The synthesis, photophysical and thermal properties of novel 7-hydroxy-4-methylcoumarin tetrasubstituted metallophthalocyanines with axial chloride ligand

Article abstract of DOI:10.1016/j.dyepig.2011.10.006

This work reports the synthesis of 7-hydroxy-4-methylcoumarin tetrasubstituted Ruthenium (III)(4a), Indium (III)(4b), Tin (IV)(4c) phthalocyanines bearing axial chloride ligand for the first time. These new metallophthalocyanines show good solubility in m

Full text of DOI:10.1016/j.dyepig.2011.10.006

Dyes and Pigments 93 (2012) 1463e1470
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
The synthesis, photophysical and thermal properties of novel
7-hydroxy-4-methylcoumarin tetrasubstituted metallophthalocyanines
with axial chloride ligand
,
,
a
c
Jun-Jie Guo a b, Shi-Rong Wang a , Xiang-Gao Li , Ming-Yue Yuan
*
a School of Chemical Engineering, Tianjin University, 300072 Tianjin, China
b School of Science, Tianjin University of Commerce, 300134 Tianjin, China
c College of Science, Agricultural University of Hebei, 071001 Baoding, China
a r t i c l e i n f o
a b s t r a c t
Article history:
This work reports the synthesis of 7-hydroxy-4-methylcoumarin tetrasubstituted Ruthenium (III)(4a),
Indium (III)(4b), Tin (IV)(4c) phthalocyanines bearing axial chloride ligand for the first time. These new
metallophthalocyanines show good solubility in many organic solvents. This study also investigates the
photophysical (fluorescence quantum yield and lifetime) properties of compounds 4a, 4b and 4c. The
fluorescence of these three metallophthalocyanines is effectively quenched by the addition of 1,4-
benzoquinone (BQ). The thermal stability studies indicate that both 4a and 4b are stable up to 300 ꢀC.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 3 August 2011
Received in revised form
6 October 2011
Accepted 7 October 2011
Available online 25 October 2011
Keywords:
Phthalocyanines
Fluorescence quantum yields
Fluorescence lifetime
Thermal stability
Axial coordination
7-Hydroxy-4-methylcoumarin
1. Introduction
more soluble than the corresponding octa-substituted due to the
formation of isomers and the high dipole moment that results from
Phthalocyanines are important blue and green 18-
p
electron
the unsymmetrical arrangement of the substituents at the
periphery [12].
macrocyclic conjugated compounds which play a major role in
modern technology with application in many fields such as
semiconductor devices [1], photodynamic therapy [2e4], organic
light-emitting devices [5], sensors [6], non-linear optics [7], and
photovoltaic solar cells [8e10]. They have high chemical and
thermal stability and novel photophysical, photochemical, redox
and coordination properties. A particularly attractive feature of Pcs
is the dependence of properties of the molecule on the nature of the
peripheral functional groups, as well as the electronic properties of
the central metal cations in the phthalocyanine ring [11]. Unsub-
stituted phthalocyanines are not very soluble and tend to aggregate
in solution which results in the fast decay of the excited states.
While the solubility can be increased by addition of alkoxy groups
to peripheral positions or introducing of axial coordination groups
to the central metal, tetrasubstituted phthalocyanines are usually
In the fields of sustainable energy production, solar power
technologies are emerging as one of the most promising alterna-
tives. Developing efficient and affordable systems, able to harvest,
convert, and store sunlight, are considered a very desirable
approach toward obtaining clean energy [13]. A large number of Pcs
as photosensitizer has been reported [14,15]. Meanwhile a good
photosensitizer is required to be in its monomeric state for
successful photo-induced energy and electron transfer [16]. So it is
imperative to synthesis novel phthalocyanine to avoid aggregation
and remain monomer.
Coumarins are fluorescent compounds that have interesting
photophysical properties. They are excellent organic dye sensitizer
because of strong absorption in visible zone [17]. The fluorescence
quantum yield (FF) of these dyes is usually very high, often close to
unity [18]. Materials containing a coumarin component are usefu-
l in many fields due to their characteristics of high emission
yield, excellent photostability and extended spectral range, such
as fluorescence images [19]. The ground and excited state,
* Corresponding author. Tel.: þ86 22 27404208; fax: þ86 22 27892279.
E-mail address: wangshirong@tju.edu.cn (S.-R. Wang).
0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2011.10.006

1464
J.-J. Guo et al. / Dyes and Pigments 93 (2012) 1463e1470
photophysical properties of 7-hydroxy-4-methylcoumarin have
been intensively investigated [20].
To the best of our knowledge, 7-hydroxy-4-methylcoumarin
tetrasubstituted ruthenium, indium and tin chloro phthalocya-
nines have not been reported. Herein we report the synthesis,
standard, respectively. A and Astd are the relative absorbance of
the sample and standard at the excitation wavelength, respec-
tively. n and nstd are the refractive indices of solvents used for
the sample and standard, respectively. Unsubstituted ZnPc (in
DMSO) (FF ¼ 0.20) [25] was employed as the standard. Both the
sample and the standard were excited at the same relevant
wavelength.
fluorescence
and
thermal
properties
of
7-hydroxy-4-
methylcoumarin tetrasubstituted metallophthalocyanines with
axial chloride ligand.
2.3.2. Fluorescence quenching by 1,4-benzoquine(BQ)
Fluorescence quenching experiments of 4a, 4b and 4c were
carried out by addition of different concentrations of the BQ to
a fixed concentration of the complexes, and the concentrations of
the BQ in the resulting mixtures were 0, 0.008, 0.016, 0.024, 0.032
and 0.040 M. The Fluorescence spectra of substituted metal-
lophthalocyanines (4a, 4b and 4c) at each BQ concentration were
recorded, and the changes in Fluorescence intensity related to BQ
concentration by the SterneVolmer (SeV) equation [26] were
shown in Eq. (2)
2. Experimental
2.1. Materials
All solvents were reagent-grade quality and were obtained from
commercial suppliers. All of them were dried and purified as
described by Perin and Armarego [21]. Ruthenium(III) chloride,
indium(III) chloride, tin(Ⅱ) chloride, K2CO3, 1,5-diazabicyclo[4.3.0]
non-5-ene(DBU), deuterated CDCl3 and DMSO, were purchased
from commercial suppliers too.
I0
¼ 1 þ KSV½BQꢁ
(2)
I
2.2. Measurements
Where I0 and I are the maximal fluorescence intensities of the fluo-
rophoreintheabsenceandpresenceofquencher, respectively. [BQ]is
the concentration of the quencher. KSV is the SterneVolmer rate
constant obtained from the slop. As shown in Eq. (3) kq is the bimo-
Infrared spectra in KBr pellets were recorded on BIO-RAD
FIS3000 spectrophotometer. UVevisible/NIR spectra were recor-
ded on a Nicoet Evolution 300 spectrophotometer. 1H NMR spectra
were recorded with an INOVA 500MHz spectrometer. Mass spectra
were recorded on a MALDI (Matrix Assisted Laser Desorption
Ionization) Bruker Autoflex TOF (III) using 2,5-dihydroxybenzoic
acid (DHB) as matrix. Element Analyses were carried out on
a Vario Micro cube Analyzer. XPS spectra were recorded using
a Kratos Axis Ultra DLD spectrometer employing a monochromated
AleKa X-ray source (hv ¼ 1486.6 eV), hybrid (magnetic/electro-
static) optics and a multi-channel plate and delay line detector
(DLD). All XPS spectra were recorded using an aperture slot of
300*700 microns, survey spectra were recorded with a pass energy
of 80 eV, and high resolution spectra with a pass energy of 40 eV. In
order to subtract the surface charging effect, the C1s peak has been
fixed at a binding energy of 284.6 eV. Fluorescence excitation and
emission spectra were recorded on a Varian Cary Eclipse spectro-
fluorometer. Fluorescence lifetimes were measured using a time
correlated single photon counting setup (TCSPC) (FluoroLog3,
HORIBA Jobin Yvon) with a NanoLED-460 laser as excitation source
(HORIBA Jobin Yvon). The optical filter in front of the detector was
630 nm to leach the light below it. And the peak present was
10,000, channels were 1024. All luminescence decay curves were
measured at the maximum of emission peak. The data were
analyzed with the program FluoroLog3 (HORIBA Jobin Yvon). The
support plane approach [22] was used to estimate the errors of the
decay times. Thermo gravimetric analyses were recorded on a Q500
Thermo gravimetric analyzer.
lecular quenching rate constant (Mꢂ1ꢃSꢂ1) and
sF is the main excited
singlet lifetime of fluorophore (s1) in the absence of the quencher.
KSV ¼ Kq$sF
(3)
2.4. Synthesis
7-hydroxy-4-methylcoumarin(1) [27], 4-Nitrophthalonitrile(2)
[28] was prepared according to the literature.
2.4.1. Synthesis of 7-(3,4-dicyanophenoxy)-4-methylcoumarin (3)
7-hydroxy-4-methylcoumarin (1.232 g,
7 mmol) and 4-
nitrophthalonitrile (0.865 g, 5 mmol) was dissolved in dry DMF
40 ml. After 20 min stirring, finely ground anhydrous K2CO3 (1.035 g,
7.5 mmmol) was added portionwise over 2 h. And ensuring the
mixture was stirred vigorously at room temperature till all 4-
nitrophthalonitrile disappeared. Then the reaction mixture was
poured into cold water (100 ml) to give the precipitate. After filtered,
the solid was purified by silica gel column chromatography using
ethyl acetate and cyclohexane as eluent. The product was soluble in
acetone, ethyl acetate, tetrahydrofuran, chloroform, dichloro-
methane, dimethylformamide and dimethylsulfoxide. Yield:
0.962g, 63.7%, m.p. 228e230ꢀC; IR nmax/cmꢂ1 (KBr pellet): 3073
(CHar), 2920e2855 (CHalkyl), 2230 (C^N), 1735(C]O), 1622(C]C),
1261 (AreOeAr0); 1H NMR (DMSO)
dppm: 8.15 (d, 1H, AreH), 7.95
(d, 1H, AreH), 7.89 (d, 1H, AreH), 7.58 (q, 1H, AreH), 7.29 (d, 1H,
AreH), 7.21 (q, 1H, AreH), 6.40 (s, 1H, C]CH), 2.46(s, 3H, CH3).
2.3. Fluorescence behavior
DMF and other solvents were dried and freshly distilled before
use. Measurements were carried out at room temperature of 20 ꢀC.
2.4.2. Synthesis of 2,9,16,23-tetrakis(7-coumarinoxy-4-methyl)-
phthalocyaninatoruthenium(4a)
A
mixture of RuCl3ꢃ3H2O (0.209g, 0.8 mmol), 7-(3,4-
2.3.1. Fluorescence quantum yields
dicyanophenoxy)-4-methylcoumarin (0.906 g, 3 mmol), DBU (10
drops) and octanol 40 ml were stirred and refluxed for 36 h under
a nitrogen atmosphere. After cooling, the solution was dropped into
petroleum to give greenish precipitate. The solid was washed with
water to remove unreacted RuCl3ꢃ3H2O. And then it was extracted
by methanol till colorless. At last the crude product was dissolved in
dichloromethane. After filtering and concentrating, the green
product was purified by silica gel column chromatography using
Fluorescence quantum yields (FF) were determined by the
comparative method (Equation (1)) [23,24].
F$Astd$n2
FF
¼
FFðstdÞ
(1)
F
std$A$n2std
Where F and Fstd are the areas under the florescence emission
curves of the metallophthalocyanines (4a, 4b and 4c) and the

J.-J. Guo et al. / Dyes and Pigments 93 (2012) 1463e1470
1465
Scheme 1. Synthesis of 7-hydroxy-4-methylcoumarin tetrasubsitituted metallophthalocyanines complexes.
dichloromethane and ethanol as eluent. The product was soluble in
acetone, tetrahydrofurane, chloroform, dichloromethane, dime-
thylformamide and dimethylsulfoxide. Yield: 0.250 g, 24.8%; m.p.:
>300 OC; IR nmax/cmꢂ1 (KBr pellet): 3061 (CHar), 2919e2854
(CHalkyl), 1732(C]O), 1602(C]C), 1273(AreOeAr0); 1H NMR
0.8 mmol), 7-(3,4-dicyanophenoxy)-4-methylcoumarin (0.906 g,
3 mmol), DBU (10 drops) and octanol 40 ml. Yield: 0.241 g, 23.1%;
m.p.: >300 OC; IR nmax/cmꢂ1 (KBr pellet): 3065 (CHar), 2931e2846
(CHalkyl), 1729(C]O), 1601(C]C), 1265(AreOeAr0); 1H NMR
(CDCl3) dppm: 9.55e9.66 (m, 4H, PceH), 9.16e9.22 (m, 4H, AreH),
(DMSO)
d
ppm: 9.24e9.33 (m, 4H, Pc-H), 8.85e8.93 (m, 4H, AreH),
8.02e8.12 (m, 4H, AreH), 7.50e7.77 (m, 8H, PceH), 7.36e7.38 (m,
4H, AreH), 6.30 (s, 4H, C]CH), 2.50 (s, 12H, CH3); MS(MALDIeTOF)
m/z: Calc. 1398; Found: 1363 [M ꢂ Cl]þ, 1328 [M ꢂ 2Cl]þ; Anal. Calc.
for C72H40N8O12Cl2Sn: C, 61.82; H, 2.88; N, 8.01; Found: C, 61.73; H,
2.96; N, 7.97.
7.85e7.95 (m, 4H, AreH), 7.18e7.42 (m, 8H, PceH), 7.05e7.08 (m,
4H, AreH), 6.36 (s, 4H, C]CH), 2.50 (s, 12H, CH3); MS(MALDIeTOF)
m/z: Calc.1345; Found: 1310 [M
C72H40N8O12ClRu: C, 64.26; H, 3.00; N, 8.33; Found: C, 64.31; H,
2.95; N, 8.25.
ꢂ
Cl]þ; Anal. Calc. for
3. Results and discussion
2.4.3. Synthesis of 2,9,16,23-tetrakis(7-coumarinoxy-4-methyl)-
phthalocyaninatoindium (4b)
3.1. Synthesis and characterization
Compound 4b was prepared and purified according to the
procedure described for 4a, starting from InCl3ꢃ4H2O (0.234 g,
0.8 mmol), 7-(3,4-dicyanophenoxy)-4-methylcoumarin (0.906 g,
3 mmol), DBU (10 drops) and octanol 40 ml. Yield: 0.589 g,
57.8%; m.p.: >300 OC; IR nmax/cmꢂ1 (KBr pellet): 3064 (CHar),
2921e2851(CHalkyl), 1717(C]O), 1605(C]C), 1271(AreOeAr0);
The route for the synthesis of 2,9,16,23-tetrakis(7-coumarinoxy-
4-methyl)-metallophthalocyanines 4a, 4b, 4c is given in Scheme 1.
7-(3,4-dicyanophenoxy)-4-methylcoumarin 3 was prepared by
a base catalyzed nucleophilic aromatic nitro displacement of 7-
hydroxy-4-methylcoumarin
1
with 4-nitrophthalonitrile
2
1H NMR (CDCl3)
d
ppm: 9.03e9.11 (m, 4H, PceH), 8.68e8.72 (m,
according to the published procedures [29]. The reaction was
carried out by using K2CO3 as the nitro-displacing base at room
temperature in dried dimethylformamide as the solvent.
Therefore cyclotetramerization of 7-(3,4-dicyanophenoxy)-4-
methylcoumarin 3 in the presence of RuCl3ꢃ3H2O, InCl3ꢃ4H2O or
SnCl2ꢃ2H2O and DBU in octanol gave the 2,9,16,23-tetrakis (7-
coumarinoxy-4-methyl) substituted Ruthenium, Indium or Tin
phthalocyanine derivatives respectively.
4H, AreH), 7.83e7.86(m, 4H, AreH), 7.58e7.72 (m, 8H, PceH),
7.34e7.29 (m, 4H, AreH), 6.24 (s, 4H, C]CH), 2.49 (s, 12H, CH3);
MS(MALDIeTOF) m/z: Calc. m/z: Calc.1358; Found:1323
[M ꢂ Cl]þ; Anal. Calc. for C72H40N8O12ClIn: C, 63.61; H, 2.97; N,
8.24; Found: C, 63.55; H, 2.93; N, 8.12.
2.4.4. Synthesis of 2,9,16,23-tetrakis(7-coumarinoxy-4-methyl)-
phthalocyaninatotin (4c)
Compound 4c was prepared and purified according to the
procedure described for 4a, starting from SnCl2ꢃ2H2O (0.180 g,
Spectral data of the newly synthesized compounds are consis-
tent with the proposed structures. Comparison of the IR spectral
data clearly indicated the formation of compound 3. The new bands

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J.-J. Guo et al. / Dyes and Pigments 93 (2012) 1463e1470
Table 1
Fluorescence and UVevisible spectral properties of 4a, 4b, 4c in DMF.
Compound Q-band Excitation Emission Stokes Fluorescene
wavelength wavelength wavelength shift
quantum yield
FF
(nm)
(nm)
(nm)
(nm)
(
)
4a
4b
4c
650
693
678
677
687
703
694
697
704
17
10
1
0.005
0.016
0.009
the three sets of aromatic protons at 9.16e9.22, 8.02e8.12,
7.36e7.38 ppm as multiplets. The spectrum also gives two sets of Pc
rings at 9.55e9.66, 7.50e7.77 ppm as multiplets means 12 protons
too. The unsaturated protons at 6.30 ppm and methyl protons at
2.50 ppm as signets indicate each 4 protons at the same time. The
mass spectra which were obtained by MALDIeTOF (2,5-
dihydroxybenzoic acid was used as matrix) were consistent with
assigned formulations without chlorine atoms [32].
Survey XPS scans show the presence of C, O, N, Cl and the cor-
responding metal with no other elements being observed
[33,34,35]. Fig. 1. shows the XPS spectrum of 4c as an example: C 1s
(284.6 eV), O 1s (531.9 eV), N 1s (398.5 eV). The XPS Cl 2p spectrum
consists of 2p3/2 and 2p1/2 with the intensity ratio 2:1. The
components are located at 198.3 and 200.0 eV that corresponds to
the MeCl bonding [33,35]. The binding energy of the Sn 3d5/2 level
is measured to be 487.1 eV and the 3d3/2 is 495.5 eV. Other than the
identical N 1s, O 1s, C 1s and Cl 2p peaks, the XPS spectra for 4a and
4b show Ru 3d5/2 and In 3d5/2 peaks at 281.1 and 444.91 eV,
respectively. Most importantly the XPS determined N:Metal:Cl
ratio are 8:1:1, 8:1:1 and 8:1:2 for 4a, 4b and 4c in excellent
agreement with the stoichiometry of the complexes.
Fig. 1. XPS spectrum of 4c.
of AreOeAr at 1265 cmꢂ1 and disappearance of the eOH and eNO2
bands at 3500 cmꢂ1 and 1536e1349 cmꢂ1 prove the compound 3
was formed. All the complexes show peaks between 1000 and
700 cmꢂ1 which may be assigned to phthalocyanines skeletal
vibrations [30]. The complexes show characteristic vibrations due
to aromatic CH stretching at ca. 3061e3065 cmꢂ1,carbonyl C ¼ O
stretching at ca. 1717e1732 cmꢂ1 and ether group (CeOeC) at
1261e1273 cmꢂ1
.
The 1H NMR spectra of phthalocyanines 4ae4c are almost
identical. The expected signals are observed in accordance with the
proposed phthalocyanine structures [31]. Both complex types are
expected to have isomers due to the presence of a substituent on
either peripheral position. 4a shows two sets of multiplets at
9.24e9.33 and 7.85e7.95 ppm for the phthalocyanine ring, inte-
grating for 12 protons. The aromatic protons are observed as
multiplets at 8.85e8.93, 7.85e7.95, 7.05e7.08 ppm integrating 12
protons. Unsaturated and methyl protons are appeared at 6.36 ppm
(4 protons) and 2.50 ppm (12 protons) as singlets. 4b also give
similar signals with 2 sets of multiplets for Pc ring at 9.03e9.11,
7.58e7.72 ppm and 12 protons for aryl protons at 8.68e8.72,
7.83e7.86, 7.29e7.34 ppm respectively. And 4 unsaturated protons
at 6.24 ppm and 12 methyl protons at 2.49 ppm as signets are found
too. The 1H NMR of 4c shows similar spectral figures as 4a, 4b with
3.2. Ground state electronic absorption
The ground state electronic absorption spectra (Fig. 2.) show
monomeric behavior evidence by a single Q-band, typical of met-
allophthalocyanine complexes [36].
The
pep
* Soret transition toward the second singlet excited
state is observed at around 320 nm. The shoulder between 400 and
460 nm may due to a charge transfer from the electron-rich
phthalocyanine ring to the electron-poor central metal. The Q-
bands are seen in the near infrared region 600e720 nm. It is
Fig. 3. Aggregation behavior of 4b in DMF at different concentrations: (A) 2.5 ꢄ 10ꢂ6
(B) 5 ꢄ 10ꢂ6, (C) 10 ꢄ 10ꢂ6, (D) 15 ꢄ 10ꢂ6 and (E) 20 ꢄ 10ꢂ6 M.
,
Fig. 2. Ground state electronic absorption spectra of 4a, 4b, 4c in DMF.

J.-J. Guo et al. / Dyes and Pigments 93 (2012) 1463e1470
1467
reported, for phthalocyanines, loss of symmetry will result in
splitting of spectra [37]. All of the three metallophthalocyanines in
our research show splitting Q-bands for that Ru, In and Sn are larger
metal not fitting into the Pc ring.
studied metallophthalocyanines (4ae4c). The BeereLambert law
was obeyed for all of the three compounds at concentrations
ranging from 2.5 ꢄ 10ꢂ6 to 2 ꢄ 10ꢂ5 M.
The Q-band absorption maxima in DMF of the three metal-
lophthalocyanines are observed at different wavelength. As shown
in Table 1, 4b (Q-band at 693 nm) and 4c (Q-band at 678 nm) are
bathochromic-shifted relative to 4a (Q-band at 650 nm) which
agrees with the electronegativity of the central metal.
Aggregation is usually depicted as a coplanar association of
rings progressing from monomer to dimmer and higher
order complexes. It is dependent on the concentration, nature of
3.3. Fluorescence spectra and properties
Shown in Fig. 4, are the Q-bands absorption, fluorescence exci-
tation and emission spectra of the metallophthalocyanines 4ae4c
in DMF. The shapes of excitation spectra were similar to the
absorption spectra and are mirror images to the fluorescence
emission spectra for all the phthalocyanines (4ae4c). Fluorescence
emission peaks were observed at: 694 nm for 4a, 697 nm for 4b and
704 nm for 4c in DMF. The fluorescence excitation and emission
spectra of Complexes are typical of phthalocyanines, with Stokes’
the
solvent,
nature
of
the
substituents,
complexed
metalions and temperature [38]. In this study, the aggregation
behavior of 7-hydroxy-4-methylcoumarin tetrasubstituted metal-
lophthalocyanines (4ae4c) was investigated at different concen-
trations in DMF (Fig. 3. for complex 4b as an example). As the
concentration was increased, the intensity of the absorption of the
Q-band maxima also increased and there were no new bands
(normally blue shifted) due to the aggregated species for all the
shifts (lEm
maxima of excitation and absorption spectra are different
Dl lExci lQ), especially for 4a (27 nm) and 4c (25 nm), sug-
ꢂ
lExci) ranging from 1 to 17 nm (Table 1). The Q-bands
(
¼
ꢂ
gesting a large structure change between the ground and excited
states. These phenomena are attributed to the fact that Ru, In and
Sn are metals with large atomic numbers that can be displaced
a
b
c
Fig. 4. UVevis absorption (Abs), excitation (Exci) and fluorescene emission (Emi) spectra of compound 4a, 4b, 4c in DMF. Excitation wavelengths: 610 nm for 4a, 618 nm for 4b and
635 nm for 4c.

1468
J.-J. Guo et al. / Dyes and Pigments 93 (2012) 1463e1470
Fig. 7. SterneeVolmer plots for benzoquinone (BQ) quenching of 4a, 4b, 4c. [MPc]:
1.00 ꢄ 10ꢂ5 M in DMF. [BQ] ¼ 0, 0.008, 0.016, 0.024, 0.032, 0.040 M.
Table 3
Fluorescence quenching data for 4a, 4b, 4c in DMF.
Fig. 5. Photoluminescence decay curve of 4a, 4b, 4c in DMF.
Compound
KSV (Mꢂ1
)
kq/1010 (Mꢂ1 Sꢂ1
)
4a
4b
4c
35.86
26.61
22.99
0.8
29.6
5.75
Table 2
Fluorescence lifetime of 4a, 4b, 4c in DMF.
Compound
s1/ns
a1/%
s2/ns
a2/%
4a
4b
4c
4.5
0.09
0.4
87.44
97.70
85.29
1.41
1.84
1.97
12.65
2.30
14.71
heavier metal Sn enhances more intersystem crossing (through
spin orbit coupling), then afford lower FF. The lowest fluorescence
quantum yield observed for 4a is due to the open-shell nature of
a
normalized (to 100) fractional amplitude.
the metal which promotes dep interactions thereby quenching the
singlet state of the complexes. Also the enhanced spin orbit
coupling might be responsible for the lowering of fluorescence
quantum yields [41].
from the core of the Pc ring on excitation, hence resulting into a loss
of symmetry [39].
Fig. 5 shows the time-resolved fluorescence decay curve for 4a,
4b and 4c in DMF, indicating a biexponential decay. Fluorescence
3.4. Fluorescence quantum yields (FF) and fluorescence lifetime (sF
)
lifetime (sF) refers to the average time a molecule stays in its
The fluorescence quantum yields (FF) of compounds 4a, 4b, 4c
are given in Table 1. The FF values are found be less than 0.1 due to
the presence the heavy atom (Ru, In, and Sn). The values of FF vary
much upon the central metals. Because of different spineorbit
coupling for different metals, the heavier the central metal is, the
stronger the spineorbital coupling and the shorter the energy gap
between S1 and T1 states, and therefore the more probability of
intersystem crossing from S1 to T1 states, which results in low
quantity of FF [6,40]. Both 4b and 4c are close shell MPcs, the
excited state before fluorescing. The nature and the environment
of a fluorophore determine its fluorescence lifetime. Shown in
Table 2, are the two kinds of lifetime of metallophthalocyanines
4ae4c of S1 state. The shorter lifetime s1 of 4b and 4c is due to
the intersystem crossing processing to the triplet state enhanced
by In and Sn atom [6]. The lifetime of 4a is extraordinarylonger
than 4b and 4c for the nature of Ru metal. 4a, 4b and 4c have
a similar lifetime of s2. This emission of the photoproduct is due
to the photo-induced metal ejection process. It is as a result of
photoexcitation, the metal ion changes its position in a vertical
direction with respect to the plane of phthalocyanine macrocycle.
If the metal does not return quickly (on S1 surface) to its
chelating ring an emission characteristic for metal-free phthalo-
cyanine could be recorded [39,42,43]. The elemental analysis of
the samples can not show the presence of such impurity at the S0
state. In our study, Both 4a and 4c show larger Dl
(
lExci
ꢂ
lQ) so
the proportion of s2 is more than that of 4b. While the amplitude
of s2 is significantly smaller than that of s1 indicating s1 is the
main decay of the three compounds.
Table 4
Thermal properties of 4a, 4b, 4c.
Compound
T5% (ꢀC)a
D (ꢀC)b
Yc (%)c
4a
4b
4c
322
370
175
400
450
191
65.3
65.2
59.4
a
The temperature for which the weight loss is 5%.
The temperature for which the compound is decomposed.
Char yield at 600 OC.
b
c
Fig. 6. Fluorescence emission spectral changes of 4b (1.00 ꢄ 10ꢂ5 M) on addition of
different concentrations of BQ in toluene. [BQ] ¼ 0, 0.008, 0.016, 0.024, 0.032, 0.040 M.

J.-J. Guo et al. / Dyes and Pigments 93 (2012) 1463e1470
1469
4. Conclusions
In the present work, we have successfully synthesized three
novel 7-hydroxy-4-methylcoumarin tetrasubstituted metal-
lophthalocyanines with axial chloride ligand (4a, 4b, 4c). All of the
three phthalocyanines show excellent solubility in various solvents
such as acetone, tetrahydrofurane, chloroform, dichloromethane,
dimethylformamide and dimethylsulfoxide. In the ground state
absorption all of the three metallophthalocyanines show splitting
Q-bands for that Ru, In and Sn are large metals not fitting into the Pc
ring. The open-shell metallophthalocyanine (4a) shows the lowest
fluorescence quantum yields for dep interactions and spin orbital
coupling effect; while it appears the highest fluorescence lifetime
owing to the relatively lower atomic number.
The order of fluorescence quantum yields is 4b > 4c > 4a and
the main fluorescence lifetime (s1) is 4a >4c > 4b. This work also
presents the light harvesting and energy transducing tendencies of
the mixtures of metallophthalocyanine complexes with BQ. 4b
shows the highest kq value and 4a shows the lowest which is in
accordance with fluorescence quantum yields (FF). All of the three
metallophthalocyanines could serve as good light harvesters and
energy transducers. Both 4a and 4b show high thermal stability
than 4c.
Fig. 8. The TGA profile of 4a, 4b, 4c.
3.5. Fluorescence quenching studies by 1,4-benzoquinone [BQ]
Acknowledgments
The fluorescence quenching of substituted phthalocyanine
complexes (4a, 4b, 4c) by BQ in different concentration is found
to obey SterneVolmer kinetics. An essential requirement for good
light harvesting materials is the ability to undergo excited state
charge transfer with ease. The energy of the lowest excited state
for quinones is greater than the energy of the excited singlet state
of MPc complexes [44]. Therefore metallophthalocyanine fluo-
rescence quenching by BQ is via excited state electron transfer,
from the metallophthalocyanine to the BQ [45]. It is observed
that fluorescence spectrum when taken with increasing concen-
tration of BQ does not show any shift in wavelength. There is no
additional peak appearing; hence there could not be any ground-
This work was financially supported by Natural Science Foun-
dation of Tianjin China (08JCZDJC16900), Natural Science Founda-
tion of China (NSFC 21176180) and Research Fund for the Doctoral
Program of Higher Education of China (20100032110021).
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