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Synthesis and characterization of new polyfluorinated dendrimeric phthalocyanines
Polyhedron 29 (2010) 2710–2715
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Synthesis and characterization of new polyfluorinated dendrimeric phthalocyanines _ Mukaddes Özçesßmeci, Ibrahim Özçesßmeci, Esin Hamuryudan * Department of Chemistry, Istanbul Technical University, Maslak TR34469, Istanbul, Turkey
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Article history: Received 29 April 2010 Accepted 23 June 2010 Available online 1 July 2010 Keywords: Fluorinated Phthalocyanines Benzyloxy groups Aggregation Energy transfer
a b s t r a c t The synthesis of new polyfluorinated dendrimeric metallophthalocyanines (M = Zn, Ni, Co) bearing 3,5bis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)benzyloxy moieties (2–4) was achieved by cyclotetramerization of phthalonitrile derivative 1 in the presence of zinc, nickel or cobalt salts in DMF. All the target phthalocyanines were separated by column chromatography and their spectroscopic, fluorescence and energy transfer properties, and aggregation behavior were investigated in different solvents and at different concentrations in chloroform. The compounds were characterized by Fourier transform-infrared, fluorine, proton and carbon nuclear magnetic resonance, mass, ultraviolet–visible and fluorescence spectral data. The phthalocyanines (2–4) were extremely soluble in various organic solvents, such as tetrahydrofuran, acetone and dichloromethane. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Phthalocyanines (Pcs) have a two-dimensional 18 p-electron conjugated system thereby allowing the incorporation of more than 70 different metal or non-metal ions into their inner core. Modifications in the macrocycle can be made either by introduction of different central ions or by substitution of functional groups at the peripheral sites of the ring. During recent decades, metal phthalocyanines have found widespread application not only as pigments and dyes but also as chemical sensors, liquid crystals, Langmuir–Blodgett films, catalysts, non-linear optical materials, optical data storage materials, carrier generation materials in near-IR and also in medicine [1–5]. For such applications, good solubility is preferred. A critical disadvantage of unsubstituted Pcs is their low solubility in organic solvents or water. By appropriate substitution with bulky or long-chain groups in the peripheral positions of the macrocycle, these compounds can be solubilized in common organic solvents, thus increasing the field of possible applications [6–14]. Redox-active d-metal (e.g. Fe, Mn, Co) phthalocyanines exhibit very high catalytic activity in the oxidation of thiols, hydrocarbons, hydroquinones, arenes and amines [15–18]. The most promising way to increase the first oxidation potential of phthalocyanine complexes is the introduction of electron-withdrawing substituents. It has been shown that halogenated metallo tetrapyrrole derivatives are very efficient catalysts for oxidation reactions under very mild conditions [19,20].
* Corresponding author. Tel.: +90 2122856826; fax: +90 2122856386. E-mail address: [email protected] (E. Hamuryudan). 0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2010.06.023
Fluorinated metal phthalocyanines and porphyrins currently receive a great deal of attention due to their interesting electrontransfer, photosensitizing properties, along with magnetic and thermal characteristics [21–24]. The presence of pentafluorophenyl groups on the macrocycle ring can increase the catalytic activity and stability [25]. Fluoro-substituted phthalocyanines are known for their high solubility, even in polar, aprotic solvents. The increased solubility may be due to fluorine, which has the highest electronegativity of all elements [26]. In our previous studies, we have reported the synthesis, electrochemical and spectroelectrochemical properties of symmetric and asymmetric phthalocyanines [27–33]. In this step, our aim has been to design new molecules with dendritic fluoro-substituents, enhancing their solubility in common solvents and at the same time prohibiting their aggregation. We report herein the synthesis, characterization, fluorescence and energy transfer properties of new readily soluble metal phthalocyanines with up to 40 fluorine-containing substituents on the periphery for the first time, and we also report on the effects of the substituents on the spectroscopic and aggregation properties of the phthalocyanine derivatives in different solvents and at different concentrations in chloroform. 2. Experimental The IR spectra were recorded on a Perkin–Elmer Spectrum One-IR spectrometer and the electronic spectra were recorded on a Scinco Neosys-2000 double-beam ultraviolet–visible (UV–Vis) spectrophotometer. Fluorescence excitation and emission spectra were recorded on a Varian Cary eclipse fluorescence
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spectrofluorimeter. Elemental analyses were performed by the _ Instrumental Analysis Laboratory of the TÜBITAK Marmara Research Centre. 1H NMR spectra were recorded on a Bruker 250 MHz spectrometer using TMS as an internal reference. 19F NMR and 13C NMR spectra were recorded on a Varian Unity Inova 500 MHz NMR. Mass spectra were performed on Varian 711 and Bruker microflex LT MALDI-TOF MS mass spectrometers. All the reagents and solvents were of reagent grade quality obtained from commercial suppliers. All the solvents were dried and purified according to Ref. [34]. The homogeneity of the products was tested in each step by TLC (SiO2). 4-Nitrophthalonitrile and 3,5-bis(pentafluorobenzyloxy)benzyl alcohol were synthesized according to published methods [35,36].
2.1. 4-[3,5-Bis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)benzyloxy]phthalonitrile (1) 0
0
0
0
0
3,5-Bis(2 ,3 ,4 ,5 ,6 -pentafluorobenzyloxy)benzyl alcohol (1.446 g, 2.890 mmol) and 4-nitrophthalonitrile (0.500 g, 2.890 mmol) were dissolved in 15 mL of dry DMF. Anhydrous K2CO3 (0.800 g, 5.780 mmol) was added portion wise for over 2 h and the mixture was stirred vigorously at room temperature under N2 for 24 h. Then the solution was poured into ice-water (200 mL). The residue that formed was filtered off, washed with water several times until the filtrate was neutral, and then with cold methanol, and dried in vacuo. A pale beige product was purified by chromatography
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on silica gel using hexane/chloroform (100:1) to give phthalonitrile derivative (1) (Scheme 1). Yield: 0.977 g (54%). Elemental analysis, Anal. Calc. for C29H12F10N2O3: C, 55.60; H, 1.93; N, 4.47. Found: C, 55.83; H, 2.05; N, 4.62%. IR mmax/cm1: 2964–2855 (alkyl CH), 2227 (C„N), 1255 (C–O–C). 1H NMR (CDCl3), (d, ppm): 7.73 (d, H, Ar-H), 7.26 (d, H, Ar-H), 7.22 (s, H, Ar-H), 6.65 (s, 2H, Ar-H), 6.56 (s, H, Ar-H), 5.11 (s, 6H, CH2). 19F NMR (CDCl3), (d, ppm): 144.8 (d(d), 4F, o-fluorine), 154.6 (t, 2F, p-fluorine), 163.8 (m, 4F, m-fluorine). 13C NMR (CDCl3), (d, ppm): 161.69 (aromatic C–O), 159.84 (aromatic C–O), 147.03 (aromatic C–F), 146.03 (aromatic C), 145.02 (aromatic C–F), 137.79 (aromatic C–F), 135.51 (aromatic C–H), 120.15 (aromatic C–H), 119.89 (aromatic C–H), 117.86 (aromatic C), 115.69 (C„N), 115.34 (C„N), 109.92 (aromatic C–H), 108.20 (aromatic C), 107.17 (aromatic C–H), 102.39 (aromatic C–H), 70.75 (OCH2), 57.88 (OCH2). MS (ESI+), (m/z): 626.50 [M]+.
2.2. {2,9(10),16(17),23(24)-Tetrakis-[3,5-bis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)benzyloxy]phthalocyaninato}metal derivatives (2–4) A mixture of compound 1 (0.300 g, 0.480 mmol)) and 0.125 mmol anhydrous metal salt (zinc acetate 0.023 g, cobalt chloride 0.0163 g or nickel chloride 0.0163 g) and dry DMF (1.5 mL) was placed under nitrogen atmosphere in a standard sealed tube. The reaction mixture was heated and stirred at 150 °C under N2 for 48 h. After cooling to room temperature, the green mixture that formed was poured into ice-water (100 mL).
Scheme 1. The synthesis of phthalonitrile derivative 1 and phthalocyanine complexes 2–4.
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The crude product was precipitated and filtered off, washed with hot water and then with cold methanol, and dried in vacuo. Finally, purification of the product was accomplished by column chromatography on silica gel, first with chloroform/ethyl acetate (1:4) and then with acetone/toluene (1:2) as the eluent. 2.2.1. Compound 2 Yield: 0.086 g (28%). M.p. >200 °C. Elemental analysis, Anal. Calc. for C116H48F40N8O12Zn: C, 54.19; H, 1.88; N, 4.36. Found: C, 54.31; H, 1.92; N, 4.48%. IR mmax/cm1: 2925–2854 (alkyl CH), 1287 (C–O–C). 1H NMR (CDCl3), (d, ppm): 7.74 (m, 4H, Ar-H), 7.50 (d, 4H, Ar-H), 7.35 (s, 4H, Ar-H), 6.67 (s, 8H, Ar-H), 6.56 (s, 4H, Ar-H), 5.10 (d, 24H, CH2). 19F NMR (CDCl3), (d, ppm): 142.6 (d(d), 16F, o-fluorine), 152.4 (t, 8F, p-fluorine), 161.8 (m, 16F, m-fluorine). UV–Vis (CHCl3): kmax/nm (log e): 343 (5.00), 678 (4.99). MS (MALDI TOF) m/z: 2571.48 [M]+. 2.2.2. Compound 3 Yield: 0.070 g (23%). M.p. >200 °C. Elemental analysis, Anal. Calc. for C116H48F40N8O12Ni: C, 54.33; H, 1.89; N, 4.37. Found: C, 54.47; H, 1.95; N, 4.21%. IR mmax/cm1: 2924–2854 (alkyl CH), 1287 (C–O– C). 1H NMR (CDCl3), (d, ppm): 7.73 (m, 4H, Ar-H), 7.54 (m, 4H, Ar-H), 7.35 (s, 4H, Ar-H), 6.83 (s, 8H, Ar-H), 6.51 (s, 4H, Ar-H), 5.05 (s, 24H, CH2). 13C NMR (CDCl3), (d, ppm): 170.73 (aromatic C), 158.63 (aromatic C–O), 158.32 (aromatic C–O), 155.16 (aromatic C–O), 145.72 (aromatic C–F), 143.72 (aromatic C), 141.64 (aromatic C–F), 141.64 (aromatic C–F), 137.55 (aromatic C–F), 135.55 (aromatic C–H), 131.21 (aromatic C–H), 129.84 (aromatic C–H), 127.80 (aromatic C), 116.68 (aromatic C–H), 109.01 (aromatic C), 105.76 (aromatic C–H), 100.53 (aromatic C–H), 70.10 (OCH2), 56.47 (OCH2). UV–Vis (CHCl3): kmax/nm (log e): 323 (5.06), 668 (5.07). MS (ESI+), (m/z): 2564.78 [M]+. 2.2.3. Compound 4 Yield: 0.104 g (34%). M.p. >200 °C. Elemental analysis, Anal. Calc. for C116H48F40N8O12Co: C, 54.33; H, 1.87; N, 4.37. Found: C, 54.52; H, 1.97; N, 4.49%. IR: mmax/cm1: 2925–2854 (alkyl CH), 1284 (C–O–C). UV–Vis (CHCl3): kmax/nm (log e): 317 (5.04), 669 (4.94). MS (ESI+), (m/z): 2565.85 [M+H]+. 3. Results and discussion Zinc(II), nickel(II) and cobalt(II) phthalocyanines carrying four branched groups at peripheral positions were prepared according to the route shown in Scheme 1. The first step in the synthetic procedure was to obtain the phthalonitrile derivative (1) containing 3,5-bis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)benzyloxy groups. This was accomplished by a base-catalyzed nucleophilic aromatic nitro displacement of 4-nitrophthalonitrile [34] with 3,5-bis(20 ,30 ,40 , 50 ,60 -pentafluorobenzyloxy)benzyl alcohol [35]. This reaction has been used effectively in the preparation of a variety of ether- or thioether-substituted phthalonitriles. The nucleophilic substitution of 3,5-bis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy) benzyl alcohol with 4-nitrophthalonitrile in N,N-dimethylformamide using potassium carbonate as the base at room temperature for 24 h under N2 atmosphere gave compound 1 in about 54% yield. The product was purified by column chromatography. The substituted phthalonitrile derivative 1 was used to prepare zinc(II), nickel(II) and cobalt(II) phthalocyanine complexes (2–4) by its reaction with zinc(II) acetate, nickel(II) chloride or cobalt(II) chloride in DMF at 140 °C in a sealed tube. The green products were extremely soluble in various solvents, such as chloroform, dichloromethane, tetrahydrofuran, and acetone, and they were purified by column chromatography on silica gel, first with chloroform/ethyl acetate (1:4) and then with acetone/toluene (1:2) as the
eluent. As expected for monosubstituted phthalonitriles, the Pcs 2–4 are a mixture of four structural isomers and our attempts to isolate each of them have been unsuccessful [37]. All the new compounds were identified through various spectroscopic techniques, such as 1H NMR, 13C NMR, 19F NMR, FT-IR, UV–Vis, ESI-MS and elemental analysis. Spectroscopic data of the compounds 1–4 are in full agreement with the proposed structures. IR spectrum of 1 indicated C„N groups by the presence of an intense band at 2227 cm1, and also benzylic groups at 2964– 2855 cm1 and etheric (C–O–C) units at 1255 cm1. Phthalocyanines 2–4 also have very similar IR absorptions for the peripheral substituents; the clear difference is the disappearance of the sharp C„N band at 2227 cm1, which signifies the cyclotetramerization of the dinitrile. In the 1H NMR spectrum of 1, the aromatic protons appear at d 7.73, 7.26, 7.22, 6.65 and 6.56 ppm as a doublet, doublet, singlet, singlet and singlet, respectively. Also the CH2 protons of the pentafluorobenzyl and benzyl moieties were observed at 5.11 ppm. The 1 H NMR spectra of 2 and 3 were almost identical to those of the starting compound 1 except for small shifts and a slight broadening. The 13C NMR spectrum of 1 showed aromatic carbon atoms at d 161.69–102.39 ppm and aliphatic carbon atoms appeared at d 70.75 and 57.88 ppm. Also the nitrile carbons were observed at d 115.69 and 115.34 ppm. The 13C NMR spectrum of the NiPc (3) was fully consistent with the proposed structure. The 19F NMR spectra are much simpler to interpret as they usually contain only a limited number of signals. Therefore, 19F NMR spectroscopy could become a simple and efficient way to identify fluorine atoms of phenyl substituents. The 19F NMR spectra of 1 (Fig. 1) and 2 showed the expected signals of the five fluorine atoms attached to the aromatic ring. Integration of the peaks gave a 2:1:2 ratio as expected. These compounds displayed signals due to F2,6 (o-fluorine), F4 (p-fluorine) and F3,5 (m-fluorine) at d 144.8, 154.6 and 163.8 ppm for compound 1 and 142.6, 152.4 and 161.8 ppm for compound 2, respectively. The F4 signals appeared as a triplet due to F3,5 coupling, the F2,6 signals appeared as a doublet of doublets and the F3,5 signals as a multiplet in both compounds. In addition to these supportive results for the structures, the mass spectra of compounds 1–3 gave the characteristic molecular ion peaks at m/z: 626.50 [M]+, 2571.48 [M]+, 2564.78 [M]+ and 4 gave a monoprotonated molecular ion peak at m/z: 2565.85 [M+H]+, confirming the proposed structures. The UV–Vis spectra of the phthalocyanine complexes (2–4) exhibited characteristic absorptions in the Q-band region at around 678, 668 and 669 nm for MPcs (2–4) in chloroform, attributed to the p–p* transition from the HOMO (highest occupied molecular orbital) to the LUMO (lowest unoccupied molecular orbital) of the Pc2 ring, and in the B band region (UV region) at around 317–343 nm in chloroform, arising from the deeper p–p* transitions (Fig. 2). The aggregation behavior of phthalocyanines in solution, which can be followed effectively by absorption studies, is a good indication of the interactions between the aromatic macrocycles of the phthalocyanines. Aggregation, which is usually depicted as a coplanar association, is dependent on the concentration, nature of the solvent, nature of the substituents, complexed metal ions and temperature [38–40]. In this study, the aggregation behavior of 2 was investigated at different concentrations in chloroform (Fig. 3). In chloroform, as the concentration was increased, the intensity of the Q-band absorption increased in parallel, and there were no new bands due to the aggregated species [41]. It is seen that the Beer–Lambert law was obeyed for compound 2 for concentrations ranging from 1 105 to 1 106 mol dm3 (insert in Fig. 3).
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Fig. 1.
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19
F NMR spectrum of compound 1.
Fig. 2. UV spectra of ZnPc (2), NiPc (3) and CoPc (4) (5 106 M in CHCl3).
Fig. 4. UV spectra of ZnPc (2) in different solvents.
Fig. 3. UV spectra of ZnPc (2) in CHCl3 at different concentrations: 1 105 (A), 8 106 (B), 6 106 (C), 4 106 (D), 2 106 (E), and 1 106 (F) mol dm3.
Fig. 5. Plot of the Q band frequency of ZnPc (2) against (n2 1)/(2n2 + 1), where n is the refractive index of the solvent.
The electronic spectra of compound 2 in different organic solvents, such as acetone, tetrahydrofuran, chloroform, dimethyl
sulfoxide and toluene, were also analyzed (Fig. 4). It is obvious that the Q band position changes with respect to the solvent. In general,
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the red shift of the Q band increases with the ascending refractive index of the solvent. In our study, the red shift of the Q band due to the solvent for compound 2 increased in the following order: acetone < tetrahydrofuran < chloroform < dimethyl sulfoxide toluene. The electronic absorption spectra of 2 in these solvents were analyzed by using the method described originally by Bayliss [42,43]. Fig. 5 displays a plot of the Q band frequency versus the function (n2 1)/(2n2 + 1), where n is the refractive index of the solvent. The positions of the Q bands in these solvents show almost a linear dependence on this function. This linearity suggests that the shifts are caused mainly by solvation and not by a ligation effect [42]. Also, in this study we examined the fluorescence and energy transfer properties of the zero (6) [28] and first (2) generation of zinc(II) phthalocyanines (Scheme 2). This avenue, studying excitation energy transfer through dendritic architectures, has been of much current interest because of its relevance to biological lightharvesting antennas [44,45]. Excitation and emission spectra of the phthalocyanine derivatives substituted with fluorinated aryl dendron groups were obtained in THF solution. Fig. 6 shows the excitation spectra of the starting phthalonitriles 4-(20 ,30 ,40 ,50 ,60 pentafluorobenzyloxy)phthalonitrile (5) [28] and 1, and the related phthalocyanines tetrakis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalocyaninato zinc(II) (6) (G0) [28] and 2 (G1). It can be seen that as the number of aryl groups increases, more photons are collected and transmitted to the phthalocyanine core [46]. As shown in Fig. 6, the aryl dendrons 1 and 5 exhibit two absorption bands peaking at 270 and 308 nm and an emission at 340 nm for 5 and at 410 nm for 1 upon excitation at 310 nm, Fig. 7. As this emission band overlaps with the B-band of phthalocyanines, energy transfer
Scheme 2. The zero (6) and first (2) generation of the zinc(II) phthalocyanines.
Fig. 6. Excitation spectra of 4-(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalonitrile (5, 2 105 M), 1 (2 105 M), 2 (5 106 M) and tetrakis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalocyaninato zinc(II) (6, 5 106 M) in THF, monitored at 720 nm.
Fig. 7. Emission spectra of 4-(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalonitrile (5, 2 105 M), 1 (2 105 M), 2 (n = 1, 5 106 M) and tetrakis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalocyaninato zinc(II) (6, 5 106 M) and tetrakis(acetoxyethylthio)phthalocyaninato zinc(II) (7, 5 106 M) in THF, emission excited at 310 nm.
from the excited fluorinated aryl dendrons to the central phthalocyanine may occur in this series of compounds [47]. This series of dendritic phthalocyanines also exhibit an interesting photoinduced intramolecular energy transfer. Upon excitation at 310 nm, where the fluorinated aryl dendrons absorb and the absorption of phthalocyanine is weak, the dendritic phthalocyanines compounds emit weakly at about 350 nm for 6 (G0) and at about 400 nm for 2 (G1) due to the fluorinated aryl dendrons, together with an emission at 690 nm for tetrakis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalocyaninato zinc(II) (6) (G0) and at 695 nm for 2 (G1) due to a singlet–singlet energy transfer from the excited dendrons to the central phthalocyanine core (Fig. 7). The fluorescence of the aryl dendron parts was quenched and emission intensities of the phthalocyanine part around 690–695 nm were increased because of the radiative energy transfer resulting from the inner filter effect of the Pc core [46,48]. For comparison, the soluble model compound tetrakis(acetoxyethylthio)phthalocyaninato zinc(II) (7), which does not contain aromatic dendrons or fluorescence groups, was prepared [13]. This compound exhibited only a very weak emission at 690 nm, which may arise from the weak absorption at 310 nm (Fig. 7). The latter emissions of dendritic phthalocyanines are clearly due to a singlet–singlet energy transfer from the excited fluorinated aryl dendrons to the central phthalocyanine core which acts as an energy trap. The energy transfer efficiency estimated from the fluorescence quenching is not naturally 100%, probably due to
Fig. 8. Emission spectra of 2 (5 106 M) and tetrakis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalocyaninato zinc(II) (6, 5 106 M) in THF, emission excited at 610 nm.
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the methoxy group between the aryl dendron units and the phthalocyanine part [49]. The emission spectra of 2 (G1) show 5 nm Stokes shifts, compared with those of tetrakis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalocyaninato zinc(II) (6) (G0). These red shifts indicate very little molecular rearrangement in the excited state originating from intramolecular interactions [50]. The steady-state fluorescence spectra of the fluorinated aryl dendron-substituted Pc derivatives were performed in THF, upon excitation at the 610 nm Q-band absorption. Emission around 690 nm for 6 (G0) and emission around 695 nm for 2 (G1) (Fig. 8) occurred almost entirely from the phthalocyanine moiety. The excitation spectra were similar to the absorption spectra and both were mirror images of the fluorescence spectra in THF. The proximity of the wavelength of each component of the Q-band absorption to the Q-band maxima of the excitation spectra for 6 (G0) and 2 (G1) suggests that the nuclear configurations of the ground and excited states are similar and are not affected by excitation in THF. Fluorescence quantum yields (UF) were determined by the comparative method (Eq. (1)) [51]:
UF ¼ UF ðStdÞ FAStd g2 =F Std Ag2Std ;
ð1Þ
where F and FStd are the areas under the fluorescence curves of the phthalocyanines derivatives and the standard, respectively. A and AStd are the respective absorbances of the sample and the standard at the excitation wavelength and g and gStd are the refractive indices of the solvents used for the sample and the standard, respectively. ZnPc was employed as a standard in DMF (UF = 0.23) [52]. Both the sample and the standard were excited at the same wavelength. The fluorescence quantum yield was obtained for the fluorinated aryl dendrons substituted on 6 (G0) (UF = 0.28) and 2 (G1) (UF = 0.38). 4. Conclusion In this study, the 40 peripheral fluorine atoms in the structure increase the solubility of the complexes in halogenated solvents, acetone and THF. Phthalocyanines have a tendency to form stacked structures, mostly owing to their planarity. However, addition of bulky dendritic pentafluorobenzyloxy substituents has proved to be an extremely efficient way to diminish aggregation among planar molecules. Here, we have also shown that peripheral fluorinated aryl dendron moieties are acting as efficient antennas for photon-harvesting to central phthalocyanine cores. The catalytic activity and stability of these new compounds will be the subject of our future study. Acknowledgements This work was supported by the Research Fund of the Technical _ University of Istanbul and TUBITAK (Project Number: 108T448). References [1] Y. Zhang, W. Jiang, J. Jiang, Q. Xue, J. Porphyrins Phthalocyanines 11 (2007) 100.
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Synthesis and characterization of new polyfluorinated dendrimeric phthalocyanines _ Mukaddes Özçesßmeci, Ibrahim Özçesßmeci, Esin Hamuryudan * Department of Chemistry, Istanbul Technical University, Maslak TR34469, Istanbul, Turkey
a r t i c l e
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Article history: Received 29 April 2010 Accepted 23 June 2010 Available online 1 July 2010 Keywords: Fluorinated Phthalocyanines Benzyloxy groups Aggregation Energy transfer
a b s t r a c t The synthesis of new polyfluorinated dendrimeric metallophthalocyanines (M = Zn, Ni, Co) bearing 3,5bis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)benzyloxy moieties (2–4) was achieved by cyclotetramerization of phthalonitrile derivative 1 in the presence of zinc, nickel or cobalt salts in DMF. All the target phthalocyanines were separated by column chromatography and their spectroscopic, fluorescence and energy transfer properties, and aggregation behavior were investigated in different solvents and at different concentrations in chloroform. The compounds were characterized by Fourier transform-infrared, fluorine, proton and carbon nuclear magnetic resonance, mass, ultraviolet–visible and fluorescence spectral data. The phthalocyanines (2–4) were extremely soluble in various organic solvents, such as tetrahydrofuran, acetone and dichloromethane. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction Phthalocyanines (Pcs) have a two-dimensional 18 p-electron conjugated system thereby allowing the incorporation of more than 70 different metal or non-metal ions into their inner core. Modifications in the macrocycle can be made either by introduction of different central ions or by substitution of functional groups at the peripheral sites of the ring. During recent decades, metal phthalocyanines have found widespread application not only as pigments and dyes but also as chemical sensors, liquid crystals, Langmuir–Blodgett films, catalysts, non-linear optical materials, optical data storage materials, carrier generation materials in near-IR and also in medicine [1–5]. For such applications, good solubility is preferred. A critical disadvantage of unsubstituted Pcs is their low solubility in organic solvents or water. By appropriate substitution with bulky or long-chain groups in the peripheral positions of the macrocycle, these compounds can be solubilized in common organic solvents, thus increasing the field of possible applications [6–14]. Redox-active d-metal (e.g. Fe, Mn, Co) phthalocyanines exhibit very high catalytic activity in the oxidation of thiols, hydrocarbons, hydroquinones, arenes and amines [15–18]. The most promising way to increase the first oxidation potential of phthalocyanine complexes is the introduction of electron-withdrawing substituents. It has been shown that halogenated metallo tetrapyrrole derivatives are very efficient catalysts for oxidation reactions under very mild conditions [19,20].
* Corresponding author. Tel.: +90 2122856826; fax: +90 2122856386. E-mail address: [email protected] (E. Hamuryudan). 0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2010.06.023
Fluorinated metal phthalocyanines and porphyrins currently receive a great deal of attention due to their interesting electrontransfer, photosensitizing properties, along with magnetic and thermal characteristics [21–24]. The presence of pentafluorophenyl groups on the macrocycle ring can increase the catalytic activity and stability [25]. Fluoro-substituted phthalocyanines are known for their high solubility, even in polar, aprotic solvents. The increased solubility may be due to fluorine, which has the highest electronegativity of all elements [26]. In our previous studies, we have reported the synthesis, electrochemical and spectroelectrochemical properties of symmetric and asymmetric phthalocyanines [27–33]. In this step, our aim has been to design new molecules with dendritic fluoro-substituents, enhancing their solubility in common solvents and at the same time prohibiting their aggregation. We report herein the synthesis, characterization, fluorescence and energy transfer properties of new readily soluble metal phthalocyanines with up to 40 fluorine-containing substituents on the periphery for the first time, and we also report on the effects of the substituents on the spectroscopic and aggregation properties of the phthalocyanine derivatives in different solvents and at different concentrations in chloroform. 2. Experimental The IR spectra were recorded on a Perkin–Elmer Spectrum One-IR spectrometer and the electronic spectra were recorded on a Scinco Neosys-2000 double-beam ultraviolet–visible (UV–Vis) spectrophotometer. Fluorescence excitation and emission spectra were recorded on a Varian Cary eclipse fluorescence
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spectrofluorimeter. Elemental analyses were performed by the _ Instrumental Analysis Laboratory of the TÜBITAK Marmara Research Centre. 1H NMR spectra were recorded on a Bruker 250 MHz spectrometer using TMS as an internal reference. 19F NMR and 13C NMR spectra were recorded on a Varian Unity Inova 500 MHz NMR. Mass spectra were performed on Varian 711 and Bruker microflex LT MALDI-TOF MS mass spectrometers. All the reagents and solvents were of reagent grade quality obtained from commercial suppliers. All the solvents were dried and purified according to Ref. [34]. The homogeneity of the products was tested in each step by TLC (SiO2). 4-Nitrophthalonitrile and 3,5-bis(pentafluorobenzyloxy)benzyl alcohol were synthesized according to published methods [35,36].
2.1. 4-[3,5-Bis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)benzyloxy]phthalonitrile (1) 0
0
0
0
0
3,5-Bis(2 ,3 ,4 ,5 ,6 -pentafluorobenzyloxy)benzyl alcohol (1.446 g, 2.890 mmol) and 4-nitrophthalonitrile (0.500 g, 2.890 mmol) were dissolved in 15 mL of dry DMF. Anhydrous K2CO3 (0.800 g, 5.780 mmol) was added portion wise for over 2 h and the mixture was stirred vigorously at room temperature under N2 for 24 h. Then the solution was poured into ice-water (200 mL). The residue that formed was filtered off, washed with water several times until the filtrate was neutral, and then with cold methanol, and dried in vacuo. A pale beige product was purified by chromatography
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on silica gel using hexane/chloroform (100:1) to give phthalonitrile derivative (1) (Scheme 1). Yield: 0.977 g (54%). Elemental analysis, Anal. Calc. for C29H12F10N2O3: C, 55.60; H, 1.93; N, 4.47. Found: C, 55.83; H, 2.05; N, 4.62%. IR mmax/cm1: 2964–2855 (alkyl CH), 2227 (C„N), 1255 (C–O–C). 1H NMR (CDCl3), (d, ppm): 7.73 (d, H, Ar-H), 7.26 (d, H, Ar-H), 7.22 (s, H, Ar-H), 6.65 (s, 2H, Ar-H), 6.56 (s, H, Ar-H), 5.11 (s, 6H, CH2). 19F NMR (CDCl3), (d, ppm): 144.8 (d(d), 4F, o-fluorine), 154.6 (t, 2F, p-fluorine), 163.8 (m, 4F, m-fluorine). 13C NMR (CDCl3), (d, ppm): 161.69 (aromatic C–O), 159.84 (aromatic C–O), 147.03 (aromatic C–F), 146.03 (aromatic C), 145.02 (aromatic C–F), 137.79 (aromatic C–F), 135.51 (aromatic C–H), 120.15 (aromatic C–H), 119.89 (aromatic C–H), 117.86 (aromatic C), 115.69 (C„N), 115.34 (C„N), 109.92 (aromatic C–H), 108.20 (aromatic C), 107.17 (aromatic C–H), 102.39 (aromatic C–H), 70.75 (OCH2), 57.88 (OCH2). MS (ESI+), (m/z): 626.50 [M]+.
2.2. {2,9(10),16(17),23(24)-Tetrakis-[3,5-bis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)benzyloxy]phthalocyaninato}metal derivatives (2–4) A mixture of compound 1 (0.300 g, 0.480 mmol)) and 0.125 mmol anhydrous metal salt (zinc acetate 0.023 g, cobalt chloride 0.0163 g or nickel chloride 0.0163 g) and dry DMF (1.5 mL) was placed under nitrogen atmosphere in a standard sealed tube. The reaction mixture was heated and stirred at 150 °C under N2 for 48 h. After cooling to room temperature, the green mixture that formed was poured into ice-water (100 mL).
Scheme 1. The synthesis of phthalonitrile derivative 1 and phthalocyanine complexes 2–4.
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The crude product was precipitated and filtered off, washed with hot water and then with cold methanol, and dried in vacuo. Finally, purification of the product was accomplished by column chromatography on silica gel, first with chloroform/ethyl acetate (1:4) and then with acetone/toluene (1:2) as the eluent. 2.2.1. Compound 2 Yield: 0.086 g (28%). M.p. >200 °C. Elemental analysis, Anal. Calc. for C116H48F40N8O12Zn: C, 54.19; H, 1.88; N, 4.36. Found: C, 54.31; H, 1.92; N, 4.48%. IR mmax/cm1: 2925–2854 (alkyl CH), 1287 (C–O–C). 1H NMR (CDCl3), (d, ppm): 7.74 (m, 4H, Ar-H), 7.50 (d, 4H, Ar-H), 7.35 (s, 4H, Ar-H), 6.67 (s, 8H, Ar-H), 6.56 (s, 4H, Ar-H), 5.10 (d, 24H, CH2). 19F NMR (CDCl3), (d, ppm): 142.6 (d(d), 16F, o-fluorine), 152.4 (t, 8F, p-fluorine), 161.8 (m, 16F, m-fluorine). UV–Vis (CHCl3): kmax/nm (log e): 343 (5.00), 678 (4.99). MS (MALDI TOF) m/z: 2571.48 [M]+. 2.2.2. Compound 3 Yield: 0.070 g (23%). M.p. >200 °C. Elemental analysis, Anal. Calc. for C116H48F40N8O12Ni: C, 54.33; H, 1.89; N, 4.37. Found: C, 54.47; H, 1.95; N, 4.21%. IR mmax/cm1: 2924–2854 (alkyl CH), 1287 (C–O– C). 1H NMR (CDCl3), (d, ppm): 7.73 (m, 4H, Ar-H), 7.54 (m, 4H, Ar-H), 7.35 (s, 4H, Ar-H), 6.83 (s, 8H, Ar-H), 6.51 (s, 4H, Ar-H), 5.05 (s, 24H, CH2). 13C NMR (CDCl3), (d, ppm): 170.73 (aromatic C), 158.63 (aromatic C–O), 158.32 (aromatic C–O), 155.16 (aromatic C–O), 145.72 (aromatic C–F), 143.72 (aromatic C), 141.64 (aromatic C–F), 141.64 (aromatic C–F), 137.55 (aromatic C–F), 135.55 (aromatic C–H), 131.21 (aromatic C–H), 129.84 (aromatic C–H), 127.80 (aromatic C), 116.68 (aromatic C–H), 109.01 (aromatic C), 105.76 (aromatic C–H), 100.53 (aromatic C–H), 70.10 (OCH2), 56.47 (OCH2). UV–Vis (CHCl3): kmax/nm (log e): 323 (5.06), 668 (5.07). MS (ESI+), (m/z): 2564.78 [M]+. 2.2.3. Compound 4 Yield: 0.104 g (34%). M.p. >200 °C. Elemental analysis, Anal. Calc. for C116H48F40N8O12Co: C, 54.33; H, 1.87; N, 4.37. Found: C, 54.52; H, 1.97; N, 4.49%. IR: mmax/cm1: 2925–2854 (alkyl CH), 1284 (C–O–C). UV–Vis (CHCl3): kmax/nm (log e): 317 (5.04), 669 (4.94). MS (ESI+), (m/z): 2565.85 [M+H]+. 3. Results and discussion Zinc(II), nickel(II) and cobalt(II) phthalocyanines carrying four branched groups at peripheral positions were prepared according to the route shown in Scheme 1. The first step in the synthetic procedure was to obtain the phthalonitrile derivative (1) containing 3,5-bis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)benzyloxy groups. This was accomplished by a base-catalyzed nucleophilic aromatic nitro displacement of 4-nitrophthalonitrile [34] with 3,5-bis(20 ,30 ,40 , 50 ,60 -pentafluorobenzyloxy)benzyl alcohol [35]. This reaction has been used effectively in the preparation of a variety of ether- or thioether-substituted phthalonitriles. The nucleophilic substitution of 3,5-bis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy) benzyl alcohol with 4-nitrophthalonitrile in N,N-dimethylformamide using potassium carbonate as the base at room temperature for 24 h under N2 atmosphere gave compound 1 in about 54% yield. The product was purified by column chromatography. The substituted phthalonitrile derivative 1 was used to prepare zinc(II), nickel(II) and cobalt(II) phthalocyanine complexes (2–4) by its reaction with zinc(II) acetate, nickel(II) chloride or cobalt(II) chloride in DMF at 140 °C in a sealed tube. The green products were extremely soluble in various solvents, such as chloroform, dichloromethane, tetrahydrofuran, and acetone, and they were purified by column chromatography on silica gel, first with chloroform/ethyl acetate (1:4) and then with acetone/toluene (1:2) as the
eluent. As expected for monosubstituted phthalonitriles, the Pcs 2–4 are a mixture of four structural isomers and our attempts to isolate each of them have been unsuccessful [37]. All the new compounds were identified through various spectroscopic techniques, such as 1H NMR, 13C NMR, 19F NMR, FT-IR, UV–Vis, ESI-MS and elemental analysis. Spectroscopic data of the compounds 1–4 are in full agreement with the proposed structures. IR spectrum of 1 indicated C„N groups by the presence of an intense band at 2227 cm1, and also benzylic groups at 2964– 2855 cm1 and etheric (C–O–C) units at 1255 cm1. Phthalocyanines 2–4 also have very similar IR absorptions for the peripheral substituents; the clear difference is the disappearance of the sharp C„N band at 2227 cm1, which signifies the cyclotetramerization of the dinitrile. In the 1H NMR spectrum of 1, the aromatic protons appear at d 7.73, 7.26, 7.22, 6.65 and 6.56 ppm as a doublet, doublet, singlet, singlet and singlet, respectively. Also the CH2 protons of the pentafluorobenzyl and benzyl moieties were observed at 5.11 ppm. The 1 H NMR spectra of 2 and 3 were almost identical to those of the starting compound 1 except for small shifts and a slight broadening. The 13C NMR spectrum of 1 showed aromatic carbon atoms at d 161.69–102.39 ppm and aliphatic carbon atoms appeared at d 70.75 and 57.88 ppm. Also the nitrile carbons were observed at d 115.69 and 115.34 ppm. The 13C NMR spectrum of the NiPc (3) was fully consistent with the proposed structure. The 19F NMR spectra are much simpler to interpret as they usually contain only a limited number of signals. Therefore, 19F NMR spectroscopy could become a simple and efficient way to identify fluorine atoms of phenyl substituents. The 19F NMR spectra of 1 (Fig. 1) and 2 showed the expected signals of the five fluorine atoms attached to the aromatic ring. Integration of the peaks gave a 2:1:2 ratio as expected. These compounds displayed signals due to F2,6 (o-fluorine), F4 (p-fluorine) and F3,5 (m-fluorine) at d 144.8, 154.6 and 163.8 ppm for compound 1 and 142.6, 152.4 and 161.8 ppm for compound 2, respectively. The F4 signals appeared as a triplet due to F3,5 coupling, the F2,6 signals appeared as a doublet of doublets and the F3,5 signals as a multiplet in both compounds. In addition to these supportive results for the structures, the mass spectra of compounds 1–3 gave the characteristic molecular ion peaks at m/z: 626.50 [M]+, 2571.48 [M]+, 2564.78 [M]+ and 4 gave a monoprotonated molecular ion peak at m/z: 2565.85 [M+H]+, confirming the proposed structures. The UV–Vis spectra of the phthalocyanine complexes (2–4) exhibited characteristic absorptions in the Q-band region at around 678, 668 and 669 nm for MPcs (2–4) in chloroform, attributed to the p–p* transition from the HOMO (highest occupied molecular orbital) to the LUMO (lowest unoccupied molecular orbital) of the Pc2 ring, and in the B band region (UV region) at around 317–343 nm in chloroform, arising from the deeper p–p* transitions (Fig. 2). The aggregation behavior of phthalocyanines in solution, which can be followed effectively by absorption studies, is a good indication of the interactions between the aromatic macrocycles of the phthalocyanines. Aggregation, which is usually depicted as a coplanar association, is dependent on the concentration, nature of the solvent, nature of the substituents, complexed metal ions and temperature [38–40]. In this study, the aggregation behavior of 2 was investigated at different concentrations in chloroform (Fig. 3). In chloroform, as the concentration was increased, the intensity of the Q-band absorption increased in parallel, and there were no new bands due to the aggregated species [41]. It is seen that the Beer–Lambert law was obeyed for compound 2 for concentrations ranging from 1 105 to 1 106 mol dm3 (insert in Fig. 3).
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Fig. 1.
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19
F NMR spectrum of compound 1.
Fig. 2. UV spectra of ZnPc (2), NiPc (3) and CoPc (4) (5 106 M in CHCl3).
Fig. 4. UV spectra of ZnPc (2) in different solvents.
Fig. 3. UV spectra of ZnPc (2) in CHCl3 at different concentrations: 1 105 (A), 8 106 (B), 6 106 (C), 4 106 (D), 2 106 (E), and 1 106 (F) mol dm3.
Fig. 5. Plot of the Q band frequency of ZnPc (2) against (n2 1)/(2n2 + 1), where n is the refractive index of the solvent.
The electronic spectra of compound 2 in different organic solvents, such as acetone, tetrahydrofuran, chloroform, dimethyl
sulfoxide and toluene, were also analyzed (Fig. 4). It is obvious that the Q band position changes with respect to the solvent. In general,
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the red shift of the Q band increases with the ascending refractive index of the solvent. In our study, the red shift of the Q band due to the solvent for compound 2 increased in the following order: acetone < tetrahydrofuran < chloroform < dimethyl sulfoxide toluene. The electronic absorption spectra of 2 in these solvents were analyzed by using the method described originally by Bayliss [42,43]. Fig. 5 displays a plot of the Q band frequency versus the function (n2 1)/(2n2 + 1), where n is the refractive index of the solvent. The positions of the Q bands in these solvents show almost a linear dependence on this function. This linearity suggests that the shifts are caused mainly by solvation and not by a ligation effect [42]. Also, in this study we examined the fluorescence and energy transfer properties of the zero (6) [28] and first (2) generation of zinc(II) phthalocyanines (Scheme 2). This avenue, studying excitation energy transfer through dendritic architectures, has been of much current interest because of its relevance to biological lightharvesting antennas [44,45]. Excitation and emission spectra of the phthalocyanine derivatives substituted with fluorinated aryl dendron groups were obtained in THF solution. Fig. 6 shows the excitation spectra of the starting phthalonitriles 4-(20 ,30 ,40 ,50 ,60 pentafluorobenzyloxy)phthalonitrile (5) [28] and 1, and the related phthalocyanines tetrakis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalocyaninato zinc(II) (6) (G0) [28] and 2 (G1). It can be seen that as the number of aryl groups increases, more photons are collected and transmitted to the phthalocyanine core [46]. As shown in Fig. 6, the aryl dendrons 1 and 5 exhibit two absorption bands peaking at 270 and 308 nm and an emission at 340 nm for 5 and at 410 nm for 1 upon excitation at 310 nm, Fig. 7. As this emission band overlaps with the B-band of phthalocyanines, energy transfer
Scheme 2. The zero (6) and first (2) generation of the zinc(II) phthalocyanines.
Fig. 6. Excitation spectra of 4-(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalonitrile (5, 2 105 M), 1 (2 105 M), 2 (5 106 M) and tetrakis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalocyaninato zinc(II) (6, 5 106 M) in THF, monitored at 720 nm.
Fig. 7. Emission spectra of 4-(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalonitrile (5, 2 105 M), 1 (2 105 M), 2 (n = 1, 5 106 M) and tetrakis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalocyaninato zinc(II) (6, 5 106 M) and tetrakis(acetoxyethylthio)phthalocyaninato zinc(II) (7, 5 106 M) in THF, emission excited at 310 nm.
from the excited fluorinated aryl dendrons to the central phthalocyanine may occur in this series of compounds [47]. This series of dendritic phthalocyanines also exhibit an interesting photoinduced intramolecular energy transfer. Upon excitation at 310 nm, where the fluorinated aryl dendrons absorb and the absorption of phthalocyanine is weak, the dendritic phthalocyanines compounds emit weakly at about 350 nm for 6 (G0) and at about 400 nm for 2 (G1) due to the fluorinated aryl dendrons, together with an emission at 690 nm for tetrakis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalocyaninato zinc(II) (6) (G0) and at 695 nm for 2 (G1) due to a singlet–singlet energy transfer from the excited dendrons to the central phthalocyanine core (Fig. 7). The fluorescence of the aryl dendron parts was quenched and emission intensities of the phthalocyanine part around 690–695 nm were increased because of the radiative energy transfer resulting from the inner filter effect of the Pc core [46,48]. For comparison, the soluble model compound tetrakis(acetoxyethylthio)phthalocyaninato zinc(II) (7), which does not contain aromatic dendrons or fluorescence groups, was prepared [13]. This compound exhibited only a very weak emission at 690 nm, which may arise from the weak absorption at 310 nm (Fig. 7). The latter emissions of dendritic phthalocyanines are clearly due to a singlet–singlet energy transfer from the excited fluorinated aryl dendrons to the central phthalocyanine core which acts as an energy trap. The energy transfer efficiency estimated from the fluorescence quenching is not naturally 100%, probably due to
Fig. 8. Emission spectra of 2 (5 106 M) and tetrakis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalocyaninato zinc(II) (6, 5 106 M) in THF, emission excited at 610 nm.
M. Özçesßmeci et al. / Polyhedron 29 (2010) 2710–2715
the methoxy group between the aryl dendron units and the phthalocyanine part [49]. The emission spectra of 2 (G1) show 5 nm Stokes shifts, compared with those of tetrakis(20 ,30 ,40 ,50 ,60 -pentafluorobenzyloxy)phthalocyaninato zinc(II) (6) (G0). These red shifts indicate very little molecular rearrangement in the excited state originating from intramolecular interactions [50]. The steady-state fluorescence spectra of the fluorinated aryl dendron-substituted Pc derivatives were performed in THF, upon excitation at the 610 nm Q-band absorption. Emission around 690 nm for 6 (G0) and emission around 695 nm for 2 (G1) (Fig. 8) occurred almost entirely from the phthalocyanine moiety. The excitation spectra were similar to the absorption spectra and both were mirror images of the fluorescence spectra in THF. The proximity of the wavelength of each component of the Q-band absorption to the Q-band maxima of the excitation spectra for 6 (G0) and 2 (G1) suggests that the nuclear configurations of the ground and excited states are similar and are not affected by excitation in THF. Fluorescence quantum yields (UF) were determined by the comparative method (Eq. (1)) [51]:
UF ¼ UF ðStdÞ FAStd g2 =F Std Ag2Std ;
ð1Þ
where F and FStd are the areas under the fluorescence curves of the phthalocyanines derivatives and the standard, respectively. A and AStd are the respective absorbances of the sample and the standard at the excitation wavelength and g and gStd are the refractive indices of the solvents used for the sample and the standard, respectively. ZnPc was employed as a standard in DMF (UF = 0.23) [52]. Both the sample and the standard were excited at the same wavelength. The fluorescence quantum yield was obtained for the fluorinated aryl dendrons substituted on 6 (G0) (UF = 0.28) and 2 (G1) (UF = 0.38). 4. Conclusion In this study, the 40 peripheral fluorine atoms in the structure increase the solubility of the complexes in halogenated solvents, acetone and THF. Phthalocyanines have a tendency to form stacked structures, mostly owing to their planarity. However, addition of bulky dendritic pentafluorobenzyloxy substituents has proved to be an extremely efficient way to diminish aggregation among planar molecules. Here, we have also shown that peripheral fluorinated aryl dendron moieties are acting as efficient antennas for photon-harvesting to central phthalocyanine cores. The catalytic activity and stability of these new compounds will be the subject of our future study. Acknowledgements This work was supported by the Research Fund of the Technical _ University of Istanbul and TUBITAK (Project Number: 108T448). References [1] Y. Zhang, W. Jiang, J. Jiang, Q. Xue, J. Porphyrins Phthalocyanines 11 (2007) 100.
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