Monofunctional amines substituted fluorenylidene bridged cyclotriphosphazenes: 'Turn-off' fluorescence chemosensors for Cu2+ and Fe3+ ions

Article abstract of DOI:10.1016/j.poly.2015.09.013

In the present work, the reaction of 2,2,4,4-tetra(anilino)-6,6-dichlorocyclotriphosphazene (4) and 2,2,4,4-tetra(2-naphthylamino)-6,6-dichlorocyclotriphosphazene (5) with 4,4′-(9-fluorenylidene)diphenol, FDP, (6) and 4,4′-(9-fluorenylidene)dianiline FDA (7) were studied in THF and new aniline (8 and 9) and 2-naphthylamine (10 and 11) substituted FDP-bridged cyclotriphosphazenes and aniline (12) and 2-naphthylamine (13) substituted FDA-bridged cyclotriphosphazene derivatives were obtained. All newly synthesized monofunctional amines substituted fluorenylidene bridged cyclotriphosphazenes (8-13) were fully characterized by elemental analysis, ¹H and ³¹P NMR spectroscopies, MALDI-TOF mass spectrometry and UV-Vis electronic absorption spectra. The florescence properties of the synthesized new compounds were studied. The chemosensory behavior of the compounds against to metal ions was also investigated. The obtained fluorenylidene bridged 2-naphthylamine substituted cyclotriphosphazenes (10, 11 and 13) showed fluorescence chemosensor behavior with high selectivity for Fe³⁺ and Cu²⁺ ions in the solution.

Full text of DOI:10.1016/j.poly.2015.09.013

Accepted Manuscript
Monofunctional amines substituted Fluorenylidene Bridged Cyclotriphospha-
zenes: ‘Turn-Off’ Fluorescence Chemosensors for Cu2+ and Fe3+ ions
Elif Şenkuytu, Esra Tanrıverdi Eçik, Mahmut Durmuş, Gönül Yenilmez Çiftçi
PII:
S0277-5387(15)00515-X
http://dx.doi.org/10.1016/j.poly.2015.09.013
POLY 11527
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
23 July 2015
6 September 2015
Please cite this article as: E. Şenkuytu, E.T. Eçik, M. Durmuş, G.Y. Çiftçi, Monofunctional amines substituted
Fluorenylidene Bridged Cyclotriphosphazenes: ‘Turn-Off’ Fluorescence Chemosensors for Cu2+ and Fe3+ ions,
Polyhedron (2015), doi: http://dx.doi.org/10.1016/j.poly.2015.09.013
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Monofunctional aminessubstituted Fluorenylidene
Bridged Cyclotriphosphazenes: ‘Turn-Off’ Fluorescence
Chemosensors for Cu2+ and Fe3+ ions
Elif 1enkuytu*, Esra Tanrıverdi Eçik, Mahmut Durmu2, Gönül Yenilmez Çiftçi
Department of Chemistry, Gebze Technical University, Gebze 41400, Kocaeli, Turkey
E-mail: senkuytu@gtu.edu.tr; Fax: +90 2626053101; Tel: +90 2626053063
KEYWORDS: Cyclotriphosphazenes, Fluorenylidene, Fluorescence, Chemosensor, Fe3+ and
Cu2+ ions.
1

ABSTRACT
In the present work, the reaction of 2,2,4,4-tetra(anilino)-6,6-dichlorocyclotriphosphazene (4)
and 2,2,4,4-tetra(2-naphthylamino)-6,6-dichlorocyclotriphosphazene (5) with 4,4a-(9-
fluorenylidene)diphenol, FDP, (6) and 4,4a-(9-fluorenylidene)dianiline FDA (7) were studied
in THF and new aniline (8 and 9) and 2-naphthylamine (10 and 11) substituted FDP- bridged
cyclotriphosphazenes and aniline (12) and 2-naphthylamine (13) substituted FDA- bridged
cyclotriphosphazene derivatives were obtained. All newly synthesized monofunctional amines
substituted fluorenylidene bridged cyclotriphosphazenes (8-13) were fully characterized by
1
elemental analysis, H and 31P NMR spectroscopies, MALDI-TOF mass spectrometry and
UV-Vis electronic absorption spectra. The florescence properties of the synthesized new
compounds were studied. The chemosensory behavior of the compounds against to metal ions
was also investigated. The obtained fluorenylidene bridged 2-naphthylamine substituted
cyclotriphosphazenes (10, 11 and 13) showed fluorescence chemosensor behavior with high
selectivity for Fe3+ and Cu2+ ions in the solution.
1. Introduction
2

Development of new fluorescent chemosensor is a challenging field in supramolecular
chemistry and nowadays, many examples of fluorescent chemosensors or reagents are
reported [1-3]. Ion sensing in cellular media is especially important for understanding of
biochemical processes [4]. Among the essential transition metals in biological systems, the
most abundant are Fe, Zn and Cu atoms [5, 6]. Especially, the fluorescent sensor for Cu2+ ion
is used to clarify the physiological role of metal ion in tissues [7, 8]. The disturbed
homeostasis of iron and zinc ions is suspected to play causative roles in many diseases such as
hepatitis and cancer disease [9-12]. Also, the relative concentration of Fe2+/Fe3+ is important
for the biological sensing and imaging. Several scientists have focused on construction of
selective and sensitive transition metal ion sensors for understanding essential recognition
events in chemistry and biology [13].
Cyclotriphosphazene, six-membered ring, offers a rigid platform for multifunctional
molecular arrangements and ring is resistant to the various reaction conditions. Over the past
century nucleophilic substitution reactions of cyclotriphosphazene have been extensively
investigated [14-16]. Generally, reactions of this ring with difunctional reagents may lead to
different types of products such as open chain bridged, spiro, ansa, oligomer, polymer or their
mixtures. The formation of these products depends on many factors such as the chain length
of the difunctional reagents, used solvent, base, temperature and the nature of the reacting
functional groups [17-20]. Thus cyclotriphosphazenes are a very interesting class of
inorganic−organic hybrid compounds because it is possible to decorate cyclotriphosphazene
core depending on the substituted side groups. They have wide applications such as organic
light emitting diodes [21], biomedical materials such as anticancer and antimicrobial agents
[22-26], liquid crystals [27, 28], and electrical conductivity [29]. Cyclotriphosphazenes have a
potential application to detect metal ions in biological and environmental media as well but
studies in this field are very limited. Only, on/off fluorescent rhodamine-based hexapodal Fe3+
3

probe and fluorenylidene bridged cyclotriphosphazenes fluorescence probe for Cu2+ and Fe3+
are reported so far [30, 31]. The results of this study have encouraged us to developing new
chemosensor containing cyclotriphosphazene core.
In the present study, firstly the reactions of N3P3Cl6 (1) with aniline (2) and 2-
naphthylamine
(3)
were
studied
and
and
2,2’,4,4’-tetrakis(anilino)-6,6’-
dichlorocyclotriphosphazene
(4)
2,2’,4,4’-tetrakis(2-naphthylamino)-6,6’-
dichlorocyclotriphosphazene (5) were obtained. Then the reactions of these compounds (4)
and (5) with 4,4a-(9-fluorenylidene)diphenol, (FDP), (6) in THF gave target FDP-bridged
cyclotriphosphazene compounds (8-11). The same approach was used for the synthesis of
FDA-bridged cyclotriphosphazene compounds (12 and 13) by the reaction of compounds 4
and 5 with 4,4a-(9-fluorenylidene)dianiline, (FDA), (7). The new substituted mono (8, 10, 12
and 13) and double (9 and 11) fluorenylidene bridged cyclotriphosphazene derivatives were
fully characterized by means of elemental analysis, UV-Vis, 1H, and 31P NMR spectroscopies
and MALDI-TOF mass spectrometry. We also investigated fluorescence behavior of these
compounds by UV-Vis electronic, florescence spectroscopy. The chemosensor properties of
the newly synthesized cyclotriphosphazene compounds against to metal ions (Fe3+ and Cu2+)
were determine in solution.
4

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Scheme 1. The synthesis route of aniline and 2-naphthylamine substituted FDA and FDP bridged
cyclotriphosphazenes.
5

2. Experimental Section
2.1. Materials and Methods. Hexachlorocyclotriphosphazene (Otsuka Chemical Co., Ltd)
was purified by fractional crystallization from n-hexane. Aniline (99%), 2-naphthylamine
(99%), 4,4a-(9-fluorenylidene)diphenol (99%) and (4,4a-(9-fluorenylidene)dianiline (99%)
were obtained from Aldrich. Tetrahydrofuran (199.0%), dichloromethane (199.0%), n-hexane
(≥95.0%) and triethylamine (99.0%) were obtained from Merck. THF was distilled over a
sodium–potassium alloy under an atmosphere of dry argon. Silica gel 60 (230–400 mesh) for
column chromatography was obtained from Merck. CDCl3 and THF-d6 for NMR
spectroscopy is obtained from Goss Scientific. All reactions were monitored using thin-layer
chromatography (TLC) on Merck silica gel plates (Merck, Kieselgel 60, 0.25 mm thickness)
with F254 indicator. Column chromatography was performed on silica gel (Merck, Kieselgel
60, 230-400 mesh; for 3g crude mixture, 100g silica gel was used in a column of 3 cm in
diameter and 60 cm in length). All reactions were carried out under an argon atmosphere.
Melting points were measured on a Gallenkamp apparatus using a capillary tube. Elemental
analyses were obtained using a Thermo Finnigan Flash 1112 Instrument. Positive ion and
linear mode MALDI-MS of compounds were obtained in dihydroxybenzoic acid as MALDI
matrix using nitrogen laser accumulating 50 laser shots using Bruker Microflex LT MALDI-
1
TOF mass spectrometer. H and 31P NMR spectra were recorded in CDCl3 and THF-d6
solutions on a Varian INOVA 500 MHz spectrometer using TMS as an internal reference for
1H NMR and 85% H3PO4 as an external reference for 31P NMR. Electronic absorption spectra
in the UV–Vis. region were recorded with a Shimadzu 2101 UV-Vis spectrophotometer.
Fluorescence excitation and emission spectra were recorded on a Varian Eclipse
spectrofluorometer using 1 cm path length cuvettes at room temperature.
6

2.2. Synthesis
Aniline (4), and 2-naphthylamine (5) substituted cyclotriphosphazene compounds were
prepared and purified according to the literature procedures [32, 33].
2.2.1. Reaction of 2,2,4,4-tetra(anilino)-6,6-dichlorocyclotriphosphazene (4) with 4,4a-(9-
fluorenylidene)diphenol (FDP) (6) in a 1:2 ratio to form compounds 8 and 9.
2,2,4,4-tetra(anilino)-6,6-dichlorocyclotriphosphazene (4), (2.00 g, 3.48 mmol) and 4,4a-(9-
fluorenylidene)diphenol(FDP) (6) (0.611 g, 1.74 mmol) were dissolved in 100 mL of dry THF
under an argon atmosphere in a 250 mL three-necked round-bottomed flask. The reaction
mixture was cooled in an ice-bath and NaH (60% oil suspension, 3.06 g, 76.58 mmol) in 40
mL of dry THF was quickly added to a stirred solution under an argon atmosphere. The
reaction mixture was refluxed for 6 days and the reaction followed on TLC silica gel plates
using n-hexane:THF (2:1) as the eluent. Two products were observed on TLC plate. The
reaction mixture was filtered to remove the formed sodium chloride and the solvent was
removed under reduced pressure. The resulting colorless oily crude product was subjected to
column chromatography, using n-hexane:THF (2:1) as the eluent. The aniline substituted
FDP-mono bridged cyclotriphosphazene derivative (8) was obtained as first product from the
column, (0.60 g, 0.42 mmol, % 24, m.p. 120 oC), Rf=0.41. Anal.Calc. For C73H64Cl2N14O2P6:
C, 61.39; H, 4.66; N, 13.73, M, 1426.13. Found: C, 61.44; H, 4.50; N, 13.73 %, MS (MALDI-
TOF) m/z: 1449.82 [M+Na]+. 1H NMR, CDCl3, 298oK: ꢀ ppm, 7.74, d, 2H, (Hf); 7.42, td, 2H,
(He); 7.25-7.14, m, 4H, (Hc, Hd); 7.04-6.95, m, 32H, (Hk, Hl); 6.96-6.83, m, 8H, (Hb, Ha);
6.85-6.77, m, 8H, (Hm); 5.45, t, 4H, NH ; 4.85, t, 4H, NH. The aniline substituted FDP-
double bridged cyclotriphosphazene derivative (9) was obtained as second product from the
o
column, (0.12 g, 0.05 mmol, % 4, m.p. 95 C), Rf=0.30. Anal.Calc. For C98H80N14O4P6: C,
7

69.09; H, 4.73; N, 11.51, M, 1703.62. Found: C, 69.07; H, 4.70; N, 11.49 %, MS (MALDI-
1
TOF) m/z: 1704.45 [M+H]. H NMR, CDCl3, 298oK: ꢀ ppm, 7.72, d, 4H, (Hf); 7.30, td, 4H,
(He); 7.15-7.02, m, 8H, (Hc, Hd); 6.94-6.86, m, 32H, (Hk, Hl); 6.84-6.73, m, 16H, (Hb, Ha);
6.71-6.66, m, 8H, (Hm); 5.75, t, 4H, NH ; 4.75, t, 4H, NH.
2.2.2. Reaction of 2,2,4,4-tetra(2-naphthylamino)-6,6-dichlorocyclotriphosphazene (5) with
4,4a-(9-fluorenylidene)diphenol (FDP) (6) in a 1:2 ratio to form compounds 10 and 11.
2,2,4,4-tetra(2-naphthylamino)-6,6-dichlorocyclotriphosphazene (5), (1.00 g, 1.29 mmol) and
4,4a-(9-fluorenylidene)diphenol (FDP) (6) (0.226 g, 0.65 mmol) were dissolved in 100 mL of
dry THF under an argon atmosphere in a 250 mL three-necked round-bottomed flask. The
reaction mixture was cooled in an ice-bath and NaH (60% oil suspension, 0.05 g, 1.29 mmol
ol) in 40 mL of dry THF was quickly added to a stirred solution under an argon atmosphere.
The reaction mixture was refluxed for 6 days and the reaction followed on TLC silica gel
plates using n-hexane:THF (5:4) as the eluent. Two products were observed on TLC plate.
The reaction mixture was filtered to remove the formed sodium chloride and the solvent was
removed under reduced pressure. The resulting colorless oily crude product was subjected to
column chromatography, using n-hexane:THF (5:4) as the eluent. The 2-napthilamine
substituted FDP-mono bridged cyclotriphosphazene derivative (10) was obtained as first
o
product from the column, (0.41 g, 0.21 mmol, % 18, m.p. 125 C), Rf=0.41. Anal.Calc. For
C105H80Cl2N14O2P6: C, 69.04; H, 4.41; N, 10.73, M, 1826.60. Found: C, 69.02; H, 4.39; N,
10.71 %, MS (MALDI-TOF) m/z: 1827.23 [M+H]+. 1H NMR, CDCl3, 298oK: ꢀ ppm, 7.80, d,
2H, (Hf); 7.72-7.64, d, 8H, (Hl); 7.60-7.10, m, 6H, (He, Hc, Hd); 7.50-7.20, m, 40H, (Hm,
Hk, Hn, Hr, Hp); 7.00-6.85, m, 8H, (Hs); 6.70, m, 4H, (Hb); 6.62, m, 4H, (Ha); 5.75-5.65, m,
8H, NH. The 2-napthilamino substituted FDP-double bridged cyclotriphosphazene derivative
8

(11) was obtained as second product from the column, (0.12 g, 0.05 mmol, % 4, m.p. >250
oC), Rf=0.33. Anal.Calc. For C130H96N14O4P6: C, 74.21; H, 4.60; N, 9.32, M, 2104.09. Found:
1
C, 74.20; H, 4.58; N, 9.30 %, MS (MALDI-TOF) m/z: 2104.33 [M]+. H NMR, THF-d6,
298oK: ꢀ ppm, 7.75, d, 4H, (Hf); 7.67-7.61, d, 8H, (Hl); 7.53-7.18, m, 12H, (He, Hc, Hd);
7.54-7.17, m, 40H, (Hm, Hk, Hn, Hr, Hp); 7.08-6.99, m, 8H, (Hs); 7.02, d, 8H, (Hb); 6.80, d,
8H, (Ha); 5.70-5.40, m, 8H, NH.
2.2.3. Reaction of 2,2,4,4-tetra(anilino)-6,6-dichlorocyclotriphosphazene (4) with 4,4a-(9-
fluorenylidene) dianiline (FDA) (7) in a 1:2 ratio to form compound 12.
2,2,4,4-tetra(anilino)-6,6-dichlorocyclotriphosphazene (4), (1.00 g, 1.74 mmol) and 4,4a-(9-
fluorenylidene)dianiline (FDA) (7) (0.31 g, 0.87 mmol) were dissolved in 100 mL of dry THF
under an argon atmosphere in a 250 mL three-necked round-bottomed flask. The reaction
mixture was cooled in an ice-bath and NaH (60% oil suspension, 0.06 g, 1.74 mmol) in 40 mL
of dry THF was quickly added to a stirred solution under an argon atmosphere. The reaction
mixture was stirred for 4 days at room temperature and the reaction followed on TLC silica
gel plates using n-hexane–THF (2:1) as the eluent. Only one product was observed on TLC
plate. The reaction mixture was filtered to remove the formed sodium chloride and the solvent
was removed under reduced pressure. The resulting colorless oily crude product was
subjected to column chromatography, using n-hexane-THF (2:1) as the eluent. The aniline
substituted FDA-bridged cyclotriphosphazene derivative (15) was obtained, (0.15 g, 0.08
o
mmol, %5, m.p. 195 C), Rf=0.64. Anal.Calc. For C73H66Cl2N16P6: C, 61.56; H, 4.67; N,
15.74, M, 1424.16. Found: C, 61.54; H, 4.65; N, 15.72 %, MS (MALDI-TOF) m/z: 1425.28
[M+H].1H NMR, CDCl3, 298oK: ꢀ ppm, 7.74, d, 4H, (Hf); 7.42, td, 2H, (He); 7.25-7.14, m,
9

4H, (Hc, Hd); 7.12-6.95, m, 32H, (Hk, Hl); 6.96-6.83, m, 8H, (Hb, Ha); 6.85-6.77, m, 8H,
(Hm); 5.45, t, 4H, NH; 4.85, t, 4H, NH.
2.2.4. Reaction of 2,2,4,4-tetra(2-naphthylamino)-6,6-dichlorocyclotriphosphazene (5) with
4,4a-(9-fluorenylidene)dianiline (FDA) (7) in a 1:2 ratio to form compound 13.
2,2,4,4-tetra(2-naphthylamino)-6,6-dichlorocyclotriphosphazene (5), (0.60 g, 0.77 mmol) and
4,4a-(9-fluorenylidene)dianiline (FDA) (7) (0.13 g, 0.38 mmol) were dissolved in 100 mL of
dry THF under an argon atmosphere in a 250 mL three-necked round-bottomed flask. The
reaction mixture was cooled in an ice-bath and NaH (60% oil suspension, 0.03 g, 0.77 mmol)
in 40 mL of dry THF was quickly added to a stirred solution under an argon atmosphere. The
reaction mixture was refluxed for 3 days and the reaction followed on TLC silica gel plates
using n-hexane–THF (8:5) as the eluent. Only one product was observed on TLC plate. The
reaction mixture was filtered to remove the formed sodium chloride and the solvent was
removed under reduced pressure. The resulting colorless oily crude product was subjected to
column chromatography, using n-hexane–THF (8:5) as the eluent. The 2-napthilamine
substituted FDA-bridged cyclotriphosphazene derivative (13) was obtained, (0.11 g, 0.05
o
mmol, % 40, m.p. 146 C), Rf=0.48. Anal.Calc. For C105H82Cl2N16P6: C, 69.12; H, 4.53; N,
4.12.28, M, 1824.47. Found: C, 69.10; H, 4.51; N, 12.26 %, MS (MALDI-TOF) m/z: 1825.33
[M+H]+. 1H NMR, CDCl3, 298oK: ꢀ ppm, 7.65, d, 2H, (Hf); 7.55-7.45, d, 8H, (Hl); 7.50-7.15,
m, 10H, (He, Hc, Hd, Hb); 7.55-7.26, m, 40H, (Hm, Hk, Hn, Hr, Hp); 7.15-7.00, m, 8H, (Hs);
6.91, d, 4H, (Ha); 5.85-5.60, m, 10H, NH.
10

3. Results and Discussion
3.1. Synthesis and characterization
In this study, the reaction of 2,2’,4,4’-tetrakis(aniline)-6,6’-dichlorocyclotriphosphazene
(4) and 2,2’,4,4’-tetrakis(2-naphthylamino)-6,6’-dichlorocyclotriphosphazene (5) with di-
functional alcohol such as 4,4a-(9-fluorenylidene)diphenol, (FDP), (6) and di-functional
amine such as 4,4a-(9-fluorenylidene)dianiline (FDA), (7) groups were investigated. The
monofunctional amines substituted fluorenylidene bridged cyclotriphosphazenes (8-13) were
synthesized (Scheme 1) and fully characterized by means of elemental analysis, MALDI-TOF
1
1
mass spectrometry, H and 31P NMR spectroscopies. The mass, elemental analysis and H-
NMR data for each new isolated compound are provided as part of the analytical data in the
experimental section. The 31P NMR chemical shifts and phosphorus–phosphorus coupling
constants of newly synthesized compounds (8-13) are summarized in Table 1. The mass
spectra of compounds (8-13) were obtained by MALDI-TOF-MS. Mass spectra results of all
compounds clearly show the major molecular ion peaks, which confirmed the exact
composition for the proposed structures. The molecular ion peak of compound 11 is shown as
m/z (M+) at 2104.3 (Fig. S1).
The proton decoupled 31P NMR spectra of aniline substituted mono FDP-bridged
cyclotriphosphazene (8) and aniline substituted double FDP-bridged cyclotriphosphazene (9)
are depicted as Figures S2a and S2b, respectively as examples. The proton decoupled 31P
NMR spectra of compounds (8 and 9) showed as AX2 spin systems due to the environments
for the two different phosphorus nuclei of the cyclotriphosphazene ring. The proton decoupled
31P NMR spectrum of the compound 8 has shown two signal. The signals consisted of one
triplet for the –P(OCl) groups (ꢀ=23.3 ppm) and a doublet for the -P(R)2 (R=NHPh) groups
(ꢀ= 4.9 ppm), in which those have two bond–coupling constants phosphorous and
11

2
phosphorous, average of ca JPP=52.9 Hz. Spectrum of compound 9 showed one doublet of
doublets for the -PO2 group (ꢀ= 11.8 ppm) and one doublet for the -P(R)2 (R=NHPh) group
(ꢀ= 5.2 ppm). Compound 12 (aniline substituted mono FDA-bridged cyclotriphosphazene)
has shown an AX2 spin system in the proton decoupled 31P NMR. The resonance for the
–P(NHCl) group was observed at ꢀ=23.3 ppm as a triplet and the -P(R)2 (R=NH Naphthyl)
group was observed at ꢀ=4.8 in this spectrum.
The proton decoupled 31P NMR spectra of 2-naphthylamine substituted mono FDP-
bridged cyclotriphosphazene (10), 2-naphthylamine substituted double FDP-bridged
cyclotriphosphazene (11) compounds are depicted as Figs. 1a and 1b, respectively as
examples. While the proton decoupled 31P NMR spectra of compounds 10 and 12 showed as
AX2 spin systems, compound 11 showed as AB2 spin systems, due to the close chemical
shifts for the two different phosphorus nuclei of the cyclotriphosphazene ring. The proton
decoupled 31P NMR spectrum of the compound 10 has shown two signal. The signals
consisted of one triplet for the –P(OCl) groups (ꢀ=20.3 ppm) and a doublet for the -P(R)2
(R=NH Naphthyl) groups (ꢀ= 3.6 ppm). Spectrum of compound 11 showed one doublet of
doublets for the -PO2 group (ꢀ= 6.3 ppm) and one doublet for the -P(R)2 (R=NH Naphthyl)
group (ꢀ= 3.6 ppm). For the 2-naphthylamine substituted mono FDA-bridged
cyclotriphosphazene compound (13), the resonance for the –P(NHCl) group was observed at
ꢀ=23.4 ppm as a triplet and the -P(R)2 (R=NH Naphthyl) group was observed at ꢀ=5.2 in this
spectrum.
1
The H NMR data also confirmed the structures of newly synthesized compounds 8-
13. The aromatic protons for all compounds were observed at between 7.8 and 6.6 ppm and
1
some of them were distinguishable from each other, H NMR spectrum of compound 9 is
shown as an example in Figure S3. In addition, NH protons for all compounds were observed
at between 5.8 - 4.7 ppm
12

Figure 1. The proton decoupled 31P NMR spectra of (a) 2-naphthylamine substituted mono
FDP- bridged cyclotriphosphazene derivatives in CDCl3 solution (10); (b) 2-naphthylamine
substituted gem-bis FDP- bridged cyclotriphosphazene (11) derivatives in d6-THF solution.
13

Table 1.31P {1H} NMR parameters for synthesized cyclotriphosphazene compounds.
Spin
2J(PP)
[Hz]
δ (31P NMR)[ppm]
Compounds
System
PR2
R:(NHNaptl)
1.91
PR2
PCl2
PClO
PO2
PClNH
2JAX,2JAB
R:(NHNaptl)
(4) (a,b)
(5) (a,c)
(8) (a)
25.77
-
-
-
AX2
AX2
AX2
AX2
AX2
AB2
AX2
AX2
53.21
53.31
52.91
64.43
61.40
70.1
24.69
-
-
-
-
4.92
5.29
-
1.01
-
-
-
-
-
-
-
23.30
-
-
(9) (a)
-
11.84
-
-
(10) (a)
(11) (d)
(12) (a)
(13) (a)
20.32
-
-
3.66
3.67
-
-
-
-
6.31
-
-
-
23.32
4.89
-
52.88
52.68
-
23.41
5.23
(a) 202.38 MHz 31P NMR chemical shifts (ppm) in CDCl3.
(b) [32]
(c) [33]
(d) 202.38 MHz 31P NMR chemical shifts (ppm) in d6-THF
3.2. Ground state electronic absorption and fluorescence properties
The ground state electronic absorption spectra of newly synthesized aniline and 2-
naphthylamine substituted fluorenylidene bridged cyclotriphosphazene derivatives (8-13)
were measured in tetrahydrofuran (THF) solution. Different absorption bands were observed
in the UV region of electronic spectra (Fig. S4 as examples for compounds 8 and 10). Two
absorption bands were observed at approximately 275 and 310 nm in the UV region of
electronic spectra for aniline substituted fluorenylidene bridged cyclotriphosphazene
compounds (8, 9 and 12). Six absorption bands were observed at approximately 270, 280,
290, 310, 330 and 340 nm in the UV region of electronic spectra for 2-naphthylamine
substituted fluorenylidene bridged cyclotriphosphazene compounds (10, 11 and 13). The
compounds 8, 9 and 12 gave different emission bands at 312 and 323 nm in THF (Fig. S5).
The fluorescence emission spectra of the 2-naphthylamine substituted fluorenylidene bridged
14

cyclotriphosphazene derivatives (10, 11 and 13) are shown in Figure S6. These compounds
gave intense emission peaks at 370 nm. The 2-naphthylamine substituted fluorenylidene
bridged cyclotriphosphazenes (10, 11 and 13) showed higher fluorescence emission than that
of other cyclophosphazene compounds 8, 9 and 12 in THF (Fig. S5 and Fig. S6). These
compounds (10, 11, and 13) also showed higher fluorescence behavior than chlorine
substituted counterparts which were studied our previously work [30, 33]. This can be
explained by non-covalent 4 – 4 interactions increasing number of conjugated 4-electrons in
the aromatic ring systems of the substituted groups. These measurements show that the
compounds 10, 11 and 13 exhibited highly fluorescence behavior in THF solutions. However,
the other bridged cyclotriphosphazene derivatives showed very weak fluorescence in this
solvent. For this reason, only 2-naphthylamine substituted fluorenylidene bridged compounds
were tested for metal ion sensing.
3.3. Chemosensor properties to metal ions
The metal binding capability of fluoren molecules may allow the use of the newly synthesized
fluorenylidene bridged cyclotriphosphazene derivatives as metal sensors. In this study, 2-
naphthylamine substituted fluorenylidene bridged cyclotriphosphazene compounds (10, 11
and 13) were tested to a variety of metal ions (Mg2+, Ca2+, Ba2+, Mn2+, Fe3+, Co2+, Ni2+, Cu2+,
Zn2+, Cd2+, Li+, Na+, K+ and Cs+) using by fluorescence spectrometry. All fluorescence
emission spectral studies were performed in THF solutions at room temperature. The aqueous
solutions of the corresponding metal chlorides (nitrate derivative for Ag ion) were used as the
source of metal ions. The fluorescence spectra of the new 2-naphthylamine substituted
fluorenylidene bridged cyclotriphosphazene derivatives (10, 11 and 13) exhibited little
enhancement by the addition of the 5 µL of 1.00x10-2 M metal solutions except for Fe3+ and
15

Cu2+. A significant decrease in the fluorescence intensities were observed by the addition of
the Fe3+ and Cu2+ cations to the THF solutions of substituted cyclophosphazene compounds
(10, 11 and 13), while no or minimal change was observed with the other metal ions (Fig. 2 as
an example for compound 10, Figs. S7 and S11 in Supporting Information for other
compounds).
The titration of the probe compounds (10, 11 and 13) with Fe3+ or Cu2+ cations showed
a decrease in the fluorescence intensities with increasing concentrations of these cations
(Figure 3A for Cu2+ titration and Figure S8A for Fe3+ titration as an example for compound
10, Figs. S9A, S10A, S12A and S13A in Supporting Information for other compounds). The
graphs from a Benesi-Hildebrand analysis showed a non-linear behavior for all studied
cyclotriphosphazene chemosensor compounds interactions with Fe3+ ions indicating the
stoichiometry of between these chemosensors and Fe3+ or Cu2+ cations are different from 1:1
(Figure 3B for Cu2+ titration and Figure S8B for Fe3+ titration as an example for compound
10, Figs. S9B, S10B, S12B and S13B in Supporting Information for other compounds). The
continuous variation method was also used for the determination of the stoichiometry between
the new 2-naphthylamine substituted fluorenylidene bridged cyclotriphosphazene
chemosensors and detected metal cations. The resulting Job's with a maximum mole fraction
for Cu2+ or Fe3+ cations was observed as 0.33 (Figure 3C for Cu2+ titration and Figure S8C for
Fe3+ titration as an example for compound 10, Figs. S9C, S10C, S12C and S13C in
Supporting Information for other compounds), indicating that cyclotriphosphazene molecules
and Cu2+ or Fe3+ ions preferred 2:1 stoichiometry for the formation of complexes between the
chemosensor compounds (10, 11 and 13) and Fe3+ or Cu2+ cations in THF solutions.
16

Compound 10, Mg,
Ca, Ba, Mn, Co, Ni,
Zn, Cd, Li, Na, K ,
700
750
600
450
300
150
0
600 Cs
500
400
10+Metal Ions 10
300
200
100
Fe/Cu
0
300
350
400
450
500
Wavelength(nm)
Figure 2. The fluorescence intensity of the compound 10 with and without metal ions in THF
solution. Addition of Fe+3 and Cu2+ ions to the solution prevent fluorescent emission hence
provide a selective detection.
17

ꢇꢀꢀ
ꢆꢀꢀ
ꢅꢀꢀ
ꢀꢀ
ꢅ
0 M
Cu
10x10-2 M
ꢄꢀꢀ
ꢃꢀꢀ
ꢂꢀꢀ
ꢁꢀꢀ
ꢀ
ꢃꢁꢀ
ꢃꢅꢀ
ꢄꢁꢀ
ꢄꢅꢀ
ꢁꢀ
ꢅꢀ
ꢄ:0VCVJ$ꢁ.ꢃ^JI_
50
0
ꢆ
ꢇ
800
-50
-100
-150
-200
-250
-300
600
400
200
0
(0.3)
0
0.2
0.4
0.6
0.8
1
0
20
40
1/[M]
60
80
100
Mole Fraction of Fe (X)
Figure 3. (A) Fluorescence response of chemosensor 10 to various equivalents of Cu+2. (B)
The Benesi-Hildebrand graph and (C) Job's plot of 10-Cu+2 complexes in THF solutions. The
total concentration of 10 and Cu+2 was 1x10-2 M. The excitation wavelength was 295 nm. The
monitored wavelength was 370 nm (compound 10 C: 5x10-6 M).
18

4. Conclusion
In summary, we have been synthesized 4,4a-(9-fluorenylidene)diphenol (FDP) and
4,4a-(9-fluorenylidene)dianiline (FDA) bridged aniline and 2-naphthylamine substituted
cyclotriphosphazenes for the first time. All newly synthesized compounds (8-13) were
1
characterized by elemental analysis, MALDI-TOF mass spectrometry, UV-Vis, H NMR and
31P NMR spectroscopies. The fluorescence behavior of compounds 8-13 was investigated by
florescence spectroscopy in THF solutions. In addition, the effects of metal ions on the
fluorescence behavior of the compounds were studied in order to determine potential using of
these compounds as chemosensors for metal ions. A significant decrease in the fluorescence
signals were observed by the addition of the Cu2+ and Fe3+ cations among the fifteen different
metal ions. The newly synthesized FDP and FDA bridged 2-naphthylamine substituted
cyclotriphosphazene derivatives (10, 11, 13) preferred formation of 2:1 (ligand: metal)
complexes with both Fe3+ and Cu2+ ions. FDP and FDA bridged substituted
cyclotriphosphazene derivatives showed highly selectivity towards Cu2+ and Fe3+ ions and
these newly synthesized compounds showed potential using as chemosensors for these metal
ions in THF solution.
19

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21

ASSOCIATED CONTENT
1
Supporting Information Available: Example H NMR, the graphs of titrations of FDP-
bridged compounds with Cu2+ and Fe3+ ions and the Benesi-Hildebrand graphs and Job's plots
were given as Supporting Information.
AUTHOR INFORMATION
Corresponding Author
*E-mail: senkuytu@gtu.edu.tr
ACKNOWLEDGMENTS
The authors thank the Scientific and Technical Research Council of Turkey for financial
support TUBITAK (Grant 111T085).
22

Monofunctional amines substituted Fluorenylidene Bridged
Cyclotriphosphazenes: ‘Turn-Off’ Fluorescence Chemosensors for Cu2+
and Fe3+ ions
Elif 1enkuytu*, Esra Tanrıverdi Eçik, Mahmut Durmu2, Gönül Yenilmez Çiftçi
The synthesis and characterization of the first series of amine substituted
fluorenylidene-bridged cyclotriphosphazene derivatives were reported in this study. The
florescence properties and chemosensor behaviors of the synthesized new compounds
against to metal ions were studied. The fluorenylidene bridged 2-naphthylamino
substituted cyclotriphosphazenes showed fluorescence chemosensor behavior with high
selectivity for Fe3+ and Cu2+ ions in the solution.
23

Monofunctional amines substituted Fluorenylidene Bridged
Cyclotriphosphazenes: ‘Turn-Off’ Fluorescence Chemosensors for Cu2+
and Fe3+ ions
Compound 10,
700
Mg, Ca, Ba, Mn,
Co, Ni, Zn, Cd,
Li, Na, K , Cs
600
500
400
300
200
100
0
Fe/Cu
300
350
400
450
500
Wavelength(nm)