Synthesis and photophysical properties phthalocyanine-pyrene dyads

Article abstract of DOI:10.1016/j.dyepig.2011.08.013

Metal-free, zinc (II) and nickel(II) phthalocyanines (3-5) with a 1-pyrenylmethoxy substituent on each benzo group were prepared from 4-(1-pyrenylmethoxy)phthalonitrile (2). The new compounds have been characterized by elemental analyses, IR, UV/vis, mass

Full text of DOI:10.1016/j.dyepig.2011.08.013

Dyes and Pigments 92 (2012) 954e960
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Dyes and Pigments
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Synthesis and photophysical properties phthalocyanineepyrene dyadsq
a
b
a,
_
*
Ibrahim Özces¸ meci , Ali Gelir , Ahmet Gül
a Department of Chemistry, Technical University of Istanbul, Maslak 34469, Istanbul, Turkey
b Department of Physics, Technical University of Istanbul, Maslak 34469, Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Metal-free, zinc (II) and nickel(II) phthalocyanines (3e5) with a 1-pyrenylmethoxy substituent on each
benzo group were prepared from 4-(1-pyrenylmethoxy)phthalonitrile (2). The new compounds have
been characterized by elemental analyses, IR, UV/vis, mass and 1H NMR spectroscopy. The electronic
Received 27 May 2011
Received in revised form
9 August 2011
Accepted 21 August 2011
Available online 8 September 2011
spectra exhibit an intense pep
* transition of pyrene unit identity together with characteristic Q and B
bands of the phthalocyanine core. The energy transfer to phthalocyanine core and radiative decays of the
pyrene emission and phthalocyanine core were examined. Energy transfer through methoxy bridges has
been confirmed by ultraviolet irradiation of pyrene antenna leading to red light emission in 3 and 4.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Phthalocyanine
Pyrene
Antenna effect
Energy transfer
Fluorescence
Synthesis
1. Introduction
serve as models for the study of energy and electron-transfer
processes in artificial photosynthetic systems. Organic materials
Phthalocyanines (Pcs) with planar or nearly planar structures have
an extended network of -electrons. Because of their special elec-
that absorb at various wavelengths of visible light and fluorescence
with high efficiency are good candidates for organic photoelec-
tronic devices such as photosensitizing solar cells [13] and organic
light emitting diodes [14].
p
tronic and optical properties and good processibility, substituted
phthalocyanines have established themselves in many applied fields
such as active materials for organic electronics [1], gas sensors [2],
photovoltaic cells [3], electrochromic devices [4] nonlinear optics [5],
photodynamic reagents for cancer therapy [6] and electrocatalytic
reagents [7]. Their high thermal and chemical stability, well defined
optical absorption, semiconducting and photoconducting properties,
ability to coordinate a large variety of central atoms and the ease of
their preparation add to their broad applicability [8]. It is well known
that the electrochemical and spectroscopic properties of phthalocy-
anine derivatives can be tuned by varying the central metal atom,
Phthalocyanines exhibit excellent chemical and photochemical
properties, but poor fluorescent properties [15]. The interaction of
a fluorescence probe with a phthalocyanine core may change the
fluorescent characteristics of the aromatic structure. For example, it
may be the binding process where fluorescent probe bind chemi-
cally or physically to the phthalocyanine molecules, thereby
causing a shift in their fluorescence spectra or a change in the
fluorescence intensity [16,17]. On the other hand, pyrene (Py) and
its derivatives, having a high quantum yield and lifetime (0.65 and
410 ns, respectively, in ethanol at 293 K), have been used as valu-
able molecular probes for fluorescence spectroscopy. Its fluores-
cence emission spectrum is very sensitive to the solvent polarity, so
Py has been used as a probe to determine solvent environments.
This is due to its excited state having a different, non-planar
structure than the ground state [18].
changing the size of the
p-conjugation, or alternating the type,
number, and positions of the substituents on the macrocycle ligands
[9e12].
Despite the considerable use of individual Pc as chromophores,
multichromophoric systems where Pc are covalently linked to
other electro or photoactive units such as organic moieties that
have fluorescent nature are of great interest. These systems can also
As an energy transfer process, “Antenna effect”, where the
fluorescent moiety has been attached directly to the unsaturated
macrocycle or fused to it, has been frequently used, but the
combination of these two functionalities through saturated groups
as in the case of Pc derivatives is rather rare [19,20].
q
Dedicated to Professor Michael Hanack on the occasion of his 80th birthday.
* Corresponding authors. Tel.: þ90 212 285 68 27; fax: þ90 212 285 63 86.
E-mail address: ahmetg@itu.edu.tr (A. Gül).
0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2011.08.013

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955
The aim of the present work was to synthesize a series of
metallo and metal-free phthalocyanines functionalized with
peripheral 1-pyrenylmethoxy substituents and to explore the
energy transfer between the Py units and the macrocyclic core. Py
has been chosen as a substituent for this study as it is a thermally
very stable unit which can act as an antenna to harvest and transfer
energy efficiently to longer wavelength emitters in blends or
composite structures [21]. Here we report the consequence of
1-pyrenylmethoxy substituent on the intensity of the fluorescence
emission spectra of metal-free and zinc Pcs as well as its effect on
energy transfer to phthalocyanine core.
(eNH), 3042 (AreH), 2948 (alkyl-CH), 1215 (CeOeC); 1H NMR
(d-DMSO): 8.24e7.33 (br, 48H, AreH), 5.90 (br s, 8H, OCH2), ꢁ4.05
(bs, 2H, eNH); UVeVis lmax (nm) (log ) in THF: 726 (5.14), 694
3
(5.13), 341 (5.27), 326 (5.18), 282 (5.13), 269 (4.95); Anal. calcd. for
C100H58N8O4; C, 83.66; H, 4.07; N, 7.81; found: C, 83.82; H, 4.16;
N, 7.68%. MS: m/z 1435.24 [M]þ.
2.2.3. Tetra(1-pyrenylmethoxy)phthalocyaninatozinc (II) (4)
A mixture 0.5 mmol (0.179 g) of 4-(1-pyrenylmethoxy)phtha-
lonitrile (2) and 0.125 mmol (0.023 g) of anhydrous Zn(OAc)2 with 2
drop DBU in 1.5 ml hexanol was heated and stirred at 160 ꢀC for 6 h
under N2 in a sealed tube. After cooling to room temperature, the
suspension was dissolved in 1 ml DMF and poured into 150 ml ice-
water mixture. After that, precipitated greeneblue solid was
filtered off. The precipitate was first refluxed in chloroform and
then washed subsequently with ethanol and acetone and then
dried in vacuo. Purification of the product was accomplished by
column chromatography on silica gel first with ethanol then with
2. Experimental
2.1. Equipments and materials
IR spectra were recorded on a PerkineElmer Spectrum One
FT-IR spectrometer, electronic spectra on a Scinco Neosys-2000
double-beam ultravioletevisible (UVevis) spectrophotometer
using 1 cm path length cuvettes at room temperature. Elemental
analyses were performed by the Instrumental Analysis Laboratory
of the TUBITAK Marmara Research Centre. 1H NMR spectra were
recorded on a Bruker 250 MHz spectrometer using TMS as internal
reference. Mass spectra were performed on Ultima Fourier Trans-
form and Varian 711 mass spectrometer. Fluorescence excitation
and emission spectra were recorded by using Varian Cary Eclipse
Fluorescence Spectrophotometer. All reagents and solvents were of
reagent grade quality obtained from commercial suppliers. All
solvents were dried and purified according to [22]. The homoge-
neity of the products was tested in each step by TLC (SiO2).
4-nitrophthalonitrile was prepared according to a reported proce-
dure [23]. 1-pyrenylmethanol (1) was prepared according to a re-
ported procedure [24].
THF as the eluent. Yield: 52 mg (27.8%); m.p. > 200 ꢀC. IR (cmꢁ1):
y
3037 (AreH), 2952 (alkyl eCH), 1215 (CeOeC); 1H NMR (d-DMSO):
8.24e7.71 (br, 48H, AreH), 5.95 (br s, 8H, OCH2); UVeVis lmax (nm)
(log ) in THF: 679 (5.21), 346 (5.39), 331 (5.27), 282 (5.16), 268
3
(4.97); Anal. calcd. for C100H56N8O4Zn; C, 80.13; H, 3.77; N, 7.48;
found: C, 80.22; H, 3.68; N, 7.54%. MS: m/z 1497.98 [M]þ.
2.2.4. Tetra(1-pyrenylmethoxy)phthalocyaninatonickel (II) (5)
A mixture 0.5 mmol (0.179 g) of 4-(1-pyrenylmethoxy)phtha-
lonitrile (2) and 0.125 mmol (0.016 g) of anhydrous NiCl2 with 2
drop DBU in 1.5 ml hexanol was heated and stirred at 160 ꢀC for 6 h
under N2 in a sealed tube. After cooling to room temperature, the
suspension was dissolved in 1 ml DMF and poured into 150 ml ice-
water mixture. After that, precipitated greeneblue solid was
filtered off. The precipitate was first refluxed in chloroform and
then washed subsequently with ethanol and acetone and then
dried in vacuo. Purification of the product was accomplished by
column chromatography on silica gel first with ethanol then with
2.2. Synthesis
2.2.1. 4-(1-pyrenylmethoxy)phthalonitrile (2)
THF as the eluent. Yield: 55 mg (29.6%); m.p. > 200 ꢀC. IR (cmꢁ1):
y
4-Nitrophthalonitrile (0.173 g, 1.0 mmol) and 1-pyrenylmethanol
(1) (0.232 g, 1.0 mmol) were added successively with stirring to dry
DMSO (10 ml). After they were dissolved, anhydrous K2CO3 (0.5 g,
3.5 mmol) was added portion wise over 2 h and the mixture was
stirred vigorously at room temperature for further 24 h. Then, the
reaction mass was poured into cold water (50 ml) and the precipitate
formed was filtered off, washed successively first with water, then
with cold hexane, and then with cold diethyl ether and dried in vacuo.
3032 (AreH), 2948 (alkyl eCH), 1219 (CeOeC); 1H NMR (d-DMSO):
8.09e7.63 (br, 48H, AreH), 5.85 (br s, 8H, OCH2); UVeVis lmax (nm)
(log ) in THF: 684 (5.15), 347 (5.32), 332 (5.14), 283 (5.13), 269
3
(4.94); Anal. calcd. for C100H56N8NiO4; C, 80.13; H, 3.78; N, 7.51;
found: C, 80.31; H, 3.62; N, 7.64%. MS: m/z 1493.28 [Mþ1]þ.
2.3. Fluorescence studies
Yield: 235 mg (65.6%); m.p. 194 ꢀC. IR,
y
(cmꢁ1): 3081e3043
Comparative method was used to determine the quantum yields
of the compounds (3 and 4) as described in [18]. In this method, the
quantum yield of a compound is determined by using a standard
which has similar fluorescence properties as the compound has.
Also at least 5 samples of the standard and the compound with
different concentrations must be prepared to be able to carry out
the relation between the absorbance and the fluorescence emis-
sion. All measurements of the standard and the compound must be
performed at the same environmental conditions with the same
instrumental settings.
(AreH), 2918 (alkyl-CH), 2229 (C^N), 1251 (CeOeC); 1H NMR
(d-DMSO):8.34e7.67 (br, 12H, AreH), 5.90 (br s, 8H, OCH2) UVeVis
lmax (nm) (log ) in THF: 345 (4.60), 329 (4.44), 275 (4.72), 266 (4.53);
3
Anal. calcd. for C25H14N2O; C, 83.78; H, 3.94; N, 7.82; found: C, 83.92;
H, 3.86; N, 7.65%; MS: m/z 358.22 [M]þ.
2.2.2. Tetra(1-pyrenylmethoxy)phthalocyanine (3)
A mixture 0.5 mmol (0.179 g) of 4-(1-pyrenylmethoxy)phtha-
lonitrile (2) and 1.0 mmol of lithium metal in 1.5 ml of pentanol was
heated and stirred at 142 ꢀC for 2 h under N2 in a sealed tube. The
resulting green suspension was cooled to ambient temperature.
After that, reaction mass was dissolved in 1 ml DMF and poured
into 100 ml ice-water mixture with the addition 4 ml conc HCl. In
this mixture Li2Pc formed was converted into H2Pc. The precipitate
formed was filtered off and the crude product was subsequently
treated with boiling acetone, ethanol, hexane and then dried in
vacuo. Purification of the product was accomplished by column
chromatography on silica gel first with ethanol then with THF as
The quantum yield of a compound according to comparative
method is given by Eq. (1):
slopeðAc ꢁ IcÞ n2c
FF;C
¼
FF;std
(1)
2
slopeðAstd ꢁ Istd
Þ
nstd
where FF,C and FF,std are the quantum yields of the compound
and the standard, nc and nstd are the refractive indices of the
solution of the compound and the standard, slope (Ac ꢁ Ic) and
slope (Astd ꢁ Istd) are the slopes of the graphs plotted between the
eluent. Yield: 46 mg (25.7%); m.p. > 200 ꢀC. IR
y
(cmꢁ1): 3264

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integrals of the fluorescence spectra and the absorbances for the
compound and the standard at different concentrations,
respectively.
In this paper Rhodamine-101 (S) was used as standard which
has excitation and emission peaks at 369 nm and 586 nm,
respectively, and has quantum yield, FF ¼ 1 in ethanol [18]. These
wavelengths are in the region of the wavelengths of the compounds
(3) (lexc ¼ 347 nm, lem ¼ 728 nm) and (4) (lexc ¼ 347 nm,
lem ¼ 691 nm) studied in this work. 5 different concentrations of
(3), (4) and (S) ranging between 10ꢁ6 M and 10ꢁ7 M were used and
all measurements were performed at 20 ꢀC. The refractive indices of
(3), (4) and (S) are 1.464, 1.457 and 1.364, respectively.
Excitation energy transfer or resonance energy transfer (RET)
occurred from Py units of 3 and 4 to H2Pc core of 3 and ZnPc core of
4. This energy transfer from donor (Py units) to acceptor (H2Pc and
ZnPc core of 3 and 4) studies was determined according to the
Förster theory by accumulating both the donor and acceptor [25].
Transfer efficiency,
3 T, from donor to acceptor is given by
D A
DFA
I
3
¼
(2)
is the increase in the integral of the fluorescence emis-
T
I
where D A
I
sion spectra of the acceptor upon binding of donor to acceptor, ID is
the integral of fluorescence spectrum of the donor before binding to
the acceptor and FA is the quantum yield of the acceptor in the
absence the acceptor.
Scheme 1. Synthesis of 1-pyrenylmethoxy substituted phthalocyanines.
product obtained in these reactions is a mixture of positional
isomers which are expected to show chemical shifts that differ
slightly from each other. The inner NH protons of 3 were also
identified in the 1H NMR spectra with a broad chemical shift,
3. Results and discussions
The starting point for novel phthalocyanine structures with four
Py units bound to the periphery is through base-catalysed aromatic
nitro displacement of 4-nitrophthalonitrile with 1 in DMSO; K2CO3
was used as the base for this nucleophilic aromatic displacement
[26,27]. This reaction has been used in the preparation of a variety
of ether or thioether-substituted phthalonitriles [28e30]. The solid
product 2 was obtained in a yield of 65.6%.
Conversion of 2 into phthalocyanine was accomplished through
the usual cyclotetramerization reaction in the presence of a reduc-
tant and/or metal salt, i.e., lithium was used to obtain the metal-
free derivative 3, while the metal salt [Zn(OAc)2, NiCl2] and a suit-
able solvent, such as hexanol were required for the metal phtha-
locyanines 4 and 5 (Scheme 1). This procedure yields a mixture of
four geometric isomers with a 1-pyrenylmethoxy group at the 2- or
3- position of each benzo-ring in the phthalocyanine molecule.
These phthalocyanines are soluble to a certain extent in donor
solvents such as DMSO, DMF and THF. Characterization of the
products involved combination of elemental analysis and spectro-
scopic data (UVeVis, FT-IR, 1H NMR, and Mass spectroscopy).
Spectral investigations for all these products were consistent with
the assigned structures.
d
¼ ꢁ4.05 ppm as a consequence of the 18
planar molecule. 1H NMR spectra of 3e5 exhibited the aliphatic CH2
protons as a singlet peaks at around
¼ 5.85e5.95 ppm and the
aromatic protons as a broad peaks at around
¼ 7.33e8.24 ppm. In
p-electron system of the
d
d
the mass spectra of 3e5 the presence of the characteristic molec-
ular ion peaks at m/z ¼ 1435.24 [M]þ for 3, m/z 1497.98 [M]þ for 4
and m/z 1493.28 [Mþ1]þ for 5 confirmed the proposed structures.
Electronic absorption spectra of compounds 3e5 combine the
spectral features of both the phthalocyanines and the Py (Fig. 1).
The absorption spectrum of Py units is dominated by two intense
bands of similar intensity around 345 nm and 275 nm as observed
In the IR spectrum of dinitrile compound 2, aromatic CeH and
C^N stretching vibrations appeared at 3081e3043 cmꢁ1 and
2229 cmꢁ1, respectively. This sharp C^N peak disappeared in the IR
spectra of the phthalocyanines. In addition, the characteristic
vibrations of the aromatic CeH and aromatic CeOeC were
observed at 1598 and 1251 cmꢁ1, respectively. 1H NMR spectrum of
2 exhibited the aliphatic CH2 protons as a singlet at
and the aromatic protons at around
d
¼ 6.02 ppm
d
¼ 7.67e8.34 ppm. In the mass
spectra of 2 the presence of the characteristic molecular ion peaks
at m/z ¼ 358.22 [M]þ confirmed the proposed structure.
The 1H NMR spectra of compounds 3e5 are somewhat broader
than the corresponding signals in the starting dinitrile derivative.
This broadening is likely due to chemical exchange caused
by aggregationedisaggregation equilibria and the fact that the
Fig. 1. UV spectra of 3e5 (5 ꢂ 10ꢁ6 M) and 1e2 (2 ꢂ 10ꢁ5 M) in THF.

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957
in the spectra of compounds 1 and 2; after conversion into
phthalocyanine, on the other hand, electron absorption spectra of
compounds 3e5 have intense absorbtion around 345 nm due to the
overlap of phthalocyanine Soret band and the absorption of Py
units. Visible part of the spectrum around 600e700 nm (Q-band)
Triton X to the solutions (Fig. 3). The results indicate no appreciable
aggregation which can be decomposed by the addition of Triton X.
Changes in the absorbance values are only those which correspond
to lowering of the concentrations. By evaluating these observations,
it can clearly be concluded that the phthalocyanine derivatives
(3e5) did not show aggregation behaviour in THF at the concen-
tration range studied.
Fluorescence emission spectra of 1, S, 3 and 4 were represented
in Fig. 4. Since the fluorescence quantum yield (FF) of 5 is
predictably low (<0.01) due to the open-shell nature of the
attributed to the
pep
* transition from the highest occupied
molecular orbital (HOMO) to the lowest unoccupied molecular
orbital (LUMO) of the Pcꢁ2 ring. Metallophthalocyanine 4 and 5
showed intense single Q-band absorptions at 679 nm for 4 and
684 nm for 5, while metal-free phthalocyanine 3 showed the ex-
pected Q-band splitting around 694 nm and 726 nm as a result of
D2h symmetry. An apparent difference between the Q-band
absorption spectra of 4 and 5 is rather broad absorbances in the
higher energy side of the spectrum in nickel compound which
might be due to higher planarity and lower tendency to axial
coordination of the solvents [31,32].
Increasing the concentration leads to aggregation, which is
easily observed by the values of the Q-bands, which shift to higher
energies [33] by a parallel decrease in the molar absorption coef-
ficient. The aggregation behaviour of the phthalocyanine
complexes (3e5) were also investigated at different concentrations
in THF (Fig. 2). In THF, as the concentration was increased, the
intensity of absorption of the Q-band also increased and no new
bands (normally blue shifted) due to the aggregated species were
observed for the all phthalocyanine complexes (3e5). In addition,
apparent molar extinction coefficient of samples 3e5 in this
concentration range (2.0 ꢂ 10ꢁ5e6.125 ꢂ 10ꢁ7 M) remained almost
constant as expected from BeereLambert law as seen in Fig. 2. It
indicates the presence of mainly a pure monomeric form [34]. It is
generally accepted that addition of a surfactant, e.g. Triton X, leads
decomposition of aggregates. In order to verify this phenomena,
electronic spectra of the Pcs 3e5 were taken also after addition of
Fig. 2. Absorption spectra at different concentrations and LamberteBeer law plots of
3e5 in THF.
Fig. 3. Absorption spectral changes for 3e5 upon the addition of Triton X.

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I. Özces¸meci et al. / Dyes and Pigments 92 (2012) 954e960
0.6
0.5
0.4
0.3
0.2
0.1
0.0
1.0
0.8
0.6
0.4
0.2
0.0
400
500
600
700
800
0.00
0.02
0.04
0.06
0.08
0.10
Wavelength(nm)
Absorbance
Fig. 4. Fluorescence emission spectra of samples 3 (
), 4 ($$$$$$$$$), 1 ($$ - $$ - $$ -)
Fig. 5. Integrals of fluorescence spectra versus absorbances at different concentrations
for the samples S (C), 3 (B) and 4 ( ).
;
in THF and S (- - - -) in ethanol. The concentration of each sample is 2 ꢂ 10ꢁ7 M. The
excitation wavelengths are around 345 nm for samples 3, 4 and 1 and 369 nm for S.
emission spectrum of 1 and the excitation spectra of 3 and 4 is
observed in this figure. This overlap is a clear evidence of the energy
transfer from Py units to the Pc core of 3 and 4 after covalently
binding of 1 as substituents to Pc [18,37].
complexes [35], it was not included in this figure. As seen from this
figure that 3 and 4 have characteristic emission peaks of both Pcs
(728 nm and 688 nm) and Py (394 nm and 378 nm). By comparing
the emission spectra of 3 and 4, it can be concluded that the binding
of Zn into the cavity of Pc caused a blue shift from 728 nm to
688 nm in the emission spectrum [36]. Another important point in
this figure is the excimer emission [18] at around 465 nm appeared
in the fluorescence spectra of 3 and 4 which is not observable in the
fluorescence spectrum of 1. This excimer emission shows that in
both phthalocyanine complexes (3 and 4) the Py units around Pc
core come close enough to each other so as to make an excimer
energy level. One of the reasons to observe such an excimer
emission may be the aggregation of phthalocyanine complexes (3
or 4), but it has been clearly shown and discussed in detail in the
previous paragraphs that the phthalocyanine complexes (3 or 4) do
not aggregate in THF (Fig. 2). By eliminating the aggregation
probability, it may be concluded that the excimer energy level is the
intrinsic property of 3 and 4 meaning that the Py units around Pc
core are close enough to each other to form excimer energy level.
This excimer energy level may also be an indicator of the success of
the synthesis of complexes 3 and 4.
Fig. 7 shows the fluorescence spectra of 2 ꢂ 10ꢁ7 M 3 and
a mixture of 8 ꢂ 10ꢁ7 M 1 and 2 ꢂ 10ꢁ7 M H2Pc (tetra(acetox-
yethylthio) phthalocyanine) [38]. The latter has been preferred as
a similar Pc derivative without pyrenyl substituents. It is clearly
seen in this figure that the fluorescence emission intensity of the
free 1 is bigger than that of the covalently bound pyrenyl groups in
3. Since the distance between 1 and H2Pc molecules in the mixture
solution is sufficiently long, 1 cannot transfer its excitation energy
to H2Pc. However, after covalently binding of 1 to H2Pc to produce 3
by the mechanism described in Scheme 1, the fluorescence emis-
sion of bound 1 (Py units of 3) decreased considerably and a red-
shift from 717 nm to 728 nm occurred in the fluorescence emis-
sion of H2Pc core of 3. This decrease in the fluorescence emission
intensity of Py units of 3 can be considered as an indication of the
excitation energy transfer from Py units in 3 to the Pc core of 3 as
suggested before due to the overlap between the emission
The integrals of the fluorescence spectra of S, 3 and 4 with
respect to absorbances for different concentrations are given in
Fig. 5. By using the slopes of the plots in this figure and Eq. (1), the
quantum yields of 3 and 4 were calculated as 0.18 and 0.25,
respectively. It was recently shown by Bartelmess et al. [36] that
binding a Py unit to ZnPc as substituent does not change the
quantum yield of ZnPc. In this reference only one Py unit was
bonded to ZnPc as substituent and the quantum yield of ZnPc with
and without Py was determined as 0.27. In our study four Py units
were bonded to ZnPc and the quantum yield was calculated as 0.25.
It can be concluded from this comparison that substituting ZnPc
with Py units does not change the quantum yield considerably.
However, the situation for H2Pc is different than ZnPc. It was shown
in [36] and in this paper that upon binding Py units to H2Pc as
substituents, the quantum yield decreases depending on the
number of the substituents. In [34], after binding one Py unit, the
quantum yield decreased to 0.28 from 0.34 and here in this paper it
decreased to 0.18 after binding four Py units as substituents. It can
be clearly concluded that substituting H2Pc with Py units changes
the quantum yield considerably.
1.0
0.8
0.6
0.4
0.2
0.0
300
350
400
450
500
Wavelength (nm)
Fig. 6. Fluorescence excitation spectra of samples 3 (
), 4 ($$$$$$$$$), and the
In Fig. 6 the excitation spectra of 3, 4 and the emission spectrum
of 1 were represented together. A considerable overlap between the
fluorescence emission spectrum of 1 (- - - -) in THF. The concentration of each sample
is 2 ꢂ 10ꢁ7 M. The excitation wavelength for 1 is 345 nm.

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959
80
60
40
20
0
calculated as 0.64 and 0.66, respectively. Such high energy transfer
efficiency values can be explained by the stable absorption energy
levels of both the donor and the acceptors. As seen in Fig. 1 that the
absorption spectra of the donor and the acceptors did not change
considerably before and after conjugation.
4. Conclusion
In summary, we have synthesized and characterized new
phthalocyanines bearing four 1-pyrenylmethoxy pendant arms
peripherally. These phthalocyanines emit essentially red light after
selective ultraviolet or visible irradiation. In the case of ultraviolet
irradiation, these systems comprising central phthalocyanines
linked to peripheral photon-harvesting pyrene moieties have been
shown to act as efficient antennas. Since the absorption energy
levels were not affected upon binding, efficient energy transfers
were calculated. Also it was concluded that binding of Py units to
ZnPc did not change the quantum yield of ZnPc while it changed the
quantum efficiency of H2Pc considerably.
400
500
600
700
800
Wavelength (nm)
Fig. 7. Fluorescence emission spectra of 2 ꢂ 10ꢁ7 M sample 3 (- - - -) and mixture of
8 ꢂ 10ꢁ7 M 1 and 2 ꢂ 10ꢁ7 M H2Pc (Tetra(acetoxyethylthio) phthalocyanine) in THF.
The excitation wavelength is 345 nm for each sample.
Acknowledgement
spectrum of 1 and the excitation spectrum of 3 in Fig. 6. In addition
to this decrease, an increase in the fluorescence emission of H2Pc
core of 3 is expected. But this was not observed in Fig. 7. This may be
due to the lower quantum yield of 3, FF ¼ 0.18, in comparison with
the quantum yield of unconjugated H2Pc, FF ¼ 0.34 [36].
The fluorescence spectra of 2 ꢂ 10ꢁ7 M 4 and the mixture of
8 ꢂ 10ꢁ7 M 1 and 2 ꢂ 10ꢁ7 M ZnPc (tetra(acetoxyethylthio) zinc(II)
phthalocyanine without Py units) [38] are represented in Fig. 8. The
results obtained from the fluorescence spectrum of 4 are very
similar to the results obtained for 3 (Fig. 7). As observed in 3, after
covalently binding of 1 to ZnPc, the fluorescence emission intensity
of Py units of 4 decreased considerably. As mentioned in the above
paragraph that this decrease in the fluorescence emission of Py
units of 4 indicates that the energy of the excited Py units in 4 is
transferred to the ZnPc core of 4. In addition to this decrease, an
increase in the fluorescence emission of ZnPc core of 4 was also
observed.
This work was supported by the Research Fund of the Technical
University of Istanbul.
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