Synthesis, characterization and investigation of electrochemical and spectroelectrochemical properties of peripherally tetra 4-phenylthiazole-2-thiol substituted metal-free, zinc(II), copper(II) and cobalt(II) phthalocyanines

Journal of Molecular Structure 1141 (2017) 643e649

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Synthesis, characterization and investigation of electrochemical and spectroelectrochemical properties of peripherally tetra 4-phenylthiazole-2-thiol substituted metal-free, zinc(II), copper(II) and cobalt(II) phthalocyanines Ümit Demirbas¸ a, *, Hakkı Türker Akçay b, Atıf Koca c, Halit Kantekin a a

Department of Chemistry, Faculty of Science, Karadeniz Technical University, Trabzon, Turkey
an University, Rize, Turkey Department of Chemistry, Faculty of Arts and Sciences, Recep Tayyip Erdog c _ Department of Chemical Engineering, Engineering Faculty, Marmara University, Istanbul, Turkey b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 10 January 2017 Received in revised form 8 April 2017 Accepted 10 April 2017 Available online 12 April 2017

In this study novel peripherally tetra 4-phenylthiazole-2-thiol substituted metal-free phthalocyanine (4) and its zinc(II) (5), copper(II) (6) and cobalt(II) (7) derivatives were synthesized and characterized by a combination of various spectroscopic techniques such as FT-IR, 1H-NMR, UVevis and MALDI-TOF mass. Electrochemical characterizations of metallo-phthalocyanine complexes were conducted by voltammetric and in situ spectroelectrochemical measurements. CoIIPc went [CoIIPc
2]/[CoIPc
2]1-, [CoIPc
2]1-/ [CoIPc
3]2-, [CoIPc
3]2-/[CoIPc
4]3- and [CoIIPc
2]/[CoIIPc
2]1þ reduction and oxidation processes respectively. Differently ZnIIPc only showed four ligand-based reductions and two ligand based oxidation processes. © 2017 Elsevier B.V. All rights reserved.

Keywords: Phthalocyanine Phenylthiazole Electrochemistry Spectroelectrochemistry

1. Introduction The phthalocyanines are important macrocyclic dyes attracting interest of scientists studying much different scientific areas such as electrochromic displaying systems [1], photo-voltaic optics [2], non-linear optics [3], solar cells [4], semiconductors [5] and optical storage devices [6]. In the back of these superior functionalities of phthalocyanines lie their thermal-photo stabilities, excellent visible light absorbtion properties and strong 18 p electronic structure that determine electrochemical properties. Thiazoles, thanks to their pharmacological and biological properties, are a significant heterocyclic compound class is used in many different applications such as anti-cancer, anticonvulsant, anti-parkinson, antiviral, antifungal, anti-inflammatory and antidiabetic [7e11]. In addition their medical usage, thiazole derivatives are extensively studied in electrochemistry [12e16]. However while there are few electrochemical studies on thiazole substituted phthalocyanines [17,18] there is no study in literature

about the electrochemical and spectroelectrochemical properties of phenylthiazole substituted phthalocyanines. In this context, the main motivation of this work is the investigation of the electrochemical and spectro-electrochemical properties of the phenylthiazole substituted phthalocyanines. Especially phthalocyanine metal complexes have been used in various technological fields and most of these are generally related with the electrochemical activities of these complexes [19,20]. No doubt the central metal of phthalocyanine ring and their substituents affects significantly the electrochemical behaviors of the complexes [21e24]. Therefore, determination of the redox features of newly synthesized complexes is important in order to predict their possible usage in different technological areas. 2. Experimental The experimental setup, used materials, and the spectra were given in the supplementary material. 2.1. Synthesis

* Corresponding author. Department of Chemistry, Karadeniz Technical University, 61080, Trabzon, Turkey. E-mail address: [email protected] (Ü. Demirbas¸). http://dx.doi.org/10.1016/j.molstruc.2017.04.023 0022-2860/© 2017 Elsevier B.V. All rights reserved.

2.1.1. 3-(2-Methylbenzo[d]thiazol-5-yloxy)phthalonitrile (3) 4-phenylthiazole-2-thiol (1) (2.00 g, 10.35 mmol) and 4-

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nitrophthalonitrile (2) (1.79 g. 10.35 mmol) were dissolved in dried DMF (15 mL). Anhydrous K2CO3 (2.14 g 15.53 mmol) was added portion by portion within 2 h to the reaction mixture and the mixture stirred at 60  C for 3 days under inert nitrogen atmosphere. Then, the mixture was poured into 250 mL ice-water, stirred for 2 h at room temperature and finally filtered off. The brown solid product was crystallized from ethanol. Yield 1.59 g (48%), mp 184e186  C, C17H9N3S2. IR (ATR, cm
1): 3115, 3053, 2989, 2971, 2232 (C^N), 1578, 1474, 1278, 1038, 827, 740. 1H-NMR (CDCl3), (d: ppm): 7,90e7.89 (d, 2H Ar-H); 7.82 (s, 1H Ar-H); 7.76e7.71 (dd, 2H Ar-H); 7.68 (s, 1H Ar-H); 7.48e7.44 (dd, 2H, Ar-H); 7.41e7.38 (d, 1H, Ar-H); 13 C-NMR (CDCl3), (d: ppm): 157.92, 155.20, 143.11, 133.71, 133.15, 132.54, 132.38, 129.00, 128.98, 126.39, 117.80, 116.73, 115.00, 114.68, 113.78. MS (ESI), (m/z): Calculated: 319.02; Found: 320.00 [MþH]þ.

2.1.2. General procedure for synthesis of phthalocyanines (4e7) The mixture of phthalonitrile compound (3) (0.2 g. 0.63 mmol), n-pentanol (5 mL), 1,8-diazabicyclo [4.5.0] undec-7-ene (DBU) (5 drops), no metal salt for compound (4) and equivalent amounts of anhydrous Zn(CH3COO)2 for compounds (5), CuCI2 for compound (6) and CoCI2 for compound (7) were heated to 160  C and stirred for 24 h at this temperature. After cooling to room temperature, the reaction mixture was precipitated by the addition of hexane and filtered off. After washing with hot ethyl acetate, acetone and ethanol the solid product was purified with column chromatography by using silica gel and chloroform-methanol solvent system. 2.1.2.1. Peripherally tetra(4-phenylthiazole-2-thio) substituted metalfree phthalocyanine (4). Solvent system for column

Scheme 1. Synthetic route of novel metal-free (4), zinc(II) (5), copper(II) (6) and cobalt(II) (7) phthalocyanines.

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chromatography was chloroform:methanol (100:2). Yield: 76 mg (38%), mp > 300  C, C68H38N12S8. IR (ATR, cm
1): 3286(eNH), 3098, 3063, 2988, 2915, 1600, 1408, 1318, 1010, 893, 823, 704. 1H-NMR (CDCI3), (d: ppm): 7.66 (bs, 12H, Ar-H), 7.17 (bs, 24H, Ar-H). UVevis (CHCI3, 1  10
5 M): lmax/nm (log ε): 702 (5.08), 675 (5.10), 642 (4.87), 615 (4.72), 338 (5.07). MS (MALDI-TOF), (m/z): Simulated: 1278, Found: 1279 [MþH]þ. 2.1.2.2. Peripherally tetra(4-phenylthiazole-2-thio) substituted Zn(II) phthalocyanine (5). Solvent system for column chromatography was chloroform:methanol (100:3). Yield: 135 mg (64%), mp > 300  C, C68H36N12S8Zn. IR (ATR, cm
1): 3100, 3065, 2974, 2906, 1599, 1474, 1304, 1022, 907, 827, 741. 1H-NMR (DMSO-d6), (d: ppm): 8.51 (bm, 12H, Ar-H), 7.90 (bm, 6H, Ar-H), 7.65 (bm, 6H, ArH), 7.48 (bm, 12H, Ar-H). UVevis (CHCI3, 1  10
5 M): lmax/nm (log ε): 684 (5.18), 615 (4.51), 347 (4.82). MS (MALDI-TOF), (m/z): Simulated: 1340, Found: 1341 [MþH]þ. 2.1.2.3. Peripherally tetra(4-phenylthiazole-2-thio) substituted Cu(II) phthalocyanine (6). Solvent system for column chromatography was chloroform:methanol (100:2.5). Yield: 109 mg (52%), mp > 300  C, C68H36N12S8Cu. IR (ATR, cm
1): 3101, 3060, 2987, 2972, 2920, 1600, 1474, 1309, 1018, 918, 824, 721. UVevis (CHCI3, 1  10
5 M): lmax/nm (log ε): 680 (5.12), 615 (4.58), 346 (4.86). MS (MALDI-TOF), (m/z): Simulated: 1339, Found: 1340 [MþH]þ. 2.1.2.4. Peripherally tetra(4-phenylthiazole-2-thio) substituted Co(II) phthalocyanine (7). Solvent system for column chromatography was chloroform:methanol (100:2). Yield: 92 mg (44%), mp > 300  C, C68H36N12S8Co. IR (ATR, cm
1): 3100, 3064, 2989, 2972, 1600, 1474, 1308, 1019, 930, 825, 722. UVevis (CHCI3, 1  10
5 M): lmax/nm (log ε): 671 (5.14), 608 (4.58), 335 (5.07). MS (MALDI-TOF), (m/z): Simulated: 1335, Found: 1336. [MþH]þ. 3. Results and discussion 3.1. Synthesis and characterization The synthetic pathway of the novel compounds was shown in Scheme 1. The substituted phthalonitrile compound (3) was synthesized by nucleophilic aromatic nitro displacement reaction of 4phenylthiazole-2-thiol (1) and 4-nitrophthalonitrile (2) in the presence of K2CO3. The new vibration appeared at 2232 cm
1 verified the formation of phthalonitrile (3) according to IR spectral data (Fig. S1). The disappearance of the SH signal of compound (1) and presence of the new aromatic protons in 1H-NMR spectra of the compound (3), represent that the substitution was occurred (Fig. S2). In 13C-NMR of the compound (3) is another evidence for proposed structure, the new bands observed at 116.73, 115.00, 114.68 and 113.78 ppm could be defined as carbons of nitrile groups and the phenyl carbons to which these groups are attached (Fig. S3). The [MþH]þ peak was monitored at m/z: 320.0 in the mass spectra of phthalonitrile (3) verified the formation of phthalonitrile (Fig. S4). The 4-phenylthiazole-2-thiol substituted metal-free (4), zinc(II) (5), copper(II) (6) and cobalt(II) (7) phthalocyanines were synthesized by cyclic tetramerization reaction of the phthalonitrile compound (3). The structural characterization of novel phthalocyanines was performed by various spectroscopic methods such as FT-IR, 1HNMR, UVeVis and MALDI-TOF techniques. The disappearance of eC^N vibrational band of phthalonitrile (3) in the IR spectra was supported the formation of novel phthalocyanines (4e7) (Fig. S5 The IR spectra of compound (6), as an example of IR spectra of metallophthalocyanines). The inner core eNH vibrations of metalfree phthalocyanine (4) were observed at 3286 cm
1 and these

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peaks was verified the formation of target structure (Fig. S6). The peak observed at 3286 cm
1 was the major differences between the IR spectra of metal-free (4) and metallophthalocyanines (5e7). The 1H-NMR spectra of phthalocyanines (4) (Fig. S7) and (5) (Fig. S8) were recorded in CDCl3 and DMSO-d6 at room temperature. Because of the presence of paramagnetic copper (II) and cobalt (II) ions, the 1H-NMR measurement of compounds (6 and 7) could not be performed [25]. The 1H-NMR spectra of metal free phthalocyanine (4) confirmed the proposed structure. The chemical shift observed at 7.66 ppm as a broad singlet belongs to protons of phthalocyanine core and thiazole proton while other signals observed at 7.17 ppm belongs to other protons of peripherally substituted groups (Fig. S7). The integration ratio of the two bands confirmed the proposed structure. For metal free phthalocyanine (4), the typical shielding of inner core protons could not be observed due to the strong aggregation between phthalocyanine molecules at the concentration of NMR measurement [26]. In the 1 H-NMR spectrum of the zinc (II) (5) phthalocyanine, chemical shifts, due to insufficient solubility of the compound and its aggregation in NMR solvent were observed as several broad multiplet band along the aromatic region. Signals at aromatic region observed at 8.51 ppm for 12H, 7.90 ppm for 6H, 7.65 for 6H and 7.48 ppm for 12H (Fig. S8). In the mass spectra of novel phthalocyanines, the [MþH]þ peaks observed at 1279, 1341, 1340 and 1336 amu. for compound (4e7) confirmed the proposed structures. All molecular ion peaks of the compounds (4e7) were consistent with the simulated mass spectral data (Fig. S9 The MALDI-TOF mass spectra of compound (5), as an example mass spectra of phthalocyanines). Fig. 1 shows the absorption spectra of compounds (4e7) in chloroform at 1  10
5 mol/dm3 concentration. The ground state electronic absorption spectra of metallo-phthalocyanines showed monomeric behavior evidenced by a single (narrow) Q band with their D4h symmetry. The Q bands of novel metallo-phthalocyanines (5e7) were observed at 684, 680 and 671 nm respectively. Different from metallo-phthalocyanines, the Q band transitions were observed at 702 and 675 nm for metal-free phthalocyanine (4) due to its non-degenerate D2h symmetry. The B bands of all novel phthalocyanines (4e7) were observed at 338, 347, 346 and 335 nm respectively. This data are consistent with absorption spectra of metal-free and metallo-phthalocyanines in literature [27e31]. 3.2. Electrochemical and spectroelectrochemical measurements While CoPc complexes were reported as MPcs having redox active metal center, H2Pc, CuPc and ZnPc are known as MPcs having redox inactive Pc core. While H2Pc, CuPc and ZnPc illustrated

Fig. 1. Absorption spectra of compounds (4e7) in chloroform at concentration of 1  10
5 mol dm
3.

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Table 1 Voltammetric data of the complexes. All data were given versus Ag/AgCl. Complexes

Redox processes

a

H2Pc (4) (in DMSO)

[H2Pc1-]1þ/[H2Pc0]2þ [H2Pc2-]/[H2Pc1-]1þ [H2Pc2-]/[H2Pc3-]1[H2Pc3-]1-/[H2Pc4-]2[H2Pc4-]2-/[H2Pc5-]3[ZnIIPc1-]1þ/[ZnIIPc0]2þ [ZnIIPc2-]/[ZnIIPc1-]1þ [ZnIIPc2-]/[ZnIIPc3-]1[ZnIIPc3-]1-/[ZnIIPc4-]2[ZnIIPc4-]2-/[ZnIIPc5-]3[CuIIPc1-]1þ/[CuIIPc0]2þ [CuIIPc2-]/[CuIIPc1-]1þ [CuIIPc2-]/[CuIIPc3-]1[CuIIPc3-]1-/[CuIIPc4-]2[CuIIPc3-]1-/[CuIIPc4-]2[ CoIIIPc2-]1þ/[CoIIIPc1-]2þ [CoIIPc2-]/[CoIIIPc2-]1þ [CoIIPc2-]/[CoIPc2-]1[CoIPc2-]1-/[CoIPc3-]2[CoIPc3-]2-/[CoIPc4-]3-

1.12 0.83
0.60
0.94
1.59 1.01 0.82
0.62
0.95
1.62 (
1.79) 0.97 0.80
0.65
1.03
1.67 1.05 0.57
0.29
1.29
2.10

ZnPc (5) (in DMSO)

CuPc (6) (in DMSO)

CoPc (7) (in DMSO)

a b c d

E1/2 (V)

DEp (mV)

DE1/2

b

c

d

76 71 69 72 102 72 69 62 64 92 78 76 69 71 89 98 68 63 68 79

0.85 0.87 0.93 0.90 0.67 0.88 0.91 0.95 0.97 0.62 0.86 0.88 0.92 0.90 0.72 0.89 0.54 0.96 0.90 0.56

1.43

Ip,a/Ip,c

1.44

1.45

0.86

E1/2 values (Epa þ Epc)/2) were recorded at 0.100 Vs-1 scan rate. DEp ¼ Epa
Epc. Ip,a/Ip,c for reduction, Ip,c/Ip,a for oxidation processes. DE1/2 ¼ E1/2 (first oxidation)
E1/2 (first reduction).

similar redox behaviors, CoPc gave different electrochemical responses than the former ones. Therefore, voltammetric and in situ spectroelectrochemical (SEC) analyses of ZnPc and CoPc were discussed here as examples for MPcs having redox inactive and redox active metal centers respectively. Electrochemical characterizations of the complexes were carried out with cyclic voltammetry (CV) and square wave voltammetry (SWV) measurements in DMSO/ TBAP electrolyte system on GCE. CV and SWVs of the complexes were analyzed in order to derive the fundamental electrochemical parameters including ratio of anodic to cathodic peak currents (Ip,a/ Ip,c), the half-wave potentials (E1/2), peak to peak potential separations (DEp) and difference between the first oxidation and reduction processes (DE1/2). These parameters are listed in Table 1. DE1/2 and E1/2 values were used to support the proposed structure of the complexes. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were determined from DE1/2 and E1/2 values. Ranging of DE1/2 values from 1.02 to 1.49 V have been found in agreement with those values of the published monomeric phthalocyanine compounds, bearing redox active and inactive metal centers [32]. Fig. 2 represents CV and SWV responses of ZnIIPc in DMSO/TBAP on a GCE working electrode. ZnIIPc undergoes four reduction couples, Red1 at
0.62 V, Red2 at
0.95 V, Red3 at
1.62 V, and Red4 at
1.79 V and two oxidation couples at Ox1 at 0.82 V, and Ox2 at 1.01 V. These redox couples are analyzed in order to determine redox mechanism with E1/2, Ip,a/Ip,c, DEp and DE1/2. Former there reduction processes behave as electrochemically and chemically reversible. Since while Ip,a/Ip,c values of these couples are approximately unity at all scan rates, DEp values are ranged between 60 and 110 mV with respect to scan rates ranging from 0.010 to 1.00 Vs1scan rates. Moreover, the last reduction process is chemically irreversible. Similarly the oxidation reactions have quasi reversible characters with respect to Ip,a/Ip,c, and DEp values. E1/2 of the redox couples. DE1/2 of the complex (1.44 V) reflect the energy band gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), which is in harmony with the reported for ZnPc complexes [32,33]. Redox mechanism of the complex and spectra and color of the electrogenerated species were determined with SEC measurements.

Fig. 2. (a) CVs of ZnIIPc (5) (5.0  10
4 mol dm
3) recorded at various scan rates and (b) SWVs of ZnIIPc (5) recorded at 0.100 Vs-1 scan rate on a GCE working electrode in DMSO/TBAP electrolyte.

Fig. 3 shows in-situ spectroelectrochemical and in-situ electrocolorimetric of ZnIIPc in DMSO/TBAP electrolyte. ZnIIPc has redox inactive ZnII center, thus it gave common ordinary spectral changes for the Pc based electron transfer reactions. Under open circuit potential, ZnIIPc gives a split Q band at 644 and 681 nm due to the

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647

Fig. 3. In-situ UVevis spectral changes of ZnIIPc (5) in DMSO/TBAP electrolyte. a) Eapp ¼
0.80 V b) Eapp ¼
1.30 V, (c) Eapp ¼ 0.90 V, d) Chromaticity diagram (each symbol represents the color of electro-generated species; ,: [ZnIIPc2-]; B:[ZnIIPc2-]1-; D: [ZnIIPc3-]2-; : [ZnIIPc1-]1þ. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 4. Fig.4 CV and SWV of CoIIPc (7) (5.0  10
4 mol dm
3) recorded at recorded at 0.100 Vs-1 scan rate on a GCE working electrode in DMSO/TBAP electrolyte.

aggregation. At
0.80 V constant applied potential, the intensity of the band assigned to the aggregated species at 644 nm decreases and the band at 681 nm remains as unchanged at the beginning of the process. At the same time, a new band is observed at 585 nm. Then while both of the bands at 644 and 681 nm decrease in intensity, the band at 585 nm continues to increase with shifting to 568 nm (Fig. 3a) under the same potential application. These spectral changes illustrate the reduction of aggregated and then non-aggregated species under the same potential application. General trend of the spectral changes indicates Pc based character

of the first reduction process. Especially decreasing the Q bands and observation of new bands in the MLCT region illustrates the reduction of the neutral [ZnIIPc2] to [ZnIIPc3-]1- species [34e36]. Isosbestic points are observed at the beginning of the process at 616 and 670 nm and new isosbestic points at 452, 602, 712, and 772 are formed during the latter part of the reduction process. These changes in the isosbestic points indicate presence of more than two different species, which support presence of the aggregated [ZnIIPc2-], non-aggregated [ZnIIPc2-], and monoanionic [ZnIIPc3-]1species. During the second reduction process, while the Q band continues to decrease, the band at 568 nm shifts to 560 nm due to the formation of dianionic [ZnIIPc4-]2- species (Fig. 3b). During the first oxidation reaction, electrogenerated cationic form of [ZnIIPc2-] decomposes; therefore, all bands decrease in intensity as shown in Fig. 3c. Distinct color changes are especially observed during the reduction reactions as shown in the chromaticity diagram in Fig. 3d. Cyan color (x ¼ 0.2524 and y ¼ 0.3534) of the neutral [ZnIIPc2-] turns to blue (x ¼ 0.2213 and y ¼ 0.3193) after the first reduction reaction. Deep blue color (x ¼ 0.2635 and y ¼ 0.199) is obtained for the dianionic [ZnIIPc4-]2- species (Fig. 3d). The distinct color differences between the electrogenerated species illustrates its possible usage in different optic applications. CoIIPc has redox active CoII center thus, its redox responses are significantly different from those of the MPcs having redox inactive metal centers. Redox activity of CoII center comes from the energy level of the d orbital of CoII, which is located between the HOMOLUMO energy levels. This phenomenon is observed clearly with

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Fig. 5. Fig.5 In-situ UVevis spectral changes of CoIIPc (7) in DMSO/TBAP electrolyte. a) Eapp ¼
0.60 V b) Eapp ¼
1.50 V, (c) Eapp ¼ 0.70 V, d) Chromaticity diagram (each symbol represents the color of electro-generated species; ,: [CoIIPc2-]; B:[CoIPc2-]1-; D: [CoIPc3-]2-; : [CoIIPc2-]/[CoIIIPc2-]1þ. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

CV, SWV and SEC measurement. Fig. 4 shows CV and SWV responses of CoIIPc in DMSO/TBAP. CoIIPc undergoes three reduction reactions at
0.29 V,
1.29 V, and
2.10 V and two oxidation reactions at 0.57 V and 1.05 V. While the first reduction reaction is electrochemically and chemically reversible, other reductions have quasi-reversible character. The first oxidation process behaves as chemically irreversible due to the succeeding chemical reactions. This chemical reaction might be the coordination of DMSO to the oxidized [CoIIIPc2-]1þ species. Electron transfer reactions of coordinated [DMSO-CoIIIPc2-]1þ and non-coordinated [CoIIIPc2-]1þ species at different potentials cause the slitting of the cathodic wave of the first oxidation couple. Especially the first reduction and first oxidation processes CoIIPc are observed at very small potentials with respect to those of ZnIIPc, since these processes are proposed as metal-based electron transfer processes. It is well reported that MPcs having redox inactive metal centers such as ZnPc only give the ring based first reduction reaction after ca.
0.60 V and they have HOMO-LUMO gap or DE1/2 between 1.40-1.80 V). However for CoIIPc gives the first reduction process at
0.29 V and the first oxidation process at 0.57 V, which decreases DE1/2 to 0.86 V. These data support metal-based characters of Red1 and Ox1 processes of CoIIPc. Assignments of the redox reactions were also performed in detail with SEC measurements. Fig. 5 shows in-situ UVevis spectral changes and chromaticity diagram of CoIIPc in DMSO electrolyte. During the reduction reactions, spectral changes assigned to the sequential metal-ring-ring reductions are observed. As shown in Fig. 5a, during the first reduction reaction, shifting of the Q band from 665 nm to 708 nm

and increasing a new band at 480 nm are characteristic spectral changes for [CoIIPc
2]/[CoIPc
2]1- process [34e37]. This process gives clear isosbestic points at 574 and 690 nm, which indicates reversibility of the process and production of one type reduced species. Under
1.50 V constant applied potential (Red2), while the Q band decreases in intensity, intensity of the region at around 550 nm increases (Fig. 5b). These spectral changes are characteristic changes for the reduction of [CoIPc
2]1- to [CoIPc
3]2- species. During this process, the isosbestic points at around 630 and 725 nm oscillate continuously due to the chemical reaction succeeding to the redox process. With respect to the spectral changes given in Fig. 5c, it is easy to assign the first oxidation process to [CoIIPc
2]/ [CoIIIPc
2]1þ redox reaction, since shifting of the Q band to the longer wavelengths are characteristic response for a metal based process. Due to the enhancing the redox process with metal based redox reactions, more distinct color changes are observed during the redox reactions as shown in Fig. 5d. Cyan color (x ¼ 0.2528 and y ¼ 0.359) of the neutral changes to the yellow (x ¼ 0.358 and y ¼ 0.3900), purple (x ¼ 0.3471 and y ¼ 0.2915), and light green (x ¼ 0.2894 and y ¼ 0.3657) during the first and second reduction and first oxidation processes respectively. 4. Conclusions In this study, we synthesized tetra 4-phenylthiazole-2-thiol substituted novel peripherally metal-free (4), zinc(II) (5), copper(II) (6) and cobalt(II) (7) phthalocyanines for the first time. We characterized these novel pthalocyanines by FT-IR, 1H-NMR,

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