Phthalocyanines with rigid carboxylic acid containing pendant arms

Polyhedron 25 (2006) 39–42 www.elsevier.com/locate/poly

Phthalocyanines with rigid carboxylic acid containing pendant arms Ayfer Kalkan, Zehra Altuntasß Bayır

*

Department of Chemistry, Technical University of Istanbul, TR34469 Maslak, Istanbul, Turkey Received 6 June 2005; accepted 25 June 2005 Available online 18 August 2005

Abstract Metal-free and metallophthalocyanines (Zn, Co) substituted with four carboxybiphenyloxy groups on the peripheral positions were prepared from 4-(4 0 -carboxybiphenyloxy)phthalonitrile. Esterification of all of the biphenylcarboxylic acid groups of metalfree phthalocyanine with hexanol afforded 2,9,16,23-tetrakis(4 0 -carbhexyloxybiphenyloxy) phthalocyanine. These new compounds have been characterised by 1H NMR, 13C NMR, FT-IR, UV–Vis and mass spectroscopies. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Phthalocyanine; Biphenylcarboxylic acid; Zinc; Cobalt

1. Introduction Phthalocyanine is a close relative of the porphyrin macrocycle and is the parent compound of one of the most studied class of functional organic materials. The most important and extensive application of phthalocyanines is to be used as colorants. Furthermore, phthalocyanine and its derivatives displaying interesting photophysical properties, electron transfer ability and reduction–oxidation behaviour are studied for applications in electrophotography, photovoltaic cells, fuel cells and electrochromic displays [1,2]. Recent years, remarkable progress has been made in the use of phthalocyanine derivatives as sensitisers for photodynamic therapy (PDT) of cancer [3,4]. PDT employs the combination of light and photosensitiser. Photosensitiser is getting excited after the absorption of light of proper wavelength. It is followed by a singlet oxygen production by energy transfer from activated photosensitiser. Phthalocyanines display cytotoxic effects when activated by light. Especially, water soluble

zinc and aluminium phthalocyanine complexes have good photosensitising properties for PDT [5–7]. The main restricting factor of phthalocyanines is a rather low solubility in organic solvents. Periferal substitution of phthalocyanines with alkyl, alkoxy, alkythio chains or bulky groups enhances their solubility drastically [8–18]. The introduction of carboxy or amino groups gives water-soluble products. The synthesis of soluble phthalocyanines should provide them new optical, electronic, redox and magnetic properties which could increase the field of possible applications [19–21]. Recently, we have reported on the synthesis, separation and characterisation of unsymmetrical and symmetrical phthalocyanines [22–25]. This paper describes metal-free and metallo phthalocyanines (Zn, Co) carrying biphenylcarboxylic acid substituents on the periphery. Also, all of the biphenylcarboxylic acid substituents of the metal-free phthalocyanine were esterified with hexanol.

2. Experimental *

Corresponding author. Tel.: +90 212 285 32 23; fax: +90 212 285 63 86. E-mail address: [email protected] (Z.A. Bayır). 0277-5387/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2005.06.056

IR spectra were recorded on a Perkin–Elmer Spectrum One FT-IR (ATR sampling accessory)

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A. Kalkan, Z.A. Bayır / Polyhedron 25 (2006) 39–42

spectrophotometer, electronic spectra on a Unicam UV2 spectrophotometer. 1H NMR spectra were recorded on Bruker 250 MHz and Inova 500 spectrometers using TMS as internal reference. Mass spectra were performed on Ultima Fourier Transform and Varian 711 mass spectrometer. All reagents and solvents were of reagent grade quality obtained from commercial suppliers. The homogeneity of the products was tested in each step by TLC. All solvents were dried and purified as described by Perrin and Armarego [26]. The solvents were stored over molecular sieves. 4-Nitrophthalonitrile (1) [27] was synthesised according to published methods.

first with water, then with ethanol and acetone finally dried in vacuo. Yield: 0.34 g, 17%. M.p. >200 °C. IR mmax/(cm
1): 3310 (N–H), 3050 (Ar–H), 1683 (C@O), 1598, 1522, 1470, 1250, 1181, 1091, 1003, 926, 825, 771; 1H NMR (d-DMSO): 8.01–7.38 (m, 44H, Ar–H); UV–Vis kmax (nm) (log e) in DMSO: 288 (4.77), 340 (4.36), 668 (4.41), 700 (4.40); MS (MALDI-TOF): m/z 1363.4 [M+], 1317.4 [M+
COOH
H]. Anal. Calc. for C84H50N8O12: C, 74.01; H, 3.67; N, 8.22. Found: C, 73.99; H, 3.65; N, 8.19%. 2.3. 2,9,16,23-Tetrakis(4 0 -carboxybiphenyloxy)phthalocyaninatozinc(II) (4)

2.1. 4-(4 0 -Carboxybiphenyloxy)phthalonitrile (2) 4-Nitrophthalonitrile (0.5, 2.89 mmol) and an excess of 4 0 -hydroxy-4-biphenylcarboxylic acid (1.24 g, 5.78 mmol) were dissolved in 10 ml dry DMF. Anhydrous K2CO3 (1.59 g, 11.56 mmol) was added portion wise over 2 h and the mixture was stirred vigorously at room temperature under N2 for 48 h. The reaction mixture was poured into water (100 ml) and the pH of solution was adjusted to 1 by addition of aqueous hydrochloric acid. The precipitated solid was filtered, washed with water until the filtrate was neutral, and then dried. Finally, a pale beige product was crystallised from methanol–water. Yield: 0.54 g, 55%. M.p. >200 °C. IR mmax/(cm
1): 3055 (Ar–H), 2238 (C„N), 1681 (C@O), 1588, 1522, 1489, 1268, 1242 (C–O–C), 1183, 1007, 839, 776, 1H NMR (d-DMSO): 13.03 (s, 1H, OH), 8.14 (d, 2H, Ar–H), 8.05 (d, 1H, Ar–H), 7.85 (m, 4H, Ar–H), 7.49 (d, 1H, Ar–H), 7.46 (d, 1H, Ar–H), 7.34 (d, 2H, Ar–H); 13C NMR (d-DMSO, APT): 167.58 (C@O), 161.24 (aromatic C), 154.57 (biphenyl C), 143.66 (biphenyl C), 136.85 (biphenyl C), 136.81 (aromatic CH), 130.48 (biphenyl CH), 130.17 (biphenyl C), 129.66 (biphenyl CH), 127.22 (biphenyl CH), 123.45 (aromatic CH), 122.82 (aromatic CH), 121.26 (biphenyl CH), 117.22 (aromatic C), 116.37 (C„N), 115.85 (C„N), 108.93 (aromatic C); UV–Vis kmax (nm) (log e) in THF: 291 (4.63). Anal. Calc. for C21H12N2O3: C, 74.11; H, 3.55; N, 8.23. Found: C, 74.10; H, 3.52; N, 8.22%. 2.2. 2,9,16,23-Tetrakis(4 0 -carboxybiphenyloxy)phthalocyanine (3) 4-(4 0 -Carboxybiphenyloxy)phthalonitrile (0.50 g, 1.47 mmol) was dissolved in 6 ml dry 1-pentanol and heated at 140 °C under N2. After addition of elemental lithium (0.07 g, 10.3 mmol) a green colour appeared in a few seconds. The suspension was stirred under reflux for 1 h. Then, the mixture was cooled to room temperature. The reaction mixture was acidified with HCl and the resulting precipitate was centrifuged off. The precipitated blue-green coloured solid was filtered and washed

The metal-free phthalocyanine 3 (0.20 g, 0.14 mmol) was dissolved in 20 ml dry DMF and anhydrous zinc acetate (0.27 g, 1.46 mmol) was added and the mixture was heated under stirring for 24 h at 80 °C. After cooling to room temperature, the suspension was added to diethyl ether (100 ml) and the precipitated green solid was filtered. The crude product was treated with CH3COOH (10 ml) for 2 h then filtered off and washed with ethanol, acetone and then dried in vacuo. Yield: 0.10 g, 48%. M.p. >200 °C. IR mmax/(cm
1): 3050 (Ar– H), 1688 (C@O), 1600, 1522, 1472, 1250, 1184, 1092, 1004, 928, 827, 773; 1H NMR (d-DMSO): 12. 78 (br s, 4H, OH), 8.01–7.31 (m, 44H, Ar–H); UV–Vis kmax (nm) (log e) in DMSO: 289 (4.78), 347 (4.47), 679 (4.51); MS (FAB): m/z 1426.3 [M+]. Anal. Calc. for C84H48N8O12Zn: C, 70.72; H, 3.37; N, 7.85. Found: C, 70.70; H, 3.34; N, 7.83%. 2.4. 2,9,16,23-Tetrakis(4 0 -carboxybiphenyloxy)phthalocyaninatocobalt(II) (5) A mixture of 3 (0.25 g, 0.18 mmol) and anhydrous cobalt(II)chloride (0.24 g, 1.84 mmol) was heated in dry DMF (20 ml) at 80 °C under N2 with stirring for 18 h. The resulting green suspension was cooled and then added drop wise to diethyl ether (100 ml). The precipitate was stirred with CH3COOH for 2 h and then filtered off. The green product was washed several times with hot ethanol and acetone to remove unreacted materials and then dried in vacuo. Yield: 0.13 g, 51%. M.p. >200 °C. IR mmax/(cm
1): 3050 (Ar–H), 1687 (C@O), 1598, 1522, 1470, 1250, 1182, 1090, 1004, 927, 826, 771; UV–Vis kmax (nm) (log e) in DMSO: 289 (4.68), 343 (4.40), 664 (4.41); MS (MALDI-TOF): m/z 1420.3 [M+]. Anal. Calc. for C84H48N8O12Co: C, 71.04; H, 3.38; N, 7.89. Found: C, 71.02; H, 3.37; N, 7.86%. 2.5. 2,9,16,23-Tetrakis(4 0 -carbhexyloxybiphenyloxy)phthalocyanine (6) A mixture of 3 (0.20 g, 0.14 mmol), dicyclohexylcarbodiimide (DCCI) (0.36 g, 1.76 mmol), toluene-p-sulfonic

A. Kalkan, Z.A. Bayır / Polyhedron 25 (2006) 39–42

acid (0.03 g, 0.14 mmol) and 1-hexanol (0.22 ml, 1.76 mmol) was stirred in dry pyridine (15 ml) under N2 for 72 h. The suspension was filtered and the solvent was evaporated in vacuum. The residue was dissolved in chloroform (10 ml) and washed first with a solution of 10% Na2CO3 (50 ml) and then with water. The chloroform phase was dried over anhydrous Na2SO4 and finally the solvent was evaporated in vacuo. The green product was washed with 20 ml of ethanol–cyclohexane (1:1) mixture and then purified by column chromatography with silica gel using THF as eluent. Yield: 0.05 g, 21%. IR mmax/(cm
1): 3310 (N–H), 3080 (Ar–H), 2927– 2870 (alkyl CH), 1689 (C@O), 1599, 1522, 1470, 1250, 1180, 1091, 1004, 927, 825, 771; 1H NMR (d-chloroform): 8.10–7.36 (m, 44H, Ar–H), 4.33 (t, 8H, OCH2), 1.78–1.65 (m, 32H, CCH2C), 0.93 (t, 12H, CH3); UV– Vis kmax (nm) (log e): 287 (4.75), 338 (4.55), 668 (4.66), 699 (4.68); MS (FAB): m/z 1698.8 [M]. Anal. Calc. for C108H98N8O12: C, 76.34; H, 5.76; N, 6.59. Found: C, 76.31; H, 5.75; N, 6.59%.

41 CN

HOOC

OH

+

1

HOOC CN

ROOC

O O N N

Scheme 1 shows the synthesis of the target phthalocyanines 3–6. The first step in the synthetic procedure was to obtain 4-(4 0 -carboxybiphenyloxy)phthalonitrile (2). 2 was prepared from 4-nitrophthalonitrile and 4 0 -hydroxy-4-biphenylcarboxylic acid in DMF. K2CO3 was used as the base for this nucleophilic aromatic displacement [28]. The most usual method to prepare metal-free phthalocyanines is the cyclotetramerisation of a phthalic acid derivative such as phthalonitrile or diiminoisoindoline. A practical way of achieving this goal is the treatment of a phthalonitrile with lithium alkoxide, giving rise to the corresponding alkali metal phthalocyanine and it can be subsequently demetallated to the metal-free phthalocyanine with a mineral acid. In the present work, the latter was chosen for synthesising the metal-free phthalocyanine 3; i.e., cyclisation of 2 by using lithium in 1-pentanol, and then acidification with HCl resulted with the formation of 3. The crude product obtained by metallation of metalfree phthalocyanine 3 with zinc acetate in dry DMF was insoluble in all common solvents. Such insoluble products were encountered frequently as a result of complexation between the COOH groups and the zinc(II) ions [4]. After treatment of the product with acetic acid, desired zinc phthalocyanine 4 with free carboxy groups are obtained. The same route was also applied for synthesising cobalt phthalocyanine 5. As expected, all the phthalocyanines synthesised during this work are a mixture of positional isomers starting with the phthalonitrile precursor 2 with a single substituent [2]. However, our attempts to separate

CN

O 2

N

3. Results and discussion

CN

O 2N

N M

N

ROOC

COOR N

N N

O

O

3 M=

2H

4

COOR 5

Zn 2+

Co2+

R= H

6 M= 2H R= C 6 H 13

Scheme 1.

these isomers by column chromatography and, also by HPLC methods using different solvents were not successful. The phthalocyanines 3–5 are only soluble in DMSO and DMF. The biphenylcarboxylic acid substituents on the phthalocyanine core bring out a vast number of possibilities for binding with different groups. To achieve a better solubility of 3, hexyl substituents were introduced into the biphenyl units. Esterification of all the COOH groups in 3 with hexanol to give tetrakis(4 0 -carbhexyloxybiphenyloxy)phthalocyanine 6 was accomplished in pyridine in the presence dicyclohexylcarbodiimide and 4-toluenesulfonic acid as catalyst for 72 h at room temperature. 6 shows good solubility in organic solvents such as CHCl3, THF, CHCl2. Characterisation of the products involved a combination of methods including elemental analysis, 1H and 13 C NMR, UV/Vis, IR and mass spectroscopy. The

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A. Kalkan, Z.A. Bayır / Polyhedron 25 (2006) 39–42

spectroscopic data of the new compounds were in accordance with the structures. When IR spectrum of 1 is compared with that of 2, a distinct difference is the disappearance of the aromatic –NO2 band at 1548 cm
1 and the appearance of a new absorption at 1242 cm
1 attributable to aromatic (C–O–C) [29]. In the IR spectrum of 2 the presence of C„N and C@O groups is indicated by the intense stretching bands at 2238 and 1681 cm
1. 1H NMR spectrum of 2 exhibited the aromatic protons around 7.34– 8.14 ppm and the COOH proton at 13.03 ppm. The 13 C NMR spectral data are in accord with expected structure. The 13C APT (Attached Proton Test) NMR spectrum of 2 indicated the nitrile carbons at 116.37 and 115.85 ppm as expected [30]. Protonated aromatic and unsaturated carbon atoms appeared in the range at d 161.24–108.93 ppm. Also the carbon atom of carboxylic acid was observed at the lowest field at d 167.58 ppm. A diagnostic feature of the phthalocyanine formation from 2 is the disappearance of the C„N peak of the reactant. The IR spectra of metal-free 3 and metallo phthalocyanines (4, 5) are very similar. The significant difference is the presence of NH vibrations of the inner phthalocyanine core which are assigned to a weak band at 3310 cm
1 in the metal-free molecule. In the 1H NMR spectrum of 3 aromatic protons appeared at 8.01– 7.38 ppm. COOH protons and inner core NH protons could not be observed probably due to the broad nature of these peaks in the presence of intense resonances of phthalocyanine ring and the biphenyl group [31]. 1H NMR spectrum of 4 showed the aromatic protons at 8.01–7.31 ppm and COOH protons at 12.78 ppm. In the IR spectrum of 6 indicated the presence of alkyl groups by the intense stretching bands at 2927– 2870 cm
1. Chemical shifts due to the alkyl protons of 6 were observed between 4.33 and 0.93 ppm as expected. A close investigation of the mass spectra of the phthalocyanines confirmed the proposed structure. In the mass spectrum of 3 in addition to the [M+] peak at 1363.4 a fragment ion corresponding to the loss of COOH–H [M+
46] is easily identified. The phthalocyanines show typical electronic spectra with two absorption regions, the Q band around 600– 700 nm and the B band in the near UV region around 300–350 nm, both correlate to p–p* transitions [32– 34]. The split form of Q band in 3, which is characteristic for metal-free phthalocyanines, is observed at kmax 700 and 668 nm. The presence of absorption band in 3 in the near UV region at kmax 340 nm also show B band. The Q band absorption of metallophthalocyanines is observed as a single band of high intensity in the visible region. The metallophthalocyanines 4 and 5 showed the expected absorptions of the Q and B bands appearing at 679, 664 nm and 347, 343 nm, respectively.

Acknowledgements This work was supported by the Research Fund of the Technical University of Istanbul and State Planning Organization (DPT).

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