AIEE based “turn-on” fluorescent sensor for Al3+ ions and induced tetraphenylethene self-assemblies

Article abstract of DOI:10.1016/j.orgel.2020.105820

Cu²⁺ is an eminent trace metal ion in the human body as a structural cofactor that can enhance immune function. Aluminum is one of the most abundant elements found in the earth's crust and most biological tissues appear in Al³⁺ form.

Full text of DOI:10.1016/j.orgel.2020.105820

Organic Electronics 85 (2020) 105820
Contents lists available at ScienceDirect
Organic Electronics
journal homepage: http://www.elsevier.com/locate/orgel
AIEE based “turn-on” fluorescent sensor for Al3þ ions and induced
tetraphenylethene self-assemblies
,
,
Zejun Xua 1, Yanan Liua 1, Ruitong Wanga, Junheng Zhanga, Juan Chenga, Sufang Chenb,
Menghe Miaoc, Daohong Zhanga
,
*
a Key Laboratory of Catalysis and Energy Materials Chemistry of Ministry of Education & Hubei Key Laboratory of Catalysis and Materials Science, Hubei R&D Center of
Hyperbranched Polymers Synthesis and Applications, South-Central University for Nationalities, Wuhan, 430074, China
b Key Laboratory for Green Chemical Process of Ministry of Education, Hubei Key Laboratory of Novel Reactor and Green Chemical Technology, School of Chemical
Engineering and Pharmacy, Wuhan Institute of Technology, Wuhan, Hubei, 430205, China
c CSIRO Manufacturing, 75 Pigdons Road, Waurn Ponds, Victoria, 3216, Australia
A R T I C L E I N F O
A B S T R A C T
Cu2þ is an eminent trace metal ion in the human body as a structural cofactor that can enhance immune function.
Aluminum is one of the most abundant elements found in the earth’s crust and most biological tissues appear in
Al3þ form. Hg2þ is probable to cause cancer with high toxicity. However, excess accumulation of Al3þ, Cu2þ or
Hg2þ in the body leads to many diseases. Therefore, detecting the level of Al3þ, Cu2þ and Hg2þ are very
Keywords:
Self-assembly
AIEE
Carbohydrazide derivative
Fluorescence sensor
important for human health. However, preparing a suitable single probe for the simultaneous detection of Al3þ
,
Cu2þ and Hg2þ remains a challenge. TPE-based carbohydrazide derivative (TPE-Ch) was synthesized by the one-
pot reaction. The TPE-Ch displayed notable AIE and AIEE phenomena and can act as a fluorescence sensor that
turns on toward Al3þ in ethanol/water mixtures (fw ¼ 70%) and turns off toward Cu2þ or Hg2þ. TPE-Ch can
produce various assemblies by coordination with Al3þ, Cu2þ and Hg2þ, including nanospheres, tree-like assembly
morphology and belt-like superstructures. Optical microscopy (OM), scanning electron microscopy (SEM), X-ray
diffraction (XRD), and fluorescence spectrography were employed to characterize the self-assemblies.
1. Introduction
[8]. However, it is still a challenge to prepare a suitable single probe for
the simultaneous detection of Al3þ, Cu2þ and Hg2þ [12,13].
A multifunctional probe that changes selective recognition of mul-
tiple ions offers great application prospects [1,2]. Cu2þ is an eminent
trace metal ion in the human body as a structural cofactor that can
enhance immune function [3,4]. Aluminum exists in most organisms in
the form of Al3þ. However, excess accumulation of Cu2þor Al3þ in the
body leads to many diseases [5], and Hg2þ is probable to cause cancer
with high toxicity [6,7]. Therefore, detecting the level of Al3þ, Cu2þ and
Hg2þ are very important for human health. Recently, several fluorescent
probes for the selective recognition of Al3þ, Cu2þ or Hg2þ have been
reported [1,8–11]. The pyrene-appended pyrazoline compound (PY–I)
displayed an excellent sensitive response to Al3þ [10]. The tetraphe-
Recently, aggregation induced emission (AIE) of tetraphenylethylene
(TPE) molecules have been used in various fields, such as biological
probes [14–17], chemical sensing, optoelectronic systems [18,19], and
self-assembly systems [20,21]. TPE based micro/nano-structures, such
as fibers, nanowires, microflowers, and their applications were investi-
gated [22–28]. Therefore, it would be of great interest to synthesize a
TPE derivative for the simultaneous detection of Al3þ, Cu2þ and Hg2þ
and to investigate Al3þ, Cu2þ/Hg2þ-induced TPE self-assembly.
Herein, we have successfully designed and synthesized TPE-based
carbohydrazide derivative (TPE-Ch) that displays AIE phenomena and
AIEE properties with fluorescence-sensing capability that “turns-on” for
Al3þ ions and “turns-off” for Cu2þ/Hg2þ. TPE-Ch could produce various
assemblies by coordination with Al3þ, Cu2þ and Hg2þ, including nano-
spheres, tree-like assembly morphology and belt-like superstructures.
nylethylene derivative (probe 2) showed sensitive response to Cu2þ
,
with detection limit of 0.5 μM [9]. Yongfeng Zhou group reported the
self-assembly of alternating copolymer vesicles for the highly selective
and sensitive of aqueous Hg2þ, and the detection limit is about 53 nM
We hypothesized that the intermolecular π-π stacking, the integration of
* Corresponding author.
E-mail address: zhangdh27@163.com (D. Zhang).
1
These authors contributed equally to this work.
https://doi.org/10.1016/j.orgel.2020.105820
Received 15 January 2020; Received in revised form 25 May 2020; Accepted 25 May 2020
Available online 4 June 2020
1566-1199/© 2020 Elsevier B.V. All rights reserved.

Z. Xu et al.
Organic Electronics 85 (2020) 105820
dissolved in ethanol solvent mixed with Hg2þ or Cu2þ. The self-assembly
was performed on a clean surface of the glass substrate. The morphology
of the self-assemblies was recorded using optical microscopy (OM) at
500� magnification and scanning electron microscopy (SEM).
3. Results and discussion
TPE-Ch was synthesized according to Scheme 1 [29]. TPE-CHO was
prepared by modifying a method reported in the literature [30] with
90% yield as shown in Scheme 1. TPE-CHO was then grounded with
carbohydrazide to form the carbohydrazide derivative TPE-Ch in 85%
yield as an off-white powder. TPE-Ch was characterized by 1H NMR and
LC-TOF mass spectrometry in the supplementary information.
To determine the AIE feature of TPE-Ch, the emission behavior of the
compound in the ethanol/water system was investigated [31]. Fig. 1
shows the photoluminescent (PL) emission spectra of TPE-Ch in etha-
nol/water mixtures with different water fractions (fw). Obviously, with
the increase of fw (fw ≦ 60%), the weak emission intensity of TPE-Ch
increases slightly and the fluorescence peak red-shifted from 450 to
467 nm. However, when fw > 60%, the emission intensity enhanced
dramatically and exhibited a red-shift to 485 nm (fw ¼ 90%), showing
about tenfold enhancement at fw ¼ 90% compared with that in pure
ethanol solution (Fig. 1b). This suggests a remarkable AIE property
(Scheme 2) [32,33]. Even in solid-state, this TPE-Ch displayed strong
bluish-green emission with a maximum at 488 nm.
Scheme 1. Synthesis route of TPE-Ch.
metal coordination along with other H-bonding are the key drivers in the
self-assembly processes.
2. Experimental section
Preparation for fluorescence measurements: TPE-Ch (10 mM)
stock solution was prepared in EtOH. The solution of TPE-Ch was then
diluted to 10 μM for fluorescence spectral researches with EtOH/water
mixed solvents having different water fractions (fw: changing from 0% to
The selectivity of TPE-Ch to various metal ions (Kþ, Naþ, Ca2þ, Al3þ
,
90%). Stock solutions of Kþ, Naþ, Ca2þ, Al3þ, Zn2þ, Cu2þ, Cd2þ, Fe3þ
,
Cu2þ, Zn2þ, Cd2þ, Hg2þ and Fe3þ) was examined in ethanol/water (fw
¼
and Hg2þ (10 mM) were dissolved in distilled water. Fluorescence
70%) solution. The fluorescence spectra were obtained by excitation at
355 nm. The major turn-on fluorescence of TPE-Ch was showed in the
addition of Al3þ while turn-off by presented of Hg2þor Cu2þ. As shown in
Fig. 2, the probes themselves showed fluorescence emission at 484 nm.
The emission enhancement of TPE-Ch increased gradually with
response of TPE-Ch (10
μ
M) with different concentrations of Al3þ, Cu2þ
and Hg2þ (0–200
μM) in water-EtOH mixtures (fw ¼ 70%) were deter-
mined. The samples in a quartz cell of 10 mm path length, exciting at
355 nm wavelength and using a slit width of 5 nm having an integration
time of 0.1 s to record emission scans from 370 to 700 nm.
increasing Al3þ concentration (0–100
μM) and reached 3-fold when
Preparation for self-assembly samples: TPE-Ch (500
μM) was
Fig. 1. (a) Fluorescence spectra of TPE-Ch (10
μM, λEx: 355 nm) in ethanol-water mixtures (EtOH/H2O) with different water fractions (fw). (b) Plots of I/I0 vs fw of
TPE-Ch, where I ¼ emission intensity of fw, and I0 ¼ emission intensity in ethanol solution. Inset: images of TPE-Ch at fw¼0%, 60% and 90% under UV lamp.
Scheme 2. TPE-Ch displayed AIE phenomena and AIEE properties based “turn-on” for Al3þ
.
2

Z. Xu et al.
Organic Electronics 85 (2020) 105820
Fig. 2. (a) Fluorescence spectra of TPE-Ch (10
μ
M) with various metal ions (Kþ, Naþ, Ca2þ, Al3þ, Cu2þ, Zn2þ, Cd2þ, Hg2þ and Fe3þ) in ethanol/water mixtures (fw
¼
70%). Fluorescence spectra of TPE-Ch (10
μ
M) with increasing concentrations (0–200
μ
M) of (b) Al3þ, (c) Cu2þ and (d) Hg2þ in ethanol/water mixtures (fw ¼ 70%).
added 5 equiv. of Al3þ at 484 nm due to the AIEE effect (Scheme 2) [29].
Nevertheless, a significant decrease in fluorescence intensities of TPE-Ch
due to gradual addition of Cu2þ or Hg2þ, which supports further
self-assembly of TPE-Ch induced by Cu2þ or Hg2þ. The detection limit
for Al3þ, Cu2þ and Hg2þ were estimated to be 2.5, 1.6 and 3.5
μM,
respectively. Conversely, slight effect on fluorescence was observed after
the addition of other cations (Kþ, Naþ, Zn2þ, Fe3þ and Cd2þ). In etha-
nol/water mixtures (fw ¼ 0%), the Ø of TPE-Ch was 14.66%. In etha-
nol/water mixtures (fw ¼ 70%), tfhe Ø of TPE-Ch, TPE-Ch-Al3þ
,
f
TPE-Ch-Hg2þ, TPE-Ch-Cu2þ were 16.29%, 15.87%, 32.81% and 28.24%
respectively. In ethanol/water mixtures (fw ¼ 0%), the lifetime of
TPE-Ch was 2.45 ns? In ethanol/water mixtures (fw ¼ 70%), the lifetime
of TPE-Ch, TPE-Ch-Al3þ, TPE-Ch-Hg2þ, TPE-Ch-Cu2þ were 6.46 ns, 6.93
ns, 6.81 ns and 7.39 ns respectively. And the sensing time limit for Al3þ
Cu2þ and Hg2þ were 3, 10 and 12 s, respectively.
,
The self-assembly behaviors of TPE-Ch before and after adding metal
ions (including Cu2þ, Hg2þ, Al3þ, Ca2þ, Kþ, Ba2þ, Mg2þ, and Zn2þ) were
studied by an OM and SEM. Metal ions with different coordination
modes might have helped the assembly growth. As the EtOH solvent
slowly volatilized at a temperature under 25 �C and relative humidity
50%, the self-assemblies of TPE-Ch before and after adding metal ions
(including Al3þ, Ca2þ, Kþ, Ba2þ, Mg2þ, and Zn2þ) under the OM
appeared as small spheres with uniform size and close arrangement
(Fig. 3a). The SEM images further showed that with the volatilization of
the solvent it assembled into nanospheres with diameters in the range of
500–800 nm (Fig. 3a1). However, after adding Hg2þ, we observed that
the small particles displayed regular patterns of a snowflake- or tree-like
assemblies (Fig. 3b). Subsequently, the SEM analysis revealed that the
branches of the tree were assembled from hollow nanoparticles (inset in
Fig. 3b1), probably self-assembly caused by induction of Hg2þ. As shown
in Fig. 3c, the addition of Cu2þ causes the self-assembly morphology of
Fig. 3. a-c) Optical micrographs (OM) and a1-c1) corresponding scanning
electron microscope (SEM) images of (a-a1) TPE-Ch, (b-b1) TPE-Ch-Hg2þ and (c-
c1) TPE-Ch -Cu2þ self-assemblies.
3

Z. Xu et al.
Organic Electronics 85 (2020) 105820
Fig. 4. (a) Dynamic light scattering (DLS)-based particle size analysis of self-assemblies. (b) X-ray diffraction (XRD) spectra of TPE-Ch, TPE-Ch-Cu2þ and TPE-
Ch-Hg2þ
.
Fig. 5. Fluorescence spectra of TPE-Ch (100
μ
M) with increasing amounts of (a) Cu2þ, (b) Hg2þ and (c) Al3þ in solid-state. (d) Fluorescence spectra of TPE-Ch (100
μ
M) with various metal ions (Al3þ, Cu2þ, and Hg2þ) in solid-state.
TPE-Ch to change from sphere to one-dimensional belt-like superstruc-
assembly mechanism (Fig. 4). DLS is a very suitable method to investi-
gate the time sequence of self-assembly, which monitors the dispersed or
aggregated state of molecules. As shown in Fig. 4a, the self-assembly
particle size after adding Cu2þ and Hg2þ decreased to 19.9 nm and
6.0 nm from 217.7 nm in the initial TPE-Ch solution in ethanol solvent.
These results are consistent with the observation obtained from the OM
and SEM analyses. The XRD pattern of TPE-Ch revealed a crystalline
material giving peaks at 13.7�, 18.5�, and 20.9�, indicating that a strong
tures formed by bundles of fibers longer than 800 μm. The SEM image
confirmed that the fibre bundles were comprised of spliced long fibre
sheets (Fig. 3c1), which are generally several micrometers wide and tens
of micrometers long. Thus the metal ions had a great influence on the
assembly morphology of the TPE-Ch system.
As discussed above, metal ions (Hg2þ and Cu2þ) played a vital role in
inducing self-assembly. DLS and XRD were used to elucidate the
4

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Organic Electronics 85 (2020) 105820
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Declaration of competing interest
There are no conflicts of interest to declare.
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