Synthesis and properties of axially-phenoxycyclotriphosphazenyl substituted silicon phthalocyanine

Article abstract of DOI:10.1016/j.poly.2009.09.035

An hydroxyl substituted hexa(phenoxy)cyclotriphosphazene (3) is reacted with silicon phthalocyanine (4), SiPc(Cl)₂, to give an axially-disubstituted phenoxycyclotriphosphazenyl silicon phthalocyanine (5). In this study, an axially phosphazene s

Full text of DOI:10.1016/j.poly.2009.09.035

Polyhedron 29 (2010) 675–682
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and properties of axially-phenoxycyclotriphosphazenyl substituted
silicon phthalocyanine
*
Bünyemin Çoßsut, Serkan Yeßsilot, Mahmut Durmusß , Adem Kılıç, Vefa Ahsen
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:
An hydroxyl substituted hexa(phenoxy)cyclotriphosphazene (3) is reacted with silicon phthalocyanine
(4), SiPc(Cl)2, to give an axially-disubstituted phenoxycyclotriphosphazenyl silicon phthalocyanine (5).
In this study, an axially phosphazene substituted phthalocyanine complex synthesized at the first time.
Newly synthesized silicon phthalocyanine complex has been fully characterized by elemental analysis,
ESI mass spectrometry, FT-IR, 1H, 13C and 31P NMR spectroscopy. Photophysical (fluorescence quantum
yield and lifetime) and photochemical (singlet oxygen generation and photodegradation quantum yield)
properties of complex 5 are reported in DMSO. The fluorescence quenching behaviour of this complex by
1,4-benzoquinone (BQ) is also reported in DMSO.
Received 3 September 2009
Accepted 30 September 2009
Available online 24 October 2009
Keywords:
Silicon phthalocyanine
Cyclotriphosphazene
Fluorescence
Singlet oxygen
Quantum yield
Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction
can be tailored via appropriate substituted groups on phosphorus
atoms. For example, it is possible to design materials with special
Phthalocyanines (Pcs), which were first developed as industrial
pigments, have been actively explored in various technological
applications [1] such as optical recording photovoltaics, photo-
copying, gas sensing, liquid crystal and photodynamic therapy
(PDT).
Axially-substituted silicon phthalocyanines (SiPcs) are of great
interest to scientists because they are not able to aggregate due
to their special structural features [2], thus avoiding fluorescence
quenching. Therefore, they are very attractive targets to study
photophysical processes [3]. In the past few years, different axi-
ally-substituted silicon Pcs have been synthesized bearing a wide
variety of active moieties such as carotenoid, azo, tetrathiafulva-
lene, porphyrin and several ester and/or ether derivatives includ-
ing phenyl, terphenyl, thienyl and pyrenyl system which have
been studied to determine energy or electron transfer processes
[4–8].
properties such as inflammable textile fibers and advanced elasto-
mers [11], anticancer agents [12], hydraulic fluids and lubricants
[13], electrical conductivity [14], and flame retardant properties
[15]. Recently there has been considerable interest in fluorescent
compounds based on cyclic phosphazene cores [16] or cyclolinear
polymers with the cyclotriphosphazene units [17] for development
of electroluminescent devices.
We have previously described the synthesis of cyclotriphosp-
hazenyl-rings substituted on peripheral position of a phthalocya-
nine macrocycle and their photophysical and photochemical
properties have been also investigated [18,19].
To our best knowledge, there is no report that synthesis of
cyclotriphosphazene being linked to phthalocyanines as axially
groups. The nature of substituents on axially positions can strongly
influence essential parameters of a phthalocyanine, such as its sol-
ubility, aggregation behaviour, electronic absorption and fluores-
cence spectral properties. Therefore, we want to investigate the
effects of cyclotriphosphazenyl group substituted on axially posi-
tion of silicon phthalocyanine. In this work, we report the molecu-
lar design, synthesis, photophysical and photochemical properties
of axially-disubstituted phenoxycyclotriphosphazenyl silicon
phthalocyanine (5) at the first time. Photophysical (fluorescence
quantum yield and lifetime) and photochemical (singlet oxygen
generation and photodegradation quantum yield) properties of
axially-disubstituted phenoxycyclotriphosphazenyl silicon phtha-
locyanine (5) are reported in DMSO. The fluorescence quenching
behaviour of this complex by BQ is also reported in DMSO.
The cyclic and polymeric phosphazenes are an important class
of inorganic heterocyclic ring systems in basic and applied science
[9]. They are usually prepared by nucleophilic substitution reac-
tions of alkoxides, aryloxides or amines on halocyclophosphazenes
or high polymers [10] and their physical and chemical properties
* Corresponding author. Address: Department of Chemistry, Gebze Institute of
Technology, P.O. Box 141, Gebze 41400, Kocaeli, Turkey. Tel.: +90 262 6053108; fax:
+90 262 6053101.
E-mail address: durmus@gyte.edu.tr (M. Durmußs).
0277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.09.035

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B. Çoßsut et al. / Polyhedron 29 (2010) 675–682
the standard. The absorbance of the solutions at the excitation
wavelength ranged between 0.04 and 0.05.
Natural radiative lifetimes ( 0) were determined using Photo-
chemCAD program which uses the Strickler–Berg equation [24].
2. Experimental
2.1. Materials
s
The fluorescence lifetimes (sF) were evaluated using Eq. (2).
Hexachlorocyclotriphosphazene (Otsuka Chemical Co. Ltd.) was
purified by fractional crystallization from n-hexane. The deuter-
ated solvents (CDCl3 and toluene-d8) for NMR spectroscopy and
the following chemicals were obtained from Merck; cyclohexene,
ethanol, phenol, Pd(OH)2, K2CO3, NaH, acetone, triethylamine, sil-
ica gel 60, tetrahydrofuran. 1,3-diphenylisobenzofuran (DPBF)
were purchased from Fluka. All other reagents and solvents were
reagent grade quality and obtained from commercial suppliers.
SiPc(Cl)2 [20], 1,1,3,3,5-pentaphenoxy-5-chlorocyclotriphosphaz-
atriene (1) [18], 1,1,3,3,5-pentaphenoxy-5-[(4-hydroxy)phenoxy]-
cyclotriphosphazatriene (2) [18] and 1,1,3,3,5-pentaphenoxy-5-
[(4-hydroxy)phenoxy]-cyclotriphosphazatriene (3) [18] were syn-
thesized and purified according to the literature procedures.
sF
s0
UF
¼
ð2Þ
The experimental errors in the determination of the UF
were ꢁ5% (determined several values).
,
sF and s0
2.4. Photochemical parameters
2.4.1. Singlet oxygen quantum yields
Singlet oxygen quantum yield (UD) determinations were car-
ried out using the experimental set-up described in literature
[25–27]. Typically, a 3 ml portion of the respective axially-phen-
oxycyclotriphosphazenyl substituted silicon phthalocyanine (5)
solution (absorbance ꢁ 1.0 at the irradiation wavelength) contain-
ing the singlet oxygen quencher was irradiated in the Q band re-
gion with the photo-irradiation set-up described in Refs. [25–27].
Singlet oxygen quantum yields (UD) were determined in air using
the relative method with ZnPc (in DMSO) as reference. DPBF was
used as a chemical quencher for singlet oxygen in DMSO. Eq. (3)
was employed for the calculations:
2.2. Equipment
Elemental analysis was carried out using Thermo Finnigan Flash
1112 Instrument. UV–Vis spectra were recorded with a Shimadzu
2001 UV spectrophotometer. Fluorescence excitation and emission
spectra were recorded on a Varian Eclipse spectrofluorometer
using 1 cm pathlength cuvettes at room temperature. Infrared
spectra were recorded on a Bio-Rad FTS 175C FT-IR spectropho-
tometer using KBr pellets. The mass analyzer was a Bruker Dalton-
ics (Bremen, Germany) MicrOTOF mass spectrometer equipped
with an orthogonal electrospray ionization (ESI) source. The instru-
ment was operated in 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 radio-
frequency (RF) was 800.0 Vpp. Analytical thin layer chromatogra-
phy (TLC) was performed on 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 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
Std
R ꢀ I
USDtd
ð3Þ
abs
UD
¼
RStd ꢀ Iabs
where USDtd is the singlet oxygen quantum yield for the standard
ZnPc (USDtd = 0.67 in DMSO) [28]. R and RStd are the DPBF photoble-
aching rates in the presence of the respective sample (5) and stan-
Std
abs
dard, respectively. Iabs and I are the rates of light absorption by
the sample (5) and standard, respectively. To avoid chain reactions
induced by DPBF in the presence of singlet oxygen [29], the concen-
tration of quencher was lowered to ꢁ3 ꢂ 10ꢃ5 mol dmꢃ3. Solutions
of sensitizer (absorbance = 1 at the irradiation wavelength) contain-
ing DPBF was prepared in the dark and irradiated in the Q band re-
gion using the set-up described above. DPBF degradation at 417 nm
was monitored. The light intensity 6.60 ꢂ 1015 photons sꢃ1 cmꢃ2
was used for UD determinations.
chromatography was performed on silica gel 60 P F254.
1H, 13C
and 31P NMR spectra were recorded in CDCl3 and toluene-d8 solu-
tions on a Varian 500 MHz spectrometer.
2.4.2. Photodegradation quantum yields
Photodegradation quantum yield (Ud) determination of com-
plex 5 was carried out using the experimental set-up described
in literature [25–27]. Photodegradation quantum yield of complex
5 was determined using Eq. (4),
Photo-irradiations were done using a General Electric quartz
line lamp (300 W). A 600 nm glass cut off filter (Schott) and a water
filter were used to filter off ultraviolet and infrared radiations,
respectively. An interference filter (Intor, 670 nm with a band
width of 40 nm) was additionally placed in the light path before
the sample. Light intensities were measured with a POWER
MAX5100 (Molelectron detector incorporated) power meter.
ðC0 ꢃ CtÞ ꢀ V ꢀ NA
Ud
¼
ð4Þ
Iabs ꢀ S ꢀ t
where C0 and Ct are the sample (5) concentrations before and after
irradiation, respectively, V is the reaction volume, NA is the Avoga-
dro’s constant, S is the irradiated cell area and t the irradiation time
Iabs is the overlap integral of the radiation source light intensity and
2.3. Photophysical parameters
2.3.1. Fluorescence quantum yields and lifetimes
Fluorescence quantum yields (UF) were determined by the
comparative method (Eq. (1)) [21,22],
the absorption of the sample (5).
A
light intensity of
2.20 ꢂ 1016 photons sꢃ1 cmꢃ2 was employed for Ud determination.
F ꢀ AStd
ꢀ
g2
2.5. Fluorescence quenching by 1,4-benzoquinone (BQ)
UF
¼
UFðStdÞ
ð1Þ
FStd ꢀ A ꢀ g2Std
Fluorescence quenching experiments on the axially-phenoxycy-
clotriphosphazenyl substituted silicon phthalocyanine (5) were
carried out by the addition of different concentrations of BQ to a
fixed concentration of the phthalocyanine complex (5), and the
concentrations of BQ in the resulting mixtures were 0, 0.008,
0.016, 0.024, 0.032 and 0.040 mol dmꢃ3. The fluorescence spectra
of phthalocyanine complex (5) at each BQ concentration were
where F and FStd are the areas under the fluorescence emission
curves of the sample (5) and the standard, respectively. A and AStd
are the respective absorbances of the sample and standard at the
excitation wavelengths, respectively. g2 and gS2td are the refractive
indices of solvents used for the sample and standard, respectively.
Unsubstituted ZnPc (in DMSO) (UF = 0.20) [23] was employed as

B. Çoßsut et al. / Polyhedron 29 (2010) 675–682
677
recorded, and the changes in fluorescence intensity related to BQ
concentration by the Stern–Volmer (S–V) equation [30] (Eq. (5)):
ene-d8) d = 9.05 [>P(PhO)2 ], 9.52 [>P (OPh)SiPc]; 2J(P,P) = 74.2 Hz;
MS (ESI) m/z (%): 1958(100) [M+H]+.
I0
I
¼ 1 þ KSV½BQꢄ
ð5Þ
3. Result and discussion
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; and
is the product of the bimolecular quenching constant (kq) and the
3.1. Synthesis and characterization
The synthetic route of the compounds presented in this work is
shown in Scheme 1. Compounds 1 [31], 2 [18], 3 [18] and SiPc(Cl)2
[20] were synthesized according to previously published methods.
Compound 5 was obtained from a nucleophilic displacement reac-
tion of 3 with SiPc(Cl)2 under nitrogen atmosphere with sodium
hydride as the base. The product was purified by preparative TLC
on silica gel using hexane: THF (3:2) as the eluent. The structure
of the compound 5 is shown in Fig. 1. The newly synthesized com-
pound 5 was characterized by FT-IR, 1H, 13C and 31P NMR, mass
spectrometry and elemental analysis. All the results were consis-
tent with the predicted structure as shown in the experimental
section. The FT-IR spectra features peaks at around 1265 cmꢃ1
(br) (P@N), 950 cmꢃ1 (P–O) for phosphazene ring and aromatic
C–H stretching around 3059 cmꢃ1 for phthalocyanine skeleton as
expected. The elemental analysis results and the mass spectral
data for 5 were consistent with the assigned formulation. The mass
spectrum of 5 was obtained by ESI mass spectrometry. Mass spec-
tral identification is based on matching measured accurate mass
and isotopic pattern of a sample. Theoretical and measured isoto-
pic patterns as an additional identification tool to accurate mass
determination of 5 and the positive ion ESI mass spectrum is given
in Fig. 2. The peak group representing the protonated molecular ion
of 5 was observed at 1958 Da mass (Fig. 2). Since the compound 5
shows non-first order 31P NMR spectrum, it is necessary to carry
out simulation analysis to get the appropriate spectral parameters.
Following this analysis, the proton-decoupled 31P NMR spectrum
fluorescence lifetime sF, i.e.
KSV ¼ kq ꢀ sF
ð6Þ
The ratios I0/I were calculated and plotted against [BQ] according to
Eq. (5), and KSV determined from the slope (the experimental errors
in the determination of the KSV value was ꢁ5%).
2.6. Synthesis of compound 5
A mixture of dichloro(phthalocyaninato) silicon (4) (100 mg,
0.16 mmol) and 3 (231 mg, 0.33 mmol) in dry toluen (10 ml) was
stirred and then sodium hydride (13.2 mg, 0.33 mmol) was added
to this mixture. After refluxing under nitrogen for 10 h, the reac-
tion mixture was cooled to room temperature, and than the solvent
was evaporated to dryness under reduced pressure. The crude
product was purified by preparative TLC on silica gel using hexane:
THF (3:2) as the eluent. Dark green product was obtained; Yield:
105 mg (33%). Anal. Calc. for C106H74N14O14P6Si (1957): C, 63.74;
H, 3.91; N, 10.01. Found: C, 63.64; H, 3.86; N, 10.05%. FT-IR mmax
/
cmꢃ1 (KBr pellet); 3059 (ArCH), 1591 (ArC@C), 1265 (P@N), 1125
(C–O), 950 (P–O); 1H NMR(CDCl3) d = 6.21–7.50 (m, 48H, ArH),
8.40 and 9.70 (m, 16H, ArCH of SiPc); {1H}13C NMR (CDCl3)
d = 151.81 (ArC), 149.80 (ArCH), 136.04 (ArC), 129.48 (ArCH),
128.52 (ArCH), 125.79 (ArCH), 124.88 (ArCH), 121.15(ArCH),
121.05 (ArCH), 119.49 (ArCH), 117.91 (ArCH); {1H}31P NMR (tolu-
O O
P
Cl Cl
P
OH
O O
P
N
P
N
P
N
P
N
THF
O
O
THF
NaH
O
O
O
+
Cl
Cl
+
N
N
P
Cl
Cl
N
P
O
O
O
K2CO3
N
P
N
Cl
O
OH
2
1
THF/EtOH
cyclohexene
Pd(OH)2
Cl
N
O O
P
N
N
N
P
N
P
Toluene/NaH
O
O
O
O
N
N
Si
Cl
+
5
N
N
N
N
OH
3
4
Scheme 1. Chemical structure and synthetic pathway of 1–5.

678
B. Çoßsut et al. / Polyhedron 29 (2010) 675–682
N
O
P
N
O
P
O
N
N
N
N
O
N
O
N
N
O
O
N
P
O
O
O
Si
O
P
N
O P
O
P
O
N
N
N
Fig. 1. Structure of the axially-phenoxycyclotriphosphazenyl substituted silicon phthalocyanine complex (5).
Fig. 2. Positive-ion mode electrospray ionization (ESI) mass spectrum of 5. See inset: (a) experimental isotopic pattern and (b) theoretical isotopic pattern.
of compound 5 was shown as the expected typical AB2 pattern [18]
and the resonances belonging to phosphorous atoms were ob-
served at ca. 9.05 ppm for >P(PhO)2 and at ca. 9.52 ppm for
>P(OPh)SiPc, also the magnitude of the 2J(P,P) at ca. 74.2 Hz (Fig. 3).
gation in these solvents suggesting that the substitution effect of
the phenoxycyclotriphosphazenyl group as axial substituent on
the phthalocyanine ring.
The aggregation behaviour of the axially-disubstituted phen-
oxycyclotriphosphazenyl silicon phthalocyanine (5) complex was
investigated at different concentrations in DMSO (Fig. 5). In DMSO,
as the concentration was increased, the intensity of the Q band
absorption also increased and there was no new bands (normally
blue shifted) due to the aggregated species for complex 5 (Fig. 5).
Thus, the complex 5 did not show aggregation in DMSO at
different concentrations. Beer–Lambert law was obeyed for this
complex (5) in the concentrations ranging from 1.4 ꢂ 10ꢃ5 to
3.2. Ground state electronic absorption and fluorescence spectra
The electronic spectrum of the axially-disubstituted phenoxy-
cyclotriphosphazenyl silicon phthalocyanine (5) showed intense
Q absorption band at 684 nm in DMSO (Fig. 4). The spectra showed
monomeric behaviour evidenced by a single (narrow) Q band, typ-
ical of metallated phthalocyanine complexes for 5 in DMSO [32].
The B-bands were broad due to the superimposition of the B1
and B2 bands at around 350 nm (Fig. 4).
Aggregation is usually depicted as a coplanar association of
rings progressing from monomer to dimer and higher order com-
plexes. It is dependent on the concentration, nature of the solvent,
peripheral substituents, complexed metal ions and temperature
[33,34]. In the aggregated state the electronic structure of the com-
plexed phthalocyanine rings is perturbed resulting in alternation of
the ground and excited state electronic structure [35]. In this
study, the aggregation behaviour of the axially-disubstituted phen-
oxycyclotriphosphazenyl silicon phthalocyanine (5) was investi-
gated at different solvents (chloroform, DMF, THF, toluene,
dichloromethane and DMSO). The complex 5 did not show aggre-
4 ꢂ 10ꢃ6 mol dmꢃ3
.
Fig. 6 shows the absorption, fluorescence emission and excita-
tion spectra for axially-disubstituted phenoxycyclotriphosphaze-
nyl silicon phthalocyanine (5) complex in DMSO. Fluorescence
emission peak was observed at 692 nm for 5 in DMSO. The excita-
tion spectrum was similar to absorption spectrum and both were
mirror images of the fluorescent spectrum in DMSO (Fig. 6). The
proximity of the wavelength of each component of the Q band
absorption to the Q band maxima of the excitation spectrum for
complex 5 suggests that the nuclear configurations of the ground
and excited states were similar and not affected by excitation in
DMSO. The observed Stokes shift was 8 nm and typical of MPc
complexes in DMSO.

B. Çoßsut et al. / Polyhedron 29 (2010) 675–682
679
Fig. 3. Proton-decoupled 31P NMR spectrum of 5 in toluene-d8 solution.
1.2
0.8
0.4
0
300
400
500
600
700
800
Wavelength (nm)
Fig. 4. Absorption spectrum of axially-phenoxycyclotriphosphazenyl substituted silicon phthalocyanine complex (5) in DMSO. Concentration = 1.00 ꢂ 10ꢃ5 mol dmꢃ3
.
3.3. Fluorescence quantum yields and lifetimes
Lifetime of fluorescence (sF) was calculated using the Strickler–
Berg equation. Using this equation, a good correlation has been
[22] found for the experimentally and theoretically determined
fluorescence lifetimes for the unaggregated molecules as is the
case in this work for 5 in DMSO. sF value of the axially-disubsti-
tuted phenoxycyclotriphosphazenyl silicon phthalocyanine (5)
The fluorescence quantum yield (UF) of the axially-disubsti-
tuted phenoxycyclotriphosphazenyl silicon phthalocyanine (5)
complex (UF = 0.17) was typical of MPc complexes in DMSO. The
UF value of the substituted complex (5) is slightly lower than for
unsubstituted ZnPc (UF = 0.20) in DMSO.
complex (sF = 3.11 ns) was longer when compared to unsubstitut-

680
B. Çoßsut et al. / Polyhedron 29 (2010) 675–682
1.6
1.2
0.8
0.4
0
1.6
1.2
0.8
0.4
0
y = 81714x + 0.2146
R2 = 0.9979
A
0.00E+00 2.00E-06 4.00E-06 6.00E-06 8.00E-06 1.00E-05 1.20E-05 1.40E-05
F
Concentration
300
400
500
600
700
800
Wavelength (nm)
Fig. 5. Aggregation behaviour of 5 in DMSO at different concentrations: 14 ꢂ 10ꢃ6 (A), 12 ꢂ 10ꢃ6 (B), 10 ꢂ 10ꢃ6 (C), 8 ꢂ 10ꢃ6 (D), 6 ꢂ 10ꢃ6 (E), 4 ꢂ 10ꢃ6 (F) mol dmꢃ3
.
500
400
300
200
100
0
0.25
0.2
0.15
0.1
0.05
0
Excitation
Emission
Absorption
500
600
700
800
Wavelength (nm)
Fig. 6. Absorption, excitation and emission spectra of the compound 5 in DMSO. Excitation wavelength = 655 nm.
ed ZnPc (
s
F = 1.22 ns) [36] in DMSO. The natural radiative lifetime
than silicon phthalocyanine derivatives having different substitu-
ents on the axially position in literature [37–40]. The sF value, ob-
tained as a result of this study, is almost similar with axially
substituted silicon phthalocyanine derivatives in literature [37–
40].
(
s
0) value of the axially-disubstituted phenoxycyclotriphosphaze-
nyl silicon phthalocyanine (5) complex ( 0 = 18.29 ns) was also
longer when compared to unsubstituted ZnPc ( 0 = 6.80 ns) in
s
s
DMSO [36]. The rate constant for fluorescence (kF) value of the
complex 5 (kF = 5.46 ꢂ 107 sꢃ1) was lower than unsubstituted ZnPc
(kF = 1.47 ꢂ 108 sꢃ1) in DMSO [36].
3.4. Singlet oxygen quantum yields
Fluorescence quantum yield (UF) and lifetime (sF) values of em-
ployed axially-disubstituted phenoxycyclotriphosphazenyl silicon
phthalocyanine complex (5) resemble with those of axially substi-
tuted silicon phthalocyanine complexes in the literature that ran-
Singlet oxygen quantum yield (UD) was determined in DMSO
using a chemical method using DPBF as a quencher. The disappear-
ance of DPBF spectra was monitored using UV–Vis spectrophotom-
eter. Many factors are responsible for the magnitude of the
determined quantum yield of singlet oxygen including; triplet ex-
ged from 0.02 to 0.14 for UF and 2.54–5.40 ns for
sF, respectively
[37–40]. The UF value, obtained as a result of this study, is higher

B. Çoßsut et al. / Polyhedron 29 (2010) 675–682
681
250
200
150
100
50
1.4
1.2
1
y = 10.262x + 1.012
R2 = 0.9907
0.8
0.6
0.4
0.2
0
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
[BQ]
0
665
685
705
725
745
765
785
Wavelength (nm)
Fig. 7. Fluorescence emission spectral changes of 5 (1.00 ꢂ 10ꢃ5 mol dmꢃ3) on addition of different concentrations of BQ in DMSO. [BQ] = 0, 0.008, 0.016, 0.024, 0.032 and
0.040 mol dmꢃ3 (inset: Stern–Volmer plot for BQ quenching of 5).
cited state energy, ability of substituents and solvents to quench
the singlet oxygen, the triplet excited state lifetime and the effi-
ciency of the energy transfer between the triplet excited state
and the ground state of oxygen.
There was no change in the Q band intensity during the UD
determination, confirming that complex was not degraded during
singlet oxygen study. The UD value of the axially-disubstituted
phenoxycyclotriphosphazenyl silicon phthalocyanine (5) complex
is 0.22 in DMSO and it is lower than unsubstituted ZnPc value
the ability to undergo excited state charge transfer with ease,
and Pc-quinone systems have proved to be favoured candidates
in this respect [26,44].
The fluorescence quenching of the axially-disubstituted phen-
oxycyclotriphosphazenyl silicon phthalocyanine (5) by BQ in
DMSO was found to obey Stern–Volmer kinetics, which is consis-
tent with diffusion-controlled bimolecular reactions. Fig. 7 shows
the quenching of the axially-disubstituted phenoxycyclotriphosp-
hazenyl silicon phthalocyanine (5) complex by BQ in DMSO. The
slope of the plots shown at inset of Fig. 7 gave KSV value of complex
5. The KSV value of the axially-disubstituted phenoxycyclotri-
phosphazenyl silicon phthalocyanine (5) is 10.26 dm3 molꢃ1 and
it is lower than unsubstituted ZnPc (31.90 dm3 molꢃ1) [36] in
DMSO. KSV value of employed the axially-disubstituted phenoxycy-
clotriphosphazenyl silicon phthalocyanine complex (5) is similar
compared to silicon phthalocyanine derivatives in literature
[40,45]. The bimolecular quenching constant (kq) value of the axi-
ally-disubstituted phenoxycyclotriphosphazenyl silicon phthalo-
cyanine (5) is 0.351 ꢂ 1010 dm3 molꢃ1 sꢃ1 and it is also lower
than for unsubstituted ZnPc (2.611 ꢂ 1010 dm3 molꢃ1 sꢃ1) [36] in
DMSO, thus axially substitution of the silicon phthalocyanine with
phenoxycyclotriphosphazenyl group seems to decrease the kq val-
ues of the complex.
In this work, we present a study of the light harvesting and en-
ergy transducing tendencies of mixtures of silicon phthalocyanine
(5) and BQ. The effective quenching of the complex’ fluorescence
by BQ suggests that systems that are composite of silicon phthalo-
cyanine (5) and quinones could well serve as good light harvesters
and energy transducers. We are at present looking at the possibil-
ity of architecting silicon phthalocyanine (5)-quinone conjugates,
which should be more efficient as a mimicker of the natural
photosynthesis.
(UD = 0.67) [28] in DMSO. Singlet oxygen quantum yield (UD) va-
lue of employed the axially-disubstituted phenoxycyclotriphosp-
hazenyl silicon phthalocyanine complex (5) is similar compared
to axially substituted phthalocyanine derivatives in literature that
ranged from 0.04 to 0.41 [37–42].
3.5. Photodegradation study
Degradation of the molecules under irradiation can be used to
study their stability and this is especially important for those mol-
ecules intended for use as photo catalysts. The collapse of the
absorption spectra without any distortion of the shape confirms
clean photodegradation not associated with phototransformation.
The spectral changes observed for axially-disubstituted phenoxy-
cyclotriphosphazenyl silicon phthalocyanine (5) during confirmed
photodegradation occurred without phototransformation.
Ud values indicate that the stability of the molecules towards
the light irradiation. Stable phthalocyanine complexes show Ud
values as low as 10ꢃ6 and for unstable molecules, values of the or-
der of 10ꢃ3 have been reported [43]. The photodegradation value of
the axially-disubstituted phenoxycyclotriphosphazenyl silicon
phthalocyanine (5) is 1.06 ꢂ 10ꢃ4 and it is less stable to degrada-
tion compared to unsubstituted ZnPc (Ud = 2.61 ꢂ 10ꢃ4) [36] in
DMSO. Thus the substitution of silicon phthalocyanine with phen-
oxycyclotriphosphazenyl group seems to decrease the stability of
the complex in DMSO.
4. Conclusion
In the presented work, the synthesis of new axially-disubsti-
tuted phenoxycyclotriphosphazenyl silicon phthalocyanine (5)
was described and this complex was fully characterized by stan-
dard methods (elemental analysis, IR, 1H, 13C and 31P NMR spec-
troscopy, electronic spectroscopy and mass spectrum). The
3.6. Fluorescence quenching studies by BQ
Pc complexes may also be used as photosynthetic mimickers.
An essential requirement for a good photosynthetic mimicker is

682
B. Çoßsut et al. / Polyhedron 29 (2010) 675–682
[16] J. Xu, C.L. Toh, K.L. Ke, J.J. Li, C.M. Cho, X. Lu, E.W. Tan, C. He, Macromolecules 41
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photophysical and photochemical properties of the axially-disub-
stituted phenoxycyclotriphosphazenyl silicon phthalocyanine (5)
was also described and compared with unsubstituted ZnPc which
was used as standard. This new axially substituted silicon phthalo-
cyanine is soluble in most solvents such as chloroform, toluene,
DMSO, etc. In solution, the absorption spectra of the axially-disub-
stituted phenoxycyclotriphosphazenyl silicon phthalocyanine (5)
showed monomeric behaviour evidenced by a single (narrow) Q
band, typical of metallated phthalocyanine complexes in used sol-
vents such as DMSO, DMF, THF, chloroform, toluene and dichloro-
methane. The fluorescence quantum yield of complex 5 was typical
for MPcs. This complex (5) has average singlet oxygen quantum
yields (UD). The axially substitution of silicon phthalocyanine with
phenoxycyclotriphosphazenyl group seems to decrease the stabil-
ity of this complex when compared to unsubstituted ZnPc in
DMSO. The complex 5 showed lower Ksv and kq values when com-
pared to the unsubstituted ZnPc in DMSO.
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