Structural and chemosensor properties of FDA and FDP derivatives of fluorenylidene bridged cyclotetraphosphazenes

Article abstract of DOI:10.1016/j.poly.2016.04.046

The first series of 4,4′-(9-fluorenylidene)diphenol (FDP) (5) and 4,4′-(9-fluorenylidene)dianiline (FDA) (6) bridged and open chained cyclotetraphosphazene derivatives (15-23) have been synthesized. Their florescence and chemosensor properties are reported. Nucleophilic substitution reactions of octachlorocyclotetraphosphazene (1) with mono-functional reagents [phenol (2), 2-naphthol (3) and 1-hydroxypyrene (4)] were carried out and the heptasubstituted derivatives (8, 11 and 14) were obtained. Then the reactions of 8, 11 and 14 with 4,4′-(9-fluorenylidene)diphenol (FDP) (5) and 4,4′-(9-fluorenylidene)dianiline (FDA) (6), respectively gave bridged and open chained compounds. The structures of the synthesized compounds (7-23) were verified by elemental analyses, mass spectrometry, UV Vis, ¹H and ³¹P NMR techniques and fluorescence spectroscopy. The metal sensing properties of the novel bridged open chain cyclotetraphosphazene derivatives were also examined by fluorescence spectroscopy. These complexes showed high selectivity for Cu²⁺ and Fe³⁺ ions in solution.

Full text of DOI:10.1016/j.poly.2016.04.046

Accepted Manuscript
Structural and chemosensor properties of FDA and FDP derivatives of fluore-
nylidene bridged cyclotetraphosphazenes
Elif Şenkuytu, Gönül Yenilmez Çiftçi
PII:
S0277-5387(16)30153-X
http://dx.doi.org/10.1016/j.poly.2016.04.046
POLY 11984
DOI:
Reference:
Polyhedron
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Accepted Date:
23 February 2016
20 April 2016
Please cite this article as: E. Şenkuytu, G.Y. Çiftçi, Structural and chemosensor properties of FDA and FDP
derivatives of fluorenylidene bridged cyclotetraphosphazenes, Polyhedron (2016), doi: http://dx.doi.org/10.1016/
j.poly.2016.04.046
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Structural and chemosensor properties of FDA
and FDP derivatives of fluorenylidene bridged
cyclotetraphosphazenes
Elif Şenkuytu and Gönül Yenilmez Çiftçi*
Department of Chemistry, Gebze Technical University, Gebze 41400, Kocaeli, Turkey
* Corresponding author
Phone: 00 90 262 6053011 Fax: 00 90 262 6053101
yenilmez@gtu.edu.tr
1

ABSTRACT
The first series of 4,4’-(9-fluorenylidene)diphenol (FDP) (5) and 4,4’-(9-
fluorenylidene)dianiline (FDA) (6) bridged and open chained cyclotetraphosphazene
derivatives (15-23) have been synthesized. Their florescence and chemosensor properties are
reported. Nucleophilic substitution reactions of octachlorocylotetraphosphazene (1) with
mono-functional reagents [phenol (2), 2-naphthol (3) and 1-hydroxypyrene (4)] were carried
out and the heptasubstituted derivatives (8, 11 and 14) were obtained. Then the reactions of 8,
11 and 14 with 4,4′-(9-fluorenylidene)diphenol (FDP) (5) and 4,4′-(9-fluorenylidene)dianiline
(FDA) (6), respectively gave bridged and open chained compounds. The structures of the
synthesized compounds (7-23) were verified by elemental analyses, mass spectrometry, UV
1
31
Vis, H and P NMR techniques and fluorescence spectroscopy. The metal sensing properties
of the novel bridged open chain cyclotetraphosphazene derivatives were also examined by
fluorescence spectroscopy. These complexes showed high selectivity for Cu2+ and Fe3+ ions in
solution.
KEYWORDS: Cyclotetraphosphazenes, Fluorenylidene, Fluorescence Properties, Bridged
structure, Chemosensors, Cu2+ and Fe3+ ions.
2

1. INTRODUCTION
The design of fluorescent chemosensors for ions is very important for the study of ions in
biological processes since they may be linked to states of human disease. Examining the
fluorescence properties of compounds to be synthesized as new sensors, determining their
locations in the body and their usability for metal ion sensing as a fluorescence sensor are
important [1,2]. For example, the development of chemosensors for sensing Fe3+ ions has
attracted interest because they play important roles in biology, chemistry and the
environment. Iron is an important trace element and the most abundant in the cells of all
organisms [3,4]. Deficiency of Fe3+ ions causes anemia, diabetes, liver damage, Parkinson’s
disease and cancer [5,6], but an overdose of iron in humans is equally detrimental and can
cause dis-function of certain organs, such as the heart, pancreas and liver [7]. On the other
hand, copper is the third most abundant ion in the human body and plays an important role in
many physiological systems [8,9]. If the blood concentration of copper ions falls outside the
normal range [3,10], it can cause Alzheimer’s, Wisons and Manke’s diseases [11-14].
Therefore, the detection of trace amounts of Cu2+ [15,16] and Fe3+ [17,18] ions is critical.
Some organic compounds, like fluorene and pyrene, are remarkable for their fluorescence
properties, thus they and their derivatives are suitable for many applications, such as metal-
organic frameworks, fluorescent probes and applications in sensors, liquid crystals, organic
light-emitting diodes, as electrochromic applications [19-26]. Conjugated fluorenes, such as
4,4′-(9-fluorenylidene)diphenol (5) or 4,4′-(9-fluorenylidene)dianiline, (FDA) (6), have been
used for many applications and they have the potential to detect metal ions in biological and
environmental media as well. The binding of certain metal ions to the fluorene molecule may
influence the fluorescent properties of the molecule and hence indicate its presence in solution
[27-30]. Phosphazenes, particularly cyclic phosphazenes, are an important class of inorganic
heterocyclic ring containing an [N = PX2] repeat unit [31]. Some of the substituted cyclic
3

phosphazenes have high thermal stability and do not break down even under very aggressive
chemical conditions. Among this family of compounds, the chlorocyclophosphazenes N3P3Cl6
and N4P4Cl8 (1), have received maximum attention [32,33], and of these, the
cyclotriphosphazenes are the most prevalent. There has recently been considerable interest in
fluorescent compounds based on cyclic phosphazene cores or cyclo-linear polymers with
cyclotriphosphazene units for the development of electroluminescent devices [34-39]. The
reactions of octachlorocyclotetraphosphazene, N4P4Cl8, with mono-, di-, tri- and tetra-
functional reagents have been studied [31,40-47] and there are reports of
cyclotetraphosphazene compounds containing fluorescent groups [48-50]. However,
discussion on substitution with a cyclotetraphosphazene bridged structure is relatively limited
in the literature [46]. In our recent works, FDP and FDA bridged cyclotriphosphazenes,
N3P3Cl6, and their derivatives showed selectivity towards Cu2+ and Fe2/Fe3+ ions [29,51,52].
The results of these studies have encouraged us to investigate new phenol, naphthol and
pyrene modified cyclotetraphosphazene compounds containing FDP and FDA on the
cyclotetraphosphazene core.
In the current study, new fully substituted fluorenylidene bridged (15, 17, 18, 20 and 22) and
open chain (16, 19, 21 and 23) cyclotetraphosphazene compounds have been synthesized, and
their florescence and chemosensor properties are reported for the first time. All the
1
31
compounds were characterized by elemental analysis, mass spectrometry, UV Vis, H, P
NMR and fluorescence spectroscopy (15-23). In addition, the metal binding properties of the
synthesized FDP/FDA bridged and open chain cyclotetraphosphazene compounds (15, 16, 18,
19, 20) were investigated and compared by fluorescence spectroscopy.
4

Scheme 1. FDA and FDP containing cyclotetraphosphazene derivatives.
5

2. Experimental Section
2.1. General Materials and Methods.
Octachlorocyclotetraphosphazene (Otsuka Chemical Co., Ltd) was purified by fractional
crystallization from n-hexane. Sodium hydride, (60% dispersion in mineral oil) was obtained
from Merck; prior to use the oil was removed by washing with dry heptane followed by
decantation. Phenol (99%), 2-naphthol (99%), 1-hydroxypyrene (99%), 4,4′-(9-
fluorenylidene)diphenol (99%) and (4,4′-(9-fluorenylidene)dianiline (99%) were obtained
from Aldrich. Tetrahydrofuran (≥ 99.0%), dichloromethane (≥ 99.0%) and n-hexane (≥
95.0%) 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 d8-THF for NMR spectroscopy were obtained from Goss
Scientific. Elemental analyses were obtained using a Thermo Finnigan Flash 1112 Instrument.
Positive ion and linear mode MALDI-MS of the compounds were obtained in
dihydroxybenzoic acid as the MALDI matrix using a nitrogen laser, accumulating 50 laser
shots using a Bruker Microflex LT MALDI-TOF mass spectrometer. 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 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
1
capillary tube. H and 31P NMR spectra were recorded in CDCl3 and d8-THF solutions on a
1
Varian INOVA 500 MHz spectrometer using TMS as an internal reference for H NMR and
85% H3PO4 as an external reference for 31P NMR. 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
6

length cuvettes at room temperature. The NMR simulation program, available free of charge,
used was gNMR [53].
ꢀ
2.2. Synthesis
2.2.1. Reaction of octachlorocyclotetraphosphazene N4P4Cl8 (1) with phenol (2) in a 1:7 ratio
to form compounds 7, 8 and 9.
Phenol (2) (4.26 g, 45.30 mmol) was dissolved in 50 mL of dry THF under an argon
atmosphere in a 100 mL three-necked round-bottomed flask. The reaction mixture was cooled
in an ice-bath and NaH (60% oil suspension, 1.81 g, 45.30 mmol) in 20 mL of dry THF was
quickly added to the above stirred solution under an argon atmosphere.
Octachlorocyclotetraphosphazene N4P4Cl8 (1), (3.00 g, 6.47 mmol) in 20 mL of dry THF was
added to the stirred solution under an argon atmosphere. The reaction mixture was stirred for
2 days at room temperature and the reaction was followed on TLC silica gel plates using n-
hexane-CH2Cl2 (3:2) as the eluent. Three products were observed on TLC. The reaction
mixture was filtered to remove the formed sodium chloride and then the solvent was removed
under reduced pressure. The resulting colorless solid was subjected to column
chromatography, using n-hexane-CH2Cl2 (3:2) as the eluent. The first product was compound
7, 1,1,3,5,5,7-hexaphenoxy-3,7-dichlorocyclotetraphosphazene, (0.31 g, 0.36 mmol, 6%,
oily), Rf = 0.57. Anal. Calc. for C36H30Cl2N4O6P4: C, 53.42; H, 3.74; N, 6.92; M, 809. Found:
1
C, 53.40; H, 3.72; N, 6.90%. MS (MALDI-TOF) m/z: 809 [M]+. H NMR, CDCl3, 298 K, δ
ppm: 7.29-7.24 m, 12H, H1; 7.23-7.19 m, 6H, H3; 7.13-7.11 m, 12H, H2. The second product
was compound 8, 1,1,3,3,5,5,7-heptaphenoxy-7-dichlorocyclotetraphosphazene, (1.17 g, 1.35
mmol, 21%, oily), Rf = 0.47. Anal. Calc. for C42H35ClN4O7P4: C, 58.18; H, 4.07; N, 6.46; M,
1
867. Found: C, 58.16; H, 4.05; N, 6.44%. MS (MALDI-TOF) m/z: 867 [M]+. H NMR,
CDCl3, 298 K, δ ppm: 7.11-7.06 m, 14H, H1; 7.03-6.99 m, 7H, H3; 6.95-6.91 m, 14H, H2. The
third product was compound 9, 1,1,3,3,5,5,7,7-octaphenoxycyclotetraphosphazene, (0.65 g,
7

0.70 mmol, 11%, oily), Rf = 0.37. Anal. Calc. for C48H40N4O8P4: C, 62.34; H, 4.36; N, 6.06;
1
M, 924. Found: C, 62.31; H, 4.34; N, 6.06%. MS (MALDI-TOF) m/z: 924 [M]+. H NMR,
CDCl3, 298 K, δ ppm; 7.08-7.04 m, 16H, H1; 7.02-6.97 m, 8H, H3; 6.88-6.84 m, 16H, H2.
2.2.2. Reaction of octachlorocyclotetraphosphazene N4P4Cl8 (1) with 2-naphthol (3) in a 1:7
ratio to form compounds 10, 11 and 12.
2-Naphthol (3) (5.43 g, 37.73 mmol) was dissolved in 50 mL of dry THF under an
argon atmosphere in a 100 mL three-necked round-bottomed flask. The reaction mixture was
cooled in an ice-bath and NaH (60% oil suspension, 1.50 g, 37.73 mmol) in 20 mL of dry
THF was quickly added to the above stirred solution under an argon atmosphere.
Octachlorocyclotetraphosphazene N4P4Cl8 (1), (2.50 g, 5.39 mmol) in 20 mL of dry THF was
added to the stirred solution under an argon atmosphere. The reaction mixture was stirred for
5 hours at room temperature and the reaction was followed on TLC silica gel plates using n-
hexane-CH2Cl2 (3:2) as the eluent. Three products were observed on TLC. The reaction
mixture was filtered to remove the formed sodium chloride and then the solvent was removed
under reduced pressure. The resulting colorless solid was subjected to column
chromatography, using n-hexane-CH2Cl2 (3:2) as the eluent. The first product was compound
10, 1,1,3,5,5,7-hexa(2-naphthloxy)-3,7-dichlorocyclotetraphosphazene, (0.30 g, 0.27 mmol,
6%, oily), Rf = 0.51. Anal. Calc. for C60H42Cl2N4O6P4: C, 64.94; H, 3.81; N, 3.69; M, 1109.
1
Found: C, 64.92; H, 3.78; N, 3.65%. MS (MALDI-TOF) m/z: 1110 [M+H]+. H NMR,
CDCl3, 298 K, δ ppm: 7.65 d, 6H, H2 (3JH2-H3 = 8.28 Hz); 7.50, s, 6H, H1; 7.45-7.38, m, 12H,
(H3, H4); 7.35-7.30, m, 12H, (H6, H5); 7.22, d, 6H, H7 (3JH7-H6 = 8.90 Hz). The second product
was compound 11, 1,1,3,3,5,5,7-hepta(2-naphthloxy)-7-dichlorocyclotetraphosphazene, (1.62
g, 1.33 mmol, 25%, oily), Rf = 0.46. Anal. Calc. for C70H49ClN4O7P4: C, 69.06; H, 4.06; N,
1
4.60; M, 1217. Found: C, 69.04; H, 4.03; N, 4.56%. MS (MALDI-TOF) m/z: 1217 [M]+. H
NMR, THF-d8, 298 K, δ ppm: 7.68 d, 7H, H2 (3JH2-H3 = 8.30 Hz); 7.46, s, 7H, H1; 7.43-7.34,
8

m, 14H, (H3, H4); 7.31-7.28, m, 14H, (H6, H5); 7.17, d, 7H, H7 (3JH7-H6 = 8.90 Hz). The third
product was compound 12, 1,1,3,3,5,5,7,7-octa(2-naphthloxy)cyclotetraphosphazene, (0.66 g,
0.50 mmol, 9%, oily), Rf = 0.41. Anal. Calc. for C80H56N4O8P4: C, 72.51; H, 4.26; N, 4.23;
1
M, 1325. Found: C, 72.49; H, 4.23; N, 4.2%. MS (MALDI-TOF) m/z: 1325 [M]+. H NMR,
CDCl3, 298 K, δ ppm: 7.57 d, 8H, H2 (3JH2-H3 = 8.18 Hz); 7.30, td, 8H, H3 (3JH2-H3 = 8.18 Hz,
3
3JH3-H4 = 7.30 Hz); 7.26, s, 8H, H1; 7.21, td, 8H, H4 (3JH4-H3 = 7.30 Hz, JH4-H5 = 8.20 Hz);
7.19, d, 8H, H6 (3JH6-H7 = 8.90 Hz); 7.14, d, 8H, H5 (3JH5-H4 = 8.20 Hz); 6.92, d, 8H, H7 (3JH7-H6
= 8.90 Hz).
2.2.3. Reaction of octachlorocyclotetraphosphazene N4P4Cl8 (1) with 1-hydroxypyrene (4) in
a 1:7 ratio to form compounds 13 and 14.
1-Hydroxypyrene (4) (2.00 g, 9.16 mmol) was dissolved in 50 mL of dry THF under an
argon atmosphere in a 100 mL three-necked round-bottomed flask. The reaction mixture was
cooled in an ice-bath and NaH (60% oil suspension, 0.36 g, 9.16 mmol) in 40 mL of dry THF
was quickly added to the above stirred solution under an argon atmosphere.
Octachlorocyclotetraphosphazene N4P4Cl8 (1), (0.60 g, 1.29 mmol) in 20 mL of dry THF was
added to the stirred solution under an argon atmosphere. The reaction mixture was stirred for
7 hours at room temperature and the reaction was followed on TLC silica gel plates using n-
hexane-CH2Cl2 (2:1) as the eluent. Two products were observed on TLC. The reaction
mixture was filtered to remove the formed sodium chloride and then solvent was removed
under reduced pressure. The resulting colorless solid was subjected to column
chromatography, using n-hexane-CH2Cl2 (2:1) as the eluent. The first product was compound
13, 1,1,3,5,5,7-hepta(1-oxypyrene)-3,7-dichlorocyclotetraphosphazene, (0.10 g, 6.43x10-2
mmol, 5%, oily), Rf = 0.21. Anal. Calc. for C96H54Cl2N4O6P4: C, 74.18; H, 3.50; N, 3.60; M,
1
1554. Found: C, 74.15; H, 3.46; N, 3.57; %. MS (MALDI-TOF) m/z: 1554 [M+H]+. H
9

NMR, CDCl3, 298 K, δ ppm: 8.40-7.10 m, 54H, (H1-H9). The second product was compound
14, 1,1,3,3,5,5,7-hepta(1-oxypyrene)-7-chlorocyclotetraphosphazene, (0.30 g, 0.17 mmol,
15%, oily), Rf = 0.17. Anal. Calc. for C112H63ClN4O7P4: C, 77.49; H, 3.66; N, 3.23; M, 1736.
1
Found: C, 77.46; H, 3.64; N, 3.21; %. MS (MALDI-TOF) m/z: 1736 [M]+. H NMR, CDCl3,
298 K, δ ppm: 8.40-7.10 m, 63H, (H1-H9).
2.2.4. Reaction of 1,1,3,3,5,5,7-heptaphenol-7-chlorocyclotetraphosphazene (8) with 4,4′-(9-
fluorenylidene)diphenol (FDP) (5) in a 1:2 ratio to form compound 15 and 16.
1,1,3,3,5,5,7-Heptaphenoxy-7-chlorocyclotetraphosphazene (8), (0.70 g, 0.81 mmol)
and 4,4′-(9-fluorenylidene)diphenol (FDP) (5) (0.14 g, 0.41 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, 0.81 mmol)
in 40 mL of dry THF was quickly added to the stirred solution under an argon atmosphere.
The reaction mixture was refluxed for 4 days and the reaction followed on TLC silica gel
plates using n-hexane-CH2Cl2 (2:3) as the eluent. Two products were observed on TLC. The
reaction mixture was filtered to remove the formed sodium chloride and the solvent was
removed under reduced pressure. The resulting colorless solid was subjected to column
chromatography, using n-hexane-THF (2:3) as the eluent. The first product was compound
15, the phenol substituted FDP-bridged cyclotetraphosphazene derivative, (0.51 g, 0.25 mmol,
61% oily), Rf = 0.58. Anal. Calc. for C109H86N8O16P8: C, 65.09; H, 4.33; N, 5.59; M, 2011.
1
Found: C, 65.08; H, 4.31; N, 5.57 %, MS (MALDI-TOF) m/z: 2011 [M+H]+ (Fig. S1a). H
NMR, CDCl3, 298 K, δ ppm: 7.70, d, 2H, Hf, (3J = 7.23 Hz); 7.27, td, 2H, He, (3JHe-Hf = 7.23
Hf-He
3
Hz, JHe-Hd = 7.49 Hz); 7.18-7.16, q, 4H, (Hd, Hc); 7.05-6.76, q, 74H, (H1, H2, H3, Hb); 6.66, d,
4H, Ha, (3JHa-Hb = 8.65 Hz). The second product was compound 16, the phenol substituted open
chain FDP cyclotetraphosphazene derivative, (0.15 g, 0.12 mmol, 30%, oily), Rf = 0.40. Anal.
10

Calc. for C67H52N4O9P4: C, 68.16; H, 4.47; N, 4.76; M, 1181. Found: C, 68.14; H, 4.44; N,
4.74 %, MS (MALDI-TOF) m/z: 1181 [M]+. 1H NMR, CDCl3, 298 K, δ ppm: 7.66, d, 2H, Hf,
(3JHf-He = 7.56 Hz); 7.25, td, 2H, He, (3JHe-Hf = 7.56, JHe-Hd = 7.44 Hz); 7.20, d, 2H, Hc, (3JHc-Hd
=
3
7.66 Hz); 7.13, td, 2H, Hd, (3JHd-He = 7.44, 3JHd-Hc = 7.66 Hz); 7.05-6.75, q, 39H, (H1, H2, H3, Ha’,
Hb’); 6.66, d, 2H, Hb, (3JHb-Ha = 8.80 Hz); 6.51, d, 2H, Ha, (3JHa-Hb = 8.80 Hz); 5.15, s, 1H, (OH).
2.2.5. Reaction of 1,1,3,3,5,5,7-hepta(2-naphthloxy)-7-chlorocyclotetraphosphazene (11) with
4,4′-(9-fluorenylidene)diphenol (FDP) (5) in a 1:2 ratio to form compound 17.
1,1,3,3,5,5,7-Hepta(2-naphthloxy)-7-chlorocyclotetraphosphazene (11), (1.5 g, 1.23
mmol) and 4,4′-(9-fluorenylidene)diphenol (FDP) (5) (0.21 g, 0.63 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,
1.23 mmol) in 40 mL of dry THF was quickly added to the 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–CH2Cl2 (1:1) as the eluent. One product was observed on
TLC. The reaction mixture was filtered to remove the formed sodium chloride and the solvent
was removed under reduced pressure. The resulting colorless solid was subjected to column
chromatography, using n-hexane–CH2Cl2 (1:1) as the eluent. The product was compound 17,
the 2-napthole substituted FDP-bridged cyclotetraphosphazene derivative, (1.01 g, 0.37
mmol, 60%, oily), Rf = 0.47. Anal. Calc. for C165H114N8O16P8: C, 73.10; H, 4.21; N, 4.13; M,
2711. Found: C, 73.08; H, 4.20; N, 4.11 %, MS (MALDI-TOF) m/z: 2734 [M+Na]+ (Fig.
3
1
S1b). H NMR, THF-d8, 298 K, δ ppm: 7.79, d, 2H, Hf, ( JHf-He = 7.55 Hz); 7.66-7.55, q, 14H,
H2; 7.40-7.08, q, 70H, (H1, H3, H4, H5, H6); 7.35-7.27, q, 6H, (Hc, Hd, He); 7.00-6.85, q, 14H,
H7; 6.67, d, 4H, Hb, (3JHb-Ha = 8.86 Hz); 6.60, d, 4H, Ha, (3JHa-Hb = 8.86 Hz).
11

2.2.6. Reaction of 1,1,3,3,5,5,7-hepta(1-oxypyrene)-7-chlorocyclotetraphosphazene (14) with
4,4′-(9-fluorenylidene)diphenol (FDP) (5) in a 1:2 ratio to form compounds 18-19.
1,1,3,3,5,5,7-Hepta(1-oxypyrene)-7-chlorocyclotetraphosphazene (14) (0.05 g, 0.03
mmol) and 4,4′-(9-fluorenylidene)diphenol (FDP) (5) (0.005 g, 0.015 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, 0.002 g,
0.04 mmol) in 40 mL of dry THF was quickly added to the stirred solution under an argon
atmosphere. The reaction mixture was refluxed for 5 days and the reaction followed on TLC
silica gel plates using n-hexane–CH2Cl2 (2:3) as the eluent. Two products were observed on
TLC. The reaction mixture was filtered to remove the formed sodium chloride and the solvent
was removed under reduced pressure. The resulting colorless solid was subjected to column
chromatography, using n-hexane–CH2Cl2 (2:3) as the eluent. The first product was compound
18, the 1-oxypyrene substituted FDP-bridged cyclotetraphosphazene derivative, (0.01 g, 2.66
x 10-3 mmol, 9%, oily), Rf = 0.76. Anal. Calc. for C249H142N8O16P8: C, 79.76; H, 3.82; N,
2.99; M, 3746. Found: C, 79.74; H, 3.80; N, 2.96; %, MS (MALDI-TOF) m/z: 3746 [M]+
1
(Fig. S1c). H NMR, CDCl3, 298 K, δ ppm: 8.10-6.40, m, 142H, (H1-H9, Ha-Hf). The second
product was compound 19, the 1-oxypyrene substituted open chain FDP
cyclotetraphosphazene derivative, (0.03 g, 1.45 x 10-2 mmol, 51%, oily), Rf = 0.58. Anal.
Calc. for C137H80N4O9P4: C, 80.27; H, 3.93; N, 2.73; M, 2048. Found: C, 80.25; H, 3.91; N,
1
2.71; %, MS (MALDI-TOF) m/z: 2049 [M]+. H NMR, CDCl3, 298 K, δ ppm: 8.15-6.45, m,
80H, (H1-H9, Ha-Hf).
2.2.7. Reaction of 1,1,3,3,5,5,7-heptaphenol-7-chlorocyclotetraphosphazene (8) with 4,4′-(9-
fluorenylidene)dianiline (FDA) (6) in a 1:2 ratio to form compounds 20 and 21.
12

1,1,3,3,5,5,7-Heptaphenoxy-7-chlorocyclotetraphosphazene (8), (0.7 g, 0.81 mmol) and
4,4′-(9-fluorenylidene)dianiline (FDA) (6) (0.14 g, 0.41 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, 0.81 mmol)
in 40 mL of dry THF was quickly added to the stirred solution under an argon atmosphere.
The reaction mixture was refluxed for 2 days and the reaction followed on TLC silica gel
plates using n-hexane-CH2Cl2 (1:3) as the eluent. Two products were observed on TLC. The
reaction mixture was filtered to remove the formed sodium chloride and the solvent was
removed under reduced pressure. The resulting colorless solid was subjected to column
chromatography, using n-hexane-CH2Cl2 (1:3) as the eluent. The first product was compound
20, the phenol substituted FDA-bridged cyclotetraphosphazene derivative, (0.42 g, 0.20
mmol, 51%, oily), Rf = 0.66. Anal. Calc. for C109H88N10O14P8: C, 65.14; H, 4.41; N, 6.97; M,
2010. Found: C, 65.13; H, 4.40; N, 6.93 %, MS (MALDI-TOF) m/z: 2011 [M+H]+. 1H NMR,
CDCl3, 298 K, δ ppm: 7.72, d, 2H, Hf, (3J = 7.51 Hz); 7.30, td, 2H, He, (3J
= 7.51 Hz,
He-Hf
Hf-He
3JHe-Hd = 7.35 Hz); 7.26, d, 2H, Hc, (3JHc-Hd = 7.45 Hz); 7.20, td, 2H, Hd, (3JHd-He = 7.35, JHd-Hc
=
3
7.45 Hz); 6.87-7.10, q, 56H, (H1, H2); 6.78, td, 14H, H3; 6.45, d, 4H, Hb, (3JHb-Ha = 8.35 Hz);
6.45, d, 4H, Ha, (3JHa-Hb = 8.35 Hz); 4.27, d, 2H, NH, (3JPH-NH = 9.72 Hz). The second product
was compound 21, the phenol substituted open chain FDA cyclotetraphosphazene derivative
(0.16 g, 0.13 mmol, 34%, oily), Rf = 0.25. Anal. Calc. for C67H54N6O7P4: C, 68.25; H, 4.62;
N, 7.13; M, 1179. Found: C, 68.23; H, 4.60; N, 7.11 %, MS (MALDI-TOF) m/z: 1179 [M]+.
1H NMR, THF-d8, 298 K, δ ppm: 7.67, d, 2H, Hf, (3J = 7.31 Hz); 7.28-7.24, q, 4H, (He, Hc);
Hf-He
3
7.17, td, 2H, Hd, (3JHd-Hc = 7.34 Hz, JHd-He = 7.42 Hz); 7.01-6.75, q, 35H, (H1, H2, H3); 6.87 d,
2H, Hb’ (3JHb’-Ha’ = 8.02 Hz); 6.72, d, 2H, Ha’ (3JHa’-Hb’ = 8.02 Hz); 6.59, d, 2H, Hb, (3JHb-Ha = 8.35
Hz); 6.43, d, 2H, Ha, (3JHa-Hb = 8.35 Hz); 4.27, d, H, NH, (3JPH-NH = 10.08 Hz); 3.72, s, 2H, NH.
13

2.2.8. Reaction of 1,1,3,3,5,5,7-hepta(2-naphthloxy)-7-chlorocyclotetraphosphazene (11) with
4,4′-(9-fluorenylidene)dianiline (FDA) (6) in a 1:2 ratio to form compounds 22 and 23.
1,1,3,3,5,5,7-Hepta(2-naphthloxy)-7-chlorocyclotetraphosphazene (11), (1.5 g, 1.23
mmol) and 4,4′-(9-fluorenylidene)dianiline (FDA) (6) (0.21 g, 0.63 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,
1.23 mmol) in 40 mL of dry THF was quickly added to the stirred solution under an argon
atmosphere. The reaction mixture was refluxed for 2 days and the reaction followed on TLC
silica gel plates using n-hexane-CH2Cl2 (1:1) as the eluent. Two products were observed on
TLC. The reaction mixture was filtered to remove the formed sodium chloride and the solvent
was removed under reduced pressure. The resulting colorless solid was subjected to column
chromatography, using n-hexane-CH2Cl2 (1:1) as the eluent. The first product was compound
22, the 2-napthole substituted FDA-bridged cyclotetraphosphazene derivative, (0.91 g, 0.33
mmol, 54%, oily), Rf = 0.63. Anal. Calc. for C165H116N10O14P8: C, 73.10; H, 4.32; N, 5.22; M,
2710. Found: C, 73.08; H, 4.30; N, 5.20 %, MS (MALDI-TOF) m/z: 2774 [M+2H+Na+K]+.
1H NMR, CDCl3, 298 K, δ ppm: 7.82, d, 2H, Hf, (3JHf-He = 7.58 Hz); 7.68-7.54, q, 14H, H2;
7.40-7.13, q, 76H, (H1, H3, H4, H5, H6, Hc, Hd, He); 7.13-6.86, q, 14H, H7; 6.59, d, 4H, Hb,
(3JHb-Ha = 8.54 Hz); 6.38, d, 4H, Ha, (3JHa-Hb = 8.54 Hz); 4.47, d, 2H, NH, (3JPH-NH = 9.71 Hz) (Fig.
S3). The second product was compound 23, the 2-napthole substituted open chain FDA
cyclotetraphosphazene derivative, (0.28 g, 0.18 mmol, 29%, oily), Rf = 0.30. Anal. Calc. for
C95H68N6O7P4: C, 74.60; H, 4.48; N, 5.49; M, 1529. Found: C, 74.58; H, 4.46; N, 5.47 %, MS
1
(MALDI-TOF) m/z: 1745 [M+K+Na+Matrix(dihydroxybenzoic acid)]+. H NMR, CDCl3,
298 K, δ ppm: 7.67, d, 2H, Hf, (3J = 7.56 Hz); 7.59-7.51, q, 7H, H2; 7.35-7.08, q, 41H, (H1,
Hf-He
H3, H4, H5, H6, Hc, Hd, He); 7.01-6.76, q, 7H, H7; 6.81 d, 2H, Hb’ (3JHb’-Ha’ = 8.54 Hz); 6.66, d,
14

2H, Ha’ (3JHa’-Hb’ = 8.54 Hz); 6.41, d, 2H, Hb, (3JHb-Ha = 8.51 Hz); 6.29, d, 2H, Ha, (3JHa-Hb = 8.51
Hz); 4.38, d, H, NH, (3JPH-NH = 9.79 Hz); 3.85, s, 2H, NH.
3. RESULTS AND DISCUSSION
In this study, new fully substituted fluorenylidene bridged (15, 17, 18, 20 and 22) and
open chain (16, 19, 21 and 23) cyclotetraphosphazene compounds have been synthesized and
their florescence and chemosensors properties are reported. For this purpose,
octachlorocyclotetraphosphazene (1) was allowed to react with phenol (2), 2-naphthol (3) and
1-hydroxypyrene (4) to give hexa- (7, 10 and 13), hepta- (8, 11 and 14) and octasubstituted
cyclotetraphosphazene compounds (9 and 12). The heptasubstituted cyclotetraphosphazene
compounds (8, 11, and 14) were then reacted with FDP (5) and FDA (6) to give the fully
substituted (15, 17, 18, 20 and 22) and open chain (16, 19, 21 and 23) fluorenylidene bridged
cyclotetraphosphazene derivatives (Scheme 1). All the products were purified by column
chromatography and/or preparative TLC techniques. The structures of the compounds (7-23)
were verified by elemental analyses, mass spectrometry, UV Vis, 1H and 31P NMR techniques
1
and fluorescence spectroscopy. The elemental analyses, mass spectrometric and H NMR
results for each new compound are provided as part of the analytical data in the experimental
section. The 31P NMR chemical shifts and phosphorus-phosphorus coupling constants of the
isolated compounds (7-23) are summarized in Table 1. Compounds 8, 11 and 14 were reacted
with FDP (5) and FDA (6) in the presence of NaH in THF, and bridged (15, 17, 18, 20 and
22) and open chain compounds (16, 19, 21 and 23) were isolated. The mass spectrometry and
elemental analyses of compounds 15, 17, 18, 20 and 22 indicated that one chlorine atom in
the heptasubstituted cyclotetraphosphazene compounds (8, 11 and 14) was replaced with FDP
(5)/FDA (6). The mass spectra of compounds 15, 17 and 18 gave molecular ion peaks at m/z
2011.3[M]+, 2734.7[M+Na]+ and 3746.2[M]+ respectively, confirming the exact composition,
15

and no chlorine patterns for compounds 15, 17 and 18 were observed (Figs. S1a, S1b and S1c,
respectively) in the supplementary information.
3.1. NMR characterization of compounds 7-23.
The proton decoupled 31P NMR spectra of compounds 7, 10 and 13 were observed as
A2B2 spin systems due to the different environments for the two different phosphorus nuclei
on the cyclotetraphosphazene ring. The >P(OCl) group in cyclotetraphosphazene ring of 7, 10
and 13 are stereogenic, and thus it is anticipated that the hexasubstituted
cyclotetraphosphazene compounds should be chiral and exist in cis and trans forms (as
isomer mixtures, see Fig.S2 as an example for compound 7). The proton decoupled 31P NMR
spectra of compounds 15-17 were observed as AB2B’ spin systems due to the different
environments for the three different phosphorus nuclei on the cyclotetraphosphazene ring.
The proton decoupled 31P NMR spectra of compounds 8, 11, 14, 18-23 were observed as
AB2C spin systems due to the different environments for the three different phosphorus nuclei
on the cyclotetraphosphazene ring. The proton decoupled 31P NMR spectra of compounds 9
and 12 were observed as a single resonance (A4 type) at δ -12.46 and -11.96 ppm, respectively
because of the chemical environment equivalence of all the phosphorus nuclei. The proton-
decoupled 31P NMR spectra of the new fully substituted fluorenylidene bridged (15, 17, 18,
20 and 22) and open chain (16, 19, 21 and 23) cyclotetraphosphazene compounds showed
second order effects (Figure 1), so it was necessary to carry out simulation analysis to get the
appropriate spectral parameters. For example, the simulated and normal 31P NMR spectra of
2-naphthol substituted FDA-bridged cyclotetraphosphazene (22) are shown Figures 1a and
1b. The 31P NMR spectra of 15, 17, 18 and 20 are shown as examples in Figures S3-S6,
respectively in the supplementary information.
16

1
The H NMR data also confirmed the structures of the newly synthesized compounds
1
7–23. The H NMR chemical shifts and coupling constants of all the protons are given in the
experimental section. The aromatic protons for all the compounds were observed between δ
1
8.00-6.50 ppm and some of them were distinguishable from each other. The H NMR
spectrum of compound 22 is shown as an example in Figure S7. In addition, the NH protons
for compound 22 were observed at δ 4.48 ppm, which have a two bond-coupling to
phosphorous with an average 2J of ca 9.71.Hz.
P-H
Figure 1. 2-Naphthol substituted FDA- bridged cyclotetraphosphazene (22) (a) The simulated
31P NMR spectrum of 22; (b) the proton decoupled 31P NMR spectrum of compound 22; (c)
the proton coupled 31P NMR spectrum of compound 22 in CDCl3 solution.
17

Table 1. 31P NMR parameters for compounds 7-23.
δ (31P NMR) [ppm]
Comp.
Spin
2J(PP) [Hz]
System
2JAB
2JAB’
2JBB’
2JBC
A
B
B’
C
*(7)(a)
(8)(a)
(9)(a)
-6.49, -6.58
-5.25
-14.80, -14.90
-13.78
-
-
A2B2
AB2C
A4
79.90, 80.10
-
-
-
-
-
75
-
-
-13.57
78
-12.46
-
-
-
-
-
-
*(10)(a) -6.04, -6.11
-14.48, -14.51
-13.21
-
-
A2B2
80.56, 81.30
-
-
-
(11) (b)
-4.74
-
-13.06
-
AB2C
A4
70
-
-
55
-
(12)(a)
-11.96
-
-
-
-
-
*(13)(a) -5.33, -5.42
-13.31, -13.44
-13.20
-
-
A2B2
79.85, 79.54
-
-
-
(14)(a)
(15)(a)
(16)(a)
(17)(b)
(18)(a)
(19)(a)
(20)(a)
(21)(b)
(22)(a)
(23)(a)
-4.27
-12.50
-12.41
-12.30
-14.95
-14.97
-10.03
-10.11
-9.54
-
-12.85
-
AB2C
AB2B’
AB2B’
AB2B’
AB2C
AB2C
AB2C
AB2C
AB2C
AB2C
70
75
75
67
74
75
80
81
71
71
-
-
58
-
-12.46
-12.52
-12.40
-11.91
-
15
15
-
78
77
70
-
-12.39
-
-
-12.13
-
-
-13.34
-13.14
-13.14
-12.72
-12.78
-11.72
-11.70
-
67
68
78
78
69
70
-13.41
-
-
-
-12.33
-12.43
-12.18
-9.50
-12.21
(a)202.38 MHz 31P NMR chemical shifts (ppm) in CDCl3.
(b)202.38 MHz 31P NMR chemical shifts (ppm) in THF-d8.
(*)cis and trans isomer mixture
3.2. Ground state electronic absorption and fluorescence properties
The electronic absorption and fluorescence behavior of the newly synthesized
fluorenylidene bridged cyclotetraphosphazene derivatives were studied in THF. Absorption
bands were observed at approximately 240, 270, 300 and 310 nm for compounds 15-17 and
20-23, and 240, 265, 275, 330 and 345 nm for compounds 18 and 19 in the UV region of the
electronic spectra (see Figure 2a as an example for compound 18). Compounds 15-17 and 20-
23 were excited at 270 nm and compounds 18 and 19 were excited at 345 nm for the
fluorescence emission studies. The fluorescence wavelengths were observed to be red shifted
from those of phenol, naphthol and pyrene, respectively. The emission wavelength ranking
18

increases for these aryloxy substituted (FDP) bridged cyclotetraphosphazene derivatives as
phenol substituted (15) < 2-naphthol substituted (17) < 1-hydroxypyrene substituted FDP
bridged cyclotetraphosphazene (18), reflecting the increasing number of conjugated π-
electrons in the aromatic ring systems of the substituted groups (Figure 2b). In addition to
this, Figure S8 shows the fluorescence emission spectra of the FDP/FDA
cyclotetraphosphazene compounds 15-23. While the phenol (15, 16, 20 and 21) and 1-
hydroxypyrene (18 and 19) substituted FDP/FDA bridged and open chain
cyclotetraphosphazenes showed strong emissions, the 2-naphthol substituted FDP/FDA
bridged and open chain cyclotetraphosphazene derivatives (17, 22 and 23) showed low
fluorescence behaviour in THF solution. Furthermore, while these measurements showed that
the substituted bridged cyclotetraphosphazene compounds exhibited highly fluorescence
behaviour in THF solutions, the substituted open chain cyclotetraphosphazene derivatives
showed very weak fluorescence in this solvent. For this reason, only the phenol and 1-
hydroxypyrene substituted FDP/FDA bridged open chain compounds were tested for metal
ions sensing.
19

700
600
500
400
300
200
100
0
Compound 15
Compound 17
Compound 18
(b)
280
330
380
430
480
530
580
630
680
Wavalength (nm)
(a)
ꢆI1ꢄꢄ1QJ
ꢇGꢄQ`]ꢃ1QJ
ꢀ ꢁ
ꢂꢁꢁ
ꢂ ꢁ
ꢃꢁꢁ
ꢃ ꢁ
ꢁꢁ
ꢁ
ꢄꢁꢁ
ꢄ ꢁ
ꢅꢁꢁ
ꢅ:0:CVJ$ꢃ.ꢁ^JI_
Figure 2. (a) Electronic absorption and fluorescence emission spectra of compound 18 in
THF (excitation wavelength = 345 nm). (b) fluorescence emission spectra of compounds 15,
17 and 18 in THF.
3.3. Chemosensor properties to metal ions
The metal binding properties of fluorenylidene molecules may allow the use of these
molecules as metal sensors. The effects of a variety of metal ions (Li+, Na+, K+, Cs+, Mg2+,
Ca2+, Ba2+, Mn2+, Fe3+ Co2+, Pb2+, Ni2+, Cu2+, Zn2+, Ag+, Cd2+ and Al3+) on the fluorescence
properties of the newly synthesized compounds have been investigated using fluorescence
spectroscopy. All fluorescence emission spectral studies were performed in THF solutions of
the cyclotetraphosphazene compounds, while water solutions of the corresponding metal
chlorides (the nitrate derivative for the Ag ion) were used as the source of metal ions at room
20

temperature. The fluorescence spectra of the novel cyclotetraphosphazene compounds
exhibited little enhancement by the addition of the 5 µL of 5 x 10-3 M metal solutions, except
for copper (Cu2+) and iron (Fe3+). A significant decrease in the fluorescence intensities were
observed by the addition of the copper (Cu2+) and iron (Fe3+) cations, while no or minimal
change was observed with the other metal ions (see Figure 3 as an example for compound 18,
Figs. S9, S12, S15 and S18 in the Supporting Information for the other compounds).
3+
(B)
2+
(A)
Fe
Cu
500
400
300
200
100
0
Comp. 18 + M
Comp. 18
(B)
0
-50
-100
-150
-200
-250
Figure 3. (A) The fluorescence intensities of compound 18 with and without metal ions.
Addition of Fe+3 or Cu+2 ions to the solution prevent fluorescent emission, hence provide a
selective detection (5 µL of 5 x 10-3 M). (B) Fluorescence intensity changes.
21

The titration of the probe compounds(15, 16, 18, 19 and 20 with Cu2+ or Fe3+ cations
showed a decrease in the fluorescence intensities with increasing concentrations of these
cations (see Figure 4A for the Cu2+ titration and Figure 5A for the Fe3+ titration, Figs. S10A,
S11A, S13A, S14A, S16A, S17A, S19A and S20A in the Supporting Information for the
other compounds). The graphs from a Benesi-Hildebrand analysis showed non-linear
behavior for all the studied cyclotetraphosphazene chemosensor compound interactions with
Cu2+ ions, indicating that the stoichiometry of the complexes between cyclotetraphosphazene
chemosensors and Cu2+ or Fe3+ cations are different from 1:1 (see Figure 4B for the Cu2+
titration and Figure 5B for the Fe3+ titration as an example for compound 18, Figs. S10B,
S11B, S13B, S14B, S16B, S17B, S19B and S20B in the Supporting Information for the other
compounds), as mentioned by Garcia-Beltran et al. [54]. The continuous variation method was
also used for the determination of the stoichiometry between the aryloxy substituted
fluorenylidene bridged cyclotetraphosphazene chemosensors and detected metal cations. The
resulting Job plot, showing a maximum mole fraction for the Cu2+ or Fe3+ cations of 0.33 (see
Figure 4C for the Cu2+ titration and Figure 5C for the Fe3+ titration as an example for
compound 18, Figs. S10C, S11C, S13C, S14C, S16C, S17C, S19C and S20C in the
Supporting Information for the other compounds), indicated that the cyclotetaphosphazene
molecules and Cu2+ or Fe3+ ions prefer a 2:1 stoichiometry for the formation of complexes
between the chemosensor compounds 15, 16, 18, 19 and 20 and the Fe3+ or Cu2+ cations in
THF solutions. The proposed complex structure between cyclotetraphosphazene compound
18 and Fe3+/Cu2+ cations is given in Figs. 6(a) and 6(b).
22

ꢄꢁꢁ
ꢁꢁ
800
600
400
200
0
ꢈ
0 M
ꢇ
Cu2+
ꢃꢁꢁ
ꢂꢁꢁ
ꢀꢁꢁ
ꢆꢁꢁ
ꢁ
0
20
40
1/[M]
60
80
100
10x(5x10-2 M)
150
ꢉ
100
50
^ꢁ8ꢂ_
0
-50
-100
-150
0
0.2
Mole Fraction of Fe (X)
0.4
0.6
0.8
1
ꢂ ꢁ
ꢃ ꢁ
ꢁ
ꢄ ꢁ
ꢅ:0VCVJ$ꢃ.ꢁ^JI_
Figure 4. (A) Fluorescence response of chemosensor 18 to various equivalents of Cu2+. (B)
The Benesi-Hildebrand graph and (C) Job's plot of 18-Cu2+ complexes in THF solution. The
total concentration of 18 and Cu2+ was 5 x 10-1 M. The excitation wavelength was 345 nm.
The monitored wavelength was 470 nm.
ꢄꢁꢁ
800
ꢈ
ꢇ
0 M
Fe3+
600
400
200
0
ꢁꢁ
ꢃꢁꢁ
ꢂꢁꢁ
ꢀꢁꢁ
ꢆꢁꢁ
ꢁ
0
20
40
1/[M]
60
80
100
10x10-2 M
50
ꢉ
0
-50
^ꢁ8ꢂ_
-100
-150
-200
-250
0
0.2
Mole Fraction of Fe (X)
0.4
0.6
0.8
1
ꢂ ꢁ
ꢃ ꢁ
ꢁ
ꢄ ꢁ
ꢅ:0VCVJ$ꢃ.ꢁ^JI_
Figure 5. (A) Fluorescence response of chemosensor 18 to various equivalents of Fe+3. (B)
The Benesi-Hildebrand graph and (C) Job's plot of 18-Fe+3 complexes in THF solution. The
23

total concentration of 18 and Fe+3 was 1 x 10-1 M. The excitation wavelength was 345 nm. The
monitored wavelength was 470 nm.
Figure 6. The proposed structures between (a) compound 18 and Cu2+ and (b) Fe3+ ions as a
2:1 complex in aqueous solution (a similar structure is proposed for the other compounds and
Cu2+/Fe3+ ions).
4. CONCLUSIONS
In summary, phenol, 2-naphthol and 1-hydroxypyrene fully substituted fluorenylidene
(FDA/FDP) bridged and open chain cyclotretraphosphazene derivatives were synthesized and
characterized. All the synthesized compounds (7-23) were characterized by elemental
1
31
analysis, mass spectrometry, UV Vis, H and P NMR and fluorescence spectroscopies. The
fluorescence behavior of compounds 15-23 was investigated by florescence spectroscopy in
THF solution. In addition, the effects of metal ions on the fluorescence behavior of the
compounds were studied in order to determine the potential for using of these compounds as
chemosensors for metal ions. A significant decrease in the fluorescence signals were observed
by the addition of Cu2+ and Fe3+ cations, from the seventeen different metal ions tested. The
newly synthesized FDP/FDA bridged and open chain phenol and 1-hydroxypyrene substituted
24

cyclotetraphosphazene derivatives (15, 16, 18, 19, 20 and 21) preferred the formation of 2:1
(ligand: metal) complexes with both Fe3+ and Cu2+ ions. The FDP/FDA bridged and open
chain substituted cyclotetraphosphazene derivatives showed high selectivity towards Cu2+ and
Fe3+ ions and these newly synthesized compounds showed potential for use as chemosensors
for these metal ions in THF solution. The increase in the number of aromatic groups caused
the increasing florescent nature. The fluorescence properties of fluorenylidene bridged
cyclotriphosphazenes bearing phenol are quite low [55], but in this study the phenol
substituted FDP and the FDA bridged cyclotriphosphazenes show quite good fluorescence
behaviour and Fe and Cu sensor abilities. In addition to this, in the current study, the pyrene
substituted fluorenylidene bridged and open chain cyclotetraphosphazene compounds (18 and
19) showed high fluorescence results, although they had lower concentrations. Thus, the FDP
and FDA bridged and open chained cyclotetraphosphazene compounds show superior
florescence behaviour relative to the corresponding cyclotriphosphazenes.
ASSOCIATED CONTENT
1
Supporting Information Available: The H NMR spectra of compound 22, 31P NMR
spectra/J NMR spectra of compounds 7, 15, 17, 18 and 20, and the MS spectra for compounds
15, 17 and 18, the graphs of titrations of FDP/FDA-bridged compounds with Cu2+ and Fe3+
ions and the Benesi-Hildebrand graphs and Job's plots are given as Supporting Information.
This material is available free of charge via the Internet at http://pubs.rsc.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: yenilmez@gtu.edu.tr
ACKNOWLEDGMENTS
The authors thank to the Scientific and Technical Research Council of Turkey for financial
support TUBITAK (Grant 111T085).
25

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27

Structural and chemosensor properties of FDA and FDP
derivatives of fluorenylidene bridged
cyclotetraphosphazenes
Elif Şenkuytu and Gönül Yenilmez Çiftçi*
The first series of 4,4’-(9-fluorenylidene)diphenol (FDP) (5) and 4,4’-(9-
fluorenylidene)dianiline (FDA) (6) bridged and open chained cyclotetraphosphazene
derivatives (15-23) were synthesized. Their florescence and chemosensors properties are
reported. Nucleophilic substitution reactions of octachlorocylotetraphosphazene (1) with
mono-functional reagents [phenol (2), 2-naphthol (3) and 1-hydroxypyrene (4)] were carried
out and the heptasubstituted derivatives (8, 11 and 14) were obtained. The reactions of 8, 11
and 14 with 4,4′-(9-fluorenylidene)diphenol (FDP) (5) and 4,4′-(9-fluorenylidene)dianiline
(FDA) (6) respectively gave bridged and open chained compounds. The structures of
1
compounds (7-23) were verified by elemental analyses, mass spectrometry, UV Vis, H and
31P NMR techniques and fluorescence spectroscopy. The metal sensing properties of the
novel bridged and open chain cyclotetraphosphazene derivatives were also examined by
fluorescence spectroscopy. These complexes showed high selectivity for Cu2+ and Fe3+ ions in
solution.
28

Structural and chemosensor properties of FDA and
FDP derivatives of a Fluorenylidene bridged
cyclotetraphosphazenes
500
400
300
200
100
0
Comp. 18 + M
Comp. 18