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B. Çoßsut et al. / Inorganica Chimica Acta 366 (2011) 161–172
operating at 337 nm. Analytical thin layer chromatography (TLC)
was performed on silica gel plates (Merck, Kieselgel 60, 0.25 mm
thickness) with F254 indicator. Column chromatography was per-
formed on silica gel (Merck, Kieselgel 60, 230–400 mesh; for 3 g
crude mixture, 100 g silica gel was used in a column of 3 cm in
diameter and 60 cm in length) and preparative thin layer chroma-
tography was performed on silica gel 60 P F254. 1H, 13C and 31P NMR
spectra were recorded in CDCl3 or toluene-d8 solutions on a Varian
500 MHz spectrometer. Thermal properties of compounds were
investigated on Mettler Toledo TGA/SDTA 851 thermogravimetric
analysis (TGA) and differential scanning calorimeter (DSC) DSC
821e equipped with Mettler Toledo Stare software at a heating rate
of 10 °C minꢀ1 under nitrogen flow (50 ml minꢀ1).
2.3. Synthesis
1,1,3,5-Tetraphenoxy-3,5-dichlorocyclotriphosphazatriene (1),
1,1,3,3,5-pentaphenoxy-5-chlorocyclotriphosphazatriene (iii) and
hexaphenoxycyclotriphosphazene were prepared and purified
according to the literature procedures [30].
2.3.1. Synthesis of compound 2
4-(Benzyloxy) phenol (1.38 g, 6.93 mmol), dry and finely pow-
dered cesium carbonate (3.38 g, 10.4 mmol) were dissolved in
dry THF (10 ml) under argon atmosphere. The solution was trans-
ferred to a 50 ml dropping funnel and slowly dropped to the solu-
tion of 1,1,3,5-tetraphenoxy-3,5-dichlorocyclotriphosphazatriene
(2.0 g, 3.46 mmol) (1) in 10 ml dry THF under argon atmosphere.
The reaction mixture was refluxed under argon for 24 h and fol-
lowed by TLC indicating no starting material remaining. 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 (1:2) as the eluent]. 1,1,3,5-tetraphen-
oxy-3,5-[(4-benzyoxy)phenoxy]-cyclotriphosphazatriene (2) was
obtained as viscous oil; Yield: 1.86 g (84%). Anal. Calc. for
2.2.1. Fluorescence quantum yields and lifetimes
Fluorescence quantum yields (UF) were determined by the
comparative method (Eq. (1)) [26]
F ꢁ AStd ꢁ n2
UF
¼
UFðStdÞ
ð1Þ
FStd ꢁ A ꢁ n2Std
where F and FStd are the areas under the fluorescence emission
curves of the samples (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 fluorescence quan-
tum yields in different solvents. 2-Aminopyridine (in 0.1 M H2SO4)
C
50H42N3O8P3 (905): C, 66.59; H, 5.37; N, 4.48. Found: C, 66.70;
H, 5.28; N, 4.20%. 1H NMR (CDCl3) d = 6.73–7.35 (m, 38H, ArCH),
4.91 (br s, 4H, CH2); {1H}13C NMR (CDCl3) d = 156.04 (ArC),
144.61 (ArC), 137.16 (ArC), 129.62 (ArCH), 128.87 (ArCH), 127.68
(ArCH), 125.02 (ArCH), 122.17(ArCH), 121.28 (ArCH), 77.27 (CH2).
MS (ESI) m/z (%): 906 (100) [M+H]+.
(UF = 0.60) [27] was employed as the standard. Both the samples
and standard were excited at the same wavelength. The concentra-
tion of the solutions at the excitation wavelength fixed at
1 ꢂ 10ꢀ5 mol dmꢀ3. Natural radiative (
s0) life times were deter-
mined using PhotochemCAD program which uses the Strickler–Berg
2.3.2. Synthesis of compound 3
Compound 2 (1.6 g, 1.7 mmol) was dissolved in 8 ml dry THF
under argon atmosphere and 6 ml cyclohexene, palladium hydrox-
ide (20 wt% on carbon, 0.4 g) and 6 ml ethanol were added to this
solution. The mixture was refluxed for 24 h under argon atmo-
sphere. Then the reaction mixture was filtered off and solvents
were removed under reduced pressure. The crude product was
purified by preparative TLC on silica gel using hexane:THF (1:1)
as the eluent. Compound 3 was obtained as viscous oil; Yield:
1.2 g (84%). Anal. Calc. for C43H36N3O8P3 (815): C, 63.54; H, 4.85;
N, 5.05. Found: C, 63.60; H, 4.80; N, 5.20%. 1H NMR (CDCl3)
d = 6.57–7.47 (m, 33H, ArCH), 5.16 (s, 1H, OH), 5.02 (br s, 2H,
CH2); {1H}13C NMR(CDCl3) d = 155.98 (ArC-OH), 152.95 (ArC),
144.32 (ArC), 137.19 (ArC), 129.64 (ArCH), 128.91 (ArCH), 127.75
(ArCH), 125.06 (ArCH), 121.05(ArCH), 116.06 (ArCH), 77.27 (CH2).
MS (ESI) m/z (%): 816 (100) [M+H]+.
equation [28]. The fluorescence lifetimes (
Eq. (2).
s
F) were evaluated using
sF
s0
UF
¼
ð2Þ
The rate constant for florescence (kF) values were calculated
using Eq. (3).
kF ¼ UF
=sF
ð3Þ
2.2.2. Fluorescence quenching by 1,4-benzoquinone (BQ)
Fluorescence quenching experiments on the phenoxy substi-
tuted dendrimeric phosphazene derivatives (6 and 7) were carried
out by the addition of different concentrations of BQ to a fixed con-
centration of the compounds, and the concentrations of BQ in the
resulting mixtures were 0, 2.4 ꢂ 10ꢀ6, 4.8 ꢂ 10ꢀ6, 7.2 ꢂ 10ꢀ6
,
2.3.3. Synthesis of compound 4
9.6 ꢂ 10ꢀ6 and 12 ꢂ 10ꢀ6 mol dmꢀ3. The fluorescence spectra of
phenoxy substituted dendrimeric phosphazene derivatives (6 and
7) at each BQ concentration were recorded, and the changes in
fluorescence intensity related to BQ concentration by the Stern-
Volmer (S-V) equation [29] (Eq. (4)):
1,1,3,3,5-Pentaphenoxy-5-chlorocyclotriphosphazatriene (iii)
(0.87 g, 1.4 mmol) and compound 3 (1.12, 1.4 mmol) were dis-
solved in dry THF (10 ml) under argon atmosphere. After stirring
for 15 min at 40 °C, dry and finely powdered cesium carbonate
(0.66 g, 2.1 mmol) was added portion wise over 15 min with effi-
cient stirring. The mixture was stirred at 80 °C for 24 h under argon
atmosphere. Then the reaction mixture was filtered off and solvent
was removed under reduced pressure. The crude product was puri-
fied by preparative TLC on silica gel using hexane:THF (1:1) as the
eluent. Compound 4 was obtained as viscous oil; Yield: 1.5 g (77%).
Anal. Calc. for C73H60N6O13P6 (1414): C, 62.10; H, 4.51; N, 5.87.
Found: C, 62.15; H, 4.58; N, 5.61%. 1H NMR (CDCl3) d = 6.70–7.30
(m, 58H, ArCH), 5.33 (br s, 2H, CH2); {1H} 13C NMR (CDCl3)
d = 150.83 (ArC), 136.03 (ArC), 129.67 (ArCH), 128.85 (ArC),
127.70 (ArCH), 125.77 (ArCH), 125.16 (ArCH), 122.06 (ArCH),
121.22(ArCH), 115.61 (ArCH), 77.27 (CH2). MS (ESI) m/z (%): 1415
(100) [M+H]+.
I0
I
¼ 1 þ KSV½BQꢃ
ð4Þ
where I0 and I are the fluorescence intensities of fluorophore in the
absence and presence of quencher, respectively. [BQ] is the concen-
tration of the quencher and KSV is the Stern-Volmer constant which
is the product of the bimolecular quenching constant (kq) and the sF
and is expressed in Eq. (5).
KSV ¼ kq ꢁ sF
ð5Þ
The ratios of I0/I were calculated and plotted against [BQ]
according to Eq. (4), and KSV is determined from the slope.