Synthesis, thermal and photophysical properties of naphthoxycyclotriphosphazenyl-substituted dendrimeric cyclic phosphazenes

Article abstract of DOI:10.1016/j.poly.2012.01.013

The synthesis and properties of naphthoxycyclotriphosphazenyl-substituted dendrimeric cyclic phosphazenes are reported. Compound 3, [N₃P ₃(ONp)₅OPhOH], is prepared by the sequential reactions of hexachlorocyclotriphosphaze

Full text of DOI:10.1016/j.poly.2012.01.013

Polyhedron 35 (2012) 101–107
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, thermal and photophysical properties of
naphthoxycyclotriphosphazenyl-substituted dendrimeric cyclic phosphazenes
⇑
Bünyemin Çoßsut, Serkan Yeßsilot
Department of Chemistry, Gebze Institute of Technology, Gebze, Kocaeli, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and properties of naphthoxycyclotriphosphazenyl-substituted dendrimeric cyclic phosp-
hazenes are reported. Compound 3, [N3P3(ONp)5OPhOH], is prepared by the sequential reactions of
hexachlorocyclotriphosphazene with 2-naphthol and 4-benzyloxyphenol derivatives, as side groups.
The dendrimeric compounds 5, 6 and 7 have been obtained by the reactions of compound 3 with hexa-
chlorocyclotriphosphazene, N3P3Cl6, octachlorocyclotetraphosphazene, N4P4Cl8, and bisphenol bridged
cyclophosphazene, N6P6Cl10 (4), respectively. The newly synthesized compounds have been fully charac-
terized by elemental analysis, ESI, MALDI-TOF mass spectrometry, FT-IR, 1H, 13C and 31P NMR spectros-
copy. The thermal stability and fluorescence spectral properties of all these novel compounds are
investigated.
Received 17 October 2011
Accepted 5 January 2012
Available online 20 January 2012
Keywords:
Dendrimer
Cyclotriphosphazenes
31P NMR
Thermal stability
Fluorescence
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
thus producing a rigid spherical core from which to grow the
dendrons of interest. Hence there has recently been considerable
Cyclic and polymeric phosphazenes are an important class of
inorganic heterocyclic ring systems [1,2], not only because they
have wide applications due to their thermal stability, catalytic
properties, electrical conductivity, liquid crystal and biomedical
activity [3–5], but also because the reactions of various nucleo-
philes with the halogen atoms make it possible to modify the
properties and applications of the phosphazenes to a great extent.
They are usually prepared by nucleophilic substitution reactions of
alkoxides, aryloxides or amines on halocyclophosphazenes or high
polymers [6–8], and their physical and chemical properties can be
tailored via the appropriate substituted groups on the phosphorus
atoms [9]. Luminescent dendrimeric compounds are attracting
much current research interest because of their many applications,
including emitting materials for organic light emitting diodes, light
harvesting materials for photocatalysis and fluorescent sensors for
organic or inorganic analyzers [10].
interest in fluorescent compounds based on cyclic phosphazene
cores [11,12] or cyclo-linear polymers with cyclotriphosphazene
units [13] for the development of electroluminescent devices. In
phosphazene chemistry, there are many examples of organic or
inorganic side groups bearing cyclophosphazenes or polyphosp-
hazenes [3–5]. However, there are limited examples of cyclophos-
phazenes and polyphosphazenes [14,15] or organic polymers
[16,17] that bear an organic group substituted cyclophosphazene
ring as a side group. We have recently reported [18,19] that some
dendrimeric cyclic phosphazenes were prepared with phenoxy
substituted cyclic phosphazene as side groups, which possess a
single reactive group at the core to avoid side reactions. It was
found that the dendrimeric arrangement of the side groups was
more effective than the number of attached side groups for the
thermal stability and fluorescence spectral properties, as was
reported in the previous study [18]. We thought that it would
be interesting to carry out a similar synthetic strategy for the
preparation of dendrimeric cyclic phosphazenes bearing naphth-
oxycyclotriphosphazenyl groups. We have chosen the naphthoxy
substituent for the synthesis of dendrimeric structures
because molecules functionalized with the naphthalene moiety,
in addition to normal fluorescence, exhibits excimer fluorescence
as well.
Cyclophosphazenes have many advantages as useful lumines-
cent materials for electroluminescent devices. For example, substi-
tuted cyclic phosphazenes are very stable and do not breakdown
under very aggressive chemical conditions. Also the functional
groups are projected above and below the cyclophosphazene plane
Here we describe the synthesis and characterization of naphth-
oxycyclotriphosphazenyl-substituted dendrimeric cyclic phosphaz-
enes (Fig. 1) and an investigation of their thermal and photophysical
properties.
⇑
Corresponding author. Address: Department of Chemistry, Gebze Institute of
Technology, P.O. Box 141, Gebze 41400, Kocaeli, Turkey. Tel.: +90 262 6053137; fax:
+90 262 6053101.
E-mail address: yesil@gyte.edu.tr (S. Yesßilot).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2012.01.013

102
B. Çoßsut, S. Yeßsilot / Polyhedron 35 (2012) 101–107
O
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7
Fig. 1. Structures of the dendrimeric cyclic phosphazenes (5–7).
F ꢀ AStd ꢀ n2
2. Experimental
UF
¼
UFðStdÞ
ð1Þ
FStd ꢀ A ꢀ n2Std
2.1. Materials
where F and FStd are the areas under the fluorescence emission
curves of the samples (5, 6 and 7) and the standard, respectively.
A and AStd are the respective absorbance of the samples and
standard at the excitation wavelengths, respectively. The refractive
indices (n) of the solvents were employed in calculating fluores-
cence quantum yields in different solvents. 2-Aminopyridine (in
0.1 M H2SO4) (UF = 0.60) [21] was employed as the standard. Both
the samples and standard were excited at the same wavelength.
Infrared spectra were recorded on a Bio-Rad FTS 175C FT-IR spec-
trophotometer using KBr dyes. Mass spectra were acquired in the
linear mode with an average of 50 shots on a Bruker Daltonics Mic-
roflex mass spectrometer (Bremen, Germany) equipped with a
nitrogen UV-Laser operating at 337 nm. The mass analyzer was a
Bruker Daltonics (Bremen, Germany) MicrOTOF mass spectrometer
equipped with an orthogonal electrospray ionization (ESI) source.
The instrument was operated in the positive ion mode using a m/
z range of 50–3000. 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 °C. The transfer time of the source was 88 ms and
the hexapole radiofrequency (RF) was 800.0 Vpp. Analytical thin
Hexachlorocyclotriphosphazene(trimer) and octachlorocyclo-
tetraphosphazene (Otsuka Chemical Co. Ltd.) were purified by
fractional crystallization from n-hexane. The deuterated solvents
(CDCl3 and toluene) for NMR spectroscopy and the following
chemicals were obtained from Merck: cyclohexene, ethanol, 2-
naphthol, 4-benzyloxyphenoxy, Pd(OH)2, Cs2CO3, NaH, acetone,
triethylamine, silica gel 60, tetrahydrofuran. 1,8,9-Anthracenetriol
for the MALDI matrix was obtained from Fluka. All other reagents
and solvents were reagent grade quality and obtained from com-
mercial suppliers.
2.2. Equipment
Elemental analyses were carried out using a Thermo Finnigan
Flash 1112 Instrument. UV–Vis spectra were recorded with a Shi-
madzu 2001 UV Pc spectrophotometer. Fluorescence excitation
and emission spectra were recorded on a Varian Eclipse spectroflu-
orometer using 1 cm path length cuvettes at room temperature.
Fluorescence quantum yields (UF) were determined by the com-
parative method (Eq. (1)) [20].

B. Çoßsut, S. Yeßsilot / Polyhedron 35 (2012) 101–107
103
layer chromatography (TLC) was performed on Silica gel plates
2.3.3. Synthesis of compound 3
(Merck, Kieselgel 60, 0.25 mm thickness) with F254 indicator. Col-
umn chromatography was performed on silica gel (Merck, Kieselgel
60, 230–400 mesh; for 3 g; crude mixture, 100 g; silica gel was used
in a column 3 cm in diameter and 60 cm in length) and preparative
thin layer chromatography was performed on silica gel 60 P F254. 1H,
13C and 31P NMR spectra were recorded in CDCl3 and toluene-d7
solutions on a Varian 500 MHz spectrometer.
1,1,3,3,5-Pentanaphthoxy-5-[(4-benzyoxy)phenoxy]-cyclotri-
phosphazatriene (2) (1 g, 0.95 mmol) was dissolved in 10 ml of dry
THF under an argon atmosphere and 6 ml of cyclohexene, palla-
dium hydroxide (20 wt.% on carbon, 0.4 g) and 6 ml of ethanol
were added to this solution. The mixture was refluxed for 24 h
under an argon atmosphere and filtered. All of the solvents were
removed under reduced pressure. 1,1,3,3,5-Pentanaphthoxy-5-
[(4-hydroxy)phenoxy]-cyclotriphosphazatriene (3) was obtained
by crystallization in dichloromethane:n-hexane (3:1). Yield:
0.59 g (62%), m.p. 129 °C. Anal. Calc. for C56H40N3O7P3 (959): C,
70.07; H, 4.20; N, 4.38. Found: C, 70.10; H, 4.24; N, 4.36%. FT-IR
2.3. Synthesis
m
max/cmꢁ1 (KBr pellet); 3610 (OH), 3045 (ArCH), 1590 (ArC),
The bisphenol bridged cyclophosphazene compound N6P6Cl10
(bisphenol) (4) was prepared and purified according to the litera-
ture procedure [22].
1275–1184 (P@N), 960 (P–O); 1H NMR (CDCl3) d: 6.15–7.80 (m,
40H, ArCH), 5.20 (s, 1H, OH); {1H}13C NMR (CDCl3) d: 152.76
(ArC–OH), 148.50 (ArC), 144.22 (ArC), 134.07 (ArC), 129.57 (ArCH),
126.66 (ArCH), 122.11 (ArCH), 121.07 (ArCH), 117.96 (ArCH),
157.94 (ArCH). MS (ESI) m/z (%): 960 (100) [M+H]+.
2.3.1. Synthesis of compound 1
A solution of sodium naphthoxide was prepared by the drop-
wise addition of 2.26 g of 2-naphthol (15.78 mmol) in dry THF
(20 ml) to a solution of 0.80 g of 60% sodium hydride (20 mmol)
dispersion in dry THF (10 ml) at 0 °C. Hexachlorocyclotriphospha-
zene (1.00 g, 2.87 mmol) in 20 ml dry THF was added dropwise
over 0.5 h to a stirred reaction mixture of sodium naphthoxide.
The reaction mixture was stirred for 1 day under an atmosphere
of argon and the reaction was followed by TLC. Sodium hydrochlo-
ride was removed by filtration, the solvent removed under reduced
pressure, and the resulting product was subjected to column
chromatography using dichloromethane:n-hexane (1:1) as the
eluant. 1,1,3,3,5-Pentanaphthoxy-5-chlorocyclotriphosphazatriene
(1) was isolated and crystallization in dichloromethane:n-hexane
(3:1). Yield: 1.6 g (60%), m.p. 137 °C. Anal. Calc. for C50H35ClN3O5P3
(885): C, 67.70; H, 3.98; N, 4.74. Found: C, 67.60; H, 3.95; N, 4.78%.
2.3.4. Synthesis of compound 5
Trimer, N3P3Cl6, (0.009 g, 0.025 mmol) and compound 3 (0.17 g,
0.181 mmol) were dissolved in dry THF (10 ml) under an argon
atmosphere. After stirring for 15 min at 40 °C, dry and finely pow-
dered cesium carbonate (0.08 g, 0.26 mmol) was added portion-
wise over 15 min with efficient stirring. The reaction mixture
was stirred under an argon atmosphere at 80 °C for 24 h. and then
filtered. The volatile materials were evaporated under vacuum and
the product was purified by preparative TLC on silica gel using hex-
ane:THF (1:1) as the eluent. Compound 5 is a highly viscous oil.
Yield: 0.056 g (37%). Anal. Calc. for C336H234N21O42P21 (5888): C,
68.5; H, 4.01; N, 5.00. Found: C, 68.75; H, 4.08; N, 5.06%. 1H NMR
(toluene-d8) d: 11.68–12.61 (m, 234H, ArCH); {1H}13C NMR (tolu-
ene-d8) d: 142.35 (ArC), 133.74 (ArCH), 132.83 (ArC), 130.19
(ArCH), 129.80 (ArCH), MS (MALDI-TOF) m/z (%): 5889 (100)
[M+H]+.
FT-IR m
max/cmꢁ1 (KBr pellet): 3036 (ArCH), 2868 (CH), 1625–1600
(ArC@C), 1270–1210 (P@N), 1105 (C–O), 965 (P–O); 1H NMR
(CDCl3) d: 6.90–7.85 (m, 35H, ArH); {1H}13C NMR (CDCl3) d:
148.31 (ArC), 134.09 (ArCH), 131.49 (ArC), 129.96 (ArC), 128.81
(ArCH), 127.93 (ArCH), 126.89 (ArCH), 121.27 (ArCH), 118.48
(ArCH); MS (ESI) m/z (%): 886 (100) [M+H]+.
2.3.5. Synthesis of compound 6
Octachlorocyclotetraphosphazene(tetramer), N4P4Cl8, (0.009 g,
0.019 mmol) and compound 3 (0.12 g, 0.13 mmol) were dissolved
in dry THF (10 ml) under an argon atmosphere. After stirring for
15 min at 40 °C, dry and finely powdered cesium carbonate
(0.06 g, 0.19 mmol) was added portionwise over 30 min with effi-
cient stirring. The reaction mixture was stirred under an argon
atmosphere at 80 °C for 48 h. And then filtered. The volatile mate-
rials were evaporated under vacuum and the product was purified
by preparative TLC on silica gel using hexane:THF (1:1) as the
eluent. Compound 6 is highly viscous oil. Yield: 0.064 g (42%). Anal.
Calc. for C448H312N28O56P28 (7850): C, 68.54; H, 4.01; N, 5.00.
Found: C, 68.55; H, 4.05; N, 5.01%. 1H NMR (toluene-d8) d:
2.3.2. Synthesis of compound 2
4-(Benzyloxy) phenol (0.5 g, 2.48 mmol), dry and finely pow-
dered cesium carbonate (1.47 g, 4.51 mmol) were dissolved in
dry THF (10 ml) under an argon atmosphere. The solution was
transferred to a 50 ml dropping funnel and slowly dropped onto
a solution of 1,1,3,3,5-pentanaphthoxy-5-chlorocyclotriphosphaz-
atriene (2 g, 2.26 mmol) (1) in 10 ml of dry THF under an argon
atmosphere in a 50 ml three-necked round bottomed flask. The
reaction mixture was refluxed under argon for 24 h, followed by
TLC which indicated that no starting material remained. The pre-
cipitated salt (CsCl) was filtered off and the solvent was removed
under reduced pressure. The crude product was purified by column
chromatography [silica gel 60 (70–230 mesh) as adsorbent and
dichloromethane:n-hexane 1:1 as the eluent]. 1,1,3,3,5-Penta-
naphthoxy-5-[(4-benzyoxy)phenoxy]-cyclotriphosphazatriene (2)
was obtained as a viscous oil. Yield: 1.52 g (61%). Anal. Calc. for
11.76–12.60 (m, 312H, ArCH); {1H}13
C NMR (toluene-d8) d:
142.35 (ArC), 133.93 (ArCH), 132.83 (ArC), 130.19 (ArCH), 129.99
(ArCH); MS (MALDI-TOF) m/z (%): 7851 (100) [M+H]+.
2.3.6. Synthesis of compound 7
N6P6Cl10 (bisphenol) (4) (0.03 g, 0.035 mmol) and compound 3
(0.34 g, 0.35 mmol) were dissolved in dry THF (10 ml) under an ar-
gon atmosphere. After stirring for 15 min at 40 °C, dry and finely
powdered cesium carbonate (0.13 g, 0.38 mmol) was added por-
tionwise over 15 min with efficient stirring. The reaction mixture
was stirred under an argon atmosphere at 80 °C for 24 h. and then
filtered. The volatile materials were evaporated under vacuum and
the product was purified by preparative TLC on silica gel using hex-
ane:THF (1:1) as the eluent. Compound 7 is a highly viscous oil.
Yield: 0.056 g (37%). Anal. Calc. for C575H404N36O72P36 (10083): C,
68.48; H, 4.04; N, 5.00. Found: C, 68.45; H, 4.08; N, 5.02%. 1H
NMR (CDCl3) d: 11.68–12.61 (m, 398H, ArCH), 6.41 (br, 6H, CH3);
C
63H46N3O7P3 (1065): C, 72.11; H, 4.73; N, 3.94. Found: C, 72.05;
H, 4.78; N, 3.90%. FT-IR
m
max/cmꢁ1 (KBr pellet): 3035 (ArCH),
2866 (CH), 1625–1605 (ArC@C), 1260–1211 (P@N), 1105 (C–O),
955 (P–O); 1H NMR (CDCl3) d: 6.21–7.50 (m, 50H, ArH), 5.12 (br,
s, 2H, CH2); {1H}13C NMR (CDCl3) d: 155.97 (ArC), 153.10 (ArC),
150.30 (ArC), 148.42 (ArCH), 144.46 (ArC), 137.14 (ArC), 131.26
(ArC), 129.71 (ArCH), 128.87 (ArCH), 127.94 (ArCH), 126.61 (ArCH),
125.56 (ArCH), 122.01(ArCH), 121.32 (ArCH), 70.39 (CH2). MS (ESI)
m/z (%): 1050 (100) [M+H]+.

104
B. Çoßsut, S. Yeßsilot / Polyhedron 35 (2012) 101–107
{1H}13C NMR (CDCl3) d: 138.51 (ArC), 129.24 (ArCH), 125.75 (ArC),
123.01 (ArCH), 73.2 (ArCH), 68.2 (CH3); {1H}31P NMR (toluene-d8)
d: 10.41 [m, 4P, >P(OPh)2, B2], 10.77 [m, 2P, >P(OPh)(OPhO), A],
In particular, the 31P NMR spectra were carefully analyzed and
the 31P NMR chemical shifts and phosphorus–phosphorus coupling
constants (2JPNP) of compounds 1–3, 5–7 are summarized in Table
1. The proton-decoupled 31P NMR spectrum of compound 1 is ob-
served as the expected A2X spin system. The signal assignment is
straightforward, with the triplet (1P) at ca. 23.86 ppm belonging
to >P(naphthoxy)(Cl) and the doublet (2P) at ca. 8.76 ppm to
>P(naphthoxy)2. Since compounds 2 and 3 show non-first order
31P NMR spectra, it is necessary to carry out simulation analysis
to get the appropriate spectral parameters. Following this analysis,
2
10.1 (s, 1P, >PR2, C3); JP,P = 90.88 Hz; MS (MALDI-TOF) m/z (%):
10084 (100) [M+H]+.
3. Results and discussion
The synthetic routes to compounds 1–7 are shown in Scheme 1.
Compound 1 was synthesized by the reaction of 2-naphthol with
hexachlorocyclotriphosphazene. Compound 1 was reacted with
4-benzyloxyphenol in the presence of Cs2CO3 in THF to obtain
compound 2. The 4-benzyloxyphenoxy unit of compound 2 was
converted to a 4-hydroxyphenoxy group with cyclohexene in a
mixture of THF/ethanol, in the presence of Pd(OH)2 as a catalyst
to give compound 3. Compounds 5, 6 and 7 were obtained from
nucleophilic displacement reactions of 3 with N3P3Cl6, N4P4Cl8
and N6P6Cl10 (bisphenol) (4) with cesium carbonate as the base un-
der an argon atmosphere, respectively. The products were purified
by preparative TLC on silica gel using hexane:THF (1:1) as the
eluent. The newly synthesized compounds were characterized by
IR, 1H, 13C and 31P NMR, mass spectrometry and elemental analysis.
All the results were consistent with the predicted structures, as
shown in Section 2. The IR spectra of all these compounds feature
peaks at around 1200 cmꢁ1 (br) (P@N) and 960 cmꢁ1 (P–O) for a
phosphazene ring, as expected [23]. The mass spectra of com-
pounds 5, 6 and 7 were obtained by MALDI-TOF spectrometry.
Many different MALDI matrices were investigated to find an in-
tense molecular ion peak and low fragmentation. 1,8,9-Anthrace-
netriol MALDI matrix yielded the best MALDI-MS spectra. The MS
spectra of 5, 6 and 7 provided definitive characterization. The peak
group representing the protonated molecular ions of 5, 6 and 7 was
observed at 5889, 7851 and 10084 Da mass, respectively.
the 31P NMR spectra were analyzed as AB2 spin systems and the 31
P
2
NMR chemical shifts and J(PP) of compounds 2 and 3 are summa-
rized in Table 1. As an example, the simulated and observed the
proton-decoupled 31P NMR spectra of compound 3 are depicted
as the AB2 pattern in Fig. 2. Although similar AB2 patterns in the
31P NMR spectra for the side groups of compounds 5, 6 and 7 are
expected, they are observed as broad signals rather than AB2 pat-
terns. The integration of the broad signals part to the remaining
singlet of the proton-decoupled 31P NMR spectra of compounds
5, 6 and 7 gave approximately a 6:1, 6:1 and 5:1 phosphorus ratio,
respectively, that confirmed the suggested structures.
Phosphazenes are attractive compounds due to their higher
thermal stability and flame retardancy properties when compared
with their organic homologs. Owing to the excellent thermal sta-
bility and char yield performance, the aryloxy substituted polyph-
osphazene has attracted interest for its potential application in
flame retardants [24]. Differential scanning calorimetry (DSC)
studies were carried out between ꢁ40 and 100 °C with a heating
rate of 10 °C/min under a nitrogen flow to determine the transition
temperatures of the dendrimeric compounds. The Tg values of all
the new phosphazene compounds (5–7) are presented in Table 2.
Thermogravimetric analysis (TGA) was utilized to evaluate the
thermal stability of the dendrimeric compounds. The onset decom-
position temperatures (Td) are recorded at a heating rate of 10 °C/
O O
P
O O
P
O O
N
P
N
P
Cl Cl
P
OH
O
O
O
O
N
P
N
P
P
N
P
N
P
OH
THF
N
P
N
P
THF
NaH
O
N
O
O
O
O
Cl
Cl
O
O
Cl
Cl
+
N
N
Pd(OH)2
O
N
Cs2CO3
THF ,
Cl
OH
O
3
1
2
Cl
Cl
Cl Cl
P
Cl
Cl
P
N
P
N
N
P
N
P
N
P
N
N
P
N
P
Cl
THF
NaH
Cl
Cl
O
O
Cl
Cl
Cl
P
OH
HO
+
N
Cl
Cl
Cl
Cl
-78 0
C
4
R
R
N3P3Cl6
P
N
P
N
P
R
R
R
5
N
R
R
R
P
N
P
R
N
N
P
N
P
R
R
R
N4P4Cl8
THF
Cs2CO3
3 (R)
+
6
R
R
R
R
N6P6Cl10(bisphenol)
4
R
R
P
N
P
N
P
N
P
N
P
N
P
R
O
O
R
R
R
7
N
R
R
Scheme 1. Chemical structure and synthetic pathway for 1–7.

B. Çoßsut, S. Yeßsilot / Polyhedron 35 (2012) 101–107
105
Table 1
31P NMR parameters of compounds 1–3 and 5–7.a
Compounds
Chemical shifts (ppm)
>P(naphthoxy)2
2J(PP) (Hz)
>P(naphthoxy)(X)
X
N3P3R6
N4P4R8
1b
2c
3c
5
6
7
8.76
23.86
10.64
10.58
16.05d
16.13d
15.03d
Cl
–
–
–
–
–
–
–
81.6
80.2
80.2
–
–
–
10.78
10.74
16.05d
16.13d
15.03d
OPhOCH2Ph
OPhOH
OPhO(N3P3)
OPhO(N4P4)
N6P6 (bisphenol)
14.81
–
13.76
ꢁ5.97
–
a
b
c
202.38 MHz 31P NMR measurements in toluene-d7 solutions at 298 K.
Compound 1 was analyzed as an A2X spin system.
The parameters were obtained from simulation analysis.
d
Broad signals were observed for compounds 5, 6 and 7 and not calculated coupling constants.
Fig. 2. The proton decoupled 31P NMR spectrum of compound 3 (a) observed, (b) simulated.
Table 2
Thermal properties and molecular weights of 5, 6 and 7.
Compound
Tg (°C)
Td (°C)
Mw
5884
7851
10084
% Char yield
5
6
7
27.4
23.8
33.6
434
477
490
45.4
48.8
60.5
min. The curves of the TGA measurements are shown in Fig. 3 and
Td values are collected in Table 2. According to the TGA thermo-
grams of compounds 5, 6 and 7, they exhibit very good thermal
stability with decomposition temperatures (Td) in the range 434–
490 °C (Table 2). The increase of Td from compounds 5–7 can be
explained with the increasing substitution degree of napththoxy
groups. These results correlate with the previously reported results
on the thermal behavior of phenoxy based cyclophosphazenes
dendrimers [18,19]. Therefore aryloxycyclophosphazenes could
be useful candidates for flame retardant additives to organic poly-
mers [24]. The high char yields and Td values of the dendrimeric
phosphazene compounds 5, 6 and 7 make them a good flame retar-
dants in theory [25], and it could suggest that the dendrimeric
derivatives have excellent thermal properties.
Fig. 3. TGA curves of 5, 6 and 7 from 25 to 700 °C at a heating rate of 10 °C/min
under a N2 flow of 50 mL/min.
[26,27]. Although the hexakis(2-naphthyloxy)cyclotriphosphazene
showed intramolecular excimer behavior [26], the poly[bis(b-
naphthoxy)phosphazene] did not [27]. The absorption and the
The photophysical behaviors of the monomeric and polymeric
naphthoxy phosphazene derivatives have been extensively studied

106
B. Çoßsut, S. Yeßsilot / Polyhedron 35 (2012) 101–107
Fig. 4. The fluorescence emission spectra of 5, 6 and 7 in dichloromethane. Concentration: 1 ꢂ 10ꢁ6 mol dmꢁ3. Excitation wavelength: 270 nm.
fluorescence spectra of the dendrimeric phosphazenes 5, 6 and 7
were measured in dichloromethane as dilute solutions
(1 ꢂ 10ꢁ6 mol dmꢁ3
) upon being excited at 270 nm. All the
compounds display very similar absorption (276–277 nm) and
emission (389–391 nm) wavelength maxima, that are well sepa-
rated (Dk ca. 115 nm). The emission spectra of compound 5, 6
and 7 are shown in Fig. 4. The trend in the emission maxima
amongst the cyclic compounds was bisphenol bridged compound
(7) > tetrameric core phosphazene derivative (6) > trimeric core
phosphazene derivative (5), according to the number of the naph-
thol groups, as expected [18,19]. The fluorescence quantum yields
(UF) of the phosphazene derivatives were measured in CH2Cl2, and
2-aminopyridine in 0.1 M H2SO4 solution was used as a standard.
Although there are many parameters that affect the fluorescence
quantum yields [28], the fluorescence quantum yields (UF) of den-
drimeric compounds are increased with respect to the increment
of the side groups, and their values are: 0.34 for 5, 0.36 for 6 and
0.39 for 7. Apart from the emission (389–391 nm) wavelength
maxima, the emission spectra of the cyclic compounds showed
two additional emission bands consisting of a maximum at
339 nm with a shoulder at 325 nm (Fig. 4). In order to get more
information on the observed additional bands, the emission spec-
tra of compound 3 and 2-naphthol were measured under the same
conditions (1 ꢂ 10ꢁ6 mol dmꢁ3 in CH2Cl2, kexc 270 nm), as shown
in Fig. 5. Although three emission bands were observed at 325,
340 and 390 nm for compound 3, the emission spectrum of 2-
naphthol showed only two bands at 326 and 339 nm. When the
emission spectrum of 2-naphthol was taken in dichloromethane
as a concentrated solution of 1 ꢂ 10ꢁ1 mol dmꢁ3, three bands
was observed at 328, 340 and 380 nm (not shown). The appearance
of a 380 nm band in 2-naphthol originates from the formation of an
intermolecular excimer. Intramolecular monomer/excimer obser-
vation is well known [29], and excimer formation with naphtha-
lene derivatives or polyaromatic hydrocarbons occurs only in
very concentrated solutions. Therefore, we can clearly say that
the appearance of the 390 nm band in compound 3 arises from
the formation of an excimer between the naphthol units. It is well
known [9] that chlorophosphazenes (N3P3Cl6, or N4P4Cl8) are pho-
Fig. 5. The fluorescence emission spectra of 3 and 2-naphthol in dichloromethane.
Concentration: 1 ꢂ 10ꢁ6 mol dmꢁ3. Excitation wavelength: 270 nm.
tochemically inert and do not interfere with the photophysical
properties associated with the attached chromophores. Single crys-
tal X-ray analysis of hexakis(2-naphthyloxy)cyclotriphosphazene
showed [29] that the six naphthyloxy groups lie almost perpendic-
ularly above and below the nearly planar cyclotriphosphazene
core. This structural features make it possible for the three naph-
thyloxy groups to be located on the same side of the (PN)3 plane,
and they are able to align through intramolecular non-covalent
p–p interactions. Therefore it can be suggested that the excimer
interactions in compound 3 (dilute solutions of 1 ꢂ 10ꢁ5 mol dmꢁ3
in CH2Cl2) is intramolecular rather than intermolecular. Hence, the
two additional emission bands for the dendrimeric compounds 5, 6
and 7 can be derived from the intramolecular excimer formation.

B. Çoßsut, S. Yeßsilot / Polyhedron 35 (2012) 101–107
107
[6] H.R. Allcock, Phosphorus–Nitrogen Compounds, Academic Press, New York,
1972 (Chapters 6 and 7).
4. Conclusion
[7] C.W. Allen, Chem. Rev. 91 (1991) 119.
In conclusion, we have described the synthesis of a hydroxyl
substituted penta(naphthoxy)cyclotriphosphazene (3) and its den-
drimeric derivatives (5, 6 and 7) based on cyclic phosphazenes. All
the compounds have been characterized by standard spectroscopic
techniques. The thermal stability and fluorescence spectral proper-
ties of the dendrimeric compounds (5, 6 and 7) have been investi-
gated. These compounds possess both high thermal stability and
char yields and significantly more fluorescence emission on
increasing the length of the side groups, making it potentially
suitable for some industrial applications, such as flame retardant
additives to polymers or light emitting electroluminescent devices.
[8] R. de Jaeger, M. Gleria, Prog. Polym. Sci. 23 (1998) 179.
[9] M. Gleria, R. De Jaeger (Eds.), Phosphazenes: A World Wide Insight, Nova
Science Publishers, New York, 2004.
[10] D. Astruc, E. Boisselier, C. Ornelas, Chem. Rev. 110 (2010) 1857.
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Acknowledgements
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We thank the Gebze Institute of Technology (GIT) Research
Fund for partial financial support.
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