Improved colorimetric dual-emission and endued piezofluorochromism by inserting a phenyl between 9-anthryl and terpyridine

Article abstract of DOI:10.1016/j.dyepig.2016.01.019

Tridentate terpyridine is a functional building unit, and 9-anthylterpyridine has been used as ratiometric fluorescent sensor for Cd(II) and secondary sensor for pyrophosphate detection. Here we have inserted a phenyl unit between 9-anthryl and terpyridin

Full text of DOI:10.1016/j.dyepig.2016.01.019

Dyes and Pigments 128 (2016) 124e130
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Improved colorimetric dual-emission and endued
piezofluorochromism by inserting a phenyl between 9-anthryl and
terpyridine
*
Qikun Sun, Wei Liu, Wenchao Shang, Haichang Zhang, Shanfeng Xue, Wenjun Yang
Key Laboratory of Rubber-Plastics of Ministry of Education/Shandong Province, School of Polymer Science and Engineering, Qingdao University of Science &
Technology, 53 Zhengzhou Road, Qingdao 266042, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 December 2015
Received in revised form
Tridentate terpyridine is a functional building unit, and 9-anthylterpyridine has been used as ratio-
metric fluorescent sensor for Cd(II) and secondary sensor for pyrophosphate detection. Here we have
inserted a phenyl unit between 9-anthryl and terpyridine to synthesize a new terpyridine derivative,
11 January 2016
4
-(9-anthryl)phenyl terpyridine (ATP) to investigate the effect of structure change on optical prop-
Accepted 18 January 2016
Available online 27 January 2016
erties. The results show that ATP not only remains the selectively colorimetric fluorescence sensing to
2
þ
Cd but also the interval of two emission bands from ATP and ATPeCd(II) complex can be enlarged
significantly to 185 nm. Unlike 9-anthylterpyridineeCd(II) complex, ATPeCd(II) complex could be
decomplexed by most polyvalent anions. Moreover, the insertion of a phenyl ring can render ATP
eCd(II) complex remarkable piezofluorochromism with grinding-induced spectral shift of 54 nm. X-
ray diffraction and differential scanning calorimetry experiments confirm the phase transformation
between crystalline and amorphous states upon external stimuli is responsible for reversible PFC
behavior.
Keywords:
4-(9-Anthryl)phenyl terpyridine
Organic luminogen-metal complex
Cd(II) sensor
Piezofluorochromism
Polyvalent anions sensor
Two emission bands
©
2016 Elsevier Ltd. All rights reserved.
1
. Introduction
fluorescent sensing to Cd(II) (an non-essential toxic elements in
4
ꢀ
the human body) and PPi (pyrophosphate P O
, an essential
2
7
0
0
00
Pyridine, 2,2 -bipyridine, and 2,2 :6,2 -terpyridine are all
functional building blocks, and the conjugated molecules con-
taining them have aroused widespread concern and great interest
for their distinguished photophysical and electrochemical prop-
erties [1e15]. Especially, 2,2 :6,2 -terpyridine has become an
indispensable unit in supramolecular and material chemistry due
to its tridentate ligand feature, synthetic accessibility, and excel-
lent ability to bind with both low and high-oxidation state metal
ions [16e21]. Up to now, there have been a variety of reports on
the synthesis, optical and optoelectronic properties of
terpyridine-containing derivatives and their metal complexes,
and some of them exhibited interesting applications in fluores-
cence sensors, non-linear optics, and light-emitting devices
anion for normal cell function) [23]. Compared to intensity-based
fluorescent sensors (OffeOn process), ratiometric fluorescent
sensors show an obvious advantage because they can eliminate
most or all ambiguities by self-calibration through two emission
bands [24].
0
00
We have been interested in anthracene-based conjugated
molecules and found that the subtle manipulation of the conju-
gated skeletons and peripheral groups could endow anthracene-
based conjugated molecules with unique and tunable optical
and optoelectronic properties [25e30]. Here we have synthesized
a new terpyridine derivative with 9-phenylanthryl as the lumi-
nogen moiety, 4-(9-anthryl)phenyl terpyridine (ATP), to investi-
gate the effect of the insertion of phenyl unit between anthryl and
terpyridine on optical properties. It was found that the insertion of
phenyl ring could not only widen the interval of dual emission
from ATP and ATPeCd(II) complex but also enlarge the response
range to polyvalent anions. Moreover, the insertion of phenyl unit
endues ATPeCd(II) complex with remarkable piezofluorochrom-
ism [31].
[
6,22]. Recently, Jiao et al. synthesized an fluorescent terpyridine
derivative with anthryl as the chromophore exhibiting ratiometric
*
Corresponding author.
E-mail address: ywjph2004@qust.edu.cn (W. Yang).
http://dx.doi.org/10.1016/j.dyepig.2016.01.019
143-7208/© 2016 Elsevier Ltd. All rights reserved.
0

Q. Sun et al. / Dyes and Pigments 128 (2016) 124e130
125
2
. Experimental section
by column chromatography (silica gel ethyl acetate/methylene
chloride/EtOH ¼ 2/4/1, v/v/v). A pure white solid with a yield of 28%
1
2.1. Materials
(0.68 g) was obtained. H NMR (500 MHz, CDCl
3
)
d
8.92 (s, 2H), 8.74
(
d, 2H), 8.70 (d, 2H), 8.54 (s, 1H), 8.14 (d, 2H), 8.08 (d, 2H), 7.91 (m,
13
Acetonitrile (MeCN) and tetrahydrofuran (THF) were distilled
2H), 7.73 (d, 2H), 7.60 (d, 2H), 7.49 (m, 2H), 7.40 (m, 4H) ppm.
C
(
over metallic sodium) before use. 9-Bromoanthracene, 4-
NMR (125 MHz, CDCl 156.32, 156.11, 150.17, 149.21, 139.71,
3
) d
formylboronic acid, 2-acetylpyridine, tetrakis-(triphenylphos-
phine)-palladium and others were all commercial available
analytical-grade chemicals and were used as received, unless
otherwise claimed.
137.85, 136.88, 136.32, 131.91, 131.40, 130.19, 128.38, 128.00, 127.41,
126.70, 125.54, 125.17, 123.85, 121.37, 119.06 ppm.
2.4.3. Synthesis of ATPeCd(II) complex
In a 100 mL round bottom flask, ATP (97 mg, 0.2 mmol), and
2.2. Measurements
3 2 2 3
Cd(NO ) $4H O (61.6 mg, 0.2 mmol) was added to CH CN (14 mL)
and the mixture was stirred for 2 h at room temperature. The so-
1H and 13C NMR spectra were recorded on a BrukereAC500
lution was concentrated, a slight yellow solid ATPeCd(II) complex
1
(
500 MHz) spectrometer with CDCl
3
as solvent and tetramethylsi-
(98%) was obtained. H NMR (500 MHz, CDCl
3
)
d
9.05 (d, 2H), 8.6 (s,
lane (TMS) as the internal standard. The elemental analysis was
performed on PerkineElmer 2400. UVevis absorption spectra were
recorded on a Hitachi U-4100 spectrophotometer. Emission spectra
were measured with a Hitachi F-4600 spectrophotometer. The peak
wavelength of the lowest energy absorption band was used as the
excitation wavelength for the PL measurement. The fluorescence
3H), 8.44 (d, 2H), 8.17 (m, 2H), 8.12 (d, 2H), 8.04 (d, 2H), 7.74 (d, 4H),
13
7.69 (d, 2H),7.53 (m, 2H), 7.42 (m, 2H) ppm. C NMR (125 MHz,
CDCl 154.89, 151.38, 150.19, 148.24,142.13, 140.17, 135.56, 135.04,
3
) d
132.80, 131.37, 130.02, 128.63, 127.47, 127.20, 126.67, 126.17, 125.89,
125.30, 121.90, 120.51 ppm.
quantum yield (
dilution method using rhodamine B in methanol as the reference.
32] Powder wide angle X-ray diffraction (PWXD) measurements
F
) was determined at room temperature by the
3. Results and discussion
[
3.1. Synthesis and characterization of ATP and its Cd(II) complex
were performed on a Powder X-ray Diffractometry (INCA Energy,
Oxford Instruments), operating at 3 kW. Differential scanning
calorimetry (DSC) experiments were carried out on a Netzsch
4-(9-Anthryl)phenyl terpyridine (ATP) was synthesized from
the Suzuki coupling of 9-bromoanthracene and (4-formylphenyl)
boronic acid, followed by the addition of 2-acetylpyridine, KOH and
ꢁ
DSC204F1 at a heating rate of 10 C/min.
3 2
NH $H O in EtOH under reflux (Scheme 1). Detailed synthetic
2.3. Piezochromic and stimuli-recovering experiments
procedures and characterization data are provided in the
Experimental section. The ATPeCd(II) complex has been obtained
Grinding experiment: Pristine ATPeCd(II) solid was put on a glass
3 2 2 3
in quantitative yield by reacting ATP with Cd(NO ) $4H O in CH CN
plate and then ground with a metal spatula at room temperature.
Solvent-fuming experiment: The ground sample was above the
dichloromethane level and was exposed to the vapor for 30 s at
room temperature. Annealing experiment: the ground sample was
as detailed in the Experimental section. ATP and the ATPeCd(II)
complex were characterized by NMR and elemental analysis.
3.2. The responses of ATP to metal ions
ꢁ
put into an oven with the temperature 200 C for 3 min. After
external stimuli, the fluorescence images and emission spectra
were recorded at room temperature.
Tridentate terpyridine derivatives with the suitably arranged
ring nitrogen and the synthetic accessibility could be used to detect
metal cations in solution due to their good abilities to coordinate
with both low and high-oxidation state metal ions. Here we have
chosen a variety of available metal ions (salts nitrate), including
2
2
.4. Synthesis
2
þ
2þ
þ
þ
2þ
þ
2þ
3þ
2þ
3þ
2þ
2þ
.4.1. 9-(4-Formylphenyl)anthracene
Cd , Zn , Li , Na , Sr , K , Ba , Al , Mn , Cr , Co , Cu ,
3
þ
3þ
3þ
In a 100 mL round bottom flask, 9-bromoanthracene (1 g,
mmol) and 4-formylboronic acid (0.78 g, 5.2 mmol), and
M K CO were dissolved in THF (50 mL), and water (20 mL) at N
2 3 2
La , Nd , and Ce , to add into the acetonitrile (MeCN) solution of
ATP to investigate the fluorescence response behaviors. As shown
in Fig. 1, ATP solution itself emits blue with the fluorescence
4
2
þ
þ
2þ
þ
2þ
3þ
2þ
,
atmosphere. Then tetrakis-(triphenylphosphine)-palladium (0.17 g,
.15 mmol) was added into the mixture and the mixture was
quantum yield (
Ф
) of 0.72. When Li , Na , Sr , K , Ba , Al , Cu
3
þ
3þ
3þ
0
La , Nd , and Ce are added into the solution, the fluorescence
2þ
2þ
3þ
2þ
refluxed for 72 h. After that, the water was added to the mixture
and the organic phase extracted with dichloromethane was dried
color of ATP solution hardly change, but Zn , Mn , Cr , and Co
could quench the fluorescence emission of ATP solution. An inter-
esting phenomenon is that the addition of Cd could afford a red-
emitting solution whose is 0.13. These results indicate that ATP
solution could complex with Zn , Mn , Cr , Co , and Cd , and
the complexation with Cd
2
þ
over MgSO
without further purification. H NMR (500 MHz, CDCl
H), 8.55 (s, 1H), 8.13 (d, 2H), 8.04 (d, 2H), 7.64 (d, 2H), 7.58 (d, 2H),
4
. The crude product was used to the next reaction step
1
3
)
d
10.19 (s,
Ф
2
þ
2þ
3þ
2þ
2þ
1
13
2þ
7
.49 (m, 2H), 7.38 (m, 2H) ppm. C NMR (125 MHz, CDCl
42.2, 138.6, 137.3, 132.5, 131.7, 130.1, 128.9, 127.7, 126.5, 126.2,
25.6 ppm.
3
)
d
192.4,
could be used as the selectively
2þ
1
1
colorimetric fluorescence sensor for Cd detection.
Fig. 2a shows the absorption and emission spectra of ATP and
2þ
ATPeCd solutions. ATP and its Cd(II) complex have similar ab-
sorption spectra whose absorptions mainly appear before 400 nm
but different emission spectra. ATP solution shows a single-
emission band with the peak wavelength of 430 nm, and
0
0
0
00
2
.4.2. 4 -(4-(Anthracen-9-yl)phenyl)-2,2 :6 ,2 -terpyridine (ATP)
In a 250 mL round bottom flask, 2-acetylpyridine (1.22 g,
10.0 mmol), NH
3
(aqueous) (15 mL, 12.6 mmol), KOH (0.78 g,
2þ
12.0 mmol) was respectively added to a solution of 9-(4-for-
ATPeCd
solution exhibits a dual-emission profile whose two
mylphenyl)anthracene (1.04 g, 5.0 mmol) in EtOH (25 mL). The
solution was refluxed for 24 h. After cooling down to room tem-
perature, the solution was evaporated to dryness under reduced
pressure to give the crude product. The crude product was purified
peak wavelengths are at 420 and 605 nm, respectively. The short-
wavelength emission band is from the pendent phenylanthracene
segment (local emission), and the long-wavelength one could be
2
þ
ascribed to the ATPeCd complex (intramolecular transfer charge

126
Q. Sun et al. / Dyes and Pigments 128 (2016) 124e130
Scheme 1. Synthetic route and structure of new terpyridine-based luminogen (ATP) and its Cd(II) complex (ATPeCd2þ).
Fig. 1. The fluorescence colors of MeCN solution of ATP (1.0 ꢂ 10ꢀ5 M) upon adding 2.0 equiv. of various metal ions.
(
ICT) emission). The complexation happen between ATP and Cd2þ
could be confirmed further by comparing NMR spectra of ATP and
Therefore, the insertion of phenyl ring between 9-anthryl and ter-
pyridine not only retains the dual emission feature of ATPeCd(II)
complex but also significantly enlarge the interval of two emission
bands to afford more obvious ratiometric and colorimetric
fluorescence.
2
þ
ATPeCd in which the chemical shifts of protons were obviously
2
þ
changed upon the addition of Cd (Fig. 2a). Since the single crystal
of ATPeCd2 complex suitable to structure analysis is not able to be
obtained, the exact complex structure is not clear at present.
Considering that the structure characteristics of ATP and absorption
þ
The well-separated two emission bands imply that the complex
has two emission species, a long-wavelength emission species
induced by complexation and a short-wavelength one form phe-
nylanthracene segment. Since the hardly changed absorption
spectra upon complexation and the small overlap between the
spectrum of ATPeCd2 complex are the very similar to those of 9-
þ
2
þ
anthryl terpyridineeCd complex reported by Li and Yu et al. the
ATPeCd complex might also be 2:2 binding stoichiometry of ATP
and Cd . It is interesting that the peak interval of two emission
bands of ATPeCd complex is up to 185 nm, which is significantly
2
þ
2þ
2þ
emission band of ATP and the absorption band of ATPeCd com-
2
þ
plex in solution, the complex species is not a powerful intra-
molecular energy trap of phenylanthracene emission, which
2
þ
larger than that of 9-anthryl terpyridineeCd complex (130 nm).
Fig. 2. Absorption and emission spectra of ATP and ATPeCd2þ in acetonitrile at 1.0 ꢂ 10ꢀ5 M (a) and 1H NMR spectra of ATP and ATPeCd in CDCl
2þ
(b).
3

Q. Sun et al. / Dyes and Pigments 128 (2016) 124e130
127
Fig. 3. Emission spectra of ATPeCd2 in acetonitrile under different concentration (a) and emission spectra of ATP and ATPeCd solids (b).
þ
2þ
renders the complex dual emission characteristics. We have
(Fig. 4a). This suggests that ATP is not only a reversible and recy-
clable sensor for Cd but also its Cd(II) complex is a reversible and
2
þ
2þ
examined emission spectra of ATPeCd complex in MeCN under
different concentration (Fig. 3a). The total fluorescence intensities
recyclable secondary sensor for PPi. The reversible sensing behavior
2
þ
2þ
decrease with the increase of ATPeCd
concentration, but
of ATPeCd to PPi is examined over three cycles by the sequential
2
þ
2þ
different tendence in intensity change for two emission bands are
observed. The emission intensity of complex species increase
obviously while the emission intensity of ATP segment decreases
addition of PPi and Cd (Fig. 4b). ATPeCd solution emits red, and
2
þ
the addition of PPi affords an blue emission solution. When Cd is
2
þ
added to the solution of (ATPeCd þ PPi), a red emission solution
2
þ
sharply with the increase of ATPeCd concentration. Although the
emission spectra under higher concentration are not measured due
to its poor solubility, this result seems to imply the existence of
planar anthracene interactions quenching fluorescence emission,
and the interactions of emission species induced by complexation
have little effect on fluorescence emission. Meanwhile, we have
measured their solid-state emission spectra (Fig. 3b). ATP solid still
reappears, and further addition of PPi into the red emission solution
2
þ
2þ
þ
of (ATPeCd þPPi þ Cd ) reproduces the blue emission. With the
2
further addition of Cd , the solution turns dark red, and followed
by the addition of PPi, the olive green solution is observed. The deep
and dark red fluorescence color in third cycle could be ascribed to
2
þ
the introduction of water dissolving salts Cd and PPi.
2
þ
The complex of 9-anthryl terpyridine and Cd
could be
2
þ
emits blue with the peak wavelength of 437 nm, but ATPeCd
decomplexed only by PPi, which afforded a selective secondary
sensor for PPi [23]. We consider that the insertion of phenyl unit
solid is not of both blue and red emissions, just a green emission
material. This is probably caused by the different environment and
2
þ
should change the complexing strength of ATP and Cd , thus
ATPeCd(II) complex might be decomplexed by other anions. Fig. 5
shows the fluorescence images of ATPeCd(II) solution upon addi-
tion of different anions. It is observed that the red emission of
ATPeCd(II) solution is changed into the blue emission when poly-
2
þ
stacking mode of ATPeCd molecules in solution and solid states.
.3. The fluorescence response of ATPeCd2þ complex to anions
3
3
ꢀ
2ꢀ
2ꢀ
valent anions are added (Fig. 5a), such as PO
, SO4 , S O
,
It has been reported that the complex of 9-anthryl terpyridine
4
2
8
2
ꢀ
2ꢀ
2ꢀ
and Cd2 could be decomplexed by PPi based on the displacement
þ
C2O4 , CO
, and S O
, etc. In contrast, monovalent anions,
3
2
3
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
such as I , Br , Cl , SCN , NO , ClO4 , and AcO , etc. hardly cause
mode, which makes red emission of the complex change into blue
3
2
þ
significant color changes of ATPeCd(II) solution (Fig. 5b). This im-
plies that the ATPeCd(II) complex can be decomplexed by PPi and
selectively respond to polyvalent anions. The sensing mechanism of
ATPeCd(II) complex towards polyvalent anions should be similar to
emission of ligand 9-anthryl terpyridine [23]. ATPeCd solution
has two emission bands located at 422 nm and 610 nm, respec-
2
þ
tively. When a little excess of PPi is added to the stirred ATPeCd
solution, the long-wavelength emission band disappears and only
short-wavelength emission band (peak at 430 nm) same as ATP
emission remains (Fig. 4a). To this PPi-decomplexed solution,
2þ
that of the complex of 9-anthryl terpyridine and Cd (displace-
ment mode illustrated in Scheme 1). Fig. 5cef depicted the fluo-
rescence images of ATPeCd(II) in acetonitrile upon the cyclic
.2 equiv of Cd2þ is added and the red emission band reappears
1
Fig. 4. Emission spectra (a) and fluorescence images (b) of ATPeCd2þ in acetonitrile (1.0 ꢂ 10ꢀ5 M) upon the cyclic addition of PPi and Cd , respectively.
2þ

128
Q. Sun et al. / Dyes and Pigments 128 (2016) 124e130
ꢀ
5
Fig. 5. (a, b) Fluorescence images of ATPeCd(II) solution in acetonitrile (1.0 ꢂ 10 M) upon addition of different anions (2.0 equiv); (cef) Fluorescence images upon cyclic addition
2
þ
of polyvalent anions and Cd (the condition same as Fig. 4b).
addition of different polyvalent anions and Cd2þ. The results
behavior. The fluorescence images are shown in Fig. 6a. It is
observed that the ground ATPeCd(II) solid emits yellow fluores-
cence; however, when the ground solid is annealed before the
isotropic melt transition or exposed to solvent vapor (fuming above
dichloromethane at room temperature), an bluish-green fluores-
cence same as pristine solid appears. Furthermore, when the fumed
or annealed sample is re-ground, the fluorescence color is again
changed as the first grinding. This process is reproducible and in-
dicates a reversible PFC behavior.
These naked-eye-visible changes in fluorescence color were
recorded on a luminescence spectrophotometer, and the emission
spectra are depicted in Fig. 6b. As expected, the recorded emission
spectra are comparably consistent with the corresponding fluo-
rescence colors observed (Fig. 6a). The peak emission wavelengths
of ground and annealed (or fumed) states are 548 nm and 493 nm,
respectively, and from which the grinding-induced spectral shift
confirm that ATP is a reversible and selective colorimetric sensor
2
þ
for Cd , and ATPeCd(II) complex could be used as a reversible
secondary sensor for polyvalent anions.
3
.4. Piezochromic luminescence of ATPeCd2þ complex
In most, but not all, piezofluorochromic materials, the mainstay
is the aggregation-induced emission dyes, and there are only
limited organometallic or coordination compounds composed of
both metal ions and organic ligands (organicemetal complex)
could exhibit piezochromic luminescence. Since the folding or
twisted intramolecular conformations and the polytropic inter-
molecular
pep, metalemetal, or hydrogen-bonding interactions,
organicemetal complex might be promising candidates for new
PFC materials.
(
DlPFC
¼
l
pressed
ꢀ
lannealed) is calculated to be 54 nm, a
Since steric hindrance of 1,8-hydrogens on anthracene ring, ATP
is a highly twisted molecule. However, ATP is highly fluorescent
both in solution and solid-state, and does not show PFC behavior.
We have carried out the grinding experiment on ATPeCd(II) com-
plex using a metal spatula on the glass plate to examine the PFC
commendable PFC complex material.
To get further information on aggregate structure changes upon
2
þ
grinding the ATPeCd complex solid, powder wide-angle X-ray
diffraction (PWXD) and differential scanning calorimetry (DSC)
Fig. 6. Fluorescence images (a) and emission spectra (b) of ATPeCd2þ solid upon grinding, solvent-fuming, re-grinding, and annealing at room temperature under UV light
irradiation (365 nm).

Q. Sun et al. / Dyes and Pigments 128 (2016) 124e130
129
Fig. 7. X-ray diffraction patterns at room temperature (a) and DSC curves (b) of ATPeCd2 solid under pristine and ground states.
þ
experiments were conducted on the ground and as-prepared
pristine) solids. The PWXD pattern of pristine solid shows
Luminescent Materials and Devices of South China University of
Technology (SKLLMD201627).
(
sharper and intenser reflections, indicative of well-ordered
microcrystalline structures (Fig. 7a). In contrast, the ground solid
displays broad and featureless diffractogram reflecting notable
amorphous features. This indicates that grinding has induced the
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þ
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4
. Conclusions
a
2
We have inserted a phenyl ring between anthryl and terpyridine
3
to synthesize a new terpyridine derivative, 4-(9-anthryl)phenyl
terpyridine (ATP) to demonstrate the effect of the structure change
on optical properties. The insertion of phenyl ring could not only
remains the selectively colorimetric fluorescence sensing to Cd2þ
but also enlarges the interval of two emission bands from ATP and
its Cd(II) complex. Unlike 9-anthryl terpyridine, ATPeCd(II) com-
plex could be decomplexed by not only PPi but also other poly-
[
[
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2ꢀ
2ꢀ
2ꢀ
2ꢀ
, S O
8
3ꢀ
valent anions such as CO3 , SO4 , C O
, PO4 , etc.,
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