A new cyclotriphosphazene appended phenanthroline derivative as a highly selective and sensitive OFF-ON fluorescent chemosensor for Al3+ ions

Article abstract of DOI:10.1016/j.dyepig.2016.05.006

A new type of fluorescent chemosensor based on a novel cyclotriphosphazene appended phenanthroline derivative was synthesized and its sensing behavior toward metal ions was investigated by UV/vis and fluorescence spectroscopies. Addition of an Al³⁺

Full text of DOI:10.1016/j.dyepig.2016.05.006

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Dyes and Pigments 132 (2016) 230e236
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A new cyclotriphosphazene appended phenanthroline derivative as a
highly selective and sensitive OFFeON fluorescent chemosensor for
Al3þ ions
*
€
ꢀ
Emrah Ozcan, Süreyya O. Tümay, Hüsnüye Ardıç Alidagı, Bünyemin Ços¸ ut , Serkan Yes¸ ilot
Department of Chemistry, Faculty of Science, Gebze Technical University, Gebze, Kocaeli, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
A new type of fluorescent chemosensor based on a novel cyclotriphosphazene appended phenanthroline
derivative was synthesized and its sensing behavior toward metal ions was investigated by UV/vis and
fluorescence spectroscopies. Addition of an Al3þ ion to an acetonitrile solution of the phenanthroline
derivative exhibited a significant increase of fluorescence emission intensities, while 18 other metal ions
induced no spectral changes. This phenanthroline derivative, as a candidate for an OFF-ON fluorescent
chemosensor for Al3þ, was found to be highly selective and sensitive with a low limit of detection
Received 4 March 2016
Received in revised form
6 May 2016
Accepted 7 May 2016
Available online 9 May 2016
(1.825 m
g Lꢀ1).
Keywords:
© 2016 Elsevier Ltd. All rights reserved.
Phosphazenes
Phenanthroline
Al3þ ion sensor
Fluorescence
Chemosensor
Detection limit
1. Introduction
World Health Organization was reported allowable aluminium
intake into body as a 7 mg kgꢀ1 [9e11]. In contrast to other metal
cations, the detection of Al3þ is always problematic due to strong
hydration ability, poor coordination capacity and lack of spectro-
scopic characteristics of Al3þ [12e14]. Consequently, there have
been studied various methods on designing new, selective and
sensitive Al3þ detection [15e17]. While many instrumental
methods can be used for metal detection [18e21] including
inductively coupled plasma atomic emission (ICP-AES), induc-
tively coupled plasma mass spectroscopy (ICP-MS) and atomic
absorption spectroscopy (AAS), chemosensors gains great atten-
tion due to their selectivity, sensitivity and simplicity for the
determination of the different metal cations in aqueous or organic
media [22e25]. Although various chemosensors have been
described for the detection and determination other metal ions,
the design of selective and sensitive fluorescence sensors for Al3þ
ion is still important research area [26e28].
The design and construction of fluorescent chemosensors with
high selectivity and sensitivity to metal ions such as aluminium,
iron and copper have been the subject of intense study because of
their potential application in supramolecular chemistry, organic
chemistry, drug delivery, biological chemistry and environmental
research [1e3]. Among these various metal cations, aluminium is
the most plentiful metal ion and the third most plentiful of all
elements in the earth [4]. Also, aluminium is extensively use in
industrial process, pharmaceuticals and food additives [5,6].
However, over-exposure to aluminium can affect calcium ab-
sorption in bone and cause disturbances of bone development
also disturbs iron absorption in blood and cause anemia. In
addition, long-term exposure to aluminium can damage specific
cells and causes several neurological diseases such as Alzheimer’s
[7] and Parkinson’s disease [8]. Maximum acceptable daily
aluminium intake to body was determined as a 3e10 mg in a day.
Phosphazene compounds are inorganic heterocyclic compounds
which included phosphorus and nitrogen atoms and characterized
by the double bond between them [29e31]. These compounds have
halogen atoms bound to phosphorus atoms in their structure which
may easily undergo a substitution reaction with nucleophilic
compounds such as amines, alcohols, and phenols [32e34].
* Corresponding author. Department of Chemistry, Gebze Technical University,
P.O. Box: 141, Gebze 41400, Kocaeli, Turkey. Tel.: þ90 (262) 605 3015; fax: þ90
(262) 605 3005.
E-mail address: bc@gtu.edu.tr (B. Ços¸ ut).
http://dx.doi.org/10.1016/j.dyepig.2016.05.006
0143-7208/© 2016 Elsevier Ltd. All rights reserved.

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Additionally, the cyclotriphosphazenes are interesting compounds
as a core for the synthesis of new fluorescence sensors due to
substituted groups on phosphorus atoms can be used as
fluorophore and ionophore for metal detection [35,36]. There are
many examples the simple protected aminophenanthroline
derivatives and their transition metal complexes in literature
(some examples: [37e40]). To the best of our knowledge, there is
no selective phenanthroline example towards Al3þ ions in litera-
ture. It is well-known that cyclophosphazene or (pentaphenox-
ycyclophosphazene as starting material for compound 2) is
optically inert with no effect on chromophore emission therefore
there is no part in to change the emission behavior of compound 2
which is a fluorescent probe for the selective determination of Al3þ
with almost non-interference by Fe3þ although Cu2þ did interfere.
However, the contribution of having the cyclophosphazene unit
present is most probably that the steric routing of amino-
phenanthroline as pendant group attached to cyclophosphazene
core behind its main advantages such as to produce a rigid spherical
core from which to grow the fluorophore of interest and better
thermal stability.
orthogonal electrospray ionization (ESI) source. The instrument
was operated in positive ion mode using a m/z range of 50e3000.
The capillary voltage of the ion source was set at 4500 V and the
capillary exit at 210 V. The nebulizer gas flow was 0.6 bar and
drying gas flow 4 L/min. The drying temperature was set at
200 ꢂC.The transfer time of the source was 88 ms and the hexapole
radiofrequency (RF) was 800.0 Vpp. Elemental analysis was carried
out using Thermo Finnigan Flash. 1H, 13C and 31P NMR spectra were
recorded in CDCl3 solutions on a Varian 500 MHz spectrometer.
Analytical thin layer chromatography (TLC) was performed on
silica gel plates (Merck, Kieselgel 60A, 0.25 mm thickness) with
F254 indicator. Column chromatography was performed on silica
gel (Merck, Kieselgel 60A, 230e400 mesh). Suction column chro-
matography was performed on silica gel (Merck, Kieselgel 60A,
70e230 mesh).
2.3. Synthesis
The 1,1,3,3,5-pentaphenoxy-5-chlorocyclotriphosphazatriene
(1) was prepared and purified according to the literature proce-
dure [48].
In this current study, we report a phenanthroline group has
been appended with cyclotriphosphazene ring bearing five phe-
noxy substituents. We also demonstrated the sensor behavior of
phenanthroline substituted phosphazene derivate 2 for selective
fluorometric detection of Al3þ ion and determined the detection
2.3.1. Synthesis of 1,1,3,3,5-pentanaphtoxy-5-(1,10-phenanthroline-
5-amino) cyclotriphosphazatriene (2)
Sodium hydride (NaH) (0.044 g, 60%, 1.1 mmol) was added to a
stirred solution of 1,10-phenanthroline-5-amine (0.18 g,
0.94 mmol) dissolved in THF (20 mL) under an argon atmosphere.
Compound (1) (0.5 g, 0.78 mmol) in THF (20 mL) was added
dropwise to a stirred solution under an argon atmosphere for
30 min. The reaction mixture was stirred for 3 h at room temper-
ature and the reaction was followed by TLC. The precipitated salt
was then filtered off and the solvent was removed under reduced
pressure and compound 2 was isolated by column chromatography
silicagel 60 (230e400 mesh) as adsorbent and THF/n-hexane (1:1)
as the eluent. Yield 0.3 g (60%). Anal. Calc. for [C42H33N6O5P3]
Found: C,63.40; H, 4.08; N, 10.51%; requires: C, 63.48; H, 4.19; N,
10.58%. MS (ESI) m/z (%) Calc.: 795.1798; found: 795.3481 (100)
limit of compound 2 as 1.825
synthesized in a simple reaction and characterized by 1H NMR, 13
NMR, 31P NMR and ESI-mass spectrometry. Compound 2 (1
M)
m
g Lꢀ1 for Al3þ. Compound 2 was
C
m
exhibits a characteristic weak monomer emission band from the
phenanthroline moiety at 425 nm, which after addition of Al3þ
ions the emission of compound 2 - Al complex shifts to 493 nm
with a Stokes shift of 68 nm when excited at 300 nm. The stoi-
chiometry between the phenanthroline sensor and Al3þ was
determined by Job’s plot as a 3:1 (ligand: metal ion) and limit of
detection of compound 2 was calculated to be 6.764 ꢁ 10ꢀ8
M
(1.825 m
g Lꢀ1) for Al3þ ions. To the best of our knowledge, only a
few fluorescent sensors for Al3þ with moderate success have been
reported [14,41e43]. The results indicated that the detection limit
is lower than many other fluorescence sensors in the literature
[44e47].
[M þ H]þ.1H NMR (CDCl3, ppm)
d: 9.19 (s, 1H), 9.09 (s, 1H), 8.06 (d,
J ¼ 7.16 Hz, 1H), 7.82 (d, J ¼ 14.22 Hz, 2H), 7.54 (d, J ¼ 17.22 Hz, 2H),
7.18e7.14 (m, 5H), 7.07e6.98 (m, 20H), 5.43 (s, 1H, NH); {1H}13
NMR (CDCl3, ppm) :151.85, 151.00, 150.86, 150.30, 149.15, 146.78,
143.82, 136.12, 135.63, 132.93, 129.71, 129.64, 129.02, 128.51, 125.84,
125.26, 125.15, 123.63, 122.71, 121.57, 121.40, 121.24, 114.84; {1H}31
C
d
2. Experimental
P
2.1. Materials
NMR (CDCl3, ppm), assigned as an AB2 spin system d: 13.05 [dd, 1P,
P(OPh)(phenanthroline),A], 9.6 [dd, 2P, P(OPh)2, B2], 2JP,P ¼ 83.4 Hz
Hexachlorocyclotriphosphazene (Otsuka Chemical Co. Ltd) was
purified by fractional crystallization from n-hexane. The deuterated
solvent (CDCl3) for NMR spectroscopy and the following chemicals
were obtained from Merck: tetrahydrofuran (THF), silica gel 60;
Aldrich: phenol, 1,10-phenanthroline-5-amine, sodium hydride
(NaH). All other reagents and solvents were reagent grade quality
and were obtained from commercial suppliers.
and 2JP,P ¼ 5.7 Hz.
3. Results and discussion
3.1. Synthesis and structural characterization
The synthetic routes for the preparation of compounds 1 and 2
are shown in Scheme 1. Compound 1 was prepared according to a
lit. procedure [48]. Compound 2 was obtained from nucleophilic
displacement reaction of 1 with the commercially available 1,10-
phenantroline-5-amine under an argon atmosphere, with NaH as
a base. The compound 2 was purified by column chromatography
on silica gel using n-hexane:THF (1:1) as the eluent. The new
compound 2 was characterized by elemental analysis, mass spec-
trometry, 1H, 13C and 31P NMR spectroscopy. All the results are
consistent with the predicted structure as shown in the experi-
mental section. Molecular weight of 2 has been determined by ESI
mass spectrometry. Mass spectral identification is based on
matching measured accurate mass and isotopic pattern of a sample.
Theoretical and measured isotopic patterns as an additional
2.2. Equipment
Electronic absorption spectra were recorded with a Shimadzu
2101 UV spectrophotometer in the UVevisible region. Fluores-
cence excitation and emission spectra were recorded on a Varian
Eclipse spectrofluorometer using 1 cm pathlength cuvettes at
room temperature. The fluorescence lifetimes were obtained using
Horiba- Jobin-Yvon-SPEX Fluorolog 3-2iHR instrument with Flu-
oro Hub-B Single Photon Counting Controller at an excitation
wavelength of 470 nm. Signal acquisition was performed using a
TCSPC module. The mass analyzer was a Bruker Daltonics (Bremen,
Germany) MicrOTOF mass spectrometer equipped with an

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E. Ozcan et al. / Dyes and Pigments 132 (2016) 230e236
Scheme 1. Chemical structure and synthetic pathway of compound 2.
Fig. 1. Positive-ion mode electrospray ionization (ESI) mass spectrum of 2. See inset: (a) experimental isotopic pattern and (b) theoretical isotopic pattern.
Fig. 2. The 31P NMR spectra of compound 2 in CDCl3.

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identification tool to accurate mass determination of 2 and the
positive ion ESI mass spectrum is given in Fig. 1. The peak group
representing the protonated molecular ion of 2 was observed at
795.1798 Da mass (Fig. 1). The aromatic protons are shown in the
Compound 2 exhibits an absorption band has a maximum at
272 nm, which remains unchanged upon the addition of 2 equiv.
of various metal ions (Liþ, Naþ, Kþ, Csþ,Mg2þ, Ca2þ, Ba2þ, Hg2þ
,
Pb2þ, Mn2þ, Cd2þ, Agþ, Ni2þ, Cu2þ, Zn2þ, Co2þ, Cr3þ and Fe3þ) are
shown in Fig. 3. In the case of Al3þ, the absorption band has a
maximum as red-shifted to 293 nm. A clear isosbestic point was
observed at 279 nm when spectra were recorded with varying
concentrations of Al3þ. As shown in Fig. 3a, addition of 2 equiv-
alent Al3þ resulted in an obvious change indicating compound 2
had higher binding affinity towards Al3þ than other surveyed
metal ions. In order to receive more information about binding
mechanism of compound 2 towards Al3þ spectrometric titration
experiments were performed in the presence of Al3þ. As depicted
region d: 6.98e9.19 ppm. The proton signal of NH group is observed
at 5.43 ppm as broad signal. The integration of the aromatic proton
signals to the NH proton signal in the 1H NMR spectrum of com-
pound 2 gave approximately a 32:1 proton ratio that confirmed the
suggested structure (Fig. S1). 13C NMR spectrum of 2 shows all
signals for aromatic carbons between 151.85 and 114.84 ppm
(Fig. S2). The proton-decoupled 31P NMR spectrum of compound 2
signals is observed AB2 spin system and the resonances belonging
to phosphorous atoms are observed at ca. 13.05 ppm
for > P(OPh)(phenantroline) and at ca. 9.6 ppm for > P(OPh)2, also
in Fig. 3b, while the sequential addition of Al3þ ions from 5
45 M to the solution of compound 2 showed a gradual increase
mM to
2
the magnitude of the 2J(P,P) at ca. 83.4 Hz and JP,P at ca. 5.7 Hz.
m
(Fig. 2).
in absorbance at 293 nm. Consequently, compound 2 could pro-
vide as a sensitive fluorescent chemosensor for Al3þ cations. The
changes in the absorption curve of compound 2 could be assigned
to a charge transfer transition occurring between the ligand and
metal ion.
3.2. Chemosensor properties of compound 2
The UVeVis spectroscopic experiment of compound 2 was
measured in acetonitrile with dilute solutions of 1 ꢁ 10ꢀ5 M.
Compound 2 alone did not show any significant emission upon
Fig. 3. UVeVis absorption change profiles of compound 2 (10.0 mM) in CH3CN with a) various metal ions (20.0 m .
M), b) gradual addition of Al3þ