Inorganic Chemistry Communications
A fluorescent and colorimetric sensor for Al3+ based on a
dibenzo-18-crown-6 derivative
⁎
Ya-Ping Li, Xiu-Ming Liu, Ying-Hui Zhang, Ze Chang
Department of Chemistry, Tianjin Key Lab on Metal and Molecule-based Material Chemistry, Nankai University, Tianjin 300071, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A new receptor based on a dibenzo-18-crown-6 derivative is successfully synthesized and characterized. This recep-
tor reveals selective recognition toward Al3+ ion, along with colorimetric and fluorometric dual-signaling responses
based on internal charge transfer (ICT). Also, it can serve as a highly selective chemodosimeter for Al3+ with
naked-eye detection.
Received 14 February 2013
Accepted 18 March 2013
Available online 28 March 2013
© 2013 Elsevier B.V. All rights reserved.
Keywords:
Aluminum ion recognition
Dibenzo-18-crown-6 derivative
Ratiometric
Fluorescent
Chemosensor
Fluorescent chemosensors are widely used as powerful tools to detect
neutral and ionic species owing to their high sensitivity, selectivity, versa-
tility, and relatively simple handling [1]. In this regard, the design and syn-
thesis of chemosensors are currently of great interest [2–11]. On the other
hand, aluminum is the most abundant metal in the Earth's crust and has
been extensively used in modern life [12]. However, Al3+ is neurotoxic
to humans and has been found to induce many health issues, such as
Alzheimer's disease and Parkinson's disease [13]. Thus, the development
of sensors for facile detection of Al3+ is of great importance in envi-
ronmental monitoring and biological applications. Compared with
the detections of other transition-metal ions, limited examples of
Al3+ fluorescence sensors based on small molecules have been reported
through an internal charge-transfer (ICT) mechanism [14,15], and most
of the detections are due to photoinduced electron transfer (PET) process
[2,3,16]. Herein, a new chemosensor 1 with 2,3-diphenylquinoxaline
as fluorophore and 18-crown-6 moiety as chelating unit has been
reported, which exhibits high selectivity for Al3+ ions. The Al3+ de-
tection process gives rise to large changes in the absorption spectra
(from colorless to yellow), which is clearly visible to the naked eye.
Meanwhile, upon the binding of 1 with Al3+, a distinct emission
red shift based on the ICT mechanism with slight emission enhance-
ments could be observed. These results might provide explicit infor-
mation to qualitative and quantitative detection of Al3+ ions in
future application.
benzil in ethanol under a nitrogen atmosphere gave 1 in the yield of
30%. Compound 1 was then characterized by 1H NMR, ESI-MS, IR, elemen-
tal analysis and X-ray diffraction analysis.
The metal affinity of 1 toward a variety of cations: K+, Na+
,
,
Ca2+, Mg2+, Al3+, Cu2+, Co2+, Ni2+, Fe2+, Hg2+, Mn2+, Cr3+
Cd2+, Ag+, Zn2+, La3+, Eu3+, and Td3+ was investigated by absorp-
tion and fluorescence spectroscopy in CH3CN solution. As shown in
Fig. 1, without any metal ion, 1 showed an absorption band centered at
366 nm and at 258 nm. Upon addition of Al3+, the absorption band at
366 and 238 nm diminished, while new bands at 271 and 418 nm were
observed. The presence of well-defined isosbestic points at 398 and
265 nm indicates the formation of stable complex between 1 and Al3+
.
The color of the solution changes from colorless to light yellowish-green
upon addition of Al3+ as shown in Fig. 1b, which allows the detection
of Al3+ ions by naked-eyes.
In addition, fluorescence properties of 1 in the presence of the above
mentioned metal ions in CH3CN solution were investigated. As shown
in Fig. 2, the free receptor 1 exhibits a strong emission band around at
400 nm upon excitation at 334 nm. Addition of K+, Na+, Ca2+, Mg2+
,
,
Cu2+, Co2+, Ni2+, Mn2+, Cr3+, Cd2+, Ag+, Zn2+, Fe2+, La3+, Eu3+
and Td3+ induced almost no changes in the emission profiles. However,
addition of Hg2+ quenched the fluorescence to some extent. Only the ad-
dition of Al3+ ions to the solution of 1 resulted in a prominent red shift of
the fluorescence maximum of about 75 nm from 400 nm to 475 nm.
The synthetic route of 1 was outlined in Scheme 1. Compound 3 was
prepared by following the literature method [17]. The reaction of 3 with
Meanwhile, the ratio of emission intensities at 475 and 400 nm (I475 nm/
I
400 nm) changed from 30.36 to 0.04 upon addition of Al3+. The significant
red shift observed suggests that Al3+ likely interacts with the electron
donor 1 through the intramolecular charge transfer (ICT) mechanism
[14,15]. The experimental observations are confirmed quantitatively by
the DFT calculation results. As shown in Fig. S1, the LUMO of complex
⁎
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