered substituents.
3.5. Optical response of P3/Iꢀ complex toward Hg2þ
We further find that the quenched fluorescence of P3/Iꢀ com-
plex restored in the presence of Hg2þ. In order to confirm whether
P3/Iꢀ complex can be used as a selective, sensitive and anti-
interferential optical Hg2þ probe, the corresponding investigation
was carried out.
As can be seen from Fig. 5, with the addition of Hg2þ, obvious
decrease of P3/Iꢀ complex’s absorption at w365 nm takes place,
while the curves with other metal ions altered slightly as compared
to that of Hg2þ. Similar recovery trend can be observed in the
investigation of P3/Iꢀ’s fluorescence within the Hg2þ titration
process (Fig. 6). As can be seen from Fig. 6, with the incremental
addition of Hg2þ, fluorescence intensity of P3/Iꢀ increased gradu-
ally, accompanied by the alteration of its apparent color (turned
back to slight brown, Fig. 7), suggesting the distraction of Iꢀ from
P3/Iꢀ complex due to the stronger association between Iꢀ and Hg2þ
[22,23,40]. The heavy atom effect brought by Iꢀ is thus removed
and the fluorescence recovered accordingly [22,23]. It is interesting
to find that the fluorescence of P3/Iꢀ/Hg2þ system has restored
even higher than P3’s initial intense when the concentration of
Hg2þ reaches w6.65 ꢁ 10ꢀ5 M, and further remarkable enhance-
ment of the fluorescence of this system can be detected with more
Hg2þ (w8.30 ꢁ 10ꢀ5 M) (Fig. 6). Detection limit of Hg2þ reaches
To get more insight about such speculation, the fluorescence
response of bare P3 toward Hg2þ was investigated and the result is
shown in Fig. S7. As shown in Fig. S7, the fluorescence of P3
decreased monotonously with the addition of Hg2þ (which might
be due to the interaction between Hg2þ and dicyano-linked carbon
atoms in pendent TCNE) [24]. As combined with the fact that the
fluorescence of P3 also has been quenched monotonously by Iꢀ
(Fig. S4), one can deduce that the further fluorescence enhance-
ment of P3/Iꢀ with Hg2þ’s concentration above w6.65 ꢁ 10ꢀ5 M is
not stem from the presence of isolated Hg2þ or Iꢀ (not participate
into the mutual association). Such results indicate that the
extraordinary fluorescence enhancement of P3/Iꢀ is stem from the
synergic effect of Iꢀ abstraction (by the strong association between
Hg2þ and Iꢀ) and the further interaction between Hg2þ/Iꢀ complex
with the pendent TCNE, although the exact mechanism is not clear
at this stage.
w6.9 nM (according to 3s rule) [39] by this probing system. This
value is superior to our recent reports regarding triphenylamine or
carbazole-derivated CPs without the TCNE adduct (has improved
by two orders of magnitude) [22,23], and is comparable or little
To evaluate the selectivity of P3/Iꢀ toward Hg2þ, responses of a
number of common metal ions (Agþ, Al3þ, Ba2þ, Ca2þ, Cd2þ, Co2þ
,
Cu2þ, Fe3þ, Mg2þ, Ni2þ, Pb2þ, and Zn2þ) were investigated in
competition experiments. Fig. 8 illustrates the interference of these
metal ions for P3 against Hg2þ. From it we can find that the addition
of Hg2þ brought considerable fluorescence enhancement with the
existence of background cations, and all of background metal ions
just brought tiny influence for the detection of Hg2þ. Considering
that these spectra were recorded in a short time interval without
long-time standing at room temperature (20 s later with the
addition of each ion) and its anti-interference and sensitivity, P3
might be act as a promising immediacy turn-on optical probe for
Hg2þ
.
4. Conclusion
A TCNE-decorated triphenylamine-based conjugated polymer,
P3, was successfully prepared via efficient click postfunctional
addition reaction between alkynes in side chain of P2 and TCNE.
Due to the presence of triphenylamine segment in polymer back-
bone, P3 can be utilized as efficient turn-off fluorescence probe for
Iꢀ by “heavy-atom” mechanism. We further find that the probing
performance for P3/Iꢀ complex to realize turn-on detection of Hg2þ
is modified with the introduction of electron-withdrawing, cyano-
Fig. 8. Fluorescence alterations of P3/Iꢀ in THF (concentrations of P3 and Iꢀ were
1.0 ꢁ 10ꢀ5 and 3.5 ꢁ 10ꢀ4 M, respectively) in the presence of various background metal
ions (with concentration of 7.5 ꢁ 10ꢀ5 M for each ion) and with sequential addition of
Hg2þ (7.5 ꢁ 10ꢀ5 M).

W. Shi et al. / Dyes and Pigments 104 (2014) 1e7
7
containing TCNE adduct. Results support that P3/Iꢀ complex can act
as potential anti-interferential, selective and sensitive Hg2þ optical
probe.
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Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2013.12.016.
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